PROTEIN AND ENERGY RELATIONSHIPS IN THE BROILER CHICKEN .12. DIETARY-PROTEIN AND TRIIODOTHYRONINE (T-3) EFFECTS ON THE RESPONSE OF BROILERSTO ISOPROTERENOL AND CYCLIC ADENOSINE-MONOPHOSPHATE IN-VITRO

Indian River male broiler chickens (7-d-old) were fed on diets contain ing 120, 210 or 300 g crude protein/kg+0 or 1 mg triiodothyronine (T-3 )/kg diet (Expt 1) and 120, 150, 180 or 210 g crude protein/kg+0 or 1 mg T-3/kg diet (Expt 2) to determine the effects of crude protein leve l and T-3 on growth and metabolism, Body composition of chickens was d etermined by a combination of dissection of muscle and abdominal fat p ads, and chemical extraction (Expt 1). In vitro lipogenesis (IVL) was determined in both experiments by incubating liver explants for 2 h at 37 degrees in the presence of 10(-4) M-dibutyryl cyclic AMP (cAMP) or 10(-5) M isoproterenol (ISO) and 10(-2) M-[2-C-14]acetate. Acetate in corporation into total Lipid was an indication of IVL. Activity ratios for each of these additions relative to control (-cAMP-ISO) were calc ulated to ascertain basal v. inhibited rates of IVL. The relative musc le mass was increased by increasing crude protein from 120 to 210 g/kg diet but not from 210 to 300 g/kg diet. Dietary T-3 decreased total b ody Lipid regardless of the dietary crude-protein level. Increasing di etary crude protein decreased (P < 0.05) basal IVL (-cAMP-ISO) but not IVL (+cAMP). Dietary T-3 decreased basal IVL in birds fed on the diet s containing 120 and 210 g crude protein/kg but had little effect on t he two inhibited states of lipogenesis (+cAMP or +ISO). The component of lipogenesis sensitive to in vitro inhibition is also the component under dietary control.