Central thermoregulatory effect of insect neuropeptide leucopyrokinin (LPK) in rats

摘要

It was reported previously that intracerebroventricular administration of synthetic insect octapeptide leucopyrokinin (pGlu-Thr-Ser-Phe-Thr-Pro-Arg-LeuNH_2) at the dose of 20 nmol exerts significant hipothermic effect in rats reversed by prior administration of naloxone, an antagonist of opioid receptors [1]. The present study was undertaken to confirm our preliminary results and determine effect of lower doses LPK on rectal temperature in rats. Experiments were conducted on adult Wistar rats with implanted polyethylene cannulas into the lateral brain ventricle (icv). LPK was injected icv in the range of doses 1-20 nmols. Rectal temperature was recorded before and 20, 40, 70, 100, 130 min and 24 h after LPK administration. We found that LPK at the dose of 20 nmol induced significant hipothermia, while lower doses of 1, 5, and 10 nmols induced significant hiperthermia, which was not blocked by prior administration of naloxone. Both LPK effects (hiper- and hipothermia) were most pronounced 40 min after administration of this peptide. The dose response curve displayed an evident bimodal dose dependent effect. We conclude that hiperthermic effect of LPK is opioid independent, while hipothermic effect is mediated by central opioid receptors.