Abstract-Angiotensin-converting enzyme (ACE) inhibitor improves the impaired hyperpolarization and relaxation to acetylcholine (ACh) via endothelium-derived hyperpolarizing factor (EDHF) in arteries of spontaneously hypertensive rats (SHR). We tested whether the angiotensin type 1 (AT 1 ) receptor antagonist also improves EDHF-mediated responses and whether the combined AT 1 receptor blockade and ACE inhibition exert any additional effects. SHR were treated with either AT 1 receptor antagonist TCV-116 (5 mg ⅐ kg) (SHR-E), or their combination (SHR-T&E) from 8 to 11 months of age. Age-matched, untreated SHR (SHR-C) and Wistar Kyoto (WKY) rats served as controls (nϭ8 to 12 in each group). Three treatments lowered blood pressure comparably. EDHF-mediated hyperpolarization to ACh in mesenteric arteries in the absence or presence of norepinephrine was significantly improved in all treated SHR. In addition, the hyperpolarization in the presence of norepinephrine was significantly greater in SHR-T&E than in SHR-E (ACh 10 Ϫ5 mol/L with norepinephrine: SHR-C Ϫ7; SHR-T Ϫ19; SHR-E Ϫ15; SHR-T&E Ϫ22; WKY Ϫ14 mV). EDHF-mediated relaxation, assessed in the presence of indomethacin and N G -nitro-L-arginine, was markedly improved in all treated SHR. Hyperpolarization and relaxation to levcromakalim, a direct opener of ATP-sensitive K ϩ -channel, were similar in all groups. These findings suggest that AT 1 receptor antagonists are as effective as ACE inhibitors in improving EDHF-mediated responses in SHR. The beneficial effects of the combined AT 1 receptor blockade and ACE inhibition appears to be for the most part similar to those of each intervention. (Hypertension. 2000;36:575-580.) Key Words: endothelium-derived factors Ⅲ angiotensin Ⅲ arteries Ⅲ hypertension Ⅲ drug therapy E ndothelial cells play an important role in the regulation of vascular tone through the release of relaxing factors such as nitric oxide (NO), 1 prostacyclin, and endothelium-derived hyperpolarizing factor (EDHF). 2-4 EDHF relaxes underlying smooth muscle cells by producing membrane hyperpolarization through the opening of K ϩ channels. 4 -7 The identity of EDHF is yet to be determined, but possible candidates include cytochrome P450-derived arachidonic acid metabolites, 8,9 K ϩ itself, 10 or the electrical couplings via gap junctions. 11 Endothelium-dependent relaxation is impaired in hypertension. 7,[12][13][14] Although the mechanisms for this impairment seem to vary, we have shown that the impaired EDHFmediated hyperpolarization partly accounts for the decreased endothelium-dependent relaxation in mesenteric arteries of adult spontaneously hypertensive rats (SHR). 7,14 Furthermore, antihypertensive treatment with either the angiotensinconverting enzyme (ACE) inhibitor enalapril or a combination of hydralazine and hydrochlorothiazide restores EDHFmediated responses. 15 In addition, enalapril tends to be more beneficial than the traditional combination therapy, despite a comparable blood pressure reduction, 15 which raises the possibility that the re...

Background-The vascular endothelium releases endothelium-derived hyperpolarizing factor (EDHF). The mesenteric arteries of 6-to 8-month-old spontaneously hypertensive rats (SHRs) exhibit an impairment of the hyperpolarization induced by acetylcholine via EDHF. Methods and Results-We determined whether antihypertensive treatment can improve EDHF-mediated responses inSHRs. Beginning at age 8 to 9 months, the animals were treated with either enalapril (40 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 ) (SHR-Es) or a combination of hydralazine (25 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 ) and hydrochlorothiazide (7.5 mg ⅐ kg Ϫ1 ⅐ d Ϫ1 ) (SHR-Hs) for 3 months. The control groups were age-matched SHRs (SHR-Cs) and Wistar Kyoto rats (WKYs). The two treatments lowered the blood pressure to comparable extents. The acetylcholine-induced hyperpolarization in the mesenteric artery of treated SHRs improved to a level comparable to that in WKYs (acetylcholine 10 Ϫ5 mol/L with norepinephrine 10

Abstract-Vascular relaxation via endothelium-derived hyperpolarizing factor (EDHF) declines in association with aging and also with hypertension, and antihypertensive treatment improves the endothelial dysfunction connected with hypertension. We tested whether the angiotensin-converting enzyme inhibitor improves EDHF-mediated responses in normotensive rats, with special reference to the age-related process. Wistar-Kyoto rats (WKY) were treated with either 20 mg ⅐ kghydrochlorothiazide (WKY-H group) from 9 to 12 months of age. Twelve-month-old WKY (WKY-O) and 3-month-old WKY (WKY-Y) served as controls (nϭ6 to 10 in each group). The 2 treatments lowered systolic blood pressure comparably. EDHF-mediated hyperpolarization to acetylcholine (ACh) in mesenteric arteries was significantly improved in WKY-E, but not in WKY-H, compared with WKY-O, and the hyperpolarization in WKY-E was comparable to that in WKY-Y (hyperpolarization to 10 Ϫ5 mol/L ACh in the presence of norepinephrine: WKY-O, Ϫ14Ϯ2 mV; WKY-E, Ϫ22Ϯ3 mV; WKY-H, Ϫ15Ϯ2 mV; and WKY-Y, Ϫ28Ϯ0 mV). EDHF-mediated relaxation, as assessed by relaxation to ACh in norepinephrine-precontracted rings in the presence of indomethacin and NO synthase inhibitor, was also significantly improved in WKY-E, but not in WKY-H, to a level comparable to that in WKY-Y (maximum relaxation: WKY-O, 45Ϯ6%; WKY-E, 63Ϯ8%; WKY-H, 43Ϯ4%; and WKY-Y, 72Ϯ4%). Hyperpolarization and relaxation to levcromakalim, an ATP-sensitive K ϩ channel opener, were similar in all groups. These findings suggest that the angiotensin-converting enzyme inhibitor prevents the age-related decline in EDHF-mediated hyperpolarization and relaxation in normotensive rats, presumably through an inhibition of the renin-angiotensin system. (Hypertension. 2000;36:581-587.)

1 The actions of troglitazone, pioglitazone, metformin and beza®brate, agents that improve insulinresistance, on voltage-dependent Ca 2+ channels in arterial smooth muscle cells were examined by use of the conventional and nystatin-perforated whole-cell clamp methods. Single cells were freshly isolated from resistance mesenteric arteries of guinea-pigs. The actions of these agents on 77 mM K + -induced contraction of the isolated arteries were also examined with the use of isometric tension recording. 2 The thiazolidinedione derivatives, troglitazone and pioglitazone, inhibited whole-cell Ca 2+ currents in a dose-dependent manner with dissociation constants of 3.0 mM and 44.9 mM and Hill coecients of 0.61 and 0.68, respectively. These two agents inhibited the 77 mM K + -induced contraction with similar potencies as those inhibiting the Ca 2+ currents. Metformin and beza®brate had no apparent eects on the Ca 2+ current or high K + -induced contraction. 3 The inhibitory action of troglitazone on Ca 2+ currents was not aected by the command potential, the holding potential, or the stimulation frequency, suggesting that its mode of the action diers from that of known organic Ca 2+ channel antagonists. 4 The inhibitory action of troglitazone on Ca 2+ currents was not aected by the addition of insulin to, or the removal of glucose from, the solutions. 5 In conclusion, the thiazolidinedione derivatives directly inhibited the voltage-dependent Ca 2+ channels in a dierent manner from that of organic Ca 2+ channel antagonists. This inhibitory action on Ca 2+ channels was not a common feature of insulin-sensitizing agents.

Abstract-Stimulation of vascular ␤-adrenoceptors leads to membrane hyperpolarization, presumably via the ␤-adrenoceptor/G s protein/adenylate cyclase signaling cascade; the ionic mechanisms of this phenomenon remain unclear. ␤-Adrenoceptor-mediated vascular relaxation is impaired with aging; however, little is known concerning whether ␤-adrenoceptor-mediated hyperpolarization is altered with aging. We sought to determine the ionic mechanisms of isoproterenol-induced hyperpolarization in the rat mesenteric resistance artery, as well as the age-related changes in isoproterenol-induced hyperpolarization and their underlying mechanisms. Isoproterenol-induced hyperpolarization was inhibited by high-K ϩ solution and glibenclamide (10 Ϫ6 mol/L), an inhibitor of ATP-sensitive K ϩ channels (K ATP ), but not by apamin, iberiotoxin, or charybdotoxin, inhibitors of Ca 2ϩ -activated K ϩ channels. Isoproterenol-induced hyperpolarization was markedly less in aged rats (Ն24 months) than in adults rats (12 to 20 weeks) (3ϫ10 Ϫ6 mol/L; Ϫ3.1 versus Ϫ9.9 mV; PϽ0.001; nϭ8 to 9). Cholera toxin (10 Ϫ9 g/mL), an activator of G s , evoked hyperpolarization only in adult rats. Hyperpolarization to forskolin, a direct activator of adenylate cyclase, was also reduced to some extent in aged rats (10 Ϫ5 mol/L; Ϫ8.8 versus Ϫ13 mV; PϽ0.05; nϭ6), whereas hyperpolarization to levcromakalim, a K ATP opener, was comparable in both groups. These findings suggest that isoproterenol elicits hyperpolarization via an opening of K ATP in the rat resistance artery and that isoproterenol-induced hyperpolarization is attenuated in aged rats mainly because of a defective coupling of ␤-adrenoceptors to adenylate cyclase and partly because of a defect at the level of adenylate cyclase, but not because of an alteration of K ATP per se. (Hypertension. 1999;34:222-228.)