Bradykinin and Respiratory Mucous Membranes: Analysis of Bradykinin Binding Site Distribution and Secretory ResponsesIn VitroandIn Vivo

Abstract

Bradykinin (BK) and lysyl-BK (lys-BK, kallidin) have been proposed as potentially important mediators of rhinorrhea. Possible mechanisms by which BK might contribute to rhinorrhea were investigated by several approaches. (1) The autoradiographic distribution of 125I-BK binding sites in human inferior turbinate nasal mucosa was determined. (2) The effects of BK and lys-BK and antagonists on radiolabeled respiratory glycoconjugate (RGC) release from human nasal mucosa was measured. (3) The secretory effects of BK were studied in cat tracheal mucosa maintained in short-term explant culture, and in ferret trachea maintained in Ussing chambers. (4) The effects of BK on macromolecule secretion in guinea pig nasal mucosa was studied in vivo. Autoradiographic examination of human nasal mucosa revealed that 125I-BK specifically bound to small muscular arteries, venous sinusoids, and submucosal fibers. No specific binding to submucosal glands or goblets cells was noted. Human nasal fragments secreted significantly increased amounts of RGC in response to 10 .mu.M BK (15.0% .+-. 1.8 compared with control values; mean .+-. standard error of the mean; n = 7; p < 0.01 by Student''s unpaired t test), 10 .mu.M lys-BK (12.2% .+-. 3.3; n = 5; p < 0.05), and 100 .mu.M methacholine (35.7% .+-. 2.3; p < 0.0001). The addition of 1 .mu.M BK, or 1 .mu.M lys-BK, did not induce release. The addition of the BK receptor antagonist des-Arg9-[Leu8]-BK(10 .mu.M) or inhibition of arachidonic acid metabolism with 50 .mu.M nordihydrogualaretic acid or 65 .mu.M ibuprofen inhibited the prosecretory effect of 10 .mu.M BK. Cat trachea explants did not release RGC in response to 10 nM to 10 .mu.M of BK. In ferrets, application of 1 .mu.M BK to the mucosal surface of the trachea increased the flux of 35S-glycoconjugates by 38% compared wtih control values (not statistically significant by unpaired t test). Methacholine stimulated respiratory glycoconjugate release from cat (71.7% .+-. 15.4 increase in response to 100 .mu.M; p < 0.05) and ferret (22.5% increase in response to 10 .mu.M; p < 0.005) tracheal tissues. When applied topically to guinea pig nasal mucosa, 10 .mu.M BK induced secretion of albumin (a measure of vascular permeability) but did not affect total protein (a measure of glandular plus vascular secretion). These data indicate that BK most likley binds to vessels and may directly alter vascular tone or permeability in human nasal mucosa. BK may also stimulate sensory nerves. Because BK receptors were not demonstrated on submucosal glands, it seems likely that there are no direct effects of BK on glandular secretion. Instead, the increased glycoconjugate release noted with human nasal mucosa may reflect an indirect response that was inhibitable by NDGA and ibuprofen, suggesting that stimulation of arachinoid formation may in turn cause glycoconjugate release. These data suggest that BK may act primarily upon blood vessles to affect vascular tone and permeability and indirectly to induce a minor degree of glandular secretion.