Effects of Phoneutria nigriventer venom on rabbit vascular smooth muscle

1. The effects of Phneutria nigriventer venom (PNV) on rabbit vascular smooth muscle have been investigated. De-endothelialized vascular strips were superfused in a cascade system with oxygenated (95% O2 + 5% CO2) Krebs solution at 37 degrees C. 2. Phoneutria nigriventer venom (0.3-30 micrograms) produced dose-dependent and short-lived contractions of both venous (cava, mesenteric and jugular veins) and arterial (pulmonary and mesenteric arteries) tissues. 3. Methysergide (5.0 microM) did not significantly affect PNV-induced contractions in venous tissues (cava and mesenteric veins) or pulmonary artery, indicating that serotonin is not involved in the contraction. This was confirmed when PNV was dialyzed (24-48 h) since the contracting activity was still observed on the above tissues. In addition, the spasmogenic activity induced by dialyzed PNV was greatly reduced by incubating the venom with trypsin. 4. Neither tetrodotoxin (3.0 microM) nor phenoxybenzamine (0.05 microM) significantly affected PNV-induced contractions, suggesting that voltage-dependent sodium channel activation or endogenous catecholamine release from autonomic nerve endings on the vascular walls do not play a role in the response to PNV. 5. Our results demonstrate that PNV contains non-dialyzable components, probably peptides, that are responsible for the contractile activity on rabbit veins and pulmonary artery strips.