PITUITARY-ADRENAL ACTIVATION IN RATS WITH HEREDITARY HYPOTHALAMIC DIABETES INSIPIDUS

Abstract

ABSTRACT Pituitary adrenal activation in rats with hereditary hypothalamic diabetes insipidus (DI) and normal control rats (Brattleboro strain) was studied under various conditions. Plasma corticosterone concentration was essentially the same in resting DI and control rats. No significant difference in plasma corticosterone was observed after giving the animals ether, histamine, vasopressin or acetylcholine. Since DI rats lack vasopressin, these findings provide some evidence that vasopressin is unlikely to be the physiological corticotrophin releasing factor (CRF). Epinephrine induced a smaller increase in plasma corticosterone in DI rats than control animals, but the difference was not statistically significant. However, intraperitoneal injection of 0.9% saline resulted in significantly less elevation of plasma corticosterone in DI rats than normal. This suggests certain differences in responses between normal and DI rats depending upon the intensity or nature of the stress. Hypothalamic CRF in control and DI rats was determined using rats treated with chlorpromazine, morphine and Nembutal®. The CRF of hypothalami of DI rats was about half of that of control animals. In the extracts of posterior pituitary lobes, corticotrophin (ACTH) activity was found in almost the same amount in DI and control rats. The posterior pituitary lobe of DI rats lacked CRF activity when tested in neurohypophysectomized rats. Histological examination of the adrenals of DI rats revealed normal structure, suggesting normal ACTH secretion at rest.