MODULATION OF MORPHINE ACTION BY LAURIC ACID

Intraperitoneal administration of lauric acid (C-12) at the high doses, 100-1000 mumol/kg, showed weak but dose-dependent antinociceptive effect in mice. Pretreatment of the animals with 0.1 mumol/kg of i.p. C-12 tended to suppress the antinociceptive effect of 7 mg/kg of s.c. morphine and daily combination of this dose of C-12 with 10 mg/kg of s.c. morphine blocked the development of antinociceptive tolerance to morphine. However, increasing or decreasing of the dose of C-12 resulted in the loss of its modulatory effect on morphine. The strict dose-dependency of C-12 in its action on morphine suggests that there is a regulatory role for C-12, a medium length straight chain fatty acid, in the endogenous pain inhibitory system.