Tryptophan feeding induces sensitivity to short daylengths in photorefractory hamsters

The annual cycle of reproduction in the golden hamster (Mesocricetus auratus) is characterized by gonadal regression in response to decreasing daylengths in fall. However, hamsters become refractory to the inhibitory effects of short daylengths in late winter when gonadal recrudescense occurs. Our results show that addition of tryptophan to the diet of photorefractory hamsters causes them to respond to short daylengths in a manner similar to photosensitive hamsters in winter. Similar tryptophan treatment did not influence testes weights and fat stores of hamsters maintained on long daylengths.