Endocrine Control of Sexual Maturation In The Female Pig and Sexual Differentiation of the Stimulatory Oestrogen Feedback Mechanism

Abstract

Sexual maturation, culminating in puberty and fertility, is a complex process which may involve maturational changes at all levels of the central nervous system—hypothalamo—pituitary—gonadal axis. It is the purpose of this review, based on published and unpublished work from our own laboratory, as well as the work of others, to summarize our present knowledge of the control of sexual maturation in the female pig. Although several other pituitary hormones and adrenal function may be relevant to the process of sexual maturation, because of the restricted availability of such data in the pig only the control of gonadotrophin secretion and ovarian function will be considered. Where information necessary for the understanding of sexual maturation in the pig is lacking, references will be made to work in other species. However, no attempt is made to integrate these data into a general concept of sexual maturation. The description of the ontogeny of ovarian morphology and steroidogenesis will be followed by a consideration of the developmental pattern of gonadotrophin secretion, attempting to correlate them with the maturation of ovarian function and changes in the responsiveness of the ovary to gonadotrophins. Another aspect to be discussed is the responsiveness of the pituitary to luteinizing hormone (LH) releasing hormone at different stages of development. Special attention will be paid to the ontogeny of negative and positive gonadal steroid feedback control of gonadotrophin secretion as well as to the sexual differentiation of the LH surge mechanism.