LIPOPROTEIN-LIPASE AND METABOLIC-ACTIVITIES IN INCUBATED BOVINE ADIPOSE-TISSUE EXPLANTS - EFFECTS OF INSULIN, DEXAMETHASONE, AND FETAL BOVINE SERUM

An in vitro system was used to study the regulation of lipoprotein Lip ase (LPL) activity in bovine adipose tissue. The utilization of two en ergetic and Lipogenic substrates, acetate and glucose, and the activit y of glucose-g-phosphate dehydrogenase (G6PDH), an enzyme involved in de novo Lipogenesis, were also studied. Nine nonlactating, nonpregnant Holstein cows were given limited amounts of feed for 10 d, then they were overfed for 3 to 5 wk. Samples of perirenal adipose tissue were i ncubated for 24 or 48 h. Insulin(2 mU/mL) increased(P < .001) daily gl ucose and acetate utilization and attenuated(P < .001) the loss of G6P DH activity detected after I or 2 d of incubation. Dexamethasone (DEX, 10 nM) added to the insulin-supplemented medium decreased(P < .02) gl ucose utilization, but it did not change acetate utilization or G6PDH activity. A higher concentration of DEX (100 nM) potentiated (P < .004 ) the ability of insulin to attenuate the decrease in G6PDH activity w ithout changing substrate utilization. Under basal conditions, LPL act ivity was decreased by approximately 66% after 2 d of incubation. The decline in LPL activity was attenuated by insulin addition (P < .02) a nd was further attenuated (P < .004) by 100 nM of DEX. The addition of 10% fetal bovine serum alone to the medium had no effect on LPL activ ity, and fetal bovine serum decreased this activity when it was added to the insulin-supplemented medium.