Leptin indirectly affects estrous cycles by increasing metabolic fuel oxidation.
In previous experiments, lean Syrian hamsters fasted on days 1 and 2 of the estrous cycle failed to show sex behavior and ovulation normally expected to occur on the evening of day 4. The first goal of the present experiment was to determine whether systemic treatment with the ob (obese) protein leptin could reverse the effects of fasting on estrous cyclicity, social behaviors, and ovulation rate. Fasting-induced anestrus was reversed and normal sex and social behavior and ovulation rate were restored in hamsters injected intraperitoneally with 5 mg/kg leptin every 12 h during fasting on days 1 and 2 of the estrous cycle. A second goal was to test whether the effects of leptin could be prevented by treatment with pharmacological agents that block the oxidation of metabolic fuels. Glucose oxidation was blocked by treatment with 2-deoxy-d-glucose (2DG) and fatty acid oxidation was blocked by treatment with methyl palmoxirate (MP). 2DG (1000 mg/kg) or MP (20 mg/kg) was administered at doses that did not induce anestrus in hamsters fed ad libitum. As in the first experiment, fasting-induced anestrus was reversed by leptin treatment. However, when each injection of leptin was preceded by an injection of 2DG or MP, leptin treatment did not reverse fasting-induced anestrus. In summary, estrous cyclicity was not restored when oxidation of metabolic fuels was blocked, despite high endogenous levels of leptin. These results are consistent with the hypothesis that leptin acts indirectly on the reproductive system by increasing fuel oxidation.
Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA. js0v@lehigh.edu
J E
JE
Schneider
M D
MD
Goldman
S
S
Tang
B
B
Bean
H
H
Ji
M I
MI
Friedman
D000374:Aggression; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D006224:Cricetinae; D003847:Deoxyglucose / Q000494:pharmacology; D004734:Energy Metabolism / Q000187:drug effects*; D004852:Epoxy Compounds / Q000494:pharmacology; D004971:Estrus / Q000187:drug effects* / Q000502:physiology*; D005215:Fasting / Q000502:physiology; D005260:Female; D007004:Hypoglycemic Agents / Q000494:pharmacology; D020738:Leptin; D008647:Mesocricetus; D010060:Ovulation / Q000187:drug effects; D010084:Oxidation-Reduction; D011187:Posture / Q000502:physiology; D011422:Propionates / Q000494:pharmacology; D011506:Proteins / Q000494:pharmacology*; D012726:Sexual Behavior, Animal / Q000187:drug effects; D014621:Vagina / Q000502:physiology
D000963:Antimetabolites; D004852:Epoxy Compounds; D007004:Hypoglycemic Agents; D020738:Leptin; D011422:Propionates; D011506:Proteins; D003847:Deoxyglucose; C017522:methyl 2-tetradecylglycidate