Increased Renal Reabsorption of Osmotically Free Water by the Toad (Bufo marinus) in Response to Neurohypophysial Hormones

Abstract

Neurohypophysial extracts or dehydration produce a pronounced antidiuresis in Bufo marinus. The antidiuretic mechanism was studied by following creatinine, inulin and free-water clearances in unanesthetized toads. Urine was collected directly from the ureters to avoid errors due to water reabsorption through the bladder. A decrease in free-water clearance is a consistent feature and accounts for most of the antidiuresis. There may also be a decrease in filtration rate. The effect of neurohypophysial hormones on free water excretion is attributed to an increase in the permeability of the tubule to the osmotic inflow of water. The similarity between the action of neurohypophysial hormones on the skin, the bladder and the renal tubule of Amphibia suggests a common mechanism, namely the dilatation of pores. The hypothesis is also advanced that the antidiuretic action of neurohypophysial hormones on the mammalian kidney depends on the same mechanism.