Progesterone stimulates testosterone secretion in male rats.

In male rats, serum testosterone (T) and progesterone (P) levels fluctuate with daily periodicities that appear to be inversely related. To further investigate this interrelationship between serum T and P levels, we studied the effects of exogenous P on serum androgen levels. At 6--8 h after administration of P, serum T and DHT levels were consistently increased without any alterations in the serum LH and FSH levels. Following disruption of the hypothalamo-pituitary-adrenal axis either by adrenalectomy or by anterior hypothalamic deafferentiation, procedures known to abolish serum T and P periodicities, P was again effective in raising serum T concentrations without altering the serum gonadotropin values. These results show that P may directly enhance testicular secretion, and thus support the possibility that the observed adrenal influence on daily testicular T secretion pattern may be hormonally mediated via P secretion.