Hemodynamic-inotropic response to beta-blocker with intrinsic sympathomimetic activity in patients with congestive cardiomyopathy

A review of why and how we may use beta-blockers in congestive heart failure

The history of the use of beta-blockers for congestive heart failure, beginning with the innovative seminal study by the Swedish group in 1975 to studies in 1995, is reviewed and shows that almost all trials favored the use of beta-blockers. They tended to demonstrate an increase in ejection fraction, a decrease in left ventricular mass, and in some studies, even a decrease in mortality. Even after the introduction of angiotensin-converting enzyme inhibitors, additional improvement in function and mortality was observed. Patients with nonischemic dilated cardiomyopathy derived more benefit from beta-blockers than did patients with ischemic cardiomyopathy. Least likely to benefit were patients treated for <2 months, patients with alcoholic cardiomyopathy, and those with marked intercellular fibrosis. Although the starting dose of metoprolol, the most common beta-blocker used, may have to be as low as 2.5 mg/d, mortality analysis failed to show a decrease in sudden death unless the dose was raised to about 300 mg/d, a dose at which beta-selectivity is generally not expected to be present. The non-beta-specific bucindolol or carvedilol may ultimately be preferred to metoprolol because they are better tolerated initially due to a slight vasodilatation effect. Initial studies with carvedilol showed remarkable promise in reducing mortality. However, these agents cannot yet be said to have been studied adequately.

Pathophysiologic and pharmacologic rationales for clinical management of chronic heart failure with beta-blocking agents

An understanding of the important role of neurohormonal compensatory mechanisms in heart failure has been translated into therapeutic options that can improve cardiac function, alter disease progression, and improve survival. Angiotensin-converting enzyme inhibitors are of proven benefit in this regard, and beta-adrenergic receptor antagonists are potentially another such class of agents. By inhibiting the myocardial effects of chronic adrenergic activation, beta blocking agents may improve left ventricular function or delay its deterioration in patients with heart failure. Aside from blocking beta-adrenergic receptors, other ancillary properties inherent in third-generation beta-blocking agents (such as vasodilation) may exert additional favorable effects. Clinical data generated in subjects with heart failure indicate that beta-antagonist therapy exerts its physiologic and clinical effects through neurohormonal antagonism, generally analogous to angiotensin-converting enzyme inhibitors. Virtually all controlled long-term studies show that beta-blocking agents improve cardiac function and hemodynamics in patients with chronic heart failure, but large-scale trials are needed to ascertain a favorable effect on the natural history of heart failure.

Adverse effects of epinephrine in patients with advanced left ventricular dysfunction: analysis of ventriculo-arterial coupling

We examined the response of ventriculo-arterial coupling to epinephrine in 19 patients with normal left ventricular function and with left ventricular dysfunction of various degrees using a conductance catheter. They were divided into three groups: group I, seven patients without left ventricular wall motion abnormality; group II, six patients with ejection fraction of 45-60%; group III, six patients with ejection fraction of 28-40%. Changes in the slope of the end-systolic pressure-volume relationship (end-systolic elastance), the effective arterial elastance, the ratio of effective arterial elastance to end-systolic elastance and the ventricular work efficiency during administration of two different doses of epinephrine (0.05 and 0.1 micrograms/kg/min) were compared among the three groups. At baseline there were no significant differences among the three groups in the ratio of effective arterial elastance to end-systolic elastance, or ventricular work efficiency. At the lower dose of epinephrine, the mean ratio of effective arterial elastance to end-systolic elastance decreased and the mean ventricular work efficiency increased in any groups. At the higher dose of epinephrine the mean ratio of effective arterial elastance to end-systolic elastance further decreased and the mean ventricular work efficiency further increased in groups I and II. However, the mean ratio of effective arterial elastance to end-systolic elastance did not decrease but the mean ventricular work efficiency even decreased in group III. Thus, in patients with advanced left ventricular dysfunction, even a high dose of epinephrine does not modulate the ventriculo-arterial coupling to increase ventricular work efficiency.

Long-term (2 year) beneficial effects of beta-adrenergic blockade with bucindolol in patients with idiopathic dilated cardiomyopathy

Beta-adrenergic blockade represents a promising therapeutic approach to idiopathic dilated cardiomyopathy. Bucindolol, a new beta-blocker, showed favorable effects in a short-term (3 month) trial in idiopathic dilated cardiomyopathy. To assess long-term response, 20 study patients (7 of 9 patients previously assigned to the placebo group and 13 of 14 patients previously assigned to bucindolol therapy) received long-term bucindolol therapy and were followed up for a mean of 23 +/- 4 months (range 17 to 30). The mean patient age was 49 years (range 29 to 66) and the median duration of disease was 11 months (range 1 to 190). Ten patients were in functional class II and 10 were in class III; 15 patients were men. At the end of the common follow-up time, all 20 patients were alive, 17 continued to receive bucindolol (mean dose 176 mg/day, range 25 to 200), and 2 underwent cardiac transplantation. Left ventricular ejection fraction increased from a baseline value of 25 +/- 8% to 35 +/- 13% (n = 19 pairs, p less than 0.001). Functional class improved in 12, was unchanged in 5 and deteriorated in 3 (p = 0.056). Exercise time was maintained (9.4 +/- 3.1 versus 9.1 +/- 3.5 min, n = 19, p = NS), as was maximal oxygen uptake (19.2 +/- 4.9 versus 18.8 +/- 5.7 ml/kg per min, n = 19, p = NS). Thus, long-term bucindolol therapy leads to substantial increases in ejection fraction and to improved functional class while stable exercise performance is maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Usefulness of bucindolol in congestive heart failure

The sympathetic hyperactivity of congestive heart failure (CHF) may worsen cardiovascular function by down-regulation of myocardial beta-receptors. For this reason, beta blockade is proposed to be useful in CHF. Bucindolol is a new beta blocker that has intrinsic nonadrenergically-mediated vasodilation and may be valuable in treatment of CHF. To test this, 19 patients with CHF were randomized in a double-blind protocol to 3 months of treatment with bucindolol (n = 12) or placebo (n = 7). Significant improvement was seen in the bucindolol group using invasive and noninvasive tests; treadmill time increased from 445 to 530 seconds (p = 0.04), Minnesota Living With Heart Failure Questionnaire score improved from 61 to 40 (p = 0.0001), cardiac output increased from 4.0 to 4.7 (p = 0.02), and systemic vascular resistance decreased from 1,888 to 1,481 (p = 0.04). Also, peak exercise heart rate and pulmonary capillary wedge pressure decreased significantly with treatment. There were no changes in the placebo group. We conclude that bucindolol may be an effective treatment for CHF when administered chronically and that its nonadrenergic vasodilation may be an important feature.

Neuroendocrine changes post myocardial infarction: effects of xamoterol

This study reports the effects of the new beta 1 adrenoceptor partial agonist, xamoterol, on neuroendocrine activity after acute myocardial infarction (AMI). Fifty-one consecutive patients with AMI were randomized to treatment with xamoterol, 200 mg twice a day, or placebo; patients were also stratified as to whether or not diuretic therapy was given for left ventricular dysfunction. Noradrenaline, plasma renin activity (PRA), and atrial natriuretic factor (ANF) were measured over a 10-day period. Noradrenaline concentrations are higher (p less than 0.05) in patients treated with diuretics at the time of admission and fell over the subsequent 10 days (p less than 0.01). Treatment with xamoterol did not affect this noradrenaline response to myocardial infarction. PRA was also significantly higher in the patients treated with diuretics, and there was a nonsignificant trend for xamoterol to blunt the PRA response in these patients. There was no difference in ANF levels between those patients who were treated with diuretics and those who were not; xamoterol did not affect ANF. Thus xamoterol does not further elevate noradrenaline levels as do conventional beta blockers, and it does not activate the renin-angiotensin system as do potent nonselective beta agonists. Furthermore, xamoterol does not increase ANF levels, probably because it is not negatively inotropic. We conclude that xamoterol does not cause deleterious neuroendocrine changes in patients with AMI even in those treated for heart failure.

Long-term beta-blocker vasodilator therapy improves cardiac function in idiopathic dilated cardiomyopathy: a double-blind, randomized study of bucindolol versus placebo

PURPOSE

Bucindolol is a potent nonselective beta-blocking agent with vasodilatory properties. In this study, we evaluated the effects of long-term bucindolol therapy in the treatment of heart failure from idiopathic dilated cardiomyopathy.

PATIENTS AND METHODS

Patients were eligible for enrollment if they had symptomatic heart failure, idiopathic dilated cardiomyopathy, and left ventricular ejection fraction less than 0.40. All patients received an initial test dose of 12.5 mg bucindolol orally every 12 hours for two or three doses. Patients tolerating the test dose were randomly assigned (double-blind) to receive bucindolol or placebo in a 3:2 ratio. Study medication was begun at a dose of 12.5 mg orally every 12 hours and gradually increased over a 1-month period until either a maximum tolerated dose or a target dose of 100 mg every 12 hours was reached. Study medication was then continued for an additional 2 months.

RESULTS

A total of 24 patients were enrolled into the study. Twenty-three patients tolerated bucindolol test challenge; 14 were randomized to receive bucindolol, and nine were randomly assigned to receive placebo. The placebo group (age 56 +/- 2 years) was significantly older than the bucindolol group (46 +/- 3 years), but by all other clinical and hemodynamic parameters the two groups were comparable. Twenty-two of 23 patients completed the study. Patients treated with bucindolol had significant improvements in clinical heart failure symptoms and in resting hemodynamic function, including an increase of left ventricular ejection fraction (0.26 +/- 0.02 to 0.35 +/- 0.09, p = 0.003), cardiac index (2.2 +/- 0.1 to 2.5 +/- 0.4 L/minute/m2, p = 0.014), and left ventricular stroke work index (25 +/- 3 to 35 +/- 7 g.m/m2, p = 0.002) and a decrease in pulmonary artery wedge pressure (17 +/- 3 to 10 +/- 5 mm Hg, p = 0.005) and heart rate (86 +/- 3 to 75 +/- 9 beats/minute, p = 0.012). Patients treated with bucindolol also had a significant increase in exercise left ventricular ejection fraction (0.26 +/- 0.03 to 0.32 +/- 0.14, p = 0.015) and reduction in questionnaire-measured symptoms (p = 0.007) and New York Heart Association functional class (p less than 0.001). However, total treadmill exercise duration and maximal oxygen consumption with exercise did not change. No changes in rest or exercise parameters were observed in the placebo-treated group. Central venous plasma norepinephrine concentration decreased significantly in the bucindolol-treated group (423 +/- 79 to 212 +/- 101 pg/mL, p = 0.010), but was unchanged in the placebo-treated group.

CONCLUSION

Bucindolol is well tolerated in patients with idiopathic dilated cardiomyopathy and congestive heart failure, and therapy for 3 months is associated with improved resting cardiac function, improved heart failure symptoms, and a reduction in venous norepinephrine concentration.

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute hemodynamic effects of norepinephrine inhibition in patients with severe chronic congestive heart failure

The pathophysiologic role of high levels of circulating catecholamines in patients with congestive heart failure remains unclear. To assess the hemodynamic contribution of circulating catecholamines, metyrosine (alpha-methyl-p-tyrosine), an inhibitor of catecholamine synthesis, was administered to nine patients with acutely decompensated chronic congestive heart failure. Baseline left ventricular ejection fraction averaged 23.3 +/- 9.9%, whereas cardiac output averaged 3.69 +/- 1.03 liters/min, with a pulmonary wedge pressure of 27.4 +/- 8.5 mm Hg. After 48 h of metyrosine administration, plasma norepinephrine concentration decreased from 919.4 +/- 810.6 to 335.4 +/- 143.1 pg/ml (p less than 0.05). Plasma epinephrine concentration averaged 176.4 +/- 166.0 pg/ml at baseline, and was unchanged during metyrosine administration. Despite the significant decrease in circulating norepinephrine, no significant hemodynamic changes were observed during metyrosine administration. These results suggest that high levels of circulating norepinephrine may be more a marker of severe congestive heart failure than an important contributor to the underlying pathophysiology at this advanced stage of the disease process.

The relationship of the sympathetic nervous system and the renin-angiotensin system in congestive heart failure

Congestive heart failure is a complex clinical syndrome characterized by circulatory and metabolic abnormalities. It has been apparent for more than 25 years that the sympathetic nervous system and the renin-angiotensin-aldosterone system are markedly activated in the late stages of heart failure. These two systems interact to facilitate sympathetic drive and promote salt and water retention. Circumstantial evidence is now accumulating to indicate that excessive sympathetic drive and angiotensin II activity may contribute to the pathophysiology of heart failure. These observations suggest that a dual strategy of modulating sympathetic nervous system activity to the heart while blocking angiotensin II activity may provide a rational therapeutic approach to the treatment of heart failure. Xamoterol, a beta 1 partial agonist, may enhance myocardial contractile force in the steady state, while acting to inhibit excessive sympathetic drive during exercise or severe heart failure. The concomitant use of a converting-enzyme inhibitor would be expected to blunt the detrimental effects of excessive angiotensin II activity. Modulation of adrenergic drive coupled with inhibition of marked angiotensin II activity may be potentially more effective in the treatment of congestive heart failure than either strategy used alone.

Beta-adrenergic blocking drugs in the treatment of congestive heart failure

Experimental and clinical data suggests that increased serum catecholamines may have predominantly detrimental effects in patients with congestive heart failure. Some investigators have proposed use of beta-blockers in heart failure as a means of ameliorating the harmful effects of the excess catecholamines. The clinical experience to date with use of these agents as therapy in congestive heart failure is limited but does suggest a future role for beta-blockers as adjunct therapy in a select population of patients with heart failure.

The cardiovascular pharmacology of xamoterol, cicloprolol, prenalterol and pindolol in the anaesthetised dog

An anaesthetised dog preparation was used to examine the pharmacological profiles of xamoterol, cicloprolol, prenalterol and pindolol. The effects of these agents on heart rate and hind limb perfusion pressure revealed that xamoterol is highly cardioselective and has no significant agonist activity at beta 2-receptors and no membrane stabilising effect. These pharmacological properties are not complicated by the formation of active metabolites and may explain the clinical benefits in the long-term treatment of heart failure.

Vasodilator and inotropic drugs for the treatment of chronic heart failure: distinguishing hype from hope

During the past 10 years, more than 80 orally active vasodilator and inotropic agents have been tested in the clinical setting to evaluate their potential utility in the treatment of chronic heart failure. Although the initial reports of all of these drugs suggested that each represented a major therapeutic advance, only three agents--digoxin, captopril and enalapril--have produced consistent long-term hemodynamic and clinical benefits in these severely ill patients. Most of the other drugs that have been tested have not (to date) distinguished themselves from placebo therapy in large-scale, controlled trials, even though these agents produce hemodynamic effects that closely resemble those seen with digitalis and the converting-enzyme inhibitors. These observations suggest that the hemodynamic derangements that characteristically accompany the development of left ventricular dysfunction cannot be considered to be the most important pathophysiologic abnormality in chronic heart failure. Although cardiac contractility is usually depressed in this disease, positive inotropic agents do not consistently improve the clinical status of these patients. Similarly, although the systemic vessels are usually markedly constricted, drugs that ameliorate this vasoconstriction do not consistently relieve symptoms, enhance exercise capacity or prolong life. Hence, correction of the central hemodynamic abnormalities seen in heart failure may not necessarily provide a rational basis for drug development, and future advances in therapy are likely to evolve only by attempting to understand and modify the basic physiologic derangements in this disorder.

Late systolic indices of ventricular function: noninvasive derivation in congestive heart failure

The slopes of end-systolic pressure/end-systolic dimension and volume relations have been found to be relatively load-independent indices of left ventricular contractility. Noninvasive determination of these relationships has been performed in normal subjects and has been found to reflect baseline and drug-induced changes in ventricular contractility. Three late systolic indices of ventricular contractility were noninvasively determined in subjects with chronic congestive heart failure to determine the feasibility of the method and to assess the linearity and slopes of the relationships in this population. All relations were linear with individual correlation coefficients ranging from 0.86 to 0.99. The mean +/- SD slope was 42.8 +/- 26.4 mm Hg/cm for the end-systolic pressure-dimension relation, 0.59 +/- .42 mm Hg/ml for the end-systolic pressure-volume relation, and 48.7 +/- 32.2 mm Hg/cm for the peak systolic pressure-end-systolic dimension relation. All slopes were markedly reduced compared to those reported in normal individuals. The relative degree of depression was greater for the pressure-volume slope than for the pressure-dimension slope, which is explained by the relationship between volume and dimension in dilated ventricles. These data indicate that measurement of late systolic indices of ventricular contractility by this noninvasive technique is feasible in subjects with congestive heart failure and yields reduced slopes consistent with the diminished contractile state of this population. Pressure-volume rather than pressure-dimension relations may more accurately reflect inotropic state in dilated ventricles.

Acute hemodynamic effects of pindolol and propranolol in patients with dilated cardiomyopathy: relevance of intrinsic sympathomimetic activity

The administration of beta-blocking agents to patients with poor left ventricular (LV) function may result in clinical and hemodynamic deterioration. The beta antagonist pindolol has intrinsic sympathomimetic activity (ISA) and therefore may be better tolerated. To test this hypothesis 30 patients with a precatheterization diagnosis of dilated cardiomyopathy were randomly assigned to three groups to receive intravenous injections of placebo, propranolol, or pindolol. The baseline ejection fraction and hemodynamics were similar for all groups. For propranolol 1 mg, 2 mg, 3 mg, and 4 mg doses were given 5 minutes apart until a maximum dose of 10 mg was reached, until a 25% reduction in the heart rate or mean arterial pressure occurred, or until clinical deterioration developed. For pindolol, 0.1 mg, 0.2 mg, 0.3 mg, and 0.4 mg boluses were used with the same end points. Baseline hemodynamics were measured and repeated 15 minutes after the last dose of each drug was administered. The mean number of doses given was similar for both groups: 3.3 doses for the propranolol group and 3.4 for the pindolol group. Compared to propranolol, pindolol caused less of a reduction in heart rate, cardiac output, cardiac index, stroke volume index, and stroke work index and less of an increase in the mean right atrial pressure, mean pulmonary arterial pressure, mean pulmonary capillary wedge pressure, left ventricular end-diastolic pressure, and pulmonary vascular resistance; there was a decrease in systemic vascular resistance. These differences were statistically significant for changes in heart rate, right atrial pressure, cardiac index, and systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)

Preservation of the end-systolic pressure/end-systolic dimension relation following pindolol in congestive heart failure

Beta blockade may adversely affect inotropic state of the ventricle, resulting in exacerbation of congestive heart failure in subjects with reduced ventricular function. In normal subjects, ventricular contractility appears to be preserved following administration of beta blockers with intrinsic sympathomimetic activity (ISA). The inotropic state of the ventricle was assessed in seven subjects with congestive heart failure (mean ejection fraction = 23 +/- 5%) before and after administration of the ISA beta blocker, pindolol, with the use of the noninvasively derived end-systolic pressure/end-systolic dimension (ESP/ESD) relation. The mean slope of the ESP/ESD relation was 36.3 +/- 20.4 mm Hg/cm at baseline and increased to 45.0 +/- 25.2 mm Hg/cm following five consecutive 10 mg oral doses of pindolol (p = ns). Other simultaneously derived inotropic indices that included percent fractional shortening, mean delta P/delta T, velocity of circumferential fiber shortening, and preejection period-to-left ventricular ejection time ratio showed directionally similar changes toward a mild increase in contractility. These results indicate that the slope of the left ventricular ESP/ESD relation is not altered following repeated dosing with pindolol in subjects with congestive heart failure. This reflects a preservation of inotropic state following administration of this ISA beta blocker in a population with severely compromised ventricular function.

Prognostic importance of the immediate hemodynamic response to nifedipine in patients with severe left ventricular dysfunction

To determine the clinical significance of the occurrence of hemodynamic deterioration after the administration of calcium channel blocking drugs, nifedipine (20 mg orally) was administered to 29 patients with severe left ventricular dysfunction. Thirteen patients showed hemodynamic improvement with the drug (Group 1), as shown by a notable increase in cardiac index associated with a modest decrease in mean arterial pressure. The other 16 patients exhibited hemodynamic deterioration after nifedipine (Group 2), as reflected by a decline in right and left ventricular stroke work indexes accompanied by a marked hypotensive response. These differences were not related to differences in the peripheral vascular response to nifedipine, because both groups showed similar decreases in systemic and pulmonary vascular resistances. Groups 1 (hemodynamic improvement) and 2 (hemodynamic deterioration) were similar with respect to all demographic variables and pretreatment left ventricular performance (cardiac index, left ventricular filling pressure and systemic vascular resistance). Yet, the 1 year actuarial survival in patients in Group 1 was substantially better than that in patients in Group 2 (67 versus 23%, p = 0.009). Group 2, however, had higher values for plasma renin activity (17.7 +/- 6.0 versus 4.3 +/- 1.4 mg/ml per h, p less than 0.05), lower values for serum sodium concentration (134.6 +/- 1.2 versus 139.2 +/- 0.6 mEq/liter, p less than 0.05) and higher values for mean right atrial pressure (15.8 +/- 2.0 versus 7.9 +/- 1.4 mm Hg, p less than 0.01) than did patients in Group 1.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of dietary mackerel oil on the recovery of cardiac function after acute ischaemic events in the pig

To investigate the effects of fish oil nutrition on cardiac haemodynamics and the biochemical response to ischaemia-reperfusion, young pigs (5 weeks old) were fed a 9% lard fat diet or a mixed diet of 4.5% mackerel oil and 4.5% lard fat for 16 weeks. In the mackerel oil fed pigs plasma cholesterol and triglyceride levels decreased by 22% and 58% (both p less than 0.05), respectively, while levels in the animals which received only lard fat did not change. The n-6 fatty acids present in cardiac and platelet membrane phospholipids underwent a partial replacement by n-3 fatty acids in the mackerel oil fed pigs. Under anaesthesia, multiple coronary artery occlusions (5 min) were interrupted by 10 min of reperfusion. The extent of recovery of cardiac function and reduction of adenine nucleotide levels were similar for both dietary groups. The incidence of reperfusion arrhythmias was significantly lower and the reactive hyperaemic responses were of longer duration in the mackerel oil fed animals. These effects cannot be explained by diet-induced alterations in thromboxane B2/6-keto-PGF1 alpha ratio, although a marked reduction in absolute levels of both prostaglandins was seen in the mackerel oil fed pigs (p less than 0.05). In conclusion, dietary fish oil caused changes in membrane fatty acid composition and plasma prostaglandin levels, although these did not affect alterations of cardiac performance during and after short periods of ischaemia.