Influence of extracellular magnesium on the contractile and endothelium-dependent dilatory responses of feline mesenteric arteries.

To clarify the effect of extracellular magnesium on the vascular reactivity of feline isolated mesenteric arteries, the effects of slight alterations in the extracellular magnesium concentration on the contractile and endothelium-dependent dilatory responses were investigated in vitro. The contractions, induced by noradrenaline 10(-8)-10(-5) M, were not affected in the mesenteric artery at low extracellular magnesium (0.8 mM versus to the normal, 1.2 mM). High (1.6 and 2.0 mM) magnesium exerted a modest inhibitory effect on the contractile responses. This depression of the contraction was accompanied with a significant shift to the right in the EC50 value for noradrenaline. The endothelium-dependent relaxations induced by acetylcholine 10(-8)-10(-5) M, were inhibited by high (1.6 and 2.0 mM) magnesium. Lowering of the extracellular magnesium concentration to 0.8 mM, however, failed to alter the dilatory potency of acetylcholine. The depression of the dilatory responses was also accompanied with a shift to the right in the EC50 values for acetylcholine. The present results show, that contractions and endothelium-dependent relaxations of the mesenteric artery are modulated by the extracellular magnesium asymmetrically: slight magnesium deficiency does not affect these responses, whereas elevation of the concentration of this ion inhibits both processes. Extracellular magnesium probably affects rather the binding of these contractile and endothelium-dependent dilatory agonists to their receptors than the calcium influx into the endothelial- and smooth muscle cells in this vessel.     

Ethanol Inhibition of N-Methyl-D-Aspartate-Stimulated Endogenous Dopamine Release from Rat Striatal Slices: Reversal by Glycine

N-Methyl-D-aspartate stimulated a concentration-dependent release of endogenous dopamine from rat striatal slices. The threshold for activation was between 10 and 25 microM and reached a maximum at 1 mM. Release was completely blocked by magnesium or tetrodotoxin. Ethanol (10-200 mM) significantly inhibited the N-methyl-D-aspartate-stimulated release of dopamine by 20-45%, with half-maximal inhibition occurring at approximately 21 mM. Addition of ethanol plus increasing concentrations of magnesium resulted in a greater inhibition of N-methyl-D-aspartate-stimulated dopamine release than that observed with magnesium alone. However, this effect appeared to be due to a noninteractive additive effect of the two antagonists, as the IC50 value for magnesium inhibition was not significantly altered by ethanol. Glycine, which had no effect on dopamine release by itself, completely reversed the inhibitory effects of ethanol (25 mM) at low micromolar concentrations. These results suggest that ethanol may produce its effects in striatal slices by interfering with a glycine modulatory site of the N-methyl-D-aspartate receptor-ionophore complex.     

The effect of myosin ATPase inhibition on metabolic and functional recovery of isolated rat heart after global ischemia

The effect of myosin ATPase inhibitor, 2,3-butanedione monoxime (BDM) used in the range of concentrations 1.25–10.0 mM), on recovery of functions of isolated rat heart subjected to normothermic (37 °C) total ischemia for 35 min has been investigated. BDM perfusion was performed at a flow rate of 4 ml/min during 5 min before ischemia (BDM-I) or before 25-min reperfusion (BDM-R). Control hearts were perfused with Krebs solution at the same flow rate. The highest functional recovery of heart and coronary vessels was observed during infusion of 2.5 mM BDM before ischemia. At the end of reperfusion ATP and phosphocreatine (PCr) content in hearts of this group was significantly higher whereas the level of lactate was two times lower than in control; total creatine content (ΣCr) did not differ from the initial level. Similar but less pronounced changes in the improvement of aerobic metabolism and maintenance of ΣCr after reperfusion were also observed in the case of infusion of 2.5 mM BDM before reperfusion. They were consistent with reduced recovery of functions of heart and coronary flow compared with these parameters observed in the BDM-I group. 2.5 mM BDM caused almost 2-fold decrease in release of cardiac lactate dehydrogenase into myocardial perfusate in the BDM-I and BDM-R groups (compared with control); this suggests lower damage of cell membranes. These results suggest that improvement of energy supply of postischemic cardiomyocytes may be a key factor determining cardioprotector effectiveness of short-term administration of BDM before ischemia.     

Antiarrhythmic effect of magnesium sulfate against occlusion-induced arrhythmias

The antiarrhythmic effect of magnesium sulfate (Mg) as well as the hemodynamics were studied using the coronary ligation and reperfusion models in rats.In the study on coronary ligation arrhythmia, i.v. administration of Mg (0.6, 2, 6, 20 and 60 \sgmaelig;mol) was conducted at 5 min after coronary ligation. Mg had an action to decrease the total number of premature ventricular contraction (PVC), the duration of ventricular tachycardia (VT), the frequency of VT and ventricular fibrillation (Vf) and the mortality ratio for 30 min after coronary ligation. In the 6-60 \sgmaelig;mol groups, significant antiarrhythmic action (p < 0.01 vs. control) was attained.In the study on reperfusion arrhythmia, i.v. administration of Mg (20, 60 and 200 \sgmaelig;mol) was conducted at 4 min after coronary ligation, and at 1 min after ligation, the coronary artery was reperfused. Mg had an action to decrease the frequency of Vf, the mortality ratio and the duration of VT and Vf and to extend the interval between the initiation of reperfusion and the occurrence of VT and Vf for 10 min after reperfusion. In the 200 \sgmaelig;mol group, significant antiarrhythmic action (p < 0.05 vs. control) was attained. Administration of Mg decreased the heart rate and blood pressure.We concluded that Mg can control myocardial ischemia-induced and reperfusion-induced arrhythmia and that sudden cardiac death which occurs as a result of arrhythmia can be prevented.     

The role of alpha 1-adrenergic stimulation in inositol phosphate metabolism during post-ischaemic reperfusion.

The aim of this study was to elucidate the mechanism of enhanced inositol phosphate metabolism during reperfusion. Inositol phosphate stores were prelabelled by perfusing isolated rat hearts for 1 h with [3H]inositol (1.5 microCi/ml). LiCl (10 mM) and prazosin (0.3 microM) were subsequently added 15 min before (i) 20 min control perfusion; (ii) 20 min normothermic ischaemic cardiac arrest (NICA); (iii) 20 min NICA followed by 1 min reperfusion. The ventricles were freeze-clamped before determination of isotopical incorporation of [3H]inositol into the inositol phosphates (Dowex anion exchange chromatography) and InsP3 levels (Amersham InsP3 assay system). In addition, noradrenaline release into the perfusate was also assessed (HPLC and electrochemical detection). The results showed: (i) increased noradrenaline release into the perfusate immediately after the onset of reperfusion; (ii) significant depression of [3H]inositol incorporation into inositol phosphates and InsP3 levels after 20 min NICA; (iii) reperfusion caused an immediate significant increase in isotopical incorporation of [3H]inositol into inositol phosphates as well as InsP3 levels; (iv) the alpha 1-adrenergic blocker, prazosin (0.3 microM), completely inhibited the reperfusion-induced increase in inositol phosphate metabolism. These observations suggested that increased alpha 1-adrenergic receptor stimulation by noradrenaline might be responsible for the stimulation of ventricular inositol phosphate metabolism during postischaemic reperfusion.     

Effect of beta-hydroxybutyrate and acetoacetate on insulin and glucagon secretion from perfused rat pancreas

To elucidate the physiological significance of ketone bodies on insulin and glucagon secretion, the direct effects of beta-hydroxybutyrate (BOHB) and acetoacetate (AcAc) infusion on insulin and glucagon release from perfused rat pancreas were investigated. The BOHB or AcAc was administered at concentrations of 10, 1, or 0.1 mM for 30 min at 4.0 ml/min. High-concentration infusions of BOHB and AcAc (10 mM) produced significant increases in insulin release in the presence of 4.4 mM glucose, but low-concentration infusions of BOHB and AcAc (1 and 0.1 mM) caused no significant changes in insulin secretion from perfused rat pancreas. BOHB (10, 1, and 0.1 mM) and AcAc (10 and 1 mM) infusion significantly inhibited glucagon secretion from perfused rat pancreas. These results suggest that physiological concentrations of ketone bodies have no direct effect on insulin release but have a direct inhibitory effect on glucagon secretion from perfused rat pancreas.     

The Effect of Pentamidine on Ribosomes of the Parasitic Flagellate Crithidia (Strigomonas) oncopelti

SYNOPSIS. The effects of the trypanocidal drug, pentamidine, on the ribosomal fraction of Crithidia oncopelti have been investigated in vivo and in vitro. Addition of the drug to ribosomes isolated from the organisms led to release of magnesium and some protein from the particles. The ribosomes were aggregated when significant release of magnesium had occurred. Loss of magnesium was dependent on density of the ribosomal suspension but not on the magnesium concentration. Spermine, propamidine and stilbamidine had a similar effect in releasing magnesium from the particles. The majority of pentamidine (80%) or stilbamidine (70%) added to suspensions of ribosomes became bound to the particles and could not readily be removed by washing. Stilbamidine was not released in the presence of adenosine triphosphate. Slight stabilisation of 80S particles was observed in the presence of pentamidine and absence of magnesium.
Incubation of organisms in the presence of growth-inhibitory concentrations of pentamidine led to no significant change in the ribosomal content of the organisms, even when complete inhibition of the ability to incorporate C¹⁴-glycine into nucleic acid and protein had occurred. There was no significant decrease in the magnesium content of ribosomes isolated from organisms incubated in the presence of pentamidine.     

Effect of ascorbic acid on release of acetylcholine from synaptic vesicles prepared from different species of animals and release of noradrenaline from synaptic vesicles of rat brain.

Low concentrations of L-ascorbic acid caused release of acetylcholine from isolated synaptic vesicles (rat, guinea-pig and rabbit) in the presence of 2mM ATP, 2 mM MgCl₂ and 10^?5 M CaCl. The half maximum effect was obtained with about 2 to 2.5 ωM L-ascorbic acid, and the effect was inhibited by addition of 1mM EGTA. The release of noradrenaline from rat synaptic vesicles was also enhanced by L-ascorbic acid, but the concentration for half maximal stimulation was about 20 ωM, indicating that noradrenaline release was less sensitive to L-ascorbic acid than acetylcholine release. The physiological function of L-ascorbic acid in the brain is discussed in relation to release of transmitters.     

Metabolic basis for contractile dysfunction following chronic partial bladder outlet obstruction in rabbits

Our study is designed to correlate nitrite concentration, an index of nitric oxide (NO) release with mast cell peroxidase (MPO), a marker of cardiac mast cell degranulation and cardioprotective effect of ischaemic preconditioning in isolated perfused rat heart subjected to 30 min of global ischaemia and 30 min of reperfusion. Ischaemic preconditioning, comprised of four episodes of 5 min global ischaemia and 5 min of reperfusion, markedly reduced the release of lactate dehydrogenase (LDH) and creatine kinase (CK) in coronary effluent and incidence of ventricular premature beats (VPBs) and ventricular tachycardia and fibrillation (VT/VF) during reperfusion phase. Ischaemia-reperfusion induced release of MPO was markedly reduced in ischaemic preconditioned hearts. Increased release of nitrite was noted during reperfusion phase after sustained ischaemia in preconditioned hearts as compared to control hearts. No alterations in the release of nitrite was observed immediately after ischaemic preconditioning. However, ischaemic preconditioning markedly increased the release of MPO prior to global ischaemia. It is proposed that cardioprotective and antiarrhythmic effect of ischaemic preconditioning may be ascribed to degranulation of cardiac mast cells. Depletion of cytotoxic mediators during ischaemic preconditioning and consequent decreased release of these mediators during sustained ischaemia-reperfusion may be associated with preservation of structures in isolated rat heart responsible for NO release.     

Correction of disorders of electric stability of the heart and arrhythmia by using a synthetic analog of acetylcholine

It was shown in experiments on Wistar male rats that ethyl, 3/2, ethyl, 2/2, dimethylhydrazine propionate iodate (EDIHYP), a synthetic acetylcholine analogue, eliminates in situ the fall of the ventricular fibrillation threshold and the extrasystole observed on the background of vagal bradycardia in experimental myocardial infarction and postinfarction cardiosclerosis. The elimination of disturbed heart electric stability was not accompanied by cholinergic, negative chronotropic effect of the drug. In isolated heart, high concentrations of EDIHYP (10(-4) M) had negative chronotropic effect but lacked antiarrhythmic effect in local ischemia and reperfusion. The bradycardia induced by EDIHYP was absent and the antiarrhythmic effect was strikingly pronounced on the background of muscarinic receptors blockade with atropine. Thus EDIHYP realizes its antiarrhythmic effect not via muscarinic receptors but by some other way which requires studying by methods of molecular pharmacology.     

Stimulation of inositol phospholipid breakdown in pig brain miniprisms by carbachol and monoamines: effect of K+

1. The effects of carbachol, monoamines and K+ upon the rate of inositol phospholipid breakdown in pig brain miniprisms have been investigated. 2. In the striatum, carbachol (EC50 approx. 1 microM) and noradrenaline (EC50 approx. 25 microM) stimulated inositol phospholipid breakdown, whereas 5-hydroxytryptamine (1-1000 microM) was without effect. 3. The rate of inositol phospholipid breakdown was increased by raising the assay [K+] to greater than or equal to 40 mM. In the hippocampus and hypothalamus, a synergistic effect between K+ and carbachol was noted, whereas in the striatum, the effects were additive. 4. In striatal and hippocampal miniprisms, dopamine also increased inositol phospholipid breakdown, albeit only at high (greater than or equal to 1 mM) concentrations. Dopamine (1 mM) reduced the stimulation produced by noradrenaline (1 mM), suggesting that the effect of dopamine is due to a weak noradrenergic action of this catecholamine.     

Regulation by cations of adenylate cyclase activity in chicken tissues

The effects of magnesium and sodium ions on adenylate cyclase activity in plasma membranes from chicken heart and eggshell gland mucosa were studied. It was found that the increase in magnesium chloride concentration from 5 to 40 mM results in the stimulation (4.1-fold) of the adenylate cyclase activity. The increase in sodium chloride concentration up to 150 mM stimulated the enzyme activity 2-fold. The stimulation of adenylate cyclase by magnesium and sodium ions was less pronounced in the eggshell gland. GTP did not activate adenylate cyclase. The activating effect of magnesium and sodium ions was accompanied by the attenuation of the enzyme sensitivity to NaF, guanylyl imidodiphosphate and isoproterenol. Activation by guanylyl imidodiphosphate was completely abolished in the presence of 40 mM magnesium chloride. It is assumed that high concentrations of the salt promote subunit dissociation of the adenylate cyclase regulatory protein and its interaction with the catalytic subunit in the presence of endogenous nucleotides. The differences in the adenylate cyclase sensitivity to cations in chicken heart and eggshell gland mucosa correlate with the amount of pertussis toxin substrate.     

Effect of leu-enkephalin and the delta-sleep-inducing peptide, M (DSIP), on endogenous noradrenaline release by brain synaptosomes in the rat

Fluorometry was employed to measure the noradrenaline (NA) content in rat brain synaptosomes depending on the duration of incubation, depolarization effects (40 mM KCl or 1.5 mM ouabain), composition of the synaptosomal fraction and concentration of the peptides. The 10-minute incubation in a potassium medium of a suspension of light synaptosomes was used as an optimal test-system for studying the peptide action. Leu-enkephalin inhibited the depolarization-induced NA release. The effect was abolished by naloxone. The delta-sleep-inducing peptide (DSIP) did not influence the neurotransmitter release at concentrations of 10(-8)-10(-5) M. A mixture of amino acids imitating the amino acid composition of the DSIP influenced spontaneous release of NA. This effect is discussed in connection with the physiological action of the peptide on its intraventricular injection.     

The effect of zinc on reperfusion arrhythmias in the isolated perfused rat heart

Considerable evidence suggests that free radicals engendered by redox-active metals, particularly iron and copper, are causative agents in reperfusion injury following ischemia. This study demonstrates that perfusion of the isolated rat heart with a buffer containing zinc, a non-redox active metal similar to copper in its coordination chemistry, inhibits the development of ventricular arrhythmias during reperfusion. Zinc was employed as the bishistidine complex, Zn--His2, to maintain solubility and permeability. Zn--His2 exerted an antiarrhythmic activity as hearts spent a longer time in normal sinus rhythm and a shorter time in ventricular fibrillation during reperfusion following 10 min of regional ischemia. However, Zn--His2 also produced a negative inotropic and chronotropic effect, evident during equilibration and ischemia. In the course of experiments which began in Israel and continued in the U.S. it was necessary to use two different sources of rats. Hearts from the two sources manifested different sensitivities to the concentrations of Zn--His2, although their physiological effects were similar. Differential activity responses were noted for antiarrhythmic activity, negative inotropic and chronotropic properties, and toxicity. In both groups of untreated hearts the incidence of ventricular fibrillation after ischemia was 100%. Ventricular fibrillation was reduced to 17% at 37.5 microM Zn--His2 in the U.S.-bred rat hearts and to 9% at 200 microM Zn--His2 in those from Israel. These changes in Zn--His2 treated animals were accompanied by a decrease in lactate dehydrogenase release from the myocardium during reperfusion. None of the protective effects was due to histidine alone. These results indicate that zinc prevents ventricular arrhythmias during reperfusion following regional ischemia and may prevent membrane damage, possibly, by reduction of free radical formation.     

Differential presynaptic effects of hexachlorocyclohexane isomers on noradrenaline release in cerebral cortex.

To investigate presynaptic effects of hexachlorocyclohexane (HCH) isomers, the release of noradrenaline (NA) in brain tissue was analyzed using rat cerebral cortical slices preloaded with [3H]-NA. gamma-HCH (lindane) 50 microM significantly enhanced the [3H]-NA release evoked by 15-25 mM K+. alpha- and beta-HCH (50 microM) did not produce any significant effect on K(+)-evoked [3H]-NA release. delta-HCH (50 microM) induced a significant decrease of the 25 mM K(+)-evoked release of [3H]-NA. The effect of the gamma- and delta-HCH isomers on the presynaptic action of the alpha 2-agonist clonidine and the alpha 2-antagonist yohimbine was also studied. The presynaptic inhibitory effect of clonidine and the stimulatory effect of yohimbine on [3H]-NA release was attenuated by lindane and delta-HCH, respectively. These results are consistent with a presynaptic action of the HCH isomers on noradrenergic release processes.     

Chemical sympathectomy and diurnal fluctuations of noradrenaline calorigenic action in the rat

In the rat, in which a diurnal fluctuation of the sensitivity to noradrenaline was previously found, the effect of injected 6-hydroxydopamine (6-OHDA) was investigated. The heat production and catecholamines contents in the interscapular brown adipose tissue, heart and adrenals were measured. Chemical sympathectomy induces a disappearance of diurnal fluctuation in the sensitivity to injected noradrenaline. In these animals a lower capacity for heat production was found. However, a significant calorigenic effect of injected noradrenaline in 6-OHDA-treated animals was still present. In sympathectomized animals a depletion of noradrenaline from interscapular brown adipose tissue and the heart was observed. Besides, a change in adrenaline/noradrenaline ratio was found in the adrenals.     

Vasopressin decreases total free fatty acids but enhances release of radioactivity from isolated hepatocytes labelled with [3H]arachidonic acid

The short-term effects of vasopressin on free fatty acids and lysophospholipids were investigated in hepatocytes isolated from fed rats. Over the time period 0.25 to 10 min vasopressin decreased the steady-state concentrations of palmitic, stearic and oleic acids measured by gas liquid chromatography in extracts of cells incubated at 0.1 mM extracellular Ca2+. The concentrations of arachidonic and linoleic acids did not change. In hepatocytes labelled with [3H]arachidonic acid and incubated at 1.3 mM extracellular Ca2+ vasopressin or the Ca2+-selective ionophore A23187 increased the rate of accumulation of radioactivity in the incubation medium by 40%. The action of A23187 was dependent on extracellular Ca2+. When hepatocytes labelled with 32Pi were treated with vasopressin, no change in the amounts of [32P]lysophosphatidylethanolamine or [32P]lysophosphatidylcholine was observed. It is concluded that the action of vasopressin on hepatocytes is associated with the release of arachidonic acid or metabolites of arachidonic acid but is not accompanied by a general increase in the steady-state concentrations of free fatty acids and lysophospholipids.     

Regulation of calcium-dependent [3H]noradrenaline release from rat cerebrocortical synaptosomes by protein kinase C and modulation of the actin cytoskeleton.

The effects that active phorbol esters, staurosporine, and changes in actin dynamics, might have on Ca2+ -dependent exocytosis of [3H]-labelled noradrenaline, induced by either membrane-depolarizing agents or a Ca2+ ionophore, have been examined in isolated nerve terminals in vitro. Depolarization-induced openings of voltage-dependent Ca2+ channels with 30 mM KCl or 1 mM 4-aminopyridine induced limited exocytosis of [3H]noradrenaline, presumably from a readily releasable vesicle pool. Application of the Ca2+ ionophore calcimycin (10 microM) induced more extensive [3H]noradrenaline release, presumably from intracellular reserve vesicles. Stimulation of protein kinase C with phorbol 12-myristate,13-acetate increased release evoked by all secretagogues. Staurosporine (1 microM) had no effect on depolarization-induced release, but decreased ionophore-induced release and reversed all effects of the phorbol ester. When release was induced by depolarization, internalization of the actin-destabilizing agent DNAase I into the synaptosomes gave a slight increase in [3H]NA release and strongly increased the potentiating effect of the phorbol ester. In contrast, when release was induced by the Ca2+ ionophore, DNAase I had no effect, either in the absence or presence of phorbol ester. The results indicate that depolarization of noradrenergic rat synaptosomes induces Ca2+ -dependent release from a releasable pool of staurosporine-insensitive vesicles. Activation of protein kinase C increases this release by staurosporine-sensitive mechanisms, and destabilization of the actin cytoskeleton further increases this effect of protein kinase C. In contrast, ionophore-induced noradrenaline release originates from a pool of staurosporine-sensitive vesicles, and although activation of protein kinase C increases release from this pool, DNAase I has no effect and also does not change the effect of protein kinase C. The results support the existence of two functionally distinct pools of secretory vesicles in noradrenergic CNS nerve terminals, which are regulated in distinct ways by protein kinase C and the actin cytoskeleton.     

Differential modulation of citrate synthesis and release by fatty acids in perfused working rat hearts

The objective of this study was to test the effect of increasing fatty acid concentrations on substrate fluxes through pathways leading to citrate synthesis and release in the heart. This was accomplished using semirecirculating work-performing rat hearts perfused with substrate mixtures mimicking the in situ milieu (5.5 mM glucose, 8 nM insulin, 1 mM lactate, 0.2 mM pyruvate, and 0.4 mM oleate-albumin) and 13C methods. Raising the fatty acid concentration from 0.4 to 1 mM with long-chain oleate or medium-chain octanoate resulted in a lowering ( approximately 20%) of cardiac output and efficiency with unaltered O2 consumption. At the metabolic level, beyond the expected effects of high fatty acid levels on the contribution of pyruvate decarboxylation (reduced >3-fold) and beta-oxidation (enhanced approximately 3-fold) to citrate synthesis, there was also a 2.4-fold lowering of anaplerotic pyruvate carboxylation. Despite the dual inhibitory effect of high fatty acids on pyruvate decarboxylation and carboxylation, tissue citrate levels were twofold higher, but citrate release rates remained unchanged at 11-14 nmol/min, representing <0.5% of citric acid cycle flux. A similar trend was observed for most metabolic parameters after oleate or octanoate addition. Together, these results emphasize a differential modulation of anaplerotic pyruvate carboxylation and citrate release in the heart by fatty acids. We interpret the lack of effects of high fatty acid concentrations on citrate release rates as suggesting that, under physiological conditions, this process is maximal, probably limited by the activity of its mitochondrial or plasma membrane transporter. Limited citrate release at high fatty acid concentrations may have important consequences for the heart's fuel metabolism and function.     

Effect of lacidipine on ischaemic and reperfused isolated rabbit hearts

Lacidipine is a new developed dihydropyridine calcium-antagonist, showing a slow onset and long lasting-selective activity.To assess whether the administration of lacidipine protects the myocardium in a dose-dependent manner against ischaemia and reperfusion, isolated rabbit heart were infused with three different concentrations of lacidipine: 10^–10; 10^–9; 10^–8 M. Diastolic and developed pressures were monitored; coronary effluent was collected and assayed for CPK activity and for noradrenaline concentration; mitochondria were harvested and assayed for respiratory activity, ATP production and calcium content and tissue concentration of ATP, creatine phosphate (CP) and calcium were determined. Occurrence of oxidative stress during ischaemia and reperfusion was also monitored in terms of tissue content and release of reduced (GSH) and oxidized (GSSG) glutatione. Treatment with lacidipine at 10^–10 and 10^–9 M had no effects on the hearts when perfused under aerobic condition, whilst the higher dose reduced developed pressure of 36%. The ischaemic-induced deterioration of mitochondrial function was attenuated. On reperfusion treated hearts recovered better than the untreated hearts with respect to left ventricular performance, replenishment of ATP and CP stores and mitochondrial function. The reperfusion-induced tissue and mitochondrial calcium overload, release of CPK and of noradrenaline and oxidative stress were also significantly reduced. The effects of lacidipine were dose-dependent. The lower concentration (10^–10 M) failed to modify ischaemic and reperfusion damage. The dose of 10^–9 M was cardioprotective, but the best effect was found at 10^–8 M.It is concluded that lacidipine infusion provides a dose dependent protection of the heart against ischaemia and reperfusion. Because this protection occurred also at 10^–9 M, in the absence of negative inotropic effect during normoxia and of a coronary dilatory effect during ischaemia, it cannot be attributed to an energy sparing effect or to improvement of oxygen delivery. From our data we can envisage two other major mechanism:-1) membrane protection-2) reduction of oxygen toxicity. The ATP sparing effect occurring at 10^–8 M is likely to be responsable for the further protection.