Biomedical subjects

V Ralevic

Publications and source records attributed to V Ralevic.

At least 37 records · Page 2Linked to original sources

PubMed1997

Calcitonin gene-related peptide (CGRP)-evoked inotropism during hyper- and hypo-sensory-motor innervation in rat atria.

1. Positive inotropic responses to calcitonin gene-related peptide (CGRP) were evaluated in atria isolated from in vivo rat models of hyper-sensory-motor innervation (following neonatal guanethidine treatment) and hypo-sensory-motor innervation (following neonatal capsaicin treatment), to explore the hypothesis that functional responsiveness of atrial myocardium to CGRP may correlate with tissue levels of the sensory-motor neurotransmitters. Comparative of inotropic responses to CGRP following in vitro treatment of atria with guanethidine was also performed. 2. Following long-term guanethidine treatment, positive inotropic responses to CGRP were significantly attenuated, while supersensitivity to the sympathetic transmitter noradrenaline was shown. Maximal inotropic responses to CGRP (30 nM) were 214.0 +/- 28.1 (n = 8) and 146.8 +/- 21.7 mg (n = 8; P < 0.01) increase of the basal contractile tension in control and treated preparations, respectively. The pD2 values for noradrenaline were 6.71 +/- 0.12 (n = 8) and 7.26 +/- 0.13 (n = 6; P < 0.01) in control and treated atria, respectively. Acute application of guanethidine in vitro did not modify the positive inotropism by CGRP or the beta-adrenoceptor agonist isoprenaline. 3. Sensory-motor hypoinnervation following chronic treatment with capsaicin did not affect the inotropic responses to CGRP. Neither guanethidine nor capsaicin treatment affected the contractile apparatus of myocytes, as demonstrated by similar basal contractile tension as well as calcium-evoked inotropic responses in control and treated preparations. 4. In summary, increased sensory-motor innervation, following long-term sympathectomy with guanethidine, resulted in attenuation of the inotropic responses of the rat atrium to CGRP, while no changes in the inotropic responses were seen following sensory-motor denervation with capsaicin. Down-regulation of CGRP receptors or altered post-receptor signalling may be involved in the reduced responsiveness to CGRP.

Adrenergic alpha-Agonists↗

PubMed1997

Effects of hibernation on neural and endothelial control of mesenteric arteries of the golden hamster.

The effects of hibernation on mesenteric arterial innervation and function were examined using pharmacological and immunohistochemical techniques in age-matched controls, cold-exposed controls, and 4-wk-hibernated golden hamsters. Electrical field stimulation of the isolated mesenteric arterial bed elicited frequency-dependent vasoconstriction. The sensitivity of responses was significantly increased in tissues from hibernating animals compared with cold-exposed controls. Vasoconstrictor responses to exogenous norepinephrine were also increased in hibernation. However, there was a significant decrease in sensitivity of vasoconstriction to ATP in hibernated and cold-exposed tissue compared with age-matched controls. In preparations preconstricted with methoxamine, endothelium-dependent vasodilator responses to acetylcholine and ATP were similar among the groups. Immunohistochemical investigation of mesenteric arteries revealed no differences among the groups in density of innervation by nerves immunoreactive for tyrosine hydroxylase, neuropeptide Y, and calcitonin gene-related peptide. Postjunctional changes appear to occur in hibernation, leading to augmentation of sympathetic vasoconstriction, which is consistent with the increase in peripheral vascular resistance in hibernation. Endothelium-dependent vasodilatation is not significantly changed in hibernation in the hamster mesenteric arterial bed.

Acetylcholine↗

PubMed1997

Sympathetic neurotransmission in isolated rat atria after sensory-motor denervation by neonatal treatment with capsaicin.

Long-term interactions between sympathetic and sensory-motor nerves have been shown in several tissues. Previous investigations in this laboratory have demonstrated an increase in cardiac sensory-motor innervation after neonatal sympathectomy by guanethidine and an increase of perivascular sympathetic neurotransmission after neonatal treatment by capsaicin. The present study evaluated the effects of sensory-motor denervation on sympathetic neurotransmission in the heart. Newborn rats were injected with capsaicin or its vehicle (Tween 80). Sympathetic neurotransmission was studied in isolated atria driven at a constant rate (4 Hz) by measuring cardiac responses to electrical field stimulation, in the presence of atropine 1 microM. Inotropism of tyramine, norepinephrine and calcitonin gene-related peptide was also tested. Neonatal capsaicin treatment did not affect cardiac responses to trains of an increasing number (2-32) of field pulses. Moreover, inotropic responses to tyramine did not differ between control, capsaicin- and Tween 80-treated preparations. Neither maximal effect nor pD2 values were significantly different between the groups. Similarly, the inotropism of calcitonin gene-related peptide was comparable in all groups of atrial preparations. In marked contrast to earlier papers on blood vessels, this study shows a lack of effect of sensory-motor denervation by neonatal capsaicin treatment on cardiac sympathetic neurotransmission. The different neuronal plasticity of vascular and cardiac sensory innervation will be discussed. The present results also indicate that capsaicin-induced sensory-motor denervation is not associated with changes in cardiac responsiveness to calcitonin gene-related peptide.

Animals↗

PubMed1996

Innervation and nitric oxide modulation of mesenteric arteries of the golden hamster.

Immunohistochemical and pharmacological techniques were used to examine perivascular nerves, endothelium and the effects of inhibition of nitric oxide synthesis on responses in mesenteric arteries/perfused mesenteric arterial beds of the Golden hamster. Frequency-dependent vasoconstrictions to electrical field stimulation and dose-dependent vasoconstrictions to noradrenaline were significantly augmented by NG-nitro-L-arginine methyl ester (10(-5) M), an inhibitor of nitric oxide synthase. In preparations with tone raised with methoxamine (10 microM) dose-dependent relaxations to ATP, but not to acetylcholine, were blocked by NG-nitro-L-arginine methyl ester. In the presence of guanethidine (5 microM) to block sympathetic neurotransmission there was no neurogenic relaxation to electrical field stimulation. Furthermore, the sensory neurotoxin capsaicin (0.05-5 nmol) did not elicit relaxation. Immunohistochemical studies demonstrated dense plexuses of fibres immunoreactive for tyrosine hydroxylase and neuropeptide Y, a plexus of moderate density for calcitionin gene-related peptide and an absence of fibres immunoreactive for substance P and vasoactive intestinal polypeptide. Of particular interest is the finding that whereas sympathetic perivascular nerves and nitric oxide regulate the function of hamster mesenteric arteries, there is no apparent motor function of calcitonin gene-related peptide-containing sensory nerves.

Animals↗

PubMed1996

Mesenteric and hepatic vascular reactivity in Donryu rats with and without a cholesterol-supplemented diet.

Vascular function of Donryu rats fed on a normal or cholesterol-supplemented diet was examined in the isolated perfused mesenteric arterial bed and portally perfused liver. In mesenteric preparations, frequency-dependent vasoconstriction to electrical field stimulation (4-32 Hz, 1 ms, 90 V, 30 s) and dose-dependent vasoconstriction to noradrenaline (0.15-1500 nmol) was similar in both groups. Dose-dependent vasoconstriction to alpha, beta-methylene ATP (0.05-500 nmol) via P2x purinoceptors was significantly impaired in Donryu rats fed on a cholesterol-supplemented diet. In preparations with raised tone (methoxamine 5-35 microM), there was no significant difference in endothelium-dependent relaxation to acetylcholine and ATP, or endothelium-independent relaxation to sodium nitroprusside. In liver preparations, there was no difference in frequency-dependent vasoconstriction to electrical field stimulation (2-32 Hz, 1 ms, 90 V, 30 s), or dose-dependent vasoconstriction to noradrenaline (0.05-500 nmol) and alpha, beta-methylene ATP (0.05-500 nmol) between the groups. In conclusion, in mesenteric arteries, but not in the hepatic portal vasculature of Donryu rats fed on cholesterol P2x purinoceptor function is impaired, but sympathetic neurotransmission is unaffected. Mesenteric endothelial and smooth muscle function is unimpaired.

Acetylcholine↗

PubMed1996

Effect of chronic vitamin E deficiency on sympathetic and sensorimotor function in rat mesenteric arteries.

1. Mesenteric arterial beds from male rats deprived of vitamin E for 12 months postweaning were isolated and perfused at 5 ml min-1. 2. The basal perfusion pressure of vitamin E-deficient preparations was significantly higher (34.0 +/- 1.9 mmHg, n = 15) than in age-matched controls (26.1 +/- 2 mmHg, n = 14; P < 0.01). 3. At basal tone, vasoconstrictor responses to electrical field stimulation (EFS) were not attenuated by vitamin E deficiency; at high stimulation frequencies, responses were enhanced. According to dose-response curves, exogenous noradrenaline was significantly more efficacious in preparations from vitamin E-deficient rats (P < 0.05). 4. In preparations with tone raised by methoxamine (6-20 microM) and in the presence of guanethidine (5 microM), EFS of perivascular sensorimotor nerves elicited frequency-dependent vasodilatation which was significantly attenuated by vitamin E deficiency. There was no difference in relaxation to calcitonin gene-related peptide (CGRP; 1.5 x 10(-11) mol), or to the sensory neurotoxin capsaicin (5 x 10(-11) mol). 5. Immunohistochemical analysis of CGRP-containing nerves in the superior mesenteric artery showed no differences in density of innervation. 6. In conclusion, chronic vitamin E deficiency impairs sensorimotor vasodilatation in rat mesenteric arteries; this does not appear to be due to changes in postjunctional receptors, or to a depletion of transmitter (CGRP) content of the superior mesenteric artery. Sensorimotor nerves appear to be more vulnerable than sympathetic nerves to chronic vitamin E deficiency.

Animals↗

PubMed1996

Mesenteric vasodilator responses in cirrhotic rats: a role for nitric oxide?

The contribution of nitric oxide to mesenteric arterial vasodilator responses was investigated in the isolated perfused mesenteric arterial bed of cirrhotic rats (carbon tetrachloride/phenobarbitone; n = 6). Age-matched (n = 9) and phenobarbitone-treated rats (n = 9) served as controls. Responses to the endothelium-dependent dilators acetylcholine and adenosine 5'-triphosphate (ATP) and the smooth muscle dilator (NO donor) sodium nitroprusside were investigated after tone was raised by continuous infusion of methoxamine, before and during infusion of the NO synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 30 mumol/L) +/- L-arginine (1 mmol/L). A significant hyporesponsiveness to methoxamine infusion in cirrhotic preparations (P < .05) was not fully corrected by L-NAME. There was no difference in the percentage vasodilator response to acetylcholine in the cirrhotic group compared with controls; L-NAME significantly and reversibly inhibited the dilator response in all groups. ATP elicited dose-dependent vasodilation that, in the absence of L-NAME, did not differ between the groups. By contrast, in the presence of L-NAME, ATP (5 x 10(-8) mol) produced pronounced, reversible vasoconstriction only in cirrhotic animals (P < .02). Vasodilatation attributable to sodium nitroprusside (5 x 10(-8) mol) was significantly attenuated in cirrhotic rats. The methoxamine data support the concept of mesenteric hyposensitivity to vasoconstrictor agents in cirrhosis that may be at least partly NO mediated. Increased NO activity in smooth muscle leading to decreased guanylate cyclase availability may account for the diminished vasodilator responses to sodium nitroprusside in cirrhotic preparations. The unchanged responsiveness to vasodilatation by acetylcholine (ACh) and the vasoconstriction to ATP observed during NO blockade in cirrhotic animals indicate that mesenteric endothelial NO is unchanged or possibly diminished.

Acetylcholine↗

PubMed1996

Portal vascular responsiveness to sympathetic stimulation and nitric oxide in cirrhotic rats.

AIMS/METHODS: The modulatory role of nitric oxide in portal vasoconstrictor responses was investigated in the isolated perfused liver of cirrhotic rats (induced by carbon tetrachloride/phenobarbitone; n = 6). Age-matched (n = 5) and phenobarbitone-treated rats (n = 5) served as controls. RESULTS: At a constant flow rate of 5 ml/min there was no difference in basal perfusion pressure between the groups. Responses to electrical field stimulation of perivascular nerves caused frequency-dependent increases in perfusion pressure that were not significantly different between the groups. In contrast, dose-dependent vasoconstrictor responses to bolus injections of noradrenaline were up to two-fold greater than those observed in controls (p < 0.05). Vasoconstrictor responses to bolus injections of methoxamine (a selective alpha 1-adrenoceptor agonist) or adenosine 5'-triphosphate (ATP, a cotransmitter with noradrenaline in sympathetic nerves) were dose-dependent and similar between the groups. Infusion of the nitric oxide synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 30 microM) had no effect on basal tone or on responses to electrical field stimulation or injected agents. A step-wise increase in flow to 10, 15 and 20 ml/min produced a similar increase in perfusion pressure within each group. At increased flow, there was a decrease in responsiveness to noradrenaline (5 nmol) in preparations from all groups. In the presence of the K+ channel inhibitor glibenclamide (5 microM), the effect of noradrenaline in the cirrhotic group at flow rates of 5, 10 and 15 ml/min was maintained to a significantly greater extent than in either control group, suggesting that ATP-sensitive K+ channels in the portal venous bed may be activated in cirrhosis. CONCLUSIONS: We conclude that portal vasoconstriction associated with noradrenaline, but not with sympathetic nerve stimulation, methoxamine or ATP, is enhanced in cirrhosis. Nitric oxide does not appear to play a modulatory role in these responses.

Adenosine Triphosphate↗

PubMed1996

Vasoconstrictor function of the rat isolated perfused mesenteric arterial bed seven days after hypophysectomy.

The effect of removal of the pituitary on mesenteric arterial function was examined in adult male rats that had undergone hypophysectomy 7 days earlier. Sham-operated rats and weight-matched rats served as controls. The body weight of hypophysectomized rats decreased from 220.75 +/- 0.48 g to 188.03 +/- 2.53 g (n = 7). Sham-operated controls gained weight, from 223 +/- 1.47 to 275.85 +/- 3.45 g (n = 8). Frequency-dependent vasoconstriction to electrical field stimulation (2-32 Hz, 90 V, 1 ms, 30 s) was significantly augmented after hypophysectomy. The maximal constrictor response of hypophysectomized preparations, 215.5 +/- 14.9 mm Hg (n = 6), was approximately twice that of the sham-operated controls, 100 +/- 6.1 mm Hg (n = 7) and weight-matched controls 109.8 +/- 5.8 mm Hg (n = 8). Norepinephrine (NE) (0.05-1,500 nmol) elicited dose-dependent vasoconstriction; the maximal response was significantly augmented after hypophysectomy, 221.71 +/- 15.9 (n = 7) as compared with 148.0 +/- 16.0 mm Hg (n = 8) in sham-operated controls and 146.3 +/- 8.7 mm Hg (n = 7) in weight-matched controls. Dose-dependent vasoconstrictor responses to ATP, 5-hydroxytryptamine, vasopressin, and endothelin were similar between the groups. High-performance liquid chromatography analysis showed no difference in NE content of the superior mesenteric artery from hypophysectomized and sham-operated controls. Hypophysectomy of rats caused an increase in sympathetic constrictor function of the mesenteric arterial vasculature that appeared to involve postjunctional adrenoceptors rather than prejunctional mechanisms and was not due to arrested growth or the smaller size of the mesenteric preparations.

Animals↗

PubMed1996

Effects of hypophysectomy on purinergic and noradrenergic contractility of the rat vas deferens.

1. The effects of removal of the pituitary on vas deferens contractile function were examined in young adult male rats having undergone hypophysectomy 7 days previously. Sham-operated age-matched rats served as controls. Responses to electrical field stimulation (EFS), and exogenous noradrenaline (NA) and beta, gamma-methylene ATP (beta, gamma-meATP) were tested. 2. Hypophysectomized rats lost weight over the 7 days. Body weights were 267.2 +/- 3.9 g (n = 7) in controls and 195.3 +/- 1.56 g (n = 5) with hypophysectomy. The wet weight of the vas deferens from rats with hypophysectomy, 22.8 +/- 1.8 mg (n = 5) was approximately half that of the controls, 41.3 +/- 1.2 mg (n = 7). The contractile response to KCl was smaller in hypophysectomized preparations (0.97 +/- 0.9 g, n = 5) than in controls (2.91 +/- 0.2 g, n = 7). 3. The alpha 1-adrenoceptor antagonist prazosin (1 microM) was more effective as an inhibitor of the tonic than of the twitch component of the contractile response, indicating a dominant adrenergic component. However, alpha, beta-methylene ATP was also effective at inhibiting the tonic component, indicating that ATP is also released secondarily to NA. 4. Absolute contractions to EFS of vas deferens from hypophysectomized rats were smaller than those of the controls; however, when corrected for the difference in smooth muscle function (expressed as a percentage of the contraction to 120 mM KCl), the twitch response was significantly greater than in the controls at frequencies of up to 16 Hz, maximal responses being unaffected. In contrast, the tonic response was not significantly different between the two groups. 5. The sensitivity of contractions evoked by NA (1-300 microM) was less in vas deferens from hypophysectomized rats than in the controls. 6. Contractions of the vas deferens to beta, gamma-meATP (1-300 microM) were greater in hypophysectomized rats than in the controls. 7. In conclusion, the present results indicate that hypophysectomy of rats causes an increase in the twitch, but not the tonic component of the vas deferens contractile response to EFS. This appears to be due to an increase in the number or sensitivity of postjunctional P2X-purinoceptors, there being a reduction in sensitivity to NA.

Adenosine Triphosphate↗

PubMed1996

Mesenteric arterial function in the rat in pregnancy: role of sympathetic and sensory-motor perivascular nerves, endothelium, smooth muscle, nitric oxide and prostaglandins.

1. The effects of pregnancy on mesenteric arterial function were examined in constantly perfused (5 ml min-1) mesenteric arterial beds isolated from 21-day pregnant rats. The function of sympathetic and sensory-motor perivascular nerves, endothelium and smooth muscle was examined. The role of nitric oxide and prostaglandins in vasoconstrictor function was tested by use of NG-nitro-L-arginine methyl ester (L-NAME; 100 microM) and indomethacin (10 microM), respectively. 2. Electrical field stimulation (EFS; 4-32 Hz, 1 ms, 90V, 30s) at basal tone elicited frequency-dependent vasoconstriction which was markedly reduced in preparations from pregnant rats at all frequencies. Vasoconstrictor responses to vasopressin and endothelin were also reduced in pregnancy and there was a trend towards a reduction in maximal responses to noradrenaline (NA). In contrast, there was no difference in vasoconstrictor responses to ATP, 5-hydroxytryptamine (5-HT) or angiotension II. 3. L-NAME (100 microM) augmented responses to EFS, NA, ATP and vasopressin in control mesenteric arterial preparations. In contrast, L-NAME augmented responses only to EFS in pregnancy, having no significant effect on responses to NA, ATP and vasopressin. 4. Indomethacin (10 microM) attenuated responses to NA and vasopressin, but not to EFS, in controls and in pregnancy. Responses to ATP were attenuated by indomethacin in controls but not in pregnancy. 5. Mesenteric preparations from pregnant rats were resistant to having tone raised by continuous perfusion with methoxamine. Despite an approximately 10 fold greater concentration of methoxamine, there was a significantly smaller increase in tone in preparations from pregnant, 34.27 +/- 4.8 mmHg (n = 11) compared to control, 65.92 +/- 5.4 mmHg (n = 11), rats. EFS (4-12 Hz, 60 V, 0.1 ms, 30s) in the presence of guanethidine (5 microM) to block sympathetic neurotransmission elicited frequency-dependent vasodilatation due to activation of sensory-motor nerves. Percentage relaxations were similar in preparations from pregnant and non-pregnant rats. 6. Dose-dependent endothelium-dependent vasodilatations to acetylcholine and ATP were similar in preparations from pregnant and non-pregnant rats. Endothelium-independent vasodilatation to sodium nitroprusside and to calcitonin gene-related peptide were also similar between the two groups. 7. There was no significant difference in the basal perfusion pressure of mesenteric arterial beds from control (21.3 +/- 1.0 mmHg, n = 24) and pregnant (20.2 +/- 1.2 mmHg, n = 23) rats. However, a step-wise increase in perfusate flow from 5 to 10, 15, 20 and 24ml min-1 produced smaller increases in perfusion pressure in pregnancy compared to the controls. L-NAME (100 microM) or indomethacin (10 microM) had no significant effect on the relationship between flow and perfusion pressure. 8. The present results show that prejunctional changes are involved in blunted sympathetic vasoconstriction of rat mesenteric arteries in pregnancy. Non-specific postjunctional changes are implicated in the reduced constrictor responses to applied methoxamine, vasopressin and endothelin, but not to ATP. In contrast, sensory-motor nerves and endothelium-dependent and -independent vasodilatation was unchanged. The decrease in receptor-mediated mesenteric arterial constrictor responsiveness in pregnancy does not appear to be due to acute modulation by NO or prostaglandins, but may involve changes in the distensibility of the bed and/or changes in wall thickness.

Acetylcholine↗

PubMed1996

Relative contribution of P2U- and P2Y-purinoceptors to endothelium-dependent vasodilatation in the golden hamster isolated mesenteric arterial bed.

1. P2-purinoceptors were characterized pharmacologically in the constantly perfused isolated mesenteric arterial vascular bed of the golden hamster. Vasoconstrictor and vasodilator responses to the nucleotides ATP, ADP, 2 methylthio ATP (2MeSATP), alpha,beta-methylene ATP (alpha,beta-meATP) and uridine 5'-triphosphate (UTP) and a role for ATP in sympathetic constriction were examined. 2. At basal tone nucleotides elicited dose-dependent vasoconstriction with an observed rank order of potency of alpha,beta-meATP >> 2MeSATP > ATP = ADP > UTP (based on the doses required to elicit constrictor responses of 25 mmHg). Adenosine had no vasoconstrictor action at doses up to 5 mumol. After application of a single dose (0.5 mumol) of alpha,beta-meATP preparations were desensitized to constriction by subsequent application of nucleotides. 3. Electrical field stimulation (4-64 Hz, 90 V, 1 ms, 30 s) elicited frequency-dependent constrictions which were abolished by guanethidine (5 microM) and by prazosin (1 microM). 4. The non-selective P2-purinoceptor antagonist suramin (100 microM) did not significantly affect vasoconstrictor responses to ATP. The P2X-selective purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 3 microM), virtually abolished responses to ATP. When the endothelium was removed vasoconstrictor responses to ATP and noradrenaline were augmented. 5. In preparations with tone raised with methoxamine (10-80 microM) nucleotides elicited vasodilatation with an observed potency order of ATP = UTP > ADP >> adenosine. 2MeSATP had relatively minor vasodilator effects and at the highest dose tested (50 nmol) elicited only vasoconstriction. alpha,beta-meATP did not elicit vasodilatation but produced further constriction of the raised tone preparation. At the highest doses of ATP and ADP (0.5 microM) responses were biphasic with vasoconstriction preceding vasodilatation. After removal of the endothelium, with the exception of adenosine, vasodilator responses to purines and to UTP were abolished; vasoconstriction to ATP, ADP, UTP and 2MeSATP was evident at the highest doses. 6. Suramin (100 microM) inhibited vasodilatation to both ATP and UTP and abolished responses to 2MeSATP. PPADS (3 microM) inhibited relaxation to 2MeSATP but did not affect relaxation to ATP, UTP, adenosine and acetylcholine and ADP. 7. Reactive blue 2 (30 microM) blocked vasodilator responses to ATP, UTP, 2MeSATP and acetylcholine; it was without effect when used at 3 microM. 8. The results of this study show that ATP elicits vasoconstriction of mesenteric arteries of the golden hamster via P2X-purinoceptors located on the smooth muscle, and vasodilatation via P2U-receptors which are located on the endothelium. 2MeSATP has marginal vasodilator activity, suggesting that P2Y-purinoceptors contribute minimally to relaxation to ATP in hamster mesenteric arteries.

Adenosine Diphosphate↗

PubMed1996

Discrimination by PPADS between endothelial P2Y- and P2U-purinoceptors in the rat isolated mesenteric arterial bed.

1. The main aim of this study was to characterize the antagonistic effects of pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) at coexisting endothelial P2Y- and P2U-purinoceptors. Studies were conducted in Krebs-perfused mesenteric arterial preparations isolated from the rat, with tone raised by methoxamine (5-50 microM). 2. Purine and pyrimidine compounds elicited vasodilatation with a rank order of potency of 2-methylthio ATP (2-MeSATP) = ADP > ATP = UTP > P1, P3-diadenosine triphosphate (Ap3A) > P1, P2-diadenosine pyrophosphate (Ap2A) > NADP > adenosine. 8-para-Sulphophenyltheophylline (8-PSPT; 3 microM) had no effect on vasodilator responses to 2MeSATP, ADP, ATP, UTP, Ap3A or NADP, but blocked responses to adenosine and the maximal response to Ap2A. 3. PPADS (3-100 microM) attenuated vasodilator responses to the P2Y-selective agonists 2MeSATP and ADP, shifting the dose-response curves to the right. The pA2 values for PPADS at 2MeSATP and ADP were 5.97 +/- 0.69 and 5.98 +/- 0.86 respectively. In contrast, PPADS had no effect on vasodilator responses mediated by the P2U-selective agonist, UTP, or on vasodilator responses mediated by ATP. 4. PPADS (10 microM) was used to characterize responses mediated by the adenine dinucleotides; dose-response curves for vasodilator responses to Ap3A and NADP, but not those to Ap2A, were shifted to the right by PPADS. The estimated pA2 values for the effect of PPADS on Ap3A and NADP were 6.38 and 6.26 respectively. 5. Indomethacin (10 microM) had no effect on vasodilator responses to 2MeSATP, ADP, ATP or UTP. 6. In conclusion, these results show that PPADS is an antagonist at endothelial P2Y- but not P2U-purinoceptors in rat mesenteric arteries. These receptors cannot be discriminated by inhibition of prostaglandin synthesis; P2Y-purinoceptors are, however, sensitive to ADP. Selective antagonism by use of PPADS showed that ATP acts at P2U- and not P2Y-purinoceptors. Ap3A and NADP mediate vasodilatation via P2Y-purinoceptors, whereas vasodilatation to Ap2A is mediated partly via P1- and possibly via P2U-purinoceptors.

Animals↗

PubMed1996

Vasoconstrictor responsiveness of the rat mesenteric arterial bed in cirrhosis.

1. The effects of cirrhosis on mesenteric vascular reactivity were assessed in constantly perfused mesenteric arterial beds isolated from cirrhotic rats (carbon tetrachloride with phenobarbitone, n = 6), and from phenobarbitone-treated and untreated age-matched controls (n = 4,5). 2. At a constant flow rate of 5 ml min-1 there was no difference in basal perfusion pressure between the groups. Electrical field stimulation (EFS; 4-32 Hz, 90V, 1 ms, 30 s) of perivascular nerves caused frequency-dependent increases in perfusion pressure which were not different between the groups. Dose-dependent vasoconstrictor responses to exogenous noradrenaline (NA), methoxamine (an alpha 1-adrenoceptor agonist), adenosine 5'-triphosphate (ATP) and vasopressin were also similar between the groups. 3. The nitric oxide (NO) synthesis inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 30 microM) augmented constrictor responses to NA, EFS, methoxamine and vasopressin in all groups, and as shown for EFS and NA, this was reversed by L-arginine (300 microM). However, the maximum constrictor responses of cirrhotic preparations in the presence of L-NAME were significantly lower than those of both groups of control animals at the highest frequency of EFS (32 Hz) and highest doses of NA (0.15 and 0.5 mumol) and, compared to phenobarbitone-treated controls, methoxamine (5 mumol). Responses to ATP were significantly augmented by L-NAME only in the cirrhotic group. 4. A step-wise increase in perfusate flow to 10, 15 and 20 ml min-1 produced a broadly similar increase in perfusion pressure within each group. At increased flow rates, cirrhotic preparations were hyporesponsive to NA (15 nmol) compared to the phenobarbitone-treated animals but not the untreated controls. Glibenclamide (5 microM) or L-NAME (30 microM) had no significant effect on the relationship between flow and perfusion pressure or on responses to NA at the different flow rates. 5. We conclude that sympathetic neurotransmission is unchanged in cirrhosis. Endogenous NO is important in modulation of constriction in both normal and cirrhotic states. Changes in NO may occur in cirrhosis, although the role of this in hyporesponsiveness of cirrhotic preparations to NA at higher flow rates and to the greater potentiation of ATP-mediated constriction in the presence of L-NAME, together with the impact of factors such as changes in calcium and potassium channels, is not entirely clear.

Adenosine Triphosphate↗

PubMed1996

Effects of short- and long-term sympathectomy on vasoconstrictor responses of the rat mesenteric arterial bed.

1. The effects of short- and long-term sympathectomy were evaluated on vasoconstrictor function of constantly perfused mesenteric arterial beds isolated from rats: the effects of short-term sympathectomy were assessed at 3 and 8 days after 6-hydroxydopamine (6-OHDA) treatment of adult rats; the effects of long-term sympathectomy were assessed in adult rats treated at youth with guanethidine. 2. The relative degree of residual sympathetic innervation of the mesenteric arterial preparations was assessed by responses to electrical field stimulation (EFS; 16 Hz, 1 ms, 90 V, 30 s). Control responses were 95.6 +/- 3.9 mmHg (n = 35). Responses after sympathectomy were: 3 days after 6-OHDA, 2.9 +/- 0.9 mmHg (n = 15) < 8 days after 6-OHDA, 14.1 +/- 2.1 mmHg (n = 14) < guanethidine, 21.1 +/- 4.1 mmHg (n = 16). 3. Three days after 6-OHDA treatment there was an increase in the sensitivities of response to vasopressin and endothelin, producing leftward shifts of the dose-response curves of 0.66 +/- 0.11 and 0.88 +/- 0.13 log units respectively (n = 7-11), and a small increase in sensitivity of responses to noradrenaline (NA) and ATP. The maximal response to 5-hydroxytryptamine (5-HT) was increased. In contrast, there was a decrease in maximal constriction to NA and to the alpha 1-adrenoceptor agonist methoxamine. The alpha 2-adrenoceptor agonist clonidine did not elicit vasoconstriction at basal tone. There was no difference in vasodilator responses to the beta-adrenoceptor agonist isoprenaline in preparations with tone raised with prostaglandin F2 alpha (PGF2 alpha; 0.1-0.3 microM). 4. Eight days after 6-OHDA sympathectomy there was no significant difference in sensitivities or maximal responses to ATP, vasopressin and endothelin, but a small increase in the sensitivity of responses to 5-HT. Maximal responses to NA and methoxamine were significantly lower than the controls, but sensitivities were similar. There was no significant difference in vasodilator responses to isoprenaline in PGF2 alpha-raised tone preparations. 5. After long-term guanethidine sympathectomy maximal responses to 5-HT and NA were significantly reduced. Responses to ATP, vasopressin and endothelin were unchanged. 6. In mesenteric arterial preparations from untreated rats, ouabain (0.1 mM), a blocker of the Na+/K+ pump, significantly augmented the sensitivity and maximal responses to EFS, NA, methoxamine and 5-HT. Responses to ATP, vasopressin and endothelin were unaffected. 7. It is concluded that in the rat mesenteric arterial bed, short-term sympathectomy, where only 3% of the sympathetic nerve-mediated response remained, results in non-uniform changes in sensitivity and maximal responses to different vasoconstrictors, which cannot be entirely explained by changes in the Na+/K+ pump. Most of these changes disappeared at 8 days after 6-OHDA treatment, when nerve-mediated responses had partially returned. After long-term guanethidine sympathectomy, there was little change in responses to vasoconstrictors, and nerve-mediated responses were reduced to 22%. Although the variable factors are complex, it appears that in general, changes in responses of smooth muscle to vasoconstrictor substances after sympathetic denervation only occur if there is near-complete loss of nerve-mediated responses.

Adrenergic alpha-Agonists↗

PubMed1996

Depression of endothelial nitric oxide synthase but increased expression of endothelin-1 immunoreactivity in rat thoracic aortic endothelium associated with long-term, but not short-term, sympathectomy.

Recent pharmacological studies have shown that perivascular nerves can influence the development and function of vascular endothelial cells (ECs). However, morphological studies have not yet been carried out to investigate whether these functional changes are associated with changes in vasoactive substances in ECs. We used postembedding electron microscopy (EM) triple gold-labeling immunocytochemistry to study the effects of short-term sympathectomy (3 days after 6-hydroxydopamine [6-OHDA] treatment) and long-term sympathectomy (guanethidine and 8 days after 6-OHDA) on the distribution of vasoactive substances in ECs of the rat thoracic aorta. The post-embedding immunocytochemistry, which can detect levels of label in individual cells, showed that there was a significant decrease in endothelial NO synthase (NOS3)-labeled, serotonin (5-HT)-labeled, and substance P (SP)-labeled, but a significant increase in endothelin-1 (ET-1)-labeled, gold particles in ECs after long-term, but not after short-term (3-day), sympathectomy. In conclusion, our results show that long-term sympathectomy causes an increase in ET-1 and decrease in NOS3, 5-HT, and SP immunoreactivity in ECs of the thoracic aorta. Our data also indicate that postembedding EM triple gold-labeling immunocytochemistry is a valuable technique for quantitative studies of the content of vasoactive substances in ECs.

Animals↗

PubMed1995

Effects of streptozotocin-diabetes on sympathetic nerve, endothelial and smooth muscle function in the rat mesenteric arterial bed.

Mesenteric arterial function was assessed in constantly perfused preparations isolated from rats 12 weeks after treatment with streptozotocin (65 mg kg-1, i.p.) to induce diabetes. Frequency-dependent vasoconstrictor responses to electrical field stimulation of sympathetic nerves (4-32 Hz, 0.1 ms, 90V, 30 s) were severely attenuated in preparations from streptozotocin-diabetic rats, although dose-dependent vasoconstrictions to the sympathetic cotransmitters noradrenaline and ATP, as well as to potassium chloride, were not significantly changed. Dose-dependent relaxations to the endothelium-dependent vasodilators acetylcholine and ATP were significantly impaired in preparations from streptozotocin-diabetic rats, although endothelium-independent vasodilatation to sodium nitroprusside was unimpaired. These results suggest 12 weeks after induction of streptozotocin-diabetes in rats there is pre-junctional impairment of sympathetic neurotransmission and impaired endothelial function of the mesenteric arteries. This is in contrast to our previous findings that at 8 weeks after induction of streptozotocin-diabetes sympathetic nerve and endothelial function is normal, although sensory-motor vasodilatation is severely attenuated. It is suggested that selective changes occur in mesenteric arterial function after streptozotocin treatment depending on the duration of diabetes; sensory-motor nerves are affected first, followed by sympathetic nerves and the endothelium, while the smooth muscle is relatively resistant to change.

Acetylcholine↗

PubMed1995

Role of nitric oxide in the actions of substance P and other mediators of inflammation in rat skin microvasculature.

The role of nitric oxide in inflammatory responses to substance P and other mediators of inflammation was examined in rat skin microvasculature in a blister base raised on the hind footpad. Superfusion of substance P (1 microM) over the blister base caused an increase in plasma extravasation and a vasodilator response which was not maintained. N(G)-Nitro-L-arginine (100 microM), an inhibitor of nitric oxide biosynthesis, attenuated vasodilatation and plasma extravasation due to substance P. The inactive isomer N(G)-nitro-D-arginine was without effect. Neurokinin A (1 microM), 5-hydroxytryptamine (1 microM), ATP (50 microM) and vasoactive intestinal polypeptide (1 microM) elicited vasodilation, which for vasoactive intestinal polypeptide was maintained even after washout. 5-Hydroxytryptamine and neurokinin A, but not ATP or vasoactive intestinal polypeptide, significantly increased plasma extravasation. Vasodilatation to neurokinin A, 5-hydroxytryptamine and ATP, and the increase in plasma extravasation due to neurokinin A and 5-hydroxytryptamine were unaffected by N(G)-nitro-L-arginine (100 microM), whereas vasodilation due to vasoactive intestinal polypeptide was significantly attenuated. These findings suggest that in rat skin microvasculature in vivo, nitric oxide is involved in vasodilator responses due to substance P and vasoactive intestinal polypeptide, and plasma extravasation due to substance P, but does not contribute significantly to vasodilatation induced by neurokinin A, 5-hydroxytryptamine or ATP, or the plasma extravasation induced by neurokinin A or 5-hydroxytryptamine.

Adenosine Triphosphate↗