Modulatory Effects of Oxytocin-Specific Antagonist and Atropine on Uterine Contractions Induced by Methanol Extract of Tacazzea apiculata In Vitro

Abstract

Background: Uterotonic agents are vital in the management of labour, postpartum haemorrhage, and uterine dysfunction. Although Tacazzea apiculata is traditionally used for labour induction, its mechanism of action remains unknown. This study evaluated the mechanism underlying the uterotonic activity of the methanol stem extract of TA using isolated uterine strips from non-pregnant albino rats.

Methods: Estradiol-pretreated non-pregnant female rats (0.1 mg/kg, s.c.) were sacrificed by quick blow on the head, and uterine strips (~2 cm) were mounted in organ baths containing De Jalon's solution at 37°C and aerated with carbogen. Isometric contractions were recorded using a force transducer and PowerLab system. Concentration–response curves were generated for oxytocin (6.64 × 10⁻⁶–53 × 10⁻⁵ mg/ml), acetylcholine (4 × 10⁻⁷–16 × 10⁻⁷ mg/ml), prostaglandin (2 × 10⁻⁶–16 × 10⁻⁶ mg/ml), and the extract (0.08–0.64 mg/ml). Tissues were pre-incubated with atosiban (4 × 10⁻⁵ mg/ml) or atropine (4 × 10⁻⁶ mg/ml) for 3 min before agonist addition. Data were analyzed using GraphPad Prism (version 6) and expressed as mean ± SEM (n = 5), with significance at P < 0.05.

Results: The extract produced concentration-dependent uterine contractions comparable to standard agonists at higher concentrations. Atosiban significantly inhibited responses to both oxytocin (P = 0.011) and the extract (P = 0.0001), indicating oxytocin receptor involvement. Atropine abolished acetylcholine responses but only partially inhibited extract-induced contractions, suggesting partial muscarinic receptor involvement.

Conclusion: The methanol stem extract of TA exerts uterotonic effects via oxytocin receptor activation with additional contribution from muscarinic pathways.