Amlodipine and benazeprilat differently affect the responses to endothelin-1 and bradykinin in porcine ciliary arteries: effects of a low and high dose combination.

PURPOSE: Visual field defects caused by vasospasm are often encountered in ophthalmology as a feature of glaucoma with poor response to conventional treatment. Combination therapy with drugs acting via different mechanisms might be more effective. Therefore, the effects of the calcium antagonist amlodipine and the angiotensin converting enzyme (ACE) inhibitor benazeprilat at low and high dose combination on contractions to endothelin-1 and endothelium-dependent relaxations to bradykinin were examined in porcine ciliary arteries. METHODS: Segments of the arteries were suspended in myographs for isometric tension recording. RESULTS: Pretreatment of the vessels with either amlodipine, the low or high dose combination significantly reduced the sensitivity to endothelin-1 as compared to control (concentration shift 18.3-fold, 14.2-fold, 23.3-fold respectively; p < 0.05), while benazeprilat was ineffective. The maximal response to endothelin-1 (10(-7) M) was most inhibited by the high dose combination which reduced the contractions by 49% as compared to control (p < 0.05). The low dose combination and amlodipine alone were less effective (reduction: 25%; p < 0.05 and 20%; n.s., respectively). On the other hand, benazeprilat enhanced the sensitivity (concentration shift 73-fold; p < 0.05) and maximal relaxation to bradykinin (by 27%; p < 0.01), whereas amlodipine or the low or high dose combination were ineffective. CONCLUSIONS: These findings indicate that amlodipine and benazeprilat differently affect vascular function of ciliary arteries. A high dose combination of both substances was most effective in inhibiting contractions to endothelin-1, suggesting a potentiating effect of the two compounds. In contrast, endothelium-dependent relaxations to bradykinin were enhanced by benazeprilat alone, but not when combined with amlodipine.

Effect of aging and hypertension on contractility of resistance arteries: modulation by endothelial factors.

The effects of aging and hypertension on contraction were examined in rat mesenteric resistance arteries of 12- and 74-wk-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). The vessels were suspended in myographs (37 degrees C, 95% O2-5% CO2) filled with modified Krebs-Ringer bicarbonate solution. Isometric tension was measured. Contractions to KCl (100 mM) were similar in adult WKY and SHR; they increased in senescent WKY (P < 0.05) but decreased in senescent SHR (P < 0.05). Responses to norepinephrine (% of KCl) were comparable in all four groups. However, blockade of nitric oxide (NO) production with NG-nitro-L-arginine methyl ester (L-NAME) enhanced the sensitivity to norepinephrine in senescent animals, particularly in SHR. Inhibition of cyclooxygenase with indomethacin prevented increased sensitivity to norepinephrine after NO blockade. Responses to angiotensin (ANG) II were not affected by aging and hypertension, but the thromboxane receptor antagonist SQ-30741 reduced ANG II-induced contractions only in SHR of both ages (P < 0.05). Aging increased responses to ANG I in SHR but decreased it in WKY (P < 0.05). In quiescent rings with endothelium, acetylcholine caused contractions in the presence of L-NAME in adult and senescent SHR but not in WKY (P < 0.05). SQ-30741 prevented these contractions (P < 0.05). Contractions to the thromboxane analogue U-46619 were reduced only in senescent SHR (P < 0.05). Thus aging increases and hypertension decreases contractility of smooth muscle in rat mesenteric resistance arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial dysfunction in aorta of the spontaneously hypertensive, stroke-prone rat: effects of therapy with verapamil and trandolapril alone and in combination.

The effects of chronic therapy with the angiotensin-converting enzyme (ACE) inhibitor trandolapril and/or Ca2+ antagonist verapamil on endothelial and vascular smooth muscle (VSM) function were studied in spontaneously hypertensive, stroke-prone rats (SHRSP). Dosages decreasing systolic blood pressure (SBP) by 20% were administered orally (p.o.) by gavage as monotherapy or combination therapy for 8 weeks, beginning at age 6 weeks. Combination therapy dosages were the same as those used in monotherapy (trandolapril 0.7 mg/kg/day verapamil 20 mg/kg/day) in one group; the second group received only half the monotherapy dosage. The study was placebo-controlled and performed in parallel groups. Isometric tension was measured in aortic rings suspended in organ chambers (95% C2/5% CO2; 37 degrees C). SBP decreased in all groups, as compared with placebo [30-47 mm Hg, analysis of variance (ANOVA), p < 0.05], but decrease was more pronounced in rats receiving high-dose combination (76 mm Hg, ANOVA, p < 0.05). In norepinephrine (NE)-contracted rings, endothelium-dependent relaxation to acetylcholine (ACh) was augmented similarly with all forms of therapy (maximal relaxations 89-94%) as compared with placebo (64 +/- 6%, p < 0.05). In contrast, the response to sodium nitroprusside (SNP) was similar in all groups (NS). In quiescent rings, ACh elicited endothelium-dependent contractions (in the presence of N omega-monomethyl-L-arginine, L-NAME) that were not affected by therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial vasoconstrictor prostanoids modulate contractions to acetylcholine and ANG II in Ren-2 rats.

We investigated vascular function in mouse Ren-2 transgenic rats with hypertension. Mesenteric resistance arteries of transgenic and Sprague-Dawley rats (controls) were isolated at ages 6 and 12 wk and suspended in myographs for isometric tension recording. Systolic blood pressure was higher in transgenic than control rats (P < 0.05). Contractions to norepinephrine and endothelin-1 were comparable in transgenic and control rats, but the sensitivity decreased with age in both strains (P < 0.05). Contractions to angiotensin I were comparable in 6-wk-old transgenic rats and controls, but the response to angiotensin I was more pronounced in transgenic rats at 12 wk of age. Contractions to angiotensin II were higher in transgenic rats and decreased with age in both strains. Preincubation with the cyclooxygenase inhibitor meclofenamate or the thromboxane receptor antagonist SQ-30741 blunted the response only in 6-wk-old transgenic rats. In quiescent vascular rings, acetylcholine evoked endothelium-dependent contractions after inhibition of nitric oxide formation by N omega-nitro-L-arginine methyl ester only in transgenic rats. These contractions were inhibited by SQ-30741 (P < 0.05) but not by the thromboxane synthase inhibitor CGS-13080. Contractions to the thromboxane analogue U-46619 were comparable in both strains at the age of 6 wk; sensitivity was increased in transgenic rats at 12 wk (P < 0.05). In conclusion, in mesenteric resistance arteries of Ren-2 transgenic rats I) contractions to angiotensin I and II but not to norepinephrine and endothelin-1 are increased, and 2) acetylcholine as well as angiotensin II modulate endothelium-dependent contractions mediated by prostaglandin H2. These alterations together with increased sensitivity to thromboxane could contribute to maintenance as well as to impaired tissue perfusion of this form of hypertension.

Mechanisms of adrenomedullin-induced dilatation of cerebral arterioles.

BACKGROUND AND PURPOSE: Adrenomedullin is a recently discovered vasoactive peptide that is structurally related to calcitonin gene-related peptide (CGRP). Adrenomedullin is produced by vascular endothelium and smooth muscle and is present in the brain. The goals of this study were to determine (1) whether adrenomedullin produces dilatation of cerebral arterioles and whether this effect is mediated by activation of CGRP receptors and (2) whether vasodilatation to adrenomedullin was mediated by K+ channels. METHODS: Diameter of cerebral arterioles (mean +/- SE baseline, 46 +/- 1 microns) was measured using a closed cranial window in anesthetized rats. RESULTS: Application of rat adrenomedullin (10(-7) and 10(-6) mol/L) increased vessel diameter by 16 +/- 3% and 45 +/- 8% (n = 5), respectively. Vasodilator responses to repeated application of adrenomedullin were reproducible. Pretreatment of cerebral arterioles with the specific CGRP1 receptor antagonist CGRP-(8-37) (5 x 10(-7) mol/L) selectively inhibited the vasodilator responses to adrenomedullin without inhibiting responses to ADP (10(-5) to 10(-3) mol/L). Responses to adrenomedullin (10(-7) and 10(-6) mol/L) were 14 +/- 1% and 40 +/- 3% before and 2 +/- 2% and 6 +/- 1% after CGRP-(8-37), respectively (P < .01). Glibenclamide (10(-6) mol/L), an inhibitor of ATP-sensitive K+ channels, reduced the responses to adrenomedullin without attenuating responses to ADP. Responses to adrenomedullin were 19 +/- 4% and 35 +/- 6% before and 6 +/- 3% and 19 +/- 5% after glibenclamide, respectively (P < .05). Iberiotoxin (10(-7) mol/L), an inhibitor of calcium-dependent K+ channels, also significantly attenuated responses to adrenomedullin and did not inhibit vasodilatation to papaverine. Responses to adrenomedullin were 16 +/- 2% and 55 +/- 8% before and 12 +/- 4% and 26 +/- 3% after iberiotoxin, respectively (P < .01 for 10(-6) mol/L adrenomedullin). CONCLUSIONS: Adrenomedullin produces substantial dilatation of cerebral arterioles in vivo, and the response is mediated in large part by activation of CGRP1 receptors. Cerebral vasodilatation to adrenomedullin appears to be dependent on activation of K+ channels.

Effects of calcium channel blockers on the response to endothelin-1, bradykinin and sodium nitroprusside in porcine ciliary arteries.

Calcium channel blockers are increasingly used in ophthalmology, for instance in patients with visual field defects caused by vasospasm. Endothelin is a new vasoactive peptide which also has been implicated in hypoperfusion of the ophthalmic circulation. This study investigated the effects of the calcium channel blockers on the response to endothelin-1, bradykinin and sodium nitroprusside in isolated porcine ciliary arteries (diameter 200-250 microns). Isolated porcine ciliary arteries were suspended in myograph systems filled with modified Krebs-Ringer solution (37 degrees C; 95% O2/5% CO2) for isometric tension recording. Endothelin-1 (10(-12) -10(-7) M) induced potent concentration-dependent contractions of porcine ciliary arteries (PD50 = 8.3 +/- 0.1; n = 7). Lacidipine (10(-5) -10(-7) M) and nifedipine (10(-5) M) significantly reduced the contractions and decreased the sensitivity to endothelin-1 as compared to control (P < 0.03). On the other hand, endothelium-dependent relaxations to bradykinin (10(-10) -10(-6) M) and endothelium-independent relaxations to sodium nitroprusside (10(-10) -10(-4) M) remained unaffected by the calcium channel blocker. These findings demonstrate that in porcine ciliary arteries, the calcium channel blockers selectively inhibit endothelin-1-induced contractions, while leaving endothelium-dependent and endothelium-independent relaxations unaffected. This property of calcium channel blockers may contribute to the clinical efficacy of this class of drugs in patients with ocular vasospasms.

Propofol-induced relaxation of rat mesenteric arteries: evidence for a cyclic GMP-mediated mechanism.

Experiments were designed to evaluate whether guanosine 3',5'-cyclic monophosphate (cGMP)-mediated mechanisms contribute to vasodilation via propofol in rat mesenteric resistance arteries. Ring segments were suspended in the myograph system for isometric tension recording, and responses to propofol were tested in the presence and absence of methylene blue (MB), an inhibitor of guanylate cyclase. At concentrations > or = 1 microM, propofol caused concentration-dependent relaxation of vessel rings precontracted with U46619 (a thromboxane analog). The effect was not affected by N-monomethyl-L-arginine (L-NMMA; 50 microM). MB (5 microM) reversed propofol-induced vasodilation by 30% (p < 0.001). In contrast, MB has no effect on nifedipine-inhibited vasocontraction. The propofol-induced relaxation was further tested in rings incubated in Ca2+-free solution. U46619-induced contractions were significantly reduced by propofol (40 microM) but not by nifedipine (1 microM). Propofol reduced to a similar degree the contractions obtained to exogenously added calcium chloride in the absence and the presence of MB. Furthermore, propofol (10-100 microM) increased cGMP content in cultured bovine vascular smooth-muscle cells. Soluble guanylate cyclase inhibitors, such as MB and LY83583, attenuated this effect. This investigation suggests that propofol-induced relaxations in small arteries, in addition to inhibition of calcium influx, are mediated by increases of cGMP in the smooth muscle cells.

Improvement of relaxation in an atherosclerotic artery by gene transfer of endothelial nitric oxide synthase.

Gene transfer with replication-deficient adenovirus is a useful tool to study vascular biology. We have reported that overexpression of endothelial nitric oxide (NO) in carotid arteries from normal rabbits augments vasorelaxation mediated by NO. In this study, we tested the hypothesis that adenovirus-mediated gene transfer of endothelial nitric oxide synthase (eNOS) improves impaired relaxation of atherosclerotic vessels. We used 2 replication-deficient adenoviruses: AdeNOS, which carries cDNA for eNOS, and Adbetagal, which expresses beta-galactosidase. Common carotid arteries from 10 New Zealand White (NZW; plasma cholesterol, 79+/-13 mg/dL) and 10 Watanabe heritable hyperlipidemic (WHHL; plasma cholesterol, 452+/-39 mg/dL) rabbits were incubated in organ culture with AdeNOS, Adbetagal, or vehicle alone. Carotid arteries from WHHL rabbits had mild to moderate atherosclerotic lesions. Histochemical staining for beta-galactosidase and immunohistochemistry for eNOS indicated transgene expression in the endothelium and adventitia in both NZW and WHHL rabbits. Expression of eNOS determined with Western blot analysis after incubation with AdeNOS tended to be higher in vessels from WHHL rabbits than NZW rabbits. Effects of transgene expression on vascular function were examined by recording isometric tension 1 day after transduction. After precontraction with phenylephrine, acetylcholine produced significantly less relaxation in vessels from WHHL rabbits than in vessels from NZW rabbits. Relaxation in response to acetylcholine was greater in carotid arteries from both NZW and WHHL rabbits that were transfected with AdeNOS than in vessels treated with vehicle or Adbetagal. Vasorelaxation in response to acetylcholine was inhibited by Nomega-nitro-L-arginine. Responses to sodium nitroprusside were similar after treatment with vehicle alone, Adbetagal, or AdeNOS in both groups of rabbits. Thus, overexpression of eNOS with an adenoviral vector improves impaired NO-mediated relaxation in atherosclerotic arteries.