Abstract
Abstract Prostaglandin E1 (PGE1) inhibits contractions of dog isolated tracheal muscle stimulated by different agents, but the degree of inhibition varies with the agent used. Low concentrations of PGE1 completely block the stimulant effect of 5-hydroxytryptamine, but even large concentrations of PGE1 do not completely antagonize the contractions caused by acetylcholine. The inhibitory effect of PGE1 is blocked by methysergide and not by propranolol, morphine or dihydroergotamine. PGE1 does not relax depolarized smooth muscle, although bradykinin and isoprenaline do. It is concluded that in tracheal smooth muscle, PGE1 interacts with cell membranes close to the 5-hydroxytryptamine D receptors. This causes activation of the smooth sarcoplasmic reticulum, leading to accumulation of calcium ions and relaxation.
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