Effect of some hormones on the rate of the triacylglycerol/fatty-acid substrate cycle in adipose tissue of the mouse in vivo

A method is described for the measurement of the rate of the triacylglycerol/fatty-acid cycle in adipose tissue of the mouse in vivo, which depends upon the incorporation of tritium from 3HH2O into the glycerol and fatty-acid moieties of triacylglycerol. The rate of the cycling is increased two-fold by feeding, an effect that is completely abolished by the beta-adrenergic blocker propranolol. The beta-adrenergic agonist fenoterol increased the rate of cycling five-fold in white adipose tissue and three-fold in brown adipose tissue. Cold exposure had no effect on the rate of cycling in white adipose tissue but increased the rate almost two-fold in brown adipose tissue. The increased rate of cycling during feeding, which may be due to increased sympathetic nervous activity, is consistent with the view tha the role of cycling is to increase sensitivity of metabolic control systems when required.