Differential sensitivity to angiotensin II in pregnant rabbits.

Threshold concentrations for angiotensin II and barium chloride were determined in the perfused hind limb of the nonpregnant, pseudopregnant, and pregnant rabbit. The threshold concentration for these vasoconstrictors was defined as the amount of drug per milliliter of hind limb blood flow which would increase hind limb blood pressure by 4 mm Hg. There was no difference in the mean angiotensin II threshold concentration between the nonpregnant and pseudopregnant rabbits. The angiotensin II dose for the pregnant rabbits was double that of the first two groups. There was no significant difference in the mean barium chloride threshold concentration between the three groups. This difference in the pregnant angiotensin II threshold concentration with no difference in barium chloride threshold concentration indicates a change in vascular sensitivity which is dependent upon a specific angiotensin II-receptor interaction and is not inherent in the contractile response of the vessel, nor is it mimicked by pseudopregnancy.