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Mechanism of rat uterine smooth muscle contraction induced by endothelin‐1

1 Endothelin (ET)‐1 has been demonstrated to cause contraction of uterine smooth muscle. We investigated the role of ET receptor subtypes (ETA and ETB receptors) in ET‐1‐induced contraction of rat uterine smooth muscle by using the ETA receptor antagonist BQ‐123 and the ETB receptor agonist BQ‐3020. 2 ET‐1 caused a contraction with superimposed oscillations of the rat isolated uterus suspended in Krebs‐Ringer solution; both the amplitude of contraction as well as the oscillation frequency increased in a dose‐dependent manner (10−11–10−7 m). 3 BQ‐123 (10−6 m) markedly shifted the dose‐response curve of ET‐1 for both contractile effects and oscillation frequency to the right. 4 BQ‐3020 (10−11–3 × 10−7 m) did not cause uterine contraction; neither did it affect the dose‐response curve of ET‐1 for either the contractile effect or the increase in oscillation frequency. Thus, stimulation of ETB receptors is not involved in these responses. 5 The present findings suggest that ET‐1‐induced contractile responses and the increase in oscillation frequency in rat uterine smooth muscle is mediated through ETA receptors, and that ETB receptors, play no role in these responses.