ISOLATION AND CARDIOVASCULAR ACTIVITY OF A 2ND BRADYKININ-RELATED PEPTIDE ([ARG(0),TRP(5),LEU(8)] BRADYKININ) FROM TROUT

Previous work has shown that incubation of heat-denatured plasma from the rainbow trout Oncorhynchus mykiss with porcine pancreatic kallikre in generates [Lys(0),Trp(5),Leu(8)] bradykinin (trout [Lys(0)]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-P ro-Leu-Arg (trout [Arg(0)]BK). Bolus injections of both trout [Arg(0)] BK and [Lys(0)]BK (> 100 pmol/kg) into the dorsal aorta of conscious t rout produced multiphasic effects on arterial blood pressure. An initi al presser 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 [Arg(0)] BK (10 nmol/kg) was approximat ely one-fourth of the maximum rise produced by angiotensin II in the s ame animals. Intracerebroventricular injections of trout [Arg(0)]BK (5 00 pmol) into conscious trout had no effect on arterial blood pressure or heart rate. Trout [Arg(0)]BK did not affect the tension of vascula r rings from trout efferent branchial and caeliacomesenteric arteries and anterior cardinal vein. Trout des[Arg(9)]BK had no effect on cardi ovascular 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).