Inhibitory action of opioid peptides on ouabain-sensitive Na+-K+ and Ca2+-dependent ATPase activities in bovine cardiac sarcolemma

The Role of Endogenous Opioids in Cardioprotection

The opioid system involves opioid receptors (OPRs) and endogenous opioid peptides.This chapter will focus on the distribution of OPRs in the cardiovascular system, the expression pattern in the heart, the activation by opioid peptides, and the effects of OPRs activation with potential relevance in cardiovascular performance. In the heart, OPRs are co-expressed with beta adrenergic receptors (β-ARs) in the G-protein-coupled receptor (GPCR) superfamily, functionally cross-talk with β-Ars and modify catecholamine-induced effects. They are involved in cardiac contractility, energy metabolism, myocyte survival or death, vascular resistance. The effects of the opioid system in the regulation of systemic circulation at both the central and peripheral level are presented. The pathways are discussed under physiological (i.e., aging) and pathological conditions (atherosclerosis, heart failure, essential hypertension, ischemic stress). Stimulation of OPRs not only inhibits cardiac excitation-contraction coupling, but also protects the heart against hypoxic and ischemic injury. An enhanced sensitivity to opioids of endocrine organs and neuronal systems is operative in hypertensive patients. The opioid system can be pharmacologically engaged to selectively mimic these responses via cardiac and nervous signaling. The clinical opportunities for the use of cardioprotective effects of opioids require future investigations to provide more specific details of the impact on cardiac performance and electrophysiological properties.

Acute effects of beta-endorphin on cardiovascular function in patients with mild to moderate chronic heart failure

BACKGROUND

Cardiomyocytes produce opioid peptides and receptors. beta-Endorphin is increased in the plasma of patients with congestive heart failure (CHF). We evaluated whether an intravenous infusion of beta-endorphin exerted any effect on cardiovascular function and on the neurohormonal milieu in patients with mild to moderate CHF.

METHODS

According to a double-blind, placebo-controlled design, 10 patients (5 men, age 46.9 +/- 8.2 years [mean +/- SD]) with CHF and New York Heart Association functional class II to III received, in random order, 1-hour intravenous infusion of beta-endorphin (500 microg/h) and, on a separate occasion, received placebo and underwent echocardiographic and laboratory measurements at baseline and during infusions.

RESULTS

beta-Endorphin significantly increased left ventricular ejection fraction (LVEF) (P =.0001) and stroke volume (P =.0001), and reduced systemic vascular resistance (P =.031) in patients with CHF. These changes were paralleled by a significant increase in plasma levels of glucagon (P =.0001), GH (P =.0001), and IGF-1 (P =.0001), and a significant decrease in plasma levels of endothelin (P =.0001) and catecholamines (P =.01). No hemodynamic and neurohormonal changes were observed during the placebo study in any patient.

CONCLUSIONS

We conclude that a short-term, high dose infusion of beta-endorphin improves LVEF, reduces systemic vascular resistance, blunts the neurohormonal activation, and stimulates the GH/IGF-1 axis in patients with mild to moderate CHF.

Emprego do propofol, isofluorano e morfina para a anestesia geral de longa duração em bezerros

Foram estudadas características da bioquímica do sangue, da pressão arterial e da freqüência de pulso de 12 bezerros mantidos sob anestesia por 13 horas, utilizando-se propofol para a indução e isofluorano para manutenção, associados à administração de morfina intra-tecal. Os valores de freqüência de pulso, pressão arterial e glicemia apresentaram pequenas variações e se mantiveram próximos dos valores de referência para bezerros anestesiados. Ao longo do período de anestesia houve aumento significativo, mas discreto, do hematócrito, hemoglobina, pCO2, CO2 total, bicarbonato e potássio. O pH do sangue, pO2, Na+ e Ca++ apresentaram reduções significativas. Este protocolo anestésico foi seguro para a manutenção de bezerros anestesiados por período prolongado.

The involvement of sodium ions in the positive inotropic effect of naloxone

1. The opiate antagonist naloxone induces a positive inotropic effect in isolated cardiac muscles. 2. The response to naloxone is dependent on the presence of Na+ in the bathing solution, is proportional to the rate of electrical stimulation, and increased in the presence of veratridine. 3. Lowering [K+]o to 50% augments the response, while complete removal of K+ from the extracellular solution attenuates the response to naloxone. 4. Maximal concentration of naloxone decreases the inotropic effect of the cardiac glycoside ouabain. 5. The results indicate the involvement of intracellular sodium accumulation in the positive inotropic effect of naloxone, probably through the inhibition of the sarcolemmal Na(+)-K+ pump.

Kappa and delta opioid receptor stimulation affects cardiac myocyte function and Ca2+ release from an intracellular pool in myocytes and neurons

We investigated the effects of mu, delta, and kappa opioid receptor stimulation on the contractile properties and cytosolic Ca2+ (Cai) of adult rat left ventricular myocytes. Cells were field-stimulated at 1 Hz in 1.5 mM bathing Ca2+ at 23 degrees C. The mu-agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (10(-5) M) had no effect on the twitch. The delta-agonists methionine enkephalin and leucine enkephalin (10(-10) to 10(-6) M) and the kappa-agonist (trans-(dl)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclo-hexyl]- benzeneacetamide)methanesulfonate hydrate (U-50,488H; 10(-7) to 2 x 10(-5) M) had a concentration-dependent negative inotropic action. The sustained decrease in twitch amplitude due to U-50,488H was preceded by a transient increase in contraction. The effects of delta- and kappa-receptor stimulation were antagonized by naloxone and (-)-N-(3-furyl-methyl)-alpha-normetazocine methanesulfonate, respectively. In myocytes loaded with the Ca2+ probe indo-1, the effects of leucine enkephalin (10(-8) M) and U-50,488H (10(-5) M) on the twitch were associated with similar directional changes in the Cai transient. Myofilament responsiveness to Ca2+ was assessed by the relation between twitch amplitude and systolic indo-1 transient. Leucine enkephalin (10(-8) M) had no effect, whereas U-50,488H (10(-5) M) increased myofilament responsiveness to Ca2+. We subsequently tested the hypothesis that delta and kappa opioid receptor stimulation may cause sarcoplasmic reticulum Ca2+ depletion. The sarcoplasmic reticulum Ca2+ content in myocytes and in a caffeine-sensitive intracellular Ca2+ store in neurons was probed in the absence of electrical stimulation via the rapid addition of a high concentration of caffeine from a patch pipette above the cell. U-50,488H and leucine enkephalin slowly increased Cai or caused Cai oscillations and eventually abolished the caffeine-triggered Cai transient. These effects occurred in both myocytes and neuroblastoma-2a cells. In cardiac myocyte suspensions U-50,488H and leucine enkephalin both caused a rapid and sustained increase in inositol 1,4,5-trisphosphate. Thus, delta and kappa but not mu opioids have a negative inotropic action due to a decreased Cai transient. The decreased twitch amplitude due to kappa-receptor stimulation is preceded by a transient increase in contractility, and it occurs despite an enhanced myofilament responsiveness to Ca2+. The effects of delta and kappa opioids appear coupled to phosphatidylinositol turnover and, at least in part, may be due to sarcoplasmic reticulum Ca2+ depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Heterogeneity of immunoreactive dynorphin B-like material in human, rat, rabbit and guinea-pig heart

Immunoreactive dynorphin B-like material (ir-dyn B) was detected in acetic acid extracts of human atrial specimens and of rat, rabbit and guinea-pig atria and ventricles by a validated radioimmunoassay. Levels were high in rabbit atrium (66.76 +/- 7.04 pmol/g) but lower and superimposable in human and rat atria (28.18 +/- 3.20 and 30.22 +/- 2.45 pmol/g, respectively). Gel permeation chromatography revealed ir-dyn B eluting close to column exclusion and in forms with an apparently higher molecular weight than authentic dyn B in human and rat samples. In contrast, almost all the immunoreactivity from rabbit and guinea-pig acetic extracts eluted as a single peak in the region of standard dyn B. Reverse-phase high performance liquid chromatography of the pooled gel chromatography fractions of this peak showed up a molecular form with the same retention time as authentic dyn B and a second minor peak of unknown immunoreactive material eluting three fractions earlier. Digestion with carboxypeptidase B excluded the hypothesis that this latter could be dyn B-Arg14. Therefore, it might be a metabolite of endogenous dyn B recognized by the antibody used in this study.

Effect of morphine on Na+,K(+)-ATPase from homogenate of synaptosomes and of synaptic membrane of rat cerebral cortex

Effects of morphine on noradrenaline release from rat cerebrocortical synaptosomes and on the Na+,K(+)-ATPase activity in homogenates of synaptosomes and of synaptic membranes were examined. Both morphine (10(-3)-10(-5) M) and methionine-enkephalin (M-Enk; 10(-5) M) inhibited the enhanced [3H]noradrenaline [( 3H]NA) release evoked by high concentrations of K+ from synaptosomes and these inhibitory actions were antagonized by naloxone (10(-4), 10(-5) M). Morphine (10(-3)-10(-5) M) and M-Enk (10(-5) M) stimulated the Na+,K(+)-ATPase activity in homogenates of synaptosomes but not of synaptic membranes in the incubation medium containing 2.2 X 10(-6)-4.7 X 10(-7) M free Ca2+ and these stimulatory effects were antagonized by naloxone. In homogenates of synaptic membranes, the same concentrations of morphine and M-Enk stimulated the Na+,K(+)-ATPase activity suppressed by FeCl2 (5 X 10(-7) M) but not by CuCl2 nor ZnCl2, and these stimulatory effects were antagonized by naloxone. Significant levels of Fe2+ were liberated from synaptosomes during the preparation of synaptic membrane using distilled water. These results suggest that both morphine and M-Enk stimulate the suppressed Na+,K(+)-ATPase activity by interacting with Fe2+ at opioid receptor sites, and they may play a role in the suppression of membrane depolarization and/or the release of NA through their stimulatory action on the Na+,K(+)-ATPase activity probably suppressed by Fe2+ in the rat cerebral cortex.

Inhibition of noradrenaline release from cerebrocortical synaptosomes and stimulation of synaptosomal Na+,K(+)-ATPase activity by morphine in rats

The effects of morphine on noradrenaline (NA) release from rat cerebrocortical synaptosomes and on the synaptosomal Na+,K(+)-ATPase activity were determined. Morphine (10(-3)-10(-5) M) caused a dose-related inhibition of enhanced prelabelled [3H]NA release evoked by a high concentration of K+ from synaptosomes and this inhibitory action of morphine was antagonized by the specific antagonist naloxone (10(-4), 10(-5) M). Morphine dose-dependently stimulated the synaptosomal Na+,K(+)-ATPase activity but not Ca2(+)-ATPase activity in the incubation medium containing 2.2 x 10(-6)-4.7 x 10(-7) M free Ca2+, and this stimulatory effect was antagonized by naloxone. These results suggest that morphine may have some role in the suppression of membrane depolarization and/or the release of NA through its stimulatory action on the Na+,K(+)-ATPase activity in rat cerebral cortex.

Opioid receptors in rat cardiac sarcolemma: effect of phenylephrine and isoproterenol

The present study demonstrates the presence of opioid receptors in the rat cardiac sarcolemma isolated by the hypotonic LiBr-shock procedure. Opioid binding was measured by using [3H]U69 593, [3H](2-D-penicillamine,5-D-penicillamine)enkephalin ([3H]DPDPE) or [3H][D-Ala2,MePhe4,Gly-(ol)5]enkephalin ([3H]DAGO) as selective radioligands for K, delta and mu opioid receptors, respectively. Both the K- and delta-selective ligands exhibited highly specific (75-86%) binding, saturable at a concentration of about 20 nM. No specific binding for the selective agonist DAGO was observed. A marked increase in both [3H]U69 593 and [3H]DPDPE binding was observed after incubation of the sarcolemma with the alpha-adrenoceptor agonist phenylephrine or with the beta-adrenoceptor agonist isoproterenol. These stimulatory effects were associated with an increase in the Bmax values, a decrease in the Kd values, and were completely antagonized by the respective antagonists phentolamine and propranolol.

Endogenous opiates: 1987

This paper is the tenth installment of our annual review of the research during the past year involving the endogenous opiate system. It covers the nonanalgesia and behavioral studies of the opiate peptides published in 1987. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal activity; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical activity; locomotor activity; sex, pregnancy, and development; immunology and cancer; and other behavior.

Opioids stimulate sarcolemmal NAD(P)H-vanadate dehydrogenase activity

The present study demonstrates that the bovine cardiac sarcolemma possesses an NAD(P)H dehydrogenase activity which is able to oxidize both NADH and NAD(P)H in the presence of vanadate as an electron acceptor. The NADH dehydrogenase activity was significantly higher than the NAD(P)H dehydrogenase activity and both of them were almost completely inhibited by superoxide dismutase and atebrin and markedly reduced by the addition of the protonophore 2,4-dinitrophenol. The incubation of the sarcolemma in the presence of 10(-10), 10(-9), 10(-8) M methionine-enkephalin, a prevalent delta-opioid receptor agonist, or dynorphin A (1-17), a prevalent kappa-receptor agonist, produced a dose-dependent increase in the NAD(P)H dehydrogenase activity, with 10(-10) and 10(-9) M dynorphin A (1-17) more effective than the corresponding doses of methionine-enkephalin. The preincubation of the sarcolemma in the presence of superoxide-dismutase, atebrin or 2,4-dinitrophenol strongly inhibited the opioid-stimulated dehydrogenase activity. The stimulatory action elicited by 10(-8) M methionine-enkephalin or dynorphin A (1-17) was completely antagonized by 10(-8) M naloxone or Mr 1452, respectively, whilst 10(-8) M naloxone exerted only a partially antagonistic action against the effect produced by 10(-8) M dynorphin A (1-17), significantly more accentuated than the action of 10(-8) M Mr 1452 versus the same dose of methionine-enkephalin.