Enkephalins and Endorphins. Clinical, pharmacological and therapeutic implications

Capillary electrophoretic competitive immunoassay with laser-induced fluorescence detection for methionine-enkephalin

Immunoassays are commonly used in bioresearch for the detection and quantification of small proteins and macromolecules in biological fluids and other complex matrices. In this report, a competitive immunoassay using capillary electrophoresis (CE) with laser-induced fluorescence was developed for methionine-enkephalin (ME). The method is based on the competitive reaction between the ME and fluorescein conjugated ME (ME-F) with anti-ME antibody, capillary electrophoresis separation of the ME-antibody bound and free ME-F, followed by the laser-induced fluorescence detection of the fluorescent species. With the optimized separation conditions, it was possible to separate the antibody bound and free fluorescien conjugated ME by a capillary electrophoresis-laser-induced fluorescence (CE-LIF) analysis using an uncoated fused-silica capillaries. The results concluded that the assay specificity, selectivity and accuracy were excellent.

An immunoassay for Leu-enkephalin based on a C-terminal aequorin-peptide fusion

Recently we demonstrated that the fusion of an octapeptide to the C-terminus of a cysteine-free mutant of aequorin showed no inhibitory effect on the luminescence activity of the photoprotein. This observation is of particular importance when the use of aequorin as a label in the development of immunoassays for peptides whose activity lies in their C-terminal region or the epitope for antibody recognition is at their C-terminus is desired. In the case of opioid peptides, antibodies are directed toward their C-terminus as they differ from each other at this terminus. The goal of this study was to develop an immunoassay for Leu-enkephalin, a mammalian opioid peptide, using a C-terminal aequorin-peptide fusion protein. For that, the N-terminus of Leu-enkephalin was genetically fused to the C-terminus of a cysteine-free mutant of aequorin. It was observed that the C-terminal conjugated aequorin maintained its luminescence activity. An immunoassay for Leu-enkephalin was then developed using the aequorin-Leu-enkephalin fusion protein as a labeled analyte in a competitive as well as in a sequential binding mode. It was demonstrated that aequorin can be used as a label in peptide assays in which it is critical that the peptide's C-terminus be free for activity and/or for antibody recognition.

Plasma concentrations of beta-endorphin, adrenocorticotropic hormone, and cortisol in drinking and abstinent chronic alcoholics

Previous studies of the relationship between the endogenous opioid system and alcohol consumption have reported contradictory results. To shed light on this connection, we compared plasma concentrations of beta-endorphin, adrenocorticotropic hormone, and cortisol in 70 alcoholic persons after different periods of abstinence and a group of 80 control subjects. Plasma beta-endorphin was decreased in alcoholics (18.61 +/- 1.38 vs. 39.31 +/- 3.44 pg/ml), even after more than 10 years' abstinence. This effect may mediated by the tetrahydroisoquinoline system, and may thus result from chronic alcohol consumption. On the other hand, lowered circulating concentrations of beta-endorphin may be a cause, rather than an effect, of alcoholism. Plasma levels of adrenocorticotropic hormone and cortisol did not differ in alcoholics and controls (19.29 +/- 1.66 vs. 13.27 +/- 1.85 pg/ml for ACTH, 20.37 +/- 0.78 vs. 17.22 +/- 0.64 ng/ml for cortisol), and thus appear to have no relation with chronic alcohol consumption.

Acupuncture as a detoxification treatment: an analysis of controlled research

The research literature on the use of acupuncture as a substance abuse treatment is reviewed. In recent years numerous descriptive reports have been published concerning the efficacy of acupuncture in alleviating withdrawal symptoms with substance abusers attempting abstinence. While a limited number of experimental design studies have been conducted in this area, results from controlled studies generally support that acupuncture can be effective in assisting active drug and alcohol users become abstinent. Controlled, experimental research on acupuncture and related techniques used as substance abuse treatments are reviewed. An overview regarding acupuncture and related procedures used as substance abuse treatments is first provided. Animal and human studies on acupuncture's usefulness in alleviating opiate withdrawal symptoms are presented, followed by studies concerning other substance abuse problems (i.e., alcohol, tobacco and cocaine). Possible physiological mechanisms related to acupuncture's effects are reviewed.

Short-term effects of naloxone on hemodynamics and baroreflex function in conscious dogs with pacing-induced congestive heart failure

OBJECTIVES

The purpose of this study was to determine the effects of naloxone on systemic hemodynamics and reflex function in dogs with congestive heart failure induced by rapid pacing.

BACKGROUND

We have shown previously that naloxone, an opiate receptor antagonist, improves cardiac output, aortic blood pressure, systolic performance and the baroreflex function in conscious dogs with chronic right-sided congestive heart failure. However, whether endogenous opioids also play a role n mediating the reduction of myocardial and baroreflex function in animals with left heart failure remains controversial.

METHODS

We administered naloxone (1 mg/kg body weight) and normal saline solution to 15 dogs with pacing-induced congestive heart failure (225 beats/min for 8 weeks) and 11 control dogs. In addition to systemic hemodynamic measurements, the slope of pressure-area relation obtained from echocardiography with intravenous bolus injection of phenylephrine was taken as a load-independent index of myocardial contractility. Baroreflex function was estimated by the slope of the regression line relating systolic aortic pressure and RR interval.

RESULTS

Plasma beta-endorphin levels were elevated in dogs with congestive heart failure. Naloxone administration increased heart rate, mean aortic pressure, first derivative of left ventricular pressure, cardiac output and myocardial contractility in pacing-induced congestive heart failure. These changes correlated significantly with basal plasma beta-endorphin levels and were accompanied by increases in plasma beta-endorphin and catecholamines after naloxone administration. However, unlike the hemodynamic and cardiac effects of naloxone, baroreflex function did not change after naloxone in dogs with congestive heart failure.

CONCLUSIONS

The increase in basal plasma beta-endorphin suggests that the endogenous opiate system is activated in left-sided congestive heart failure. Because naloxone improves the systemic hemodynamics and myocardial contractile function under this condition, the endogenous opioids appear to play an important role in mediating the myocardial depression that occurs in heart failure. However, the endogenous opiate system has no apparent effect on the regulation of baroreflex control in heart failure induced by rapid pacing.

Acupuncture heroin detoxification: a single-blind clinical trial

The increasing prevalence of HIV infection among injection drug users mandates the development of innovative treatments. While extensive clinical experience suggests that acupuncture detoxification is both safe and acceptable to those in withdrawal, little research has been conducted to assess its efficacy as a treatment modality. In this first controlled study of acupuncture heroin detoxification, 100 addicted persons were randomly assigned, in a single-blind design, to the standard auricular acupuncture treatment used for addiction or to a "sham" treatment that used points that were geographically close to the standard points. Attrition was high for both groups, but subjects assigned to the standard treatment attended the acupuncture clinic more days and stayed in treatment longer than those assigned to the sham condition. Additionally, attendance varied inversely with self-reports of frequency of drug use, suggesting that those with lighter habits found the treatment modality more helpful. Limitations of the study are discussed.

Analgesics abuse: theoretical and practical considerations

Three important issues must be addressed in any attempt to determine whether combination painkillers play a role in analgesic nephropathy. The first issue, namely that of a causal link between the combination itself and nephrotoxicity, has never been adequately documented. On the contrary, there is much evidence that the combination as such has no influence whatsoever. The cause of the nephrotoxicity is most likely the painkilling mechanism, i.e. the antagonism to prostaglandins; the most potent prostaglandin-antagonists, the non-steroidal anti-inflammatory drugs, whether used in combination or singly, also most frequently cause renal pathology. The second issue, i.e. the safety of combination painkilling drugs in comparison with that of single substances, is intimately bound up with the advantages of the former with respect to both activity and the activity-side-effects ratio. The third issue, abuse, should be recast in a broader context. The central element here is not the painkilling drug but rather the labile personality of the user in conjunction with a more or less stressful environment in which a wide variety of drugs and stimulants are available and taken for better 'coping'. To a great extent analgesics abuse can be prevented by information (i.e. social medicine). In a broader perspective, man experiences considerable difficulty adapting to the sweeping social, technological and ideological changes of recent decades, and this transition contributes in no small measure to the analgesics problem. It should be a priority of government to find remedies for this state of affairs.

Plasma beta-endorphin levels in chronic alcoholics

In order to test the possible relationship between the chronic consumption of alcohol and the opioid system, we have measured the plasma levels of beta-endorphin in a group of 31 alcoholic patients and compared the results with those of a control group of 16 subjects. Our results show that chronic consumption of alcohol induces a significant decrease in beta-endorphin (beta-end) plasma levels regardless of either the disease suffered by the alcoholic patient or of the time of abstinence studied (one month maximum). Thus we believe that the beta-end decrease may well be due to the patients' alcoholism and that it might be mediated by the tetrahydroisoquinoline system, or be a cause of alcoholism rather than a consequence.

Naloxone-induced abdominal distress in the horse

Endogenous opioid peptides have been implicated in the regulation of pain perception, behaviour, gastrointestinal activity and other physiological responses. However, the functional role of these peptides in the horse has yet to be elucidated. The opioid antagonist, naloxone, is often administered to infer endogenous opioid effects. In the present study, naloxone (0.75 mg/kg bodyweight) was administered to eight Thoroughbred racehorses and a number of behavioural and autonomic responses were measured. Naloxone produced rapid onset diarrhoea, restlessness, abdominal checking, tachycardia, tachypnoea, paradoxical yawning and diaphoresis. These responses described an acute abdominal distress syndrome similar to spasmodic colic. Results from this study suggest that, in the horse, endogenous opioids: 1) influence behaviour, 2) modify intestinal activity and sensation, and 3) if perturbed, may be involved in pathophysiology of colic.

Determination of leucine enkephalin and methionine enkephalin in equine cerebrospinal fluid by microbore high-performance liquid chromatography and capillary zone electrophoresis coupled to tandem mass spectrometry

The performance of microbore high-performance liquid chromatography and capillary zone electrophoresis, both equipped with on-line tandem mass spectrometric detection capability, was evaluated critically for the determination of endogenous amounts of leucine enkephalin and methionine enkephalin in equine cerebrospinal fluid. Using an identical sample clean-up and enrichment procedure, capillary zone electrophoresis-mass spectrometry is limited in its concentration detection capacity owing to its much smaller injection volume. Leucine enkephalin was identified in post-mortem equine cerebrospinal fluid at the 1-5 ng/ml level by liquid chromatography-mass spectrometry.

The role of endogenous opioids in congestive heart failure: effects of nalmefene on systemic and regional hemodynamics in dogs

We studied the role of endogenous opiates and their interrelationships with the sympathetic nervous system in an experimental preparation of right-sided congestive heart failure (CHF) produced by surgical tricuspid avulsion and progressive pulmonary arterial constriction. Three groups of dogs with CHF and one group of sham-operated dogs were studied. One group of dogs with CHF was given normal saline as pretreatment, while the other two groups were pretreated with either propranolol alone (beta-blockade) or propranolol plus prazosin (alpha- plus beta-blockade). CHF was characterized by weight gain, ascites, elevated right atrial pressure, tachycardia, and reduced cardiac output. Compared with sham-operated animals, animals with CHF exhibited significantly higher baseline levels of plasma beta-endorphin and cortisol. Furthermore, only the animals with CHF responded to the opiate receptor-antagonist nalmefene with significant increases in plasma beta-endorphin, cortisol, and adrenocorticotropic hormone. Administration of nalmefene increased aortic blood pressure, cardiac output, left ventricular dP/dt and dP/dt/P, and blood flow to the myocardium, skeletal muscle, and kidneys in dogs with CHF, but had no appreciable effects in sham-operated dogs. beta-Receptor blockade abolished the increase in cardiac output, left ventricular performance, and blood flow produced by nalmefene, but had no effect on the pressor response to nalmefene. The increase in mean aortic pressure in the beta-blockade group was accompanied by an increase in skeletal muscle vascular resistance. Addition of prazosin in the alpha- plus beta-blockade group abolished the increases in mean aortic pressure and skeletal muscle vascular resistance, suggesting that the changes after propranolol probably resulted from unmasking of alpha-receptor-mediated vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of immunoreactive beta-endorphin in vitro from pituitaries of young and old male rats

The release of immunoreactive beta-endorphin (IR-BE) in vitro from the anterior pituitary (AP) and the neurointermediate lobe of the pituitary (NIL) from old male rats was significantly greater than from the AP and NIL from young male rats. In addition, the content and concentration of IR-BE in the AP and NIL was significantly greater in old than in young male rats, as was the concentration of IR-BE in the plasma. Chromatographic analysis revealed that in old male rats, the increase in IR-BE contained in and released by the AP and NIL, and found in the plasma, represented an increase in a peptide which coeluted with beta-endorphin rather than beta-lipotropin. These data suggest that both the AP and the NIL contribute to the elevation in plasma levels of IR-BE observed in old male rats, and that the increase in pituitary and plasma IR-BE in old male rats represents an increase in beta-endorphin.

Opioid biology: the next set of questions

A range of biologically different opioid peptides are synthesised as components of three distinct precursors, pro-opiomelanocortin, proenkephalin, and prodynorphin. They interact with a number of receptors which have so far been characterised as mu, delta, kappa, sigma, and epsilon. It is unclear which ligands bind to which receptors under physiological circumstances, but preferential in vitro interactions include enkephalins with delta receptors, dynorphin with kappa receptors, and beta-endorphin with epsilon receptors. Post-translational processing determines which of several opioid products are produced from each precursor, but the identity of the enzymes involved and regulation of processing is unknown. Opioid involvement in the neuroendocrine and cardiovascular systems is reviewed. Naloxone-sensitive opioid mechanisms are implicated in the control of gonadotrophin and adrenocorticotropic hormone secretion and in the hypotension of various types of shock. The investigation of possible dynorphin involvement in neurohypophysial function is taking place because vasopressin and dynorphin A (1-8) have been shown to coexist in the neurosecretory vesicles of magnocellular neurons.