Cardiovascular effects of hydralazine HCl administration in horses.

Six standing awake adult horses were instrumented for measurement of mean arterial, central venous, and pulmonary arterial blood pressures (mm of Hg), thermodilution cardiac output (ml/kg/min), and pulmonary arterial blood temperature (C). Total peripheral resistance was calculated from these values. Base-line data were accumulated, and a single dose of hydralazine HCl (0.5 mg/kg) was administered IV. Horses were monitored for 420 minutes after hydralazine administration. Mean arterial and central venous blood pressures did not change from the base-line values. Cardiac output and heart rate were increased above base-line values for 260 minutes. Total peripheral resistance was decreased for 240 minutes. Pulmonary arterial blood temperature was decreased for 60 minutes after drug administration. Mean pulmonary arterial pressure relative to the base-line mean was intermittently decreased during the study. Intravenously administered hydralazine HCl appears to be an effective vasodilator, with moderate duration of action in horses.