Differential Kolaviron Attenuated Contractile Responses to Agonists on Isolated Rabbit Aorta in Na+-K+ Pump Blockade

O K Uche, J O Ofeimun


The mechanism of kolaviron-induced vascular smooth muscles (VSMs) responses has not been fully
characterised. The present study investigated the effect and mode of action of kolaviron a biflavanoid-complex and major
component of Garcinia Kola-fraction on differential contractile responses to agonists-[phenylephrine (PHE) and histamine
(HIST)] on VSMs of rabbit isolated aortic rings in K+-free physiological salt solution (KFPSS). Cumulative concentration
responses to PHE and HIST were examined on 2 mm ring segments of the thoracic aortae which were suspended in 20 ml
organ baths containing physiological salt solution (PSS) for measurement of isometric contractions, at 370C and pH 7.4. The
medium was bubbled with 95% O2, 5% CO2, and rings were given an initial load of 1g. Cumulative contractile responses to
the agonists were studied in normal PSS (control) and following 30 minutes exposure to K+-free PSS and/or 800µg/mL
kolaviron. Contractile responses were expressed as percentage of 80 mM K+ contractions in normal PSS. Maximal
contractions (Emax) induced by PHE and HIST compared with high K+ contraction in the various preparations were
differentially altered following exposure to K+-free or 800µg/mL kolaviron in both intact (+E) and endothelium
denuded (-E) rings. Based on the efficacy (Emax) and potency (EC50) values for the dose-response curves of the agonists, it is
concluded that enhanced differential contractile responses elicited by agonists in K+-free PSS were significantly attenuated
by kolaviron concentration-dependently. This observation probably suggests the existence of another pathway of kolaviron
mode of action in vascular smooth muscle reactivity.

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