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.