CSF beta-endorphin and leu-enkephalin levels in the acute and chronic stages of cerebral infarction

Cerebral ischemia/reperfusion injury in rat brain: effects of naloxone

The pathogenesis of cerebral ischemia/reperfusion (I/R) involves cytokine/chemokine production, inflammatory cell influx, astrogliosis, cytoskeletal protein degradation and breakdown of the blood-brain barrier. (-)-Naloxone is able to reduce infarct volume and has been used as a therapeutic agent for cerebral I/R injuries. However, its effects on the mentioned pathophysiologic changes have scarcely been addressed. Cerebral I/R was produced by occluding and opening bilateral common carotid artery and unilateral middle cerebral artery in Sprague-Dawley rats. After cerebral I/R, the degradation of neuronal microtubule-associated protein-2 (MAP-2) was strongly associated with astrogliosis, inflammatory cell infiltration, cytokine/chemokine overproduction, and matrix metalloproteinase-9 activation. (-)-Naloxone pretreatment suppresses post-ischemic activation and preserves more MAP-2 protein. Therefore, (-)-naloxone administration might be an effective therapeutic intervention for reducing ischemic injuries.

Effects of halothane, alpha-chloralose, and pCO2 on injury volume and CSF beta-endorphin levels in focal cerebral ischemia

Anesthetic agent, arterial pCO2 level, and opioid peptides have all been implicated in the pathophysiology of experimental stroke models. The effects of halothane, alpha-chloralose, and differing concentrations of arterial pCO2 on injury volume and CSF beta-endorphin levels were studied in a feline model of experimental focal cerebral ischemia. The type of anesthetic agent used had no effect on injury volume following 6 h of focal cerebral ischemia. Over a 6-h period, beta-endorphin levels significantly increased from 10.1 +/- 5.0 fmol/mL at zero time to 14.4 +/- 7.2 fmol/mL at 6 h under halothane anesthesia (p < 0.05), whereas they did not significantly change (10.1 +/- 6.7 to 7.8 +/- 4.7 fmol/mL) under alpha-chloralose anesthesia. In contrast, hypercapnia had no effect on beta-endorphin levels, but significantly increased injury volume from 30.6 +/- 5.7% of the ipsilateral hemisphere under normocapnic conditions to 37.1 +/- 5.9% under hypercapnic conditions (p < 0.05). These results suggest that hypercapnia increases injury volume in a feline model of focal cerebral ischemia, and pCO2 should be controlled in experimental focal cerebral ischemia models.

The effects of naloxone on retinal ischemia in rats

The efficacy of naloxone (NL), a broad spectrum opioid antagonist, on retinal ischemia, was evaluated in a rat model of retinal ischemia with histopathologic and morphometric criteria. Two intraperitoneal injections of naloxone 3 mg/kg given immediately and 6 hr after reperfusion showed beneficial effects to the retina as evaluated at 2, 7, and 14 days after reperfusion. Morphologically, the naloxone-treated group showed better-preserved ganglion cells, nerve fiber layer, and inner nuclear layer. Morphometrically, in the treated groups, inner retinal thickness at all three time points and ganglion cell counts at 7 days showed higher values than vehicle controls. This beneficial effect of naloxone was dose-dependent with a minimal effective total dose of 6 mg/kg. A possible role of opiate receptors in retinal ischemia is suggested.

A double blind randomized pilot trial of naloxone in the treatment of acute ischemic stroke

Attention has focused on naloxone, an opiate receptor antagonist, because of its potential benefit in reversing neurological damage after acute cerebral ischemia. To evaluate the safety and possible efficacy of high-dose naloxone in ischemic stroke patients we planned a double blind pilot study. Between January 1989 and May 1990 24 patients were randomly assigned to the naloxone or placebo group according to age and neurological deficit. Naloxone was given in a loading dose of 5 mg/kg over 10 minutes followed by a 24-hour infusion at the rate of 3.5 mg/kg/h. 10 patients experienced minor side effects but none of them had to discontinue the treatment. 9 patients improved: 6 in the naloxone group and 3 in the placebo group, but no significant difference was found using the non parametric Mann-Whitney test. Our study suggests that naloxone is safe at the dose used, but the results do not support the planning of similar trials on a larger scale.

Alterations in Na(+)-K(+)-ATPase activity and beta-endorphin content in acute ischemic brain with and without naloxone treatment

The Na(+)-K(+)-adenosine triphosphatase (Na(+)-K(+)-ATPase) activity and beta-endorphin immunoreactivity were determined in rat brain at the acute stage of ischemia produced by unilateral occlusion of the middle cerebral artery (MCA). The effect of pretreatment with naloxone on these activities was also evaluated in the same model. After MCA occlusion, Na(+)-K(+)-ATPase activity was promptly reduced in the ischemic hemisphere and remained at a lower level than in the contralateral hemisphere during 90 minutes of ischemia. A single intraperitoneal 0.5-mg injection of naloxone prior to MCA occlusion attenuated the inactivation. On the other hand, beta-endorphin immunoreactivity was significantly increased following ischemia. The increase was marked in the ischemic hemisphere and was also observed in the contralateral hemisphere; this increase was not affected by the administration of naloxone. These results indicate the possibility that naloxone contributes to protecting the brain from ischemia through stabilizing the cellular membrane. The possible mechanism by which naloxone attenuates the inactivation of Na(+)-K(+)-ATPase in the ischemic brain is discussed in view of alterations of the central beta-endorphin system during ischemia.

Serum leucine-enkephalin in bronchial carcinoma and its relation to tumour location

Serum concentrations of the opioid peptide leucine-enkephalin were measured by radioimmunoassay in 30 patients with histologically confirmed bronchial carcinoma and 10 control subjects. This peptide, which is present in greatest amounts in the central and autonomic nervous systems, has previously been found in bronchial neoplasms. The mean serum concentration of leucine-enkephalin was significantly greater in the patients with carcinoma (1035 pg/ml) than in the control subjects (426 pg/ml). In the 23 patients with a tumour in non-apical regions of the lung, however, the mean concentration of the peptide (422 pg/ml) did not differ significantly from that in control subjects; serum concentrations in the seven patients with an apical neoplasm (mean 3050 (range 1259-5820) pg/ml) were significantly greater than values in either the control subjects or the patients with non-apical lung tumours. All seven subjects with an apical tumour had one or more features of Horner's syndrome and the three with all four components of the syndrome had the highest serum concentrations. Serum concentrations of leucine-enkephalin were unrelated to tumour type or presence of metastatic disease. No patient had evidence of metastases in the central nervous system or adrenal glands. Raised serum concentrations of leucine-enkephalin in patients with an apical tumour probably reflect invasion of cervical sympathetic ganglia with release of the peptide into the circulation rather than elaboration of the peptide by the neoplasm.

Increased levels of Met-enkephalin-like immunoreactivity in the spinal cord CSF of rats with adrenal medullary transplants

Recent work in our laboratory has demonstrated that the transplantation of adrenal medullary tissue into the spinal cord subarachnoid space can reduce pain sensitivity, particularly following nicotinic stimulation. This analgesia most likely results from the release of opioid peptides from the implanted chromaffin cells since it is blocked by the opiate antagonist naloxone. The purpose of the present study was to more directly measure opioid peptide release from adrenal medullary implants in the spinal cord using spinal cord superfusions. Basal levels of Met-enkephalin-like immunoreactivity (MELI) in spinal cord superfusates of animals with adrenal medullary implants was twice that in animals with control implants. The injection of nicotine further increased MELI release in adrenal medullary, but not control implanted animals. Both the basal MELI levels and the MELI levels following nicotine were correlated with reduced pain sensitivity in animals with adrenal medullary implants. Morphological studies revealed good long-term survival of grafted chromaffin cells. Results of this study suggest that it is possible to increase opioid peptide levels and concomitantly decrease pain sensitivity by the transplantation of adrenal medullary tissue into the spinal cord subarachnoid space.