Endocrine Abstracts (2001) 2 P76

Leptin and body fat: their roles in the control of reproductive activity in male Rhabdomys pumilio

C Jackson & RTF Bernard

Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa.

Reproductive activity of male Rhabdomys pumilio is inhibited by exposure to a combination of reduced ambient temperature and food availability. However, the extent of this inhibition is reduced in mice that have maintained a body fat reserve. To determine if body fat stimulates reproduction via leptin, we treated 5 non-scrotal mice with exogenous leptin (40 micrograms subcutaneously twice per day for four days). A further 5 mice served as untreated controls. To determine if body fat stimulates reproduction by serving as a source of energy, we blocked fat metabolism using mercaptoacetate. In this experiment 36 adult, male mice were exposed to 26 degC and a high-fat diet until all mice were overweight and scrotal. The mice were then divided into 4 groups; 3 of which received a food restricted diet (10 percent reduction), two of these groups received either saline or mercaptoacetate subcutaneously (600 micromoles per day), and the third group, no treatment. The fourth group received food ad libitum and no treatment. The experiment ran for 4 weeks at 15 degC. At the end of each experiment, mice were sacrificed and weighed, reproductive organs were removed, weighed and fixed for histological examination, and blood was collected for testosterone, LH and leptin assays. Exogenous leptin had no significant effect on body mass, reproductive organ mass or hormone levels. In the second experiment we expected that treatment with mercaptoacetate would inhibit fat metabolism and exaggerate the reproductive inhibition caused by reduced ambient temperature and food restriction. This did not occur and mice treated with mercaptoacetate had the same fat scores as those treated with saline, and mercaptoacetate had no significant effect on the mass of the reproductive organs. The results from both experiments are equivocal and further experiments will be undertaken to examine the role of body fat in controlling reproduction.

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