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Pregnancy-induced decrease in the relaxant effect of terbutaline in the late-pregnant rat myometrium: role of G-protein activation and progesterone
Reduced ability of terbutaline to relax late-pregnancy rat uterus linked to G-protein activity and progesterone
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Abstract
Terbutaline's effectiveness in inhibiting uterine contractions decreases as pregnancy approaches term.
- Inhibition of contractions by terbutaline diminished from early to late pregnancy, indicated by changes in EC50 and maximal inhibition values.
- Plasma progesterone levels dropped as pregnancy progressed, which may be linked to the reduced effectiveness of terbutaline.
- A notable increase in the number of beta-adrenergic receptors was observed on the last day of pregnancy, corresponding with receptor mRNA levels.
- The ability of terbutaline to activate G-proteins decreased continuously from days 15 to 20 and fell below baseline levels by day 22.
- Progesterone pretreatment reversed the effects of terbutaline, enhancing the density of beta2-adrenergic receptors and their mRNA levels.
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