The effects of meal feeding on the incorporation of D-[U- 14C]-glucose into tissue lipids and glycogen as a function of increasing intravenous glucose dose

Abstract

The in vivo incorporation of D-[U- 14C]-glucose into lipids and glycogen of adipose tissues, muscle tissues, and liver was measured 1 hr after the i.v. injection of increasing glucose doses (0.75, 1.5 and 2.5 g glucose/kg of body weight) in meal-fed and ad libitum-fed rats. In both perirenal and epididymal fat tissue, the levels of 14C-label in the total lipid extract was significantly higher in meal-fed than in nibbling rats at all glucose doses. As the glucose dose increased, the 14C-label in the lipids of both adipose tissues in meal-fed rats increased more than would be expected, assuming a linear dose dependency. In adipose tissues of nibbling rats, glucose dose dependency was linear. The 14C radioactivity in heart muscle lipids was significantly higher in meal-fed rats at all three glucose doses. In the diaphragm, this effect was seen only at the two higher doses; in liver, only at the highest dose; in skeletal muscle, there was no difference at any of the dose levels. The incorporation of 14C-label into tissue glycogen exhibited an entirely different pattern. Muscle glycogen synthesis tended to reach a plateau at the middle glucose dose in meal-fed rats, whereas it increased sharply with increasing glucose dose in nibbling rats. Indeed, muscle glycogen synthesis was much greater in nibbling rats than would be expected, assuming linear dose dependency. It was concluded that the two groups of rats responded quite differently to the increasing glucose load. The excess glucose tended to be incorporated into lipid in meal-fed rats and to muscle glycogen in nibbling rats.