Testosterone levels influence rat plasma leptin turnover

CASTROGIOVANNI D. (1), GAILLARD R.C. (2), * SPINEDI E. (1,2)

Munich, Germany

Congreso; 10th Meeting of the European Neuroendocrine; 2002

ENEA

It has been reported that gonadectomy, in both sexes, decreases energy expenditure and that short half-lives of hormones could be directly related to higher energy expenditure. Thus, our study was designed to explore whether the endogenous sex steroid milieu could influence leptin turnover in the rat. For this purpose, several groups (n = 6 rats per group) of adult (81 days of age) Wistar rats (intact males, intact females as well as 21 day-orchidectomized and ovariectomized) were anesthetized (Ketamine/Rompun).One hour later, blood samples were drawn before (sample time zero) and 2.5, 5, 15, 30 and 60 min after i.v. administration of leptin (Prepro Tech Inc.; 1.5 µg/100 g BW/100 µl of heparinized NaCl solution). Plasma testosterone, estradiol and leptin concentrations were measured by specific radioimmunoassays. As expected, plasma estradiol concentrations were higher (p < 0.05) in intact female than male rats and, conversely, plasma testosterone levels were significantly (p < 0.05) greater in intact male than female animals. On day 21 post-gonadectomy, homologous plasma sex steroid concentrations were not detectable. The results showed that plasma leptin concentrations (throughout a 60 min-period) was higher in intact female than in intact male rats. Whereas ovariectomy did not affect leptin levels compared to those measured in intact female animals, orchidectomy was accompanied by significantly higher leptin levels than in normal male rats. In addition, leptin levels were similar in gonadectomized animals of both sexes, demonstrating that in absence of testosterone there was no difference in leptin turnover between male and female animals. These results clearly suggest that, in contrast to estradiol, testosterone could play a role on the plasma leptin turnover by shortening plasma leptin half-life, possibly due to its effect on increasing energy expenditure.