Endogenous prostaglandins and mechanical tension in canine trachealis muscle

Prostaglandin E (PGS) is synthesized and released in isolated canine trachealis muscle (CTM), and the PGE threshold concentration for an effect on isometric tension is very low, indicating this prostaglandin is a most likely candidate for an endogenous prostaglandin that modulates or regulates tension. Prostaglandin F (PGF) is also released, but the threshold concentration for a mechanical effect is probably too high for endogenous PGF to have a direct effect on tension in this muscle. Indomethacin and aspirin, at concentrations commonly used to inhibit prostaglandin synthetase, had effects on tension, membrane potential, and membrane resistance, but these effects were not appropriate if their only action was to inhibit PGE or PGF concentration in CTM. Release of PGE from CTM was increased fourfold by treatment with carbachol, but even under this condition, where presumably cell [PGE] was increased, electrophysiological studies failed to give convincing evidence that the actions of indomethacin on mechanical tension were related to inhibition of PGE or PGF synthesis.