Natriuresis after adrenal enucleation: effect of spironolactone and dexamethasone.
After adrenal enucleation, rats have an impaired ability to excrete a salt load because of enhanced collecting duct reabsorption. This antinatriuretic effect, thought to be secondary to a mineralocorticoid-like substance secreted by the enucleate gland, can be reversed by treatment with spironolactone or dexamethasone. To define the renal mechanisms involved in this drug-induced natriuresis we have utilized clearance and micropuncture techniques in enucleate saline-expanded rats that were treated with either spironolactone (S) or dexamethasone (D), or were untreated (U). Sodium excretion was clearly increased after S, 13.9, and D, 19.3 mueq/min vs. u, 5.9 mueq/min. The mechanisms of this natriuresis, however, were dissimilar. Spironolactone-treated rats were not different from untreated rats except with regard to function beyond the superficial late distal tubule, where U rats reabsorbed over 50% of the delivered sodium. In the S group 38% of the excreted sodium was added along this tubular locus, 5.2% of the filtered sodium reaching the late distal tubule and 7.3% appearing in the urine. These data demonstrate that the natriuresis after S is secondary to the net addition of sodium beyond the superficial late distal tubule. Spironolactone may work by inhibiting a mineralocorticoid-like product of the enucleate gland and, thereby, eliminate the sodium-retaining effect of this product. The natriuresis after D, however, can be explained solely on the basis of a markedly increased filtered load of sodium traversing the nephron.
D000315:Adrenalectomy; D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology*; D005919:Glomerular Filtration Rate / Q000187:drug effects; D007668:Kidney / Q000187:drug effects / Q000502:physiology; D008297:Male; D009318:Natriuresis / Q000187:drug effects*; D051381:Rats; D012964:Sodium / Q000378:metabolism; D013148:Spironolactone / Q000494:pharmacology*
D013148:Spironolactone; D003907:Dexamethasone; D012964:Sodium