Specific receptors for des-Asp1-angiotensin II (("angiotensin III") in rat adrenals

The specific binding of angiotensin II and des-Asp1-angiotensin II ("angiotensin III") III") to rat adrenals was studied with the use of the tritiated peptides. The binding sites having maximal affinity for angiotensin II were characterized by an equilibrium dissociation constant of 3.3 to 5.2 X 10(-9) M. Angiotensin III was able to interact with these sites, and also with a class of sites with very high affinity, characterized by an equilibrium dissociation constant of 1 to 2 X 10(-10) M. These sites exhibited a greater affinity for the heptapeptide angiotensin III than for the octapeptide angiotensin II. These findings, together with the known potent aldosterone stimulating effect of angiotensin III and its presence in rat plasma, suggest that this heptapeptide could be the physiologically important steroidogenic angiotensin in this species.