| The insect kinins are small molecular nuropeptides. The first members of the insect neuropeptide family were isolated on the basis of the ability to stimulate contraction of the isolated cockroach hindgut. They have been isolated from a number of insects, including species of Dictyoptera, Diptera, Lepidoptera, and Orthoptera. It is the C-terminal pentapeptide sequence common to all insect kinins that seems to be necessary to elicit both the diuretic and the myotropic response in vitro.Insect kinins are involved in modulating a variety of biological actions, such as stimulating fluid secretion, depolarising the transepithelial potential of Malpighian tubules, regulation of lipid concentration in the haemolymph and protein synthesis in the fat body, inhibiting larvae weight gain , delaying larvae development, inhibiting digestive enzyme release.The present thesis was focused to evaluate the effects of the insect kinin and its core pentapeptide on the colonic motility of mouse. LK-Ⅷand FYPWGa were synthesized by solid phase peptide synthesis. The bioactivities and mechanisms were investigated by isolated mouse distal colon assay. The experiment results showed that FYPWGa (0.5-10μM) dose-dependently induced the contraction of mouse distal colon, with an EC50 of 2.1×10-6 M. The max response about 47% to control (1μM cabachol) when the peptide concentration was up to 10-5 M. Cholinergic antagonist atropine (10-5 M) and hexamethonium (10-4 M) had no influence on the activities of FYPWGa (10-5 M). Opioid receptors antagonist, naloxone (2.7×10-5 M) almost fully blocked the FPYWGa-induced (10-5 M) contraction of the distal colon. The L type Ca2+ channel antagonist, Nifedipine (10-6 M) completely abolished the FYPWGainduced(10-5 M) colonic contraction without affecting the baseline contractions. These findings showed that the contraction of the mouse distal colon induced by FYPWGa may be involved opioid receptors and L-type Ca2+ channel, but unrelated to cholinergic pathway.
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