Effect of Gonadotropin-Releasing Hormone on Gonadotropin Biosynthesis in Pituitaries of the Frog, Rana Pipiens1

Abstract

Previous studies indicated that the chronic elevation in LH and FSH secretion from frog pituitaries stimulated with GnRH is dependent upon continued protein synthesis. To determine if GnRH is able to stimulate the de novo synthesis of gonadotropins (Gth: FSH and LH), anterior pituitaries from frogs were incubated in vitro with 35S-methionine in the presence or absence of 100 ng/ml GnRH. Glands stimulated with GnRH secreted elevated levels of FSH and LH, including higher amounts of newly synthesized Gth. Continual exposure to GnRH for 8 h did not affect the pituitary content of either immunoassayable Gth (labeled + unlabeled) or newly synthesized Gth. However, GnRH stimulation did increase the total amount (secreted + pituitary) of newly synthesized Gth. GnRH did not stimulate Gth synthesis in females. The temporal pattern of GnRH-stimulated secretion of newly synthesized Gth from male pituitaries was also determined. A lag period of 60-90 min occurred prior to appreciable secretion of radiolabeled Gth. Secretion of radiolabeled hormone then increased and reached a plateau before decreasing. After 6 h of stimulation, approximately 30% of the radiolabeled Gth still remained within the pituitary. These results are the first direct evidence that GnRH can stimulate the biosynthesis of Gth in a nonmammalian species.