A pharmacological study of the control of nasal cooling in the dog.

Air temperature differences between the internal and external nars (Ti-e), a qualitative measure of nasal blood flow, and the rate and ionic content of the mucous secretion of the lateral nasal gland, were determined in conscious, chronically instrumented dogs at both 25 degrees C and 42 degrees C environmental temperature, before and after administration of epinephrine, propanolol, phenoxybenzamine, acetylcholine and atropine. B. At 25 degrees C, epinephrine increased Ti-e. This was unaffected by propranolol, but returned to control values with phenoxybenzamine. Acetylcholine and atropine had no effect. At 42 degrees C, acetylcholine increased Ti-e; this was not reversed with atropine. Epinephrine caused a slight decrease in Ti-e at 42 degrees C. C. acetylcholine reduced mucous flow at 25 degrees C; atropine further decreased the flow. Changes in ionic content of the mucous suggest that cholinergic mechanisms affect pressure in the excretory duct of the gland. Epinephrine decreased the mucous flow at 42 degrees C; this was reversed with propranolol. D. It was concluded that nasal blood flow and lateral nasal gland mucous flow both possess sympathetic tone at 25 degrees C, the former being alpha-adrenergic, the latter beta-adrenergic. This tone appears important in reducing heat and water loss under normal conditions, and its reduction at high temperatures allows maximum efficiency of nasal cooling. The role of the parasympathetic system in respiratory heat and water exchange in the dog appears somewhat equivocal.