Continuing our studies on proctolin (Arg-Tyr-Leu-Pro-Thr) we performed the synthesis and biological evaluation of 52 analogues substituted in position 2, 3, 4, and 5 of the peptide chain. The peptides were bioassayed for cardiotropic activity in vitro on Tenebrio molitor and myotropic activity on foregut of Schistocerca gregaria. Twenty analogues retained 20-80% of proctolin activity.
A comparison between vitellogenesis in virgin and mated females of Tenebrio molitor showed significant differences at each investigated developmental stage. Yolk protein deposition in oocytes, measured as an increase in their size parameters (length, width, and volume), proceeded much faster and was more efficient in mated females as compared to virgins. In fertilized females the gonadotropic cycle showed a cyclicity with an eight-day period while virgin females finish their vitellogenic stage after the first cycle. These differences were reflected in changes in the rate of protein synthesis in the fat body of females completing vitellogenesis or entering the next oogenetic cycle. In the haemolymph, in addition to a large (158 kDa) and two small (56 kDa and 45 kDa) subunits of vitellogenin, there was an abundance of proteins of 80 kDa and 60 kDa.
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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