Emilie F Rissman

Journal - Biology of Reproduction

Abstract :

Biology of Reproduction, Vol 22, 277-280, Copyright © 1980 by Society for the Study of Reproduction The gonads of adult hamsters are regressed by 6-10 weeks exposureto short daylengths. This effect is mediated by the pineal glandand can be simulated by appropriately timed injections of melatonin.Exposure of newborn hamsters to short daylengths has no discernibleeffect on maturation of the hamster reproductive system. Thehypothesis that prepubertal refractoriness to photoperiod reflectsinsensitivity of the neuroendocrine axis to melatonin was tested.Male hamsters exposed to 14 h of light/day (14L:10D) were injectedonce daily between 3 and 14 weeks of age with 25 µg melatoninor with an oil vehicle. Testicular condition was assessed at7, 10 and 14 weeks of age. Animals treated with melatonin from3 weeks of age had significantly smaller testes than did controloil treated hamsters at 7 and 10 weeks of age. The testes ofother animals treated with melatonin beginning at 7 weeks ofage were not significantly different from those of oil injectedanimals at 10 weeks of age and both of these groups had significantlylarger testes than did animals treated with melatonin from 3weeks of age. By week 14 the testes of all animals treated withmelatonin showed substantial regression. Prepubertal hamstersare able to respond to the antigonadal actions of melatonin.It is suggested that failure of short day exposure to affectthe rate of gonadal maturation is not due to target tissue insensitivitybut rather reflects the intrinsic latency of the neuroendocrinesystem’s responsiveness to the antigonadal agents of thepineal gland.Note: ACKNOWLEDGMENTS This research was supported by USPHS Grant HD-02982 to Irving Zucker. I thank Darlene Frost, Susan McCamant, Eric Bittman and Laura Beasley for their technical assistance and Rosemary Hendrick for typing the manuscript. I am especially grateful to Irving Zucker and Phyllis Grey Johnston for their help and guidance.