Amphibian toxins from the skin of <i>Bufo regularis</i> have inhibitory effect on electrically invoked contractile response and bimodal effects on tone of longitudinal muscle of guinea pig ileum

Abstract

The skins of some amphibians contain potentially bioactive principles that may have pharmaceutical, medicinal, toxicological or chemical importance. In addition, such active principles can be used as tools in biomedical research. The present study aims at isolating and purifying bioactive principles from the skin of Bufo regularis and studying their effect on isolated longitudinal smooth muscle strip of guinea pig ileum. High performance liquid chromatography (HPLC) was used to isolate toad toxins. The effects of crude, semi-purified and purified extracts were tested on longitudinal smooth muscle of guinea pig ileum using organ bath method. Effect of the toxins was studied on electrically-induced contractile response and the basal tone of the longitudinal muscle strip. HPLC purification resulted in four different bioactive components with a λ_max UV absorbance pattern of around 295 nm. When tested on guinea pig ileum they had persistent inhibitory effect on the electrically-induced contractile responses. The pattern of effect was initial excitatory followed by long lasting inhibitory effect on tone of longitudinal muscle. The HPLC eluate at 79^th min in methanol preparative run corresponding to the eluate at 40^th min in the acetonitrile run had the maximum bioactivity. Hence, it was concluded that the skin of B. regularis contains four different components which vary in their potency on isolated smooth muscle strip of guinea pig ileum.

Keywords: Bufo regularis, organ bath, longitudinal muscle of ileum, toad toxin, electrical field stimulation