Effect of hypophysectomy and pituitary stalk transection on α-melanocyte-stimulating hormone-like immunoreactivity in the brain of the frog, Rana ridibunda pallas

Abstract

The existence of an α-MSH-like molecule in the frog brain led us to investigate the role of the pituitary gland in the maintenance of the α-MSH content in 3 different regions of the brain. Acetic acid extracts of hypothalamus, rhombencephalon and telencephalon were analyzed by means of a highly specific radioimmunoassay for α-MSH in normal, sham-operated, pituitary disconnected and hypophysectomized frogs. Transection of the pituitary stalk gave rise to a significant decrease in α-MSH content in the intermediate lobe of the pituitary gland (−71% after 3 days), but did not affect α-MSH content in the distal lobe or in the brain. Eight days after total hypophysectomy, an α-MSH-like immunoreactive compound, co-eluting with synthetic α-MSH on Sephadex G-25, was found in the 3 brain regions studied. Removal of the whole pituitary gland did not significantly modify α-MSH content in the hypothalamus and the telencephalon. A slight increase in α-MSH was even observed in the rhombencephalon of hypophysectomized animals. Furthermore, no modification in α-MSH immunoreactivity occurred in any region of hypophysectomized animals. These results demonstrate the existence of α-MSH-like material in the brain of Rana ridibunda and establish that brain α-MSH in the frog is not of pituitary origin.