Influence of extracellular calcium on in vitro uterine muscle contractions stimulated by acetone leaf extract of Anogeissus leiocarpa

The effect of extracellular calcium on isolated uterine muscle contractions stimulated by acetone leaf extract of Anogeissus leiocarpa was investigated in a rat. About 12 m segment of the uterine muscle strip was mounted initially in a thermostatically regulated organ bath (37°C) containing normal Physiological Salt Solution (PSS; De Jalon) and later inphysiological salt solution devoid of CaCl2. The extract contracted the uterine muscle preparation in a concentration-related manner in normal PSS, with 0.53 mg/ml as the lowest active concentration. This contractile response was abolished by the calcium channel blocker, verapamil HCl (2 µg/ml). The extract however, did not evoke any contractile activity on the isolated tissue in a calcium-free media (PSS), even when caffeine (2 mmol) known to release calcium via the calcium induced-calcium release (CICR) mechanism was added to the perfusate. The results demonstrated the requirement for extracellular calcium for the extract mediated contractions and the inability of the extract to access calcium from intracellular storage sites such as the sarcoplasmic reticulum and the mitochondria. Therefore, the influx of Ca2+ into the cell cytosol is a pre-requisite for the extract-mediated uterine muscle contraction. Key word: Anogeissus leiocarpa, thermostatically organ bath, verapamil, caffeine, uterus.