Studies were performed in anesthetized dogs to evaluate the cardiac and systemic effects of intravenously administered dobutamine and to determine its direct effects on the renal and femoral vascular beds. The results demonstrated that dobutamine possessed an inotropic efficacy similar to that of isoproterenol and norepinephrine; its chronotropic effect was similar to or greater than that of norepinephrine. In contrast to norepinephrine, dobutamine increased cardiac output and reduced total peripheral resistance with minimal effects on mean aortic pressure. Studies on the denervated hind limb demonstrated that dobutamine stimulated both alpha and beta receptors. The dose of dobutamine which produced a 50% increase in femoral blood flow was 180 times the required dose of isoproterenol and the dose which produced a 50% increase in contractile force was 43 times the required dose of isoproterenol. Studies on the renal vasculature demonstrated that dobutamine caused no dopaminelike renal vasodilator activity and only minor vasodilation mediated by beta receptors. We concluded that dobutamine is more cardioselective than is isoproterenol. The dobutamine-induced decrease in peripheral resistance observed in the whole dog was presumably due to increased myocardial contractility coupled with a greater net effect of beta-adrenergic vasodilation than alpha-adrenergic vasoconstriction. Studies with reserpine-treated dogs showed that all dobutamine-induced effects were due to a direct action on receptors.
1. The cardiovascular effects of sodium glutamate were investigated in anaesthetized dogs with bolus injections, intravenous infusions and rabbit isolated papillary muscles. 2. The intravenous bolus injections of sodium glutamate resulted in slight, transient decreases in contractile force at doses of 58 and 117 mg/kg, which were followed by brief increases in blood pressure. 3. Sodium glutamate had no effect on contractile responses of isolated papillary muscles at any of the concentrations used. 4. Infusions of glutamate produced no change in blood pressure, an increase in cardiac output, and a decrease in heart rate, total peripheral resistance and femoral vascular resistance. 5. The infusion of sodium glutamate into animals with no renal function resulted in an increased plasma osmolality and a decreased haematocrit. 6. The results from this study show that sodium glutamate had minimal cardiovascular effects. The results from the infusion data suggest that glutamate increases intravascular volume by an osmotic effect.
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