Inhibitory effect of leptin on the rat ovary during the ovulatory process

ANALÍA G. RICCI; MARÍA PAULA DI YORIO; ALICIA GRACIELA FALETTI

Reproduction

Año: 2006 vol. 132 p. 771 - 780

1470-1626

The aims of this study were to investigate the negative action of leptin on some intraovarian ovulatory mediators during the ovulatory process and to assess whether leptin is able to alter the expression of its ovarian receptors. Immature rats primed with gonadotrophins were used to induce ovulation. Serum leptin concentration was diminished 4 h after hCG administration whereas the ovarian expression of leptin receptors, measured by Western Blot, was increased by the gonadotrophin treatment. Serum progesterone level, ovulation rate and ovarian prostaglandin E content were reduced in rats primed with eCG/hCG and treated with acute doses of leptin (5 doses of 5 µg each). These inhibitory effects were confirmed by in vitro studies, where the presence of leptin reduced the concentrations of progesterone, prostaglandin E and nitrites in the media of both ovarian explants and pre-ovulatory follicles cultures. We also investigated whether these negative effects were mediated by changes in the expression of the ovarian leptin receptors. Since leptin treatment did not alter the expression of ovarian leptin receptor, the inhibitory effect of leptin on the ovulatory process may not be mediated by changes in the expression of its receptors at ovarian level, at least at the concentrations assayed. In summary, the ovulatory process was significantly inhibited in response to an acute treatment with leptin, and this effect may be due, at least in part, to the direct or indirect impairment of some ovarian factors such as prostaglandins and nitric oxide.