Central and peripheral nervous system regulation of fat metabolism.

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1. Effects of ventromedial hypothalamic (VMH) stimulation on lipid metabolism and thermogenesis in brown adipose tissue (BAT) were studied in rats. Electrical stimulation of VMH was found to cause a marked increase in the rate of triglyceride synthesis in BAT preferentially and a rapid rise in the temperature of this tissue. Since stimulation of VMH has already been known to induce breakdown of triglycerides in adipose tissues, these results suggest that VMH stimulation increases thermogenesis in BAT by accelerating both the breakdown and resynthesis, that is, the turnover, of triglycerides. The thermogenic and lipogenic responses of BAT to VMH stimulation were almost completely abolished by surgical sympathetic denervation of BAT, indicating that the effects of VMH stimulation are mediated by the sympathetic nerve supply of this tissue.2. Effects of bilateral lesions of VMH on BAT metabolism were studied in rats, in relation to a development of obesity after hypothalamic lesions. Elec … More trolytic lesions of VMH led to accumulation of triglycerides and hypertrophy of BAT, which were associated with enlargement of constituent adipocytes and their apparent transformation from multiloculated structure of lipid droplets into the uniloculated structure. The rate of fatty acid synthesis in BAT and its temperature rise in response to sympathetic nerve stimulation were both reduced markedly after VMH lesions. These results indicated that thermogenesis in BAT was impaired in rats with VMH lesions by decreasing triglyceride turnover in the tissue, which might contribute to the development of obesity induced by VMH lesions.3. Effects of surgical vagotomy and sympathectomy on diurnal fluctuation of the activity of HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis, were studied in rat liver. Bilateral subdiaphragmatic vagotomy suppressed the normal diurnal fluctuation of the enzyme activity, whereas hepatic sympathectomy tended to amplify the enzyme fluctuation. The result suggests that the diurnal fluctuation of cholesterogenic activity of the liver is under neural influences. Less