Dopamine infusion in man. Plasma catecholamine levels and pharmacokinetics

The physiological basis of renal nuclear medicine

Renal physiology underpins renal nuclear medicine, both academic and clinical. Clearance, an important concept in renal physiology, comprises tissue uptake rate of tracer (tissue clearance), disappearance rate from plasma (plasma clearance), appearance rate in urine (urinary clearance) and disappearance rate from tissue. In clinical research, steady-state plasma clearances of para-amino-hippurate and inulin have been widely used to measure renal blood flow (RBF) and glomerular filtration rate (GFR), respectively. Routinely, GFR is measured at non-steady state as plasma clearance of a filtration agent, such as technetium-99m diethylenetriaminepentaacetic acid. Scaled to three-dimensional whole body metrics rather than body surface area, GFR in women is higher than in men but declines faster with age. Age-related decline is predominantly from nephron loss. Tubular function determines parenchymal transit time, which is important in renography, and the route of uptake of technetium-99m dimercaptosuccinic acid, which is via filtration. Resistance to flow is defined according to the pressure-flow relationship but in renography, only transit time can be measured, which, being equal to urine flow divided by collecting system volume, introduces further uncertainty because the volume is also unmeasurable. Tubuloglomerular feedback governs RBF and GFR, is regulated by the macula densa, mediated by adenosine and renin, and can be manipulated with proximal tubular sodium-glucose cotransporter-2 inhibitors. Other determinants of renal haemodynamics include prostaglandins, nitric oxide and dopamine, while protein meal and amino acid infusion are used to measure renal functional reserve. In conclusion, for measuring renal responses to exogenous agents, steady-state para-amino-hippurate and inulin clearances should be replaced with rubidium-82 and gallium-68 EDTA for measuring RBF and GFR.

Neighborhood socioeconomic deprivation and individual-level socioeconomic status are associated with dopamine-mediated changes to monocyte subset CCR2 expression via a cAMP-dependent pathway

Social determinants of health (SDoH) include socioeconomic, environmental, and psychological factors that impact health. Neighborhood socioeconomic deprivation (NSD) and low individual-level socioeconomic status (SES) are SDoH that associate with incident heart failure, stroke, and cardiovascular mortality, but the underlying biological mechanisms are not well understood. Previous research has demonstrated an association between NSD, in particular, and key components of the neural-hematopoietic-axis including amygdala activity as a marker of chronic stress, bone marrow activity, and arterial inflammation. Our study further characterizes the role of NSD and SES as potential sources of chronic stress related to downstream immunological factors in this stress-associated biologic pathway. We investigated how NSD, SES, and catecholamine levels (as proxy for sympathetic nervous system activation) may influence monocytes which are known to play a significant role in atherogenesis. First, in an ex vivo approach, we treated healthy donor monocytes with biobanked serum from a community cohort of African Americans at risk for CVD. Subsequently, the treated monocytes were subjected to flow cytometry for characterization of monocyte subsets and receptor expression. We determined that NSD and serum catecholamines (namely dopamine [DA] and norepinephrine [NE]) associated with monocyte C-C chemokine receptor type 2 (CCR2) expression (p < 0.05), a receptor known to facilitate recruitment of monocytes towards arterial plaques. Additionally, NSD associated with catecholamine levels, especially DA in individuals of low SES. To further explore the potential role of NSD and the effects of catecholamines on monocytes, monocytes were treated in vitro with epinephrine [EPI], NE, or DA. Only DA increased CCR2 expression in a dose-dependent manner (p < 0.01), especially on non-classical monocytes (NCM). Furthermore, linear regression analysis between D2-like receptor surface expression and surface CCR2 expression suggested D2-like receptor signaling in NCM. Indicative of D2-signaling, cAMP levels were found to be lower in DA-treated monocytes compared to untreated controls (control 29.78 pmol/ml vs DA 22.97 pmol/ml; p = 0.038) and the impact of DA on NCM CCR2 expression was abrogated by co-treatment with 8-CPT, a cAMP analog. Furthermore, Filamin A (FLNA), a prominent actin-crosslinking protein, that is known to regulate CCR2 recycling, significantly decreased in DA-treated NCM (p < 0.05), indicating a reduction of CCR2 recycling. Overall, we provide a novel immunological mechanism, driven by DA signaling and CCR2, for how NSD may contribute to atherogenesis. Future studies should investigate the importance of DA in CVD development and progression in populations disproportionately experiencing chronic stress due to SDoH.

Dopaminergic Inhibition of Human Neutrophils is Exerted Through D1-Like Receptors and Affected By Bacterial Infection

BACKGROUND

Dopamine (DA) affects immune functions in healthy subjects and during disease by acting on D1-like (D1 and D5) and D2-like (D2, D3 and D4) dopaminergic receptors (DR), however its effects on human polymorphonuclear leukocytes (PMN) are still poorly defined.

METHODS

We investigated DR expression in human PMN and the ability of DA to affect cell migration and reactive oxygen species (ROS) production. Experiments were performed on cells from healthy subjects (HS) and from patients (Pts) with bacterial infections as well, during the acute phase and after recovery. Some experiments were also performed in mice KO for the DRD5 gene.

RESULTS

PMN from HS express both D1-like and D2-like DR, and exposure to DA results in inhibition of activation-induced morphological changes, migration and ROS production which depend on the activation of D1-like DR. In agreement with these findings, DA inhibited migration of PMN obtained from wild-type mice, but not from DR D5 KO mice. In Pts with bacterial infections, during the febrile phase D1-like DR D5 on PMN were downregulated and DA failed to affect PMN migration. Both D1-like DR D5 expression and DA-induced inhibition of PMN migration were however restored after recovery.

CONCLUSION

Dopaminergic inhibition of human PMN is a novel mechanism which is likely to play a key role in the regulation of innate immunity. Evidence obtained in Pts with bacterial infections provides novel clues for the therapeutic modulation of PMN during infectious disease.

N-arylpiperazine-containing compound (C2): An enhancer of sunitinib in the treatment of pancreatic cancer, involving D1DR activation

Previous studies showed that dopamine (DA) significantly reduces the frequency of cancer stem-like cells (CSC) and enhances the efficacy of sunitinib (SUN) in the treatment of breast cancer and non-small cell lung cancer (NSCLC). To overcome the shortcomings of DA in clinical practice, the purpose of this study was to investigate the efficacy as well as the underlying mechanism of an orally available, N-arylpiperazine-containing compound C2, in the treatment of pancreatic cancer when used alone or in combination with SUN. Our results showed that C2 and SUN exerted synergistic effects on inhibiting the growth of SW1990 and PANC-1 pancreatic cancer cells. C2 significantly inhibited colony formation and migration of both cells. SW1990 xenograft and patient-derived xenograft (PDX) models were utilized for pharmacodynamic investigation in vivo. C2 alone showed little inhibition effect on tumor growth but increased the anti-tumor efficacy of SUN in both xenografts. Moreover, C2 down-regulated CSC markers (CD133 and ALDH) of both cancer cells and up-regulated the expression of dopamine receptor D1 (D1DR) in tumor. Besides, the SW1990 tumor growth was dose-dependently inhibited when the cells were pretreated with C2 before implantation. C2 increased intratumoral cAMP level, and the combination with D1DR specific antagonist SCH23390 reversed the above-mentioned effects of C2 both in vitro and in vivo, indicating the activation of D1DR may be involved in the underlying mechanism of C2 action. In summary, C2 could reduce the CSC frequency and enhance the anti-cancer effect of SUN in the treatment of pancreatic cancer, demonstrating its potential in cancer therapy.

Dopamine D1 receptor agonists inhibit lung metastasis of breast cancer reducing cancer stemness

The leading causes of death in breast cancer patients are disease recurrence and metastasis. Growing evidence has suggested that metastasis possibly originates from cancer stem-like cells (CSCs). Previous studies indicated dopamine decreased CSC frequency through activating dopamine D₁ receptor pathway. Hence, this study explored the efficacy of two dopamine D₁ receptor agonists in lung metastasis of breast cancer and the preliminary mechanism. The two dopamine D₁ receptor agonists, fenoldopam (FEN) and l-stepholidine (l-SPD), performed well in decreasing lung metastasis in 4T1 breast cancer model. And the cGMP in the primary tumor was significantly elevated while cAMP mildly elevated in FEN and l-SPD dosing groups. CSC markers (CD44⁺/CD24^- and ALDH⁺) and MMP2 in 4T1 primary tumor were repressed after dopamine D₁ receptor agonist administration while E-cadherin up-regulated. FEN and l-SPD also inhibited cancer stemness and cell motility in vitro, and the inhibitory effects could be reversed by dopamine D₁ receptor antagonist SCH23390. Besides, FEN impacted the white blood cell increase caused by breast cancer disease showing decreased neutrophils but increased lymphocytes. Drug safety was verified in aspects of body weight, organ index and tissue section. In conclusion, dopamine D₁ receptor agonists FEN and l-SPD showed efficacy in inhibiting metastasis along with good safety in breast cancer, thus providing an alternative for anti-metastasis therapy in the future. Furthermore, this study also indicates that dopamine D₁ receptor may be a possible target for metastatic breast cancer treatment and even other cancers at a late stage.

Comparing the Rates of Dopamine Hemodynamic Effect Onset after Infusion through Peripheral Veins in Three Regions

Background

Dopamine is an inotropic agent that is often selected for continuous infusion. For hemodynamic stability, the rate of infusion is controlled in the range of 5-15 μg/kg/min. This study aimed to compare the time intervals from the administration of dopamine to the onset of its hemodynamic effects when dopamine was administered through three different peripheral veins (the cephalic vein [CV], the great saphenous vein [GSV], and the external jugular vein [EJV]).

Methods

Patients in group 1, group 2, and group 3 received dopamine infusions in the CV, GSV, and EJV, respectively. A noninvasive continuous cardiac output monitor (NICCOMO™, Medis, Ilmenau, Germany) was used to assess cardiac output (CO) and systemic vascular resistance (SVR). Six minutes after intubation, baseline heart rate (HR), systolic blood pressure (BP), diastolic BP, mean arterial pressure (MAP), CO, and SVR values were recorded and dopamine infusion was initiated at a dose of 10 μg/kg/min. Hemodynamic changes at 0, 4, 8, 12, and 15 minutes postinfusion were recorded.

Results

No statistically significant differences were observed among the three groups with respect to the rate of hemodynamic change. In all groups, systolic BP, diastolic BP, MAP, and SVR tended to increase after decreasing for the first 4 minutes; in contrast, HR and CO decreased until 8 minutes, after which they tended to reach a plateau.

Conclusions

For patients under general anesthesia receiving dopamine at 10 μg/kg/min, there were no clinical differences in the effect of dopamine administered through three different peripheral veins.

Pharmacokinetics of centhaquin citrate in a rat model

OBJECTIVE

Centhaquin citrate is a novel agent being developed for use in the treatment of haemorrhagic shock. It has decreased mortality in rat, rabbit and pig models of hypovolaemic shock compared to hypertonic saline and lactated Ringer's resuscitation. The pharmacokinetics of centhaquin citrate have not been described to date.

METHODS

Sixteen male Sprague Dawley rats were given an intravenous bolus of 0.45 mg/kg centhaquin citrate. Rats were divided into two groups; plasma concentrations were measured at five time points for each group within 24 h after administration. Competing compartmental pharmacokinetic models were assessed. The nonparametric adaptive grid function within the Pmetrics package for R was used for parameter estimation. Predicted concentrations were calculated using population median and individual Bayesian posterior parameters.

KEY FINDINGS

A two-compartment model of centhaquin citrate best fit the data. Median (IQR) values for elimination coefficient (Ke), volume of distribution (V) and intercompartmental transfer rates (Kcp, Kpc) were 8.8 (5.2-12.8) h(-1), 6.4 (2.8-10.4) l, 11.9 (4.6-15.0) h(-1) and 3.7 (2.3-9.1) h(-1), respectively.

CONCLUSION

This is the first report of the pharmacokinetic parameters of centhaquin citrate in a rat model. Centhaquin citrate was found to have a short half-life with a large volume of distribution.

Preterm lambs given intravenous dopamine show increased dopamine in their cerebrospinal fluid

AIM

Dopamine is used as an inotropic medication in preterm infants. The preterm human blood brain barrier (BBB) is permeable to intravascular dopamine, and the impact of exogenous dopamine on the preterm brain remains unknown. The preterm lamb model may be suitable for studying the cerebral impact of dopamine therapy whether its BBB permeability is similar to preterm human infants. We aimed to examine BBB permeability to exogenous dopamine in the preterm lamb, by measuring dopamine levels in the cerebrospinal fluid (CSF).

METHODS

Nine preterm foetal lambs (125-130 days, term = 147 days) were given either dopamine at 10 μg/kg/min (dopamine, n = 4) or saline (control, n = 5). CSF, and plasma samples were taken for dopamine assay.

RESULTS

The median (range) baseline CSF dopamine level for the combined control and dopamine groups (n = 9) was 0.10(0.03-0.16) ng/mL, and baseline plasma dopamine was 0.30(0.13-0.84) ng/mL. The dopamine lambs showed increase in CSF dopamine to 3.91(1.87-11.35) ng/mL with plasma dopamine increased to 14.2 (9.1-57.9) ng/mL. No change was found in the control lambs.

CONCLUSION

In the preterm lamb, the BBB permeability and pharmacokinetics to dopamine infusion are similar to findings in the preterm human infant, supporting applicability of the preterm lamb model for studying effects of dopamine infusion in the preterm human brain.

Endomyocardial biopsy in a patient with hemorrhagic pheochromocytoma presenting as inverted Takotsubo cardiomyopathy

A 29-year-old female patient presented with shock and dyspnea due to heart failure and pulmonary edema. Echocardiography indicated excessive contraction limited to the left ventricular apex and akinesis of the basal and middle ventricle, which were confirmed by emergency left ventriculography. The finding was diagnostic of inverted Takotsubo cardiomyopathy. An abdominal computed tomography scan showed a tumor in the left adrenal gland with a central low-density area, and the plasma and urinary catecholamines were strikingly elevated. Taken together, these findings suggested the presence of a hemorrhagic pheochromocytoma. A myocardial biopsy in the very acute stage on the day of admission revealed neutrophilic infiltration and contraction-band necrosis, which was indistinguishable from the previously reported pathology in the acute phase of idiopathic Takotsubo cardiomyopathy without pheochromocytoma. The diagnosis of pheochromocytoma in this case was confirmed 7 weeks later by surgical removal of the left adrenal gland with massive hemorrhage at the center of the pheochromocytoma. The marked similarity of the endomyocardial pathology between this case and cases with idiopathic Takotsubo cardiomyopathy strongly points to catecholamine excess as a common causality for Takotsubo cardiomyopathy with or without pheochromocytoma.

Neuronal source of plasma dopamine

BACKGROUND

Determinants of plasma norepinephrine (NE) and epinephrine concentrations are well known; those of the third endogenous catecholamine, dopamine (DA), remain poorly understood. We tested in humans whether DA enters the plasma after corelease with NE during exocytosis from sympathetic noradrenergic nerves.

METHODS

We reviewed plasma catecholamine data from patients referred for autonomic testing and control subjects under the following experimental conditions: during supine rest and in response to orthostasis; intravenous yohimbine (YOH), isoproterenol (ISO), or glucagon (GLU), which augment exocytotic release of NE from sympathetic nerves; intravenous trimethaphan (TRI) or pentolinium (PEN), which decrease exocytotic NE release; or intravenous tyramine (TYR), which releases NE by nonexocytotic means. We included groups of patients with pure autonomic failure (PAF), bilateral thoracic sympathectomies (SNS-x), or multiple system atrophy (MSA), since PAF and SNS-x are associated with noradrenergic denervation and MSA is not.

RESULTS

Orthostasis, YOH, ISO, and TYR increased and TRI/PEN decreased plasma DA concentrations. Individual values for changes in plasma DA concentrations correlated positively with changes in NE in response to orthostasis (r = 0.72, P < 0.0001), YOH (r = 0.75, P < 0.0001), ISO (r = 0.71, P < 0.0001), GLU (r = 0.47, P = 0.01), and TYR (r = 0.67, P < 0.0001). PAF and SNS-x patients had low plasma DA concentrations. We estimated that DA constitutes 2%-4% of the catecholamine released by exocytosis from sympathetic nerves and that 50%-90% of plasma DA has a sympathoneural source.

CONCLUSIONS

Plasma DA is derived substantially from sympathetic noradrenergic nerves.

Low-dose dopamine in the intensive care unit

For much of the last four decades, low-dose dopamine has been considered the drug of choice to treat and prevent renal failure in the intensive care unit (ICU). The multifactorial etiology of renal failure in the ICU and the presence of coexisting multisystem organ dysfunction make the design and execution of clinical trials to study this problem difficult. However, in the last decade, several meta-analyses and one large randomized trial have all shown a lack of benefit of low-dose dopamine in improving renal function. There are multiple reasons for this lack of efficacy. While dopamine does cause a diuretic effect, it does very little to improve mortality, creatinine clearance, or the incidence of dialysis. Evidence is also growing of its adverse effects on the immune, endocrine, and respiratory systems. It may also potentially increase mortality in sepsis. It is the opinion of the authors that the practice of using low-dose dopamine should be abandoned. Other drugs and treatment modalities need to be explored to address the serious issue of renal failure in the ICU.

Dopamine infusion and anterior pituitary gland function in very low birth weight infants

BACKGROUND

Previous studies demonstrated that dopamine infusion reduces plasma concentration of thyroxine (T4), thyroid stimulating hormone (TSH), prolactin (PRL), and growth hormone (GH) in adults, children, and infants.

OBJECTIVES

The purpose of this prospective observational study was to evaluate the relationship between dopamine infusion and the dynamics of T4, TSH, PRL, and GH in preterm newborns weighing less than 1,500 g (very low birth weight infants, VLBW) admitted in a neonatal intensive care unit of a university hospital over a one year period.

METHODS

A total of 97 preterm newborns were enrolled and divided into two groups: group B included hypotensive infants treated with plasma expanders and dopamine infusion; group A was the control group including newborns who were never treated with dopamine. The newborns were studied dynamically through blood samples taken every day till 10 days. Newborns of group B were studied during dopamine infusion and after its withdrawal.

RESULTS

Among the VLBW newborns who were given dopamine, the four pituitary hormones had different dynamics: a reduction of T4, TSH, and PRL levels was noticed since the first day of treatment, and a rebound of their levels was evident since the first day after its interruption. On the contrary, the postprandial GH levels were roughly constant: GH plasma concentrations were in fact a little lower in newborns treated with dopamine, and a slight increase was observed after its withdrawal. However, observed differences were not statistically significant.

CONCLUSIONS

The results suggest that dopamine infusion reduces T4, TSH, and PRL plasma levels in preterm VLBW infants and have no effect on postprandial GH rate. This hormonal suppression reverses rapidly after dopamine withdrawal. This observation suggests that the iatrogenic pituitary suppression probably cannot produce long-term injuries.

Dopamine or norepinephrine infusion during thoracic epidural anesthesia? Differences in hemodynamic effects and plasma catecholamine levels

BACKGROUND

During thoracic epidural anesthesia, an intravenous dopamine infusion augments the systemic pressure response and modifies plasma catecholamine levels. If such an altered response occurs when norepinephrine is infused is not clear. Therefore, dopamine and norepinephrine induced circulatory and catecholamine responses were studied before and during thoracic epidural anesthesia.

METHODS

Nine chloralose-anesthetized dogs were equipped with thoracic epidural catheters. Dopamine (5, 10, and 20 microg kg(-1) min(-1)), and norepinephrine (0.1, 0.25, and 0.5 microg kg(-1) min(-1)) were infused before and during epidural anesthesia, while cardiovascular performance and plasma catecholamine changes were studied.

RESULTS

Thoracic epidural anesthesia decreased arterial pressure, and cardiac contractility. The systemic pressure response induced by dopamine was augmented during epidural anesthesia. Norepinephrine did not increase arterial pressure and myocardial contractility as markedly as dopamine, and cardiac output was not altered. Thoracic epidural anesthesia attenuated the plasma norepinephrine level. Plasma dopamine levels were augmented by the dopamine infusion during epidural anesthesia, while plasma norepinephrine levels were attenuated. In contrast, norepinephrine augmented the plasma norepinephrine levels during epidural anesthesia. In general, plasma norepinephrine levels were three to six times higher during a norepinephrine infusion compared to a dopamine infusion.

CONCLUSION

The cardiovascular response to a graded dopamine infusion is augmented during thoracic epidural anesthesia, while norepinephrine-induced effects are unaltered. The modified plasma catecholamine levels may contribute to the hemodynamic differences between dopamine and norepinephrine infusions during thoracic epidural anesthesia.

Pharmacokinetics and pharmacodynamics of dopamine and norepinephrine in critically ill head-injured patients

OBJECTIVE

To explore the pharmacokinetics and pharmacodynamics of dopamine and norepinephrine.

DESIGN

Prospective, controlled, trial.

SETTING

Neurosciences critical care unit.

PATIENTS

Eight patients with a head injury, requiring dopamine or norepinephrine infusions to support cerebral perfusion pressure (CPP).

INTERVENTION

Patients received in randomised order, either dopamine or norepinephrine to achieve and maintain a CPP of 70 mmHg, and then, following a 30-min period of stable haemodynamics, a CPP of 90 mmHg. Data were then acquired using the second agent. Haemodynamic measurements were made during each period and a blood sample was obtained at the end of each study period for analysis of plasma catecholamine concentrations

MEASUREMENTS AND RESULTS

Plasma levels of norepinephrine and dopamine were significantly related to infusion rates but did not have a simple linear relationship to haemodynamic parameters. However, there was a significant quadratic relationship between the infusion rate of dopamine and cardiac index (r2=0.431), and systemic vascular resistance index (r2=0.605), with a breakpoint (at which cardiac index reduced and SVRI increased) at a dopamine plasma level of approximately 50 nM/l (corresponding to an infusion rate of approximately 15 microg.kg(-1).min(-1)).

CONCLUSIONS

Norepinephrine and dopamine have predictable pharmacokinetics; however, those of dopamine do not fit a simple first-order kinetic model. The pharmacodynamic effects of dopamine and norepinephrine show much inter-individual variability and unpredictability. Plasma levels of dopamine appear to relate to variations in adrenergic receptor effects with break points that reflect expectations from infusion-rate related pharmacodynamics.

Dopamine infusion and hypothyroxinaemia in very low birth weight preterm infants

The purpose of this study was to assess the relationship between transient hypothyroxinaemia of prematurity (THOP) in very low birth weight newborns and dopamine administration. A total of 172 newborns was enrolled in a prospective observational study and divided into three groups: group A included newborns who were never treated with dopamine; group B were infants in whom dopamine treatment was discontinued for at least 6 h before the congenital hypothyroidism screening and group C included infants who were given dopamine during the screening. Among those newborns given dopamine, the THOP incidence was higher (11.6% in group A; 53.8% in group B; 89.3% in group C), and the vales of TSH (1.67+/-2.32 microU/ml in group A; 1.29+/-1.74 microU/ml in group B; 0.89+/-1.34 microU/ml in group C) and thyroxine (6.1+/-2.2 microg/dl in group A; 3.9+/-1.9 microg/dl in group B; 2.4+/-1.4 microg/dl in group C) were significantly lower. These differences were further confirmed even after gestational age stratification and mathematical correction for differences in clinical conditions. The effects of dopamine appear to be dose-dependent.

CONCLUSION

Even if it cannot be excluded that reduced thyroid stimulating hormone and thyroxine concentrations are caused by non-thyroidal illness, the results suggest that the infusion of dopamine reduces the thyroid stimulating hormone and thyroxine levels in very low birth weight newborns.

Bad medicine: low-dose dopamine in the ICU

Low-dose dopamine administration (ie, doses < 5 microg/kg/min) has been advocated for 30 years as therapy in oliguric patients on the basis of its action on dopaminergic renal receptors. Recently, a large, multicenter, randomized, controlled trial has demonstrated that low-dose dopamine administered to critically ill patients who are at risk of renal failure does not confer clinically significant protection from renal dysfunction. In this review, we present the best evidence and summarize the effects of low-dose dopamine infusion in critically ill patients. We review the history and physiology of low-dose dopamine administration and discuss the reasons why dopamine is not clinically effective in the critically ill. In addition to the lack of renal efficacy, we present evidence that low-dose dopamine administration worsens splanchnic oxygenation, impairs GI function, impairs the endocrine and immunologic systems, and blunts ventilatory drive. We conclude that there is no justification for the use of low-dose dopamine administration in the critically ill.

Kinetic interactions of dopamine and dobutamine with human catechol-O-methyltransferase and monoamine oxidase in vitro

Dopamine and dobutamine are often infused together into acutely ill patients requiring temporary support of cardiac and renal function, but whether these catecholamines affect the metabolic clearance of each other is not established. We determined the kinetics of dopamine and dobutamine as substrates and inhibitors of each other, i.e., apparent V(max), K(m), and K(i), with crude preparations of human blood mononuclear cell catechol-O-methyltransferase (COMT) and platelet monoamine oxidase (MAO) at pH 7.4 and 37 degrees C. Values of V(max) for dopamine and dobutamine as substrates for COMT were 0.45 and 0.59 nmol of 3-O-methyl product formed per milligram of protein per minute, whereas those for K(m) were 0.44 and 0.05 mM, respectively. Dopamine and dobutamine were competitive inhibitors of each other in this reaction. The K(i) for dopamine as an inhibitor of dobutamine methylation was 1.5 mM, whereas that for dobutamine as an inhibitor of dopamine methylation was 0.015 mM. Dopamine but not dobutamine was a substrate for MAO. The V(max) for dihydroxyphenylacetaldehyde formation from dopamine was 0.29 nmol/mg protein/min and the K(m) for dopamine was 0.38 mM. Dobutamine was a noncompetitive inhibitor of dopamine oxidation in this reaction (K(i) congruent with 1.19 mM). The high apparent K(m) and K(i) values derived for dopamine and dobutamine when tested with these two human enzymes in vitro suggest that these catecholamines do not interfere with the metabolism of each other when both are infused together at therapeutic concentrations.

Airway oximetry improves monitoring of dopamine effects in pediatric cardiac patients

OBJECTIVE

Simple, preferably noninvasive measurements of cardiac output are useful in pediatric patients receiving inotropic support. Oxygen saturation in pulmonary artery (Svo(2)) gives information about oxygen delivery and demand. Many inotropic drugs influence oxygen consumption. When effects on Svo(2) are studied, after a change in inotropic drug dosage, a change in oxygen consumption needs to be considered to accurately estimate the change in cardiac output. The aim of this investigation was to study whether information on inspired to end-tidal oxygen concentration difference (Fi-eto(2)) in addition to Svo(2) would improve estimation of changes in cardiac output.

DESIGN

Prospective observational study of Fi-eto(2), Svo(2), and oxygen saturation from central vein (Scvco(2)) for measurements of circulatory and metabolic effects of changes in dopamine dosage.

SETTING

Intensive care unit in a children's hospital.

PATIENTS

Twenty patients (age 4 days to 98 months) were studied after cardiac surgery.

INTERVENTIONS

Dopamine was administered in doses of 5, 10, 0, and 5 microg x kg(-1) x min(-1), 20 mins on each level.

MEASUREMENTS AND MAIN RESULTS

Cardiac output, measured with thermodilution, oxygen saturation from systemic artery (Sao(2)), Svo(2), and Scvco(2) were measured at 15 mins on each dopamine dose. Oxygen consumption was calculated by using the Fick equation. Fi-eto(2) was measured continuously with a paramagnetic oxygen analyzer. Both cardiac output and oxygen consumption were affected by changes in dopamine dosage. Relative changes in cardiac output were poorly correlated to the change in 1/Sa-vo(2) (r(2) =.54). Using Fi-eto(2) improved correlation between changes in cardiac output and changes in Fi-eto(2)/Sa-vo(2) (r(2) =.72). When Svo(2) was replaced by Scvco(2), the correlation between changes in cardiac output and changes in Fi-eto(2)/Sa-cvco(2) was only slightly altered (r(2) =.69).

CONCLUSIONS

Dopamine affects oxygen consumption as well as cardiac output. The accuracy of Svo(2)-based estimations of changes in cardiac output after dopamine is enhanced if changes in Fi-eto(2) are also considered. The more easily achievable Scvco(2) gave equivalent information as Svo(2).

Modulation of chemokine production in lung microvascular endothelial cells by dopamine is mediated via an oxidative mechanism

Serum concentrations of catecholamines are high in patients with sepsis or acute respiratory distress syndrome (ARDS). Because chemokines mediate the recruitment of neutrophils into inflammatory sites, we addressed the question of whether dopamine (DA) is able to influence chemokine production in endothelial cells under basal and proinflammatory conditions. To this end, lung microvascular endothelial cells (LMVEC) were stimulated or not for 24 h with the bacterial toxins lipopolysaccharide (LPS) (1 microg/ml) or lipoteichonic acid (LTA) (10 microg/ml) in the presence or absence of various concentrations of DA (1-100 microg/ml). Whereas under basal and stimulatory conditions, the addition of DA to endothelial cells dose-dependently increased IL-8 production, the production of ENA-78 and Gro-alpha was significantly inhibited (P < 0.01). This effect could still be demonstrated when the cells were stimulated for up to 3 h with LPS before DA administration. Similar findings were detected for the mRNA expression of these chemokines. The influence of DA on chemokine production was not receptor mediated and could be prevented by antioxidants or radical scavengers. Moreover, addition of H(2)O(2) to endothelial cells gave results similar to those observed with DA stimulation, suggesting a pivotal role for reactive oxygen species in DA-mediated modulation of chemokine production in endothelial cells. Our data thus demonstrate that DA administration results in the induction of oxidative stress, with profound effects on endothelial chemokine production.

In vitro study on antioxidant potential of various drugs used in the perioperative period

BACKGROUND

Since surgical trauma not only intensifies the oxidative stress by generating reactive oxygen species (ROS), but also weakens the biological defense system against ROS attack, the antioxidant activity of drugs used during the perioperative period, which possibly normalizes the impaired redox state in the patient, is of fundamental importance and great clinical interest.

METHODS

We have applied the phycoerythrin fluorescence-based assay, in which 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH)-generated peroxyl radical attacks B-phycoerythrin (B-PE) to lead to a sensitive decrease in its fluorescence intensity linearly, to evaluate the antioxidant activity of major drugs in anesthetic practice.

RESULTS

By the protective effect on B-PE fluorescence decay, the antioxidant activities of the drugs were classified into three groups: Group I drugs, which only slowed B-PE fluorescence decay (nicardipine, verapamil, diltiazem, ephedrine, aminophylline, vecuronium, lidocaine, mepivacaine, midazolam, thiamylal, droperidol, ketamine, hydroxyzine, butorphanol, prednisolone, hydrocortisone, betamethasone, dexamethasone, methylprednisolone, and furosemide); Group II drugs, which protected B-PE oxidation completely and stopped fluorescence decay in a certain duration (dopamine, epinephrine, norepinephrine, dobutamine, isoproterenol, and buprenorphine); and Group III drugs, which had no protective effect on B-PE oxidation (nitroglycerin, prostaglandin E1, neostigmine, pancuronium, suxamethonium, atropine, bupivacaine, pentazocine, and heparin).

CONCLUSION

These results indicate that Group I and II drugs exert some antioxidant activity in vitro, as measured by their protection of fluorescence decay of B-PE. Careful consideration of these properties might, then, serve to facilitate more efficient drug application.

Dopamine stimulation of cardiac beta-adrenoceptors: the involvement of sympathetic amine transporters and the effect of SKF38393

1. Mechanisms underlying beta-adrenoceptor stimulation by dopamine were examined on guinea-pig Langendorff-perfused hearts and isolated cells from the right atrium, by using the chronotropic effects and the enhancement of L-type Ca2+ current (ICa,L) in the presence of prazosin as indicators of beta-adrenoceptor stimulation. Dopamine-induced overflow of noradrenaline (NA) concentrations was measured by high-performance liquid chromatography. 2. Dopamine caused positive chronotropic effects with an EC50 of 2.5 microM and induced NA overflow with a similar EC50 (1.3 microM). The chronotropic effect of dopamine was abolished by bisoprolol (1 microM). 3. The effects of dopamine were maintained during prolonged application, whereas the effects of tyramine faded with time. Dopamine (3 microM) restored the chronotropic effects and the NA release suppressed by pretreatment with tyramine, suggesting a de novo synthesis of NA during the exposure to dopamine. 4. Dopamine (3 microM)-induced NA release was not affected by tetrodotoxin, omega-conotoxin, rauwolscine, ICI118551 or sulpiride, but was inhibited by desipramine, a NA uptake inhibitor (IC50 approximately 1 microM). It was also not affected by GBR12909 and bupropion, dopamine uptake inhibitors in the central nervous system. 5. SKF38393, a D1 receptor partial agonist, potently inhibited the 3 microM dopamine-induced release of NA (IC50 approximately 0.1 microM). D1 receptors are not involved in the DA-induced release of NA, since SCH23390 (3 microM), a potent D1 antagonist, inhibited the NA release only slightly, and dihydrexidine (1 microM) and chloro-APB (1 microM), full D1 agonists, caused no significant NA release. 6. SKF38393 inhibited tyramine-induced overflow of NA, and potentiated the field stimulation-induced NA release. SKF38393 and desipramine retarded the decay of the stimulation-induced tachycardia in a similar manner. These results indicate that SKF38393 is a potent monoamine transport inhibitor and a useful tool for the functional evaluation of indirectly-acting sympathomimetic agonists in the heart. In the presence of SKF38393 (10 microM), dopamine at 1 microM showed no chronotropic effect. 7. Voltage clamp experiments with isolated atrial cells revealed that dopamine is a weak partial agonist. The EC50 for ICa,L stimulation by dopamine was high (13 microM). As a result, dopamine at 1 microM did not affect ICa,L. Bisoprolol abolished the stimulation of ICa,L by dopamine (30 microM), and dihydrexidine (1 microM) did not affect ICa,L. 8. It was concluded that the cardiac effects of dopamine at clinically relevant concentrations (< 1 microM) result almost exclusively from the indirect effect of beta adrenoceptor stimulation, involving the release of NA from sympathetic nerve terminals. The roles of the direct stimulation of beta adrenoceptors by dopamine at these concentrations and the stimulation of postjunctional D1 receptors seem negligible. The desipramine- and SKF38393-sensitive monoamine transporter mediates the release of NA.

Alterations in dopamine clearance and catechol-O-methyltransferase activity by dopamine infusions in children

OBJECTIVE

To determine the role of catechol-O-methyltransferase (COMT) in the biodisposition of pharmacologic concentrations of dopamine.

DESIGN

The study was an open-label dose escalation trial in which dopamine was employed as the sole exogenous catecholamine. The dosage was adjusted to achieve improvements in cardiac output or to augment renal function.

SETTING

A 16-bed pediatric intensive care unit serving both medical and surgical patients.

PATIENTS

The study was performed using 14 dopamine-treated and five untreated control patients. Children ranged in age from 16 days to 12 yrs; five of the treated patients and two of the untreated controls were female. All but one of the study patients were enrolled within 24 hrs of palliative or corrective surgery for congenital heart disease. Control patients had noncardiac surgical procedures. Both treated and control groups were similar with respect to severity of illness, as judged by Therapeutic Intervention Scoring System score.

INTERVENTIONS

All treated patients received dopamine as a continuous intravenous infusion. Infusion rates were determined by caregivers and ranged from 3.0 to 20 micrograms/kg/min.

MEASUREMENTS AND MAIN RESULTS

Serial, timed blood samples were obtained from patients and control subjects for the determination of plasma dopamine concentrations and for the determination of mononuclear cell COMT activity. Measured rates of dopamine infusion (3.0 to 18.3 micrograms/kg/min) were consistently less than the nominal rates (3.0 to 20.0 micrograms/kg/min) of infusion (p < .0001) due in part to calculations based on the hydrochloride salt rather than dopamine base. At similar steady-state infusion rates, plasma dopamine concentrations varied over a four-fold range, with steady-state concentrations at even the lowest infusion rate exceeding endogenous concentrations by at least ten-fold. Variations in steady-state plasma dopamine concentration reflected large age-associated variations in dopamine clearance, which was found to be saturable at concentrations of > 200 ng/mL. Mononuclear cell COMT activity was assessed simultaneously in these patients. Baseline COMT activity varied over a six-fold range and was unrelated to dopamine clearance or patient age. COMT activity increased two- to six-fold in dopamine-treated patients with plasma steady-state dopamine concentrations of > 100 ng/mL.

CONCLUSIONS

These data demonstrate marked age and concentration-dependent differences in dopamine clearance that account for large interindividual differences in the steady-state plasma dopamine concentrations in patients receiving similar infusion rates. While concomitant variability in COMT activity is observed, the lack of correlation between dopamine clearance and COMT activity suggests that COMT is not rate-limiting for the clearance of exogenously administered dopamine.

Renal and neurohormonal changes following simultaneous administration of systemic vasoconstrictors and dopamine or prostacyclin in cirrhotic patients with hepatorenal syndrome

BACKGROUND/AIMS

Intravenous ornipressin in cirrhotic patients with hepatorenal syndrome causes marked improvement of systemic hemodynamics and suppression of plasma renin and norepinephrine but only moderate improvement of renal function. This study was designed to investigate whether these beneficial effects could be enhanced by the simultaneous administration of dopamine. The renal effects of the i.v. infusion of norepinephrine plus prostacyclin in patients with hepatorenal syndrome were also assessed.

METHODS

Renal plasma flow, glomerular filtration rate, free water clearance, sodium excretion and the plasma levels of renin and norepinephrine were measured in baseline conditions and during the administration of ornipressin (6 i.u./h) and ornipressin (6 i.u./h) plus dopamine (2 micrograms/kg.min) in nine patients with hepatorenal syndrome. Five additional patients with hepatorenal syndrome were studied prior to and following the administration of norepinephrine (0.45 +/- 0.1 microgram/kg.min) and norepinephrine (0.85 +/- 0.2 microgram/kg.min) plus prostacyclin (5 ng/kg.min).

RESULTS

Despite a significant increase in arterial pressure and marked suppression of plasma renin activity during ornipressin and ornipressin plus dopamine administration, no significant improvement in renal function was observed. Norepinephrine and norepinephrine plus prostacyclin also failed to increase renal perfusion and glomerular filtration rate.

CONCLUSIONS

The combined administration of systemic vasoconstrictors (ornipressin or norepinephrine) and vasodilators (dopamine or prostacyclin), at the doses used in the current study and for a short period of time, does not improve renal function in cirrhotic patients with hepatorenal syndrome. The current study does not confirm a potential role for ornipressin in the treatment of hepatorenal syndrome.

Plasma concentration and acute clinical effects of docarpamine, orally active dopamine prodrug, in infants

Currently, there are no data available on the optimal doses and efficacy of docarpamine in infants. In the present study, three doses of docarpamine, 15.0-20.4 (19.0 +/- 1.9; mean +/- SD) mg/kg per dose every 8 h to 10 infants suffering heart failure. Age and bodyweight were from 1 to 4 (1.4 +/- 1) months and 2960-5160 (3350 +/- 872) g, respectively. In all infants, plasma concentrations of free dopamine were measured 1, 2 and 3 h after the first administration. Heart rate and systolic blood pressure were examined before and at the same time as the first administration. In seven infants, the 24 h urinary output and urinary excretion of electrolytes and creatinine before and during docarpamine were measured. Peak plasma concentration of free dopamine (ng/mL) was achieved after 1 or 2 h of administration, 0-163.1 (37.9 +/- 47.2) and 0-105.0 (37.8 +/- 39.3), respectively. The concentration had decreased rapidly by 3 h to 0-34.2 (12.4 +/- 11.0). Both heart rate (b.p.m.) and blood pressure (mmHg) tended to increase from 120-154 (140 +/- 15) and 56-90 (76 +/- 11) to a peak of 124-162 (148 +/- 14) and 70-92 (79 +/- 8), respectively (P = 0.197, P = 0.289). There were no significant changes in urinary output or excreta. Oral docarpamine of 15-20 mg/kg per dose can achieve plasma free concentrations of dopamine that increase heart rate and systolic blood pressure.

A randomized crossover trial of levodopa in congestive heart failure

BACKGROUND

The short- and long-term effects of levodopa (L-dopa), an oral dopaminergic prodrug, were assessed in patients with severe left ventricular dysfunction.

METHODS AND RESULTS

Initially, 26 patients were included in the study group. After clinical, radiographic, and radionuclide examination, each patient underwent right heart catheterization (Swan-Ganz thermodilution catheter). Plasma noradrenaline levels were measured. In two patients, a favorable hemodynamic response to L-dopa was not observed, another two required permanent pacemaker implantation. These four patients were excluded from the study. Two patients required permanent pacemaker implantation. The remaining 22 patients with favorable hemodynamic response to L-dopa (increase in cardiac index, stroke volume index, reduction in total systemic resistance) were randomized in a nonblinded fashion to the conventional (11 patients) or conventional plus L-dopa (11 patients) treatment groups. During the study period, two patients, one from each group, died. They were excluded from the analysis. The final analyzed study group consisted of 20 men, aged 33-69, in New York Heart Association functional class IV (9 patients) and III (11 patients). The cause of congestive heart failure was primary dilated cardiomyopathy in 11 patients and ischemic heart disease in 9 patients. After 3 months' treatment, all patients were crossed over. Clinical, radiographic, radionuclide, and hemodynamic evaluation was repeated at the end of the 3-month treatment period. After 3 months of therapy with L-dopa in each group (covariance analysis), there was improvement in clinical, radiographic (relative heart volume, -128 mL/m2), radionuclide (left ventricular ejection fraction, +4.6; right ventricular ejection fraction, +4.8%), hemodynamic (mean pulmonary wedge pressure, -8 mmHg; total systemic resistance, -1.8 Wu; total pulmonary resistance, -3.5 Wu), and neurohumoral (noradrenaline, -218 pg/mL) measures.

CONCLUSIONS

The addition of L-dopa to conventional therapy has beneficial short- and long-term effects in patients with severe left ventricular dysfunction.

Are the cardiovascular actions of dopamine altered by isoflurane?

Dopamine seems theoretically to be a rationale choice when adrenergic support is needed to counter undesired cardiovascular depressant effects of isoflurane. Although the cardiovascular effects of isoflurane (ISO) and exogenous dopamine (DA) are well documented, there are no reports on their pharmacological interaction. The effects of ISO 1.4% (MAC 1.0) on the cardiovascular response to exogenous DA were studied in dogs during chloralose anesthesia. Instrumentation included catheterizations of the femoral artery (for aortic pressures and heart rate, HR), the pulmonary artery (for thermodilution cardiac output, CO, and pulmonary arterial pressures) and the left ventricle (for tip-manometer measured left ventricular end-diastolic pressure, LVEDP). ISO per se decreased HR (-16%), mean arterial pressure (MAP; -33%), CO (-29%), left ventricular dP/dt (LV dP/dt; -51%), and increased pulmonary artery occlusion (PAOP; +64%) and LVEDP (+28%). Prior to ISO, DA increased MAP, CO stroke volume (SV), LV dP/dt and LV dP/dt/SAP (systolic arterial pressure) at the dose 10 micrograms.kg-1.min-1. At the dose 20 micrograms.kg-1.min-1 DA, besides these effects, increased PAOP and mean pulmonary artery pressure (MPAP). During ISO, DA at the dose 10 micrograms.kg-1.min-1 restored MAP, CO, and SV to pre-ISO control levels, while LV dP/dt was increased to +96% above the pre-ISO control level. At the dose 20 micrograms.kg-1.min-1, DA increased MAP (+33%), LV dP/dt (+172%), PAOP (+132%) and MPAP (+50%) above pre-ISO control levels. The cardiac effects of DA were similar to when it was given alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine and the sick euthyroid syndrome in critical illness

OBJECTIVE

The sick euthyroid syndrome is a poorly understood hallmark of critical illness. Dopamine is a natural catecholamine with hypophysiotrophic properties, that is used as an inotropic agent of first choice in intensive care medicine. We explored the effect of dopamine infusion (5 micrograms/kg/min) on the sick euthyroid syndrome of critically ill patients.

PATIENTS AND DESIGN

In a prospective, randomized, controlled and open-labelled study of critically ill, adult polytrauma patients (n = 12), we evaluated the effect of prolonged (83-296 hours) dopamine infusion (5 micrograms/kg/min i.v.) on the thyroid axis. The effect of brief (15-21 hours) dopamine administration was documented in an additional randomized, controlled, cross-over study involving 10 patients. The median age of the studied patients was 29 (16-83) years.

MEASUREMENTS

Serum TSH concentrations were measured by IRMA. The TSH profiles were obtained by blood sampling every 20 minutes for 9 hours during two consecutive nights. Serum T4, T3 and reverse T3 concentrations were measured by RIA once per study night.

RESULTS

Withdrawal of prolonged dopamine infusion was found to elicit a tenfold increase of serum thyrotrophin concentrations, a 57 and 82% rise of T4 and T3 respectively, and an increase of the T3/rT3 ratio, resulting in virtual normalization of the thyroid axis within 24 hours. The brief dopamine infusion was documented to have a suppressive effect on the thyroid axis within 24 hours.

CONCLUSIONS

Dopamine infusion appears to induce or aggravate the sick euthyroid syndrome in critical illness. As a consequence, the sick euthyroid syndrome of severely ill patients receiving dopamine may be not an adaptive mechanism, but a condition of iatrogenic hypothyroidism.

Pharmacokinetics of cardiovascular drugs in children. Inotropes and vasopressors

Infants and children with congenital or acquired heart disease and children with systemic disease often require pharmacological support of their failing circulation. Catecholamines may serve as inotropic (enhance myocardial contractility) or vasopressor (elevate systemic vascular resistance) agents. Noncatecholamine inotropic agents, such as the cardiac glycosides or the bipyridines, may be used in place of, or in addition to, catecholamines. Developmental changes in neonates, infants and children will affect the response to inotropic or pressor therapy. Maturation of the gastrointestinal tract, liver and kidneys alters absorption, metabolism and elimination of drugs, although there are few clear examples of this among the vasoactive drugs considered in this review. Changes in body composition affect the volume of distribution (Vd) and clearance (CL) of drugs. Developmentally based pharmacodynamic differences also affect the responses to both therapeutic and toxic effects of inotropes. These pharmacodynamic differences are based in part upon developmental changes in myocardial structure, cardiac innervation and adrenergic receptor function. For example, the immature myocardium has fewer contractile elements and therefore a decreased ability to increase contractility; it also responds poorly to standard techniques of manipulating preload. Available data suggest that dopamine and dobutamine pharmacokinetics are similar to those in adults. Wide interindividual variability has been noted. A consistent relationship between CL and age has not been demonstrated, although one investigator demonstrated an almost 2-fold increase in the CL of dopamine in children under the age of 2 years. The CL of dopamine appears to be reduced in children with renal and hepatic failure. Fewer data are available regarding the pharmacokinetics of epinephrine (adrenaline), norepinephrine (noradrenaline) and isoprenaline (isoproterenol). Digoxin pharmacokinetics have been extensively evaluated in infants and children. The Vd for digoxin is increased in infants and children. Children beyond the neonatal period display increased CL of digoxin, approaching adult values during puberty. Although it was previously thought that children both needed and tolerated higher serum concentrations of digoxin than adults, more recent studies indicate that adequate clinical response can be achieved with serum concentrations similar to those aimed for in adults, with decreased toxicity. Evaluation of studies of digoxin pharmacokinetics is complicated by the presence of an endogenous substance with digoxin-like activity on radioimmunoassay. Limited studies of amrinone pharmacokinetics in infants and children indicate a dramatically larger Vd, and a decreased elimination half-life in older infants and children, compared with values observed in adults.

The effects of dopamine infusion on the postoperative energy expenditure, metabolism, and catecholamine levels of patients after esophagectomy

Although dopamine is one of the most widely used vasoactive agents, its postoperative thermogenic and metabolic effects have not been studied. In this study, the effects of low-dose dopamine, given at 5 microgram/kg/min, on resting energy expenditure (REE), metabolism, and plasma catecholamine levels were examined in eight postsurgical patients. Dopamine infusion increased REE from 1,839 +/- 171 kcal/day to 2,071 +/- 170 kcal/day, and it decreased to 1,867 +/- 141 kcal/day after cessation of the infusion. Dopamine also increased the plasma levels of glucagon from 109.4 +/- 8.7 pg/ml to 132.5 +/- 8.0 pg/ml, and it decreased to 102.9 +/- 11.1 pg/ml after cessation of the infusion. The plasma levels of dopamine before, during, and after the infusion were 116.1 +/- 18.3, 161.1 +/- 25.6 and 121.4 +/- 17.2 ng/ml, respectively. Insulin and glucose were affected by dopamine, but changes in their plasma levels did not parallel the dopamine levels. Epinephrine and norepinephrine were increased by the infusion of dopamine and continued to increase even after its cessation. The results of this study revealed that low-dose dopamine increased REE in postsurgical patients and that this might be associated with the concomitant increase in plasma glucagon.

Cardiovascular depression by isoflurane and concomitant thoracic epidural anesthesia is reversed by dopamine

Interactive effects between exogenous dopamine (DA) and isoflurane (I) combined with thoracic epidural blockade (TEA) were studied in dogs during chloralose anesthesia. The I-TEA intervention per se decreased heart rate (HR; 28%), mean arterial pressure (MAP; 63%), cardiac output (CO; 54%), left ventricular dP/dt (LVdP/dt; 75%) and LVdP/dt/systolic arterial pressure (SAP; 42%). Prior to the I-TEA intervention, dopamine increased MAP, CO, LVdP/dt, LVdP/dt/SAP and stroke volume (SV) already at the dose 10 micrograms.kg-1.min-1 and, additionally, increased mean pulmonary artery pressure (MPAP) at the dose 20 micrograms.kg-1.min-1. During the I-TEA intervention, the DA-induced increases in MAP and systemic vascular resistance (SVR) were significantly higher than prior to I-TEA, as indicated by significant ANOVA interactive effects. At the dose 10 micrograms.kg-1.min-1, DA restored MAP, CO, LVdP/dt, LVdP/dt/SAP and SV to levels found before the I-TEA intervention, while HR was restored first at the dose 20 micrograms.kg-1.min-1. At the dose 20 micrograms.kg-1.min-1, DA also increased MAP (39%), LVdP/dt (119%), LVdP/dt/SAP (73%), SVR (28%) and MPAP (70%) above levels prior to I-TEA. To conclude, exogenous dopamine effectively and dose-dependently counters cardiovascular depression induced by the anesthetic technique of combining I and TEA. The pressor and systemic vasoconstrictor actions of dopamine are potentiated by conjoint administration of I and TEA.

Metabolic and haemodynamic effects of dopamine plus domperidone in volunteers

There are no studies of the relationship between infusion rate of dopamine and the arterial and venous dopamine plasma concentration and the resulting haemodynamic and metabolic effects. Dopamine was administered to seven volunteers using five infusion rates (1, 3, 6, 9, 13 micrograms/kg per minute) in an escalating sequence lasting for 30 min for each step. Since dopamine can cause nausea and vomiting, this relationship was investigated after administration of domperidone for infusion rates above 3 micrograms/kg per minute. Haemodynamic effects were assessed using 2-dimensional echocardiography. During the highest infusion rate the arterial plasma dopamine concentration reached 1,379 +/- 181 nmol/l. There was a linear correlation between the dopamine infusion rate and both the arterial and the venous plasma concentration. There was no significant change in heart rate or diastolic blood pressure. Systolic blood pressure, ejection fraction and cardiac index increased in a dose-dependent manner. Systemic vascular resistance decreased during the two low doses of dopamine and was not different from baseline values during the three high infusion rates. The plasma concentrations of glucose and non-esterified fatty acids increased from 5.3 +/- 0.4 to 0.68 +/- 0.9 nmol/l, and from 360 +/- 119 to 971 +/- 307 mumol/l, respectively, during the 13 micrograms/kg per minute infusion rate. As the plasma noradrenaline concentration increased up to 7.84 +/- 2.46 nmol/l in correlation to the dopamine plasma concentration, an indirect sympathomimetic effect may contribute to the actions of dopamine plasma concentration.

Combined effects of adrenergic and intravenous anesthetic agents on inositol monophosphate levels in rat liver prisms

Combined effects of adrenergic and intravenous anesthetic agents on phosphatidylinositol (PI) turnover were studied using rat liver prisms incubated with [3H]myo-inositol. Rat liver prisms responded to epinephrine, norepinephrine and phenylephrine dose-dependently with an increase in inositol monophosphate (IP1) formation but they did not respond to ephedrine. Dopamine-induced effects were seen only at concentrations as high as 10(-4) mol.l-1. The enhancement of IP1 formation induced by epinephrine was potentiated by thiamylal at concentrations of 10(-5) mol.l-1 and 10(-4) mol.l-1, remained unaffected by ketamine, fentanyl or midazolam, but was dose-dependently inhibited by droperidol. The present results from in vitro studies of liver cell metabolism suggest that alpha-adrenergic agents in combination with barbiturates may potentiate liver cell damage by activation of PI turnover and interrelated intracellular Ca++ accumulation.

Effects of dopamine infusion on plasma catecholamines in preterm and term newborn infants

Newborn infants (21 preterm and 13 term) received dopamine infusions at a low (2.5-3.4 micrograms/kg per min) and/or high (5-10 micrograms/kg per min) infusion rate and changes in plasma catecholamines were monitored. The mean baseline values for dopamine, noradrenaline and adrenaline were between 240 and 560, 125 and 144 and 62 and 82 pg/ml, respectively. During low-rate infusion of dopamine, there was a significant increase in plasma dopamine (20-100 fold), noradrenaline (three- to five-fold) and adrenaline (threefold). Administration of dopamine at the high rate resulted in an even larger increase in the plasma catecholamines (dopamine, 100-300 fold; noradrenaline, seven- to eightfold; adrenaline, four- to sixfold). In a double-log plot, there was a highly significant correlation between the plasma concentrations of dopamine and noradrenaline (r = 0.77; P less than 0.001). In conclusion, infusion of dopamine in term and preterm newborn infants is accompanied by an enhanced sympatho-adrenal tone which may contribute to the cardiovascular effects of dopamine in these patients.

Do we need a dopaminergic agent in the management of the critically ill?

1. The stimulation of dopaminergic receptors is in principle attractive to increase urine and sodium excretion in patients with compromised renal blood flow. 2. However, a protective role of dopaminergic agents on renal function has not been well established. Most of the trials have been performed with dopamine, a substance which can have vasoconstrictive properties, even at relatively low doses in the critically ill patient. 3. Perhaps other dopaminergic agents without alpha-adrenergic effects such as dopexamine could be more advantageous. Randomized, prospective, controlled clinical studies should be performed to test the hypothesis that dopaminergic agents can reduce the incidence of acute tubular necrosis in critically ill patients.

Changes in hemodynamics and myocardial metabolism following discontinuation of a dopamine or dobutamine infusion

Hemodynamics and myocardial metabolism were studied in 20 anesthetized dogs following discontinuation of a dopamine (DA) or dobutamine (DB) infusion. Both groups showed significant decreases in HR, AP, dP/dt, CI, MBFI, and MVO2. Discontinuation of DA decreased lactate extraction, whereas this did not occur with DB. The arteriocoronary venous differences in reduction-oxidation electrical potential (delta Eh) decreased significantly immediately following an abrupt discontinuation of the DA infusion, whereas DB maintained delta Eh at a constant level during and following infusion. Thus, aerobic metabolism was maintained following the discontinuation of DB, and anaerobic metabolism in the myocardium was accelerated immediately following discontinuation of the DA infusion. Although the mechanism that produces the differences observed between DA and DB following discontinuation is not understood, it may result from stimulation of alpha 1-receptors in the myocardium, produced by the residual high level of myocardial tissue norepinephrine (NE) following the termination of DA. A high tissue level of NE combined with a low plasma level of DA may cause an oxygen imbalance of the myocardium, demonstrated by an increase in myocardial oxygen demand and by a reduction in coronary blood flow. It is speculated that this mechanism of oxygen imbalance is a possible explanation for the anaerobic metabolism observed following DA discontinuation.

Pharmacokinetics of dopamine in critically ill newborn infants

Dopamine pharmacokinetics was investigated in 14 critically ill newborn infants ranging from 27 to 43 weeks of gestational age and from 0.9 to greater than 4 kg birth weight. Plasma clearance rate was determined from dopamine levels during controlled infusions under actual clinical conditions. Dopamine was administered in stepwise increasing doses up to 8 micrograms/kg/min. Dopamine concentration and dopamine clearance rate were determined from duplicate samples drawn during each infusion in each patient. Steady-state plasma dopamine concentrations and plasma clearance rates were observed within 20 minutes at each infusion. Plasma dopamine concentration ranged from 0.5 ng/ml before infusion to almost 70 ng/ml at an infusion rate of 4 to 8 micrograms/kg/min. There was a linear correlation between infusion rate and plasma dopamine concentration (r = 0.68, p less than 0.001). Neither plasma dopamine concentration nor infusion rate had a significant effect on clearance rate. These data are consistent with first-order kinetics for administered dopamine in critically ill neonates over the range of concentrations studied.

Effects of dopamine on intestinal hemodynamics and motility during epidural analgesia in the cat

The effects of dopamine on intestinal blood flow (IBF) and intestinal contraction rate (ICR), and on mean arterial pressure (MAP) and heart rate (HR) were studied in eight cats before and during epidural analgesia (EDA). Before EDA, dopamine 5 and 10 micrograms.kg-1.min-1 had no effect on IBF, MAP and HR, but the higher infusion rate decreased ICR by 71 +/- 19% (mean +/- 1 s.e.mean) (P less than 0.01). EDA significantly increased IBF when intestinal arterial pressure was maintained at an unchanged level by means of a pump, and transiently increased ICR and intestinal tone, but reduced MAP by 46 +/- 8% (139 +/- 11 to 75 +/- 9 mmHg, P less than 0.01) and HR by 26 +/- 3% (248 +/- 7 to 184 +/- 8 beats.min-1, P less than 0.01). During EDA, dopamine increased IBF further, the response being similar at both infusion rates. 5 micrograms.kg-1.min-1 increased HR by 26 +/- 7 beats.min-1 (P less than 0.01) and MAP by 19 +/- 9 mmHg (ns). The corresponding values at 10 micrograms.kg-1.min-1 were 65 +/- 14 beats.min-1 (P less than 0.01) and 35 +/- 8 mmHg (P less than 0.01), respectively, Vascular autoregulation appeared to be unaffected by dopamine and EDA. The effect of dopamine on ICR was not significantly different to what was seen before EDA. It is concluded that the effects of dopamine on IBF, MAP and HR were markedly different during EDA as compared to before the block and that ICR was reduced by dopamine, while it was transiently increased by EDA.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dopamine on plasma growth hormone and prolactin concentrations under anaesthesia

Five patients with acromegaly and five patients with prolactinoma undergoing general anaesthesia were studied. Concentrations of plasma growth hormone in patients with acromegaly and concentrations of plasma prolactin in patients with prolactinoma were measured before anaesthesia, when 250 mg levodopa was administered orally, and after anaesthesia when dopamine was infused intravenously at a rate of 5 micrograms/kg.min. There was no difference in hormonal (growth hormone or prolactin) response to either treatment in the anaesthetized and the awake states. These findings indicate that the functioning of dopamine receptors in the anterior pituitary is not affected by anaesthesia.

Hemodynamic comparison of dopexamine hydrochloride and dopamine in ischemic left ventricular dysfunction

The hemodynamic dose-response effects of intravenous dopexamine hydrochloride (0.5 to 2.0 micrograms/kg/min) have been compared with dopamine (2.5 to 10 micrograms/kg/min) in 12 patients with ischemic left ventricular dysfunction in an open randomized crossover study. Both drugs increased cardiac output and decreased systemic vascular resistance. Dopexamine hydrochloride appeared to increase heart rate more than dopamine although this did not reach statistical significance. Dopexamine hydrochloride produced small increases in systolic and decreases in diastolic blood pressure, whereas dopamine had a biphasic effect resulting in a decrease in mean blood pressure at low doses and an increase at the highest dose studied. With increasing dosage, there was a trend toward more vasodilator activity with dopexamine hydrochloride than with dopamine. Dopexamine hydrochloride produced fewer adverse effects than dopamine.

Effects of dopamine on the portal circulation after therapeutic hepatic artery ligation

The effects of exogenous dopamine (2, 4 and 6 micrograms.kg-1.min-1 i.v.) on the portal circulation were studied in six patients following therapeutic hepatic artery ligation. Portal blood flow (PBF) was measured by the continuous thermodilution technique. Portal venous pressure (PVP, n = 3) was monitored through the thermodilution catheter to allow derivation of preportal vascular resistance (PVR). Blood samples were taken through the portal venous catheter for measurement of dopamine. A significant increase in PBF and a decrease in PVR were observed during graded i.v. dopamine infusion. Thus, PBF was 961 +/- 119 ml.min-1 during control conditions and increased to 1446 +/- 221 ml.min-1 during the dopamine infusion at 6 micrograms.kg-1.min-1. No significant changes in mean arterial pressure or PVP were observed during dopamine administration. The pharmacokinetics of dopamine did not differ from that previously reported in patients with an intact arterial supply. In conclusion, our data indicate that exogenous dopamine consistently increases PBF by preportal vasodilation, also in patients with a surgically restricted hepatic arterial blood supply.

Sustained hemodynamic improvement during long-term therapy with levodopa in heart failure: role of plasma catecholamines

Long-term therapy with oral sympathomimetic amines in patients with heart failure has been limited by the eventual development of diminished pharmacologic efficacy. However, a previous investigation in five subjects with heart failure suggested that long-term ingestion of levodopa, which is decarboxylated endogenously to dopamine, produces a sustained improvement in cardiac function. In the present study, levodopa was administered orally (1.5 to 2.0 g) to 14 patients with heart failure while hemodynamic responses and plasma catecholamines were monitored. Initially, an increase in cardiac index and stroke volume index was accompanied by a decline in systemic vascular resistance, mean pulmonary capillary wedge pressure and mean right atrial pressure. Heart rate and mean arterial pressure were unchanged. Plasma concentrations of dopamine rose substantially after drug ingestion and correlated significantly with changes in cardiac index (r = 0.73, p less than 0.05). After 12 weeks of treatment with levodopa, the changes in cardiac index, stroke volume index, systemic vascular resistance and plasma dopamine levels persisted (n = 12 patients). Moreover, a significant decrease occurred in the heart rate at rest. Although there was an initial tendency for plasma norepinephrine concentrations to increase, a return to control levels was documented after long-term treatment. Thus, tolerance to the hemodynamic actions of levodopa did not develop during long-term administration of the drug. The hemodynamic responses observed can be ascribed to the activation of beta 1-adrenoceptors and dopamine1 receptors by dopamine generated from levodopa. The dopamine2 activity of dopamine does not appear to be responsible for the improvement in cardiac performance produced by levodopa.

Pulmonary and systemic hemodynamic effects of central venous and left atrial sympathomimetic drug administration in the dog

Systemic vasopressor or inotropic therapy may exacerbate existing pulmonary hypertension; the optimal agent and route of administration in this situation are unknown. The systemic and pulmonary hemodynamic effects of four sympathomimetic agents (dopamine, epinephrine, norepinephrine, and phenylephrine) during central venous and left atrial administration were investigated in the anesthetized dog. All four drugs increased both systemic and pulmonary artery pressures. Dopamine and epinephrine increased cardiac output and reduced systemic vascular resistance. Phenylephrine decreased cardiac output and increased systemic vascular resistance and left atrial pressure. Norepinephrine did not significantly affect cardiac output, systemic vascular resistance, or left atrial pressure. None of the four drugs affected pulmonary vascular resistance. The ratio of systemic to pulmonary vascular resistance decreased with epinephrine and increased with phenylephrine. There were no hemodynamic differences related to the route of infusion for any of the four drugs. However, pulmonary arterial concentrations of the three drugs measured (dopamine, epinephrine, and norepinephrine) were markedly lower during left atrial compared to central venous drug administration; systemic drug concentrations were similar or increased during left atrial compared to central venous drug administration. It is concluded that the relative effects on the systemic and pulmonary circulations differ for the four drugs; rational choice of a vasopressor will depend upon the hemodynamic situation and the desired effect. Left atrial catecholamine administration is effective in decreasing pulmonary arterial drug concentrations and may decrease adverse pulmonary effects in clinical practice.

Dopamine pharmacokinetics in critically ill newborn infants

To compare clinical responses with plasma concentrations of dopamine and to compare dopamine pharmacokinetics in infants of different gestational age or clinical condition, dopamine was administered under carefully controlled conditions of dose and rate of infusion. The dose was increased stepwise from 1 to 2, to 2 to 4, and 4 to 8 micrograms/kg/min. Plasma concentrations of catecholamines, including dopamine, were compared with blood pressure, heart rate, and Doppler cardiac output. The data were analyzed to determine the threshold or minimal plasma concentration of dopamine necessary to produce discernible effects. Plasma clearance rate was calculated from steady-state plasma concentrations. The average threshold for increases in mean arterial pressure was 50% below that for increases in heart rate. Improvements in arterial pressure were noted before and at lower thresholds than for increases in heart rate. Serial echocardiographic data showed dose-dependent increases in cardiac output and stroke volume without significant change in heart rate or systemic vascular resistance. Thresholds and plasma clearance values were similar in infants of gestational age 27 to 42 weeks and birth weights 900 to 4300 g. Administration of dopamine at initial dosages lower than commonly recommended, followed by incremental increase in dose, may be associated with improved left ventricular performance with avoidance of undesirable tachycardia and arrhythmias.

Refractory hyperdynamic shock associated with alcohol and disulfiram

After massive alcohol intake, a patient under disulfiram therapy developed a severe cardiovascular collapse unresponsive to dopamine but successfully reversed with norepinephrine. Resistance to dopamine could be related to norepinephrine depletion caused by disulfiram. Norepinephrine could, therefore, represent the treatment of choice of these life-threatening conditions.

The hemodynamic effects of ibopamine, a dopamine congener, in patients with congestive heart failure

Ten patients with congestive heart failure underwent noninvasive and invasive hemodynamic testing before and sequentially after the administration of ibopamine to determine the cardiovascular effects of this oral dopamine congener. Single doses of 200, 400 and 600 mg were administered to all patients and 5 repeated doses of 200 or 400 mg were studied in 8. Hemodynamic effects occurred as early as 30 minutes and lasted up to 4 hours after dosing. In general, ibopamine elicited statistically significant dose-related increases in cardiac output and reductions in the derived resistance of the systemic and pulmonary circulations. A biphasic response in central and peripheral pressures was observed; up to 1 hour after administration, ibopamine elevated mean right and left atrial pressures and pulmonary and systemic arterial pressures with a significant reduction of these measurements beyond 1 hour. It did not alter heart rate. Repeated doses qualitatively affected hemodynamics similar to the initial dose and did not appear to be accompanied by short-term tolerance. While oral ibopamine elicits some favorable hemodynamic effects in humans with cardiac failure, the biphasic hemodynamic response is generally undesirable in the majority of these patients.

Dopamine reverses cardiovascular depression of toxic doses of pentobarbitone in dogs

Pentobarbitone, 20 mg X kg-1 IV followed by infusion of 25 mg X kg-1 X hr-1, produced a progressive decrease in mean arterial pressure in dogs from 113 +/- 17 mmHg (SD) after one hour of infusion to 82 +/- 21 mmHg after 3.5 hours and to 49 +/- 22 mmHg after 5.5 hours. EEG silence occurred at 3.6 +/- 0.6 hours. In dogs similarly treated with pentobarbitone, a two hour infusion of dopamine 5 micrograms X kg-1 X min-1 beginning at the time of EEG silence prevented the further decrease in pressure and restored pressure to 87 +/- 18 mmHg. The mechanism for this effect of dopamine was an increase in cardiac output as systemic vascular resistance was unaffected by dopamine. The cardiac output increase was mainly the result of an increase in stroke volume as heart rate increased only slightly. Since reduced stroke volume was the main reason why pentobarbitone lowered blood pressure, the effect of dopamine on stroke volume and thus on blood pressure makes it an appropriate antagonist to the cardiovascular effects of toxic doses of pentobarbitone.