Effects of catecholamines on thermoregulation in pigeons.

1 In unanaesthetized pigeons, kept at room temperature (20-23 degrees C) the effects on cloacal temperature were examined of catecholamines, phenoxybenzamine and propranolol, injected into the cerebral ventricles.2 Noradrenaline, adrenaline, dopamine and isoprenaline caused a fall in cloacal temperature.3 Phenoxybenzamine produced a long-lasting small rise in cloacal temperature. This rise is attributed to removal of the hypothermic effect of noradrenaline released continuously from adrenergic neurones ending in the anterior hypothalamus. Propranolol produced a slight fall in cloacal temperature.4 The hypothermic effects of noradrenaline, adrenaline and dopamine were prevented by phenoxybenzamine but not by propranolol. They are therefore attributed to activation of alpha-adrenoceptors.5 The hypothermic effect of isoprenaline was not prevented by either phenoxybenzamine or propranolol. The effect can therefore not be attributed to activation of either alpha or beta-adrenoceptors. Propranolol actually accentuated the isoprenaline-induced hypothermia.