We have shown that the
venom of the South American rattlesnake Crotalus durissus terrificus induces a long-lasting antinociceptive effect mediated by activation of kappa- and
delta-opioid receptors. Despite being mediated by
opioid receptors, prolonged treatment with the
crotalid venom does not cause the development of peripheral tolerance or abstinence symptoms upon withdrawal. In the present study, we have isolated and chemically characterized a novel and potent antinociceptive
peptide responsible for the oral
opioid activity of this
crotalid venom. The amino acid sequence of this
peptide, designated
crotalphine, was determined by mass spectrometry and corroborated by solid-phase synthesis to be <EFSPENCQGESQPC, where <E is
pyroglutamic acid and the two
cysteine residues forming a
disulfide bond. This 14-amino-acid residue sequence is identical to the gamma-chain sequence of
crotapotin, a non-toxic component of this
snake venom.
Crotalphine, when orally administered (0.008-25mug/kg), induces antinociceptive effect in the
prostaglandin E(2)- and
carrageenin-induced
mechanical hyperalgesia models in rats and in the hot-plate test in mice.
Crotalphine was also effective when administered by intravenous (0.0032-0.04mug/kg) or intraplantar (s.c., 0.00006-0.3mug/paw) routes. In the
mechanical hyperalgesia models,
crotalphine shows a long-lasting (5 days) antinociceptive effect. d-Phe-
Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr
amide (
CTOP) and N,N-diallyl-Tyr-Aib-Aib-
Phe-Leu (ICI 174,864), antagonists of mu- and
delta-opioid receptors, respectively, did not alter the antinociceptive effect of the
peptide, whereas
nor-binaltorphimine, an antagonist of
kappa-opioid receptors, blocked this effect. These results indicate that
crotalphine induces antinociception mediated by activation of
kappa-opioid receptors and may contribute to the antinociceptive effect of the
crotalid venom.