NEUROHYPOPHYSIS AND WATER METABOLISM IN THE TOAD, BUFO BUFO (L.)

Abstract

The role of the neurohypophysis in the water metabolism of the toad was investigated by sectioning of the praeoptic-hypophysial tract. The neural lobe of the neurohypophysis degenerated after this operation. Seven weeks after the sectioning the lobe was reduced to about one-third of the normal size and it contained little or no neurosecretory substance stainable with Gomori''s haematoxylin. Two weeks after the operation at a time when the neural lobe was probably not functioning the toads showed a normal oliguretic response to water deprivation. When undisturbed operated and control toads were transferred from water to a saturated atmosphere the diureses in both groups fell within 24 hours to 1-2% of the values in water. Both normal and operated toads showed increased rates of urine flow during periods of restlessness. Dehydration increases the permeability of the amphibian skin to water. The effect of dehydration on water uptake in water was measured in toads 3, 6 and 14 weeks after operation. Even toads with completely degenerated neural lobes responded as strongly to dehydration as the controls. Dehydration for three or more days corresponding to a weight loss of 25-30% reduced the water balance activity of the neurohypophysis to about one half of normal, or less. Apparently, therefore, water balance principle is liberated from the neurohypophysis during dehydration, but the cutaneous and renal responses to dehydration have so far been found to be independent of neurohypophysial activity in the toad.