Some actions of sodium nitroprusside and glyceryl trinitrate on guinea-pig isolated trachealis muscle.

The smooth muscle relaxant actions of sodium nitroprusside and glyceryl trinitrate have been compared to those of aminophylline and isoprenaline on isolated guinea pig trachealis muscle. Ethacrynic acid (0.25 X 10(-4) M), an alkylator of sulphydryl groups, interacted differently with the four agents. In the presence of ethacrynic acid the concentration response curve of the muscle preparation to sodium nitroprusside and glyceryl trinitrate was shifted to the higher concentration ranges and the maximum response was severely reduced. The concentration response curve for isoprenaline was shifted to the higher concentration ranges with no change in the maximum response and the response to aminophylline was unchanged. These results argue against common intermediate sites of action involving sulphydryl groups of the four agents in guinea-pig trachealis.