NK-3R Background Information Substance P (SP) and neurokinin-A (NK-A) are members of the tachykinins, and they function as modulators of the immune and hematopoietic systems (2). The tachykinins interact with each of three cloned neurokinin (NK) receptors (NK-1R, NK-2R, NK-3R), with SP and NK-A exhibiting binding preferences for NK-1R and NK-2R, respectively (2). NK-4R shares close homology with NK-3R, and both have nearly identical pharmacologicl properties (1). In the normal ileum and colon, NK-1R and NK-2R are localized to smooth muscle cells of the muscularis mucosae and propria and to a few inflammatory cells of the lamina propria (3). NK-1R expression is also found in the muscular wall of submucosal blood vessels, enteric neurons and, to a lesser degree, in surface epithelial cells (3). NK-3R is found in the spinal cord in both lamina X and lamina II (4,5).
