Direct Modulation Of Hormone Secretion By Nerve Fibers In The Anterior Pituitary Of The Rat

A considerable amount of peptides immunoreactive nerve fibers have been identified in recent years in the pars distalis of adenohypophysis of mammals, which contain substance P (SP), calcitonin gene-related peptides (CGRP), galanin, etc. by using a sensitive immunocytochemical method. These fibers originate, at least in part, from the hypothalamus. and have close relationship with hormone-secreting cells by making synaptic connections with somatotrophs, lactotrophs and corticotrophs in the anterior pituitary. But the functional existence of these nerve fibers in the regulation of hormone secretion is unknown. The present work was undertaken to investigate the possible modulating effect of the nerve fibers on the secretion of hormones in the anterior pituitary. Electrical field stimulation (EFS) was employed to excite the nerve terminals in anterior pituitary quarters of male rats under static incubation, and the released hormones including ACTH, PRL and FSH in the medium were detected by radioimmunoassay. It was found that: 1). The ACTH release from the anterior pituitary was significantly enhanced by EFS of varied parameters in our experimental system, among these parameters, the effect of EFS with strength 30mA, duration 0.5ms. frequency 10Hz on ACTH release was significantly reduced by adding TTX or veratridine. indicating the neural component of this effect of EFS on ACTH secretion, which was also demonstrated in a perfusion experiment. The dispersed cultured anterior pituitary cells did not respond to the EFS of the same parameter. 2). EFS of 30mA, 0.5ms. 10Hz that had no influence on PRL secretion from anterior pituitary in culture, could lightly, but significantly inhibit PRL basal release...