The relationship between angiotensin and aldosterone

The effect of aldosterone and the renin-angiotensin system on sodium, potassium and chloride transport by proximal and distal rat colon in vivo

1. The roles of aldosterone and angiotensin in the direct control of epithelial sodium transport in vivo have been investigated by measurement of electrical p.d. changes and of the fluxes of sodium, potassium and chloride in rat colon, an organ actively involved in electrolyte homoeostasis. Exogenous angiotensin and aldosterone were given by both short- and long-term infusions and endogenous secretion of the hormones was varied by dietary sodium variation and by nephrectomy and/or adrenalectomy. 2. In vitro angiotensin has been shown to influence colonic salt and water absorption but in the present in vivo experiments administered angiotensin had no significant action on p.d. or on the ionic fluxes of the proximal or distal colon. The increase in p.d. produced by infusing aldosterone was unaffected by giving angiotensin concurrently. The effect of sodium depletion in stimulating sodium absorption and potassium secretion was completely abolished by adrenalectomy but was unaffected by nephrectomy. 3. During prolonged infusion of angiotensin into adrenalectomized rats, a small fall in faecal fluid and sodium content was observed, but this change would have little significance in sodium homoeostasis. 4. Aldosterone and sodium depletion stimulated sodium absorption in both proximal and distal colon but significant increase in potassium secretion was demonstrable only in the distal colon. Bicarbonate secretion (by calculation) was unaffected. In the proximal colon, the increased sodium absorption appeared to be accompanied by increased chloride absorption while in the distal colon it was principally the sodium-potassium exchange that was increased. 5. Adrenalectomy reduced potassium secretion in both proximal and distal colon but sodium absorption was only significantly reduced in the proximal colon. 6. It was concluded that there is no evidence that angiotensin in the living animal has a role as an important salt retaining hormone by direct epithelial action. Aldosterone has a considerable effect which is independent of the presence of angiotensin, and which differs in proximal and distal colon in regard to the relative effects on chloride absorption and potassium secretion.

Hypertension corrected by discontinuing chronic sodium bicarbonate ingestion. Subsequent transient hypoaldosteronism

A 52 year old man with a long history of marked hypertension, peptic ulcer disease, nephrocalcinosis and intermittent hypercalcemia was referred to be evaluated for primary aldosteronism suspected on the basis of low plasma renin activity, hypokalemia and blood pressure responsive to spironolactone. Aldosterone excretion, however, was extremely low. Alkaluria, high urinary sodium excretion and hypercalciuria were observed. The patient admitted to chronic ingestion of large amounts of baking soda. Upon cessation of alkali abuse, his blood pressure fell dramatically; orthostatic hypotension, concomitant azotemia, hemoconcentration, hyperkalemia and weight loss occurred. Despite dramatic elevation in plasma renin activity, urinary aldosterone excretion remained low during this period. Adrenal glucocorticoid secretion was intact. All abnormalities of sodium, potassium and aldosterone subsequently returned to normal. A 10 day challenge with oral sodium bicarbonate was associated with a rise in blood pressure, but serum calcium remained normal. The patient remains normotensive 15 months after discontinuing alkali abuse.

Renin, angiotensin II, and adrenal corticosteroid relationships during sodium deprivation and angiotensin infusion in normotensive and hypertensive man

The responses of plasma renin activity, plasma angiotensin II, plasma aldosterone, cortisol, and corticosterone to sodium deprivation and to angiotensin II infusion (100 ng/min) were measured in 8 normotensive patients and in 17 patients with essential hypertension. Following sodium deprivations, plasma renin activity rose from 0.513 ± 0.100 to 1.029 ± 0.124 ng/ml hour -1 in normotensive patients and from 0.406 ± 0.077 to 0.629 ± 0.059 ng/ml hour -1 in hypertensive patients. Plasma angiotensin II did not parallel changes in plasma renin activity: in normotensive patients plasma angiotensin II was unchanged by sodium deprivation (31.8 ± 6.0 compared with 30.1 ± 4.6 pg/ml), but in hypertensive patients it rose from 22.2 ± 3.4 to 36.4 ± 5.1 pg/ml. Plasma aldosterone rose equally in both groups following sodium deprivation (5.8 ± 1.3 to 15.3 ± 2.4 ng/100 ml for normotensive patients and 5.9 ± 1.4 to 14.4 ± 1.6 ng/100 ml for hypertensive patients) and angiotensin infusion (5.8 ± 1.3 to 10.4 ± 2.1 ng/100 ml in sodium-loaded normotensive patients, 15.3 ± 2.4 to 19.6 ± 3.6 ng/100 ml in sodium-deprived normotensive patients, 5.9 ± 1.4 to 11.4 ± 2.7 ng/100 ml in sodium-loaded hypertensive patients, and 14.4 ± 1.6 to 22.2 ± 2.6 ng/100 ml in sodium-deprived hypertensive patients). However, changes in endogenous plasma angiotensin II did not correlate with the rise in plasma aldosterone caused by sodium deprivation, and, despite much larger increases in plasma angiotensin II during angiotensin II infusion, plasma aldosterone showed smaller rises than those accompanying sodium deprivation. Plasma renin activity fell during angiotensin II infusion, in both groups of patients during both sodium loading and sodium deprivation, and, hence, the infusion constitutes a potent feedback inhibition of renin release in normotensive and hypertensive man. Plasma cortisol and corticosterone were unaltered by sodium deprivation but fell significantly with the angiotensin II infusion.