Influence of ketamine and its interactions with morphine and nalbuphine on the level of enkephalins in some parts of the brain and spinal cord.

The aim of this paper was to study the influence of ketamine in a dose of 80 or 160 mg/kg ip on the level of leu-enkephalin (LENK) or met-enkephalin (MENK) in some parts of the brain and spinal cord, as well as to examine the interaction of ketamine with morphine or nalbuphine on this effect. The influence of ketamine on enkephalins release into the brain perfusate was also studied. Ketamine decreased the spinal cord enkephalins concentration mainly in cervical and lumbar part. These effect was antagonized by naloxone. Ketamine administered in a higher dose increased LENK release, and decreased the release of MENK into the brain perfusate. Morphine (20 mg/kg ip) increased the level of LENK in the hypothalamus, decreased the concentrations of MENK in the medulla oblongata and in the cervical part of the spinal cord, and increased the level of this neuropeptide in the thoracic part of the spinal cord. These effects were antagonized by ketamine. Ketamine and morphine administered simultaneously affected the level of enkephalins in some of the studied parts of the brain and spinal cord. Nalbuphine administered in doses ranging from 1 to 20 mg/kg changed the level of enkephalins in some parts of the central nervous system. Ketamine and nalbuphine administered simultaneously changed the level of enkephalins in the spinal cord and in the hypothalamus. It is concluded that: the decrease of the level of enkephalins in the spinal cord is an evident feature of ketamine action mediated probably by opioid receptors. Ketamine affects the release of LENK and MENK from the brain in a different way.(ABSTRACT TRUNCATED AT 250 WORDS)