Radioimmunoassay of enkephalins. Regional distribution in rat brain after morphine treatment and hypophysectomy.

Using highly sensitive and highly specific antisera methionine- and leucine-enkephalin levels were determined in various areas of the rat brain. The highest content of both enkephalins was found in the striatum and the hypothalamus, whereas in the hippocampus, the cerebellum and the cortex only a low content was present. The ratio methionine-enkephalin/leucine-enkephalin was about three. Neither acute or chronic morphine treatment nor precipitated morphine withdrawal induced significant changes in enkephalin levels in any brain region. Also hypophysectomy did not affect the enkephalin content of the various brain regions.