The effect of anesthesia or restraint on triacylglycerol turnover in the rat

A comparison of triacylglycerol metabolism was made among anesthetized, restrained and unanesthetized-unrestrained rats. The method utilized for the comparison was the determination of triacylglycerol turnover following the intravenous injection of [3H]glycerol. Peak appearance of triacyl[3H]glycerol was 25 min in unanesthetized-unrestrained rats but 35 and 45 min in restrained and anesthetized rats, respectively. Using serial plasma triacylglycerol determinations as an index of steady-state in all three groups, it was found that only the anesthetized and unanesthetized-unrestrained animals could be used for kinetic analysis. In these two animal preparations, apparent fractional catabolic rates were calculated and found to be lower in anesthetized (0.014 min-1) compared to unanesthetized-unrestrained animals with chronic indwelling cannulas (0.029 min-1). Apparent total catabolic rates, calculated from the plasma triacylglycerol mass and estimated plasma volume, were reduced by 50% in anesthetized animals. It is concluded that wide differences in triacylglycerol metabolism exist in these rat preparations which should be considered in the interpretation of future studies. The unanesthetized-unrestrained rat model may represent the closest approximation to the normal physiologic state.