Isolation and cardiovascular activity of a second bradykinin-related peptide ([Arg⁰,Trp⁵,Leu⁸] bradykinin) from trout

Previous work has shown that incubation of heat-denatured plasma from the rainbow trout Oncorhynchus mykiss with porcine pancreatic kallikrein generates [Lys⁰,Trp⁵,Leu⁸]bradykinin (trout [Lys⁰] BK). We have now isolated a second BK-related peptide from kallikrein-treated trout plasma with the primary structure: Arg-Arg-Pro-Pro-Gly-Trp-Ser-Pro-Leu-Arg (trout [Arg⁰]BK). Bolus injections of both trout [Arg⁰]BK and [Lys⁰]BK (>100 pmol/kg) into the dorsal aorta of conscious trout produced multiphasic effects on arterial blood pressure. An initial pressor response of short duration (1-2 min) was followed by a fall in pressure (to below basal values in 11 out of 15 animals) and then by a sustained rise in pressure lasting up to 60 min. The maximum rise in pressure produced by trout [Arg⁰] BK (10 nmol/kg) was approximately one-fourth of the maximum rise produced by angiotensin II in the same animals. Intracerebroventricular injections of trout [Arg⁰]BK (500 pmol) into conscious trout had no effect on arterial blood pressure or heart rate. Trout [Arg⁰]BK did not affect the tension of vascular rings from trout efferent branchial and caeliacomesenteric arteries and anterior cardinal vein. Trout des [Arg⁹] BK had no effect on cardiovascular parameters, either in vivo or in vitro, indicating that the C-terminal arginine residue of the peptide is important in interaction with the trout kinin receptor(s).