General Pharmacology-the Vascular System最新文献

KMUP 880723 (0.5, 1.0, and 3.0 mg/kg, iv) produced dose-dependent hypotensive and bradycardia responses in pentobarbital-anesthetized Wistar rats. KMUP 880723 (1.0 mg/kg, iv) also markedly inhibited both the tachycardia effects induced by (−)isoproterenol and arterial pressor responses induced by phenylephrine. In the isolated Wistar rat right atria, left atria, and guinea pig tracheal strips, KMUP 880723 competitively antagonized the (−)isoproterenol-induced positive chronotropic effects, inotropic effects, and tracheal relaxation effects in a concentration-dependent manner. The parallel shift to the right of the concentration–response curve of (−)isoproterenol suggested that KMUP 880723 was a β₁/β₂-adrenoceptor competitive antagonist. The apparent pA₂ values were 6.89±0.10 in the right atria, 7.02±0.09 in the left atria, and 6.59±0.11 in the trachea, indicating that KMUP 880723 was a nonselective β-adrenoceptor blocker. In thoracic aorta experiments, KMUP 880723 also produced a competitive antagonism of norepinephrine-induced contraction with a pA₂ value of 7.14±0.06. In isolated rat thoracic aorta, KMUP 880723 more potently relaxed the contractions induced by norepinephrine (3×10⁻⁶ M) than those by high K⁺ (75 mM). In the radioligand-binding assay, the pK_i values of [³H]CGP-12177 binding to rat ventricle and lung membranes were 6.56 and 6.40, respectively, and the value of [³H]prazosin binding to rat brain membranes was 6.66. These results further confirmed the α/β-adrenoceptor blocking activities of KMUP 880723 reported in the functional studies. We conclude that KMUP 880723 is a nonselective β-adrenoceptor antagonist with α-adrenoceptor blocking-associated vasorelaxant activity.

The contribution of endothelial factors and mechanisms underlying decreased acetylcholine-induced relaxation and endothelial inhibitory action on phenylephrine-induced contraction were evaluated in aortas of two-kidney, one-clip hypertensive (2K-1C) and normotensive (2K) rats. Relaxation induced by acetylcholine in 2K-1C precontracted by phenylephrine was lower [Maximum Effect (ME): 71.33±3.36%; pD₂: 7.050±0.03] than in 2K (ME: 95.26±1.59%; pD₂: 7.31±0.07). This response was abolished by N^G-nitro-l-arginine (L-NNA) in 2K-1C, but was only reduced in 2K (ME: 29.21±9.28%). Indomethacin had no effect in 2K-1C, and slightly attenuated acetylcholine-induced relaxation in 2K. The combination of L-NNA and indomethacin almost abolished acetylcholine-induced relaxation in 2K-1C, while in 2K, the inhibition (ME: 56.61±8.95%) was lower than the effect of L-NNA alone. During the KCl-induced precontraction, 2K and 2K-1C aortas showed similar acetylcholine-induced relaxation (43.50±5.64% vs. 41.60±4.36%), which was abolished by L-NNA. The levels of cGMP produced in response to acetylcholine were not different between 2K and 2K-1C. The sensitivity to sodium nitroprusside was lower in phenylephrine-precontracted aortas from 2K-1C than 2K, as showed by the pD₂ values (7.72±0.20 vs. 8.59±0.17), and this difference was abolished in aortas precontracted by KCl. The membrane potential was less negative in 2K-1C than in 2K (−41.57±1.19 vs. −51.00±1.13 mV) and hyperpolarization induced by acetylcholine was lower in 2K-1C than in 2K aortas (6.00±0.66 vs. 13.27±1.61 mV). Phenylephrine-induced contraction in aortas with endothelium was similar in both groups, and increased by the endothelium removal. This increase was lower in 2K-1C (from 1.32±0.06 to 1.90±0.21 g) than 2K (from 1.49±0.07 to 2.83±0.18 g). L-NNA and the endothelium removal had similar effect in 2K-1C (1.85±0.18 g) and were lower in 2K (2.18±0.20 g). Indomethacin decreased phenylephrine-induced contraction only in 2K. In conclusion, our major finding was a selective defect in smooth muscle membrane hyperpolarization, which could explain the decreased relaxation to acetylcholine and the attenuated inhibitory effect of endothelium on the contractile function in 2K-1C aortas.

The current study was performed to determine the effect of calcium store depletion with cyclopiazonic acid (CPA) on the pre- and postglomerular vasoconstrictor responses to angiotensin II (ANG II) and norepinephrine (NE). CPA treatment significantly attenuated the afferent arteriolar response to 10 nM ANG II by 51% and to 1000 nM NE by 19%. Efferent arteriolar responses to ANG II and NE were also greatly attenuated in the presence of CPA. These data demonstrate that afferent and efferent arteriolar responses to ANG II and NE depend on release of calcium from CPA-sensitive intracellular stores. Furthermore, the postglomerular response to these agents exhibits a greater dependency on calcium release from intracellular stores.

Hyperthyroidism was induced by subcutaneous injections of l-thyroxine (T₄) (500 mg/kg/day) for 3 days in order to study whether adrenergic and muscarinic receptor-mediated vascular responses alter at an early stage of the disease. T₄ treatment was sufficient to induce a significant degree of thyroid weight loss, tachycardia, cardiac hypertrophy, and an elevation in serum T₄ levels. The tension of aortic ring preparations isolated from rats was measured isometrically to investigate the influence of acute hyperthyroidism. The contractions induced by norepinephrine (NE) were significantly suppressed in aortic rings from rats treated with T₄ compared with control rats. N^G-nitro-l-arginine (l-NOARG), an inhibitor of nitric oxide synthase (NOS), significantly enhanced NE-induced contraction in aortic rings from both control and T₄-treated rats, and the enhancement was greater in rats treated with T₄ than control rats. The relaxations induced by either acetylcholine (ACh) or sodium nitroprusside (SNP) were also significantly enhanced by T₄ treatment. l-NOARG abolished the relaxation induced by ACh in aortic rings from both control and T₄-treated rats. l-NOARG shifted SNP-induced relaxation curves of aortic rings from those of control rats to the left, but not with rats treated with T₄. T₄ treatment showed no influence on the amount of endothelial NOS (eNOS) protein. These results suggest that vascular responses alter at an early stage of hyperthyroidism and that it may be due to a modification in the NO system which is independent from the amount of eNOS protein.

Catecholamines, neuropeptide Y (NPY) and angiotensin II (Ang II) are known to participate in the central control of blood pressure. However, the modulation of these neurotransmitter receptors in response to a hypertensive stimulus is not appropriately established. The purpose of the present study was to examine binding parameters of α₂-adrenergic, NPY and Ang II receptors in the nucleus tractus solitarii (NTS) and paraventricular hypothalamic nucleus (PVN) following a hypertensive stimulus in the aortic-coarcted rat by means of quantitative receptor autoradiography. No changes were seen in binding parameters of α₂-adrenergic and NPY receptors in the NTS of the hypertensive rat compared to control. However, an increased affinity (54%) of noradrenaline competing for ³H-PAC was seen in the PVN. Moreover, an increased binding (49%) of ¹²⁵I-PYY was also observed in the PVN. The affinity of Ang II for ¹²⁵I-Sar¹Ile⁸-Ang II binding sites was also increased (57%) in the NTS of the hypertensive rat. No changes in the binding parameters of radioactive Ang II were observed in the PVN. The results suggest that systems involved with hypertension like Ang II in the NTS and catecholamines in the PVN might collaborate in the development/maintenance of high blood pressure in the aortic-coarcted rat.

1. We compared the endothelium-dependent responses of thoracic aortic rings obtained from male and female spontaneously hypertensive rats (SHR) in order to explore gender differences in the normalization of the high blood pressure by antihypertensive drug therapy and in the correction of the endothelial dysfunction found in these animals. 2. Concentration–effect curves to acetylcholine (ACh) and sodium nitroprusside (SNP) were obtained using aortic rings isolated from male and female rats pretreated or not with losartan for 24 h or 15 d. The responses achieved and the EC50s were determined. 3. Losartan, AT₁ receptor antagonist, normalized (around 125 mmHg) the high blood pressure levels in 100% of the females and in 53.3% of males SHR within 24 h of initiating the treatment and remained normal during the remainder of the treatment period (15 d). 4. Losartan (15 d) corrected the decreased response to ACh in male and female SHR, independently of the normalization of blood pressure in male SHR. 5. An increased sensitivity to SNP was observed after chronic treatment with losartan in aortic rings from female SHR. 6. Ridogrel, a TXA₂/PGH₂ receptor antagonist, restored the decreased response to ACh in aortic rings from male and female SHR. 7. These results suggest that there are gender-related differences in the normalization of the high blood pressure levels by losartan in SHR. The decreased response to ACh observed in male and female is corrected after sustained (15 d) reduction of high blood pressure. In female but not in male SHR, correction seems to involve an increased sensitivity of the smooth muscle to nitric oxide.

Various vanilloid-type β-adrenoceptor blockers were studied on guinea pig right atrium and trachea and rat colon. In addition, we also investigated their β₁-, β₂-, and β₃-adrenoceptor binding affinities. All these β-adrenergic antagonists inhibited (−)isoproterenol-induced positive chronotropic effects of the right atrium and tracheal relaxation responses in a concentration-dependent manner. Some of these agents prevented the inhibition of rat colon spontaneous motility by (−)isoproterenol. Of the agents tested, we found that ferulidilol, eugenodilol, eugenolol, isoeugenolol, and ferulinolol, as well as propranolol and metoprolol, possessed β₃-adrenoceptor blocking activities, others were nearly without effectiveness. Furthermore, the binding characteristics of vanilloid-type β-adrenergic antagonists were evaluated in [³H]CGP-12177, a β₁/β₂-adrenoceptor blocker and a β₃-adrenoceptor agonist, binding to β₁-, β₂-, and β₃-adrenoceptor sites in rat ventricle, lung, and interscapular brown adipose tissue (IBAT) membranes, respectively. Eugenodilol, eugenolol, metoprolol, isoeugenolol, and ferulinolol were less potent than both propranolol and ferulidilol in competing for the β₃-adrenoceptor binding sites. From the results of in vitro functional and binding studies, we suggested that propranolol, ferulidilol, eugenodilol, eugenolol, metoprolol, isoeugenolol, and ferulinolol all possessed β₃-adrenoceptor blocking activities. On the other hand, we also found that eugenodilol, eugenolol, metoprolol, isoeugenolol, and ferulinolol had a low lipid solubility in comparison with propranolol and ferulidilol. In conclusion, we proposed that β₃-adrenoceptor antagonistic actions of these vanilloid-type β-blockers were positively correlated with their lipid solubility.

Effects of bimoclomol, the novel heat shock protein (HSP) coinducer, was studied in various mammalian cardiac and rabbit aortic preparations. Bimoclomol decreased the ST-segment elevation induced by coronary occlusion in anesthetized dogs (56% and 80% reduction with 1 and 5 mg/kg, respectively). In isolated working rat hearts, bimoclomol increased coronary flow (CF), decreased the reduction of cardiac output (CO) and left ventricular developed pressure (LVDP) developing after coronary occlusion, and prevented ventricular fibrillation (VF) during reperfusion. In rabbit aortic preparations, precontracted with phenylephrine, bimoclomol induced relaxation (EC₅₀=214 μM). Bimoclomol produced partial relaxation against 20 mM KCl, however, bimoclomol failed to relax preparations precontracted with serotonin, PGF₂ or angiotensin II. All these effects were evident within a few minutes after application of bimoclomol. A rapid bimoclomol-induced compartmental translocation of the already preformed HSPs may explain the protective action of the compound.

Several recent studies have provided evidence that many of the hemodynamic and mitogenic actions of angiotensin II (Ang II) are mediated by endothelin-1 (ET-1). We hypothesized that Ang II and ET-1 act synergistically to promote a decline in renal function and the development of renal fibrosis in the deoxycorticosterone acetate (DOCA)-salt model of malignant hypertension and renal dysfunction. Experiments were conducted to determine the effects of ET_A receptor antagonism (A-127722) and AT₁ receptor antagonism (candesartan cilexetil) on the development of renal fibrosis and the decline of renal function. Surgery was conducted on male, Sprague–Dawley rats to remove the right kidney and implant subcutaneously a time-release pellet containing DOCA. DOCA-treated rats were also given 0.9% NaCl to drink. After recovery from surgery, rats received one of four treatments via the drinking solution: (1) candesartan cilexetil (10 mg/kg/day), (2) A-127722 (10 mg/kg/day), (3) candesartan cilexetil plus A-127722, or (4) untreated controls. Over the course of a 3-week treatment period, systolic arterial pressure in all groups were elevated. However, this increase was significantly attenuated in the group given combined A-127722 and candesartan, but not with candesartan alone. Creatinine clearance, used as a measure of GFR, was significantly higher in rats treated with either or both drugs. At the end of the study, renal medullary tissue was harvested for determination of TGF-β and fibronectin content (ELISA). TGF-β levels were not reduced by either ET_A, AT₁, or combined ET_A and AT₁ receptor blockade. Likewise, fibronectin content was similar among groups. These studies indicate that combined ET_A and AT₁ receptor blockade may produce some improvement on hemodynamics, but have no effect on progression of renal damage in this non-renin-dependent model of hypertension.

Samultang has been traditionally used for treatment of ischemic heart and brain diseases in oriental medicine. However, little is known about the mechanism by which Samultang rescues the myocardial and neuronal cells from ischemic damage. This study was designed to evaluate whether the water extract of Samultang may modulate the production of nitric oxide (NO) in LPS and PMA treated-C6 glial cells to protect the cells from NO-induced cytotoxicity. C6 glial cells treated with both LPS and PMA significantly produced a large amount of NO compared to untreated, PMA, or LPS-treated cells. In parallel with NO production, cotreatment of LPS and PMA induced the severe apoptotic death of C6 glial cells. However, Samultang significantly reduced both cell death and NO production by LPS/PMA in a dose-dependent manner. In addition, the modulatory effects of Samultang on LPS/PMA-induced cytotoxicity and NO production could be mimicked by exogenous treatments of N^GMMA, a nitric oxide synthase (NOS) inhibitor, and pyrrolidine dithiocarbamate (PDTC), a strong NF-κB inhibitor. Treatment of C6-glial cells with LPS/PMA induced the transcriptional activation of NF-κB, which was markedly inhibited by Samultang. Taken together, we suggest that the protective effects of Samultang against LPS/PMA-induced cytotoxicity may be mediated by the suppression of NO synthesis via down-regulation of NF-κB activation.