Response of lipogenic enzymes to overfeeding in liver and adipose tissue of light and heavy breeds of chicks.

Abstract

1. Chicks, 3-d-old, of a heavy breed (HB) and a light breed (LB) were overfed for 18 d. The activities of acetyl-CoA carboxylase (EC6.4.1.2; CBX), fatty acid synthetase (FAS), ATP citrate lyase (EC4.1.3.8; CCE), NADP-malate dehydrogenase (decarboxylating) (EC1.1.1.40; ME), 6-glucose-6-phosphate dehydrogenase (EC1.1.1.49; G6PDH) and phosphogluconate dehydrogenase (EC1.1.1.44; 6PGDH) were determined in abdominal adipose tissue (AT) and liver samples of overfed andad lib.-fed chicks. Size and fat content of liver and adipose tissue were also determined in order to evaluate the extent of obesity.2. Onad lib.-feeding HB chicks consumed more food, gained more weight and deposited more fat than the corresponding LB chicks. Their lipogenic enzymes were more active than in the LB chicks in both adipose tissue and liver. The increase in food consumption (%) that could be achieved by overfeeding was three times greater in the LB chicks than in the HB chicks.3. Overfeeding increased the weight and fat content of liver and AT in both breeds. The specific activities of CBX, FAS, CCE and ME in liver and AT increased in the LB chicks only and the total activities of liver and AT enzymes increased much more in the LB chicks than in the HB chicks in which the increase was derived mainly from tissue enlargement.4. The activity of the pentose cycle dehydrogenases was very low in liver, but in AT about one third of the NADPH generating capacity could be accounted for by these dehydrogenases.5. The results show that lipogenic enzymes of chicks respond to an increased substrate flux. It is suggested that the enlarged liver, the higher participation of AT in lipogenesis and the uninterrupted supply of cropstored excess food enable the chick to accommodate the increased amounts of substrate with only moderate enzymic adaptation.