Production of [Asn¹,Val⁵] angiotensin II and [Asp¹ ,Val⁵] angiotensin II in kallikrein-treated trout plasma (T60K)

Incubation of heat-denatured plasma from the rainbow trout Oncorhynchus mykiss with porcine pancreatic kallikrein generates, in addition to bradykinin-related peptides, previously uncharacterized peptides that contract mammalian and amphibian vascular smooth muscle. Using rings of vascular smooth muscle from the bullfrog systemic arch as bioassay, we have isolated two myotropic peptides whose primary structures were established as: Asn-Arg-Val-Tyr-Val-His-Pro-Phe ([Asn¹,Val⁵]angiotensin II) and Asp-Arg-Val-Tyr-Val-His-Pro-Phe ([Asp¹,Val⁵]angiotensin II). These peptides are the same as those generated in salmon plasma by an extract of kidney. The data raise the possibility that activation of the kallikrein-kinin system in trout generates both bradykinin-related and angiotensin II-related peptides that may act synergistically in the regulation of blood pressure.