Ontogeny and function of the pituitary-gonadal axis during fetal development in sheep

The fetal pituitary-gonadal axis is extremely active during development reaching a peak at mid-gestation which is followed by a period of suppression lasting until the onset of puberty. Plasma LH and FSH concentrations are higher at mid-gestation than during early gestation and immediately before birth. The synthesis of the specific beta-subunits of LH and FSH in the pituitary gland during fetal develop ment is dependent on the actions of GnRH from the hypo-thalamus. At mid-gestation LH and FSH concentrations are lower in males compared with female fetuses, due to the negative feedback effects of testosterone present in the circulation of male fetuses. However, the development of sex-steroid feedbacks is not the sole factor responsible for the late gestation decline in gonadotrophin secretion, but a combination of CNS and steroid 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 fetal Life could have long-term consequences for testicular function and adult reproductive ability.