In conditions of chronic heart failure, however, this ratio decreases to as low as 3:2, primarily due to down-regulation of the Bi receptors During such conditions, B2 stimulation results in even larger increases in cAMP levels than Bi stimulation, further emphasizing the importance of B-adrenoceptor stimulation with pharmacologic agents
Dobutamine is a synthetic adrenergic agonist with activity at Bi- and B-adrenoceptors, with limited activity at ai-receptors. The main clinical effects of dobutamine are increased Cl and peripheral vasodilatation, with resultant increased organ perfusion in patients with chronic congestive heart failure. Dobutamine has been shown to be efficacious in patients recovering from cardiac surgery, with fewer arrhythmias than isoproterenol and larger increases in cardiac output than dopamine Dobutamine has been shown to have no significant effect on renal blood flow, glomerular filtration rate, sodium excretion, or free water clearance in patients with major vascular surgery. While it may be used as an inotropic agent, the major limitation of dobutamine in cardiac surgery is the incidence of tachycardia.
Dopamine, at higher doses (3 to 7 Mg/kg/min), can be used to stimulate B-adrenoceptors as an inotropic agent or to stimulate ce-adrenoceptors (>7 Mg/kg/ min) as a pressor agent. At these higher doses, however, tachycardia is a common complication. In lower doses (0.5 to 3jug/kg/min) dopamine benefits by augmenting regional blood flow to splanchnic (including renal) beds. In addition, activation of DA-1 receptors in the collecting tubules of the kidneys inhibits sodium reabsorption with subsequent natriuresis and associated diuresis. This increase in sodium and water excretion is additive to the increased glomerular filtration induced by vasodilatation and may be of benefit in the postoperative cardiac patient. birth control online
Dopexamine is a synthetic adrenergic compound that stimulates both B2- and dopaminergic DAi adrenoceptors. The main clinical effects of dopexamine are increased Cl and vasodilatation, especially in the splanchnic (renal) vascular beds. Because dopexamine is a selective ^-agonist, this drug offers potential advantages in cases of acute myocardial dysfunction, including low cardiac output in the perioperative period. However, dopexamine also has indirect effects (similar to dopamine), which include inhibition of presynaptic reuptake of norepinephrine. This effect may reduce the benefits of dopexamine in patients with chronic heart failure.