Purification, structural characterization, and cardiovascular activity of cod bradykinins

Incubation of plasma from the Atlantic cod Gadus morhua with trypsin generated two peptides identified as [Trp(5),Leu(8)]bradykinin (cod BK) and [Arg(0),Trp(5),Leu(8)] bradykinin (cod [Arg(0)]BK). Bolus intraarterial injections of synthetic cod [Arg(0)] BK (0.1-10 nmol/kg) into conscious cod produced an immediate increase in ventral aortic pressure that was of relatively short duration (<5 min) and an increase in heart rate. Cod [Arg(0)]BK was similar to 10 times more potent than cod BK, and the maximal presser response produced by the peptide was significantly (P < 0.05) greater. Bolus intra-arterial injections of either mammalian BK or cod des-Arg(9),[Arg(0)]BK, in doses up to 100 nmol/kg, had no effect on pressure or heart rate. The data indicate that the ligand binding properties of the BK receptors in cod are different from those of the mammalian B-1- and B-2-receptor subtypes. The presser response to 1 nmol/kg cod [Arg(0)]BK was reduced (by 51 +/- 6%; P < 0.05) in prasozin-treated fish, whereas in enalapril-treated fish, the response to the peptide was enhanced (by 42 +/- 12%; P < 0.05). The data indicate an involvement of catecholamines but not an activation of the renin-angiotensin system in mediating the vasopressor action of BK in the cod.