Effect of hypothalamic lesions on pituitary melanocyte-stimulating hormone.

Abstract

SUMMARY The effect on the content of melanocyte-stimulating hormone (MSH) activity in the pituitary of electrolytic lesions placed in different regions of the hypothalamus was studied in male rats. Lesions in the paraventricular nuclei resulted, after 15 days, in a decrease of pituitary MSH activity to 20·4 ± 4·5%/mg. gland as compared with the controls, without changes in the weight of the hypophyses. In a group of animals in which the lesions failed to destroy the paraventricular nuclei completely the MSH activity in the pituitary was 66·4 ± 7·5% of that of controls and the weight of the gland was significantly higher. Hypothalamic lesions in the median eminence of the tuber cinereum produced 24 hr. later a decrease of pituitary MSH activity to 6·6 ± 0·8%, but 15 days later the values/mg. gland were almost normal. Lesions placed in the mammillary bodies or in the nucleus caudatus did not affect pituitary MSH content. Extracts of stalk-median eminence or posterior lobe from animals with lesions in the paraventricular nuclei, failed to show MSH-releasing factor as it is found in intact animals, nor did they contain MSH-release-inhibiting factor. The results support the concept that the paraventricular nuclei are involved in the control of pituitary MSH secretion and suggest that the MSH content of the disconnected hypophysis is to some degree regulated autonomously.