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 ~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.