Hemodynamic effects of intravenous clonidine in the conscious, normotensive baboon

Baboons were given eight doses of clonidine hydrochloride (0.04--40 micrograms/kg) via indwelling femoral venous catheters. Systolic and diastolic blood pressures and heart rates were assessed for time course, magnitude of change, time-to-peak change, and duration of effect at each dosage level. The response to clonidine was found to be biphasic--an initial pressor response was followed by a depressor response. During the 2-min intravenous infusion, blood pressures rose while heart rate dropped. Blood pressures subsequently declined while heart rate remained low. Blood pressure decreases and heart rate decreases were both dose and time dependent. The 10-micrograms/kg dose was found to be maximally effective in reducing blood pressure and heart rate for long durations without also producing a substantial pressor episode during infusion.