Phosphorylase Kinase Deficiency and Decreased Fat Accumulation in Hybrid Male Mice (IxC3H) 1

Abstract

I strain mice have a deficiency of muscle phosphorylase b kinase. Their skeletal muscle shows a three- to fivefold elevation in glycogen concentration and a decreased rate of glycogen breakdown. In addition, I strain mice accumulate less fat with age or high fat diets than control mice. The purpose of this study was to determine whether phosphorylase b kinase deficiency and decreased fat accumulation of I strain mice are related. Body weight, epididymal fat pad size, adipose cell number, and size were determined in male I, C3H, and hybrid (IxC3H) mice. Since the phosphorylase kinase deficiency is sex-linked, the male offspring of the I♂ xC3H♀ cross were used. As expected, phosphorylase b kinase activity and glycogen content in I and IxC3H skeletal muscle are similar. Body weight at 16 weeks of age in IxC3H mice resembles the body weight of I mice rather than C3H mice. Epididymal fat pad weight is not significantly different in IxC3H and I mice. Epididymal fat pad weight is significantly lower in I and IxC3H mice compared to that in C3H mice. However, adipose cell number is intermediate in IxC3H mice compared to I and C3H mice. Adipose cell size is not significantly different in the three strains. These results suggest that the decreased fat accumulation in I mice is genetically expressed with phosphorylase kinase deficiency. The inability of I mice to accumulate fat may be due to decreased adipose cell number.