Two-compartment model of acute stimulation of aldosterone secretion in vivo by angiotensin II.

Sheep with a cervical adrenal autotransplant were used to establish the relationship between acute change in angiotensin II (ANG II) concentration and acute change in aldosterone secretion rate (ASR). The kinetics of 131I-labeled ANG II and unlabeled ANG II across the adrenal were consistent with distribution within a two-compartment model. ASR was found to be a linear function of the ANG II concentration predicted to occur in the second compartment, indicating that acute change in ASR is determined to a large degree by the rate of exchange of ANG II between the first and second compartments. The time required for ANG II concentration to reach 50 and 95% of steady state was estimated to be approximately 5 and 45 min, respectively. The time course for agonist distribution within the adrenal may be an important factor to consider in both the design and interpretation of experimental studies that involve the stimulation (or inhibition) of adrenocortical cells.