The overlapping effect of gonadotropins and TSH on embryonic chicken gonads.

Determination of gonadal weight, seminiferous canalicule diameter, thickness of ovarian cortex and medulla, as well as of gonadal cell counts in 20-day chicken embryos exposed to gonadotropin (FSH and LH) or TSH at 15 days of pre-hatching life has shown that the examined hormones were able to evoke gonadal response also prenatally. TSH was found to overlap gonadotropin effect in causing increase of seminiferous canalicule diameter, testicular weight and gonocyte counts. In respect of the latter two parameters TSH was even more active than an identical dose of gonadotropin. This indicates that the interstitial and germinal cell receptors of the embryonic testis are not able to differentiate between chemically related, but - in adulthood - functionally different hormones. The ovarian effect of TSH was significant in respect of enhancing organ weight and oocyte mitosis, but not significant for the other parameters.