Long-term supplementation with melatonin delays reproductive senescence inrats, without an effect on number of primordial follicles

The primary objective of the present experiment was to determine if lifelon g supplementation with melatonin delayed reproductive senescence through de creased loss of ovarian primordial follicles. Holtzman rats were divided in to three treatments on Day 10 after pupping (Day 0 = day of pupping). Treat ment 1 pups had access to water, whereas Treatment 2 and 3 pups had access to water containing 10 mu g/ml melatonin only at night (Treatment 2) or con tinuously (Treatment 3). Estrous cycles and weights of pups were monitored at selected times during the experiment; ovaries were removed for histology at 75 and 380 days of age. Vaginal opening in Treatment 2 was delayed (P < .01) compared with Treatments 1 and 3, but there was no difference (P > 0. 05) among treatments in percentage of normal length estrous cycles from vag inal opening to 75 days of age. There were fewer (P < 0.001) abnormal-lengt h estrous cycles from 180 to 380 days of age in Treatment 2 as compared wit h Treatments 1 or 3. There was no effect of treatment (P > 0.05) on number of primordial follicles. In conclusion, nighttime, but not continuous suppl ementation with melatonin, delayed puberty and reproductive senescence with out any effect on number of primordial follicles. (C) 2000 Elsevier Science Inc. All rights reserved.