Effects of aging on the in vitro release of gonadotropin-releasing hormone.

Secretion of GnRH from mediobasal hypothalami (MBH) of old (23 month) and young (2 month) male rats was studied in an in vitro superfusion system. GnRH efflux from both old and young MBH increased in response to stimulation with 20 microM norepinephrine and 40 microM naloxone; however, both basal and stimulated GnRH release were reduced from MBH of old rats despite similar hypothalamic GnRH content. The diminished basal secretion and responsiveness to two major stimuli of the GnRH neuron may be important in the well-known involution of the hypothalamic-pituitary testicular axis in aging male rats.