Long-term thiazide therapy in essential hypertension. Evidence for persistent alteration in plasma volume and renin activity

Elevation of serum lipid levels during diuretic therapy of hypertension

In a study attempting to improve coronary risk status, serum cholesterol and triglyceride levels were measured before and during treatment of 74 patients with mild primary hypertension. In 35 patients there was a satisfactory reduction in elevated blood pressure levels with diet therapy alone. In the remaining 39 patients a diuretic drug was required in addition to the diet. Diet therapy alone was followed by a decrease of 11 mg/100 ml in mean serum cholesterol (p less than 0.01 versus pretreatment value) and no change in serum triglyceride. The sue of diuretics was accompanied by an average increase of 11 mg/100 ml in serum cholesterol and of 34 mg/100 ml in serum triglyceride (p less than 0.01 versus pretreatment level for both). In a subgroup of 21 patients with greatest elevations in lipid levels during the administration of diuretics, little improvement in coronary risk status occurred because the increase in serum cholesterol balanced the decrease in systolic blood pressure, according to Framingham risk tables. If the level of serum lipids is a factor in the pathogenesis of coronary atherosclerosis then the observed effect of diuretic drugs to elevate serum cholesterol and triglyceride levels may explain, in part, the continuing high rate of occurrence of myocardial infarction during the treatment of hypertension.

Furosemide and plasma renin activity in essential hypertension

Changes in arterial blood pressure, renal electrolyte excretion, and plasma renin activity in response to repeated doses of furosemide were measured in 12 patients with essential hypertension admitted to the medical service for electrolyte balance studies. Eighty and 120 mg/day furosemide in divided doses for 5 to 10 days produced a prompt increase in renal sodium excretion. Urinary Na/K concentration ratios, which were elevated during peak natriuresis, returned to control levels following the initial diuretic response. In 2 patients with high initial levels of plasma renin activity, arterial blood pressure was not reduced by furosemide, and more potent antihypertensive agents were required to control the blood pressure. In the remaining patients, furosemide produced a significant decrease in systolic and diastolic blood pressure. There was a general upward shift of plasma renin levels in terms of 24-hour renal sodium excretion in those who demonstrated an antihypertensive response to the drug. However, the average increase in plasma renin activity after repeated doses of furosemide was not statistically significant and no correlation was demonstrated between the level of plasma renin activity after furosemide and the blood pressure lowering effect of the drug.

Control of renin release: a review of experimental evidence and clinical implications

Present knowledge of the mechanisms regulating release of renin is reviewed with particular emphasis on neural factors. Evidence is given for a direct effect of renal innervation on beta adrenergic receptors in juxtaglomerular cells, and for the involvement of reflex release of renin in conditions such as tilting and acute salt depletion. Participation of neural and nonneural mechanisms of control is also shown to occur in other conditions, such as aortic constriction and hemorrhage. The view is held that neural sympathetic factors might explain some of the renin disturbances found in essential hypertension. First, in patients with high renin hypertension part of the hypertension is renin-dependent, and these pressor levels of renin seem to be neurally induced since they can commonly be suppressed by beta adrenoreceptor blocking agents. Second, the hypothesis is presented that patients with low renin hypertension, at least those who have no volume disturbance, have a blunted sympathetic control of renin release. Therefore a sufficiently precise test of sympathetic activity, and possibly of body fluid volumes, should be associated with renin profiles for a better understanding of the pathophysiology of arterial hypertension and as a better guide to therapeutic management. Indeed, most of the available antihypertensive drugs act on sympathetic activity, body fluid volume or renin, and this multifaceted profile would provide more rational guidelines for treatment.

Comparative study of metoprolol and alpha-methyldopa in untreated essential hypertension

The hypotensive actions of metoprolol and alpha-methyldopa have been compared in 37 men with previously untreated essential hypertension; 36 belonged to stage 1 and 1 to stage 2 of the WHO classification. After four weeks of placebo treatment the patients were randomly allocated to treatment with either of the two drugs. Treatment was started with metoprolol 75 mg daily or alpha-methyldopa 375 mg and was doubled after eight weeks. Satisfactory blood pressure control was defined as systolic blood pressure below 160 mm Hg and diastolic below 95 mm Hg. The patients were examined every four weeks and in those with unsatisfactory control the dose was gradually increased up to a maximum daily dose of metoprolol 450 mg or alpha-methyldopa 2250 mg. The trial lasted for 24 weeks after randomization. Five patients dropped out of the study. After six months, satisfactory blood pressure control was recorded in 16 out of 17 patients and 14 out of 15 patients treated with metoprolol and alpha-methyldopa, respectively. The average reduction in blood pressure produced by the two drugs was comparable. One patient in the alpha-methyldopa group developed drug exanthema and two patients a positive Coombs' test. Other side effects were few and did not differ between the two compounds.

Systolic hypertension: nonhomogeneous diseases

Prospective studies have shown that systolic hypertension is associated with increased cardiovascular risk, but few physiologic studies have characterized the problem. Therefore, two groups of men (older and younger than 35 years) with systolic hypertension (systolic pressure 150 mm Hg or greater and diastolic pressure 95 mm Hg or less) were studied hemodynamically. The 13 younger patients demonstrated a hyperkinetic circulation manifested by a significantly increased heart rate, elevated left ventricular ejection rate and cardiac indexes and normal vascular resistance. The 13 older patients had a normal heart rate, significantly reduced cardiac and left ventricular ejection rate indexes, and increased vascular resistance with respect to the younger men with systolic hypertension and normotensive control subjects. Plasma volume was reduced only in the older patients (P less than 0.05). These data demonstrate that systolic hypertension should not be considered a homogeneous disease entity clinically or physiologically. The physiologic differences between the younger and older patients suggest that different mechanisms may be operative.

Treatment of benign essential hypertension: comparison of furosemide and hydrochlorothiazide

Furosemide (Impugan) 12.5, 25 or 40 mg twice daily, has been compared as an antihypertensive with hydrochlorothiazide 12.5 mg twice daily and a placebo. A double blind, cross-over design was used with a run-in period of 4 weeks, preceding five 4-week periods of treatment with these compounds alone. There were 34 patients in the trial, 17 men and 17 women. Paired comparison showed that furosemide 25 or 40 mg twice daily and hydrochlorothiazide 12.5 mg twice daily had a similar hypotensive effect, irrespective of the initial blood pressure. Furosemide 40 mg twice daily and hydrochlorothiazide 12.5 mg twice daily caused a slight fall of blood pressure as compared with placebo (0.10 greater than p greater than 0.05, p less than 0.05). There was a distinct correlation between blood pressure and age. Serum K+ fell significantly during treatment, particularly with hydrochlorothiazide 12.5 mg twice daily, as well as with furosemide 25 or 40 mg twice daily. As compared with placebo, urinary output increased significantly after furosemide 12.5, 25 or 40 mg twice daily, but it rose only to a non-significant extent after hydrochlorothiazide. The fall of blood pressure and decrease in serum K+ were linearly related. There were only a few, mild side effects which did not necessitate discontinuation of the trial.

Mechanism of immediate hemodynamic effects of chlorothiazide

The mechanism of the immediate hemodynamic effects of intravenous chlorothiazide (25 mg. per kilogram) was studied in 22 anesthetized open-chest dogs. Within 20 minutes after administration, cardiac output and stroke volume significantly fell; this was associated with decreased central venous and left ventricular end-diastolic pressures. That these hemodynamic effects were caused by, and dependent upon, volume loss through diuresis (eightfold increase in urine volume) was shown: by a return of these measurements to control levels when the volume loss (by diuresis) was corrected with 6 per cent Dextran; by prevention of the hemodynamic changes in chlorthiazide-treated dogs previously prepared with ureterocaval anastomosis; and by confirming these same hemodynamic effects by quantitatively equivalent hemorrhage. Thus, the immediate diuresis produced by chlorothiazide resulted in a contracted plasma volume (increased hematocrit and serum protein concentration) which, in turn, diminished cardiac venous return, central filling pressures, stroke volume, and cardiac output. There was no evidence demonstrated to indicate any direct myocardial effect or peripheral venodilation induced by thiazide.

Beta-adrenergic blockade in diuretic-treated patients with essential hypertension

The influence of beta-adrenergic blockade (160 mg per day of propranolol for four weeks) on plasma renin activity, plasma volume, and arterial pressure was explored in 20 patients with essential hypertension with hyper-reninemia from long-term diuretic therapy. In 15 of these patients renin activity remained elevated (range, 3.1 to 23.0 ng per milliliter). Plasma volume was unchanged in eight, increased in 11 and reduced in one. In 17 subjects mean arterial pressure decreased by more than 10 mm Hg, but these impressive reductions could not be explained by quantitative changes in either renin activity (r equals 0.1) or plasma volume (r equals 0.1). These data suggest that suppression of plasma renin activity by beta-adrenergic blockade is not attainable during diuretic therapy and is not the major factor responsible for the antihypertensive action of propranolol.

Renin: activity, reactivity and concentration in a population survey. Relationship to blood pressure

Plasma renin activity (PRA), plasma renin reactivity (PRR) and plasma re nin concentration (PRC) were measured in 47 normotensive and 4 hyperten sive subjects, none of whom were taking medication. There was a significant negative correlation between PRC and PRR of plasma. Contrary to previous reports, PRR was not increased in subjects with hypertension. The most significant finding was the negative correlation of PRC and PRA with blood pressure in normotensive subjects, but the lack of such a correlation in hypertensive subjects. This finding, plus the significantly higher PRC in hypertensive subjects, suggests a deficient suppression of renin release in hypertensive individuals.

The renin-renin substrate reaction, as it occurs in the plasma, is illustrated below (Fig. 1). Renin, a proteolytic enzyme, released from the juxtaglomerular cells of the kidney, acts upon its α2 globulin tetradecapeptide renin substrate, splitting the leucyl-leucine bond, thus causing the release of angiotensin I (AI). AI, a decapeptide, is substrate for yet another enzymatic reaction, being converted in turn to angiotensin II (AII), by the converting enzymes present in lung and plasma. This reaction sequence is undoubtedly oversimplified since it does not take into account a number of observations, the first of which was made in 1964 by Boucher and co-workers; namely that when equal amounts of purified renin were added in vitro to the plasma of different individuals, there were significant variations in the quantity of angiotensin generated.1 From this, as well as from later studies, the concept developed that plasma contained a renin inhibitor.2 These earlier observations were supported and extended by studies from Laragh's group, which reported that the plasma of patients on oral contraceptives produced exaggerated amounts of AI upon the addition of exogenous renin3,4, and these authors have referred to this phenomenon as the renin reactivity of plasma. Increased renin reactivity has since been reported in plasma of patients with essential hypertension,5, 6, 7 primary aldosteronism 8 and renovascular hypertension.6 Thus, it has been thought that this phenomenon may play a role in the hypertensive process. If reactivity of plasma is increased in the above named situations (i.e., if there is exaggerated generation of AI upon the addition of purified renin), then it follows that in vivo AI generation or AI generation on incubation of plasma at 37° should also be increased relative to the amount of endogenous renin present. Thus the ratio of plasma renin activity (PRA) to plasma renin concentration (PRC) should be greater in women on oral contraceptives,9, 10 as well as in people with the several varieties of hypertension mentioned above. The present report concerns itself, in part, with the measurement of the PRA: PRC ratio (which we use to express the reactivity of plasma) in normal and hypertensive subjects, as well as in subjects taking either estrogen-con taining compounds or various antihypertensive medications. Our results con firm the observation that considerable variation in plasma reactivity does ex ist, and that there is increased reactivity in plasma of women on oral contra ceptives or estrogen-containing compounds. Unexpected was the discovery that reactivity is inversely related to the concentration of renin. Our studies, however, failed to find increased reactivity in subjects with hypertension, and thus do not support the concept of an important role for a renin inhibitor or modifier in essential hypertension. Most important, however, was our discov ery of a highly significant inverse correlation of both PRA and PRC with blood pressure in normal people. The lack of such a correlation, as well as the finding of elevated PRC in subjects with hypertension, suggests that the person with elevated blood pressure lacks the normal capacity to diminish renin secretion.

Diuretics: mechanism of action and clinical application

Despite the bewildering number of diuretics available to the physician, these drugs can be divided into 4 main groups, characterised by their site of action on sodium reabsorption in the kidney. Drugs acting on the ascending limb of the loop of Henle have a powerful but short acting diuretic effect; they include frusemide, ethacrynic acid and bumetanide. The benzothiadiazines and related compounds have a moderate diuretic action spread over a longer period, whilst the potassium-sparing diuretics, triamterene, amiloride and spironolactone, have only a weak diuretic effect but a marked ability to diminish urinary potassium excretion. The fourth group is made up of miscellaneous substances which function as vasodilator or osmotic agents. The pathogenesis of oedema formation in heart failure is outlined and a logical approach to treatment suggested. Duiretics are being increasingly used in the treatment of non-oedematous states, in particular hypertension, diabetes insipidus and hypercalciuria; their exact role in pregnancy and acute renal failure remains controversial. Side-effects can be related to their effect on electrolyte excretion and include hypokalaemia, hyponatraemia, hyperkalaemia and hyperuricaemia. The incidence of disturbed carbohydrate tolerance in previously normal individuals is low. Other less common side-effects are also discussed.

Hypertension with aldosterone excess

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