Higher levels of specific enzymes in rat uterine muscle are linked to greater sensitivity to carbachol and oxytocin at term

Carbachol and oxytocin increased myometrial inositol phosphate production at term, enhancing uterine contractility.

• The potency of carbachol and oxytocin to induce myometrial inositol phosphate production was greater at term compared to earlier stages.
• Both agonists effectively increased contractions in the circular muscle but not in the longitudinal muscle.
• The maximal response to carbachol remained unchanged, while the response to oxytocin significantly increased at term.
• Increased responsiveness to carbachol and oxytocin was linked to the up-regulation of PLCbeta1 and PLCbeta3 enzymes.
• Administration of oestradiol during pregnancy raised PLCbeta1 and PLCbeta3 levels by 200-260%, while progesterone had no effect.
• Differences in the regulation of the phospholipase C pathway suggest distinct roles for longitudinal and circular uterine muscles during pregnancy.

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