Interrenal function in larval Ambystoma tigrinum. I. Responses to alterations in external electrolyte concentrations

Larval Ambystoma tigrinum were acclimated to distilled water, 150 mM NaCl, or 100 mM KCl to alter electrolyte balance. The effects on electrolyte balance and circulating interrenal steroids were observed by analysis of plasma and urine samples. Steroid titers were measured by radioimmunoassay. Acclimation to distilled water decreased plasma and urinary [Na+] and elevated circulating aldosterone (sixfold) and corticosterone (45%) but did not affect cortisol. Larvae acclimated to 150 mM NaCl experienced increases in plasma and urinary [Na+]. In this group aldosterone titer was depressed (47%), corticosterone was elevated (100%), and cortisol was unchanged. Salamanders acclimated to 100 mM KCl increased plasma and urinary [K+] and shifted to net renal K+ secretion. This group elevated aldosterone (150%); however, corticosterone was not significantly affected. Reciprocity between the Na+-loaded and K+-loaded groups was observed. Acclimation to high potassium stimulated fractional renal Na+ reabsorption while Na+ loading stimulated fractional K+ reabsorption. These findings are consistent with aldosterone having opposite effects on renal Na+ and K+ transport, stimulating the reabsorption of the former and the net secretion of the latter.