POTENTIAL FOR NONSHIVERING THERMOGENESIS IN PERFUSED CHICKEN (GALLUS-DOMESTICUS) MUSCLE

The humoral modulation of resting muscle heat production of chickens ( Gallus domesticus) was investigated in vitro. The resting distal lower limb was perfused via the popliteal artery at 25 degrees C without er ythrocytes at constant flow. The preparation was stable for at least 3 hr, showing a constant oxygen uptake ((M) over bar O-2) and perfusion pressure as well as adequately maintaining muscle energy charge and c reatine phosphate:creatine ratio. Noradrenaline (NOR), adrenaline (ADR ) and serotonin (5-HT) each caused a dose-dependent rise in perfusion pressure. NOR and ADR evoked increased ((M) over bar O-2) at low doses eventually followed by decreased ((M) over bar O-2) at higher agonist concentrations. 5-HT gave smaller but qualitatively similar ((M) over bar O-2) effects. The actions of 50 nM NOR were blocked by prazosin ( 10 mu M) and nitroprusside (0.5 mM), but not altered by propranolol (1 0 mu M). NOR-induced stimulatory ((M) over bar O-2) changes in the pre sence of pharmacological concentrations (1 mu M) of glucagon were more pronounced and the thermogenic concentration range of NOR was increas ed. Taken together, these in vitro findings demonstrate a potential fo r vasoconstrictor-controlled muscle nonshivering thermogenesis in bird s as in marsupials and mammals, suggesting that vascular control of mu scle((M) over bar O-2) may be a wide-spread biological mechanism. The possible implications of these findings for avian nonshivering thermog enesis are discussed. (C) 1997 Elsevier Science Inc.