Effects of exogenous [Arg(8)]-vasopressin on borderline-hypertensive Hiroshima rats

The interaction between [Arg(8)]-vasopressin and a vasopressin receptor ant agonist, [d(CH2)(5)(1), O-Me-Tyr(2), Arg(8)]-vasopressin, was examined in H iroshima rats and normotensive control rats under pentobarbital anesthesia. [Arg8]-vasopressin dose-dependently increased the arterial pressure in bot h the Hiroshima and control rats, the presser effect being greater in the H iroshima rats. After the administration of a vasopressin antagonist (0.01 m g/kg), which by itself decreased arterial pressure only in the Hiroshima ra ts, the dose-response curve for [Arg(8)]-vasopressin was much more greatly shifted to the right in the control rats. These results indicate that with or without a vasopressin antagonist, the exogenous [Arg(8)]-vasopressin ind uced more powerful presser actions in the Hiroshima rats compared to the co ntrol rats.