[Interrelations between blood pressure, blood volume, plasma renin and urinary catecholamines during beta-blockade in essential hypertension (author's transl)]

Pathophysiological Mechanisms and Correlates of Therapeutic Pharmacological Interventions in Essential Arterial Hypertension

Treating arterial hypertension (HT) remains a hard task. The hypertensive patient is often a subject with several comorbidities and metabolic abnormalities. Clinicians everyday have to choose the right drug for the single patient among the different classes of antihypertensives. Apart from lowering blood pressure, a main therapeutic target should be that of counteracting all the possible pathophysiological mechanisms involved in HT itself and in existing/potential comorbidities. All the ancillary positive and negative effects of the administered drugs should be considered: in particular, since hypertensive patients are often glucose intolerant/diabetic, carrier of serum lipids disorder, have already developed atherosclerotic diseases and endothelial dysfunction, they should not be treated with drugs negatively interfering with these conditions but with molecules that, if possible, improve them. The main pathophysiological mechanisms and correlates of therapeutic pharmacological interventions in essential HT are reviewed here.

Interference by sulphinpyrazone with the antihypertensive effects of oxprenolol

The interfering effect of sulphinpyrazone, a uricosuric agent which reduces the activity of cyclo-oxygenase, with the antihypertensive activity of oxprenolol, a non-cardioselective beta-blocker with sympathomimetic activity, has been evaluated. Ten patients with primary arterial hypertension of mild to moderate degree entered a randomized double-blind cross-over study versus placebo. They were given oxprenolol + placebo or oxprenolol + sulphinpyrazone for 15 days, and then the treatments were crossed-over for a further 15 days. Oxprenolol significantly reduced blood pressure (161 +/- 3/101 +/- 1 vs 149 +/- 4/96 +/- 2 mmHg) and heart rate (72 +/- 3 vs 66 +/- 3 beats/min). During administration of the combination with sulphinpyrazone the blood pressure increased to its pretreatment level (156 +/- 5/101 +/- 2 mmHg). The effect of oxprenolol on heart rate was not influenced by the combined treatment (67 +/- 6 beats/min). The results may be explained by 1) sulphinpyrazone-induced inhibition of prostaglandin synthesis, which could interfere with the antihypertensive activity of oxprenolol, or 2) sulphinpyrazone-induced acceleration of the metabolism of oxprenolol.

Comparative evaluation of the new vasodilator carprazidil and minoxidil in the treatment of moderate to severe hypertension

The efficacy and side effects of the new vasodilator carprazidil and the established vasodilator minoxidil were compared in 18 hypertensive patients inadequately controlled by 2 to 4 conventional drugs; the latter included diuretics, beta-blockers and/or sympatholytics and, in half the cases, vasodilators, such as hydralazine, diazoxide or the postsynaptic alpha-blocker prazosin. The vasodilators were withdrawn and, using a crossover design all patients received carprazidil (mean final dose 88 mg) and minoxidil (20 mg) for an average period of 5 to 6 months. The effects of the 2 agents appeared to be qualitatively and quantitatively similar. Both tended to cause sodium retention and an increase in heart rate, which required an increased dose of diuretic in one third of the cases or of a beta-blocker in a quarter. With this approach mean body weight and blood volume were not altered in the established phase of carprazidil or minoxidil treatment; heart rate and plasma norepinephrine tended to be only minimally increased, plasma renin was slightly increased, and plasma aldosterone and epinephrine were largely unchanged. Supine and upright blood pressure were reduced from initial values of 189/113 and 167/ 113 mm Hg, to 149/95 and 138/95 mm Hg (-18 and - 17%), respectively, during carprazidil, and to 154/95 and 141/96 mm Hg (-17 and - 15%) during minoxidil therapy. Hypertrichosis occurred with both agents in almost all patients, and limits their more prolonged use in females. No adverse side effects on haematological parameters, liver or renal function were observed, nor was antinuclear antibody detected. It is concluded that carprazidil and minoxidil are equivalent vasodilator agents in the treatment of severe hypertension, particularly in males.

Recent pathogenic aspects in essential hypertension and hypertension associated with diabetes mellitus

The sympathetic system, the body sodium-fluid volume state, the renin-angiotensin system, functional and structural characteristics of the heart and blood vessels, and some other components are important complementary factors in blood pressure regulation. A deviation from the normal equilibrium among these components, with a persisting non-physiologic increase in pressor factor(s) or in the basal vascular tone and/or cardiovascular reactivity to pressor factors, leads to hypertension. This review discusses recent observations and concepts regarding the pathogenesis of essential hypertension and hypertension associated with diabetes mellitus. It focuses on the roles of various pressor factors as well as cardiovascular pressor responsiveness in the genesis of high blood pressure and in the antihypertensive mechanism of diuretic treatment.

Effects of chronic alpha and beta adrenoceptor blockade with labetalol on plasma catecholamines and renal function in hypertension

Plasma catecholamines and renal function were evaluated in 18 patients with essential hypertension treated with the alpha and beta adrenoceptor blocking agent, labetalol. Following 6 weeks of labetalol therapy, blood levels of epinephrine and norepinephrine remained unaltered. Glomerular filtration rate and renal plasma flow were decreased similarly by about 20% (P less than 0.025). Tubular rejection fraction of sodium was increased by 36% (P less than 0.001) while sodium excretion was comparable to control conditions. Labetalol's potential to cause a mild reduction in kidney function should be considered, but may have no clinical consequences in most hypertensive patients receiving such treatment. The lack of increased plasma catecholamine levels during therapy supports the concept that labetalol's alpha-blocking potential is limited to post-junctional receptors, leaving the prejunctional feedback control of catecholamine release intact. Moreover, labetalol's blood pressure-lowering mechanism may be largely independent of changes in sympathetic nervous activity.

beta blockade with pindolol: differential cardiac and renal effects despite similar plasma kinetics in normal and uremic man

Cardiac and renal effects (measured as the reduction in exercise-induced tachycardia and PRA, respectively) and circulating drug concentrations after acute beta blockade with intravenous pindolol were compared between seven normal volunteers and six patients with terminal renal failure. Kinetic parameters were similar in both groups (total body clearance, 450 mg/min), indicating enhanced extrarenal elimination in patients. For any given drug concentration, however, the uremic patients responded to beta blockade with a greater decrease in pulse rate than did normal volunteers (P less than 0.001). Moreover, in the same group, the decrease of PRA was more marked (from 13.3 to 5.7 vs. 3.3 to 1.9 ng/ml/hr) and lasted longer (8 hours and more vs. 2 hours). Plasma aldosterone remained unchanged. These data reveal an increased dependency of both heart rate and renin release on beta adrenergic-mediated mechanisms in uremic man. They also show that kinetic findings in normal subjects cannot always be extrapolated to predict kinetic behavior in disease, and that similar kinetics do not imply similar effectiveness.

[The importance of changes in whole-body balance of sodium and noradrenaline in essential hypertension (author's transl)]

In 22 patients with essential hypertension plasma levels and urine excretions of sodium and noradrenaline were studied before, during and after long-term beta-blockade with pindolol. The relation between mean blood pressure and the quotient of sodium-/noradrenaline-excretion changed during treatment (placebo r=-0.34; pindolol r=+0.31). During placebo there existed a significant (p is less than 0.03) correlation between blood pressure and sodium-excretion which disappeared during beta-blockade. No correlation between blood pressure and noradrenaline was seen during placebo, whereas during beta-blockade a significant (p is less than 0.003) correlation was observed. In contrast to the placebo period there was a significant positive correlation between sodium- and noradrenaline-excretion during long-term treatment with pindolol. It is concluded that whole-body balance of sodium and noradrenaline is an important factor in essential hypertension.

[Behaviour of plasma renin activity during long-term treatment with propranolol (author's transl)]

17 patients (40 +/- 9 years) with essential hypertension were included in the study. A monotherapy of 120, 160 or 240 mg propranolol per day was administered orally according to the antihypertensive effect. Four weeks after treatment, blood pressure and heart rate showed a statistically significant decrease and remained unchanged over a period of six months. Plasma renin activity decreased significantly from 5.7 +/- 6.3 ng/ml/h at the beginning of the study to 1.8 +/- 1.3 ng/ml/h after 4 weeks. 5 months later however plasma renin activity increased again to 5.0 +/- 0.9 ng/ml/h. The difference was statistically significant. From 17 patients 7 (41%) had lower levels of plasma renin activity after 6 months treatment when compared with pretreatment values. In only 3 patients (18%) was plasma renin activity lower after 6 months than after four weeks. We conclude that the increase in plasma renin activity is a reactive mechanism to the reduced blood pressure under long-term conditions. The decrease of plasma renin activity in short-term treatment of essential hypertension is not a mechanism responsible for the antihypertensive effect of propranolol during long-term treatment.