Venoconstriction causes different effects in the hindquarters venous compartment of cats and dogs.

1. A study was made of venoconstrictor mechanisms in the hindquarters region of cats and dogs by the use of autoperfused hindquarter preparations, together with the measurement of vena cava blood flow (VCBF). 2. Noradrenaline, adrenaline and angiotensin II (AII) were all administered intraarterially and their ability to alter perfusion pressure and VCBF was examined. 3. All three drugs increased perfusion pressure in both cats and dogs as a result of increases in arterial resistance. At the same time, noradrenaline and adrenaline increased VCBF in cats, while AII had a variable effect. In contrast, all three drugs decreased VCBF in dogs. 4. These differences in the venoconstrictor responses obtained in cats and dogs may be explained by an action of the drugs at different loci within the venous compartment of the two species.