Vasodilatory mechanisms in the tongue and nose of the dog under heat load.

Blood flow in vessels running to the nose and tongue was measured with electromagnetic flowmeters in anaesthetized dogs. In initial experiments the effect of electrical stimulation of the stellate ganglion on blood flow to the nose and tongue was studied and suitable doses of antagonist drugs to adrenergic and cholinergic receptors determined. In subsequent experiments the effect of receptor blockade on blood flow response was examined in animals subjected to hypothalamic heating at different body temperatures induced by whole body warming. It was found that heat load provoked an increase in blood flow to the nose which was due to a decrease in the activity of nerves supplying alpha adrenergic receptors. The heat induced vasodilatation observed in the tongue occurred by the same mechanism as in the nose when the thermal load was small and respiration rate was not increased from resting levels. However, when the thermal load was greater and panting was induced, a secondary "active" component became evident, and this was mediated neither by adrenergic nor cholinergic muscarinic receptors. Fibres responsible for this active vasodilatation to the tongue were postganglionic and ran apart from the vagosympathetic trunk.