Prolactin Release in Golden Hamsters: Photoperiod and Gonadal Influences1

Abstract

Serum prolactin (PRL) in male golden hamsters was determined under a variety of experimental conditions. The pattern of daily PRL release appears to be only slightly altered by mild stress, and serum PRL levels are unaltered by castration. Exposure to short photoperiod induces a marked decline in serum PRL titers. Serum PRL levels remain depressed for 19–21 weeks of short-day treatment and then increase spontaneously. The spontaneous elevation of PRL titer appears to be relatively independent of testicular influence since it occurs at the same time in intact and castrated males, as well as in castrated males bearing testosterone implants. Spontaneous PRL release in intact males bearing testosterone implants was delayed 2 weeks. Changes in serum PRL concentrations may have a role in mediating the inhibition of testis function which occurs during exposure to short photoperiod.