Prostaglandins in the brain of rats given, acutely, and chronically, a hyperthermic dose of met-enkephalin.

An enhanced prostaglandinlike activity is shown in homogenates of brain from rats treated intracerebroventricularly with 100 microgram of metenkephalin. The increase is significantly reduced by naloxone pretreatment. A relationship is proposed between generation of prostaglandins in the brain following met-enkephalin administration and hyperthermic effect of the opiatelike factor in the rat. Normalization of prostaglandinlike activity following chronic administration of met-enkephalin in the rat may also account for the development of tolerance to its thermic effect.