Aging of the reproductive system in the male hamster: Behavioral and endocrine patterns

The present experiments were designed to characterize changes in reproductive function, both behavioral and hormonal, in the aging male golden hamster, and to determine whether or not pinealectomy or exercise would alter any reproductive parameters in aging hamsters. In the first experiment males were decapitated at 4, 11, 24 and 31 months of age and the weights of the testes and sex accessory glands recorded. Trunk blood was collected for determination of serum levels of testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Although the weights of the single seminal vesicles and epididymis were significantly lower at 31 than at 24 months, they were not less than those of postpubertal males at 4 months. Furthermore, these lower values for the 2 measures at 31 months were not accompanied by similar reductions in body weight, ventral prostate or paired testis weight. No age dependent declines in serum LH, FSH or testosterone were observed. Pinealectomy at 14 months of age did not alter any variable measured at 24 or 31 months of age. In the second experiment males were given 11 15-min tests for copulatory behavior with receptor females. Males were tested monthly between 12 and 24 months of age, except for Months 13 and 23. The frequency of mounts and intromissions, the latency to intromit and ejaculate, and the length of the postejaculatory interval were recorded. Body weight and testis width were recorded monthly and serum testosterone, LH and FSH levels were determined via cardiac puncture at 12, 18 and 24 months. Half of the animals had access to a running wheel, but no effect of the wheel on any reproductive variable was observed. The percentage of males ejaculating remained above 80% for males at all ages. There were no age dependent changes in the number of intromissions, latency to intromit or the length of the postejaculatory interval. The latency to ejaculate increased gradually but significantly after the males were 20 months old. There were no significant changes in testis width, serum testosterone, LH or FSH levels with age. The results clearly show that no serious decrements in reproductive function occur, either in behavior or in endocrine milieu, with age in the male golden hamster. Although the latency to ejaculate increased gradually with age, even the oldest males exhibited the entire copulatory sequence of behaviors when paired with receptive females.