Distribution in Rats Internal Organs of Intraperitoneally Given 125I-Labeled Heptapeptide [2-8]-Leucopyrokinin ([2-8]-LPK), a Truncated Analog of Insect Neuropeptide Leucopyrokinin.

Abstract

It was previously found that synthetic, insect-derived octapeptide leucopyrokinin (LPK) applied directly into the lateral brain ventricle induced asignificant antinociceptive effect in rats. Its synthetic truncated analog heptapeptide[2-8]-leucopyrokinin displayed astronger antinociceptive effect in comparison to native LPK. Moreover it was previously found ahigh accumulation of these both 125I-labeled peptides in adrenals, as well as in hypothalamus and in hippocampus of rats brain. The aim of the present study was to assess the distribution of 125I-labeled[2-8]-leucopyrokinin in rats' internal organs an in several parts of the brain after peripheral -intraperitoneal (i.p.) administration. The study was performed on male Wistar rats. Asynthetic[2-8]-leucopyrokinin ([2-8]-LPK) was iodinated with Na125I. On the day of experiment asolution of 125I-[2-8]-LPK was i.p. injected and the next after 1 and 24 hanimals were sacrificed by decapitation. Radioactivity levels in samples of parts of the brain and of internal organs were determined by counter Gamma Auto Count. Auniform, low accumulation 125I-[2-8]-LPK was found in evaluated samples of the brain and in internal organs. The results of the present study indicate aweak penetration into the brain and internal organs of intraperitoneally applied 125I-[2-8]-LPK in rats and correspond with previously determined weak biological effects of i.p. injected LPK and[2-8]-LPK.