Renal responses to mesotocin in adult Ambystoma tigrinum and Notophthalmus viridescens.

Renal clearance methods were used to observe responses to the posterior pituitary peptide, mesotocin, by the kidneys of adult Ambystoma tigrinum and Notophthalmus viridescens. Ambystoma tigrinum responded to hypophysectomy with a decrease in urine flow and glomerular filtration rate (GFR); however tubular water reabsorption was not affected. Treatment with 5 ng/g mesotocin returned both urine flow and GFR to control levels. Notophthalmus viridescens responded to mesotocin treatment with an increased GFR. Ambystoma tigrinum decreased both plasma [Na+] and [K+] following hypophysectomy, however mesotocin did not reverse these decreases. Urine [Na+] did not change as a result of hypophysectomy alone. This ion increased in urinary concentration following mesotocin treatment of hypophysectomized salamanders. Renal tubular reabsorption of K+ decreased following hypophysectomy; however mesotocin replacement did not reverse this. We consider it unlikely that mesotocin is involved in these tubular responses because of the failure of hypophysectomy and mesotocin replacement to consistently mirror each other.