Mechanism of kolaviron-induced relaxation of rabbit aortic smooth muscle

Abstract

There is a considerable evidence linking kolaviron (KV), a biflavanoid-complex of Garcinia kola Heckel seed (gKola) to smooth muscle relaxation. The present study was designed to characterize the mechanism of kolaviron-induced relaxation on contractile responses in ring preparations of vascular smooth muscle (VSM) of the rabbit aorta in vitro, in standard laboratory organ bath procedure. Following Phenylephrine (PE) (10^-7M), or high-K⁺ (80 mMK⁺) PSS induced contraction, KV (6, 12, 25, 50 100,200 & 400 μg/mL) was added cumulatively and relaxation responses determined in intact (+E) and endothelium-denuded (- E) aortic rings. Mechanism of KV-induced relaxation was further examined in PE or high-K⁺ precontracted +E and -E rings following 20 minutes exposures in methylene blue (MB) or ouabain (OB). To examine KV effect on extracellular Ca²⁺, tissues were exposed to a Ca²⁺- free 40 mM K⁺ depolarizing solution and Ca²⁺ as in CaCl₂ response curve constructed.

The results showed that KV causes concentration-dependent relaxation in VSM of the aorta and KV-induced relaxation was not significantly different in PE or high K⁺ mediated responses. However, relaxation was significantly different and more potent in -E compared to +E rings in PE or high-K⁺ precontractions. KV-mediated relaxation was abolished in MB and OB incubated and precontracted rings. Ca²⁺- dependent contractions in K⁺- depolarized PSS was significantly attenuated by KV. Mechanisms of KV-induced relaxation in VSM rabbit aorta is non-specific but linked to interference in calcium exchange as well as guanylate cyclase enzyme and Na⁺-K⁺ ATPase cellular activity. 

Keywords: Kolaviron, Vascular smooth muscle, rabbit aorta, phenylephrine, high-K⁺