Potential for Non-shivering 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°C without erythrocytes at constant flow. The preparation was stable for at least 3 hr, showing a constant oxygen uptake (ṀO2) and perfusion pressure as well as adequately maintaining muscle energy charge and creatine 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 ṀO2 at low doses eventually followed by decreased ṀO2 at higher agonist concentrations. 5-HT gave smaller but qualitatively similar ṀO2 effects. The actions of 50 nM NOR were blocked by prazosin (10 μM) and nitroprusside (0.5 mM), but not altered by propranolol (10 μM). NOR-induced stimulatory ṀO2 changes in the presence of pharmacological concentrations (1 μM) of glucagon were more pronounced and the thermogenic concentration range of NOR was increased. Taken together, these in vitro findings demonstrate a potential for vasoconstrictor-controlled muscle nonshivering thermogenesis in birds as in marsupials and mammals, suggesting that vascular control of muscle ṀO2 may be a widespread biological mechanism. The possible implications of these findings for avian nonshivering thermogenesis are discussed.