Effect of progesterone treatment on the development and function of neonatal rat adrenals and testes

The high progesterone (P) level of pregnancy was mimicked in neonatal male rats. The rats received 10, 30 or 100 microgram/g body weight of P in daily subcutaneous injections for 1, 2 or 3 weeks. It was expected that the treatment would yield developmental and functional changes similar to those possibly occurring under the influene of P in utero. P did not significantly affect the body weights of the animals, but significantly decreased the weights of the adrenals. Testicular weight was increased in the P-treated rats, and the number of Leydig cells was higher than in the controls. Peripheral serum testosterone and corticosterone, and testicular testosterone levels were only slightly decreased by the treatment. The changes observed in these neonatal animals suggest a regulatory function for P in the development of the fetal adrenal gland and testis.