The influence of ovariectomy on ob gene expression in rats.

Ovarian steroid hormones exert major influences on eating behaviour and body weight regulation of female rats. Ovariectomy (OVX) results in an increase in food intake and a concomitant increase in body weight, while estradiol (E2) replacement reverses these effects. In this study, we examined the influence of OVX on obese (ob) gene expression in rat adipose tissues and serum leptin concentration. Female Wistar rats, 10 weeks old, were divided into three groups: sham-operated control rats receiving corn oil (group 1, n = 4), ovariectomized rats receiving corn oil (group 2, n = 5), and ovariectomized rats receiving 17beta-E2 (10 microg/kg/day) replacement (group 3, n = 4). After 4 weeks, the rats and food consumption were weighed and serum E2 and leptin levels were measured by radioimmunoassays. Furthermore, the expression levels of ob mRNA obtained from the bilateral perimetric fat pads were estimated by Northern blot analysis. The mean weight and food consumption in group 2 were significantly (p < 0.01) heavier than those in group 1. But there were no significant differences between group 1 and group 3. The expression levels of ob mRNA in group 2 were lower than those in group 1, however, the levels of group 3 were restored to the level of group 1. On the other hand, no significant differences among the 3 groups as to serum levels of leptin were observed. The data herein clearly indicate that ovarian steroid hormones may be one of the factors involved in the regulation of ob gene.