The synergistic effect of angiotensin II and urea on systemic blood pressure

The hypertensive synergism of A-II and urea was studied in anesthetized cats. Femoral arterial pressure was measured while test substances were infused in a femoral vein. Dose-response analysis of the A-II + urea interaction suggested that A-II pressor effects and A-II + urea potentiation involve a common mechanism. Methylurea and mannitol + A-II also induce a similar potentiation. While plasma osmolality and plasma volume indicated no systemic changes, intracellular osmotic shifts may be a factor in the synergism. Since inhibition of the potentiation by indomethacin was not replicated, prostaglandins can no longer be considered important. No effect of ganglionic blockade also eliminated CNS influences as a factor. Dual infusion suggested urea-induced A-II changes were not important for the synergism. Since a synergism of A-II with amino acids occurred, alteration of A-II receptors was indicated. Thus, the A-II + urea pressor synergism may involve either intracellular osmotic shifts or a receptor modification so A-II is more accessible.