PREVENTION BY MELATONIN OF SHORT DAY INDUCED ATROPHY OF THE REPRODUCTIVE SYSTEMS OF MALE AND FEMALE HAMSTERS

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Abstract
Male and female hamsters were exposed to natural photoperiodic and temperature conditions beginning on Nov. 13, and groups of hamsters were necropsied either on Jan. 15 or on April 10. Throughout the study, 1/2 of the hamsters (control hamsters) received s.c. implants of beeswax (25 mg) every other week, while the other half received beeswax pellets containing 1 mg melatonin. Control beeswax-treated males necropsied in Jan. had atrophic testes and accessory sex organs, while the uteri of the control females were infantile in appearance. Melatonin treatment prevented atrophic responses of the testes and accessory sex organs in males and the uteri in females. Melatonin-treated hamsters killed in Jan. also had higher plasma levels of immunoreactive LH [luteinizing hormone], while in females both pituitary and plasma levels of LH were elevated after melatonin treatment. By April 10, the testes and accessory organs of control males and the uteri of control females had regenerated to the adult condition, and these organs were comparable in size to those in melatonin-treated hamsters. Pituitary glands of control males contained slightly more LH and much more FSH [follicle stimulating hormone] than pituitaries of melatonin-treated males. Melatonin-treated females necropsied in April had pituitary and plasma levels of LH and FSH similar to those in beeswax-treated females killed at the same time. Chronic melatonin treatment prevents atrophy of the reproductive organs of male and female hamsters which is associated with the shortened days of the winter.