Cadmium-induced stimulation of lipogenesis from glucose in rat adipocytes

Exposure of adipocytes of rats to CdCl2 caused acceleration of [3-3H]glucose incorporation into lipid maximally at 500 microM in Krebs-Ringer bicarbonate buffer, pH 7.4, containing 0.2% albumin. T.l.c. of the lipids extracted from adipocytes showed that Cd2+ increased labelling of di- and tri-[14C]acylglycerols predominantly. With increasing concentrations of glucose the apparent Km value was not affected by Cd2+, but the V value was increased, similarly to the effect of insulin. In the presence of insulin, Cd2+ (5 microM) exerted a consistent additive effect with a stimulatory effect of insulin on lipogenesis at all concentrations of insulin tested (5-50 mu units/ml). The stimulation was observed at a high concentration of glucose, suggesting that Cd2+ accelerated intracellular metabolism of glucose, mimicking insulin. However, although Zn2+ and Mn2+ stimulated the transport at a rate similar to that observed with insulin (200 mu units/ml), Cd2+ had no stimulating effect on the membrane transport of 3-O-methylglucose. The biological potency of Cd2+ and the insulin-like effects of Zn2+, both of which metals belong to the same group in the Periodic Table, are similar towards glucose metabolism, but quite different towards glucose transport.