Biomedical subjects

R C Webb

Publications and source records attributed to R C Webb.

At least 55 records · Page 3Linked to original sources

PubMed1997

Increase of oxytocin-induced oscillatory contractions by 4-hydroxy-2',4',6'-trichlorobiphenyl is estrogen receptor mediated.

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that are associated with decreased gestation length in women as well as other mammals. Many lightly chlorinated PCBs are hydroxylated in vivo. The PCB congener 4-hydroxy-2',4',6'-trichlorobiphenyl (4-OH-TCB) has a high affinity for estrogen receptors and exerts a uterotropic effect in vivo. This study tested the hypothesis that 4-OH-TCB increases the contractile response of midgestation uteri to oxytocin by an estrogen receptor-mediated mechanism. After in vitro treatments with 4-OH-TCB or estradiol-17beta for 20 h or 42 h, uterine explants from midgestation rats were mounted in standard muscle baths for measurement of isometric contractions. A 20-h exposure to either 4-OH-TCB (0.1, 1, or 10 microM) or estradiol-17beta (10 nM) failed to alter the contractile response to cumulative additions of oxytocin (10(-10) to 10(-7) M). However, a 42-h exposure to either 1 microM 4-OH-TCB or 10 nM estradiol-17beta significantly elevated the contractile response to oxytocin, which was abolished by cotreatment with the estrogen receptor antagonist tamoxifen (30 nM). These data support the hypothesis that the stimulatory actions of estradiol-17beta and 4-OH-TCB on oxytocin-induced oscillatory contractions are mediated by estrogen receptors. Under the conditions of this experiment, more than 20 h of treatment is required to elicit the estrogen-dependent responses.

Animals↗

PubMed1997

Dual cell cycle-specific mechanisms mediate the antimitogenic effects of nitric oxide in vascular smooth muscle cells.

OBJECTIVE: To determine the cell cycle specificity and intracellular mechanisms involved in inhibition by nitric oxide (NO) of vascular smooth muscle cell mitogenesis. METHODS: Cultured rat aortic smooth muscle cells were synchronized by serum withdrawal, treated with the NO donor S-nitroso-N-acetylpenicillamine and the cyclic GMP analog 8-Br-cGMP at various times during cell cycle progression, and DNA synthesis measured during the S phase. Two additional NO donors, 5-nitroso-glutathione and diethylamine NONOate, were used to confirm the inhibition of DNA synthesis by S-nitroso-N-acetylpenicillamine, and the ability of two antagonists of free NO to reverse the effects of NO donors was also evaluated. Bypass of ribonucleotide reductase by use of exogenous deoxynucleosides was attempted to determine whether inhibition of this S-phase enzyme was the mechanism by which NO inhibited DNA synthesis during the S phase. RESULTS: Vascular smooth muscle cell mitogenesis was inhibited by cyclic GMP (cGMP) up to late G1 phase of the cell cycle, which corresponded to the point of greatest sensitivity to exogenous NO. In contrast to cGMP, three different NO donors inhibited DNA synthesis when added to cells synchronized in S phase, beyond the restriction point of cell cycle control in late G1 phase. This S-phase inhibition was reversible by removal of the NO donor or addition of two NO antagonists and was not observed with non-NO analogs of the donors. Inhibition by NO donors in S phase was neither reversed by the guanylate cyclase inhibitor methylene blue nor mimicked by exogenous cGMP. The S-phase inhibition by all three NO donors was reversed partially by bypass of ribonucleotide reductase, establishing this enzyme as an S-phase target of NO. CONCLUSIONS: These findings demonstrate that NO inhibits smooth muscle mitogenesis by cGMP-dependent and -independent mechanisms acting at distinct points in the cell cycle. NO is the first endogenous substance to have been shown to inhibit mitogenesis beyond the restriction point in late G1 phase, suggesting that it plays a role in regulation of cells that have lost normal mechanisms of G1 growth control, such as the hyperproliferative smooth muscle cells noted in hypertension and restenosis.

Animals↗

PubMed1997

Cell cycle effects of nitric oxide on vascular smooth muscle cells.

We characterized the cell cycle block induced by nitric oxide (NO) on smooth muscle cells (SMC). We hypothesized that the inhibition of SMC proliferation by NO was due to a specific block in cell cycle progression. Treatment of cultured rat aortic SMC with the NO donors S-nitroso-N-acetylpenicillamine or S-nitrosoglutathione (0.1 mM for 48 h) resulted in a 50% decrease (P < 0.05) in the fraction of cells in the S and G2 + M phases and a corresponding increase in the G1 fraction, suggesting that NO inhibits entry into S phase, causing accumulation of cells in G1 phase. Application of both NO donors to cycling SMC resulted in a short-term, concentration-dependent (0.06-0.3 mM) inhibition of ongoing DNA synthesis as measured by radiothymidine incorporation, demonstrating that NO causes an S-phase arrest. The S-phase arrest by NO was not mimicked by exogenous guanosine 3',5'-cyclic monophosphate (cGMP, 10 mM) and was associated with, but not due to, a 20% inhibition of RNA synthesis. The S-phase block was completely reversed within 2 h of removal of the NO donors, similar to inhibition by the ribonucleotide reductase inhibitor hydroxyurea. Prolonged treatment of SMC with either NO donor (0.1 mM) did not synchronize cells at the G1-S boundary as expected after a prolonged S-phase arrest, but instead induced a quiescent G0-like state characterized by a 12- to 18-h lag before DNA synthesis returned to normal levels after NO removal. These findings demonstrate that NO inhibition of SMC proliferation is associated with two distinct and reversible cell cycle arrests, an immediate cGMP-independent S-phase block followed by a shift back in the cell cycle from the G1-S boundary to a quiescent G0-like state.

Animals↗

PubMed1997

Expression of a recombinant preproendothelin-1 gene in arteries stimulates vascular contractility.

Endothelin (ET)-1 is a potent vasoconstrictor peptide that is elevated in cardiovascular diseases. However, the biological function of ET-1 gene expression within arteries in vivo has not been determined. The effects of ET-1 gene expression were investigated using gene-transfer methods on porcine vascular cells in vitro and porcine arteries in vivo. Transfection of vascular cells with a vector encoding for human preproendothelin-1 cDNA (pVR-ppET) resulted in significant increase in active ET-1 levels in culture supernatant compared with nontransfected cells (P < 0.05). This supernatant contracted rat aortic strips at concentrations 10-fold lower than synthetic ET-1 protein, which was inhibited by the ET-A receptor antagonist BQ-123. Transfection of pVR-ppET into pig iliofemoral arteries resulted in an increase in contractile responses to angiotensin I compared with control vessels (P < 0.05), in contrast to serotonin, phenylephrine, synthetic ET-1, and angiotensin II. A mitogenic effect of recombinant ET-1 on intimal cell growth was not observed. These findings demonstrate that expression of a recombinant ET-1 gene in vivo augments vascular contractility due to an increased sensitivity to angiotensin I, suggesting a role for ET-1 in the pathogenesis of cardiovascular diseases.

Angiotensin I↗

PubMed1997

Mechanisms in the pressor effects of hepatic portal venous fatty acid infusion.

Portal venous infusion of oleate solution has pressor effects. We have examined efferent mechanisms, measured the response to sustained infusion, and determined the effect of linoleate. Eight conscious animals received concurrent infusions of prazosin or vehicle with portal venous infusion of oleate. Oleate alone increased mean arterial pressure from 109.0 +/- 4.1 to 123.0 +/- 5.8 mmHg (P = 0.02), whereas no increase in blood pressure occurred when oleate was infused with prazosin. In 10 rats, concurrent infusion of losartan had no effect on the pressor activity of portal oleate infusion. Twenty-two animals received portal oleate or vehicle as a continuous infusion for 7 days. Mean arterial pressure (126.1 +/- 2.0 vs. 107.8 +/- 2.6 mmHg, P < 0.001) and heart rate (383 +/- 5 vs. 366 +/- 5, P = 0.0257) were increased in oleate-infused animals. No differences in plasma fatty acids, glucose, insulin, pressor hormones, liver enzymes, or in vitro arterial pressor responsiveness were observed. Portal venous infusion of linoleate increased arterial pressure by 12.2 +/- 3.2 mmHg (P = 0.033). These results indicate that alpha-adrenergic activity is necessary for the acute pressor effects of portal oleate, that sustained portal oleate infusion results in persistent blood pressure elevation, and that other long-chain fatty acids besides oleate have pressor effects.

Acetylcholine↗

PubMed1997

The effects of cyclopiazonic acid on intracellular Ca2+ in aortic smooth muscle cells from DOCA-hypertensive rats.

We tested the hypothesis that cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum (SR) Ca(2+)-ATPase, increases intracellular Ca2+ concentration ([Ca2+]) in aortic myocytes and that the increase in [Ca2+]i is higher in aortic cells from deoxycorticosterone acetate (DOCA)-hypertensive rats. Male Sprague-Dawley rats, 250-300 g, underwent uninephrectomy, received a silastic implant containing DOCA (200 mg/kg) and had free access to water supplemented with 1.0% NaCl and 0.2% KCl. Control rats were also uninephrectomized, received normal tap water, but no implant. Intracellular Ca2+ measurements were performed in aortic myocytes isolated from normotensive (Systolic blood pressure = 120 +/- 3 mmHg; body weight = 478 +/- 7 g, N = 7) and DOCA-hypertensive rats (195 +/- 10 mmHg; 358 +/- 16 g, N = 7). The effects of CPA on resting [Ca2+]i and on caffeine-induced increase in [Ca2+]i after [Ca2+]i depletion and reloading were compared in aortic cells from DOCA and normotensive rats. The phasic increase in [Ca2+]i induced by 20 mM caffeine in Ca(2+)-free buffer was significantly higher in DOCA aortic cells (329 +/- 36 nM, N = 5) compared to that in normotensive cells (249 +/- 16 nM, N = 7, P < 0.05). CPA (3 microM) inhibited caffeine-induced increases in [Ca2+]i in both groups. When the cells were placed in normal buffer (1.6 mM Ca2+, loading period), after treatment with Ca(2+)-free buffer (depletion period), an increase in [Ca2+]i was observed in DOCA aortic cells (45 +/- 11 nM, N = 5) while no changes were observed in normotensive cells. CPA (3 microM) potentiated the increase in [Ca2+]i (122 +/- 30 nM, N = 5) observed in DOCA cells during the loading period while only a modest increase in [Ca2+]i (23 +/- 10 nM, N = 5) was observed in normotensive cells. CPA-induced increase in [Ca2+]i did not occur in the absence of extracellular Ca2+ or in the presence of nifedipine. These data show that CPA induces Ca2+ influx in aorta from both normotensive and DOCA-hypertensive rats. However, the increase in [Ca2+]i is higher in DOCA aortic cells possibly due to an impairment in the mechanisms that control [Ca2+]i. The large increase in [Ca2+]i in response to caffeine in DOCA cells probably reflects a greater storage of Ca2+ in the SR.

Animals↗

PubMed1997

Calcium handling by vascular myocytes in hypertension.

Calcium ions (Ca2+) trigger the contraction of vascular myocytes and the level of free intracellular Ca2+ within the myocyte is precisely regulated by sequestration and extrusion mechanisms. Extensive evidence indicates that a defect in the regulation of intracellular Ca2+ plays a role in the augmented vascular reactivity characteristic of clinical and experimental hypertension. For example, arteries from spontaneously hypertensive rats (SHR) have an increased contractile sensitivity to extracellular Ca2+ and intracellular Ca2+ levels are elevated in aortic smooth muscle cells of SHR. We hypothesize that these changes are due to an increase in membrane Ca2+ channel density and possibly function in vascular myocytes from hypertensive animals. Several observations using various experimental approaches support this hypothesis: 1) the contractile activity in response to depolarizing stimuli is increased in arteries from hypertensive animals demonstrating increased voltage-dependent Ca2+ channel activity in hypertension; 2) Ca2+ channel agonists such as Bay K 8644 produce contractions in isolated arterial segments from hypertensive rats and minimal contraction in those from normotensive rats; 3) intracellular Ca2+ concentration is abnormally increased in vascular myocytes from hypertensive animals following treatment with Ca2+ channel agonists and depolarizing interventions, and 4) using the voltage-clamp technique, the inward Ca2+ current in arterial myocytes from hypertensive rats is nearly twice as large as that from myocytes of normotensive rats. We suggest that an alteration in Ca2+ channel function and/or an increase in Ca2+ channel density, resulting from increased channel synthesis or reduced turnover, underlies the increased vascular reactivity characteristic of hypertension.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1997

Quinapril prevents hypertension and enhanced vascular reactivity in nitroarginine-treated rats.

Long-term inhibition of nitric oxide synthase (NOS) by substituted arginine analogues has previously been shown to induce systemic hypertension in several animal species; however, the precise mechanisms for the elevated blood pressure remain unclear. We hypothesized that a portion of the hypertensive response to arginine analogues was due to direct inhibition of endothelial NOS and resultant functional alterations in the vasculature that contribute to elevated systemic resistance. Adult Sprague-Dawley rats were treated for 2 weeks with an arginine analogue, N omega Nitro-L-arginine (L-NNA), alone or in combination with the angiotensin converting enzyme (ACE) inhibitor quinapril. Next, thoracic aortas were removed, cut into rings and suspended in isolated tissue baths for measurement of contractile force in response to vasoactive drugs. Our results showed that oral L-NNA treatment significantly elevated systolic blood pressure in rats that was completely prevented by quinapril. Furthermore, L-NNA treatment increased endothelium-dependent and -independent contractility and attenuated endothelium-dependent vasodilation in the thoracic aorta. These functional alterations were also attenuated by quinapril treatment. Therefore, long-term L-NNA-induced hypertension in rats is associated with enhanced vascular reactivity due both to direct inhibition of endothelial NOS and to stimulation of the renin-angiotensin system.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1997

Induction of hypercontractility in human cerebral arteries by rewarming following hypothermia: a possible role for tyrosine kinase.

Induction of hypothermia is used routinely in neurosurgical and cardiovascular operations to protect the brain from ischemic insult. However, despite a plethora of experimental evidence supporting the use of hypothermia to protect the brain from ischemia, clinical experience using deliberate hypothermia in humans has not shown a convincing benefit. The authors tested the hypothesis that hypothermia and rewarming alter tone in human cerebral vessels and may interfere with cerebral perfusion in the setting of deliberate hypothermia. They examined human cerebral arteries during hypothermia (32 degrees C and 17 degrees C) and during rewarming to delineate the direct effects of cooling and rewarming on cerebrovascular tone. Artery segments obtained from autopsy material and from specimens excised at elective temporal lobectomies were tested in tissue baths using isometric tension measurements. Temperature-induced changes in vascular tone were measured and quantified with respect to contractile responses to serotonin (5-HT; 10(-6) M). Cooling induced mild relaxation in cerebral vessels (-38 +/- 12% 5-HT response in 50 vessels from autopsy specimens, -69 +/- 10% 5-HT response in 51 vessels from lobectomy specimens). On rewarming, vessels contracted significantly beyond their baseline tone (108 +/- 18% 5-HT response in 50 vessels from autopsy specimens, 42 +/- 12% 5-HT response in 51 vessels from lobectomy specimens). Rewarming-induced hypercontractility was inhibited by the tyrosine kinase inhibitor genistein (-5 +/- 7% vs. 70 +/- 23% 5-HT response, genistein vs. control, 14 segments, p < 0.05) and enhanced by the tyrosine phosphatase inhibitor sodium orthovanadate (339 +/- 54% vs. 104 +/- 20% 5-HT response, sodium orthovanadate vs. control, five segments, p < 0.05), indicating a possible role for tyrosine kinase activation in the rewarming-induced contraction.

Aged↗

PubMed1996

Calcium channel activity increased by plasma from ischemic hindlimbs of rats: role of an endogenous NO synthase inhibitor.

We tested the hypothesis that an endogenous nitric oxide synthase (NOS) inhibitor released from ischemic hindlimbs increases the activity of calcium channels in vascular smooth muscle, thus contributing to the increased contractile response to calcium agonists. Hindlimb ischemia was generated in rats by infrarenal aortic cross clamping for 5 h, after which plasma was obtained from femoral vein blood. Incubating naive aortic rings (endothelium intact) for 2 h in plasma collected from ischemic rats significantly reduced relaxation to acetylcholine in precontracted rings and increased contraction to the calcium channel agonist, BAY K 8644. However, in isolated smooth muscle cells (without endothelium) loaded with fura-2, no difference was noted in BAY K 8644-stimulated intracellular calcium concentration. The contractile responses to sodium fluoride, serotonin, and calcium ionophore A23187 were not different in either ischemic or control plasma-incubated rings. The augmentation of the contractile response to BAY K 8644 was significantly inhibited by nitroglycerin (10-8 M) and by exposure to calcium-free solution. N omega-nitro-L-arginine (without plasma incubation)-pretreated rings also demonstrated hyperresponsiveness to BAY K 8644. The increase in responsiveness to BAY K 8644 exhibited a negative correlation with the maximal relaxation to acetylcholine (r = -0.99), suggesting that the apparent increase in activity of calcium channels is mediated through inhibition of nitric oxide by an endogenous NOS inhibitor on endothelium.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1996

Decreased sensitivity to vasoconstrictors in aortic rings after acute exposure to nitric oxide.

Nitric oxide (NO) has been postulated as a regulator of vascular reactivity, and the current study tested the hypothesis that NO-induced decreased sensitivity to vasoconstrictors persists following removal of NO. Endothelium-denuded segments of rat aorta were incubated 2-4 h at 37 degrees C with the NO donor S-nitroso-N-acetylpenicillamine (SNAP). Incubation produced rightward shifts in concentration response curves for phenylephrine [i.e., half-maximum effective concentration (EC50; in microM): control = 0.016, NO = 0.14], aluminum fluoride (i.e., EC50 in mM: control = 1.66, NO = 2.29), and KCl (i.e., EC50 in mM: control = 5.9, NO = 23.9). Similar shifts were seen for two other NO donors. The SNAP-induced shift was not attenuated by a guanylyl cyclase inhibitor, LY-83583 (10 microM) and was not mimicked by 8-bromoguanosine 3',5'-cyclic monophosphate (100 microM). It was attenuated by 1,4-naphthoquinone (50 microM), an inhibitor of endogenous mono-ADP ribosyltransferases. NO incubation increased cGMP content (4.6 +/- 0.8 vs. 1.5 +/- 0.15 pmol/mg protein), an increase unaffected by 1,4-naphthoquinone (3.3 +/- 1.0 pmol/mg protein) but prevented by LY-83583 (1.6 +/- 0.36 pmol/mg protein). ADP ribosylation of three proteins was observed in membranes from HEK 293 cells: 88,66, and 38 kDa. ADP ribosylation of the 38-kDa protein was stimulated in a concentration-dependent manner by NO but was not decreased by 1,4-naphthoquinone. In conclusion, NO produces a long-lasting inhibition of vascular contractility by both a cGMP-dependent and -independent mechanism. Based on the observations of 1,4-naphthoquinone, we conclude that the cGMP-independent mechanism is not stimulation of endogenous ADP ribosylation but some other covalent modification in the pathway that mediates contraction.

ADP Ribose Transferases↗

PubMed1996

Increased responsiveness and decreased expression of G proteins in deoxycorticosterone hypertension.

Deoxycorticosterone-salt (DOCA-salt) hypertension is characterized by elevated vasoconstriction to agonists that stimulate G protein-mediated activation of phospholipase C. However, the mechanisms responsible for the augmented responsiveness are unknown. This study tested the hypothesis that this augmented vascular responsiveness is due to elevated content of G(alpha)q, the G protein alpha-subunit that activates phospholipase C. Thoracic aortae from DOCA-salt hypertensive rats (systolic blood pressure 183 +/- 7 mm Hg) and normotensive controls (systolic blood pressure 115 +/- 2 mm Hg) were homogenized and G protein content determined. Western analysis revealed that G(alpha)i content was decreased in DOCA compared with control rats (1364 +/- 196 versus 2343 +/- 188 densitometry units, P < or = .05) with no differences observed for G(alpha)q or G(alpha)s. In addition, contractile responses in denuded femoral artery strips revealed a significant decrease in EC50 values in DOCA arteries to all of the agonists examined: aluminum fluoride (DOCA = 1.42, control = 2.34 mmol/L), mastoparan (DOCA = 0.51, control = 35 micromol/L), phenylephrine (DOCA = 0.08, control = 0.53 micromol/L), and serotonin (DOCA = 0.014, control = 0.04 micromol/L, EC20 values). Finally, arteries from DOCA rats contracted with aluminum fluoride had increased sensitivity to G protein antagonists but not to a phospholipase C inhibitor. The enhanced contractile responsiveness in the DOCA arteries may be mediated in part through decreased G(alpha)i levels. However, it is not caused by increased concentrations of G(alpha)q in the cell membrane or by increased phospholipase C sensitivity, and the increased constrictor response to G protein stimulators of phospholipase C appears to depend primarily on increased G protein sensitivity.

Aluminum Compounds↗

PubMed1996

Vascular gap junctional communication is increased in mineralocorticoid-salt hypertension.

Cells rely on gap junctions for intercellular communication, which is important for growth and contractility. For example, gap junctional communication in the uterus increases near parturition, with a concomitant increase in oscillatory contractions. Because arterial responsiveness to contractile agonists is increased in hypertension, we tested the hypothesis that gap junctional communication is increased in hypertension. We examined thoracic aortas from deoxycorticosterone acetate (DOCA)-salt hypertensive and sham normotensive rats using isolated tissue baths and Western blotting techniques. The concentration of 5-hydroxytryptamine necessary to produce a threshold response was significantly lower in aortas from DOCA-salt (4 nmol/L) compared with sham (100 nmol/L) rats; this was also true for norepinephrine and KCl. In these same aortas, the appearance of spontaneous oscillatory contractions, which are sensitive to the gap junctional inhibitor heptanol (0.3 mmol/L), was more frequent in DOCA-salt arteries (93% versus 14% in sham). Heptanol (1 mmol/L) normalized the DOCA-salt aortic contraction to 5-hydroxytryptamine to levels similar to those of the response of the sham aorta in the presence of heptanol. Western analyses revealed that the density of connexin43 immunoreactivity, the connexin being a constituent of gap junctions, was found to be threefold more abundant in aortic homogenates of DOCA-salt rats compared with that of sham rats. This finding supports the hypothesis that gap junctional communication is increased in hypertension, at least at the protein level. We speculate that this increase results in a portion of the increased vascular reactivity and appearance of contractile oscillations in vascular smooth muscle.

Animals↗

PubMed1996

Nitric oxide reversibly inhibits the migration of cultured vascular smooth muscle cells.

Augmentation of nitric oxide (NO) production in vivo decreases lesions in a variety of models of arterial injury, and inhibition of NO synthase exacerbates experimental intimal lesions. Both vascular smooth muscle cell (VSMC) proliferation and migration contribute to lesion formation. Although NO inhibits VSMC proliferation, its effects on VSMC migration are unknown. To test the hypothesis that NO inhibits VSMC migration independent of inhibition of proliferation, we examined migration of rat aortic VSMCs after wounding of a confluent culture in the presence of chemical donors of NO. Hydroxyurea was used to eliminate any confounding effect of NO on proliferation. Three NO donors, diethylamine NONOate, spermine NONOate, and S-nitrosoglutathione, exhibited concentration-dependent inhibition of both number of migrating VSMCs and maximal distance migrated. Inhibition of migration was also seen with 8-Br-cGMP, suggesting that activation of guanylate cyclase may play a role in mediating the antimigratory effects of NO. Migration resumed after removal of NO donors, as evidenced by an increase in distance migrated. Measurement of VSMC protein synthesis and mitochondrial respiration indicated that inhibition of migration by NO donors was not due to metabolic cytostasis. These findings indicate that NO reversibly inhibits VSMC migration independent of proliferation or cytotoxicity, a novel mechanism by which both endogenous and pharmacological NO may alter vascular pathology.

Animals↗

PubMed1996

Intracellular calcium stores and oscillatory contractions in arteries from genetically hypertensive rats.

Strips of tail artery from stroke-prone spontaneously hypertensive rats (SHRSP), but not from normotensive Wistar Kyoto (WKY) rats, exhibit oscillatory activity after stimulation with norepinephrine. In addition, oscillatory activity is observed in response to tetraethylammonium (TEA) in vessels from both SHRSP and WKY rats. Mechanistically, the oscillatory contractions are associated with calcium (Ca2+)-driven action potentials. We have tested the hypothesis that intracellular Ca2+ stores participate in the generation of norepinephrine-induced oscillatory contractions in tail arteries from SHRSP. Additionally, the role of intracellular Ca2+ stores on TEA-induced contractions were evaluated. Contractile force in strips of tail artery from SHRSP and WKY rats was measured, using standard muscle bath procedures, and the effect of interventions that affect the storage of intracellular Ca2+ on the oscillatory contractions was evaluated. Depletion of intracellular Ca2+ stores, with ryanodine, or inhibition of Ca2+ uptake into the sarcoplasmic reticulum (SR), with thapsigargin and cyclopiazonic acid (CPA), did not inhibit oscillatory contractions induced by norepinephrine in SHRSP vessels. However, these agents inhibited the amplitude of TEA-induced contractions in WKY strips. Bay K 8644 and A23187 inhibited TEA-induced oscillatory contractions in WKY vessels. In SHRSP tail artery Bay K 8644 inhibited both norepinephrine and TEA-induced contractions, while A23187 did not have any effect. The phospholipase C inhibitor, NCDC (3X 10(-5) M), blocked oscillatory activity induced by norepinephrine in SHRSP tail artery and TEA-induced oscillations both in SHRSP and WKY vessels. These observations suggest that Ca2+ release and Ca2+ uptake into intracellular Ca2+ stores are not involved in the contraction-relaxation cycles that characterize norepinephrine-induced oscillatory activity in SHRSP tail artery. Similarly, SR Ca2+ stores may modulate but are not essential for TEA-induced oscillatory contractions.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1996

Arachidonate metabolites and serotonin contraction of femoral arteries from DOCA-salt hypertensive rats.

Serotonin stimulates phospholipase A(2)(PLA(2)) leading to the production of prostaglandin products, several of which are vasoconstrictors. We hypothesised that the elevated vascular responsiveness to serotonin in deoxycorticosterone acetate (DOCA)-hypertensive rats is due in part to augmented production of vasoconstrictor cyclooxygenase products (e.g. PGF(2)alpha). Denuded helical strips of femoral arteries from DOCA-salt hypertensive rats (SBP 183 +/- 7 mmHg) and normotensive control rats (SBP 115 +/- 2) were used in all experiments. EC(50) values for several agonists were significantly reduced in DOCA arteries compared with controls (in mu mol/L, control vs. DOCA): PGF(2)alpha (0.99 vs. 0.23), PGE(2) (0.72 vs. 0.22), arachidonate (1.52 vs. 0.73), serotonin (0.19 vs. 0.07), noradrenaline (0.029 vs. 0.013), KCl (40.1 vs. 27.0 mmol/L) and AlF(4) (2.3 vs. 1.4 mmol/L). Treatment with indomethacin (14 mu mol/L) inhibited the responses to serotonin in DOCA arteries (EC(50) values 0.07 untreated vs. 0.70) and eliminated the responses to arachidonate but did not affect KCl or AlF(4-)contractions. Cyclooxygenase inhibitors shifted concentration response curves to serotonin in sham and DOCA tissues equally. Thus increased sensitivity to serotonin in DOCA arteries persisted following cyclooxygenase blockade. Therefore, although arachidonate products contribute to the serotonergic contraction in femoral arteries, the augmented response in arteries from DOCA hypertensive rats is not due to increased production of or sensitivity to cyclooxygenase products. Furthermore,arachidonate metabolites do not contribute to the contraction induced by either AlF(4-)or KCl in this preparation.

Aluminum Compounds↗

PubMed1996

Acetylcholine induces contraction in vergebral arteries from treated hypertensive patients.

Endothelium-dependent vasodilatation to acetylcholine is abnormal in animal models of hypertension. This abnormality reflects a change in the balance of relaxing and contracting factors produced in the vascular wall. In human cerebral arteries, endothelin has been implicated in the abnormal vasoconstrictor response following subarachnoid hemorrhage. This study tests the hypothesis that cerebral arteriolar dilatation to acetylcholine reduced in clinical hypertension due to an overproduction of endothelin. Our results show that at high concentrations of muscarinic agonist (0.3-3 microM), human vertebral arteries from hypertensive patients contract whereas those from normotensive patients remain maximally dilated. We conclude that the normal dilator response to acetylcholine is abrogated in vertebral arteries from treated hypertensive patients but endothelin-1 does not contribute to the abnormal responsiveness.

Acetylcholine↗

PubMed1996

The 5-hydroxytryptamine2B receptor and 5-HT receptor signal transduction in mesenteric arteries from deoxycorticosterone acetate-salt hypertensive rats.

One of the most profound increases in vascular responsiveness in hypertension has been observed for serotonin (5-hydroxytryptamine, 5-HT). This study investigates the hypothesis that the increase in vascular responsiveness to 5-HT is the result of altered 5-HT receptor signal transduction. Mesenteric arteries were dissected from deoxycorticosterone- (DOCA) salt hypertensive and sham-normotensive rats for use in isolated tissue experiments. Agonist contractile potencies indicated that a 5-HT2 receptor mediates contraction to 5-HT in both sham and DOCA-salt arteries. In arteries from sham rats, ketanserin (5-HT2A/5-HT2C selective), LY53857 (5-HT2 selective) and spiperone (5-HT2A/5-HT2C selective) shifted contraction to 5-HT (pKB = 8.58, 8.35 and 9.52, respectively) indicating that a 5-HT2A receptor mediates contraction in arteries from normotensive rats. By contrast, ketanserin and spiperone did not shift contraction to 5-HT in DOCA-salt mesenteric arteries (pKB > 6.52, > 7.52, respectively). LY53857 did shift the response to 5-HT in DOCA-salt mesenteric arteries (pKB = 7.85). Thus, contraction in arteries from DOCA-salt rats is predominantly mediated by 5-HT2B receptors. Unlike the 5-HT receptor in the sham mesenteric artery and aorta (5-HT2A receptor), the 5-HT receptor in DOCA-salt mesenteric arteries and stomach fundus (5-HT2B receptor) were relatively insensitive to phenoxybenzamine (10-300 nM). These data suggest that the 5-HT2B receptor is insensitive to phenoxybenzamine, is increased in number or, alternatively, has increased G protein coupling. DOCA-salt mesenteric arteries were more sensitive to contraction by the direct G protein stimulator AIF4- (-log EC50 [M]: DOCA-salt = 2.82 +/- 0.04; sham = 2.55 +/- 0.03, P < .05). PCR analyses indicated an increase in mRNA for the 5-HT2B receptor in mesenteric arteries of DOCA-salt hypertensive arteries, supporting an increase in receptor number. Taken together these studies demonstrate significant changes in 5-HT receptor signal transduction in DOCA-salt hypertension, both at the level of the receptor and G protein and may provide one reason why ketanserin has proved to be a relatively ineffective antihypertensive agent in some forms of hypertension.

Animals↗