The direction and obviousness of changes in systemic arterial and venous vascular beds occurring in combined action of two similarly acting pressor and depressor vasoactive drugs, were studied in acute experiments in cats. The changes of last and general peripheral resistance of vessels were greater under the action of the two drugs as compared to the effect of a single drug, and yet less obvious than their algebraic sum. The shifts in cardiac output and venous return were not greater than the most obvious response to a single drug. The same was true for the blood flow changes in v. v. cavae. Irrespective of the mechanism of action of vasoactive drugs and the direction of shifts of systemic AP, single and combined drugs increased the blood flow in the v. cava anterior whereas the v. cava posterior's blood flow changed in different directions.
