Influence of photoperiod and 6-methoxybenzoxazolinone on the reproductive axis of inbred LSH/Ss Lak male hamsters

Adult male Syrian hamsters of the inbred LSH/Ss Lak strain were maintained under a 14L:10D light cycle until 13 weeks of age. At this point, they were implanted s.c. with elastomer capsules that were either empty or packed with 30-40 mg of 6-methoxybenzoxazolinone (6-MBOA), a compound found naturally in some monocotyledonous plants; half of the animals from each treatment group were then kept in long days (14L:10D) or transferred to short days (9L:15D). Testicular size was measured and blood samples collected from each hamster immediately before capsule implantation and again 2, 4, 6 and 8 weeks later. Within just 2 weeks of exposure to short days the mean plasma levels of LH and FSH had significantly declined, in both the control and 6-MBOA-treated animals, and were basal within 4 weeks. Testicular size closely followed these gonadotrophin changes; within 4-6 weeks the testes from all of the short-day hamsters had completely regressed to a prepubertal size. At the end of the experiment, at Week 8, the animals were killed and various components of the hypothalamo-pituitary-testicular axis were compared between the treatment groups. The pituitary content of FSH and LH, testicular weight, mean serum level of testosterone, but not hypothalamic LHRH content or pituitary gland weight, were considerably lower in the short-day than in the long-day hamsters, regardless of whether or not they had been chronically treated with 6-MBOA. In conclusion, these results demonstrate a short-day response in male LSH/Ss Lak hamsters which is more rapid and uniform than that typically shown by outbred hamster stocks. This inbred strain is, therefore, potentially very valuable for studies of neuroendocrine mechanisms involved in mammalian photoperiodism. Additionally, although 6-MBOA can stimulate testicular growth and reproduction in microtine rodents the present results fail to demonstrate any significant effect on reproductive function in the male Syrian hamster. The study also reports on the characterization of a new conformational antiserum to LHRH which can be used in radioimmunoassays for the measurement of LHRH from three vertebrate classes (mammalian LHRH, chicken I LHRH and salmon LHRH).