Reduced norepinephrine turnover in interscapular brown adipose tissue of obese rats after ovariectomy.

Norepinephrine (NE) turnover, which is a reliable indicator of sympathetic nervous system (SNS) activity, was measured in the interscapular brown adipose tissue (IBAT), heart, and pancreas of ovariectomized (OVX), sham-operated rats receiving injections of estradiol benzoate (EB). Ovariectomized rats (OVX rats) ate much more than controls and became obese, whereas the administration of EB to obese OVX rats decreased their food intake to the level below that of sham-operated animals and body weight to the level of sham controls. The results from studies using the inhibition of NE biosynthesis with alpha-methyl-p-tyrosine or radiolabeled NE to measure NE turnover significantly demonstrated reductions in SNS activity in IBAT of OVX rats than in sham controls, whereas the injections of EB to OVX rats significantly restored the decrease of NE turnover in IBAT. NE turnover in heart and pancreas were similar in these three groups. It is suggested that reduced NE turnover in IBAT may be a major factor in the development of obesity after ovariectomy (OVX).