Effects of ovariectomy on thermogenesis in brown adipose tissue and liver in Syrian hamsters

Weight gain in ovariectomized Syrian hamsters occurs without increased food intake, which suggests that metabolic efficiency may be enhanced through a reduction in energy expenditure. We examined the effect of ovariectomy on metabolic activity in brown adipose tissue and liver. Four groups of hamsters (n = 13, each) were killed 0, 2, 4, or 16 weeks following ovariectomy. Ovariectomized hamsters rapidly gained weight without overeating. Body weights stabilized after 8 weeks and remained 12-17% above sham-operated control weights for the duration of the experiment. Weight gain in the hamsters ovariectomized for 16 weeks was characterized by significant increases in retroperitoneal white adipose tissue weight and carcass lipid content. Similar trends were seen in 2-week and 4-week ovariectomized animals. There were no differences in interscapular brown adipose tissue weight, protein content, DNA content, or norepinephrine (NE) content among sham-operated and 2-, 4-, or 16-week ovariectomized hamsters, indicating that ovariectomy had no effect on brown adipose tissue growth. Similarly, there was no difference in either sympathetic nervous system activity (estimated by the rate of NE turnover) or mitochondrial GDP binding among the four groups of hamsters. In contrast, hepatic cytochrome P-450 activity was significantly reduced 2, 4, and 16 weeks after ovariectomy. These results suggest that reduced thermogenic activity in liver, but not in brown adipose tissue, could contribute to the weight gain in Syrian hamsters after ovariectomy.