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

Abstract

Phoneutria nigriventer venom causes stimulation of capsaicin-sensitive primary afferent neurons in the rat dorsal skin, leading to neurogenic plasma protein extravasation due to the release of tachykinin NK 1 receptor agonist. In this study we further investigated the mechanisms involved in the venom-induced activation of capsaicin-sensitive primary afferent neurons. The plasma extravasation in response to venom intradermally injected was measured in Wistar rats as the local accumulation of i.v. injected 125I-labelled human serum albumin into skin sites. The tachykinin NK 1 receptor agonist, d-Ala-[ l-Pro 9,Me-Leu 8]substance P-(7–11) (GR73632; 10–100 pmol/site), induced a significant plasma leakage that was abolished by the selective tachykinin NK 1 receptor antagonist, ( S)-1-[2-[3-(3,4-dichlorphenyl)-1 (3-isopropoxyphenylacetyl) piperidin-3-yl] ethyl]-4-phenyl-1 azaniabicyclo [2.2.2]octane chloride (SR140333; 1 nmol/site), whereas the leakage after venom (1–10 μg/site) was significantly inhibited (but not abolished) by SR140333. The calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP-(8–37), failed to further reduce the residual plasma extravasation induced by venom plus SR140333. The μ-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-type voltage-sensitive Ca 2+ channel blockers (verapamil, ω-conotoxin MVIIA and MVIIC, respectively) as well as the Na + channel blockers, tetrodotoxin and carbamazepine, had no effect on the venom-induced effect. Neither the systemic treatment nor the local injection of ruthenium red prevented the venom-induced plasma extravasation. However, the vanilloid receptor antagonist, N-[2-(4-chlorophenyl) ethyl]-1,3,4,5-tetrahydro-7,8-dihydroxy-2 H-2-benzazepine-2-carbothioamide (capsazepine; 120 μmol/kg, i.v.), reduced by 48% ( P<0.05) the venom (10 μg/site)-induced plasma extravasation. A significant inhibitory effect was also observed with the P 2 purinoceptor agonists, adenosine 5′-triphosphate (ATP; 10 and 30 nmol/site) and adenosine 5′-diphosphate (ADP; 10 nmol/site). The involvement of histamine and/or 5-hydroxytryptamine (5-HT) in the venom-induced plasma extravasation was ruled out since neither histamine and 5-HT receptor antagonists nor depletion of mast cells by compound 48/80 affected the venom response. This was further supported by the failure of venom to degranulate in vitro peritoneal mast cells. In conclusion, only vanilloid receptors and P 2 prejunctional purinoceptors had an inhibitory effect on the neurogenic plasma extravasation evoked by P. nigriventer venom in rat dorsal skin.