Antidipsogenic effects of eel bradykinins in the eel Anguilla japonica

A peptide with bradykinin (BK)-like immunoreactivity was isolated from an i ncubate of heat-denatured eel plasma with porcine pancreatic kallikrein. Th e purified peptide had the following amino acid sequence: Arg-Arg-Pro-Pro-G ly-Ser-Trp- Pro-Leu-Arg. This decapeptide, named eel [Arg(0)]BK, was identi cal to two previously identified BK homologs from cod and trout. High conse rvation of the BK sequence among distant teleost species suggests an import ant function in this vertebrate group. Bolus intra-arterial injections of e el [Arg(0)]BK, BK, and [Arg(0)]-des-Arg(9)-BK (1-10 nmol/kg) caused signifi cant (P< 0.05) inhibition of drinking in seawater-adapted eels. The potency of the inhibition was ranked in the following order: [Arg(0)]BK. [Arg(0)]- des-Arg(9)-BK = BK. The BK peptides also produced an immediate, transient i ncrease followed by a sustained increase in arterial blood pressure and an initial decrease followed by an increase in heart rate. Strong tachyphylaxi s occurred for the cardiovascular effect but not for the antidipsogenic eff ect. The order of the potency of the cardiovascular actions, [Arg(0)]BK > B K > [Arg(0)]-des-Arg(9)-BK, was different from that of the antidipsogenic a ction. Slow infusions of eel [Arg(0)]BK in the dose range 1-1,000 pmol . kg (-1) . min(-1) produced concentration-dependent inhibition of drinking with out changes in arterial pressure, plasma osmolality, and hematocrit. At the infusion rate of >100 pmol . kg(-1) . min(-1), plasma concentrations of an giotensin II, a potent dipsogenic hormone in eels, increased, suggesting an interaction of the kallikrein-kinin and renin-angiotensin systems. In mamm als, BK is dipsogenic and vasodepressor, so that our data demonstrate oppos ite effects on fluid and cardiovascular regulation of BK in the eel and sug gest a new physiological role for the kallikrein-kinin system in teleost fi sh.