Potential for Non-shivering Thermogenesis in Perfused Chicken ( Gallus domesticus) Muscle

Abstract

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 (ṀO 2) 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 ṀO 2 at low doses eventually followed by decreased ṀO 2 at higher agonist concentrations. 5-HT gave smaller but qualitatively similar ṀO 2 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 ṀO 2 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 ṀO 2 may be a widespread biological mechanism. The possible implications of these findings for avian nonshivering thermogenesis are discussed.