Insulin, Prostaglandin El5 Phenylisopropyladenosine and Nicotinic Acid as Regulators of Fat Cell Metabolism

Insulin-stimulated glucose oxidation was enhanced by the addition of N6 (phenylisopropyl)adenosine (PIA), prostaglandin E1 (PGE1) or nicotinic acid during a 1-h incubation of small amounts 5-8 mg/ml) of rat fat cells. Basal lipolysis was appreciable if low numbers of fat cells were incubated per ml. Insulin inhibited basal lipolysis at 20 to 50 mugU/ml and abolished lipolysis of 100 mugU/ml was present over a l-h period. However PIA, PGE1 or nicotinic acid potentiated glucose oxidation due to the 100 mugU/ml dose of insulin indicating that these agents are not increasing glucose oxidation solely as a result of an inhibition of lipolysis. PIA, PGE1 and nicotinic acid acted synergistically with insulin in stimulating glucose oxidation and inhibiting lipolysis in the presence of norepinephrine. Insulin was unable to decrease basal cyclic AMP accumulation or the increase in cyclic AMP seen with norepinephrine and theophylline after various time periods (2 to 60 min) but PIA, PGE1 and nicotinic acid were able to inhibit cyclic AMP accumulation at all times tested.