Antihypertensive effect of E-643, a new alpha-adrenergic blocking agent

Effects of bunazosin and atenolol on serum lipids and apolipoproteins in a randomised trial

The effects of bunazosin and atenolol on serum lipids and lipoproteins after 6 months of treatment were compared in this multicentric, double-blind, randomised trial. A total of 174 patients with mild to moderate essential hypertension from 15 hospitals in Germany and Poland was included in the study. Eighty-seven were treated with the alpha-receptor blocker bunazosin and the same number with the beta-blocker atenolol. Systolic and diastolic blood pressure decreased significantly in both groups, whereas only atenolol decreased pulse rate. In the bunazosin group HDL-cholesterol was significantly increased after 6 months of treatment, whereas all other analysed parameters remained unchanged. In the atenolol group total cholesterol, LDL-cholesterol, total triglycerides, apolipoprotein E, VLDL-cholesterol and VLDL-triglycerides were significantly increased after 6 months of therapy. There was a significant difference between bunazosin and atenolol for total cholesterol, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol, triglycerides, VLDL-triglycerides and apolipoprotein B levels. As a consequence, there was a significant difference in the atherogenic index of both groups. We conclude that bunazosin is favorable in the treatment of high blood pressure, because the coronary risk is not negatively influenced as shown for atenolol.

Bunazosin in patients with impaired hepatic or renal function

Following a single oral dose of 6 mg bunazosin, a novel alpha 1-adrenoceptor antagonist, the pharmacokinetics and blood pressure behaviour of 37 patients were studied. 12 subjects had normal renal and hepatic function (mean creatinine clearance (GFR) 107 +/- 240 ml/min, antipyrine clearance (AP Cl) 47 +/- 10.2 ml/min; x +/- SD), 13 subjects had impaired renal function (mean GFR 38 +/- 11.5 ml/min, AP Cl 39 +/- 4.0 ml/min), and 12 patients had liver cirrhosis which was confirmed by liver biopsy (mean AP Cl 18 +/- 9.2 ml/min, GFR 92 +/- 8.1 ml/min). The groups studied were matched for age and body weight. The area under the plasma level time curve (AUC0-infinity) of bunazosin increased from 96.6 +/- 48.7 micrograms.ml-1.h in the normals to 157.0 +/- 101.0 micrograms.ml-1.h in the liver patients and to 298.2 +/- 199.4 micrograms.ml-1.h in patients with impaired renal function (P < 0.05). As there was a close correlation between plasma levels and antihypertensive activity of bunazosin in the present study, dosage adjustment of the alpha 1-receptor blocker in patients with impaired liver and kidney function appears to be mandatory.

Doxazosin: a newly developed, selective alpha 1-inhibitor in the management of patients with pheochromocytoma

Although surgical removal is the therapy of choice in patients with pheochromocytoma, medical management is necessary in the preoperative preparation of these patients and in inoperable cases. An alpha-adrenoceptor-blocking agent is routinely used as initial therapy to control hypertension, with a beta-blocker used as a second-step agent to control tachycardia when indicated. Doxazosin, a selective alpha 1-inhibitor used as an antihypertensive agent for the reduction of coronary heart disease risk in hypertensive patients, appears to be a good agent to control blood pressure with minimal changes in heart rate. The aim of this study was to assess the antihypertensive efficacy and safety of doxazosin when used alone or in conjunction with a beta-blocker in 24 patients with pheochromocytoma. Overall excellent or good antihypertensive efficacy was assessed by physicians in 19 of 24 patients (79.2%) enrolled in the study. Doxazosin monotherapy was effective in eight of 12 patients (66.7%), and combined therapy with a beta-blocker was effective in 11 of 12 patients (91.7%). The mean pulse rate remained constant throughout therapy. Adverse reactions were minor and transient and occurred in only three patients. Urinary and plasma catecholamine levels tended to decrease or remained unchanged during doxazosin therapy. There were no clinically hazardous abnormalities or problems in hematologic and biochemical laboratory data. Overall, doxazosin was considered very useful or useful in 83.3% of patients. In conclusion, doxazosin appears to be an excellent agent for the management of hypertension associated with pheochromocytoma.

Inhibition of post-decapitation convulsions in the rat by dibenzothiepin neuroleptics via alpha 1-adrenoceptor blockade

The mechanisms involved in inhibitory effects of isofloxythepin, a newly synthesized dibenzothiepin neuroleptic, on post-decapitation convulsions were studied in rats. Isofloxythepin (0.05-2.0 mg/kg s.c.) inhibited post-decapitation convulsions in a dose-dependent manner as shown by the decrease in the incidence and the shortening of the duration of convulsions. The convulsions were also inhibited by oxyprothepin, zotepine or chlorpromazine but not by haloperidol. Prazosin and bunazosin, both alpha 1-adrenoceptor antagonists, suppressed the post-decapitation convulsions but a non-selective alpha 2-adrenoceptor agonist, tolazoline, was without effect. The convulsions were inhibited dose dependently by clonidine, an alpha 2-adrenoceptor agonist, but were prolonged in duration by yohimbine, an alpha 2-adrenoceptor antagonist. Yohimbine antagonized the inhibitory effects of isofloxythepin, prazosin and clonidine. The noradrenaline-induced contraction of rat vas deferens was inhibited by isofloxythepin, prazosin or chlorpromazine. Isofloxythepin bound to alpha 1-receptors as did chlorpromazine in the rat brain cortex. The results imply that post-decapitation convulsions seem to be inhibited by a block of postsynaptic alpha 1-adrenoceptors, enhanced by a block of presynaptic alpha 2-adrenoceptors and reduced by isofloxythepin via the blocking of postsynaptic alpha 1-adrenoceptors. The convulsions thus could serve as a good model for studying the actions of drugs on the central nervous system alpha-adrenoceptors.

Alpha-blocker, bunazosinhydrochloride decreases cytosolic Ca++ of cultured rat aortic smooth muscle cells

Effect of alpha-blocker, bunazosinhydrochloride on cytosolic Ca++ concentration of rat aortic smooth muscle cells (SMC) was studied. Marked and sustained decrease in cytosolic Ca++ concentration of SMC was observed following the addition of 10(-7) M bunazosinhydrochloride. Furthermore, 10(-7) M bunazosinhydrochloride completely blocked the phenylephrine induced increase in cytosolic Ca++ of rat aortic SMC. It is of interest that a decrease in cytosolic Ca++ of vascular SMC was caused by alpha-blocker.

Effect of egg yolk lecithin on transdermal delivery of bunazosin hydrochloride

Transdermal delivery of bunazosin HCl and the enhancing effect of egg yolk lecithin were examined using an in-vitro hairless mouse skin preparation and rabbits for in-vivo systemic absorption. The delivery of bunazosin in-vitro was small, but it was significantly enhanced when lecithin was incorporated into the same vehicle. This enhancing effect was confirmed with other drugs in-vitro. The enhancing ability was also seen in-vivo. Very little bunazosin was delivered from a propylene glycol suspension, but levels of 100-200 ng mL-1 were achieved by the incorporation of the lechithin.

Inhibition of Ca2+ inward current in rabbit sinoatrial node by bunazosin, an alpha-adrenoceptor antagonist

The electrophysiological effects of bunazosin, a novel alpha-adrenoceptor antagonist, were examined on isolated spontaneously beating sinoatrial node preparations of the rabbit by means of a double-microelectrode voltage clamp method. Bunazosin (above 10 microM) reduced the beating frequency, and the maximum rate of rise and the amplitude of action potentials. The slope of the diastolic depolarization (phase 4) was also decreased by the drug whereas the action potential duration at 50% repolarization was prolonged. Bunazosin decreased the slow inward current (Isi) and the time-dependent potassium outward current (IK). However, the major effect was the reduction of Isi. The results indicate that bunazosin, an alpha-adrenoceptor antagonist, depresses the action potential and automaticity of the sinoatrial node by inhibition of Ca channels.

Selective alpha 1-adrenergic antagonists: therapeutically relevant antihypertensive agents

Alpha-adrenergic antagonists were the first substances to receive serious consideration as antihypertensive agents. However, their therapeutic potential in the management of essential hypertension was not realized until prazosin, a highly selective alpha 1-adrenergic antagonist, became available. A number of analogs of prazosin have now been synthesized, as have several structurally distinct alpha 1-adrenergic antagonists. Preliminary investigations suggest that these agents may also be clinically useful antihypertensive drugs. The alpha 1 receptor of arteriolar smooth muscle is the predominant adrenergic subtype determining sympathetically mediated vascular tone. Therefore, its selective blockade by an agent such as prazosin is a relevant approach to the major pathophysiologic defect in hypertension: an elevation of peripheral vascular resistance. Because prazosin has little selectivity for the alpha 2 receptor, the negative feedback control of norepinephrine release from sympathetic nerve terminals remains intact. This unique action of prazosin may explain why it effectively lowers arterial pressure without markedly increasing cardiac output, heart rate and plasma renin activity. An additional factor in the favorable therapeutic effects of this agent is its ability to induce a balanced reduction in both arteriolar and venous tone, with little change or even improvement in renal hemodynamics. The antihypertensive effects of prazosin, when used as a single agent, may be modest. However, it may be useful as initial as well as adjunctive therapy for the management of hypertension because of its high toxic to therapeutic ratio, coupled with a sustained reduction in arterial blood pressure, a low incidence of side effects, and a potentially favorable metabolic profile.