Aldosterone Response to Angiotensin Blockade in the Conscious Sodium-Depleted Rabbit

To evaluate the role of the renin-angiotensin system in the aldosterone response to sodium depletion in the conscious rabbit, angiotensin blockade was achieved with [Sar, Ala] angiotensin II and SQ 20881. After infusion of [Sar, Ala] angiotensin II (1 μg/kg/min) for 60 min into sodium-depleted animals, PAC was unchanged (33.3 ± 7.4 ng% compared with a control sodium-deplete value of 41.1 ± 8.2 ng%). When the dose was increased to 50 μg/kg/min for an additional 60 min, PAC fell to 15.4 ± 3.7 ng% (P < 0.0125), a value similar to the sodium replete value. In a second group of animals, SQ 20881 was given initially as a 7 mg/kg bolus and followed by an infusion of 60 μg/kg/min for 30 min; PAC fell from a sodium-deplete level of 86.6 ± 21.0 to 63.9 ± 18.2 ng% (P < 0.025). The infusion was extended to 60 min in five of the seven animals and PAC remained significantly reduced (63.3 ± 16.2 ng%, P < 0.01). These studies demonstrate that attenuation of the aldosterone response to sodium depletion occurred with both [Sar, Ala] angiotensin II and SQ 20881 in the conscious rabbit indicating a role for the renin-angiotensin system in this model.