1. Seven conscious dogs received arginine-vasopressin infusions (100 and 1000 fmol min−1 kg−1) through catheters implanted in the left vertebral artery or the inferior vena cava while arterial pressure, cardiac output (electromagnetic flowmeter) and heart rate were measured.
2. Despite similar increases in plasma vasopressin concentrations, intravertebral administration induced a lesser increase in mean arterial pressure and a greater decrease in heart rate than the same infusion given intravenously.
3. These results suggest that vasopressin has an effect on structures of the central nervous system involved in cardiovascular control, possibly by affecting the baroreceptor reflex.