Improved insulin responsiveness in rat adipose tissue pieces cultured with charcoal-treated albumin and oxygen

In an effort tao simulate the effects of insulin on fat cells prepared from fresh adipose tissue, pieces of epididymal adipose tissue were cultured in a medium containing charcoal-treated bovine serum albumin (BSA) with a gas phase of 100% O2. Using this system, the insulin effect on [1-14C]glucose oxidation was retained, in contrast to previous results in culture with untreated BSA in room air. Basal [1-14C]glucose oxidation was similar to fresh tissue, and insulin stimulated oxidation by 137%. In contrast to the effects of this culture system on [1-14C]glucose oxidation, tissue cultured with charcoal-treated BSA had lower basal rates of [U-14C]glucose utilization and 2-deoxyglucose uptake than either cells from fresh tissue or from tissue cultured with untreated BSA. The insulin effect on both of these measures was similar for the two culture systems and lower than for fresh tissues. Rates of lipolysis were increased in both types of cultured fat cells. Thus the improvement in [1-14C]glucose oxidation is presumably an effect on the pentose phosphate shunt, does not reflect a change in glucose transport or overall glucose utilization, and is not caused by a reduction in free fatty acid levels.