Different potencies of [Asp1, Ile5]- and [Asn1, Val5]-angiotensin II in stimulating aldosterone production from rat adrenal zona glomerulosa cells in vitro.

1. Rat adrenal zona glomerulosa cells were incubated in Krebs Ringer bicarbonate medium containing bovine serum albumin. Aldosterone production was measured by radioimmunoassay. 2. Both [Asp1, Ile5]-angiotensin II ('free acid') and (Asn1, Val5]-antiotensin II ('amide'), (10(-5) mol/l), stimulated aldosterone output but the free acid compound produced a larger increase in steroid output than the amide. 3. This difference in steroidogenic activity could not be explained by differences in purity or initial concentration or by stimulation of the contaminating fasciculata cells. 4. However, serial bioassays of the media revealed that the amide form of angiotensin was degraded more rapidly than the free acid form. 5. The different potency of these two forms of angiotensin II could explain some of the reported discrepancies of the action of angiotensin II on rat adrenal tissue or cells in vitro.