Enkephalins have a direct positive inotropic effect on cultured cardiac myocytes.

Abstract

Enkephalins have peripheral vascular effects, and enkephalinergic innervation of the heart has been reported. To determine whether enkephalins have direct effects on myocardium, we studied the effects of [Leu5]Enkephalin has been reported to increase the norepinephrine-stimulated positive chronotropic response and 45Ca uptake in guinea pig (4). Furthermore, circulatory anatomy is such that enkephalins released from adrenal medulla flow directly through the vena cava to the right heart and pulmonary circulation where they could exert direct effects. Their short half-life, however, may limit the concentrations reaching brain centers that could affect cardiovascular responses (5).There is substantial evidence that opiates and opioid peptides have cardiovascular effects. Morphine has been reported to decrease (6)(7)(8) or to increase (9, 10) myocardial contractility. However, the specificity of some of the cardiovascular effects of peripherally injected morphine and enkephalins has been questioned, and their mediation by sympathetic nerve activation (9, 10) and histamine release from mast cells (11) has been reported.Whether or not circulating or prejunctionally released opioid peptides exert a direct postjunctional effect on the cardiac myocyte is unknown. The existence of direct effects of opioid peptides on the heart cannot be concluded from studies with preparations containing intact nerve endings and catecholamine stores. Thus, a detailed analysis of the direct cardiac effects of enkephalins may best be undertaken in a preparation devoid of intact neural elements. We report here the effects of enkephalins and enkephalin-like peptides Leu- MATERIALS AND METHODSTissue Culture. Primary monolayer cultures of beating chicken embryo ventricular cells were prepared as described (12). Briefly, fragments of embryonic chicken ventricules 10 days in ovo were dissociated by repeated cycles oftrypsinization. The resulting cell suspension (4 x 105 cells per ml) was plated in 100-mm culture dishes. The medium consisted of a bicarbonate-buffered physiological salt solution containing 40% medium 199 (GIBCO), 6% fetal calf serum, and 54% balanced salt solution containing glucose. Final concentrations in the culture medium were 144 mM Na, 4.0 mM K, 0.97 mM Ca, 18 mM HCO3, 0.8 mM Mg, and 131 mM Cl. Cultures were incubated in humidified 5% C02/95% air at 37°C. Spontaneously and synchronously contracting confluent monolayers were present by 3 days in culture, at which time experiments were performed. For contractility and ion-flux experiments, cells were grown on 25-mm circular glass coverslips.Contractility Measurements. Changes in the position of a cell or attached microsphere border in a monolayer were assessed by the use of an optical-video system as described (12). Briefly, a glass coverslip with attached cells was continuously superfused in a chamber provided with inlet and exit ports. The chamber was placed on the stage of an inverted phase-contrast microscope (Leitz Diavert). The cells were magnified with a x40 ob...

Enkephalins increase cyclic adenosine monophosphate content, calcium uptake, and contractile state in cultured chick embryo heart cells.

“…10 M DALA stimulated adenylate cyclase activity 1.63-fold, a response nearly as great as the response to 1 MM isoproterenol in the same preparation (Table I). IBMX at 100 AM did not alter the stimulation of adenylate cyclase activity by DALA.…”

“…The positive inotropic effect of these compounds was antagonized by the opiate antagonist naloxone but not by fl-adrenergic, a-adrenergic, Hi, or H2 antagonists (10). Specific opiate receptors were characterized by ligand binding techniques in cell membranes.…”

Opioids in Pain and Cardiovascular Responses: Overview of Common Features

“…Opioid cardiovascular effects at peripheral sites for the most part echo their centrally-mediated reduction of blood pressure in patients (Lowenstein, et al, 1969) or animals (Lowenstein, et al, 1972) with elevated resting sympathetic tone. Although opioids have been reported in preparations of isolated myocytes to enhance contractility (Laurent, et al, 1985(Laurent, et al, , 1986, they reduce catecholamine-induced contractility and chronotropy in models with intact cardiac innervation (Ruth and Eiden, 1984;Clo, et al, 1985;Caffrey, et al, [b], 1986Liang, et al, 1987). This inhibitory effect is most striking when probed using the /3-adrenergic agonist isoproterenol (Ruth and Eiden, 1984;Clo, et al, 1985;Caffrey, et al, 1986) and is concurrent with a reduction in the calcium infiux that normally follows isoproterenol treatment (Ruth and Eiden, 1984;Laurent, et al, 1986).…”

Delta-opioid augments cardiac contraction through β-adrenergic and CGRP-receptor co-signaling

“…As of yet, there has not been a study to demonstrate whether cardiac muscle cells express DOR immunoreactivity. However, in the absence of DOR expression in myocytes, δ-opioid agonist-enhanced myocyte contractility (21) and intracellular Ca 2+ mobilization (11, 34) in cardiomyocyte cultures strongly indicating that DOR agonist mediates indirect cardiac inotropism via the activation of ICA cells in ventricular myocardium. The ICA cell was discovered by Huang et al in 1996 (12) and confirmed by Ebert & Thompson (6).…”