Beta-adrenoceptors in the Pregnant and Non-pregnant Myometrium of the Goat and Cow

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Abstract
The muscle relaxing effect of .beta.-adrenoceptor agonists was examined without and with the presence of .beta.-adrenoceptor antagonists in strips from the pregnant and non-pregnant myometrium of the goat and from the pregnant myometrium of the cow. Isoprenaline, salbutamol and ritodrine caused a dose-dependent reduction of the spontaneous contractions of the pregnant myometrium and a dose-related and parallel shift to the right of the isoprenaline dose-response curve was obtained with butoxamine but not with practolol. Isoprenaline but neither salbutamol nor ritodrine caused a dose-related reduction of the spontaneous contractions in the non-pregnant myometrium and a dose-related and parallel shift to the right of the dose-response curve of isoprenaline was brought about with propranolol but not with either butoxamine or practolol. The muscle relaxing effect of ritodrine on the pregnant myometrium of the goat and cow shown in vitro was also demonstrated in vivo in the same species within 8 h of delivery. Apparently, the .beta.-adrenoceptors in the pregnant myometrium of the goat and cow belong to the .beta.2-group whereas those in the non-pregnant myometrium cannot be classified as either .beta.- or .beta.2-adrenoceptors.