Vasoconstrictor responses after neo-intima formation and endothelial removal in the rabbit carotid artery.

1. The present study examined the responses of the rabbit carotid artery to five vasoconstrictors after neo-intima formation induced by perivascular collar treatment and evaluated the role of constitutive and inducible nitric oxide (NO) synthase and endothelial cells (ECs). 2. Ring segments of the rabbit carotid artery were mounted in organ chambers for isometric tension recording. Neo-intima-bearing vessels developed less force (Emax) in response to KCl, the thromboxane-mimetic U-46619 and 5-hydroxytryptamine (5-HT), but not to angiotensin I and II. 3. The collar-treatment increased the sensitivity to 5-HT, and decreased the sensitivity to angiotensin II. The sensitivity to U-46619 and angiotensin I remained unchanged. 4. Mechanical removal of ECs and inhibition of NO biosynthesis by NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine (L-NOARG) increased the sensitivity to 5-HT in sham and collar-treated segments to the same extent. The effects of collar-treatment and endothelial removal or treatment with inhibitors of NO biosynthesis were additive. Inhibition of NO biosynthesis failed to augment sensitivity to 5-HT after endothelial denudation. L-NOARG increased the force development to KCl in sham and collar-treated segments to the same extent. However, L-NMMA and L-NOARG failed to augment the contractile responses of neo-intima-bearing vessels to 5-HT and KCl after endothelial removal. 5. The responses to angiotensin I were not altered, either by the neo-intima or by endothelial removal. In arteries with a neo-intima the sensitivity to angiotensin II was decreased. Removal of the endothelium or incubation with L-NOARG counteracted this rightward shift and increased Emax.6. Our results demonstrate that contractions to 5-HT, angiotensin II and KCl are modulated by NO in both sham and neo-intima-bearing vessels. Inhibition of NO biosynthesis and collar treatment resulted in additive effects on the EC50 values, suggesting that the 5-HT and angiotension (AT) receptors on the smooth muscle cells are also modified by the formation of a neo-intima. Furthermore, the reduced contractile responses of segments with a neo-intima are not due to NO formed by an inducible NO synthase in those vessels.

Interaction of rilmenidine and clonidine with pre- and postjunctional alpha-adrenoceptors in rat and rabbit blood vessels and in rat kidneys.

In several blood vessels, the influence of the alpha 2-adrenoceptor agonists rilmenidine and clonidine was compared. In aortas of rat and rabbit and in the rabbit pulmonary artery, both compounds evoked contractions due to stimulation of postjunctional alpha 1-adrenoceptors. In the aorta of the rat, but not in that of the rabbit, removal of the endothelium markedly enhanced the contractions to rilmenidine and clonidine. At the alpha 1-adrenoceptors, clonidine was about 135 times more potent than rilmenidine. The activity of both substances at post- and prejunctional alpha 2-adrenoceptors was compared in the rabbit saphenous vein. Rilmenidine and clonidine evoked contractions of the vein by stimulating postjunctional alpha 2-adrenoceptors and decreased the stimulation-induced overflow of [3H]-noradrenaline by activating the prejunctional alpha 2-adrenoceptors. At the post- and prejunctional alpha 2-adrenoceptors, clonidine was about 30 times more potent than rilmenidine. These data illustrate that, although less potent than clonidine, rilmenidine is 5 times more specific for the alpha 2-adrenoceptors. In the isolated perfused rat kidney, rilmenidine and clonidine antagonized the vasoconstrictions induced by noradrenaline. Although the exact mechanism of this inhibitory response remains to be elucidated, our results indicate that rilmenidine may possess some interesting properties at the level of the renal circulation.

Prejunctional beta-adrenoceptors in the isolated perfused rat kidney: a comparative study of the beta-blockers tertatolol and propranolol.

The interaction of the beta-blocker tertatolol with the prejunctional beta-adrenoceptors of the rat renal vasculature was examined. In isolated Tyrode-perfused rat kidneys isoproterenol (5 x 10(-7) M to 2 x 10(-6) M) slightly decreased the pressor responses to noradrenaline (0.5 nmol), but markedly increased those to electrical stimulation (6 Hz). Tertatolol at 3 x 10(-7) M inhibited both effects of isoproterenol. Electrical stimulation (6 Hz) caused an overflow of intact 3H-noradrenaline from kidneys previously labelled with the 3H-transmitter; this stimulation-induced release was augmented by isoproterenol. Also this effect of isoproterenol was prevented by 3 x 10(-7) M of tertatolol. In different groups of rat kidneys labelled with 3H-noradrenaline, isoproterenol (5 x 10(-7) M) augmented the stimulation (1 Hz), induced 3H overflow and this increased transmitter output was concentration-dependently inhibited by tertatolol and propranolol; from the IC50 values it was calculated that tertatolol was 16 times more potent than propranolol. Even at concentrations up to 10(-5) M, neither tertatolol nor propranolol significantly altered the basal and stimulation-induced transmitter release from the rat kidneys. From the data we conclude that tertatolol is a powerful inhibitor of the prejunctional beta-adrenoceptors in the renal circulation of the rat. Stimulation of these receptors by beta-agonists not only enhances transmitter release but also increases the pressor responses induced by electrical stimulation.

The beta adrenoceptor blocker tertatolol causes vasodilatation in the isolated perfused vasoconstricted rat kidney.

The activity of the beta adrenoceptor antagonist tertatolol on renal vasoconstrictions was investigated. Infusion of increasing concentrations of tertatolol (10(-8) to 10(-5) M) progressively inhibited the constrictor responses to bolus injections of norepinephrine and to electrical stimulation in isolated perfused kidneys of both normotensive and spontaneously hypertensive rats. Also, in kidneys of normotensive rats the vasoconstrictions caused by serotonin and barium chloride were inhibited by tertatolol. During sustained vasoconstrictions induced by infusion of norepinephrine (6 X 10(-7) M) increasing doses of tertatolol (2.5 X 10(-7) g to 2 X 10(-5) g) caused rapid, reversible dilatations in the rat kidneys. The inhibitory responses caused by tertatolol were not antagonized by propranolol, atropine, hexamethonium, SCH23390, metoclopramide, mepyramine, cimetidine, naloxone, cocaine or indomethacin. During constrictions caused by norepinephrine, methylene blue significantly inhibited the renal vasodilatations caused by tertatolol, acetylcholine, papaverine and nitroglycerin but not those caused by atrial natriuretic factor. Unlike the other vasodilators, tertatolol did not inhibit the constrictions induced by prostaglandin F2 alpha (5 X 10(-6) M) in the rat kidneys. In canine renal arteries with endothelium, tertatolol (10(-9) to 10(-5) M) did not cause relaxations during contractions induced by norepinephrine, electrical stimulation or prostaglandin F2 alpha. Our data illustrate that tertatolol has potent vasodilator properties in the isolated perfused vasoconstricted rat kidney. The dilator response to the beta blocker cannot be inhibited by a variety of classical receptor blockers but ultimately seems to depend on the formation of cyclic GMP.

Effect of hypercholesterolemia on vascular reactivity in the rabbit. II. Influence of treatment with dipyridamole on endothelium-dependent and endothelium-independent responses in isolated aortas of control and hypercholesterolemic rabbits.

The effects of cholesterol-feeding in the presence of dipyridamole (0.60 g daily) on contractile responses and on endothelium-dependent and endothelium-independent relaxations in isolated rabbit aortas are described. The investigations were performed simultaneously with those described in Part I (Circ Res 1986; 58:552-564), where the effects of cholesterol feeding on vascular reactivity in rabbit arteries (n = 8 in each group) selected at random from the same group of animals was studied. In the hypercholesterolemic rabbits treated with dipyridamole for 8 or 16 weeks, both the increases in plasma cholesterol and the formation of fatty streaks were significantly less pronounced than in the hypercholesterolemic rabbits not receiving the drug. Segments of the isolated arteries were mounted in organ chambers for isometric tension recording. The contractions caused by acetylcholine, prostaglandin F2 alpha, norepinephrine, clonidine, and serotonin and the endothelium-independent relaxations to nitroglycerin were not significantly altered by the hypercholesterolemia in rabbits treated with dipyridamole, even after 16 weeks of treatment. Thus, the decreased responses to norepinephrine, clonidine, and nitroglycerin and the augmented responses to serotonin noted in aortas of hypercholesterolemic rabbits in Part I were absent in the dipyridamole-treated hypercholesterolemic animals. The endothelium-dependent relaxations to ATP and acetylcholine were not affected after 8 weeks of hypercholesterolemia in presence of dipyridamole, while after 16 weeks the relaxations to ATP and acetylcholine were attenuated only in the more severely affected arteries. The effects of hypercholesterolemia + dipyridamole on endothelium-dependent relaxations were significantly less pronounced than those induced by hypercholesterolemia alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of the amino-oxazoline derivative S-3341 on pre- and postjunctional alpha-adrenoceptors in isolated blood vessels.

In segments of isolated dog saphenous veins, S-3341 (10(-8) to 10(-4) M) induced concentration-dependent contractions which, like those to clonidine, were progressively inhibited by increasing concentrations of yohimbine (10(-8) to 10(-6) M) but not by prazosin (10(-8) to 10(-6) M). In strips of the rabbit main pulmonary artery, previously labelled with [3H]noradrenaline and mounted for superfusion, S-3341 and clonidine both decreased the overflow of [3H] caused by electrical stimulation; these effects of S-3341 and clonidine were inhibited by 10(-6) M of yohimbine but not by 10(-6) M of prazosin. Our results illustrate that both S-3341 and clonidine cause contraction by activation of postjunctional alpha 2-adrenoceptors and decrease noradrenaline-release by stimulating prejunctional alpha 2-adrenoceptors. At the postjunctional alpha 2-adrenoceptors clonidine is 27 times more potent than S-3341, while at the prejunctional alpha 2-adrenoceptors, clonidine is only 15 times more potent than S-3341.

Effects of Iskedyl and its two constituents raubasine and dihydroergocristine on the release of [3H]noradrenaline and [3H]serotonin in canine basilar arteries.

In strips of isolated canine basilar arteries, previously labeled with 3 X 10(-7) M of either [3H]noradrenaline or [3H]serotonin, three consecutive periods of electrical stimulation (2 Hz) evoked a reproducible overflow of the respective [3H]amine. Increasing concentrations of raubasine (7.5 X 10(-7)-7.5 X 10(-6) M) did not influence the spontaneous 3H efflux but increased the stimulation-induced 3H overflow in a concentration-dependent way. The highest concentration of raubasine used (2.5 X 10(-5) M) caused an increased spontaneous 3H efflux but no longer augmented the stimulation-induced 3H overflow. Dihydroergocristine (5.4 X 10(-8)-1.8 X 10(-6) M) did not affect the spontaneous 3H efflux; the compound slightly but significantly reduced the stimulation-evoked 3H overflow concentration dependently. High concentrations of Iskedyl (mixtures of raubasine and dihydroergocristine in a 14:1 molar ratio) augmented the spontaneous 3H efflux and moderately decreased the stimulation-induced 3H overflow. Although some quantitative differences were noted, the compounds exerted similar effects on arteries labeled with either [3H]noradrenaline or [3H]serotonin. The most important difference detected was that DHEC decreased the stimulation-induced release of [3H]serotonin more than that of [3H]noradrenaline. Our results allow a comparison of [3H]noradrenaline and [3H]serotonin release in the dog basilar artery: the basal fractional release of [3H]serotonin was higher than that of [3H]noradrenaline while the stimulation-induced overflow was equal in both groups of tissues. The constituents of Iskedyl can profoundly affect the release of the neurotransmitters. Raubasine, a presynaptic alpha-receptor antagonist, increases the stimulation-induced release of the neurotransmitters and both DHEC, a presynaptic receptor agonist, and the combination of the compounds, Iskedyl, decrease the release of the neurotransmitters.

Effect of hypercholesterolemia on vascular reactivity in the rabbit. I. Endothelium-dependent and endothelium-independent contractions and relaxations in isolated arteries of control and hypercholesterolemic rabbits.

We studied the effects of hypercholesterolemia on vascular responsiveness in different arteries isolated from rabbits: control groups of rabbits and groups receiving the atherogenic diet consisted of eight animals each. In the arteries, 16 weeks of cholesterol-rich (0.3%) diet evoked intimal lesions which were more pronounced than those noted after 8 weeks of hypercholesterolemia; the aortic arch was affected significantly more by the lesions than the abdominal aorta and the pulmonary artery. Segments of the arteries were mounted in organ chambers for isometric tension recording or for measurement of the endothelium-derived relaxant factor. Contractions caused by acetylcholine and prostaglandin F2 alpha were not altered by the hypercholesterolemia; those evoked by serotonin were moderately augmented only in the aortic arch of hypercholesterolemic rabbits. As the degree of intimal lesion formation increased, the contractions to norepinephrine and clonidine were progressively inhibited. The endothelium-independent relaxations to nitroglycerin were inhibited in only the most severely affected arteries; the endothelium-dependent relaxations to acetylcholine and adenosine triphosphate were progressively inhibited as the degree of fatty streak formation augmented. Thus, in the aortic arch, the relaxations to 3 X 10(-6) M acetylcholine, expressed as percent of the initial contraction, decreased from 86.7 +/- 3.3% in control tissues to 16.3 +/- 8.6% in the 16-week hypercholesterolemic vessels; in the abdominal aortas these relaxations averaged 93.5 +/- 2.2% in control vessels and 72.0 +/- 6.9% in the hypercholesterolemic tissues. The acetylcholine-induced release of endothelium-derived relaxant factor from the abdominal aorta was not significantly affected by the hypercholesterolemia. We conclude from these studies that in arteries obtained from hypercholesterolemic rabbits: the contractions caused by serotonergic mechanisms tend to be augmented, while those to alpha-adrenergic activation are decreased, the endothelium-independent relaxations are modified only in the more severely affected arteries, and the endothelium-dependent relaxations are progressively inhibited as the degree of fatty streak formation augments, probably because a step subsequent to the release of endothelium-derived relaxant factor is altered.

Effects of tertatolol on post- and prejunctional beta adrenoceptors.

The effects of tertatolol, a new and powerful beta adrenoceptor blocking drug, on post- and prejunctional beta receptors were investigated; canine vascular tissues (saphenous veins, coronary arteries and splenic arteries) and guinea-pig trachea and atria were used. At concentrations below 10(-5) M, tertatolol did not alter basal tension or contractile responses to electrical stimulation, norepinephrine, K+ or prostaglandin F2 alpha; at doses at or above 10(-5) M the drug-evoked contractions which were reduced by phentolamine and were absent in denervated veins. Tertatolol at 10(-5) M and 3 X 10(-5) M augmented the basal efflux of [3H] norepinephrine in saphenous veins labeled with the 3H-transmitter. In veins, 10(-5) M of tertatolol depressed the contractions caused by electrical stimulation without affecting those to exogenous norepinephrine; this concentration of the drug also inhibited the stimulation-induced overflow of [3H]norepinephrine. The major part of the present study was designed to test the beta receptor blocking properties of tertatolol and to compare its effects with those of propranolol. Tertatolol inhibited, in a concentration-dependent manner, the relaxations caused by isoproterenol in saphenous veins, splenic arteries and coronary arteries and the relaxations evoked by norepinephrine and epinephrine in coronary arteries; the potency of tertatolol was higher than that of propranolol. In trachea and right atria of the guinea-pig, tertatolol inhibited, in a concentration-dependent manner, the dose-response curves to isoproterenol; the relative potency of tertatolol was higher than that of propranolol. In dog saphenous veins, previously incubated with [3H]norepinephrine, tertatolol (10(-7)M) blocked the increased stimulation-evoked overflow of the 3H-transmitter induced by isoproterenol.(ABSTRACT TRUNCATED AT 250 WORDS)