Vascular reactivity to vasoactive agents following exposure to kolaviron in isolated aortic rings

Effect of kolaviron (KV), a biflavanoid-complex of Garcinia kola fraction was studied on [histamine (HM), phenylephrine (PE)]-induced and/or (8 x 10 or 4 x 10)M K contractile responses in ring preparations of rabbit aortae. Ring segments 2-5 mm were suspended in 20 ml organ bath containing normal physiological salt solution (PSS) and bubbled with 95% O2, 5% CO2 gas mixture for recording of isometric contractions at 37 C and pH 7.4. Following precontractions with EC70 (10 -5 HM; 10 PE)M and/or (8; 4 x 10)M K+; KV(0.3-20.0μg/mL) was added cumulatively and responses evaluated in intact (+E) and endothelium denuded (-E) aortic rings. To elucidate further mode of action of KV, relaxant effects were also examined in rings exposed to methylene blue (MB) or ouabain (OB) as well as on extracellular Calcium-dependent contractions. Kolaviron caused concentrationdepended relaxation of contractile responses in both +E and -E rings. Comparatively, KV-induced relaxant effect was significantly (p<0.05) greater in -E than in +E rings in both receptorand non-mediated responses. Relaxant effect was significantly (p<0.05) more potent in HM-induced contraction than in PEand/ or high K depolarized rings. Also KV inhibited and decreased maximal extracellular Calcium-dependent contractions; whereas KVrelaxant effect was completely abolished in MB and OB incubated precontracted rings. From these results, kolaviron causes smooth muscle relaxation in arterial blood vessel of rabbit aorta in a concentration-dependent manner in non-specific mode of action. The mechanism of action may not be unconnected with guanylate cyclase enzyme-cGMP pathway, calcium supply blockade and Na+-K+ ATPase cellular activity.