Endothelin contracts human uterine myometrium by a partly dihydropyridine‐sensitive mechanism

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Abstract
The effect of endothelin (ET), a recently discovered 21‐amino‐acid polypeptide with powerful vasoconstrictor properties, was examined on human uterine myometrial stripsin vitro. ET dose‐dependently (10‐‐11‐‐10‐‐7m) increased the contractile force (monitored as contraction amplitude) of the myometrium with significant effects at 10–8and 10‐‐7M. ET (10‐‐8m and up) also increased the basal tone of the myometrium.The calcium channel blocking agents nifedipine (10‐‐7m) and diltiazem (10‐‐6m) both inhibited the spontaneous tonic contractions of the myometrium. When ET was given in the presence of nifedipine, the tonic contractions were further inhibited, whereas the ET‐induced increase in basal tone remained. The same result was obtained with diltiazem (10‐‐6m). The results indicate that the contractility of human myometrium may be modulated by ET, and that the effects of ET on the human myometrium are only partly mediated by dihydropyridine‐sensitive calcium channels.