Dopexamine hydrochloride in the human kidney: localization, receptor binding and effect on 3'-5'-cyclic adenosine monophosphate generation

Determination of dopamine D1 receptors in the human uveo scleral tissue by light microscope autoradiography

The aim of this paper is to clarify the distribution of Dopamine D1 (DA D1) receptors in the uveo-scleral tissue of human eyes with or without elevated intraocular pressure (IOP) and to study the relationships between DA D1 receptors and uveo-scleral tissue. Samples of human uveo-scleral tissue were taken from seven men undergoing eye surgery for a traumatic lesion of the anterior segment of the eye, without involvement of the iris-corneal angle and /or from eye donors. The subjects (in whom one eye bulb had been surgically enucleated) had been previously enrolled in our medical protocols because they suffered for increased IOP, while the eye donors (of both eye bulbs) had a normal IOP. Frozen sections from the uveo-scleral tissue were submitted to biochemical characterization and to morphological autoradiographic techniques for detection of DA-D1 receptors. [3H]-SCH-23390 was used as a ligand of Dopamine D1 receptors. [3H]-SCH 23390 was bound by sections of the human uveo-scleral tissue. The pharmacological profile of the binding was consistent with the labeling of D1 receptors. Light microscope analysis was used for localization of D1 receptors and revealed an accumulation of the radioligand in the human uveo-scleral tissue. In eyes with normal IOP there is a high reaction. The Bmax of radioligand decreases in the eyes with increased IOP. The possibility that dopaminergic receptors play a role in the controlling uveo-scleral tissue functions is suggested.

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.

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.