The effect of fasting on the lipoprotein lipase activity of rat heart and diaphragm.

Recent studies have indicated that the activity of lipoprotein lipase in rat adipose tissue is related to the nutritional state of the animal. Fasting induces a fall in the activity released from surviving tissue ly heparin and in the activity of homogenates of adipose tissue, while glucose and insulin in vitro increase the heparin effect on the release of lipase from surviving adipose tissue of fasted rats. Glucose and insulin also prevent the fall in activity that occurs when tissue from fed or fasted animals is pre-incubated in buffer before preparation of the homogenates (1). Previous observations by Zemplenyi and Grafnetter suggest that the lipolytic activity of rat myocardium increases on fasting (2), and since extracts of heart tissue contain lipoprotein lipase (3) it was considered of interest to study the effect of fasting on the activity and release of this enzyme from heart tissue. The possibility that similar activity might be found in another repeatedly contracting muscle, diaphragm, was also explored.