Bioscientifica Proceedings

Abstract unavailable© 1982 The authors...

The adult testis has two essential functions, namely the synthesis and secretion of the steroid hormone testosterone and the production of mature spermatozoa. Germ cells undergo mitosis, meiosis and condensation (spermiation) in close association with Sertoli cells and in defined associations with each other within the seminiferous epithelium. Normal spermatogenesis and fertility are dependent upon paracrine interactions between the somatic cells (Sertoli, Leydig and peritubul...

This review attempts to integrate available data on embryo-maternal communication during maternal recognition of pregnancy and implantation in the pig. Progesterone (P4) is an essential hormone that makes the uterus receptive to accept conceptuses for implantation and subsequent placentation. As well as P4, the receptive stage of the endometrium is further primed by paracrine factors secreted by the conceptus prior to and during implantation. Oestro...

Inhibition of luteolysis and establishment of pregnancy in pigs results from oestrogen secretion by the conceptuses and requires progesterone produced by the corpus luteum (CL). An integral part of maternal recognition of pregnancy in the pig is the redirection of prostaglandin (PG) F2α,secretion from endocrine (blood) to exocrine (uterus) direction and an increase of PGE2 synthesis in both the endometrium and conceptus. Uterine and conceptus ...

Extended exposure of progesterone and conceptus estrogen influences the vascular compartment of the uterus and expression of many factors, such as prostaglandins (PGs), growth factors, extracellular matrix and adhesion molecules, cytokines and transcription factors. One of the supportive mechanisms by which the conceptus inhibits luteolysis is by changing PG synthesis in favor of luteoprotective PGE2. Alteration in PG synthesis may result from increased PGE synthase (mPG...

Summary. Gonadotrophins, synthesized and secreted from the basophils of the adenohypophysis, bind to various target cells and elicit a wide variety of responses. Specific receptors for gonadotrophins have been found on plasma membranes of thecal, granulosa, luteal, endometrial and myometrial cells in the female and on Leydig and Sertoli cells in the Male. Gonadotrophins exert their effects through various intracellular second messengers and control biosyn...

Abstract unavailableKeywords: gene transfer; gene modification; gene expression; livestock; transgenic animal© 1991 Journals of Reproduction & Fertility Ltd...

The roles of testicular hormones in the negative feedback regulation of the secretion and actions of GnRH in male domestic ruminants are reviewed, concentrating mainly on research conducted with rams. Testicular steroids have major feedback actions directly at the hypothalamus to inhibit the secretion of GnRH, although it is apparent that, under certain circumstances, the steroids also have actions directly at the pituitary gland. Further research is necessary to delineate the...

Abstract unavailable© 1982 The authors...

Two key hypotheses emerge in the literature regarding the impact of stress on reproduction in females of any species. First, prolonged stress impairs reproduction in females. Secondly, acute stress impairs reproduction, if it occurs at a critical time during the precisely timed series of endocrine events that induce oestrus and ovulation. We reviewed studies conducted in female pigs to find support or opposition for these hypotheses in female pigs. We also considered the...