PRENATAL GONADOTROPINS IN THE SHEEP

In sheep prenatal gonadotrophins exhibit a characteristic pattern of a ctivity with peak LH and FSH concentrations occurring at mid-gestation , followed by a period of suppression lasting until the onset of puber ty. Treatment of fetuses with the GnRH agonist buserelin has been used as a pharmacological tool to inhibit gonadotrophin secretion during f etal life. Suppression of gonadotrophin secretion from Day 70 gestatio n was found to result in a 40% reduction in the size of the testis at birth which was due to a similar magnitude reduction in the number of Sertoli cells in the testis. Buserelin had no effect on ovarian mass o r gross morphological appearance. When buserelin was, given between Da y 70 and Day 110 gestation there were no effects only testis size or m orphological appearance, suggesting that gonadotrophins regulate testi cular development during a 'critical window' late in gestation. Inhibi tion of gonadotrophin secretion during the last half of gestation was also found to have long term detrimental effects on testicular functio n in ram lambs at puberty. This was characterised by significantly red uced plasma concentrations of testosterone in the absence of any diffe rence in testis size, Given that prenatal gonadotrophins are so import ant in governing testicular development we have investigated factors w hich may disrupt the normal pattern of gonadotrophin secretion, Exposu re of the developing fetus to environmental oestrogenic chemicals has been implicated in some disorders of male reproduction, We have found that administration of the environmental oestrogenic chemical, octylph enol inhibits fetal FSH secretion, thus providing an explanation for h ow these chemicals may be having adverse effects on reproductive funct ion.