Effects of acute opiate-peptide administration on pro-opiomelanocortin cells of the intermediate lobe of the rat pituitary

Summary The effects of acute injections of synthetic opiate peptides into the lateral cerebral ventricle of young adult male rats on cells of the intermediate lobe of the pituitary were studied. Met-enkephalin (100/g) injected into anesthetized rats, or 20 g beta-endorphin administered via a previously implanted cannula to unanesthetized animals, will lead to cell degranulation and often to expanded Golgi zones and prominent regions of rough endoplasmic reticulum in secretory cells when tissue is fixed 45–60 min after peptide administration. Treatment of animals with the opiate antagonist naloxone hydrochloride prior to enkephalin injection appeared to prevent the cellular changes elicited with peptide alone. Observations suggest that opiate peptides administered to the cerebrospinal fluid may stimulate release of pro-opiomelanocortin-peptide from pituitary cells.