ONTOGENY AND FUNCTION OF THE PITUITARY-GONADAL AXIS DURING FETAL DEVELOPMENT IN SHEEP

The fetal pituitary-gonadal axis is extremely active during developmen t reaching a peak at mid-gestation which is followed by a period of su ppression lasting until the onset of puberty. Plasma LH and FSH concen trations are higher at mid-gestation than during early gestation and i mmediately before birth. The synthesis of the specific beta-subunits o f LH and FSH in the pituitary gland during fetal develop ment is depen dent on the actions of GnRH from the hypo-thalamus. At mid-gestation L H and FSH concentrations are lower in males compared with female fetus es, due to the negative feedback effects of testosterone present in th e circulation of male fetuses. However, the development of sex-steroid feedbacks is not the sole factor responsible for the late gestation d ecline in gonadotrophin secretion, but a combination of CNS and steroi d feedback is likely. Fetal gonadotrophin secretion during the latter stages of gestation is critical for normal testicular development. Any disturbance to the normal pattern of gonadotrophin secretion during f etal Life could have long-term consequences for testicular function an d adult reproductive ability.