AUTONOMOUS GONADOTROPIN-RELEASE FROM THE HUMAN PITUITARY IN-VITRO ANDFACTORS INFLUENCING THIS SECRETION

Our understanding of the hypothalamus as the sole pacemaker for episod ic hormone release has been challenged by recent observations of an au tonomous rhythmic secretion from the pituitary, independent of hypotha lamic inputs. Using an in vitro perifusion system, we were able to dem onstrate an intrinsically pulsatile gonadotropin secretion from human fetal and adult pituitaries. This high-frequency/low-amplitude release is calcium-dependent and stimulated by gonadotropin releasing hormone (GnRH) administrations. Also, the autonomous release of luteinizing h ormone (LH) appears to be temporally and functionally linked to the sp ontaneously pulsatile secretion of other anterior pituitary hormones, suggesting the existence of a common intrapituitary mechanism entraini ng these hormone pulsatilities. Further, the spontaneous and GnRH-stim ulated LH release is greater from human female fetal pituitaries than from male fetal pituitaries at mid-gestation, presumably a reflection of differences in the negative feedback actions by factors from the fe tal gonads. Collectively, we have observed an autonomous gonadotropin release from the human pituitary independent of, but facilitated by, G nRH. This spontaneous pulsatile secretion is calcium-dependent and ent rained to the release of other anterior pituitary hormones. Therefore, it may represent the activity of a common intrapituitary pulse-genera ting mechanism and its modulation by factors from inside and outside t he human pituitary.