Effect of fasting and exercise on lipid levels in muscle. A cytological and biochemical study.

Abstract

Light and electron microscopic studies on the effect of fasting and exercise on lipids in the pectoralis muscle of the pigeon have revealed considerable increase in intracellular as well as extracellular lipids (1) in fasted pigeons and (2) in normal and fasted pigeons when the muscle of one side was electrically stimulated for different periods of time. Similar increase in lipids was also seen in the contralateral quiescent muscle. These observations were confirmed by bioehemical assays of the lipid content in the muscle under identical experimental conditions. It is concluded that the intracellular muscle lipids are not immediately drawn upon for energy either during exercise or fasting as long as there is ready supply of lipids transported through the blood stream from external sources such as adipose tissue.It was also observed that the inflow of lipids into the muscle was to, the fat-utilizing red fibers and not the glycogen-utilizing white fibers, which, even normally, contain no- intracellular lipid inclusions. The intracellular transport of lipids in muscle, therefore, may be considered a selective process. The mitochondria of both types of fiber in the exercised muscle appeared to be swollen.