Subcutaneous glycerol injection fails to reduce food intake in rats fed a high protein diet.

To test whether glycerol utilization might contribute to glycerol-induced hypophagia, cumulative food intake was measured following subcutaneous glycerol injection in rats fed a high carbohydrate (HC), a high fat (HF) or a high protein (HP) diet, because food composition is known to influence the activity of several glycerol metabolizing enzymes. In additional experiments, the effect of glycerol injection on plasma glycerol, blood glucose, and liver glycogen levels was also investigated in HC-, HF-, and HP-rats. Subcutaneous glycerol injection (6.3 mmoles/kg b.w.) significantly reduced food intake in HC- and HF-rats, but failed to decrease feeding in HP-rats. Five hours after glycerol injection, plasma glycerol levels were significantly elevated in HP-rats, but did not differ from the glycerol levels of controls in HC- and HF-rats. Subcutaneous glycerol injection did not affect blood glucose concentration or liver glycogen content 5 hours after injection in any feeding group. The results suggest that oxidation of the injected glycerol might contribute to the glycerol-induced hypophagia in HC- and in HF-rats.