Abstract
To evaluate the development of the HPG axis the method of immunologic hormone inactivation was used to study male rat fetuses at different ages of gestation. From the 12th day of gestation pregnant rats were passively immunized against testosterone (T) by daily injections of rabbit antiserum with high binding capacity for T. Fetuses were studied on each day of gestation starting at day 18. Antibodies against T were detected in all fetal plasma samples. While the reduction of circulating free T by antibody binding did not affect the differentiation of the male genital tract it markedly stimulated the endocrine activity of the testes. At day 19 and all subsequent days of gestation the testicular T content -an index of circulating go-nadotropins- was significantly higher in immunized fetuses than in controls. However, this difference was not yet apparent at day 18 when the normal fetal rat testis shows its peak activity. These results indicate that in the male rat fetus the negative feedback between gonads and hypothalamo-pituitary system develops between day 18 and 19 of gestation when the differentiation of the genital tract is already well advanced.
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Bidlingmaier, F., Knorr, D. Development of the negative feedback control system of the hypothalamo-pituitary-gonadal (HPG) axis in the male rat fetus. Pediatr Res 15, 1543 (1981). https://doi.org/10.1203/00006450-198112000-00047
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DOI: https://doi.org/10.1203/00006450-198112000-00047