PURIFICATION AND CARDIOVASCULAR ACTIVITY OF [MET(1), MET(5)]-BRADYKININ FROM THE PLASMA OF A STURGEON (ACIPENSERIFORMES)

The sturgeons (Order Acipenseriformes) are extant representatives of a group of primitive Actinopterygian (ray-finned) fish that probably sh ared a common ancestor with present-day teleosts. Incubation of heat-d enatured plasma from a sturgeon (a hybrid of the shovelnosed sturgeon Scaphirhynchus platorynchus and the pallid sturgeon Scaphirhynchus alb us) with either trypsin or porcine pancreatic kallikrein generated bra dykinin-like immunoreactivity. The primary structure of sturgeon brady kinin was established as Met-Pro-Pro-Gly-Met-Ser-Pro-Phe-Arg. This ami no acid sequence contains two amino acid substitutions (Arg(1) --> Met and Phe(5) --> Met) compared with mammalian bradykinin. Bolus injecti ons of synthetic sturgeon bradykinin in doses as low as 1 pmol/kg into the dorsal aorta of unanesthetized sturgeon resulted in an immediate and significant fall in arterial blood pressure with a maximum depress or response at 300 pmol/kg. Thus, the cardiovascular response of the s turgeon to bradykinin resembles more closely the response of mammals r ather than the predominantly presser response seen in teleost fish. St urgeon bradykinin produced a strong and concentration-dependent (EC50 = 4.7 +/- 0.7 x 10(-10) M) relaxation of rings of vascular tissue from the sturgeon ventral aorta that had been pre-contracted with acetylch oline. The data indicate that sturgeon tissues are particularly respon sive to native bradykinin and suggest that the kallikrein-kinin system may have evolved before the appearance of the neopterygians (gars, bo wfin and teleosts). (C) 1998 Elsevier Science Inc.