Differential effect of vasopressin on angiotensin and norepinephrine pressor action in rats

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Abstract
The effect of vasopressin [VP] infusion on the pressor dose responses to angiotensin II [AG II] and norepinephrine [NE] was studied in pentobarbital-anesthetized and unanesthetized nephrectomized rats. Pressor VP (2-15 ng .cntdot. kg per min) given to anesthetized rats decreased sensitivity to AGII in a dose-dependent manner (r = 0.88), an effect completely reversible by dPMeTyrAVP [1-deaminopenicillamine-2-(O-methyl)-tyrosine]arginine VP], a VP vascular antagonist. Subpressor VP (0.5-1 ng .cntdot. kg-1 per min) given to unanesthetized rats diminished sensitivity to AGII in the presence or absence of pentolinium (10 mg/kg). Shifts in dose-response curves to AGII were always parallel. Dose responses to NE were not modified by VP in pentolinium-treated rats and showed a small nonparallel rightward shift in animals without pentolinium. In animals without pentolinium, the baroreflex-mediated reduction in heart rate elicited by AG II was not altered by VP infusion. VP evidently reduces AG II pressor action by diminishing pressor sensitivity to the peptide. The effect may be specific, mediated through the vascular receptor for VP and independent of actions of this hormone on the autonomic nervous system.