Control plasma renin activity and changes in sympathetic tone as determinants of minoxidil-induced increase in plasma renin activity

Increased plasma renin by vasodilators promotes the progression of abdominal aortic aneurysm

Background: It is well-accepted that antihypertensive therapy is the cornerstone of treatment for abdominal aortic aneurysm (AAA) patients with hypertension. Direct-acting vasodilators were used in the treatment of hypertension by directly relaxing vascular smooth muscle but may have destructive effects on the aortic wall by activating the renin-angiotensin system axis. Their roles in AAA disease remain to be elucidated. In this study, we used hydralazine and minoxidil, two classical direct-acting vasodilators, to investigate their influence and potential mechanisms on AAA disease. Methods and results: In this study, we investigated the plasma renin level and plasma renin activity in AAA patients. Simultaneously, age and gender ratio-matched patients diagnosed with peripheral artery disease and varicose veins were selected as the control group using a ratio of 1:1:1. Our regression analysis suggested both the plasma renin level and plasma renin activity are positively associated with AAA development. In view of the well-established relationship between direct-acting vasodilators and increased plasma renin concentration, we established a porcine pancreatic elastase-infused AAA mouse model, followed by oral administration of hydralazine (250 mg/L) and minoxidil (120 mg/L) to investigate effects of direct-acting vasodilators on AAA disease. Our results suggested both hydralazine and minoxidil promoted the progression of AAA with increased aortic degeneration. Mechanistically, the vasodilators aggravated aortic inflammation by increased leukocyte infiltration and inflammatory cytokine secretion. Conclusion and relevance: The plasma renin level and plasma renin activity are positively associated with AAA development. Direct vasodilators aggravated experimental AAA progression, which raised cautionary concerns about their applications in AAA disease.

Changes in plasma volume and extracellular fluid volume and after addition of hydralazine to propranolol treatment in patients with hypertension

In 16 patients with hypertension, BP could not be controlled satisfactorily by treatment with propranolol alone (mean dosage 325 mg/day). Plasma volume (PV) (T-1824) and extracellular fluid volume (ECV) (82Br-distribution space) were determined in these patients before and after the addition of hydralazine for three months (mean dosage 135 mg/day). After the addition of hydralazine, PV and ECV increased significantly, by 9% and 3%, respectively. Systolic and diastolic BPs decreased, by 15% and 13%. The mechanisms inducing fluid retention during treatment with hydralazine and the clinical significance of the problem are discussed. It is concluded that the addition of a diuretic to propranolol-hydralazine treatment is often well indicated.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

Calcium antagonists and their potential for antihypertensive therapy

Calcium antagonists are potent arterial vasodilators devoid of relevant chronic sympathetic reflex activation and sodium and volume retention. This favorable hemodynamic profile of action renders them suitable for monotherapy of hypertension where they act to reduce an enhanced, calcium-influx-dependent vasoconstrictor mechanism which may be brought about by altered smooth muscle cation handling and increased intracellular free calcium concentrations. Clinical studies have proved their efficacy, safety, and good tolerability alone or in combination with other drugs in uncomplicated hypertension where they are particularly effective in older and low-renin and possibly black patients. These properties and their efficacy in the treatment of severe and accelerated hypertension or hypertensive emergencies make them a valuable addition to already available drug therapy.

Minoxidil and captopril in severe hypertension

The antihypertensive efficacy of minoxidil and captopril was compared in 23 males with essential or renal parenchymatous hypertension refractory to conventional antihypertensive drug therapy. Following a pretreatment period the patients were randomly assigned to receive either minoxidil, 2.5 mg twice daily (n = 12), or captopril, 25 mg twice daily (n = 11). In patients with diastolic blood pressure greater than 95 mmHg, doses of minoxidil and captopril were increased in 2-week intervals. Patients who maintained diastolic pressure greater than 95 mmHg and/or those with intolerable side effects were switched over to the alternative substance. After a mean observation period of 12 weeks a significant decrease in systolic and diastolic blood pressure was observed (179/114 vs 148/92 mmHg in the minoxidil group; 176/111 vs 158/97 mmHg in the captopril group). The primary response rate was 75% in patients treated with minoxidil and 55% in those with captopril (not significant). After the change to the alternative substance two of the four non-responders on captopril and one of the two non-responders on minoxidil became responders. Side effects occurred significantly more often during minoxidil than captopril (p less than 0.05). The high efficacy of minoxidil and captopril in the treatment of severe hypertension refractory to conventional drugs was confirmed. Minoxidil lowered blood pressure slightly more than captopril, but it had a higher incidence of side effects than captopril.

Effects of two forms of hypertension on atherosclerosis in the hyperlipidemic baboon

We examined the relationship of hypertension and plasma renin activity to atherogenesis in 48 moderately hyperlipidemic (total serum cholesterol was about 200 mg/dl) baboons (Papio sp.). We used renal artery stenosis (two-kidney, one clip model) to produce hypertension associated with elevated plasma renin activity, and used cellophane wrapping of both kidneys (bilateral perinephritis model) to produce hypertension with normal renin activity. Renal artery stenosis and bilateral perinephritis increased both systolic and diastolic blood pressure by about 30 mm Hg. Renal artery stenosis approximately doubled, but bilateral perinephritis did not change plasma renin activity. Both hypertensive groups, to about the same degree, had significantly more extensive atherosclerosis than the control group in the abdominal aorta and brachial, iliac-femoral, and carotid arteries. The effect of hypertension was greatest in the carotid arteries where the extent of atherosclerosis was nearly tripled. Hypertension did not influence lesions in the thoracic aorta. By multiple regression analysis, very low plus low density lipoprotein cholesterol, high density lipoprotein cholesterol, and systolic blood pressure were consistently strong predictive variables for the extent of atherosclerotic lesions. Most of the effects of renal hypertension on atherosclerotic lesions appeared to be accounted for by the increase in blood pressure. In the carotid arteries, however, there was a suggestion of an effect above that due to increased blood pressure. Additional analyses indicated that these treatment effects were associated with serum potassium concentration, plasma renin activity, or other closely related variables.

Bucindolol, a beta-adrenoceptor blocker with vasodilatory action: its effect in systemic hypertension

Bucindolol is a newly developed, nonselective beta-adrenergic blocking agent with intrinsic sympathomimetic activity and direct vasodilator properties. In 14 patients with mild to moderate essential hypertension, the effects of bucindolol, hydrochlorothiazide and their combination on blood pressure (BP), heart rate (HR) and parameters of the renin-aldosterone system were compared with those after placebo. Bucindolol's antihypertensive effect was evident within the first hour after drug administration, maximal at 2 to 3 hours, and lasted for as long as 12 hours. Compared with placebo values (108 +/- 5 mm Hg), both bucindolol (97 +/- 9 mm Hg) and hydrochlorothiazide (99 +/- 10 mm Hg) alone significantly and comparably reduced the 12-hour averaged standing diastolic BP, with the combination resulting in approximately additive effects (91 +/- 9 mm Hg). Although bucindolol alone did not affect HR, it attenuated the hydrochlorothiazide-induced increase in HR. There was a tendency for bucindolol to decrease plasma renin activity. Except for transient postural hypotension in 2 patients, bucindolol was well tolerated.

Systemic and cardiac haemodynamic interactions between guanfacine and hydrallazine in hypertensive patients

The effect of guanfacine and hydrallazine on cardiovascular haemodynamics and on sympathetic nervous activity has been studied in 16 patients with essential hypertension. Two groups of patients were investigated: in Group A guanfacine brought the blood pressure back to normal (diastolic blood pressure less than or equal to 90 mmHg), and in Group B diastolic blood pressure was greater than 90 mmHg and required the addition of hydrallazine. Guanfacine significantly decreased heart rate, plasma renin activity and urinary excretion of noradrenaline, without altering cardiac contractility. In Group B, guanfacine 2 to 6 mg/day produced a significant decrease in blood pressure from 178.7/112.4 to 164.4/102.9 mmHg and in heart rate from 77.1 to 62.7 beats/min after 4 weeks of treatment. Guanfacine did not significantly alter preejection period, cardiac output or total peripheral resistance. Hydrallazine 50 to 300 mg/day caused a further reduction in blood pressure from 164.4/102.9 to 150.7/90.2 mmHg and an increase in heart rate from 62.7 to 72.1 beats/min. Limb blood flow was increased from 4.55 to 5.93 ml/100 g/min and limb vascular resistance was decreased from 39.55 to 23.6 mmHg 100 g X min/ml. Hydrallazine also caused a slight increase in plasma renin activity and urinary excretion of noradrenaline. It is concluded that guanfacine is a useful agent to block a hydrallazine-induced increase in sympathetic nervous activity.

Multiclinic comparison of labetalol to metoprolol in treatment of mild to moderate systemic hypertension

The antihypertensive effects of oral labetalol, a new alpha- and beta-adrenergic blocking agent, and metoprolol, a relatively beta1 selective adrenergic blocker, were evaluated in 91 patients with mild to moderate hypertension (standing diastolic blood pressure of 90 to 115 mm Hg) in a double-blind parallel group multicenter clinical trial. The effects of the two drugs on plasma lipids and lipoprotein fractions were also assessed. Following a four-week placebo phase, 44 patients were randomized to receive labetalol and 47 metoprolol. During a four-week titration phase, the labetalol dose was increased from 100 mg twice daily to a maximum of 600 mg twice daily to achieve a standing diastolic blood pressure of 90 mm Hg that was decreased by 10 mm Hg or more. Metoprolol was titrated from 50 mg to 200 mg twice daily. An eight-week maintenance period followed during which hydrochlorothiazide could be added. At the end of the maintenance phase, the doses of labetalol and metoprolol were tapered over a two to four day period after which patients received a placebo for one week. Blood pressure in the supine and standing position was measured at each visit. Labetalol and metoprolol both significantly (p less than 0.01) lowered the supine and standing blood pressure from baseline with no significant difference found between the two treatment groups. Both drugs lowered the heart rate; however, the rate-lowering effect was significantly greater with metoprolol (p less than 0.01). There were no significant effects of either drug on plasma lipids or lipoprotein fractions. Fatigue was the most frequently reported complaint with both drugs. Dizziness, dyspepsia, and nausea were more common with labetalol; bradycardia was more common with metoprolol. There was no blood pressure "overshoot" after withdrawing drug treatment; however, a heart rate "overshoot" was seen after metoprolol was tapered off and stopped. Labetalol is as safe and effective as metoprolol in the treatment of patients with mild to moderate hypertension.

Cardiovascular hemodynamic interactions between clonidine and minoxidil in hypertensive patients

The systemic, cardiovascular hemodynamic and biochemical interactions between clonidine and minoxidil were studied in ten patients with refractory and/or accelerated hypertension. Clonidine in oral doses of 150 to 900 micrograms/day decreased mean blood pressure (MAP) 18.6 mm Hg (p less than 0.01), average heart rate (HR) 16.4 bpm (p less than 0.01), limb blood flow 1.63 ml/100 g min (p less than 0.05), plasma renin activity (PRA) 1.13 ng/ml/hr (p less than 0.025), and urinary noradrenaline excretion rate 16.45 micrograms/24hr (p less than 0.05). Clonidine increased the preejection period index (PEPI) 12.4 msec ( p less than 0.001), but did not alter cardiac index (CI), total peripheral resistance index (TPRI), limb vascular resistance nor dopamine beta-hydroxylase activity. When minoxidil in oral doses of 5 to 22.5 mg was added, a further decrease in MAP of 24.2 mm Hg (p less than 0.01) was observed; PEPI decreased 20.6 msec (p less than 0.01), limb blood flow decreased 13.2 mm Hg/min 100 g/ml (p less than 0.05), and total peripheral resistance index decreased 13.3 mm Hg/min m2/L (p less than 0.05). Minoxidil increased average heart rate 8.2 bpm (p less than 0.05), PRA 1.68 ng/ml/hr (p less than 0.05) and urinary noradrenaline excretion rate 5.0 micrograms/24 hr (p less than 0.01). Limb blood flow, cardiac index and dopamine beta hydroxylase activity were not significantly altered by minoxidil. Neither clonidine nor minoxidil affected cardiovascular responses to treadmill exercise. We concluded that clonidine is a useful alternative agent to block a minoxidil-induced increase in sympathetic nervous activity.

Renin, renin inhibition and antihypertensive therapy

Research over the last 25 years established the renin-angiotensin-aldosterone system's important role in electrolyte and blood pressure homeostasis as well as in the pathophysiology of hypertension for which renin suppressive drugs, angiotensin antagonists and converting enzyme inhibitors provided selective pharmacological tools. Pharmacological interference with the renin-angiotensin axis in addition to reducing angiotensin-mediated vasoconstriction reduces angiotensin's effect on aldosterone, alpha-adrenoceptor mediated vasoconstriction and central activation of sympathetic nerve activity. Renin measurements serve as an endocrine marker for the activity and reactivity of the sympathetic nervous system reflecting a beta-adrenoceptor mediated response which tends to decrease with older age. Therefore, as younger the patient and as higher pretreatment renin as better the antihypertensive response to converting enzyme inhibitors and betablockers is. As lower renin and as older the age diuretic agents and calcium antagonists are more effective, the hyporesponsive renin being a co-determinant of pressure response in these patients.

Verapamil-induced vasodilator response is enhanced in essential hypertension

Forearm blood flow response to the calcium channel inhibitor verapamil, 1 75 micrograms/100 ml tissue, as measured by venous occlusion plethysmography, was found to be significantly greater in 11 patients with essential hypertension as compared to 11 age-matched normotensive subjects whereas there was no significant difference in increase in forearm blood flow between both groups to non-specific vasodilatation with sodium nitroprusside (1.2 micrograms/100 ml tissue). The increase in forearm blood flow to verapamil correlated positively with basal plasma epinephrine concentration in hypertensives. These findings support the concept of an increased dependency of arteriolar tone on calcium influx in patients with essential hypertension, an abnormally related to the activity of the sympathetic nervous system.

Comparison of oral propranolol and verapamil for combined systemic hypertension and angina pectoris. A placebo-controlled double-blind randomized crossover trial

The relative efficacies of oral verapamil, a calcium-entry blocking drug, and propranolol, a beta-adrenergic blocking drug, were compared in 12 patients who had both stable angina pectoris and mild to moderate systemic hypertension, using a placebo-controlled, double-blind, randomized crossover protocol. Compared with placebo, both propranolol and verapamil decreased the frequency of anginal attacks and the number of nitroglycerin tablets consumed, and increased exercise duration and total work; there were no significant differences in the antianginal effect of the two drugs. Both verapamil and propranolol reduced the supine and standing systolic and diastolic blood pressure measured at rest; compared with propranolol, however, verapamil had greater effects on standing diastolic blood pressure (p less than 0.002). Resting heart rate was reduced from placebo baseline with large doses of both drugs; compared with verapamil, however, propranolol exerted greater effects on resting heart rate and rate-pressure product. Plasma renin activity was increased from placebo baseline with verapamil (p less than 0.05), but was reduced with propranolol (p less than 0.05); no significant change in plasma aldosterone was seen with either drug. Verapamil appears to be a safe and effective treatment alternative to propranolol for relieving anginal symptoms, improving exercise tolerance, and reducing elevated systemic blood pressure in patients with both angina pectoris and mild to moderate systemic hypertension.

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.

Acute and long-term hypotensive effects and plasma concentrations of nifedipine in patients with essential hypertension

The acute and long-term hypotensive effects of low doses of nifedipine, and the correlation between the fall in the blood pressure (BP) and the plasma nifedipine concentration, were investigated in patients with essential hypertension. The oral administration of nifedipine 5 mg rapidly decreased BP from 163 +/- 22/101 +/- 10 to 127 +/- 12/82 +/- 9 mmHg (mean +/- SD; p less than 0.001), and increased heart rate from 72 +/- 8 to 76 +/- 6 beats/min (p less than 0.05), plasma renin activity rose from 1.2 +/- 0.6 to 1.4 +/- 0.8 ng/ml/h (p less than 0.05), and plasma nifedipine concentration was 75.6 +/- 22.0 ng/ml 30 min after administration (n = 7). The nifedipine concentration was significantly correlated both with the fall in BP (r = 0.410, p less than 0.02, n = 31) and the rise in the heart rate (r = 0.412, p less than 0.02, n = 31). Treatment with nifedipine 5 mg t.d.s. alone or in combination either with propranolol 10 mg t.d.s., or thiazide 1 tablet daily, or propranolol and thiazide, controlled BP in 36 patients during the 22 week study period. During the long-term nifedipine therapy, the plasma nifedipine level was significantly correlated with the fall in systolic (r = 0.577, p less than 0.01, n = 20) and diastolic (r = 0.595, p less than 0.01, n = 20) BP. It was concluded that the plasma nifedipine concentration could be correlated with the fall in BP, and that low doses of nifedipine, either as monotherapy or in combination, were effective in the acute and long-term treatment of patients with essential hypertension.

Catecholamines, renin, aldosterone, and blood volume during chronic minoxidil therapy

Several pressor factors were studied before and during chronic minoxidil therapy (median dose 27.5 mg/day) in 16 patients with hypertension that was refractory to conventional drugs. Following treatment with minoxidil and intensified diuretic therapy, blood pressure was decreased markedly; pulse rate, body weight, plasma volume, plasma aldosterone and epinephrine levels were not significantly altered, while plasma renin activity tended to be increased. Supine and upright plasma norepinephrine concentrations were increased by 140 (P less than 0.005) and 50% (P less than 0.05), respectively, but no significant change in urinary norepinephrine excretion was apparent. The latter parameter may not be a close index of sympathetic activity in patients with severe hypertension treated with minoxidil. While a search for underlying pheochromocytoma is always indicated in refractory hypertension, it appears mandatory to evaluate plasma catecholamines prior to or following discontinuation of treatment with minoxidil, to avoid a wrong diagnosis of pheochromocytoma.

Mechanism of renin release during renal nerve stimulation in dogs

During renal nerve stimulation, a predominant vasoconstrictory effect on small arteries would lower blood pressure in the afferent arterioles and induce arteriolar dilation and renin release by the autoregulation mechanism. This hypothesis was examined in anaesthetized dogs by stimulating renal nerves at 4 Hz which permitted continuous reduction of renal blood flow (RBF) by 30-40%; renin release increased almost equally at control and low blood pressure, and in the non-filtering kidney during ureteral occlusion. Examinations of the relationship between RBF and arterial perfusion pressure during mechanical constriction of the renal artery showed that the lowest autoregulating pressure was 25-35 mmHg higher during nerve stimulation than in control experiments, consistent with the hypothesis of arteriolar dilation. Phenoxybenzamine, an inhibitor of alpha-adrenoceptors, abolished vasoconstriction and the effect of nerve stimulation on renin release at control blood pressure; renin release rose from 0.9 +/- 0.4 to 17 +/- 5 microgram/min before, and from 1.7 +/- 0.5 to 4.6 +/- 1.4 microgram/min after phenoxybenzamine infusion. At pressures below the range of autoregulation, phenoxybenzamine did not alter renin release response to nerve stimulation. Propranolol, a Beta-adrenergic inhibitor, attenuated the effect of nerve stimulation on renin release both at control and low blood pressure. We conclude that during renal nerve stimulation (1) renin release is caused by beta-adrenergic stimulation provided the afferent arterioles are dilated and (2) that alpha-adrenergic stimulation dilated the afferent arterioles as a consequence of a predominant vasoconstrictory effect on small arteries. Hence, by inhibiting the beta-adrenergic effect by propranolol, renin release does not increase during renal nerve stimulation. Phenoxybenzamine prevents renin release at control blood pressure because afferent arterioles are not dilated during nerve stimulation. In contrast, phenoxybenzamine does not reduce renin release during nerve stimulation at low blood pressure because afferent arterioles are dilated by the autoregulating mechanism.

Effects of chronic prazosin treatment on the renin-angiotensin-aldosterone system in man

The effects of chronic prazosin treatment (3 mg/day for three weeks) on plasma renin activity (PRA) and plasma aldosterone (PA) levels were evaluated in 12 hypertensive patients, under conditions of metabolic balance. After three weeks of drug administration no significant change occurred in PRA as well as PA levels, with respect to pretreatment values, both in basal conditions and following 2 hours of ambulation. No change was observed in heart rate, while a fall in both systolic (P less than 0.02) and diastolic (P less than 0.05) blood pressure occurred in supine as well as in deambulation-stimulating condition. A mild increase in body weight (P less than 0.05) and a decrease in serum sodium (P less than 0.05) was induced by prazosin treatment. These findings are in keeping with the pharmacologic properties of prazosin, which is a selective blocker of postsynaptic alpha adrenoreceptors and therefore lowers vascular resistance without reflex sympathetic overactivity. The moderate volume expansion after prazosin does not appear to be aldosterone mediated.

Effect of minoxidil on sympathetic nervous activity in clonidine-treated hypertensive patients

The effects of clonidine and minoxidil on sympathetic nervous activity has been studied in 10 patients with accelerated or resistant hypertension. Clonidine 150 to 900 micrograms/day caused a significant decrease in blood pressure of 18.6 mm Hg, of heart rate 16.4 beats/min, of plasma renin activity 1.13ng/ml h, and of urinary noradrenaline excretion 11.55 micrograms/day, and a significant lengthening of the pre-injection period of 12.4 ms. Minoxidil 5 to 22.5 micrograms/day caused a further significant decrease in blood pressure of 24.2 mm Hg, and significant increases in heart rate 8.2 beats/min, plasma renin activity 1.68 ng/ml h and of urinary noradrenaline excretion 5.0 micrograms/day, and a significant shortening of the pre-ejection period of 20.6 ms. Neither clonidine nor minoxidil altered plasma dopamine beta-hydroxylase activity or the cardiovascular responses to treadmill exercise. It is concluded that clonidine is a useful alternative agent to block a minoxidil-induced increase in sympathetic nervous activity.

Minoxidil in the treatment of refractory hypertension

Minoxidil, a powerful vasodilator, is a very effective antihypertensive drug. Twenty-two patients, who were mostly refractory to conventional anti-hypertensive medication, were treated with this drug. There was a swift and definite drop of blood pressure in all cases. In 7 patients with renal disease, renal function did not deteriorate during the administration of minoxidil, and it improved dramatically in the eighth patient. Side effects of the drug were hirsutism, fluid retention, and in 1 patient a pruritic bullous erruption which disappeared when the drug was discontinued.

Minoxidil in the treatment of refractory hypertension

Minoxidil, a powerful vasodilator, is a very effective antihypertensive drug. It was used to treat 22 patients, most of whom were refractory to conventional antihypertensive medication. There was a swift and definite drop of blood pressure in all cases. In 7 patients with renal disease, renal function did not deteriorate during the administration of Minoxidil, and it improved dramatically in the eighth patient. Side effects of the drug were hirsutism, fluid retention, and in 1 patients a pruritic bullous eruption which disappeared when the drug was discontinued.

Clinical evaluation of a new antihypertensive vasodilating agent PR--G 138 Cl

1 The cardiovascular effects of a new substance (PR--G 138) with vasodilating action were analysed in 12 patients with moderately severe essential hypertension on a 60 mEq sodium diet in a metabolic ward. To prevent tachycardia, propranolol 40 mg four times daily was given during the control period until blood pressure (BP) was stabilized, and continued throughout the study. 2 The compound was effective in every patient except one, who also was resistant to hydrallazine and diazoxide. Mean arterial pressure was lowered from a mean control value of 121 +/- 11 supine and 118 +/- 13 standing to 98 +/- 18 and 95+/- 15 mm Hg (P less than 0.001) respectively after a single oral dosage of 5 to 15 mg PR--G 138. The effect was maximal after 1--2 h and lasted up to 6 h. 3 With adequate dosage, there was no orthostatic reaction. Pulse rate and plasma renin activity did not rise during PR--G 138 treatment, and cardiac output increased only slightly, doubtlessly as a result of the propranolol therapy. In most patients 5 mg of the drug was sufficient to cause a drop of BP to normal levels. Exercise tolerance (bicycle ergometry) was constant or improved during drug action. One patient complained of headache, but no other side effects were seen provided that propranolol was taken when the drug was given. During 3 months treatments on an out-patient basis the effect was sustained in four of eight patients. No toxic effects have been noticed.

Effect of nifedipine on plasma renin, aldosterone and catecholamines in arterial hypertension

Acute sublingual administration of nifedipine 10--20 mg to 13 hypertensive patients caused a rapid decrease in blood pressure (BP) and a concomitant increase in heart rate (HR), plasma noradrenaline (NA) and plasma renin activity (PRA); there was no significant change in plasma adrenaline (A) or aldosterone (ALDO). Basal PRA was the major determinant of the rise in PRA, as a close correlation was present between the basal value and the increase caused by nifedipine (r = 0.92), p less than 0.001). The rise in PRA was also correlated with the plasma concentration of nifedipine after 60 min (r = 0.80, p less than 0.01), but it was not correlated with the decrease in BP, the rise in HR or the increase in NA. Nifedipine 30--60 mg daily for 6 weeks caused a reduction in mean BP from 133 to 113 mmHg (p less than 0.001). Body weight and serum potassium decreased but no consistent change was noted in NA, PRA, ALDO or 24 h-excretion of catecholamines. A significant correlation was present between the change in NA and that in PRA (r = 0.74, p less than 0.01). The alterations in the various parameters in the acute and chronic studies were not correlated. The findings indicate that different regulatory mechanisms are activated during acute and chronic administration of nifedipine. It is suggested that an initial rise in sympathetic activity gradually decreases during prolonged therapy, but it still remains a determinant of PRA.

Treatment of severe hypertension with minoxidil: advantages and limitations

Minoxidil, a new peripheral vasodilator, was used in the therapy of 26 hypertensives who were previously uncontrolled on conventional medications or who had dose-limiting side effects. Minoxidil provided (1) therapeutic advantages in all patients, regardless of the etiology of their hypertension, (2) no symptoms of orthostatic hypotension or sympathetic nervous system depression, (3) a simplification of medical regimens and perhaps costs, and (4) regression of impotence in four out of seven patients. The major limiting factors encountered were (1) fluid retention with the development of congestive heart failure in three patients, (2) pericardial effusion in three patients, and (3) hypertrichosis, which reduced its acceptability in female patients.

Long-term clinical effects, bioavailability, and kinetics of minoxidil in relation to renal function

Minoxidil was used to treat 26 patients (17 to 67 years old) with severe hypertension and varying degrees of renal function. Our object was to assess long-term clinical efficacy, kinetics (acute and chronic), and bioavailability of minoxidil in chronic renal insufficiency. Minoxidil, 27 to 30 mg per day, decreased systolic and diastolic blood pressure during the first three months of therapy. Between the third and 24th months (30 months in one patient) there was no further change. Propranolol or clonidine was needed to control heart rate, and furosemide or dialysis was needed to control edema induced by minoxidil. Renal function improved in some of the mildy azotemic patients. Minoxidil kinetics after the customary dose did not differ whether the drug was taken as tablet or solution. Kinetic parameters during chronic administration of minoxidil did not differ from those after acute administration. The kinetics in chronic renal insufficiency do not differ from these in subjects with normal renal function.

Effect of propranolol on sympathetic nervous activity in hydrallazine-treated hypertensive patients

1 The effect of propranolol was examined on a) blood pressure and heart rate responses due to i.v. hydrallazine b) modification of these cardiovascular parameters during cold pressor test c) urinary catecholamine excretion rate. 2 Intravenous hydrallazine reduced significantly mean blood pressure by 15.2 mm Hg and increased heart rate by 24.9 beats/min. Propranolol reduced significantly mean blood pressure by 19.0 mm Hg and heart rate by 14.1 beats/min. Hydrallazine plus propranolol caused a significant reduction of mean blood pressure (by 37.7 mm Hg) but this was not accompanied by a significant fall in heart rate (by 3.3 beats/min). 3 During the control period, cold pressor test increased mean blood pressure by 16.0 mm Hg. Heart rate was increased by 12.5 beats/min in four patients. However, there was a reduction in heart rate (5.5 beats/min) in two other patients. During the propranolol period, cold pressor test-induced increase of mean blood pressure was not reduced but propranolol blocked the increase of heart rate. 4 Urinary catecholamine excretion rate was increased during hydrallazine administration. This excretion was not modified by propranolol.

Need for beta-blockade in hypertension reduced with long-term minoxidil

Sequential changes in plasma renin activity and urinary aldosterone and noradrenaline were assessed in eight patients with severe hypertension after minoxidil had been added to their treatment. Doses of 2.5--27.5 (mean 12.5) mg/day reduced the mean blood pressure from 166/113 +/-6/2 mm Hg to 124/88+/-4/2 mm Hg in one week. Plasma renin activity and urinary aldosterone and noradrenaline increased twofold to threefold initially but returned to baseline values within two to three weeks and remained unchanged during a mean follow-up of 5.1 months. Beta-blocking drugs were then withdrawn slowly in six patients without adverse effects, though blood pressure and heart rate increased in three patients, who required minimal doses of beta-blockers. Plasma renin activity and urinary aldosterone and noradrenaline did not change significantly after beta-blockade had been stopped. We conclude that the need for beta-blockade is greatly reduced with long-term minoxidil treatment and that it may be unnecessary in some patients.

Minoxidil therapy in children with severe hypertension

Six children, from 1.3 to 18 years of age, with severe hypertension associated with the hemolytic uremic syndrome, periarteritis, and renal transplant rejection received minoxidil, an antihypertensive agent, for three to 36 weeks. All had severe hypertension resistant to oral antihypertensive medications; five required frequent intravenous diazoxide therapy prior to minoxidil therapy. The mean pretreatment systolic and diastolic blood pressures were 176 and 117 mm Hg, respectively. Following treatment, the mean systolic and diastolic blood pressures were 133 and 82 mm Hg, respectively. Concomitant antihypertensive medications were decreased in all six patients once optimal blood pressure control was obtained. The initial dosage of minoxidil was 0.1 to 0.2 mg/kg/day; maximal dosage for blood pressure was 0.3 to 1.4 mg/kh/day. Major complications of therapy were fluid retention and hirsutism. Transient asymptomatic pericardial effusions occurred in two patients. Three patients on prolonged minoxidil therapy had persistent increases in right ventricular end diastolic diameters. Minoxidil is an effective oral antihypertensive agent for treatment of severe hypertension in pediatric patients. Avoidance of fluid retention is mandatory to prevent congestive heart failure.

Physiologic evaluation of a new antihypertensive agent: prazosin HCl

The mechanism of action of prazosin hydrochloride, a new antihypertensive agent was studied in 14 patients with essential hypertension. Mean supine blood pressure for the group fell from 148/102 +/- 3/2 (SE) mm Hg at baseline to 139/91 +/- 5/4 after eight weeks of therapy (P less than 0.05). No significant postural hypotension was noted in the patients who responded to therapy. Glomerular filtration rate (endogenous creatinine or inulin clearance) and effective renal plasma flow (PAH clearance) remained unchanged during therapy as did supine and stimulated peripheral plasma renin activity. Cardiac output did not change significantly although plasma volume increased in ten out of 12 patients in whom it was measured (P less than 0.025). Among the patients whose mean blood pressure fell 10 mm Hg or more, peripheral vascular resistance fell significantly (P less than 0.025), and the change in plasma volume was not statistically significant. Among the patients whose mean blood pressure changed less than 10 mm Hg with therapy, there was no significant change in peripheral vascular resistance and plasma volume increased significantly (P less than 0.025). Prazosin hydrochloride appears to be an effective antihypertensive agent which acts by peripheral vasodilatation. It may cause fluid retention. The drug does not appear to affect renal function or renin secretion.

The vasodilator--beta-blocker interaction--some determinants of its clinical success

A number of structurally dissimilar compounds, sharing the ability to induce vasodilatation have come into clinical usefulness as antihypertensive drugs. Their successful utilisation often depends critically on an appropriate combination with diuretics and beta-blockers. Beta-blockers can specifically inhibit the reflex cardiac stimulation which otherwise may limit the tolerability and haemodynamic value of these drugs. A synergistic antihypertensive effect has been demonstrated with hydrallazine and propranolol and possibly exists with other combinations. Generally, vasodilators are not first-line drugs in chronic therapy but are best added to beta-blockers. Variations of the dose-response and the time-course of effect are stressed as being important determinants of a successful interaction.

Effect of beta adrenergic blockade on renin response to renal nerve stimulation

The ability of d,l-propranolol to block renin secretion in response to various extrarenal stimuli, such as hemorrhage and hypoglycemia, has been interpreted to indicate the presence of an intrarenal beta receptor regulating renin release. However, two problems complicate this interpretation: (a) the stimuli have effects outside the kidney, and (b) d,l-propranolol has a local anesthetic, as well as a beta adrenergic blocking, action. In the present study, the effects of a purely intrarenal stimulus, in the form of renal nerve stimulation (RNS), on renin secretion was examined. The effects of d,l-propranolol (anesthetic and beta-blocking activity), l-propranolol (beta-blocking activity only), and d-propranolol (local anesthetic activity only) on the renin response to RNS were examined. In a control group of animals, two sequential RNS increased mean renin secretion from 401 to 1,255 U/min (P less than 0.25) and from 220 to 2,179 U/min (P less than 0.01). In a second group the first RNS increased renin secretion from 201 to 1,181 U/min (P less than 0.01), but after d,l-propranolol was given RNS did not significantly alter renin secretion (33 to 55 U/min). In a third group the initial RNS increased renin secretion from 378 to 1,802 U/min (P less than 0.025), but after l-propranolol was given RNS had no significant effect on renin secretion (84 to 51 U/min). A fourth group of dogs showed a rise in renin secretion from 205 to 880 U/min (P less than 0.001) in response to the first RNS, while the second RNS, given after an infusion of d-propranolol, caused a rise in renin secretion from 80 to 482 (P less than 0.005). The nature of the electrical stimulus was consistent in all groups and caused no detectable changes in renal or systemic hemodynamics or in urinary electrolyte excretion. The results, therefore, indicate that renin secretion can be stimulated through intrarenal beta receptors independent of changes in systemic or renal hemodynamics or in tubular sodium reabsorption. Hence the effect of beta stimulation on renin secretion would appear to result from a direct action on the renin-secreting cells of the juxtaglomerular apparatus.

Effect of antihypertensive drugs on the renin-angiotensin system

Renin release from the kidneys is controlled by four major mechanisms - renal baroreceptors, the macula densa, the sympathetic nervous system and other humoral and ionic influences. Recently, the importance of the sympathetic nervous system in modulating renin release for a variety of stimuli has become apparent. The sympathetic adrenergic nerves act on a specific beta-receptor to stimulate renin release from the kidney. Those antihypertensive drugs that inhibit adrenergic nerve transmission tend therefore to lower plasma renin. beta-Adrenoreceptor blocking drugs also generally lower plasma renin by specific inhibition of renal renin release both in animals and humans. Diuretics and vasodilators in contrast elevate plasma renin levels. Plasma renin levels in hypertensive patients are the net result of many diverse influences, and similarly in patients treated with antihypertensive drugs the plasma renin level often is the result of opposing influences. Plasma renin levels tend to return towards normal levels after treatment in hypertensive patients. Plasma renin levels may offer a guide to a more rational basis for antihypertensive therapy in the future. However, the primary aim in treatment of the hypertensive patient should be to lower his blood pressure, independent of the effect of plasma renin levels.