Comparative effects of fenoldopam mesylate and nitroprusside on left ventricular performance in severe systemic hypertension

Contractile effects of stimulation of D1-dopamine receptors in the isolated human atrium

Dopamine receptors have been claimed not to directly increase contractility in the human heart. Therefore, we performed contraction experiments in isolated electrically driven human atrial preparations (HAP). For comparison, we performed contraction experiments with left atrial preparations of transgenic mice which harbor a cardiac overexpression of human D1-dopamine receptors (D1-TG). In D1-TG, first we noted that dopamine (10 nM-10 µM cumulatively applied) in the presence of propranolol exerted a concentration- and time-dependent positive inotropic effect in D1-TG. In a similar fashion, dopamine increased force of contraction in the presence of 0.4 µM propranolol in HAP and these effects were amplified by pre-treatment with inhibitor of phosphodiesterase III (1 µM) cilostamide. Moreover, contractile effects of dopamine in the presence of propranolol 0.4 µM in HAP were antagonized by odapipam, haloperidol, or raclopride. Ten micromolars of fenoldopam in the presence of cilostamide increased force of contraction in HAP and this effect was antagonized by SCH 23390. We conclude that stimulation of human D1-dopamine receptors can increase force of contraction in the HAP.

Role of Dopamine in the Heart in Health and Disease

Dopamine has effects on the mammalian heart. These effects can include an increase in the force of contraction, and an elevation of the beating rate and the constriction of coronary arteries. Depending on the species studied, positive inotropic effects were strong, very modest, or absent, or even negative inotropic effects occurred. We can discern five dopamine receptors. In addition, the signal transduction by dopamine receptors and the regulation of the expression of cardiac dopamine receptors will be of interest to us, because this might be a tempting area of drug development. Dopamine acts in a species-dependent fashion on these cardiac dopamine receptors, but also on cardiac adrenergic receptors. We will discuss the utility of drugs that are currently available as tools to understand cardiac dopamine receptors. The molecule dopamine itself is present in the mammalian heart. Therefore, cardiac dopamine might act as an autocrine or paracrine compound in the mammalian heart. Dopamine itself might cause cardiac diseases. Moreover, the cardiac function of dopamine and the expression of dopamine receptors in the heart can be altered in diseases such as sepsis. Various drugs for cardiac and non-cardiac diseases are currently in the clinic that are, at least in part, agonists or antagonists at dopamine receptors. We define the research needs in order to understand dopamine receptors in the heart better. All in all, an update on the role of dopamine receptors in the human heart appears to be clinically relevant, and is thus presented here.

Fenoldopam for controlled hypotension during spinal fusion in children and adolescents

Fenoldopam is a dopamine1 agonist whose pharmacological effects include vasodilation of the vascular beds of the kidney, mesentery, skeletal muscle, and coronary systems, resulting in a decrease in systemic vascular resistance and mean arterial pressure. The current retrospective review outlines the use of fenoldopam for controlled hypotension during anterior or posterior spinal fusion in 10 children and adolescents, aged 8-14 years and weighing 22-61 kg. Fenoldopam was infused at a starting dose of 0.3-0.5 microg.kg-1. min-1 and increased incrementally to achieve a mean arterial pressure (MAP) of 50-65 mmHg. The desired MAP was achieved in 4-11 min (7+/-2.5 min). The fenoldopam infusion was administered for 135-225 min (160+/-25 min) in doses ranging from 0.2 to 2.5 microg. kg-1.min-1. The mean fenoldopam infusion rate for the 10 cases varied from 0.5 to 1.4 microg.kg-1.min-1 (1.0+/-0.3 microg.kg-1. min-1). No excessive hypotension or clinically significant adverse effects were noted. Statistically significant, but clinically insignificant, increases in heart rate and decreases in PaO2 were noted during the fenoldopam infusion. The baseline heart rate increased from 87+/-13 b.min-1 to a maximum of 114+/-16 b.min-1 (P < 0.0001) during the fenoldopam infusion. In the six patients undergoing posterior spinal fusion, the baseline PaO2 decreased from 232+/-7 mmHg to a low of 199+/-11 mmHg (P=0.0004) during the fenoldopam infusion. Fenoldopam can be used to provide controlled hypotension during spinal surgery in children and adolescents. Future studies, with direct comparison to other commonly used agents, are needed to better define its advantages and disadvantages as well as its effects on estimated blood loss.

DA1-receptor stimulation by fenoldopam in the treatment of postcardiac surgical hypertension

BACKGROUND

Besides adequate analgesia, sedation and ventilation, postcardiac surgical hypertension has to be treated frequently with vasoactive drugs to avoid possible complications. In this study the hemodynamic effects of the DA1-receptor agonist fenoldopam (F) are compared to those of the Ca-channel antagonist nifedipine (N).

METHODS

Postoperatively, 64 CABG-patients with a mean arterial pressure (MAP) of more than 105 mmHg over 10 min were investigated. Patients with compromised ventricular function, insufficient surgical repair, arrhythmia or an ECG unable to detect myocardial ischemia were excluded. The study drugs (initial dosage: F: 0.8; N: 0.3 micrograms.kg-1.min-1) were given continuously via a central venous catheter to reduce and to maintain the MAP between 80 and 95 mmHg. Hemodynamic parameters were determined using thermodilution technique.

RESULTS

A significant reduction of the MAP (F: from 121 +/- 11 to 83 +/- 4, N: from 119 +/- 8 to 82 +/- 9 mmHg) and of the calculated systemic vascular resistance (SVR) (F: 2110 +/- 500 to 970 +/- 200, N:1980 +/- 660 to 1020 +/- 300 dyn.s.cm-5) were noted in both groups, whereby in the F group the therapeutic goal could be achieved more quickly with the dosage regimen chosen. As a result, a marked increase of heart rate, cardiac index and stroke volume index could be observed, which was more pronounced due to the initially stronger decrease of SVR with F. There was also a stronger decrease of pulmonary vascular resistance in the F group, but the indices of right ventricular function did not differ between the groups.

CONCLUSION

Fenoldopam seems to be an efficient alternative to nifedipine, especially because of its more rapid onset of action.

Fenoldopam: a new dopamine agonist for the treatment of hypertensive urgencies and emergencies

Fenoldopam is a selective dopamine agonist that is being considered for the parenteral treatment of systemic hypertension. In both an oral and parenteral form, the drug causes peripheral vasodilation by stimulating dopamine-1 adrenergic receptors. Its pharmaco-dynamics are reviewed in this article, along with the clinical experiences in patients with hypertensive urgencies and emergencies. Intravenous fenoldopam may provide advantages over sodium nitroprusside because it can induce both a diuresis and natriuresis, is not light sensitive, and is not associated with cyanide toxicity. There is no evidence for rebound hypertension after discontinuation of fenoldopam influsion.

Fenoldopam: a review of its pharmacodynamic and pharmacokinetic properties and intravenous clinical potential in the management of hypertensive urgencies and emergencies

Fenoldopam is a dopamine agonist that causes peripheral vasodilation via stimulation of dopamine 1 (D1) receptors. The efficacy of an intravenous infusion of fenoldopam in decreasing blood pressure in patients with a hypertensive urgency, including patients who developed hypertension after coronary artery bypass graft surgery, and in a small number of patients with hypertensive emergency, is similar to that of sodium nitroprusside. However, unlike sodium nitroprusside, fenoldopam also increases renal blood flow and causes diuresis and natriuresis. There is no evidence of rebound hypertension after stopping the infusion. As the tolerability profile of fenoldopam is generally similar to that of sodium nitroprusside, fenoldopam appears to be an effective alternative to sodium nitroprusside in the immediate treatment of patients who develop severe hypertension and in whom oral treatment is not practical. Fenoldopam may be particularly useful in patients who develop hypertension after coronary artery bypass graft surgery, but further studies are required to confirm its role in hypertensive emergency.

Localization of the dopamine D1 receptor protein in the human heart and kidney

The dopamine D1 receptor has recently been identified in the rat heart and kidney. In the present study, using Western blot analysis and light microscopic immunohistochemistry, we examined D1 receptor protein expression in the human kidney and heart. Antipeptide polyclonal rabbit antiserum was raised against the third extracellular domain of the native receptor and affinity-purified using a protein-A column. Selectivity of the antiserum was validated by recognition of the D1 receptor expressed in stably transfected LTK- cells and Sf-9 cells. The immunohistochemical staining for D1 receptor protein was distributed throughout the atrium and ventricular myocardium and in the coronary vessels. In the kidney, positive immunoreactive signal was detected in the proximal and distal tubules, the collecting ducts, and the large intrarenal vasculature, whereas staining was absent in the juxtaglomerular (JG) cells and the glomeruli. D1 receptor antiserum preadsorbed against the immunizing peptide did not produce significant staining. In Western blot analysis, a single 55-kD band was detected for the D1 receptor in membranes from the D1 receptor transfected Sf-9 cells but not in nontransfected cells. In the heart and kidney, we detected a 55-kD band as well as an additional 40-kD band, which may reflect partial degradation of the receptor protein. These results provide the first evidence for the localization of the dopamine D1 receptor protein in the human heart and kidney. The similar distribution of this subtype receptor in the human heart and kidney to that in the rat supports the possible (patho)physiological significance of the peripheral dopamine system in humans.

Selective and nonselective dopamine receptor agonists: an innovative approach to cardiovascular disease treatment

Dopamine and a new group of selective and nonselective peripheral dopaminergic receptor effectors are being evaluated for the treatment of various cardiovascular disorders, including shock, CHF, and systemic hypertension. Dopamine, in relatively low intravenous doses, will stimulate both peripheral DA1 receptors, which mediate arterial vasodilation of different vascular beds, and the DA2 receptors, which mediate the inhibition of norepinephrine release. Ibopamine is a new oral, nonspecific peripheral dopaminergic agonist with an active metabolite (epinine) that is being evaluated in patients with CHF. Fenoldopam is a selective peripheral DA1 agonist now being developed as a parenteral treatment for hypertensive emergencies. Dopexamine is a parenteral agent that selectively activates both DA1 and beta 2 adrenergic receptors and is being evaluated in patients with CHF and in individuals with postoperative left ventricular dysfunction. A group of selective DA2 receptor agonists is being evaluated as long-term treatment for systemic hypertension.

Expression of the subtype 1A dopamine receptor in the rat heart

The subtype 1A dopamine receptor (D1A) has recently been detected in the rat kidney. In the present study using light microscopic immunohistochemistry, electron microscopic immunocytochemistry, and in situ amplification of mRNA, we demonstrate the D1A receptor in Sprague-Dawley and Wistar Kyoto rat hearts. For immunohistochemistry and immunocytochemistry, anti-peptide polyclonal antibodies were directed toward amino acid sequences of the third extracellular and intracellular domains of the native receptor. Selectivity was validated by recognition of the D1A receptor expressed in stably transfected LTK- cells. D1A receptor mRNA was detected with a novel transcription-based isothermal in situ amplification system as well as with reverse transcription-polymerase chain reaction. D1A receptor protein was distributed throughout the atrium and ventricular myocardium. Preimmune and preabsorption controls were negative. Electron microscopic immunocytochemistry using the protein A gold method demonstrated the D1A receptor along the cellular membranes of coronary smooth muscle cells and ventricular myocytes and in the myosin thick filaments and M-lines. D1A receptor mRNA was present in coronary vessels and myocardium in amplified but not in unamplified sections. Western blot analysis showed specific D1A bands in transfected LTK- cells and the atrium but not in nontransfected LTK- cells and the ventricle. The selective D1-like receptor agonist SKF38393 stimulated adenylyl cyclase in ventricular myocardial plasma membranes in a dose-related fashion, and the response was abolished by the selective D1-like receptor antagonist SCH23390. These results demonstrate that the D1A receptor gene and protein are expressed in normal rat heart. The physiological and pathophysiological roles and predominant cell signaling mechanism or mechanisms of this receptor remain to be determined.