FIG. 1. Effect of short photoperiod (6:18) on testicular weight and on serum LH and FSH levels in adult male hamsters transferred from a long photoperiod on day 0. Means +/- SE. During both regression and spontaneous recrudescence of the testes, changes in serum gonadotropins (particularly FSH) precede changes in testicular weight. (From: Biology of Reproduction 1975;13:475-481.)