Total and hindlimb O2 uptake and blood flow in hypoxic dogs given dopamine

Cardiovascular interactions between dopamine and hypoxia were examined in 8 anesthetized, paralyzed dogs ventilated at constant rates. Total and hindlimb (less paw) O2 uptake, blood flow, and vascular resistance were measured with and without dopamine infusion of 10 micrograms/kg . min during both normoxic and hypoxic ventilation. Another 8 dogs were similarly treated after beta-blockade with propranolol infusion (1 mg/kg). During the baseline period, normoxic dopamine significantly increased total O2 uptake, cardiac output, and stroke volume, and significantly decreased total vascular resistance in the control group. Hypoxia decreased total O2 uptake, cardiac output, and heart rate but increased total vascular resistance. Dopamine reversed each of these hypoxic changes and restored total O2 uptake to normoxic levels. Hindlimb measurements were not significantly changed by dopamine or hypoxia in the control group. During hypoxia, beta-blockade abolished dopamine's effects except for the decrease in total vascular resistance. The improvement in cardiac output and O2 transport by dopamine infusion resulted from increased stroke volume during normoxia and from increased heart rate during hypoxia.