FUNCTIONAL AND ANATOMICAL SEGREGATION OF HYPOTHALAMIC OPIATE RECEPTORS INVOLVED IN PROLACTIN AND GROWTH-HORMONE SECRETION IN CYNOMOLGUS MONKEYS

The minimum effective dose of the synthetic long-acting opiate peptide D-Ala2, MePhe4, met-(o)-ol enkephalin, which elicited prolactin (Prl) and growth hormone (GH) secretion after i.v. injection in cynomolgus monkeys was established. Following this, the hormone responses were examined after a series of bilateral injections of this met-enkephalin analog were given systematically throughout the hypothalamus in 3 animals. Marked differences between the patterns of release of the 2 hormones were noted: Prl was released more often than GH, but on several occasions GH secretion occurred without a Prl response. Saline injections were ineffective in raising the level of either hormone. The responses to intrahypothalamic injections of the peptide were antagonized in a dose dependent manner by the prior i.v. administration of naloxone. After sacrifice, the injection sites were histologically localized from semi-serial sections taken throughout the hypothalamus. Pooling the results showed that Prl release occurred following injections given throughout the medio-basal hypothalamus. There were fewer GH responses, which tended to occur from more anterior, lateral and possibly more dorsal injection sites. Functionally and anatomically segregated systems may be involved in the regulation of Prl and GH release in the monkey and possible mechanisms are discussed.