ASSESSMENT OF THE ROLE OF FOLLICLE-STIMULATING-HORMONE AND PROLACTIN IN THE CONTROL OF TESTICULAR ENDOCRINE FUNCTION IN ADULT DJUNGARIAN HAMSTERS (PHODOPUS-SUNGORUS) EXPOSED TO EITHER SHORT OR LONG PHOTOPERIOD

Exposure of adult male Djungarian hamsters (Phodopus sungorus) to a short photoperiod induces testicular atrophy To evaluate the role of FSH and prolactin (PRL) in the control of testicular endocrine function, adult Djungarian hamsters were exposed to either a long photoperiod (16L:8D per day) or a short photoperiod (GL:18D per day) for II wk After 11 wk, hamsters housed in each of these photoperiods were placed into three groups and treated s.c. daily for 7 days with 50% polyvinylpyrrolidone in saline (SAL-PVP), rat FSH (10 mu g/hamster/day) in SAL-PVP, or ovine PRL (100 mu g/hamster/day) in SAL-PVP. On Day 8, animals in each of these groups received iq. injections of saline or ovine LH (0.3 mu g/g BW); 1 h later, blood was obtained by cardiac puncture under ether anesthesia Plasma FSH, LH, PRL, androstenedione (A-dione), and testosterone levels were measured by validated RIAs. In hamsters kept in the short photoperiod, testicular weight was decreased (p < 0.001). In these animals, FSH treatment increased (p < 0.001) testicular weight, whereas PRL injections had no effect. Testicular weight in animals kept in the long photoperiod was unaffected by FSH or PRL treatment. After 12 wk of exposure to the short photoperiod, circulating PRL levels were undetectable; plasma levels of FSH (p < 0.001), LH (p < 0.05), A-dione (p < 0.005), and testosterone (p < 0.001) were significantly reduced. Administration of either FSH or PRL had no influence on plasma A-dione levels in hamsters exposed to either photoperiod. A single i.p. injection of LH increased (p < 0.001) plasma A-dione levels in all animals, but this increase was higher (p < 0.001) in long photoperiod-exposed hamsters than in animals kept in the shea photoperiod. The basal secretion of testosterone was not affected by treatment with either FSH or PRL Administration of LH increased (p < 0.001) plasma testosterone levels in ah animals, and this response was higher (p < 0.001) in hamsters exposed to the long photoperiod. However, the testosterone response to LH treatment was increased (p < 0.01) in short photoperiod-exposed hamsters previously treated with FSH but not in those treated with PRL. These results indicate that FSH treatment not only initiates testicular growth, but also increases the efficacy of LH action on testosterone secretion in adult Phodopus kept in a short photoperiod. The data also suggest that ovine PRL treatment appears unable to induce testicular growth or increase testosterone secretion in adult Djungarian hamsters, unlike golden hamsters, exposed to a short photoperiod.