Mesencephalic sites of action of an enkephalin analogue (D-Met2, Pro5)-enkephalinamide and naloxone on the anterior pituitary of male rats.

(D-Met2, Pro5)-Enkephalinamide and naloxone injected into the dorsal raphe nucleus affected luteinizing hormone (LH) and prolactin (PRL) release. Drugs given into the reticular tegmental nucleus and dorsal part of the periaqueductal gray matter induced a PRL response and their administration into the central superior midbrain raphe nucleus caused changes in growth hormone (GH) secretion. The inferior colliculus and the lateral part of the periaqueductal gray matter were ineffective sites.