Prolactin restores plasma testosterone levels and stimulates testicular growth in hamsters exposed to short day-length.

In male hamsters, light deprivation was reported to reduce both testis weight and prolactin (PRL) levels. Therefore, we decided to examine the effects of PRL on testicular function in hamsters exposed to short day-length. Adult hamsters were exposed to 5 h of light per day to induce gonadal atrophy, and, starting two months later, were injected daily with 300 mug PRL, 20 mug LH or 150 mug FSH daily for 2 1/2 weeks. In animals treated with PRL the concentration of testosterone in peripheral plasma, as well as the weights of the testes and the accessory reproductive glands, were significantly greater than in the controls. Treatment with LH or FSH had no effect on any of the parameters examined. It is suggested that changes in the rate of PRL release may mediate the effects of light on testicular function in the hamster and possibly, in other species.