Biomedical subjects

V Ralevic

Publications and source records attributed to V Ralevic.

At least 55 records · Page 3Linked to original sources

PubMed1995

Effects of vitamin E deficiency on autonomic neuroeffector mechanisms in the rat caecum, vas deferens and urinary bladder.

1. Modified sucrose-gap, standard organ-bath techniques and transmitter release studies were used to examine neuromuscular transmission in the caecum, vas deferens and urinary bladder in normal rats and in rats maintained for 12 months on a diet free of vitamin E. 2. In the caecum circular muscle, non-adrenergic, non-cholinergic inhibitory junction potentials were absent from 48 and 15% of preparations from vitamin E-deficient and control animals, respectively. Cholinergic excitatory junction potentials were absent from 83 and 8% of vitamin E-deficient and control preparations, respectively. Responses to applied noradrenaline (0.1-30 microM), alpha,beta-methylene ATP (3-100 microM) and acetylcholine (0.1-30 microM) were attenuated or absent in vitamin E-deficient tissues. Responses to applied KCl were similar in both groups. Release of [3H]noradrenaline or endogenous acetylcholine could not be evoked from vitamin E-deficient tissues. 3. In contrast, in isolated preparations of the vas deferens and urinary bladder, neuromuscular transmission by adrenergic, cholinergic and purinergic components were unaffected by long-term vitamin E deficiency. 4. In conclusion, vitamin E deficiency causes dysfunction of autonomic neuroeffector mechanisms in the smooth muscle of the rat caecum, at both a pre- and postjunctional level. The lesions in autonomic transmission mechanisms brought about by long-term vitamin E deficiency were found only in the caecum; no changes in sympathetic neuromuscular transmission were observed in the vas deferens, or in parasympathetic neuromuscular transmission in the urinary bladder.

Adenosine Triphosphate↗

PubMed1995

The intra-adrenal distribution of intrinsic and extrinsic nitrergic nerve fibres in the rat.

The intra-adrenal distribution of nitric oxide synthase (NOS)-immunoreactive nerve fibres was studied in rats subjected to various denervations. Splanchnic nerve section eliminated the NOS-immunoreactive nerve fibres which innervate adrenal chromaffin and neuronal cells. It did not affect those innervating blood vessels and zona glomerulosa, which instead were affected by adrenal demedullation. Guanethidine, 6-hydroxydopamine (6-OHDA) and capsaicin treatments, however, did not produce any change. These results suggest that nitrergic nerves which innervate adrenal medullary cells are extrinsic (largely preganglionic sympathetic), whilst those innervating the zona glomerulosa and the majority of adrenal vessels are intrinsic, and that they do not belong to nerves sensitive to the sympathetic nerve neurotoxins, guanethidine and 6-OHDA, or the sensory neurotoxin, capsaicin.

Adrenal Glands↗

PubMed1995

Pivotal role of phosphate chain length in vasoconstrictor versus vasodilator actions of adenine dinucleotides in rat mesenteric arteries.

1. The isolated perfused rat mesenteric arterial bed was used to examine the activity of the adenine dinucleotides: beta-nicotinamide adenine dinucleotide (NAD); beta-nicotinamide adenine dinucleotide phosphate (NADP); flavin adenine dinucleotide (FAD); and of the alpha,omega-diadenosine polyphosphates: adenylyl adenosine (AP1A); P1,P2-diadenosine pyrophosphate (AP2A); P1,P3-diadenosine triphosphate (AP3A); P1,P4-diadenosine tetraphosphate (AP4A); P1,P5-diadenosine pentaphosphate (AP5A); P1,P6-diadenosine hexaphosphate (AP6A). Responses were compared with those of ADP, ATP, 2-methylthio-ATP (2-meSATP) and alpha,beta-methylene ATP (alpha,beta-meATP). 2. In basal tone preparations mono- and dinucleotides elicited vasoconstriction with the order of potency: alpha,beta-meATP > or = AP5A > or = AP6A > or = AP4A > or = 2-meSATP >> ATP >> ADP. The dinucleotides NAD, NADP, FAD, AP1A, AP2A and AP3A had no effect. 3. The P2X-purinoceptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (30 microM) virtually abolished vasoconstrictor responses to AP4A, AP5A and AP6A. 4. Auto- and cross-desensitization of vasoconstrictor responses to AP4A, AP5A, AP6A, ATP and alpha,beta-meATP were observed. 5. In raised tone preparations nucleotides elicited endothelium-dependent vasodilatation with the order of potency: 2-meSATP = ADP > ATP > AP3A > AP2A > AP1A = NADP = FAD > NAD. The nucleotides AP4A, AP5A, AP6A and alpha,beta-meATP had no vasodilator effects. 6. It is concluded that the alpha,omega-adenine dinucleotides AP4A, AP5A and AP6A elicit vasoconstriction, but not vasodilatation, in the rat mesenteric arterial bed via P2x-purinoceptors. In contrast, the dinucleotides NADP, FAD, AP1A, AP2A and AP3A elicit vasodilatation, but not vasoconstriction, via endothelial P2Y-purinoceptors. 7. It is suggested that there is a crucial relationship between the structure of the alpha,omega-diadenosine polyphosphates and their activity at P2X- and P2Y-purinoceptors with a pivotal role played by the polyphosphate chain. Molecules with four or more phosphates are vasoconstrictors, while those with three or less phosphates are vasodilators.

Adenine Nucleotides↗

PubMed1995

Contractility of urinary bladder and vas deferens after sensory denervation by capsaicin treatment of newborn rats.

1. Capsaicin, a selective sensory neurotoxin, was given to newborn rats and at the age of 3 months the contractile activity of the urinary bladder detrusor muscle and vas deferens evoked by either electrical field stimulation (EFS) or exogenous adenosine 5'-triphosphate (ATP) and carbachol (urinary bladder), or ATP and noradrenaline (vas deferens) were tested. 2. EFS of the urinary bladder evoked contractions which consisted of cholinergic and purinergic components, since they could be partially blocked by either the muscarinic cholinoceptor antagonist, atropine (0.3 microM) or by desensitization of P2x-purinoceptors with alpha,beta-methylene ATP (10 microM). In capsaicin-treated rats, contractions of the urinary bladder evoked by EFS were significantly larger than those of control (vehicle-treated) animals, and this difference remained after the purinergic component of the contractions was blocked by desensitization of P2x-purinoceptors with alpha,beta-methylene ATP. However, when the cholinergic component of the contractions was blocked with atropine, the difference between the groups at 8 Hz and 16 Hz was abolished; EFS caused significantly larger contractions of the capsaicin-treated rat bladder only at frequencies of 2 Hz and 4 Hz. 3. EFS evoked contractions of the vas deferens consisted of adrenergic and purinergic components since they could be partially blocked by either the alpha-adrenoceptor antagonist, phentolamine (3 microM) or by alpha,beta-methylene ATP (10 microM). The contractions of the vas deferens were significantly larger than in the capsaicin-treated rats only at a frequency of 16 Hz. There were no differences between vas deferens contractions of the two groups either after desensitization of P2X-purinoceptors by alpha,beta-methylene ATP or in the presence of phentolamine.4. Contractions of the capsaicin-treated rat urinary bladder evoked by exogenous carbachol (0.1-100 microM) were not significantly different from those of controls, the pD2 values being 1.78 +/- 0.23 micro M and 1.90 +/- 0.20 micro M respectively. There was also no significant difference between the groups in contractions of the bladder evoked by ATP (10 micro M-3 mM).5. Contractions of the vas deferens evoked by either ATP (10 micro M-3 mM) or noradrenaline (1-1000 micro M) in the capsaicin-treated group showed no significant difference between control and capsaicin treated rats.6. In conclusion, the present results indicate that chronic capsaicin treatment increases the amplitude of contractions of the rat urinary bladder, an effect which preferentially involves the cholinergic component of the response; since the response to carbachol is unaffected, the change involves prejunctional mechanisms. In contrast, both the purinergic and adrenergic components of contraction in the vas deferens are unaffected by capsaicin. It is suggested that sensory nerves have a trophic influence on the development of parasympathetic nerves in the rat bladder; removal of sensory nerves shortly after birth results in an increase mainly in the cholinergic, and to a lesser extent purinergic component.

Adenosine Triphosphate↗

PubMed1995

Modulation by nicotinamide adenine dinucleotide of sympathetic and sensory-motor neurotransmission via P1-purinoceptors in the rat mesenteric arterial bed.

1. The pharmacological actions of the purine nucleotides beta-nicotinamide adenine dinucleotide (NAD), beta-nicotinamide adenine dinucleotide phosphate (beta-NADP), adenosine 5'-diphosphoribose (ADP-ribose), the vitamin nicotinamide and structural analogues of NAD and NADP were tested in the isolated perfused mesenteric arterial bed of the rat. Prejunctional effects of NAD were tested against sympathetic vasoconstriction at basal tone, and against sensory-motor vasodilatation at raised tone. 2. NAD and NADP had no vasoconstrictor action but were weak vasodilators of the raised-tone mesenteric arterial bed. A rank order of vasodilator potency of ADP >> ADP-ribose >> NADP > or = NAD = adenosine was observed. The P1-purinoceptor antagonist, 8-para-sulphophenyltheophylline (8-pST; 3 microM) inhibited vasodilator responses to NAD (pKB of 6.61 +/- 0.21, n = 7) and adenosine (pKB of 5.78 +/- 0.14, n = 6), but not those elicited by NADP, ADP and ADP-ribose. Nicotinamide, and analogues of NAD and NADP, namely nicotinamide-1,N6-ethenoadenine dinucleotide phosphate, beta-nicotinamide mononucleotide, nicotinamide hypoxanthine dinucleotide phosphate, nicotinamide hypoxanthine dinucleotide, nicotinamide guanine dinucleotide, and nicotinamide-1, N6-ethenoadenine dinucleotide had no vasoconstrictor or vasodilator actions (at doses of up to 50 nmol). 3. At basal tone, electrical field stimulation (EFS) (32 Hz, 1ms, 90 V, 5 s) at 2 min intervals elicited reproducible vasoconstrictor responses due to activation of sympathetic nerves. NAD and adenosine (10-100 microM) inhibited these responses in a concentration-dependent manner with similar potencies. Nicotinamide had no effect on sympathetic vasoconstriction at concentrations of up to 0.1 mM. Postjunctional effects of NAD (100 microM), as tested on constrictor responses to NA (5 nmol), accounted for approximately 60% inhibition at this concentration.4. In preparations in which tone had been raised with methoxamine (10-40 microM), EFS (8 Hz, 0.1ms,60 V, for 30 s) elicited vasodilatation due to activation of sensory-motor nerves. This vasodilatation was inhibited by NAD and adenosine (O.1-100 microM) in a similar concentration-dependent manner: pD2 values were 6.2 +/- 0.10 (n = 11) and 6.1 +/- 0.15 (n = 6) for NAD and adenosine respectively. Nicotinamide had no effect on sensory-motor vasodilatation at concentrations of up to 0.1 mM.5. Inhibition of sympathetic constriction by NAD and adenosine was antagonized by 8-pSPT (3 microM).Inhibitory effects of NAD and adenosine on sensory-motor vasodilatation were similarly antagonized by 8-pSPT (1 microM), pKB values were 6.72 +/- 0.21 for NAD and 6.36 +/- 0.22 for adenosine, resulting in parallel rightward shifts in the concentration-inhibitory effect curves.6. The adenosine deaminase inhibitor, pentostatin (1 microM), augmented the inhibitory effects of NAD and adenosine. Concentration-inhibitory effect curves for NAD and adenosine on sympathetic vasoconstriction and sensory-motor vasodilatation were shifted to the left without a change in the maximum.7. It is concluded that NAD can act as a modulator of sympathetic and sensory-motor transmission in rat mesenteric arteries via P1-purinoceptors possibly via direct actions but with a contribution of adenosine formed following breakdown of NAD or released pre- and/or post junctionally. Structure activity relationships of NAD, NADP, ADP and ADP-ribose showed that the P1-purinoceptor activity of NAD is abolished after removal of nicotinamide, or ribose plus nicotinamide, to yield the structurally-related ADP-ribose and ADP respectively, or when there is phosphorylation of the 2'-hydroxyl group of NAD to yield NADP.

Adenosine↗

PubMed1995

Contribution of P1-(A2b subtype) and P2-purinoceptors to the control of vascular tone in the rat isolated mesenteric arterial bed.

1. The direct vascular effects of adenosine and ATP were compared in the isolated and perfused mesenteric arterial bed of the rat. The actions of analogues of adenosine and ATP were also examined. 2. In preparations at basal tone, adenosine lacked vasoconstrictor actions, while ATP elicited dose-dependent vasoconstrictor responses. When the tone of preparations was raised by adding methoxamine to the perfusate, adenosine and its stable analogue, 2-chloroadenosine (2-CADO) elicited dose-dependent vasodilation. The A2 adenosine receptor agonist, 5'-N-ethylcarboxamidoadenosine (NECA) was active at lower doses than adenosine, while the A2a-selective agonist, CGS 21680 and the selective A1 agonist, N6-cyclopentyladenosine (CPA) failed to induce vasodilatation. ATP and its analogue, 2-methylthio ATP, elicited dose-dependent vasodilatation at doses 400 fold lower than adenosine. 3. Vasodilator responses to adenosine and 2-CADO were sensitive to antagonism by 1 microM 8-sulphophenyltheophylline (8-SPT) and were unaffected by inhibition of nitric oxide synthase by N omega-nitro-L-arginine methyl ester (L-NAME). In contrast, vasodilator responses to ATP were not sensitive to antagonism by 8-SPT and were almost abolished by L-NAME treatment. 4. These results indicate that in the rat mesenteric arterial bed, while both adenosine and ATP participate in the purinergic control of vascular tone, adenosine appears to be a weaker vasodilator than ATP and lacks vasoconstrictor action. A2b adenosine receptors account for the adenosine-induced vasodilatation which is independent of the production of nitric oxide.

2-Chloroadenosine↗

PubMed1995

Effects of chronic vitamin E deficiency on vascular function--a study of sympathetic nerves, smooth muscle and endothelium of the mesenteric arterial bed of the rat.

1. Male rats were deprived as weanlings of dietary vitamin E for 2, 4, 6, 10 and 12 months. Mesenteric arterial beds from these rats and from age-matched controls were isolated and perfused with Krebs solution at a constant flow rate (5 ml min-1). The function of perivascular sympathetic nerves, smooth muscle and endothelium was assessed. 2. At 12 months vitamin E deficient rats exhibited the characteristic symptoms of vitamin E deficiency, namely poor coat condition, muscle wasting, kyphoscoliosis and impaired gait. In the isolated mesenteric arterial bed electrical field stimulation (EFS) of perivascular nerves (4-32 Hz, 90 V, 1 ms, for 30 s) elicited frequency-dependent vasoconstrictor responses which were unaffected by vitamin E deficiency except at 12 months, at which age responses were significantly greater than those of the controls at 24 and 32 Hz (P < 0.01). 3. Exogenous noradrenaline (NA; 0.15-500 nmol) elicited dose-dependent vasoconstriction which was similar in vitamin E-deficient and control preparations at all ages. Potassium chloride (0.15 mmol) also produced similar vasoconstrictor responses in vitamin E-deficient and control preparations at each age. 4. Tone of the preparations was raised by continuous perfusion with methoxamine (4-70 microM), producing similar increases in perfusion pressure in vitamin E-deficient and control preparations at each age. Endothelium-dependent dose-dependent vasodilatation to adenosine 5'-triphosphate was significantly impaired in mesenteric arterial beds from 12 month-old vitamin E-deficient rats compared with the controls (P < 0.05). Relaxation to acetylcholine was not significantly different at any age. 5. Endothelium-independent vasodilatation to sodium nitroprusside was similar in vitamin E-deficient rats and age-matched controls. 6. These results suggest that long term (12 months) deprivation of dietary vitamin E may impair endothelial function in mesenteric arteries of the rat. Sympathetic perivascular nerve constrictor function was increased at 12 months. There were no functionally expressed changes in the vascular smooth muscle, which appears to be more resilient to the effects of oxidative stress in vitamin E deficiency.

Animals↗

PubMed1995

Effects of chronic vitamin E deficiency and a high polyunsaturated fatty acid diet on rat mesenteric arterial function.

1. Male rats were deprived as weanlings of dietary vitamin E and fed on a high polyunsaturated fatty acid (PUFA) diet for 6 months. Rats fed on a high PUFA or on an untreated diet served as controls. Mesenteric arterial beds were isolated and perfused at a constant flow rate (5 ml min-1) and the function of sympathetic nerves, smooth muscle and endothelium was assessed. 2. Electrical field stimulation (4-32 Hz, 90 V, 1 ms, for 30 s) elicited frequency-dependent vasoconstriction of the mesenteric arterial preparations. Response curves were similar between untreated control and PUFA-fed control groups. Maximum vasoconstrictor responses (at 24 and 32 Hz) were significantly attenuated in rats deprived of vitamin E and on a high PUFA diet compared to the PUFA-fed controls (P < 0.05). 3. Exogenous noradrenaline (NA; 0.15-500 nmol) elicited dose-dependent constriction of the mesenteric arterial beds. Preparations from rats fed on a high PUFA diet elicited significantly smaller responses compared to the control group. There was no significant difference in constrictor responses of PUFA rats deprived of vitamin E compared to the PUFA controls. Vasoconstrictor responses to doses of adenosine 5'-triphosphate (ATP) (5-5000 nmol) were significantly impaired in vitamin E-deficiency with a high PUFA diet compared to a high PUFA diet alone (P < < 0.001). Constrictor responses to potassium chloride (0.15 mmol) were significantly impaired in vitamin E-deficient PUFA rats compared to the PUFA-fed control group (P < 0.05). 4. Vasodilator responses were assessed in preparations in which tone was raised by continuous perfusion with methoxamine (4-25 microM). Mesenteric arterial beds from PUFA-fed rats deprived of vitamin E acquired significantly less tone, 59.8 +/- 4.6 mmHg (n = 7), than PUFA-fed controls 116.9 +/- 7.6 mmHg (n = 7) (P < 0.001) and were refractory to further increases in tone with further additions of methoxamine. Methoxamine-induced tone of PUFA-fed controls was greater than in P that in the untreated controls (83.9 +/- 7.4 mmHg; n = 5) (P < 0.05). Responses to the endothelium-dependent vasodilators acetylcholine (ACh) and ATP were significantly reduced in preparations from rats fed on the vitamin E-deficient high-PUFA diet compared to PUFA controls. Vasodilator responses to ACh were greater in PUFA controls than in untreated controls and this reached statistical significance at 5 nmol ACh. 5. Vasodilator responses to sodium nitroprusside, which acts directly on the vascular smooth muscle, were similar in untreated control and PUFA control groups. Responses were significantly attenuated in vitamin E-deficient PUFA rats compared to the PUFA control group (P < < 0.001). 6. These results indicate that a combination of a high PUFA diet and vitamin E deficiency impairs mesenteric arterial function at the level of the vascular smooth muscle. A high PUFA diet alone attenuates responses to NA and augments endothelium-dependent vasodilation. The detrimental effects of loss of antioxidant activity due to vitamin E-deficiency on vascular function may be exacerbated by a high PUFA diet.

Animals↗

PubMed1995

Long-term sensory denervation by neonatal capsaicin treatment augments sympathetic neurotransmission in rat mesenteric arteries by increasing levels of norepinephrine and selectively enhancing postjunctional actions.

The present study assessed the long-term effects of sensory denervation on sympathetic innervation in rat mesenteric arteries. Mesenteric arterial beds were isolated from adult rats treated as neonates with capsaicin and from vehicle-treated and untreated rats and perfused at a constant flow rate of 5 ml/min. Frequency-dependent constrictions to electrical field stimulation of sympathetic nerves were markedly augmented in capsaicin-treated rats; maximal constriction was approximately 105% and 169% greater than in vehicle-treated and control preparations, respectively. Maximal contractile responses to norepinephrine (NE) and serotonin (5-HT) were increased by approximately 57% and 85%, respectively, compared with vehicle-treated preparations without a change in the pD2 values. Vasoconstrictions to ATP, vasopressin and KCl were unchanged. In contrast, acute denervation of sensory-motor nerves by in vitro capsaicin treatment had no significant effect on vasoconstrictor responses to electrical field stimulation or to NE, ATP, vasopressin and KCl, although the pD2 value for 5-HT was slightly increased. High-performance liquid chromatographic analysis with electrochemical detection showed an approximately 100% increase in mesenteric arterial NE content after long-term capsaicin treatment. Tissue neuropeptide Y, as assessed by enzyme-linked immunosorbent analysis, was unchanged. In conclusion, long-term sensory denervation of rats produces trophic changes in mesenteric arteries as evidenced by augmented sympathetic vasoconstriction mediated both prejunctionally (increase in tissue NE) and postjunctionally (enhanced responses to NE and 5-HT).

Adenosine↗

PubMed1994

Effects of ageing on sensory nerve function in rat skin.

Human studies have shown an age-related decrease in modulation of skin vascular reactivity by sensory nerves that correlates with a decline in wound repair efficacy. Using a vacuum-induced blister model in the rat hind footpad, we have investigated age-related changes in pre- and post-terminal activity of primary afferents involved in skin neurovascular function. Changes in local skin blood flow were monitored using a laser Doppler flowmeter. Pre-terminal stimulation was achieved by electrical stimulation of the distal end of the sciatic nerve (10 V, 15 Hz and 0.5 ms) in three groups of young, old and neonatally pretreated capsaicin rats (3, 24 and 3 months old, respectively). The effect of post-terminal stimulation, achieved using local perfusion of 1 microM substance P (SP) over the blister base, was examined in young (3 months old), mature (12 months old) and aged (24 months old) rats. In addition to changes in SP responsiveness, other post-terminal changes studied included changes in smooth muscle reactivity to sodium nitroprusside (SNP), which acts directly on smooth muscle and to endothelial cell function using N-nitro-L-arginine (L-NORAG), a selective inhibitor of nitric oxide synthesis and endothelium-dependent relaxation. Electrical stimulation of the sciatic nerve in young rats induced an increase in local blood flow (within 1 min) that was maintained during the stimulation period, while the capsaicin group and the old group showed a significantly increased latency and decreased amplitude of the response.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗

PubMed1994

New insights into the local regulation of blood flow by perivascular nerves and endothelium.

Blood flow, particularly in the skin, is essential for the success of plastic surgical operations. This review describes recent studies of the perivascular nerves and vascular endothelial cells which regulate blood flow. Perivascular nerves, once considered simply adrenergic or cholinergic, release many types of neurotransmitters, including peptides, purines and nitric oxide. Cotransmission (synthesis, storage and release of more than one transmitter by a single nerve) commonly takes place. Some afferent nerves have an efferent (motor) function and axon reflex control of vascular tone by these "sensory-motor" nerves is more widespread than once thought. Endothelial cells mediate both vasodilatation and vasoconstriction. The endothelial cells can store and release vasoactive substances such as acetylcholine (vasodilator) and endothelin (vasoconstrictor). The origins and functions of such vasoactive substances are discussed. Endothelial vasoactive substances may be of greater significance in the response of blood vessels to local changes while perivascular nerves may be concerned with integration of blood flow in the whole organism. The dual regulation of vascular tone by perivascular nerves and endothelial cells is altered by aging and conditions such as hypertension, as well as by trauma and surgery. Studies of vascular tone in disease and after denervation or mechanical injury suggest possible trophic interactions between perivascular nerves and endothelial cells. Such trophic interactions may be important for growth and development of the two control systems, particularly in the microvasculature where neural-endothelial separation is small.

Aging↗

PubMed1994

Vasoconstrictor and vasodilator responses to various agonists in the rat perfused mesenteric arterial bed: selective inhibition by PPADS of contractions mediated via P2x-purinoceptors.

1. The effect of pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) on vasoconstrictor and/or vasodilator responses to various agonists and electrical field stimulation was investigated in the rat mesenteric arterial bed at basal tone and at tone raised by methoxamine (15-50 microM). 2. At basal tone, nucleotides produced vasoconstriction with the following rank order of potency: alpha,beta-methylene ATP >> 2-methylthio ATP > or = ATP = UTP. PPADS (0.3-10 microM) concentration-dependently antagonized alpha, beta-methylene ATP-, 2-methylthio ATP- and ATP-induced responses. UTP-, noradrenaline- and nerve-mediated (4-32 Hz) increases in perfusion pressure remained unaffected by 10 microM PPADS. 3. In raised tone preparations, nucleotides produced vasodilations, their rank order of potency being 2-methylthio ATP > ATP > UTP. Responses to 2-methylthio ATP were slightly antagonized, whereas ATP- and UTP-induced responses remained unaffected by 10 microM PPADS. In addition, acetylcholine- and adenosine-elicited relaxations were not influenced by 10 microM PPADS. 4. The present results confirm the previously described selective P2x antagonism by PPADS, this compound being ineffective at muscarinic M3- and adenosine P1-receptors as well as at alpha 1-adrenoceptors. There was some inhibition of P2y-purinoceptors but at a much higher concentration than required for inhibition of P2x-purinoceptors. 5. In addition, this study provides evidence for the ineffectiveness of PPADS at both vasoconstriction- and vasodilatation-mediating P2u-purinoceptors.

Adenosine Triphosphate↗

PubMed1994

Inhibition of neuropeptide Y-induced augmentation of noradrenaline-induced vasoconstriction by D-myo-inositol 1,2,6-trisphosphate in the rat mesenteric arterial bed.

The effect of the neuropeptide Y antagonist D-myo-inositol-1,2, 6-trisphosphate (alpha-trinositol) was tested against modulatory actions mediated by neuropeptide Y in the isolated rat mesenteric arterial bed. Neuropeptide Y (1 and 10 nM) had no direct postjunctional effects, but augmented vasoconstrictor responses to noradrenaline and to sympathetic nerve stimulation to an extent which was greater with the higher concentration of neuropeptide Y. The augmenting effect of neuropeptide Y at 1 nM on vasoconstriction induced by lower doses of noradrenaline was antagonized by alpha-trinositol (1 microM), producing a shift to the right of the dose-response curve. A lower concentration of alpha-trinositol (0.1 microM) had no inhibitory effect on responses to noradrenaline. Augmentation by the higher concentration of neuropeptide Y (10 nM) of noradrenaline-induced vasoconstriction was not affected by alpha-trinositol at concentrations of up to 10 microM. alpha-Trinositol did not significantly antagonize neuropeptide Y-induced augmentation of vasoconstrictor responses to sympathetic nerve stimulation. alpha-Trinositol alone did not affect vasoconstrictor responses to noradrenaline, potassium, or to sympathetic nerve stimulation. In the raised-tone preparation (tone raised with methoxamine) in the presence of guanethidine (5 microM) to block sympathetic neuro-transmission, perivascular nerve stimulation caused vasodilatation due to activation of sensory-motor nerves. Neuropeptide Y inhibited sensory-motor nerve induced vasodilatation in a concentration-dependent manner but this was not affected by alpha-trinositol (1 microM). These results suggest that alpha-trinositol can be a useful functional antagonist of neuropeptide Y-induced augmentation of vasoconstrictor responses to noradrenaline in the rat mesenteric arterial bed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Prejunctional modulation of sensory-motor nerve-mediated vasodilatation of the rat mesenteric arterial bed by opioid peptides.

In the rat isolated mesenteric arterial bed, perivascular nerve stimulation in the presence of guanethidine (5 microM) and methoxamine (30-50 microM), elicited frequency-dependent vasodilatation due to activation of sensory-motor nerves. The present study examined the modulation of this sensory-motor activity by opioid peptides. The mu-selective opioid agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (DAMGO) inhibited vasodilator responses to sensory-motor nerve stimulation. The native enkephalins [Met5]enkephalin (mENK) and [Leu5]enkephalin (IENK) were less potent, whereas the delta-selective agonist DPDPE was without effect. Naloxone (30 nM) reversed the inhibitory effects of both DAMGO and mENK. The delta opioid antagonist ICI 174864 (0.1 microM) had no effect on the inhibition by mENK. Inhibitory effects of the kappa opioid-selective agonist 3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-methanesulfonate hydrate (U-50,488H) on sensory-motor nerve-induced vasodilatation were unaffected by naloxone (0.3 microM) or by the kappa opioid receptor-selective antagonist (-)-5,9 alpha-diethyl-2-(3-furylmethyl)-2'-hydroxy-6,7-benzomorphane (MR 2266). Neither DAMGO nor mENK inhibited vasodilator responses to calcitonin gene-related peptide (CGRP), the principle vasodilator transmitter released from sensory-motor nerves in the rat mesenteric arterial bed or to the sensory neurotoxin capsaicin. In mesenteric beds from reserpine-treated rats (to abolish the catecholamine, but not opioid, content of sympathetic nerves) naloxone facilitated sensory-motor nerve-mediated vasodilatation. These results suggest that sensory-motor neurotransmission in the rat mesenteric arterial bed is inhibited by prejunctional mu, but not by delta or kappa opioid receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Impaired sensory-motor nerve function in the isolated mesenteric arterial bed of streptozotocin-diabetic and ganglioside-treated streptozotocin-diabetic rats.

1. Adult male Wistar rats were treated with streptozotocin (65 mg kg-1, i.p.) to induce diabetes. Subgroups of age-matched control and streptozotocin-treated rats were given daily injections of mixed brain bovine gangliosides (60 mg kg-1 body weight, i.p.). At eight weeks after treatment mesenteric arterial beds from rats in each of the four groups were isolated and perfused and the function of perivascular nerves (sympathetic and sensory-motor), endothelium and smooth muscle was assessed. 2. Values for basal tone of mesenteric beds from diabetic and diabetic-ganglioside rats were significantly lower than those of the control and control-ganglioside-treated rats. Perfusion pressures at basal tone were 25.55 +/- 0.8 (n = 11), 22.58 +/- 1.5 (n = 12), 28.42 +/- 1.6 (n = 12) and 30.67 +/- 1.9 (n = 12) mmHg for diabetic, diabetic-ganglioside, control and control-ganglioside-treated rats respectively. 3. There was no difference between the groups with respect to vasoconstrictor responses to sympathetic nerve stimulation, or to doses of noradrenaline. Vasoconstrictor responses to potassium chloride were also similar between the groups. 4. Perivascular nerve stimulation in the presence of the sympathetic blocker guanethidine (3 microM), with tone of the preparation raised with methoxamine (3-100 microM), elicited frequency-dependent vasodilatation of mesenteric arterial beds due to transmitter release from sensory-motor nerves. Sensory-motor nerve-induced vasodilator responses of mesenteric arterial beds from streptozotocin-diabetic and ganglioside-treated diabetic rats were significantly smaller than those of mesenteric beds from the controls (untreated and ganglioside-treated). Vasodilator responses to exogenously applied calcitonin gene-related peptide, the principal vasodilator transmitter released from these nerves, were not different between the groups. Vasodilator responses to the sensory neurotoxin capsaicin were also not different between the groups.5. Endothelium-dependent vasodilator responses to acetylcholine were similar between the groups as were those to the endothelium-independent vasodilator sodium nitroprusside.6. These results indicate that streptozotocin-induced diabetes produces marked impairment of sensory motor nerve function in the rat mesenteric arterial bed. The significantly lower basal perfusion pressures of mesenteric beds from diabetic rats compared to controls may be a reflection of sympathetic dysfunction, but no differences were apparent from the vasoconstrictor responses produced when sympathetic nerves were electrically stimulated. There was no evidence for changes in endothelial vasodilator function, or smooth muscle vasodilator and vasoconstrictor function. Ganglioside treatment did not modify any aspect of vascular function of mesenteric beds from streptozotocin-diabetic or control rats.

Acetylcholine↗

PubMed1993

The P1-purinoceptors that mediate the prejunctional inhibitory effect of adenosine on capsaicin-sensitive nonadrenergic noncholinergic neurotransmission in the rat mesenteric arterial bed are of the A1 subtype.

It has been shown that capsaicin-sensitive sensory-motor nerves contribute to the control of peripheral vascular resistance by releasing the potent vasodilator calcitonin gene-related peptide. The purpose of the present study was to characterize the P1-purinoceptor subtype that modulates capsaicin-sensitive non-adrenergic noncholinergic (NANC) neurotransmission in the rat mesenteric arterial bed. Analogs of adenosine, selective for the adenosine receptor subtypes A1 or A2, were evaluated on the vasodilator response to electrical stimulation of capsaicin-sensitive sensory-motor nerves. The order of potency of adenosine receptor agonists to inhibit the NANC neurotransmission was: the selective adenosine A1 receptor agonist N6cyclopentyl-adenosine > or = R-phenylisopropyladenosine > 5'N-ethylcarboxamide adenosine > or = 2-chloroadenosine > or = S-phenylisopropyladenosine. The A2-selective agonist CGS 21680 was devoid of any effect on NANC neurotransmission. In addition, the selective A1 receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine inhibited the effect of adenosine. None of the agonists tested showed direct action on the tone of the mesenteric vasculature. Neither N6cyclopentyladenosine nor adenosine modified the vasodilator response to exogenous calcitonin gene-related peptide. Moreover, adenosine failed to affect the vasodilator response to capsaicin. In conclusion, these results indicate that adenosine and its analogs inhibit NANC neurotransmission via prejunctional P1-purinoceptors of the A1 subtype. The inhibitory action of adenosine appears to be selective for the release of transmitters during electrical activation of sensory-motor nerve endings, adenosine being inactive on capsaicin-induced vasodilatation.

Adenosine↗

PubMed1992

Prejunctional modulation of sensory-motor nerve mediated vasodilation of the rat mesenteric arterial bed by adenosine.

The effect of adenosine on the vasodilator response of the rat mesenteric arterial bed to electrical field stimulation of perivascular sensory-motor nerves was examined. Adenosine (0.3-10 microM) produced a concentration-dependent attenuation of the vasodilator response to electrical stimulation of sensory-motor nerves, which is mediated by the sensory neuropeptide calcitonin gene-related peptide (CGRP). The adenosine receptor antagonist, 8-phenyltheophylline (1 microM) competitively antagonized the inhibitory effect of adenosine. Adenosine did not affect the vasodilator response to exogenous CGRP, thus indicating that the inhibitory action of adenosine on the vasodilator response to perivascular sensory-motor nerve stimulation was prejunctional.

Adenosine↗

PubMed1992

Flow-induced release of adenosine 5'-triphosphate from endothelial cells of the rat mesenteric arterial bed.

Adenosine 5'-triphosphate (ATP) was released into the perfusate of rat isolated mesenteric arterial beds during each of two consecutive increases in flow. There was no significant difference between the amounts of ATP released on each occasion. Substance P was also released into the perfusate by increased flow, although its release was more variable. Removal of the endothelium of the mesenteric vessels with sodium deoxycholate led to a significant reduction (74%) in the amount of ATP released compared with the release before the endothelium had been removed. This suggests that the ATP released into the mesenteric arterial perfusate during increased flow arises from endothelial cells.

Adenosine Triphosphate↗