Role of the beta 2 adrenoceptor in mediating positive inotropic activity in the failing heart and its relation to the hemodynamic actions of dopexamine hydrochloride

Lipopolysaccharide induces placental mitochondrial dysfunction in murine and human systems by reducing MNRR1 levels via a TLR4-independent pathway

Mitochondria play a key role in placental growth and development, and mitochondrial dysfunction is associated with inflammation in pregnancy pathologies. However, the mechanisms whereby placental mitochondria sense inflammatory signals are unknown. Mitochondrial nuclear retrograde regulator 1 (MNRR1) is a bi-organellar protein responsible for mitochondrial function, including optimal induction of cellular stress-responsive signaling pathways. Here, in a lipopolysaccharide-induced model of systemic placental inflammation, we show that MNRR1 levels are reduced both in mouse placental tissues in vivo and in human trophoblastic cell lines in vitro. MNRR1 reduction is associated with mitochondrial dysfunction, enhanced oxidative stress, and activation of pro-inflammatory signaling. Mechanistically, we uncover a non-conventional pathway independent of Toll-like receptor 4 (TLR4) that results in ATM kinase-dependent threonine phosphorylation that stabilizes mitochondrial protease YME1L1, which targets MNRR1. Enhancing MNRR1 levels abrogates the bioenergetic defect and induces an anti-inflammatory phenotype. We therefore propose MNRR1 as an anti-inflammatory therapeutic in placental inflammation.

Renal dopamine receptor function in hypertension

Dopamine plays an important role in the regulation of renal sodium excretion. The synthesis of dopamine and the presence of dopamine receptor subtypes (D1A, D1B, as D1-like and D2, and D3 as D2-like) have been shown within the kidney. The activation of D1-like receptors located on the proximal tubules causes inhibition of tubular sodium reabsorption by inhibiting Na,H-exchanger and Na,K-ATPase activity. The D1-like receptors are linked to the multiple cellular signaling systems (namely, adenylyl cyclase, phospholipase C, and phospholipase A2) in the different regions of the nephron. Defective renal dopamine production and/or dopamine receptor function have been reported in human primary hypertension as well as in genetic models of animal hypertension. There may be a primary defect in D1-like receptors and an altered signaling system in the proximal tubules that lead to reduced dopamine-mediated effects on renal sodium excretion in hypertension. Recently, it has been shown in animal models that the disruption of either D1A or D3 receptors at the gene level causes hypertension in mice. Dopamine and dopamine receptor agonists also provide therapeutic potential in treatment of various cardiovascular pathological conditions, including hypertension. However, because of the poor bioavailability of the currently available compounds, the use of D1-like agonists is limited to the management of patients with severe hypertension when a rapid reduction of blood pressure is clinically indicated and in acute management of patients with heart failure. In conclusion, there is convincing evidence that dopamine and dopamine receptors play an important role in regulation of renal function, suggesting that a defective dopamine receptor/signaling system may contribute to the development and maintenance of hypertension. Further studies need to be directed toward establishing a direct correlation between defective dopamine receptor gene in the kidney and development of hypertension. Subsequently, it may be possible to use a therapeutic approach to correct the defect in dopamine receptor gene causing the hypertension.

Evaluation of ventricular and arterial hemodynamics in anesthetized closed-chest mice

Transgenic and knock-out mice with cardiovascular phenotypes have created the need for methods to measure murine arterial and ventricular mechanics. The aims of this study were (1) to develop a method for the assessment of wall stress (sigma es)-rate corrected velocity of fiber shortening (Vcfc) relation and (2) to assess the feasibility of quantifying global arterial function in normal mice. This method can thus serve as a reference for future studies in genetically altered mice by establishing normal values for comparison. Ten anesthetized closed-chest mice were studied with targeted M-mode echocardiography of the left ventricle recorded simultaneously with high-fidelity aortic pressures. Data were acquired at baseline and during infusions of methoxamine and isoproterenol. Tracings were digitized to obtain end-systolic wall stress (sigma es) and rate-corrected velocity of fiber shortening (Vcfc) relationships and plots of systolic meridional wall stress. Instantaneous aortic pressures and continuous wave aortic Doppler velocities were digitized to study arterial hemodynamics. The Vcfc-sigma es relationship was inverse and linear in all mice studied with a median value of r2 = 0.94. Isoproterenol resulted in an upward shift from the baseline contractility line obtained with methoxamine (mean shift = 2.0 +/- 0.3 circ/sec). Relative to baseline the integral of wall stress decreased with isoproterenol and increased with methoxamine. Methoxamine increased mean arterial pressure and total vascular resistance and decreased heart rate, cardiac output, and arterial compliance. Isoproterenol decreased total vascular resistance and increased cardiac output. Stress-shortening relationships, systolic wall stress, and evaluation of vascular function can be obtained in a closed-chest mouse model.

Metabolic and calorigenic effects of dopexamine in healthy volunteers

OBJECTIVE

To evaluate metabolic and calorigenic effects of dopexamine in healthy volunteers.

DESIGN

Prospective, randomized trial.

SETTING

Laboratory of the University Department of Anesthesiology.

SUBJECTS

Eight volunteers.

INTERVENTIONS

After a control period, dopexamine was administered using four infusion rates (0.75, 1.5, 3.0, and 6.0 microg/kg/min).

MEASUREMENTS AND MAIN RESULTS

Blood pressure, heart rate, oxygen consumption (VO2), and the plasma concentration of potassium, glucose, lactate, and norepinephrine were measured. Typical hemodynamic responses were seen. VO2 increased from 122 +/- 11 (SD) to 150 +/- 9 mL/min/m2 during the highest dopexamine infusion rate. Plasma potassium concentration decreased only during the highest infusion rate. Plasma glucose concentration increased during infusion rates of 3 and 6 microg/kg/min of dopexamine, from 90 +/- 5 to 99 +/- 5 mg/dL (5.0 +/- 0.3 to 5.5 +/- 0.3 mmol/L), and from 87 +/- 7 to 103 +/- 11 mg/dL (4.8 +/- 0.4 to 5.7 +/- 0.6 mmol/L), respectively. Lactate did not increase during dopexamine infusion. Plasma norepinephrine concentration increased during all four infusion rates.

CONCLUSION

It was not possible to differentiate the adrenergic receptor subtype responsible for the calorigenic and metabolic effects, since the putative beta2 adrenergic-receptor agonist, dopexamine, caused an increase in the plasma concentration of the beta1 adrenergic-receptor agonist, norepinephrine. Since beta2 adrenergic receptor-mediated effects such as hypokalemia were found only at infusion rates > or = 3 microg/kg/min, the effects of dopexamine at infusion rates < 3 microg/kg/min may be mainly mediated by stimulation of dopaminergic receptors and the indirect sympathomimetic action.

Mechanics of left ventricular systolic and diastolic function in physiologic hypertrophy of the athlete's heart

As a result of a number of factors, there is tremendous diversity in the pattern of cardiac mechanics encountered in athletes. Nevertheless, several trends can be identified, and several conclusions are possible. Hypertrophy of a mild to moderate degree and out of proportion to body size is a common finding. Some athletes experience ventricular dilation with appropriate hypertrophy and preservation of the ventricular mass-to-volume ratio, whereas others manifest concentric hypertrophy with an increased mass-to-volume ratio. The functional changes that are encountered appear to be secondary to the structural alterations, and there is no evidence of altered myocardial systolic or diastolic properties. Some athletes with hypertrophy have reduced wall stress when they are evaluated at rest, and velocity of shortening is augmented because of the reduced afterload. As a result of adaptation to a high-output state, some athletes appear preload reduced when evaluated at rest. Although velocity of shortening is not affected by preload status, fractional shortening is inversely related to preload. The magnitude of systolic shortening is therefore the net result of altered preload and afterload and cannot be understood without assessing both of these parameters. When the various determinants of systolic shortening are included, contractility appears to be normal. There have been several reports of depressed contractility immediately after extreme exertion. Although the mechanism remains uncertain, several intriguing possibilities have been proposed.

Haemodynamic and renal effects of dopexamine after cardiac surgery in children

Dopexamine hydrochloride, a synthetic dopamine analog with predominantly beta and delta agonist properties, has been shown to improve cardiac performance and renal function in adults with heart failure. This study was designed to investigate the haemodynamic and renal effects of dopexamine in children after cardiac surgery. Seven children were selected in whom a need for postoperative vasodilation after cardiac surgery was anticipated. Haemodynamics and renal function were determined under baseline conditions and during a continuous infusion of dopexamine at 2 and 6 micrograms.kg-1.min-1 for 90 minutes, the sequence being randomized for the initial dose. Cardiac output was measured by thermodilution and glomerular filtration rate (GFR) and renal plasma flow (RPF) by the clearances of inulin and para-aminohippurate respectively. Dopexamine induced a dose-related increase in cardiac index (CI) expressed as mean (SD) from 3.5 (0.7) to 3.9 (0.76) and 4.5 (0.8) l.min.-1m-2 (both P < 0.05), and in heart rate (HR) from 107 (17) to 122 (17) and 136 (17) beats.min-1 (P < 0.05). Stroke volume index (SVI) and mean systemic pressure were unchanged, but pulmonary wedge pressure decreased from 14 (3) to 11 (4) and 12 (3) mmHg (both P < 0.05). Systemic vascular resistances (SVR) decreased from 24 (7) to 20 (5) mmHg.l-1.min-1.m-2 (P < 0.05), with dopexamine 6 micrograms.kg-1.min-1. Renal blood flow (RBF) increased from 319 (113) to 441 (230) and 410 (138) ml.min-1.m-2 (both P < 0.05), GFR from 115 (32) to 142 (34) and 146 (29) ml.min-1.1.73m-2 (both P < 0.05), urine output and fractional excretion of sodium respectively from 3.12 (2) to 7.16 (8) and 7.21 (6) ml.kg-1 (both P < 0.05) and from 2.24 (1) to 4.25 (3.4) (P < 0.05) and 3.15 (3.1)% (n.s.). The fraction of CI delivered to the kidneys, the fraction of RBF filtered in the kidneys, plasma renin activity and aldosterone levels remained unchanged. In children after cardiac surgery, dopexamine increases CI at the expense of a concomitant increase in heart rate and demonstrates few selective vascular systemic or intrinsic renal actions.

Arrhythmogenic potential of dopexamine hydrochloride during halothane anaesthesia in dogs

Dopexamine hydrochloride (Dopacard) is the novel synthetic catecholamine designed for use in the acute management of a low cardiac output status. In addition to dopaminergic receptor stimulation, dopexamine hydrochloride is a potent beta 2 adrenoceptor agonist with negligible direct beta 1 and no alpha adrenergic effect. The objective of this study was to compare the arrhythmogenic effects of dopexamine hydrochloride and dopamine in dogs anaesthetized with halothane (1.2 MAC). The starting dose for dopexamine hydrochloride was 3.5 micrograms.kg-1.min-1 and for dopamine was 5 micrograms.kg-1.min-1. Concentrations of the drugs were increased until four or more premature ventricular contractions within 15 seconds were produced. All dogs developed ventricular tachycardia when dopamine was administered in concentrations ranging between 18-20 micrograms.kg-1.min-1. Unlike dopamine, dopexamine hydrochloride even at concentrations as high as 50 micrograms.kg-1.min-1 did not induce any atrial or ventricular ectopic beats. Lack of beta 1 and alpha adrenergic agonist effects is a likely explanation for low arrhythmogenicity of dopexamine hydrochloride. Both drugs increase cardiac output; dopexamine hydrochloride primarily by a dose-related increase in heart rate and increased afterload. At the maximal concentration dopexamine hydrochloride increased heart rate from 114 to 150 beat.min-1, mean arterial pressure decreased from 81 mmHg to 45 mmHg and SVR decreased from 2418 to 962 dyne.sec-1cm-5. Myocardial contractility increased only moderately, as evaluated by dP/dt, which increased from 1290 to 1696 mmHg.sec-1. Dopamine had a more marked inotropic effect: the dP/dt increased, at the maximal concentration, from 1480 to 2570 mmHg.sec-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of acute beta-adrenoceptor blockade with metoprolol on the renal response to dopamine in normal humans

The present study investigated the contribution of adrenergic beta 1-receptor stimulation to the cardiovascular and renal effects of low-dose dopamine in eight normal, water-loaded humans. Metoprolol (100 mg) or placebo was administered orally at 08.00 h in a randomized, double-blind fashion on two different days. Renal clearance studies were performed during a 1 h baseline period, two 1 h periods with dopamine infusion (3 micrograms kg-1 min-1), and a 1 h recovery period. Cardiac output was measured by an ultrasonic Doppler method, and lithium clearance (CLLi) was used to estimate proximal tubular outflow. Baseline values of heart rate, systolic pressure and mean arterial pressure decreased with metoprolol compared with placebo, but cardiac output, effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) were not significantly changed. Metoprolol significantly decreased baseline CLLi and sodium clearance (CLNa) by 19% (P < 0.01) and 34% (P < 0.01), respectively. Metoprolol blunted the dopamine-induced increases in heart rate and systolic pressure, but cardiac output increased to the same extent on both study days by 26% (placebo, P < 0.05) and by 31% (metoprolol, P < 0.01), respectively. With and without metoprolol, dopamine did not significantly change GFR, and the percentage increases in ERPF were similar on the two study days (40% (P < 0.001) and 42% (P < 0.001), respectively). Dopamine increased CLLi and CLNa by 31% (P < 0.01) and 114% (P < 0.01), respectively, with placebo, and by 36% (P < 0.01) and 114% (P < 0.01), respectively, with metoprolol. Values during infusion remained significantly lower with metoprolol compared with placebo.(ABSTRACT TRUNCATED AT 250 WORDS)

[Dopexamine: a new dopaminergic agonist]

Dopexamine hydrochloride is a new synthetic catecholamine for intravenous use in low cardiac output states with co-existing raised systemic or pulmonary vascular resistance. Dopamine has been commonly used since several years in these situations. The drawbacks of dopamine include a vasoconstrictive effect with high infusion rates, and a marked tendency for ventricular ectopy due to the potent beta-1 adrenergic stimulation. Dopexamine hydrochloride has interesting vasodilator properties, with marked intrinsic agonist activity at beta-2 adrenoreceptors and a lesser agonist activity at dopaminergic receptors (DA1 and DA2). Its mild inotropic activity arises primarily from baroreceptor reflex stimulation with a possible contribution from direct stimulation of myocardial beta 2-adrenoreceptors. Dopexamine hydrochloride is responsible for an inhibition of neuronal re-uptake of catecholamines (uptake-1), producing an indirect stimulation of cardiac beta 1-receptors. This catecholamine has no effect at alpha 1 and alpha 2-adrenoreceptors, and only very weak and clinically insignificant beta 1-adrenoreceptor agonist activity. Dopexamine hydrochloride improves cardiac performance by a marked vasodilation and a mild inotropic activity. The specific activity at dopaminergic receptors increases cerebral, myocardial, splanchnic and renal blood flows. These haemodynamic effects are associated with an increase in diuresis and natriuresis. These benefits are achieved without side effects such as an increased myocardial oxygen consumption, although induced tachycardia may be responsible for chest pain/anginae pain in patients with ischaemic heart disease. In clinical practice, dopexamine hydrochloride is easy to use; the short plasma half-life (6 minutes in healthy volunteers and 11 minutes in patients with low cardiac output) allows a rapid return to pretreatment status at discontinuation of the infusion. Preliminary studies have shown that dopexamine hydrochloride can produce beneficial effects in patients with acute heart failure or with compromised left ventricular function following cardiac surgery. The drug has also been assessed in patients with septic shock, most often in association with dopamine or norepinephrine. In these patients, dopexamine produces a dose-related increase in cardiac index, stroke volume, heart rate and a decrease in systemic vascular resistance. Its use in this indication must be cautious, particularly in patients with hypotension or decreased venous return. Comparative therapeutic trials are clearly required to establish the efficiency and tolerance of dopexamine hydrochloride in comparison with dopamine and dobutamine, before its place in therapy can fully be defined.

Effects of simultaneous alterations in preload and afterload on measurements of left ventricular contractility in patients with dilated cardiomyopathy: comparisons of ejection phase, isovolumetric and end-systolic force-velocity indexes

OBJECTIVES

The study was designed to critically evaluate the clinical utility of ejection phase and nonejection phase indexes of contractile state in patients with severe left ventricular dysfunction.

BACKGROUND

Ejection phase indexes of left ventricular systolic performance are unable to differentiate contractility changes from alterations in loading conditions. Isovolumetric and end-systolic force-velocity indexes have been proposed as alternative measurements of contractile state that are load independent.

METHODS

Seventeen patients with nonischemic dilated cardiomyopathy were studied during cardiac catheterization. High fidelity central aortic and left ventricular pressure measurements were made with simultaneous echocardiographic recordings of chamber minor- and long-axis dimensions and wall thickness. Data were acquired under control conditions, during nitroprusside infusion and with dopamine (6 micrograms/kg per min).

RESULTS

Patients were classified into those without (group 1, n = 10) and those with (group 2, n = 7) a decrease in end-diastolic circumferential wall stress in response to dopamine. There were no baseline differences between the groups in functional class, left ventricular chamber geometry or cardiovascular hemodynamics. Ejection phase indexes were variably altered by changes in preload, afterload and heart rate, thereby complicating physiologic interpretation of data. Dopamine increased the commonly used isovolumetric index, maximal rate of rise in left ventricular pressure (dP/dtmax), by 64% for group 1 but by only 16% for group 2 (p less than 0.001), resulting in an underestimation of contractile state change in 41% of patients. In contrast, the left ventricular end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation, which incorporates afterload, ventricular wall mass and heart rate in its analysis, was a sensitive contractility measurement that was preload independent and equally augmented by dopamine for both groups.

CONCLUSIONS

Of the left ventricular contractility indexes evaluated, the end-systolic circumferential wall stress-rate-corrected velocity of fiber shortening relation was the most physiologically appropriate for assessing pharmacologically induced changes in inotropic state that were accompanied by complex alterations in loading conditions in patients with dilated cardiomyopathy.

Developmental modulation of myocardial mechanics: age- and growth-related alterations in afterload and contractility

Somatic growth is associated with alterations in myocardial mechanics in children with heart disease and in most animal models of congenital heart disease. However, the effect of age and body size on myocardial contractility and loading conditions in normal infants and children is not known. Therefore, 256 normal children aged 7 days to 19 years (34% less than 3 years old) were evaluated with noninvasive indexes of left ventricular contractility and loading conditions. Two-dimensional and M-mode echocardiographic recordings of the left ventricle were obtained with a phonocardiogram, indirect pulse tracing and blood pressure recordings. Left ventricular dimensions, wall thickness and pressure measurements obtained from these data were used to calculate peak and end-systolic circumferential and meridional wall stress and mean and integrated meridional wall stress. Velocity of shortening adjusted for heart rate was compared with end-systolic stress to assess contractility independently of loading status. The subjects were stratified for gender and each of the derived variables was related to age and body surface area. Ventricular shape, assessed as the major/minor axis ratio, and the circumferential/meridional stress ratio were found to be invariant with growth. The ratio of posterior wall thickness to minor axis dimension did not change with age, despite the normal age-related increase in blood pressure. The increase in pressure despite unvarying ventricular shape and wall thickness/dimension ratio resulted in a substantial increase in wall stress that was most dramatic during the first few years of life. In association with the increase in afterload, systolic function decreased with age. However, the age-related decrease in the velocity of shortening was greater than that expected from the increase in afterload alone, indicating a higher level of contractility in infants and children during the first years of life than in older subjects. The process of normal growth and development, similar to that in children with heart disease, is associated with a rapid decrease in the trophic response to hemodynamic loads, resulting in an age-associated increase in wall stress. There is a similar but somewhat more rapid decrease in contractility, with the highest values seen in the youngest patients.

Acute haemodynamic effects of dopexamine in patients with coronary arterial disease

We assessed the acute haemodynamic effects of dopexamine 1 microgram/kg/min and 3 micrograms/kg/min in 21 patients with coronary arterial disease following routine catheterisation. Patients were aged 38 to 72 years and left ventricular ejection fraction ranged from 23 to 79%. Dopexamine was well tolerated in all patients except one in whom transient ventricular arrhythmias occurred with 3 micrograms/kg/min. No patient developed angina. Dopexamine increased cardiac index (2.6 +/- 0.4 to 3.2 +/- 0.1 (P less than 0.001) and 4.0 +/- 1.0 1/min/m2 (P less than 0.001), control to 1 microgram/kg/min and 3 micrograms/kg/min, respectively) and decreased systemic vascular resistance index (3356 +/- 1506 to 2318 +/- 809 (P less than 0.001) and 2252 +/- 1973 dyne.sec.cm-5/m2 (P less than 0.001], but did not affect systemic arterial, pulmonary arterial or right atrial pressure. Maximum positive dP/dt was increased (1294 +/- 324 to 1597 +/- 505 (P less than 0.001) and 2199 +/- 819 mmHg/sec (P less than 0.001] as was left ventricular stroke work index (44 +/- 20 to 51 +/- 21 (P less than 0.05) and 56 +/- 27 g.m/m2 (P less than 0.001) control to 1 microgram/kg/min and 3 micrograms/kg/min, respectively). Left ventricular end diastolic pressure fell with 3 micrograms/kg/min from 19.8 +/- 6.9 to 12.4 +/- 4.6 mmHg (P less than 0.05) in patients with preserved left ventricular ejection fraction (greater than 50%, n = 6), but not in those with impaired left ventricular ejection fraction (less than 50%, n = 15), otherwise the effects in these two subgroups were similar. We conclude that dopexamine has both inotropic and vasodilator properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the haemodynamic effects of dopexamine and dobutamine in patients with severe congestive heart failure

Dopexamine hydrochloride is a novel compound with properties of DA1-dopaminergic and beta 2-adrenergic receptor agonism and neuronal noradrenaline uptake inhibition. It has been shown to produce beneficial renal and haemodynamic effects in patients with severe heart failure. We compared the haemodynamic effects of dopexamine (0.5 to 6 micrograms/kg/min) with those of dobutamine (5 to 25 micrograms/kg/min) in 9 patients with severe congestive heart failure. The two drugs were similar in their effects at peak infusion rates: heart rate increased (dopexamine 87 +/- 17 to 100 +/- 14; dobutamine 91 +/- 18 to 103 +/- 17 min-1), cardiac index increased (dopexamine 1.7 +/- 0.5 to 2.8 +/- 1.1; dobutamine 1.8 +/- 0.5 to 3.0 +/- 1.1 l.min-1.m-2) and systemic vascular resistance decreased (dopexamine 1553 +/- 221 to 1117 +/- 432; dobutamine 1721 +/- 347 to 1280 +/- 433 dyne.s.cm-5). Neither drug affected pulmonary artery wedge pressure (dopexamine 24 +/- 6 to 22 +/- 6; dobutamine 25 +/- 9 to 24 +/- 10 mm Hg). Dopexamine had significantly lower peak effects on left ventricular stroke work index (dopexamine 20 +/- 9, dobutamine 27 +/- 15 g.m.m-2, P less than 0.05) and cardiac power output (dopexamine 0.71 +/- 0.36, dobutamine 0.93 +/- 0.46 W, P less than 0.05). These haemodynamic effects, due largely to vasodilatation but with some contributory positive inotropy, indicate that dopexamine will be useful in the acute treatment of congestive heart failure.

Cardiac and peripheral vascular responses to adrenoceptor stimulation and blockade after cardiac transplantation

A denervated heart coupled to a periphery previously exposed to high catecholamine levels provides a unique model to study adrenoceptor physiology. Six orthotopic transplant patients (1.3 +/- 0.8 years postoperative) were age matched with six atropine-treated normal subjects. Simultaneous two-dimensionally targeted left ventricular echo-cardiograms and calibrated carotid pulse tracings were recorded. Left ventricular contractility was assessed with use of heart rate- and load-independent end-systolic indexes. Studies were performed at baseline and during dobutamine infusion with and without beta-adrenergic blockade with use of propranolol; effects were assessed during afterload changes generated by the alpha 1 agonist methoxamine. There were no differences in baseline contractility or reserve between transplant patients and normal subjects. The heart rate response to dobutamine was greater for transplant patients (p less than 0.001). In both groups, the positive inotropic and chronotropic effects of dobutamine were ablated by propranolol. Dobutamine plus propranolol (unopposed alpha 1 effect) did not change mean systemic pressure in transplant patients while markedly raising mean systemic pressures in normal subjects (36 +/- 18 mm Hg; p less than 0.001). In addition, during initial challenge with methoxamine, the transplant patients required 60% more alpha 1 agonist than did the normal subjects (p less than 0.001) to obtain a pressor effect. In summary, transplant patients who were previously in severe heart failure have normal left ventricular inotropic response to beta 1 activation and blockade, exaggerated chronotropic response to dobutamine and reduced sensitivity to stimulation with alpha 1-adrenoceptor agonists. These findings are consistent with a differential response of adrenoceptors to long-term stimulation after cardiac transplantation.