Effect of fasting on the clearing factor lipase (lipoprotein lipase) activity of fresh and defatted preparations of rat heart muscle.

The clearing factor lipase (lipoprotein lipase) activities of homogenates of fresh tissue and of acetone-ether powders have been compared in hearts from fed and starved rats. The activity of the enzyme measured in homogenates of acetone-ether powders is generally higher than that in homogenates of the fresh tissue. Activation is due to an effect of the acetone-ether treatment on enzyme which is associated with the tissue residue in fresh tissue homogenates. A similar activation occurs when the tissue residue is treated with deoxycholate. When rats are fasted, a marked increase in the clearing factor lipase activity of the heart occurs. Peak activities are reached after 10-24 hr, and thereafter the activity falls slowly. This pattern of activity is observed in homogenates of fresh tissue and of acetone-ether powders. The activity of clearing factor lipase in diaphragm muscle also increases in rats starved for 8 or 24 hr. The importance of the change in muscle clearing factor lipase activity on fasting in relation to triglyceride fatty acid utilization by this tissue is emphasized.