ANTINOCICEPTIVE EFFECT OF INTRACEREBROVENTRICULAR INJECTION OF A TETRAPEPTIDE ASN-ALA-GLY-ALA IN RATS

The antinociceptive effect of intracerebroventricular injection (icv) of Asn-Ala-Gly-Ala (NAGA), a partial sequence of beta-lipotropin, was studied in rats. The potassium iontophoresis-induced tail flick was us ed to measure the pain threshold. The antinociceptive effect of NAGA, which was dose-dependent (icv, 0.03-0.24 mmol/rat) and long-lasting (9 0 min), was reversed by naloxone (icv, 0.26 mg.kg(-1)) and inhibited b y anti-MEK serum (titre: 1:5000, 5 mu l) or anti-LEK serum (titre: 1:5 000, 5 mu l). NAGA-induced antinociception was scarcely affected by an ti-beta-EP serum (titre: 1:30 000, 5 mu l) or anti - Dyn A1-13 serum ( titre: 1:30000, 5 mu l). It was suggested that the antinociceptive eff ect of NAGA may be associated with the release of met-enkephalin and l eu-enkephalin in rat brain.