CHARACTERIZATION AND LOCALIZATION OF BRADYKININ B-2 RECEPTORS IN THE GUINEA-PIG USING A RADIOIODINATED HOE140 ANALOG

The potent bradykinin B-2 receptor antagonist analogue, [I-125]HPP-HOE 140, ([I-125]-3-4-hydroxyphenyl-propionyl-D-Arg(0)- [Hyp(3),Thi(5),D-T ic(7),Oic(8)]bradykinin), was used to localize and characterize guinea -pig tissue bradykinin B-2 receptors. Analysis of competition for the radioligand binding, using membrane preparations of lung, ileum and ut erus, revealed the presence of a high- and low-affinity binding site: at the high-affinity site, the apparent K-i for the various bradykinin B-2 receptor ligands ranged from 0.26 to 2.13 nM for HPP-HOE140, from 0.25 to 1.45 nM for HOE140, from 129 to 625 nM for D-Arg(0)[Hyp(3),Ph e(7)]bradykinin and from 0.05 to 1.11 nM for bradykinin. At the low-af finity site, the apparent K-i values ranged from 4.90 to 10.5 nM, from 1.23 to 1.90 nM, 4760 nM and from 2.01 to 62.1 nM, respectively. By c ontrast, the bradykinin B-1 receptor antagonist, des-Arg(9)[Leu(8)]bra dykinin did not compete for [I-125]HPP-HOE140 binding from membrane pr eparations at concentrations up to 1 mu M. Using in vitro autoradiogra phy on tissue sections, intense binding was observed in the lamina pro pria of the villi of ileum and the arteriolar smooth muscle cells in l ung. in the uterus, dense binding was found in the inner third of the myometrium and over epithelial cells of the glandular endometrium, whi le diffuse binding was observed throughout the endometrial stroma. In the brain, intense binding was observed in the nucleus of the solitary tract, spinal trigeminal tract and area postrema of the hindbrain, th e middle cerebral arteries, and the choroid plexus of the third and la teral ventricles. Moderate binding was observed in the CA3 region of t he hippocampus and posterior and ventroposterior thalamic nuclei. In t he spinal cord, high-density binding occurred in the laminae I and II of the dorsal horn. Unlike previous autoradiographic localization stud ies of the bradykinin B-2 receptor using radiolabeled bradykinin, the radiolabeled antagonist HPP-HOE140 did not bind to bradykinin-degradin g peptidases, such as angiotensin-converting enzyme, and displayed sub type specificity. Therefore, binding studies with [I-125]HPP-HOE140 of fers high sensitivity and specificity for characterization, quantitati on and localization of subtypes of bradykinin B-2 receptors in tissues , and offers new information on uterine and brain bradykinin B-2 recep tors.