Effects of Frog‐Skin Angiotensin II in Amphibians

The role of frog-skin angiotensin II (All) in amphibia was studied by comparing the sodium and water permeability effects of three angiotensins (All): frog skin (Ala-Pro-Gry–Ile3, Val5]Ang II), human ([Asp1, Ile5]-AII), and Japanese gooscfish ([Asn-Van-All). Frog-skin All increased the short-circuit current (SGC) significantly after it was added to the dermal side of the isolated skin of the South American frogs, Leptodactylus chaquensis and ocellatus, and the toad, Bufo arenarum, in concentrations of 10−6 M. In frogs, the effect was significant at 15 minutes and reached 45% over control after 2½ hours. The effect cannot be achieved with concentrations lower than 10−7 M. Since amiloride (10−4 M) blocked the SCC response, and absence of chloride in the bathing fluid did not, the effect is probably dependent on sodium transport. Human All (10−6 M) produced a similar response in summer frogs that had been treated with 0.1% NaCI for 14 days. Goosefish AH was ineffective at similar concentrations, and none of the angiotensins modified SCC in the toad bladder. Hydrosmotic effects could be achieved with the three angiotensins, the response being dependent on seasonal and species factors but always considerably lower than that of the neurohypophyseal peptides. Vascular reactivity of the isolated frog hind limbs was compared by dose-response curves. Potency ratios on a molar basis against frog-skin AH was 1.136 for human All and 1.193 for goosefish All. The results show that the effects of the angiotensins differ in both the response of SCC to frog-skin angiotensin and its higher vascular effects.