Adaptive changes in alpha-glycerophosphate-generating enzymes in rat liver

Abstract

Possible modulation of tri-glyceride synthesis rate by [alpha]-glycerophosphate ([alpha]-GP) availability warrants analysis of [alpha]-GP-generating enzymes in hyperlipogenic states. Soluble [alpha]-GP dehydrogenase GDH activity of rat liver is elevated in animals on high glucose or fructose diets. This study is concerned with GDH and glycerokinase (GK) responses to refeeding a low-fat, high-glucose diet after a fast. Hepatic GDH values for control, fasted, and refed rats were 194 [plus or minus ] 5.3 U/100 g body weight, 133 [plus or minus] 5.01, and 307 [plus or minus] 24.0, respectively. Corresponding values for GK were 3.7 [plus or minus] .29, 2.8 [plus or minus] .20, and 2.5 [plus or minus] .15. Glycerol feeding resulted in similar changes. In each case the fall in GK was associated with decreased uptake of glycerol from the medium by liver slices. There were relatively larger adaptive responses to TPN malic enzyme and GDH to glycerol feeding than to glucose, although HMP [hexose monophos-phate] dehydrogenase and "lipogenesis" from acetate by slices were the same in the 2 groups.