Potassium-Stimulated Angiotensin Release from Superfused Adrenal Capsules and Enzymatically Dispersed Cells of the Zona Glomerulosa*

The cells of the adrenal cortex contain angiotensin-II (AII), but whether this peptide is synthesized there (vs. internalized from the systemic circulation), whether it is secreted, and whether it is important in aldosterone production remain uncertain. To address these issues, we studied AI and AII release from superfused rat adrenal capsules and dispersed glomerulosa cells. Superfused adrenal capsules released 7-fold more AII in 270 min than the capsules originally contained (495 +/- 101 fmol AII/rat released vs. 66 +/- 8 fmol AII/rat tissue content). The amount of AI released in the same period only slightly exceeded the tissue content. In response to higher potassium concentrations in the medium (9 vs. 3.6 mM K+), adrenal capsules and dispersed glomerulosa cells both released significantly more AI and AII into the superfusate. This release of AI and AII was oscillatory. The oscillations occurred in each of 15 experiments, with a period of 45-90 min. Decapsulated adrenal glands (the zona faciculata/reticularis plus medulla) also contained and released AII, but did not respond to potassium stimulation. There was a highly significant correlation between AII and aldosterone release. This was especially apparent if aldosterone secretion was examined during oscillations of AII release (r = 0.97; P less than 0.0001). We conclude that AII is synthesized in the zona glomerulosa and can be released in response to stimuli. The close correlation between AII and aldosterone secretion suggests that locally produced AII may play an important role in aldosterone biosynthesis.