VARIATIONS IN THE BLOOD VOLUME OF THE NEURAL AND ANTERIOR LOBES OF THE PITUITARY OF THE RAT ASSOCIATED WITH NEUROHYPOPHYSIAL HORMONE-RELEASING STIMULI

Abstract

SUMMARY: Measurements of the blood volume of the neural and anterior lobes of the pituitaries of rats using ⁵¹Cr-labelled erythrocytes indicated that all stimuli examined which released neurohypophysial hormones also led to a significant increase in neural lobe blood volume. The blood volume of the anterior lobe was not altered by any of these stimuli. Experiments with parasympathetic blocking drugs indicated that this mechanism involved cholinergic pathways, a conclusion which was supported by the results of experiments with parasympathomimetic drugs. Sympathetic blockers and sympathomimetic drugs produced no appreciable effects on the blood volume responses. It is concluded that vasodilation occurs in the neural lobe of the rat associated with stimuli which are known to release neurohypophysial hormones and that this vasodilation involves cholinergic mechanisms but that these pathways may not be identical with those responsible for hormone release.