9806997 Conlon The effects of brandykinin (BK) in mammals are mediated through interaction with discrete receptors, termed B1 and B2. Activation of the kallikrein-kinin system in the teleost fish, rainbow trout and Atlantic cod generates (Arg0,Trp5,Leu8)-BK (trout/cod BK). The effects of this peptide on the motility of gastrointestinal smooth muscle and on blood pressure in these species are mediated via receptors that are pharmacologically different from each other and from mammalian B1 and B2 receptors. It is proposed to gain insight into BK receptor evolution by cloning BK receptors from a trout intestinal cDNA library and a cod genomic library and characterizing them structurally. Structure-activity relationships of trout/cod BK will be investigated by synthesizing analogs in which each amino acid residue in the peptide has been systematically replaced either by alanine or by its D-isomer. The effect of the substitutions on (a) receptor-binding properties using cultured mammalian cells that have been transiently transfected with the cloned trout and cod BK receptors, (b) elevation of arterial blood pressure in the unanesthetized cod, and (c) motility of trout stomach and cod intestine will be determined. Antagonists to the trout and cod BK receptors will be developed and their properties evaluated in these bioassays. The effect of trout/cod BK on gastric acid and pepsinogen secretion by isolated mucosa from trout stomach, electrolyte transport in the isolated trout intestine and on urine production by the trout kidney will be studied. Taken together, the data will provide insight into the properties of "ancestral" BK receptor from which the mammalian receptors may have evolved and will lead to a greater understanding of the physiological role of the kallikrein-kinin system in teleost fish.
