DEVELOPMENT OF HYPOTHALAMIC AND PITUITARY-FUNCTION IN THE PIG FETUS AND NEONATE

In the pig fetus, LH gene expression starts on day 45-50 post coitum ( p.c.). The hypothalamus takes over control of LH secretion around day 80 p.c. Fetal steroids do not seem to be prevalent in LH regulation, h owever, 2-hydroxy-estradiol-17 beta, an estradiol metabolite with some catecholamine properties reduces plasma LH levels via the catecholami ne system. Opioid genes are switched on as early as day 35 p.c. and op ioid receptors can be detected from day 50 p.c. onwards but the opioid ergic control of pituitary gonadotropin in the fetus is questionable. Interleukine-1 beta and interleukine-2 bind to opioid receptors in the brain and interleukine-1 beta has been shown to stimulate opioid prod uction. Applications of an interleukine-1 beta antagonist resulted in an increment of plasma LH levels in female but not in male fetuses. It is feasible that this effect is brought about by action of the antago nist on opioid receptors. Growth hormone gene expression can be seen i n the pituitary as early as day 45 p.c. Despite very high GH levels in the fetus, exogenous GRF induces a dramatic GH surge at day 80 p.c. a nd later in gestation. Somatostatin neither inhibits basal nor GRF-ind uced GH release in fetal and neonatal piglets. Passive immunization wi th a GRF antibody inhibited fetal GH secretion.