Production of sexual steroids in rats during pre- and early postnatal life.

To get a comprehensive picture of the normal perinatal production of sexual steroids, we determined progesterone, estradiol and testosterone content in the sera, gonads and adrenal glands of rats of both sexes between 14th day of gestation and 24th day of postnatal life. The first sign of testosterone synthesis in the testicles could be detected on the 17th day of gestation followed by a large peak between the 19th intrauterine and 4th postnatal day. A second smaller increase in testosterone production was found around the 14-15th postnatal days. The first peak matches well the time of the critical period of sexual differentiation of the rats brain. No detectable amount of steroid were found in the ovary during the perinatal period. The ovaries seem not to be involved in the early period of sexual differentiation. The small quantity of progesterone found in the sera of early postnatal animals is produced by the adrenal glands.