Increases in plasma glycerol levels precede the hypophagia following subcutaneous glycerol injection in rats

Cumulative food intake and plasma glycerol levels following subcutaneous glycerol injections were investigated in rats, because increases in plasma glycerol have been suspected to contribute to glycerol-induced hypophagia. Besides plasma glycerol, plasma non-esterified fatty acids (NEFA), plasma D-(-)-3-hydroxybutyrate (3-HB), blood glucose, and liver glycogen content were also measured. Two daily injections of 80 mg/kg body wt. glycerol did not affect food intake and failed to increase plasma glycerol 30 min after the injection. A single injection of 660 mg/kg body wt. glycerol reduced food intake and increased plasma glycerol 1-2 hours after the injection. This glycerol dose also increased liver glycogen content 1-2 hours after the injection but did not affect plasma NEFA and 3-HB. Rats injected with 660 mg/kg body wt. glycerol did not reduce feeding within the first 2 hours following the injection, when plasma glycerol levels were increased. Inhibition of feeding began at about 3 hours and continued up to 6 hours although plasma glycerol levels had declined to control values 5-6 hours after the injection. It is concluded that metabolic consequences of elevated plasma glycerol levels rather than increases in plasma glycerol levels per se elicit the food intake reduction following exogenous glycerol loads in rats.