A steady-state control analysis of the renin-angiotensin-aldosterone system

Interrelation between baroreceptor and macula densa mechanisms in the control of renin secretion

1. It was the aim of this study to examine the interrelation between 'baroreceptor' function and the macula densa signal in the control of renin secretion from the kidneys. To this end we investigated the effects of frusemide and bumetanide, two different inhibitors of the macula densa Na(+)-K(+)-2Cl- cotransport, on pressure-dependent renin release from isolated perfused rat kidneys. In addition, pressure modulation of renin secretion from hydronephrotic kidneys devoid of macula densa structures was examined. 2. Basal flow rate through isolated kidneys was 13.5 +/- 1.0 ml min-1 g-1 at a renal artery pressure of 100 mmHg and corresponding renin secretory rates were 5.5 +/- 0.5 (ng angiotensin I (Ang I) h-1) min-1 g-1 (mean +/- S.E.M., n = 15). 3. Frusemide (10-100 microM) and bumetanide (5-50 microM) increased urine flow rates and stimulated urinary sodium excretion in a dose-dependent fashion from 13.0 +/- 2.5 mumol min-1 g-1 (n = 10) under control conditions to maximal values of 38.0 +/- 5.0 (n = 5) and 37.0 +/- 2.0 mumol min-1 g-1 (n = 5), respectively. Both drugs also induced concentration-dependent decreases of the renal vascular resistance. The vasorelaxant effects of frusemide and bumetanide were paralleled by an increase of renin secretion to a maximum of 21 +/- 4 (ng Ang I h-1) min-1 g-1 (n = 10). On a molar basis bumetanide was twice as potent as frusemide in stimulating renin secretion. 4. Lowering of the perfusion pressure from 100 to 40 mmHg resulted in a prompt increase of renin release yielding secretion rates of 92 +/- 10 (ng Ang I h-1) min-1 g-1 (n = 15). In the presence of frusemide (100 microM) and bumetanide (50 microM) renin secretion rates at 40 mmHg were 97 +/- 11 and 133 +/- 24 (ng Ang I h-1) min-1 g-1 (n = 6), respectively. Renin release stimulated by bumetanide was significantly reduced to 8.0 +/- 1.5 (ng Ang I h-1) min-1 g-1 (n = 5) by elevating the perfusion pressure from 100 to 140 mmHg. 5. Lowering the renal artery pressure from 100 to 40 mmHg in isolated perfused rat hydronephrotic kidneys devoid of tubular structures increased renin secretion rates from 4.5 +/- 1.0 to 22.5 +/- 2.5 (ng Ang I h-1) min-1 (n = 5).(ABSTRACT TRUNCATED AT 400 WORDS)

Interrelation of electrolytes and renin-angiotensin system in congestive heart failure

Many of the electrolyte derangements seen in chronic heart failure are related to activation of the renin-angiotensin system. Activation of the system may cause the retention of both sodium and water; the former is primarily related to the release of aldosterone and the latter is related to an angiotensin-mediated increase in thirst and decrease in the excretion of free water. The interaction of these mechanisms may explain why patients with chronic heart failure have higher values for total body sodium but lower values for serum sodium concentration than hypertensive patients or normal subjects. Activation of the renin-angiotensin system may also cause potassium depletion, which is manifest clinically by a decrease in both total body potassium and serum potassium concentration. These electrolyte disturbances may play a role in the development of ventricular arrhythmias. The renin-angiotensin system may also contribute to the development of magnesium deficits. These hormone-electrolyte interactions have important implications in the treatment of patients with heart failure, especially those in whom the renin-angiotensin system is pharmacologically inhibited.

Computer modelling of aldosterone regulation in patients on regular hemodialysis

To evaluate the relative influence of changes in plasma renin activity, potassium, ACTH, and sodium concentrations on the secretion of aldosterone, a multifactorial analysis was performed on different sets of investigations in anephric as well as non-nephrectomized patients on regular hemodialysis. During steady-state conditions the relationship between the stimulating effect of each of these factors and combinations between these factors and the resultant plasma aldosterone concentration was analyzed. Linear models could not explain all variations in plasma aldosterone, especially not a variation found within patients. The stimulus-response curve is therefore probably non-linear and at least one or more additional factors may take part in the aldosterone regulation.

Angiotensin. II. Important role in the maintenance of arterial blood pressure

An angiotensin II antagonist, [1-sarcosine, 8-alanine]-angiotensin II, was given intravenously to anesthetized dogs with thoracic caval constriction and ascites to investigate the role of angiotensin II in the control of arterial pressure. The antagonist produced a striking fall in arterial pressure and in aldosterone secretion and an accompanying increase in plasma renin activity. In a control experiment, normal anesthetized dogs were given the angiotensin analog, but it failed to reduce arterial pressure or to influence plasma renin activity. In conscious dogs with caval constriction, the antagonist produced essentially the same drop in arterial pressure as observed in anesthetized animals. These results suggest an important role for angiotensin II in the maintenance of arterial pressure by its action on specific receptor sites in arteriolar smooth muscle and in the adrenal cortex.