The role of angiotensins in aldosterone production

The hypothesis that the COOH-terminal heptapeptide mediates the aldosterone-stimulating activity of angiotensin II was evaluated by comparing the relative effects on aldosterone production of angiotensin II and the heptapeptide to angiotensin analogues that are poorly metabolized to the heptapeptide and to a nonapeptide, des-Asp-1-angiotensin I, that is directly converted to the heptapeptide. In in vivo studies utilizing the adrenocorticotropic hormone-suppressed bilaterally nephrectomized dog, angiotensin II and the heptapeptide produced statistically significant increases in both aldosterone and cortisol secretory rates (P less than 0.001 for both relations). Sar-1-angiotensin II stimulated the production of both steroids to the same extent, but had much longer duration of action. [Poly(oAc)Seryl]angiotensin II was a weak agonist, having only about 30% of the steroidogenic potency of either angiotensin II or the heptapeptide. In equimolar concentrations des-Asp-1-angiotensin I had about one-half of the aldosterone-stimulating activity of the hepatpeptide. In in vitro studies, employing the trypsin-dispersed cat adrenal zona glomerulosa cells, the steroidogenic potency of angiotensin II and the heptapeptide was identical to maximal aldosterone production of 10(-8) M peptide concentration. By contrast, the response to Sar-1-angiotensin II was approximately a 10-fold increase in relative potency, while the response to [poly(oAc)Seryl]angiotensin II demonstrated a 10-fold decrease. These findings suggest that, although the heptapeptide may play an important role in the regulation of aldosterone production, the possibility remains open that angiotensin II could stimulate aldosterone biosynthesis without prior conversion to the heptapeptide.