A microassay for active and total renin concentration in human plasma based on antibody trapping

Factors related to first dose hypotensive effect of captopril: prediction and treatment

The blood pressure response to the first dose of captopril (6.25 mg, 12.5 mg, or 25 mg) was measured in 65 treated, severely hypertensive patients. Mean supine blood pressure was 187/108 mm Hg immediately before captopril was given. Twenty one patients experienced a fall in supine systolic pressure greater than 50 mm Hg, including five whose pressure fell more than 100 mm Hg and two whose pressure fell more than 150 mm Hg. Six patients developed symptoms of acute hypotension, including dizziness, stupor, dysphasia, and hemiparesis. Percentage reductions in blood pressure were greatest in those with secondary hypertension (p less than 0.05), high pretreatment blood pressure (p less than 0.05), and high concentrations of plasma renin and angiotensin II (p less than 0.01). No significant correlation was found between fall in blood pressure and serum sodium concentration, age, renal function, and the dose of captopril given. A severe first dose effect cannot be consistently predicted in individual patients who have received other antihypertensive drugs for severe hypertension. Such patients should have close medical supervision for at least three hours after the first dose of captopril.

The renin-angiotensin system and total body sodium and potassium in hypertensive women taking oestrogen-progestagen oral contraceptives

Measurements of total body sodium and potassium, and of components of the renin-angiotensin-aldosterone system, were made in a group of women who developed hypertension while taking oestrogen-progestagen oral contraceptives. The results were compared with similar measurements made in age-matched women with essential hypertension. Total body sodium and potassium were normal in both groups. Plasma renin-substrate was significantly elevated in the women taking oral contraceptives, while concentrations of active renin were similar and normal in both groups. Thus plasma angiotensin II was significantly elevated in the pill users; overall the product of renin and renin substrate concentrations correlated significantly with angiotensin II. The rise in plasma angiotensin II in conjunction with normal total body sodium could therefore contribute to the increase in blood pressure induced by oestrogen-progestagen oral contraceptives.

Postpartum renal failure and malignant hypertension treated with captopril

A case of postpartum renal failure and malignant hypertension in a 24-year-old woman is reported. The condition occurred three weeks after caesarian section following a normotensive pregnancy. Treatment with a converting enzyme inhibitor, captopril, for one year normalized the blood pressure, with concurrent reduction of plasma angiotension II concentration and markedly improved glomerular filtration rate. It is suggested that activation of the renin-angiotensin system may cause the hypertension and impairment of renal function in postpartum renal failure, and that use of drugs blocking the renin system may be of particular clinical value in this situation.

Peptide inhibitors of renin

Three experiments are described using new substrate analogue inhibitors of renin. The first experiment shows that introduction of a reduced isostere in the scissile peptide bond of an analogue greatly increases its ability to inhibit renin of a particular species. However, different species of renin substrate have different amino acids in their scissile bond and variation here also greatly influences the affinity of renin and substrate and hence of renin and substrate analogues. Finally, substitution of amino acids in the C-terminal adjacent to the scissile bond influences the affinity and efficacy of substrate analogues as inhibitors. In our second experiment a peptide inhibitor of dog renin, H.77, was used in an affinity column to produce a one-stage, 2000-fold, and complete purification of human renin. In our third experiment infusion of H.77 was used to lower circulating concentrations of angiotensin I and angiotensin II in conscious sodium-deplete dogs. Captopril was then given in addition to H.77 but blood pressure did not fall further, suggesting that captopril lowers blood pressure wholly or partly by reducing angiotensin II within the circulation and in extravascular sites.

Similarity of idiopathic aldosteronism and essential hypertension. A statistical comparison

There is clinical, biochemical, and pathological evidence that idiopathic aldosteronism is part of a continuum which includes low-renin and normal-renin essential hypertension. In a retrospective statistical study, 89 patients with essential hypertension have been compared with 22 cases of idiopathic aldosteronism and 34 cases of aldosterone-secreting adrenal adenomas. Measurements of serum sodium, potassium, bicarbonate, and plasma angiotensin II concentrations and estimates of exchangeable sodium and potassium were obtained for individual patients. By using various combinations of these biochemical variables, a statistic, the Mahalanobis distance, was described for each of the three populations, essential hypertension, idiopathic aldosteronism, and adrenal adenomas. For each combination of variables, the distribution of the idiopathic aldosteronism group resembled that of the essential hypertension group more closely than that of the aldosterone-secreting adrenal adenoma group. Thus, the use of this statistical technique provides further evidence of the similarity of essential hypertension and idiopathic aldosteronism.

Captopril treatment: inter-dose variations in renin, angiotensins I and II, aldosterone and blood pressure

1 The ability of captopril, 150 mg three times daily by mouth, to effect sustained reduction in plasma angiotensin II, with converse increases in circulating angiotensin I, and in active, inactive and total renin concentrations, has been assessed. 2 During prolonged treatment with captopril alone, and 12 h after the last dose of the drug, plasma angiotensin II remained approximately one-sixth of basal concentrations, while angiotensin I and renin concentrations were proportionately increased. However, further increases in angiotensin I, and in active, inactive and total renin concentrations, were seen 2 and 6 h after the morning dose of 150 mg captopril. 3 Inter-dose variations in plasma aldosterone and blood pressure were not closely related to concurrent variations in the renin-angiotensin system. 4 Arguments are presented for relying on measurements of plasma renin and angiotensin concentrations rather than of renin activity or aldosterone in assessing the effectiveness of converting enzyme inhibition.

Effect of infused captopril on blood pressure and the renin-angiotensin-aldosterone system in normal dogs subjected to varying sodium balance

Infusion of captopril at 20, 200, 2,000 and 6,000 micrograms/kg/hour into sodium-depleted conscious dogs produced a rapid, dose-dependent decrease in blood pressure and plasma angiotensin II and III, maximal suppression being achieved at 200 micrograms/kg/hour (97 +/- 14 to 65 +/- 8 [standard deviation] mm Hg, 38 +/- 10.6 to 3.2 +/- 1.5 pmol/liter and 7.0 +/- 4.8 to 1 +/- 0.5 pmol/liter, respectively). Angiotensin I concentration increased with each infusion rate to a maximal 16-fold increase at 6,000 micrograms/kg/hour (26 to 416 pmol/liter). For all infusion rates the percentage decrease in blood pressure correlated with the percentage decrease in plasma angiotensin II (r = 0.65, p less than 0.001). Infusion of captopril at 6,000 micrograms/kg/hour into sodium-loaded dogs also produced a decrease in both blood pressure (117 +/- 9 to 96.6 +/- 11 mm Hg) and plasma angiotension II (11.0 +/- 3 to 1.6 +/- 1.3 pmol/liter). Plasma aldosterone concentrations decreased whereas both blood angiotensin I and renin concentration increased. In another experiment angiotensin II was infused at 2, 6, 18 and 54 ng/kg/min into sodium-depleted dogs firstly without modification and secondly combined with captopril (6,000 micrograms/kg/hour) given for 1 hour before the angiotensin dose-response study and continued throughout. Angiotensin II infusion raised mean arterial pressure and plasma angiotensin II in each animal. However, the angiotensin II blood pressure dose-response curve was shifted downwards and to the right in the captopril-treated animals. These results suggest that arterial pressure and aldosterone secretion in normal dogs are partly dependent on the renin-angiotensin system but that not all of the acute decrease in blood pressure produced by captopril can be explained by the suppression of the acute vasoconstrictor effect of circulating angiotensin II.

Response of the renin-angiotensin-aldosterone system to upright tilting and to intravenous frusemide: effect of prior metoprolol and propranolol

1 Upright tilting in normal volunteers caused increases in plasma active and total renin, angiotensin II and aldosterone; a slight but significant fall in inactive renin accompanied these changes. 2 The alterations in the renin-angiotensin-aldosterone system on tilting took up to 1 h upright to become fully established. 3 Large intravenous doses of propranolol or metoprolol attenuated, without abolishing, the rises in active renin, angiotensin II, and aldosterone; the attenuation was most evident soon after tilting and was largely overcome by 1 h upright. Inactive renin did not fall significantly after beta-adrenoceptor blockade. 4 Intravenous frusemide caused immediate rises in plasma active, total and inactive renin, angiotensin II, and aldosterone, which then declined over 2 h despite increasing cumulative sodium losses. 5 Intravenous propranolol or metoprolol attenuated, without abolishing, these early increases in the components of the renin-angiotensin-aldosterone system after frusemide. 6 Prior oral metoprolol or propranolol, while significantly slowing the heart, did not limit the early rise in plasma angiotensin II following intravenous frusemide. 7 Thus in contrast to previous workers, we did not find that propranolol eliminated the response of the renin-angiotensin system to upright tilting; in part this difference appeared to be due to the longer tilt we employed. 8 Also in contrast to earlier work, we found attenuation by both intravenous propranolol and metoprolol of the immediate rise in renin after intravenous frusemide.

Plasma active and inactive renin in man during infusion of angiotensin II with and without prior administration of nifedipine

Release of active renin is inhibited by angiotensin II. To determine whether plasma inactive renin is also sensitive to this hormone, the effect of stepwise infusion of angiotensin II at 5,10 and 20 ng/kg/min on active and inactive renin levels was measured in six salt-replete normal subjects. Each subject received two infusions of angiotensin II on each of 2 study days. The calcium antagonist drug nifedipine (20 mg) or placebo was administered between the angiotensin infusions on each study day. During control infusions there was a significant decline in plasma active renin but no change in inactive renin was observed. Active renin concentration was increased after nifedipine treatment and suppressed to a similar degree by angiotensin II as in control infusions, with no corresponding changes in inactive renin. These studies suggest that plasma inactive renin levels are not subject to feedback inhibition by angiotensin II, and that inactive renin is not a physiologically important precursor of active renin in man.

Reversible activation-inactivation of renin in human plasma

Renin, an aspartate protease, cleaves the alpha-globulin angiotensinogen to produce the decapeptide angiotensin I, which is then converted to the vasoactive hormone angiotensin II by the action of a peptidase 'converting enzyme'. An inactive form of renin sometimes termed prorenin is present in normal human plasma. Its enzymatic activity is increased by exposure to a pH of 3.0 or 3.3 followed by dialysis towards neutral pH. Only a small proportion of the inactive renin is activated during the acid stage of dialysis, most of the activation apparently taking place during the subsequent dialysis to pH 5.7 (ref. 4) or 7.5 (ref. 5). Furthermore, if inhibitors of serine proteases are added to the plasma, the amount of inactive renin activated by this dialysis procedure is reduced. These results suggest that acid-activation is mediated by serine proteases. The role of enzymes such as plasma kallikrein, plasmin and renal kallikrein as physiological activators of inactive renin has recently been discussed. In our study of the activation of plasma inactive renin we have no found that, contrary to previous reports, complete activation of inactive renin takes place during the acid stage of dialysis. This activation can be reversed if plasma is rapidly adjusted to pH 7.4 and warmed. The next step in the acid-activation procedure, that is, dialysis to neutral pH, renders the initial acid-activation irreversible. These results were completely unexpected, and we offer an explanation that reassesses the nature of inactive renin and the activation process.