Effects of metabolic inhibitors on ingestive behavior and physiology in preweanling rat pups.

We have previously demonstrated that administration of 2-Mercaptoacetate (MA) stimulates independent intake after 1 h in 12 and 15-day-old rat pups, but not younger pups. MA also produces decreases in beta-HBA levels, consistent with the development of a role of altered fatty acid oxidation in modulating independent ingestion in rat pups by 12 days of age. The present experiments extended investigations of the role of changes in energy utilization in young rats by investigating the duration of the effects of altered fatty acid oxidation and the effects of combined blockade of fatty acid oxidation and glucose utilization. Pups were tested at 9, 12 or 15 days of age 3 or 6 h following administration of a dose of 0, 11.4, 22.8, 45.6 or 91.2 mg/kg MA. In pups aged 12 and 15 days, moderate doses of MA stimulated intake 3 h, but not 6 h, following administration. Administration of the highest dose of MA produced significant decreases in beta-HBA levels in pups at all ages when tested after 3 h, but not after 6 h. In the second set of experiments, behavioral and physiological responses to administration of MA (0, 11.4 or 22.8 mg/kg) combined with 2-Deoxyglucose (2-DG: 0, 100 or 200 mg/kg) were investigated in pups aged 6, 9, 12 or 15 days of age. The results demonstrated that while administration of 2-DG produced physiological responses, intake was not stimulated at any age by 2-DG alone or in combination with MA. In fact, in 12 and 15-day-old pups, administration of 2-DG blocked the stimulatory effects of administration of MA. Therefore, while altered utilization of glucose does not appear to be an effective stimulus for increased independent ingestion in pups at this age, altered fatty acid oxidation may be an early metabolic modulator of intake.