Foetal and neonatal development of luteinising hormone and its regulatory systems in the pig

Abstract

This review is a short summary of the "state-of-the-art" regarding the ontogeny of LH and part of its control system in the pig. The maturity of pituitary gonadotropin cells and the vascular drainage between the hypothalamus and pituitary are probably the most important steps in the developmental process of gonadotropin (LH) secretion. In the pig, these are achieved at around day 80 of foetal age, when LH cell density is comparable to that observed in adults. The hypothalamus regulates foetal pituitary LH secretion via LHRH well ahead of parturition. However, the main prerequisite of ovarian activity (ovulation), the "GnRH pulse generator", is not ready to function in the foetus. Pulsatile LH release is inducible by treatment of the foetal pituitary with LHRH, but extrahypothalamic modulating systems are not fully functioning until after birth. Likewise, there is no gonadal steroid feedback control of pituitary LH secretion up to the second week of neonatal age.