The renin angiotensin system of amphibians

Summary

Kidney extracts from several amphibian species were incubated with homologous and non-homologous serum. In a series of experiments the angiotensin formation was studied by enzyme kinetic technics, using acidified, dialysed kidney extracts and dialysed serum. In other experiments incubations were performed in the presence of Dowex 50W-X2 (NH₄ ⁺) resin. The angiotensin was then eluted from the Dowex and its pressor activity tested on the rat. If no Dowex was used in the incubation mixtures the range of the angiotensin formation was from 0 to 210 ng angiotensin formed per ml of serum. If Dowex was added, the values ranged from 0 to 300 ng angiotensin formed per ml of serum. Often angiotensinase was still present in the incubation mixtures, reducing the amount of detectable angiotensin in the incubation mixtures. Dowex protects the formed angiotensin from amphibian angiotensinases. The data suggest, however, that a large amount of angiotensin adsorbed onto the Dowex cannot be recovered. There is at least some species or class specifity of the renin-angiotensin system of the amphibians. Kidney extract of one species incubated with non-homologous serum produced less pressor substance than the same amount of kidney extract when incubated with homologous serum. Amphibian adrenal pressor substances are—at least in part—adsorbed on Dowex and can be eluted from it in a similar fashion as angiotensin.