Effect of maternal progesterone exposure on fetal testosterone in mice.

The effect of maternal exposure to progesterone on plasma testosterone levels was studied in fetal mice. A daily subcutaneous injection of 2 mg progesterone to mice from day 14 to 17 of pregnancy resulted in a significant decline of circulating testosterone levels in male fetuses (p less than 0.05). A single injection of progesterone to mothers on day 18 of pregnancy leads to the same effect in male fetuses but increased significantly plasma testosterone levels in female ones (p less than 0.01). The testes of fetuses from progesterone-exposed mothers produced in vitro less testosterone than those of controls (p less than 0.01). These results show that both long- and short-term maternal exposure to pharmacological concentrations of progesterone reduce testosterone production in the male fetus. The nature of this mechanism is yet unknown, but it is suggested that the change of plasma testosterone levels may result from a local inhibition of the fetal testicular function.