Poneratoxin (molecular weight 2932) is a 25 amino acid neuropeptide, isolated from an ant venom. It affects excitability of nerve and muscle fibres by changing the kinetics of the voltage-dependent sodium channel. The aim of the study was to investigate the analgetic effect of synthetic poneratoxin (PoTX) in adult female Wistar rats. In the first part of the study the animals received PoTX intracerebroventricularly. The analgetic effect was evaluated by a tail immersion test. In the second part of the experiment the analgetic effect of PoTX was blocked with naloxone, an opioid receptors antagonist. The study showed that poneratoxin exerts the analgetic effect in rats and this effect is not mediated by central opioid system. Therefore it was concluded that other mechanism is resposible for the effect of PoTX.
MAS MT is a myotropic decapeptide isolated from Manduca sexta. This peptide exerts stimulatory effect on insects heart-beat frequency. The present study was undertaken in order to determine a probable antinociceptive effect in rats of native synthetic decapeptide, MAS MT-I and its two analogs, heptapeptides MAS MT-II and MAS MT-III. All these peptides were applied directly into the lateral brain ventricle (icv) at three doses: 10, 25 and 50 nmol. The analgesic (antinociceptive) effect was evaluated by a tail immersion test. It was found that two doses of MAS MT-I: 25 and 50 nmol induced significant antinociceptive effect, while MAS MT-II and MAS MT-III exert a less antinociceptive effect in comparison with native MAS MT-I. Prior icv administration of naloxone, an opioid antagonist weakly blocked MAS MT-I effect. We conclude that antinociceptive effect of MAS MT-I in rats is not mediated by central opioid system.
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