Dietary crude protein levels and the effect of isoproterenol on in vitro lipogenesis in the chicken.

Experiments were conducted with male broiler breeder chickens to determine the metabolic effects of two levels of dietary crude protein fed during a protein-reversal regimen on subsequent responses to a beta-adrenergic agonist (isoproterenol) in vitro. Day-old chickens were fed diets containing either 12 or 20% crude protein until 14 d of age and then switched to the opposite diet until 28 d. In experiment 1, chickens were killed at 28 d, and in experiment 2, at intervals following the switch at 14 d. In vitro lipogenesis and lipolysis were determined. The hepatic enzymes isocitrate dehydrogenase, malic enzyme and fatty acid synthetase were determined during the 14 to 28 d of age growth period. Both in vitro lipogenesis and lipolysis were greater at 28 d when chickens were fed the 12% rather than the 20% protein diet. Neither 0 to 14 d of age dietary treatment influenced 28-d metabolic parameters. In contrast, the 12% protein diet during the first 14-d period depressed body weight (160 g vs. 320 g; p less than 0.05) and weight gain during the 14 to 28 d of age period regardless of dietary crude protein levels (508 g vs. 626 g; p less than 0.05). Lipogenesis and lipolysis were at their highest points 4 d following the dietary switch. Isoproterenol decreased in vitro lipogenesis 70% in all dietary treatment groups. Stimulated lipolysis was not affected by nutritional status and was twice the unstimulated rate.(ABSTRACT TRUNCATED AT 250 WORDS)