Spontaneous and Melatonin-Induced Testicular Regression in Male Golden Hamsters: Augmented Sensitivity of the Old Male to Melatonin Inhibition

Abstract

Effects of aging and melatonin on testicular function of golden male hamsters were investigated. Young (3–4 months) and old (22–26 months) male hamsters were maintained on a long photoperiod (14 h light, 10 h dark) and injected with graded doses of 10, 25, 50 µg melatonin or injection vehicle, at 17:00 h (3 h before lights off) for a period of 6 weeks. Old male hamsters had significantly decreased testicular weights as compared with the young counterparts, but accessory sex organ (seminal vesicles and accessory glands) weights did not differ between young and old male hamsters. All doses of melatonin suppressed testicular and accessory sex organ weights in the young as well as in the old animals. The percent decrease in testicular weight in response to melatonin treatment was significantly greater (p < 0.01) in the old than in the young hamsters. Basal plasma prolactin concentration did not differ between young and old male hamsters. Melatonin significantly decreased plasma prolactin concentrations in both age-groups. Young hamsters had greater mean plasma luteinizing hormone concentrations than old hamsters, and melatonin suppressed luteinizing hormone equally in both groups. These results indicate that the testes of the male hamster spontaneously regress during the aging process, and this may be independent of prolactin, since there was no difference in serum prolactin concentrations between young and old hamsters. The finding that melatonin injections brought about a greater percent decrease in testicular weight in the old than in the young hamsters suggests that there is an increased sensitivity of the reproductive system to melatonin inhibition in the old male hamster.

Age difference in endogenous opiate modulation of short photoperiod-induced testicular regression in golden hamsters

“…Oestrogen has been shown to be responsible for the increase in plasma ß-endorphin-like immunoreactivity in young and old female rats (Forman, Sonntag, Hylka & Meites, 1983). It is quite possible that testosterone may also affect plasma ß-endorphin-like immunoreactivity in ham¬ sters, especially since both SP (Desjardins et al 1971;Chen, 1983) and ageing (Chen, 19816) cause a decrease in testicular weight and thus plasma testosterone concentrations.…”

The changing biological roles of melatonin during evolution: from an antioxidant to signals of darkness, sexual selection and fitness

“…Originally, melatonin was believed to inhibit directly sexual function in seasonally reproducing photoperiodic animals since prolonged elevation of nocturnal levels of serum melatonin presumably suppressed the hypothalamo‐hypophyseal‐gonadal axis resulting in the involution of the reproductive organs in Syrian hamsters Mesocricetus auratus and in palm squirrels Funambulus pennanti (Reiter, 1973; Chen, 1981; Haldar & Vidhu 1997). Based on the outcome of studies that used long‐day‐breeding rodents, which are only capable of mating and producing young during the long summer days (when the daily nocturnal increase in melatonin levels is relatively short), melatonin was originally believed to be inhibitory to reproduction, i.e.…”

The protective role of melatonin and curcumin in the testis of young and aged rats

“…The effects of administration of melatonin depend on dose (Vaughan, Richardson, Petterborg, Vaughan, & Reiter, ), time of application (Hong, Rollag, & Stetson, ), age of onset (Donham, Horton, Rollag, & Stetson, ), duration of application (Amador et al, ) and the season (Skene, Massion‐Pevet, & Pevet, ) applied. Different doses of the MLT suppressed testicular and accessory sex organ weights in young and old animals (Chen, ). MLT influences steroidogenesis depending on the duration of application.…”