Observations on the hypothalamo-posthypophyseal system of the posterior lobectomized rat

Abstract

The morphological and functional effects of removal of the posterior lobe of the pituitary gland have been studied in rats, operated at least one month previously. The infundibular stem develops into a miniature posterior lobe in posterior lobectomized animals. The volume of this miniature posterior lobe is one-fourth of that of the posterior lobe of intact animals. The number of cells in the supraoptic and paraventricular nuclei of posterior lobectomized animals of a post-operative age of one month or more shows a reduction to one-half of that in intact controls. Measurements of the diameter of the nuclei of the neurons of the supraoptic nuclei suggest an increase of nuclear size in these cells. Water consumption in posterior lobectomized animals decreases with time but remains above the normal level. Dehydration causes a more pronounced depletion of neurosecretory material in the miniature posterior lobe of the posterior lobectomized rat than in the posterior lobe of normal animals. Urinary excretion of antidiuretic hormone (ADH) shows a similar increase following dehydration in intact and in posterior lobectomized animals. In contrast, hemorrhage, which causes a marked increase in the blood level of ADH in intact animals, does no longer have such an effect in chronic posterior lobectomized rats.