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 [Trp5,Leu8]bradykinin (cod BK) and [Arg0,Trp5,Leu8]bradykinin (cod [Arg0]BK). Bolus intraarterial injections of synthetic cod [Arg0]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 [Arg0]BK was approximately 10 times more potent than cod BK, and the maximal pressor response produced by the peptide was significantly (P < 0.05) greater. Bolus intra-arterial injections of either mammalian BK or cod des-Arg9,[Arg0]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 B1- and B2-receptor subtypes. The pressor response to 1 nmol/kg cod [Arg0]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.