EFFECT OF HYPOTHALAMIC LESIONS ON WATER METABOLISM OF THE TOAD BUFO MARINUS

Abstract

The rate of cutaneous water uptake after dehydration was significantly depressed in functionally neurohypophysectomized toads (Bufo marinas), which consequently regained weight much more slowly than intact toads when returned to water. Toads bearing hypothalamic lesions were able to develop an antidiuresis when removed from water to a saturated atmosphere, but the antidiuresis was solely glomerular in origin and was established more slowly than in intact animals. The fractional reabsorption of filtrate increased significantly and the relative free water clearance decreased significantly in intact toads after removal from water. These changes in tubular function, which were not seen in lesioned toads, were responsible for the development of a more rapid and effective antidiuresis in intact animals. Injections of iso-osmotic saline, oxytocin (250 mu./100 g) and vasopressin (50 mu./100 g) had no significant effect on rates of cutaneous water uptake in both intact and lesioned toads. Injections of hyperosmotic saline, however, significantly increased rates of water uptake in both groups of toads, but to a much greater extent in the intact animals. Fluid retention arising from a marked antidiuresis occurred after the injection of vasopressin and hyperosmotic saline, and there was some evidence of an antidiuretic effect of oxytocin with the doses used here. These results and their bearing on the question of the functional significance of the neurohypophysis in anuran amphibians are discussed.