The effects of pretreatment with insulin on the antinociception induced by intracerebroventricular (i.c.v.) administration of the mu-opioid receptor agonist [D-Ala2, NMePhe4, Gly-ol5]enkephalin (DAMGO) were studied in mice. Intracerebroventricular pretreatment with insulin (1 and 3 mU) for 60 min dose dependently attenuated the antinociception induced by i.c.v. DAMGO (5.6 ng) in mice. Intracerebroventricular pretreatment with a highly selective tyrosine kinase inhibitor, lavendustin A, at doses of 100 and 300 ng for 10 min, dose dependently reversed the antinociceptive effect of DAMGO (5.6 ng) in insulin-treated mice. The antinociceptive effect of DAMGO (5.6 ng, i.c.v.) was significantly reduced in C57BL/KsJ-db/db diabetic mice compared with that in age-matched control (C57BL/KsJ-db/ + + ) mice. When C57BL/KsJ-db/db diabetic mice were pretreated with lavendustin A (300 ng), the antinociceptive effect of DAMGO was significantly increased. These results indicate that tyrosine kinase may be involved in the reduction of DAMGO-induced antinociception by insulin in mice. Furthermore, the attenuation of DAMGO-induced antinociception in C57BL/KsJ-db/db diabetic mice may be due in part to increased tyrosine kinase activity as a result of hyperinsulinemia.