[A simple sensitive micromethod for measurement of human plasma renin concentration]

Contribution of the renin-angiotensin-aldosterone system to development of tolerance and fluid retention in chronic congestive heart failure during prazosin treatment

To determine the effects of the renin-angiotensin-aldosterone system on development of tolerance and fluid retention in patients with chronic congestive heart failure during long-term prazosin treatment, plasma renin concentration, aldosterone, norepinephrine and maximal exercise tolerance were measured during chronic therapy with digitalis and diuretics, to which prazosin, captopril or a combination of both drugs was added. Plasma renin concentration and aldosterone level decreased slightly during prazosin therapy and norepinephrine level increased significantly. When captopril was given, plasma renin concentration increased as expected, aldosterone level normalized and norepinephrine level decreased significantly. When prazosin was added to captopril therapy, norepinephrine level increased and plasma renin concentration and aldosterone level did not change. Exercise capacity did not increase during prazosin treatment, but was increased with captopril treatment. Prazosin treatment was associated with an increase in body weight even though the dose of furosemide was increased. Inhibition of the renin-angiotensin system did not prevent fluid retention induced by prazosin during combination therapy. These findings suggest that the renin-angiotensin-aldosterone system is not substantially involved in development of tolerance and fluid retention during prazosin therapy; stimulation of plasma norepinephrine may be of decisive importance.

Role of the renin-angiotensin system in the development of congestive heart failure in the dog as assessed by chronic converting-enzyme blockade

Hormonal factors may be important in the regulation of peripheral vascular resistance (PVR) in congestive heart failure (CHF). The role of the renin-angiotensin system in the development of CHF was studied in 16 unanesthetized dogs. CHF was induced by rapid right ventricular pacing, with and without chronic converting-enzyme inhibition (CEI) by captopril. The hemodynamic changes and the activity of renin, aldosterone, norepinephrine and vasopressin were studied. The control dogs showed a greater decrease in cardiac output and a greater increase of mean pulmonary artery pressure than the captopril-treated group. In the group with CEI, only a small, transient increase in PVR was observed during the development of CHF; in the control group, there was an increase of 94% of basal values. The control group showed a continual increase of renin, aldosterone and norepinephrine. Four control dogs showed an inappropriately high secretion of arginine vasopressin. The increase of sympathetic nervous activity was only insignificantly attenuated by angiotensin II inhibition and was without a considerable influence on PVR except for an early transient increase in vascular tone. In our animal model, the renin-angiotensin system plays an important role in the regulation of PVR in CHF. In this kind of CHF the sympathetic nervous system appears to be of minor importance for the long-term regulation of PVR. Plasma arginine vasopressin levels were increased in control dogs; this increase may contribute to the increased vascular tone.

Regulation of aldosterone secretion in dehydrated babies

The factors controlling aldosterone secretion were measured in 12 patients with moderate to severe dehydration during the first year of life. Secondary hyperaldosteronism was present in all cases (mean plasma aldosterone concentration 414.6 ng/dl), as well as increased plasma cortisol levels (mean 49.7 microgram/dl). Plasma cortisol, an indirect parameter of stimulation of the adrenal cortex by ACTH, showed the highest correlation with plasma aldosterone (r = 0.82). Despite a mean elevation of 168 ng AT/ml/h the plasma renin concentration did not seem to play the dominant role in the regulation of aldosterone secretion in these infants. High serum sodium concentrations have a clearly inhibiting effect on aldosterone secretion as shown by the negative correlation coefficient of r = 0.80.

[Hemodynamic changes after angiotensin II blockade by saralasin (author's transl)]

Saralasin, an angiotensin II inhibitor was infused in 10 hypertensive patients. A blood pressure reduction was achieved after stimulation of the renin-angiotensin-system by salt depletion. Heart rate and cardiac output failed to compensate for reduction of blood pressure. Thus circulatory reflex-mechanisms are inhibited by saralasin. A direct influence on baroreceptor mechanism and/or catecholamines is probable. Failure of the hypotensive effect of saralasin in salt-depleted patients after administration of beta-blockers supports this hypothesis.

Improvement of renin determination in human plasma using a commonly available renin standard in a radioimmunological method

A new method for the measurement of renin in human plasma is described. The method is based on the introduction of the internationally available renin standard of the Medical Research Council (MRC) London, as a calibration system. Thus, some principal disadvantages of methods expressing results in renin reaction velocity (angiotensin generation rate) only are avoided. Both renins, unknown and standard, react with a sheep substrate preparation and are handled identically throughout the whole procedure including the angiotensin I radioimmunoassay (RIA). The plasma renin concentration (PRC) is given in 10(-6) MRC-renin units (muM/ml).

RESULTS

the renin standard is free of angiotensin, angiotensinases, and angiotensinogen; it is stable on storage. Identical enzyme kinetics are shown for both renins. An interference between endogenous and exogenous substrate could be avoided. The potentially harmful influences of proteins from the enzyme incubation mixture of the RIA dose response curve are shown. The use of an angiotensin I calibration system could be omitted. Using a standard renin dilution from 250-0.9 muU/ml also the full biological range is covered. When giving an unrestricted diet the preliminary normal values of PRC are 21.9 +/- 12.6 muU/ml in recumbent and 40.1 +/- 19.8 muU/ml in upright position (n = 16,x +/- s, age 20-35 years). Earlier findings of age-dependency of PRC were confirmed.