Carl A. Gruetter

Endothelium-dependent modulation of angiotensin II-induced contraction in blood vessels

The influence of endothelium on angiotensin II-induced contraction was investigated in rings of rat aorta, bovine coronary artery, bovine intrapulmonary artery and bovine intrapulmonary vein. Destruction of endothelium significantly enhanced angiotensin II-induced contraction in rat aorta and bovine coronary artery, but not in bovine intrapulmonary artery and bovine intrapulmonary vein. Indomethacin (10(-5) M) did not alter angiotensin II-induced contraction in rat aorta or bovine coronary artery. However, hemoglobin (10(-5) M) or methylene blue (10(-5) M) significantly enhanced angiotensin II-induced contraction in rat aorta and bovine coronary artery with, but not without, endothelium. Intimal rubbing did not affect stimulation of phosphoinositide hydrolysis by angiotensin II in rat aorta. The findings demonstrate that angiotensin II-induced contraction in vascular rings can be modulated by endothelium. However, the effect of endothelium apparently depends upon the species and vascular bed from which the vessel is isolated. Results obtained using inhibitors suggest that in rat aorta and bovine coronary artery release of endothelium-derived relaxant factor (EDRF), rather than cyclooxygenase products, is involved in mediating the inhibitory influence of endothelium. Further, similar stimulation of phosphoinositide hydrolysis in intimally rubbed and unrubbed rat aorta suggests that EDRF does not modulate angiotensin II-induced contraction in this vessel by inhibiting angiotensin II stimulation of phosphoinositide hydrolysis.

Chronic estrogen alters contractile responsiveness to angiotensin II and norepinephrine in female rat aorta.

Sex hormones have been postulated to play an important role in the modulation of vascular responsiveness to endogenous vasoactive substances. This study was designed to establish the effects of chronic treatment with estrogen in vivo on subsequent contractile responsiveness of aortic rings to angiotensin II or norepinephrine in vitro. Concentration-response curves for angiotensin II were compared in aortic rings with or without endothelium isolated from ovariectomized rats (275-299 g) pretreated with 17 beta-estradiol (approximately 1 mg/kg per day) or placebo for 14 days and from normal prepubertal female rats (125-149 g) pretreated with 17 beta-estradiol (approximately 5 mg/kg per day) or placebo for 14 days. Whether or not endothelium was present, angiotensin II-induced contraction was significantly depressed in rings from 17 beta-estradiol-treated ovariectomized or prepubertal rats when compared to controls, and the pattern of the effects of 17 beta-estradiol-treatment on the concentration-response curves for angiotensin II was similar in the two models. In contrast to angiotensin II-induced contraction, norepinephrine-induced contraction was significantly enhanced in aortic rings with or without endothelium from ovariectomized rats pretreated with 17 beta-estradiol (approximately 1 mg/kg per day, 14 days) and from normal prepubertal female rats pretreated with 17 beta-estradiol (approximately 5 mg/kg per day, 14 days) when compared to controls. The results demonstrate that chronic treatment with 17 beta-estradiol selectively reduced and enhanced contractile responsiveness of aortic rings to angiotensin II and norepinephrine, respectively. Further, the results indicate that the normal prepubertal female rat is an efficient model to investigate modulation by estrogen of aortic responsiveness to vasoactive agents in vitro.

Dissociation of cysteine and glutathione levels from nitroglycerin-induced relaxation

The present study investigated possible involvement of cysteine (CSH) and reduced glutathione (GSH) as critical cellular sulfhydryls which mediate nitroglycerin (GTN)-induced cyclic GMP accumulation and relaxation in bovine coronary artery (BCA). Tolerance to the relaxant effects of GTN was induced in BCA in vitro by preincubation with 1 mM GTN for 2 h. GTN-tolerant BCA were at least 100-fold less sensitive than non-tolerant BCA to the relaxant effects of GTN. Consistent with a relationship between tolerance to both GTN-induced cyclic GMP accumulation and relaxation, cyclic GMP accumulation induced by 1 microM GTN was markedly reduced in GTN-tolerant BCA when compared with non-tolerant BCA. Incubation with 1 mM CSH for 1 h did not significantly alter GTN-induced cyclic GMP accumulation or relaxation in either GTN-tolerant or non-tolerant BCA. Levels of CSH, GSH and glutathione-disulfide (GSSG) were measured in non-tolerant BCA, GTN-tolerant BCA and GTN-tolerant BCA incubated with 1 mM CSH for 1 h. Levels of CSH and GSH were lower in GTN-tolerant BCA than in non-tolerant BCA, whereas GSSG levels were similar in both. In GTN-tolerant BCA incubated with 1 mM CSH, CSH levels were more than 10-fold above, and GSH levels were similar to corresponding values obtained in non-tolerant BCA. These data indicate that although incubation with CSH did not significantly reverse tolerance to GTN-induced cyclic GMP accumulation and relaxation in BCA, it did effectively raise the level of CSH and GSH in GTN-tolerant BCA, at least to corresponding levels found in non-tolerant BCA. These results indicate that the relaxant effects of GTN in BCA do not correlate with tissue levels of CSH and GSH. The findings do not support the hypothesis that CSH and GSH are the cellular sulfhydryls involved in mediating GTN-induced guanylate cyclase activation, cyclic GMP accumulation and relaxation in intact BCA.

5-HT2 receptors augment cholinergic nerve-mediated contraction of rat bronchi

5-Hydroxytryptamine (5-HT) potentiated contractions of isolated rat bronchi evoked by electrical field stimulation (EFS). The degree of potentiation caused by 5-HT was dependent upon concentration of the amine present in the tissue bath. The effects of antagonists selective for different subtypes of the 5-HT receptor on potentiation of EFS-induced contractions by 5-HT were examined. Propranolol, a nonselective beta-adrenoceptor antagonist which can act as a 5-HT1 receptor antagonist, did not inhibit the effect of 5-HT on EFS-induced contractile responses. Similarly, 5-HT3 receptor antagonism with MDL 72222 or ICS 205-930, did not inhibit the facilitatory effects of 5-HT. However, ketanserin, mianserin and spiperone, 5-HT2 receptor antagonists, abolished the effects of 5-HT on EFS-induced responses. These latter results suggested that the potentiation was dependent upon activation of 5-HT2 receptors thus additional experiments were conducted using the 5-HT2 receptor agonist, alpha-methyl-5-hydroxytryptamine (alpha-Me-5-HT). alpha-Me-5-HT caused a concentration-dependent potentiation of EFS-induced contractile responses comparable to that observed with 5-HT. Concentrations of alpha-Me-5-HT that significantly potentiated EFS-induced contraction were essentially without effect on airway smooth muscle contraction elicited by exogenous acetylcholine. These results are consistent with a role for 5-HT2 receptor activation in mediating the facilitatory effects of 5-HT on cholinergic nerve-mediated responses in airways.

Endothelium enhances tachyphylaxis to angiotensins II and III in rat aorta

Development of tachyphylaxis to angiotensin-induced contraction was compared in rings of rat aorta with and without functional endothelium. Rat aorta with functional endothelium rapidly developed marked tachyphylaxis to contraction induced by angiotensin II or angiotensin III. Destruction of endothelium significantly depressed, but did not prevent, development of tachyphylaxis to contractile responses induced by repeated exposure to angiotensin II or angiotensin III. The findings suggest that two mechanisms are involved in the development of tachyphylaxis to angiotensin in rat aorta, an endothelium-dependent mechanism and an endothelium-independent mechanism.

Bradykinin-induced endothelium-dependent relaxation of bovine intrapulmonary artery and vein.

Bradykinin induced relaxation and cyclic GMP accumulation in both bovine intrapulmonary artery and vein. Both the relaxant responses and the accompanying cyclic GMP accumulations were abolished or markedly reduced by intimal rubbing or pretreatment with the guanylate cyclase inhibitor, methylene blue. These findings indicate that both bovine intrapulmonary artery and vein exhibit endothelium-dependent relaxation in response to bradykinin, and that the relaxant responses in both vessels are associated with cyclic GMP accumulation.

Potentiation of 5-hydroxytryptamine-induced contraction in rat aorta by chlorpheniramine, citalopram and fluoxetine

This study examined the effects of chlorpheniramine, citalopram and fluoxetine on 5-hydroxytryptamine (5-HT)-induced contraction and 5-HT uptake in rat thoracic aortic rings in vitro. Chlorpheniramine and citalopram markedly potentiated 5-HT-induced contraction. Potentiation by fluoxetine was less pronounced. Chlorpheniramine (0.01-1 microM) and citalopram (0.1-1 microM) induced concentration-dependent parallel shifts to the left of the 5-HT concentration-response curves. The potentiation by chlorpheniramine was selective as chlorpheniramine (1 microM) did not potentiate phenylephrine-induced contraction. The potentiation did not depend upon the presence of endothelium, and was not related to H1 receptor antagonism as diphenhydramine and pyrilamine (1 microM) did not similarly enhance 5-HT-induced contractions. Whereas cocaine (1-10 microM) similarly potentiated 5-HT-induced contraction, imipramine (1-10 microM) inhibited, rather than enhanced, contraction elicited by 5-HT. In the presence of 10 microM cocaine, maximally effective concentrations of chlorpheniramine (1 microM) or citalopram (100 nM) did not induce any additional potentiation of 5-HT-induced contraction. Cooling (4 degrees C) markedly inhibited uptake of [3H]5-HT in rings with and without endothelium. Although less marked, imipramine (10 microM), cocaine (1 microM), chlorpheniramine (1 microM) and citalopram (100 nM) inhibited [3H]5-HT uptake in endothelium-intact and endothelium-denuded rings. Fluoxetine also inhibited [3H]5-HT uptake, but the inhibition was only statistically significant in endothelium-intact rings. The monoamine oxidase (MAO) inhibitor, pargyline (10-100 microM), did not significantly affect 5-HT-induced contraction. The results demonstrate that chlorpheniramine, citalopram and to a lesser extent, fluoxetine potentiate 5-HT-induced contraction in rat aorta in which neuronal 5-HT uptake is negligible. The data are consistent with inhibition of non-neuronal 5-HT uptake as at least one mechanism responsible for potentiation of 5-HT-induced contraction in rat aorta by chlorpheniramine, citalopram and fluoxetine.

Effects of 17ß-estradiol on endothelium-dependent relaxation induced by acetylcholine in female rat aorta

Estrogens have been postulated to play an important role in modulation of vascular responses to endogenous reactive substances. The effects of chronic in vivo treatment with 17 beta-estradiol on relaxant responses to acetylcholine were investigated in the rat aorta isolated from prepubertal female rats. The selectivity of effects of 17 beta-estradiol on acetylcholine-induced relaxation was evaluated using histamine, another endothelium-dependent relaxant in the rat aorta. 17 beta-Estradiol significantly enhanced endothelium-dependent relaxation induced by acetylcholine, but did not alter the vascular responses to acetylcholine in endothelium-denuded aortic rings isolated from prepubertal female rats. In contrast, 17 beta-estradiol did not change endothelium-dependent relaxation induced by histamine in endothelium-intact aortic rings. The results of the present study demonstrate that 17 beta-estradiol selectively enhances acetylcholine-induced endothelium-dependent relaxation in the rat aorta.

Histamine H1-receptors mediate endothelium-dependent relaxation of rat isolated pulmonary arteries

Histamine has been reported to cause endothelium-dependent relaxation of vascular smooth muscle and vasodilation. This study was undertaken to examine the inhibitory effects of histamine on cylindrical segments of extrapulmonary arteries isolated from male Sprague Dawley rats. In arterial segments precontracted with phenylephrine (10 microM), histamine (0.1-100 microM) elicited concentration-dependent relaxation responses. Removal of the endothelium or pretreatment with methylene blue (10 microM) abolished relaxation responses to low concentrations of histamine and markedly inhibited those caused by histamine at concentrations greater than 1 microM. Incubation of endothelium-intact arterial segments with pyrilamine (1 microM) caused a significant rightward shift of the histamine concentration-response curves. Treatment of the segments with cimetidine (100 microM) or indomethacin (10 microM) only minimally antagonized histamine-induced relaxation in arteries with endothelium. Residual relaxation responses observed in arteries stripped of endothelium were unaffected by pretreatment with cimetidine, indomethacin, or pyrilamine. The results suggest that the inhibitory effect of histamine in rat pulmonary arteries is mediated predominantly by activation of H1-receptors on the endothelium and the subsequent release of endothelium-derived relaxing factor(s).

Evidence that histamine is involved as a mediator of endothelium-dependent contraction induced by A23187 in bovine intrapulmonary vein.

This study was initiated to test the hypothesis that histamine can act as an endothelium-derived contracting factor in bovine isolated intrapulmonary vein. The effects of calcium ionophore, calcimycin (A23187), on isometric tension were compared in unstimulated rings of intrapulmonary vein with and without endothelium. A23187 (0.1-10 microM) induced concentration-related contraction when endothelium was present. Destruction of endothelium markedly inhibited A23187-induced contraction. Methylene blue, hemoglobin or NG-methyl-L-arginine significantly enhanced A23187-induced contraction only in venous rings with endothelium consistent with attenuation of the contraction by the concomitant release of endothelium-derived relaxing factor (nitric oxide) [EDRF(NO)]. Histamine H1 receptor antagonists inhibited, and iproniazid enhanced, contraction elicited by A23187. A23187 induced release of greater amounts of histamine from venous rings with than without endothelium. A23187-induced contraction was not mimicked by the mast cell activator, compound 48/80, and was not inhibited by preexposure to compound 48/80 or in the presence of cromolyn or doxantrazole. A23187-induced contraction was not inhibited by pretreatment with indomethacin, phentolamine, lipoxygenase inhibitors or superoxide dismutase. The results indicate that A23187 induces endothelium-dependent contraction in bovine intrapulmonary vein and support histamine as one major mediator involved. The association of destruction of endothelium with an inhibition of both A23187-induced contraction and histamine release is consistent with the endothelium as a source for histamine which can exert a local vasoconstrictor effect in bovine intrapulmonary vein.