Effect of enflurane on selected neuropeptides and marker enzymes in rabbit brain.

The aim of this study was to evaluate the effect of 5-, 15-, and 60-min enflurane anesthesia on the levels of Met-enkephalin, Leu-enkephalin and neuropeptide Y in discrete areas of the rabbit brain. We also evaluated the effect of enflurane anesthesia on energetic, transport and catabolic processes by measuring the activities of succinate dehydrogenase, magnesium-dependent adenosine triphosphatase and acid phosphatase in the rabbit striatum and hypothalamus. Induction of anesthesia (5 min) decreased Met-enkephalin levels in the hypothalamus and striatum, and increased them in the hippocampus and mesencephalon. Induction of anesthesia increased Leu-enkephalin levels in all brain areas studied, except for the striatum, and increased neuropeptide Y content in the hippocampus. 15- and 60-min enflurane anesthesia increased Met-enkephalin content in the hypothalamus and hippocampus. After 15- and 60-min anesthesia, and after cessation of anesthesia, Leu-enkephalin levels were increased in the hypothalamus and mesencephalon, and were decreased in the striatum and hippocampus. In the striatum, neuropeptide Y content was significantly decreased during anesthesia and after cessation of anesthesia. Histochemical analysis revealed that enflurane enhanced ATP production, catabolic processes, and the rates of exchange and transport of energetic substrates in the striatum and hypothalamus. In conclusion, enflurane affects the levels of Met, Leu-enkephalins and NPY in a manner depending on the duration of anesthesia and the brain structure. Compared with isoflurane , which was studied in our previous study enflurane produces stronger alterations in the activities of enzymatic marker in the rabbit brain. This suggests that enflurane may be less safe than isoflurane.

Influence of isoflurane on enkephalin levels and on some indicatory enzymes in the central nervous system of rabbits.

The objective of this study was to analyse the effects of isoflurane anesthesia (lasting for 15 or 60 min) and isoflurane anesthesia termination (after 1 or 24 h) on met-enkephalin (MENK) and leu-enkephalin (LENK) levels in discrete brain areas and spinal cord segments in rabbits. Moreover histochemical analysis of activities of succinate dehydrogenase, magnesium-dependent adenosine triphosphatase (Mg++ATP-ase) and acid phosphatase in the striatum and hypothalamus were carried out to evaluate the effects of isoflurane anesthesia on energetic, transport and catabolic processes. Throughout anesthesia (15 and 60 min) and after its termination (1 h) the LENK contents were increased in hypothalamus, hippocampus, mesencephalon and lumbar segment of spinal cord. Moreover, during isoflurane anesthesia and after its termination (1 h) MENK and LENK levels decreased in cervical segment and MENK content dropped in thoracic segment of spinal cord. Histochemical data indicated, that isoflurane enhanced energetic processes as well as exchange processes in neurocytes, glial cells, capillary walls and ependymal cells of the third ventricle. Measurements of acid phosphatase activity provided evidence of no signs of toxicity of isoflurane in the examined areas. The changes in enkephalin levels observed during the isoflurane anesthesia and after its termination depended on the type of examined neuropeptides, as well as on parts of the brain and spinal cord studied. The changes observed after isoflurane administration in enkephalinergic system are discussed with regard to our earlier experiments with halothane and enflurane.

Antagonistic effect of MR2266 and MR2267 on morphine or nalbuphine analgesia at the spinal levels in rats.

The aim of this paper was to study the effect of two benzomorphan derivatives MR2266 and MR2267 with predominant antagonism to kappa-opioid receptors administered intrathecally on the analgesic action of morphine and nalbuphine. Both compounds attenuated the analgesia elicited by examined opioid agonists. Our results support the hypothesis that the spinal opioid receptors take part in analgesic effect of morphine and nalbuphine. It was for the first time described that MR2267, considered as inactive enantiomer of MR2266, is an active opioid antagonist when administered intrathecally.

Influence of halothane on the level of enkephalins in discrete brain areas of rabbits.

With regard to the fact, that theory of anesthesia, based on the endogenous opioid peptides requires further investigations the aim of this paper was to measure the concentration of leucine- (LENK) or methionine-enkephalin (MENK) in discrete brain areas of rabbits during and after 1 h halothane (2% v/v) anesthesia. The level of LENK and MENK was measured in discrete brain areas using the radioimmunoassay. Animals were divided into the following groups, depending upon the duration of anesthesia: I-15 min; II-60 min; III-1 h after anesthesia termination; IV-control group of non-anesthetized animals. After halothane anesthesia evident decrease in the concentration of leu-enkephalins in hypothalamus (HT) and the opposite effect in hippocampus (H) were observed. The MENK level significantly increased after halothane (for 60 min) in hypothalamus, hippocampus and mesencephalon (M). The change in the level of LENK in the thalamus (Th), hippocampus and mesencephalon and in the level of MENK in the hypothalamus and mesencephalon persisted after withdrawal of anesthesia. It was found that the alterations in the level of enkephalins in discrete areas of rabbit's brain is a feature of halothane anesthesia. The explanation of this phenomenon is possibly important for the understanding of the mechanism of halothane anesthesia and requires further investigations.