Stimulation of Pituitary Thyrotropin Synthesis and Release by Hypothalamic Extract1

Abstract

Rat pituitary was cultured for 4,6 or 9 days at 37 C, and rat hypothalamic or cerebral cortical extract was added to the medium after 1, 3 or 6 days of culture. TSH [thyrotropin] was assayed by the McKenzle method. Release of TSH into the medium by pituitary exposed to rat cerebral cortical extract (Control) fell to very low levels after the first 3 days of culture. When rat hypothalamic extract was incorporated into the medium at the end of 3 or 6 days of culture, output of TSH by the pituitary for the following 3 days increased to levels equal to or exceeding those of the first 3 days. The total amount of TSH removed from the medium and pituitary explants cultured with hypothalamic extract for 4 or 6 days was 50-97% greater than found initially in fresh rat pituitary. These results indicate that a rat hypothalamic extract can increase synthesis as well as release of TSH by the rat pituitary in vitro.