The control of mucin secretion into the lumen of the cat trachea by alpha- and beta-adrenoceptors, and their relative involvement during sympathetic nerve stimulation.

We have tested the effects of phenylephrine, dobutamine and salbutamol, alpha-, beta 1- and beta 2-adrenoceptor agonists respectively, on the output of radiolabelled mucins into the cat trachea in situ. Phenylephrine significantly increased mucin output, an effect inhibited by the alpha-adrenoceptor antagonists, thymoxamine or prazosin, but not by propranolol. Dobutamine increased the output of 35S-labelled mucins greatly and had a smaller effect on 3H-labelled mucins. Propranolol blocked these effects but thymoxamine did not. At high doses atenolol, a beta 1-adrenoceptor antagonist, inhibited dobutamine's effect on 35S-labelled mucins. Salbutamol caused a small increase in mucin output and propranolol blocked this increase. Electrical stimulation of the sympathetic nerve supply to the trachea increased mucin output. Propranolol inhibited this effect; thymoxamine did not. We conclude that both alpha- and beta-adrenoceptors increase mucus secretion into the cat trachea but that only the beta-adrenoceptors respond to sympathetic nerve stimulation.