Glucose: a possible intermediate in the oxidation of the side chain of cholesterol in resting and stimulated rats

The effect of repeated muscular contraction on the rate of oxidation of the side chain of cholesterol was studied in anesthetized rats. The animals received an intravenous pulse-label injection of either cholesterol-26-(14)C, incorporated into rat plasma lipoproteins, or bicarbonate-(14)C. In half the animals of each group, the hind legs were repeatedly stimulated by electrical impulses. A multicompartmental analysis was attempted, based on the disappearance curve of plasma free cholesterol-(14)C and on the excretion rate of expired (14)CO(2), as well as on previously reported rates of bile acid and adrenal steroid secretion. The rate of expired (14)CO(2) originating from cholesterol-26-(14)C was much less than that predicted by the digital computer analysis; cholesterol degradation could not be evaluated since the data were incompatible with a model that assumes direct oxidation of the side chain to CO(2). A revised model was postulated in which an important fraction of the side chain of cholesterol would be converted to CO(2) only after previous conversion to glucose. Direct measurement of plasma glucose-(14)C after the injection of cholesterol-26-(14)C supported this hypothesis.