Experimental Evidence Of A Direct Neural Influence In Situ On The Secretion Of ACTH From The Rat Anterior Pituitary

A considerable amount of peptidergic nerve fibers have been morphologically identified in recent years in the pars distalis of the adenohypophysis of mammals,which contain substance P(SP),calcitonin gene -related peptides (CGRP), galanin, etc. Some of those fibers have close relationship with hormone-secreting cells by making synaptic connections with somatotrophs, lactotrophs and corticotrophs in the anterior pituitary. But the functional implications of these fibers in the regulation of hormone secretion is unknown. The present study was undertaken to investigate the possible modulating effect of the nerve fibers on the secretion of ACTH from the anterior pituitary. Electrical field stimulation(EFS)[ 30mA,0.5ms, 10Hz] was employed to excite the nerve terminals in perfused anterior pituitary quarters of male rat 96h after adrenalectomy(ADX) . Local anesthesia of the pituitary stalk was done to clarify the possible modulating effect of the nerve fibers on the hemorrhage-induced ACTH secretion from and the relative levels of POMC mRNA in the anterior pituitary . The results showed that:1) ACTH release from the anterior pituitary quarters was significantly reduced by electrical field stimulation. This effect was completely blocked by pretreatment with TTX 40min before EFS. Thus indicating an inhibitory action mediated by neural component in the anterior pituitary quarters.