Renal and vascular responses of the bullfrog (Rana catesbeiana) to mesotocin.

Although mesotocin (MT) has long been known to occur in the amphibian neurohypophysis, there have been few reports on its action among amphibians. In the present investigation, renal responses of intact bullfrogs (Rana catesbeiana) and perfused bullfrog kidneys to MT were studied. The blood pressure responses of this amphibian to MT were also analyzed. We found that MT is diuretic at low doses and that the response is dose related. At high doses the diuretic response decreases progressively and, at times, antidiuresis is observed. The changes in urine flow are proportional to the changes in glomerular filtration rate. In addition, there is a dose-related depressor effect. Data from perfused kidney studies suggest that MT may dilate the afferent glomerular vessels. The possible action of MT as a physiologically important diuretic agent is discussed.