Relative potencies of histamine H1-agonists on guinea-pig tracheal smooth muscle.

The relative potencies of a series of histamine H1-agonists in causing contraction of spirally cut strips of guinea-pig trachea, measured in the presence of cimetidine, indomethacin, methylatropine and propranolol, were similar to those reported on other guinea-pig tissues. However, whereas 2-methylhistamine and N alpha,N alpha-dimethylhistamine are apparently partial agonists in potentiating the adenosine-stimulated accumulation of cyclic AMP in slices of guinea-pig cerebral cortex, on tracheal spirals they are full agonists producing the same maximum contraction as histamine.