INVERSE CORRELATION BETWEEN SERUM TESTOSTERONE AND LEPTIN IN MEN

Besides its role in the regulation of energy balance, leptin seems to be involved in linking energy stores to the reproductive system. A gen der-dependent difference exists in plasma leptin concentration and lep tin messenger ribonucleic acid expression in rodents and humans. This difference does not seem to be explained simply by differences in the amount of body fat between genders. To elucidate the relationship of e ndogenous testosterone and leptin, we studied the serum leptin concent rations in 269 elderly nondiabetic men. In addition, to assess whether exogenously administered testosterone could influence leptin producti on, we followed the serum levels of leptin in 10 healthy men during a 12-month treatment with 200 mg testosterone enanthate, im, weekly for contraceptive purposes. We found that the serum leptin concentration c orrelated inversely (r = -0.39; P < 0.001) with that of testosterone i n elderly men. This inverse correlation was still present when body ma ss index and plasma insulin were included in the analysis. The adminis tration of testosterone to young men suppressed serum leptin from the pretreatment level of 3.4 +/- 1.4 to 1.9 +/- 0.6 mu g/L during the the rapy. After cessation of testosterone injections, serum leptin concent ration re turned back to the pretreatment level. It is concluded that testosterone has a suppressive effect on leptin production, as reflect ed by circulating levels of this hormone.