Renin-Angiotensin System in Mild Essential Hypertension

Converting enzyme inhibition in mild and moderate essential hypertension. II

In 24 patients with mild/moderate essential hypertension, we studied the effects of captopril with/without hydrochlorothiazide (Htz) on blood pressure, the renin-angiotensin system, blood bradykinin concentration (BBK), plasma volume, exchangeable sodium and glomerular filtration. Daily captopril doses of 75 and 150 mg were equally effective in reducing the blood pressure. Addition of Htz caused further blood pressure reductions. Nineteen patients attained a diastolic blood pressure less than or equal to 90 mmHg. Angiotensin converting enzyme inhibition with captopril led to a fall in plasma concentrations of angiotensin II (PAII) and renin substrate, and an increase in plasma concentrations of renin and angiotensin I. Patients starting with Htz had a higher PAII and subsequently a larger fall in blood pressure on captopril than untreated patients. BBK remained unchanged, indicating that the hypotensive action of captopril does not involve an accumulation of circulating kinin. Body fluid volumes and renal function were not affected by the various treatment regimens.

Saluretics and converting-enzyme blockade in the treatment of resistant hypertension

Blockade of the actions of the renin-angiotensin-aldosterone axis by inhibition of the angiotensin-converting enzyme with captopril is a new tool in the field of hypertension. As treatment with captopril makes pressure control volume-dependent, the addition of a saluretic is considered the best choice if an additional hypotensive agent is needed. The reason for and experience of the use of captopril in combination with saluretics for treatment of severe hypertension is reviewed. Published results indicate that captopril alone is insufficient, but as many as a third of the patients with previously uncontrollable hypertension manage well when a saluretic is added. Only one in six remains uncontrolled despite the addition of several other hypotensive agents. These observations apply to both essential and secondary forms of hypertension.

Relation between low dose of hydrochlorothiazide, antihypertensive effect and adverse effects

Thiazide diuretics are widely used in the drug treatment of hypertension but their dose-response curves for the antihypertensive and adverse metabolic effects differ. To characterize the lower end of the dose-response curve a double-blind, parallel group trial was performed as multicentre study in Scandinavia. One hundred and eleven patients with newly diagnosed or previously treated mild to moderate hypertension (untreated diastolic blood pressure of 95-115 mmHg after 4 weeks placebo) were randomly allocated to various doses of hydrochlorothiazide (3, 6, 12.5 or 25 mg) or placebo for 6 weeks. Blood pressure and biochemical variables (plasma renin activity, serum potassium, magnesium, urate, fasting glucose, total cholesterol, HDL-cholesterol, triglycerides and apolipoproteins A1 and B were measured. 12.5 mg hydrochlorothiazide had a borderline effect on blood pressure whilst 25 mg had a definite antihypertensive effect. Biochemical changes were seen in plasma renin activity, serum potassium and urate after the 12.5 and 25 mg dose. Three and 6 mg had no effect on blood pressure or metabolic parameters.

Plasma renin activity does not predict the antihypertensive efficacy of chlorthalidone

It has been established that angiotensin II stimulation may limit the antihypertensive potential of diuretic therapy in some patients. It is less clear, however, whether renin-angiotensin II stimulation is the cause of the flat blood pressure dose-response relationship to diuretics. To investigate this, 75 out-patients with essential hypertension were treated with chlorthalidone 12.5, 25 or 50 mg o.d. for 3 weeks, in a double-blind, placebo controlled cross-over study. Chlorthalidone significantly reduced blood pressure in all the groups, a plateau being reached at 25 mg o.d. Similarly, plasma renin activity was increased by each dose level of chlorthalidone, but it showed a different trend, being increased to a comparable extent at 12.5 mg and 25 mg o.d., and still higher at 50 mg o.d. Thus, greater stimulation of renin was coincident with the levelling of the blood pressure response to chlorthalidone. However no significant correlation was found between interindividual plasma renin activity and change in blood pressure, either in the entire series, or in each treatment subset. The data suggest overall that renin stimulation may influence the characteristic dose-hypotensive response relationship to diuretic agents in antihypertensive therapy, but it is unlikely that measurement of individual plasma renin activity will provide an useful guide to the optimal dose of a diuretic agents.

Changes in haemodynamics and body fluid volume due to enalapril in patients with essential hypertension on chronic diuretic therapy

In 12 patients with essential hypertension who remained hypertensive despite chronic chlorthalidone treatment, the effect of 2 weeks of additional therapy with the converting enzyme inhibitor (CEI) enalapril on blood pressure and body fluid volumes has been evaluated. The objective was to examine the influence of a diuretic-stimulated renin-angiotensin-aldosterone system (RAAS) on haemodynamics and body fluid volume. Mean arterial pressure (MAP -21%), total peripheral resistance index (TPRI -22%) and plasma aldosterone concentration (PAC -39%) were decreased, and plasma renin activity (PRA 660%) was increased. The average heart rate (HR), cardiac index (CI), plasma volume (PV), blood volume (BV), extracellular fluid volume (ECFV) and body weight (BW) remained unchanged. A negative correlation was found between the per cent changes in ECFV and PAC. Thus, body fluid volumes during chronic diuretic treatment are well preserved even when the RAAS with its sodium retaining properties is suppressed by CEI. Possible mechanisms are a volume (not angiotensin II) - dependent stimulation of aldosterone and a fall in blood pressure.

Hormonal and cardiovascular effects of losulazine hydrochloride in relation to sodium balance in nonhuman primates

Losulazine hydrochloride, a peripheral norepinephrine-depleting agent, was studied in conscious sodium-replete and sodium depleted cynomolgus monkeys. Blood pressure, heart rate, plasma renin activity, and plasma catecholamines were monitored before and after the oral administration of losulazine at a dose which caused a submaximal hypotension in sodium-replete monkeys. The hypotension observed in sodium depleted monkeys was not significantly different from that observed in sodium-replete monkeys. The hypotension from that observed in sodium-replete monkeys. The hypotension observed in both sodium states was accompanied by quantitatively similar decreases in plasma norepinephrine concentrations in the absence of significant alterations of heart rate and plasma renin activity. These results were consistent with the conclusion that losulazine reduced arterial blood pressure in nonhuman primates via peripheral norepinephrine depletion. These data also indicated that the hypotensive effect of losulazine in conscious monkeys was not dependent on alterations in renin-angiotensin system activity or on the state of sodium balance.

The renin-angiotensin system during converting enzyme inhibition with captopril in patients with severe treatment-resistant hypertension

The effect of captopril on blood pressure (BP) and various components of the renin-angiotensin system was assessed in ten severely hypertensive patients. Captopril acutely reduced the BP with a maximum decrease of 23% at 90-120 min. Maintenance treatment with captopril alone could not control the BP in any of the patients. Addition of hydrochlorothiazide markedly reduced the BP, while supplementation with propranolol caused no consistent changes. Three patients attained a supine diastolic blood pressure (SDBP) less than or equal to 90 mmHg. Only two patients had a fall in SDBP less than 10 mmHg. One patient stopped because of taste disturbances. Monitoring the renin-angiotensin system showed suppressed plasma concentrations of angiotensin II and increased levels of angiotensin I and renin, indicating the inhibition of converting enzyme activity. Plasma concentration of renin substrate decreased significantly. This observation has important implications for the methodology of renin assays. Captopril is an effective alternative in the treatment of hypertensive patients not readily controlled with conventional therapy.

Haemodynamic and hormonal changes during acute and chronic diuretic treatment in essential hypertension

The short- and long-term effects of diuretic treatment with chlorthalidone 50 mg/day on haemodynamic and hormonal parameters in patients with essential hypertension (WHO grade I) were investigated. After three days of treatment, all patients showed a rise in plasma renin activity (PRA), plasma aldosterone (PA), urinary norepinephrine excretion (UNE) and heart rate (HR), and a decrease in body weight (BW) and extracellular volume (ECV) and blood volume (BV); the change in blood pressure (BP) was variable. The changes in BP were correlated with those in BV. After three months of therapy, the signs of volume depletion tended to fade, but the lower ECV persisted. In contrast to the 4-day study, after three months the change in BP correlated inversely with changes in ECV and renin dependency (saralasin response), and positively with PRA and changes in UNE. It is concluded that the BP response to diuretic treatment is determined by the adaptation with time of the haemodynamic reactions to the volume-depleted state. Whether this adaptation will take place cannot be predicted from the control values of the parameters studied, or from acute changes observed during the first days of treatment.

Angiotensin II blockade during combined thiazide-beta-blocker treatment

Sixteen patients (11 M, 5 F), median age 41 years, with essential hypertension insufficiently controlled on hydrochlorothiazide 75 mg/day (DBP greater than or equal to 100 mmHg) were investigated. Plasma renin concentration (PRC), angiotensin II concentration (PA II), aldosterone concentration (PAC), plasma noradrenaline concentration (PNAC), plasma volume (PV) and exchangeable sodium (NaE) were determined and a saralasin-infusion (5.4 nmol/kg/min) was carried out while the patients were on thiazide alone, and in fourteen cases, repeated 3 months later after addition of a beta-blocker (propranolol 6, metoprolol 6 and atenolol 2 patients). On thiazide alone PRC, PA II and PAC was higher than normal in the group as a whole and the angiotensin II-inhibitor, saralasin, caused a significant decrease in MAP in twelve out of sixteen patients. After addition of a beta-blocker SBP and DBP decreased from 164/109 mmHg to 136/94 mmHg. PRC and PA II decreased by 40% and 58%, respectively. At this point saralasin caused no significant change in MAP. No close correlation was found between changes in BP on beta-blocker treatment and either PRC, PA II or saralasin response on thiazide treatment. PV, NaE, PAC and PNAC did not change sigificantly. It is concluded that in pts with thiazide-induced stimulation of the renin-angiotensin system (RAS) addition of a beta-blocker leads to suppression of RAS and the angiotensin II dependence of the blood pressure is nearly abolished. This mechanism might well contribute to the antihypertensive effect of beta-blockade in this particular situation. However, the pharmacological changes induced by beta-blockade are very complex, and most likely other factors are involved in the antihypertensive effect of beta-blocking drugs.

The use of an angiotensin II antagonist (saralasin) as an adjunct during renal vein catheterization

Renal vein catheterization was performed in fifteen hypertensive patients with unilateral renal disease. Samples for measurement of plasma renin concentration were obtained from each of the two renal veins and from the femoral artery (or the inferior caval vein)-before and during saralasin infusion. Saralasin infusion induced a significant decrease in blood pressure. In ten patients with lateralization of renin secretion before infusion, saralasin induced a 2-fold increase of the renin gradient across the diseased kidney, whereas there was no significant renin gradient across the contralateral kidney neither before nor after saralasin infusion. Thus, the renal venous renin ratio (diseased/contralateral) increased from a mean value of 2.10 to 4.13. In five patients without lateralization of renin secretion prior to infusion, saralasin induced a significant increase of renin gradient across both kidneys. In consequence, evidence for lateralization did not emerge and the renal vein renin ratio remained unchanged at 1.10. In cases with lateralization of renin secretion, the use of saralasin provides confirmatory evidence for strictly unilateral renin secretion with suppression of renin output from the contralateral kidney. In patients without obvious lateralization of renin secretion before saralasin, the administration of this angiotensin II inhibitor can serve to demonstrate a potential renin for renin secretion, shared by both kidneys.