Involvement of vanilloid receptors and purinoceptors in the Phoneutria nigriventer spider venom-induced plasma extravasation in rat skin

Phoneutria nigriventer venom causes stimulation of capsaicin-sensitive prim ary afferent neurons in the rat dorsal skin, leading to neurogenic plasma p rotein extravasation due to the release of tachykinin NK1 receptor agonist. In this study we further investigated the mechanisms involved in the venom -induced activation of capsaicin-sensitive primary afferent neurons. The pl asma extravasation in response to venom intradermally injected was measured in Wistar rats as the local accumulation of i.v. injected I-125-labelled h uman serum albumin into skin sites. The tachykinin NK1 receptor agonist, D- Ala-[L-Pro(9),Me-Leu(8)]substance P-(7-11) (GR73632; 10-100 pmol/site), ind uced a significant plasma leakage that was abolished by the selective tachy kinin NK1 receptor antagonist, (S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isoprop oxyphenylacetyl) piperidin-3-yl] ethyl]-4-phenyl-1 azaniabicyclo [2.2.2]oct ane chloride (SR140333; 1 nmol/site), whereas the leakage after venom (1-10 mu g/site) was significantly inhibited (but not abolished) by SR140333. Th e calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP-(8-37), failed to further reduce the residual plasma extravasation induced by venom plus SR140333, The mu-opioid receptor agonist, [D-Ala(2),Me-Phe(4),Gly-ol( 5)]enkephalin (DAMGO), and the local anaesthetic, Lignocaine, had no effect on the venom-induced plasma extravasation. Similarly, the L-, N- and P/Q-t ype voltage-sensitive Ca2+ channel blockers (verapamil, omega-conotoxin MVI IA and MVIIC, respectively) as well as the Na+ channel blockers, tetrodotox in and carbamazepine, had no effect on the venom-induced effect. Neither th e systemic treatment nor the local injection of ruthenium red prevented the venom-induced plasma extravasation. However, the vanilloid receptor antago nist, N-[2-(4-chlorophenyl) ethyl]-1,3,4,5-tetrahydro7,8-dihydroxy-2H-2-ben zazepine-2-carbothioamide (capsazepine; 120 mu mol/kg, i.v.), reduced by 48 % (P <0.05) the venom (10 mu g/site)-induced plasma extravasation. A signif icant inhibitory effect was also observed with the P, purinoceptor agonists , adenosine 5'-triphosphate (ATP; 10 and 30 nmol/site) and adenosine 5'-dip hosphate (ADP; 10 nmol/site). The involvement of histamine and/or 5-hydroxy tryptamine (5-HT) in the venom-induced plasma extravasation was ruled out s ince neither histamine and 5-HT receptor antagonists nor depletion of mast cells by compound 48/80 affected the venom response. This was further suppo rted by the failure of venom to degranulate in vitro peritoneal mast cells. In conclusion, only vanilloid receptors and P, prejunctional purinoceptors had an inhibitory effect on the neurogenic plasma extravasation evoked by P. nigriventer venom in rat dorsal skin. (C) 2000 Published by Elsevier Sci ence B.V. All rights reserved.