Immunohistochemical detection of alpha-adrenoceptor subtypes using subtype-specific antibodies in rabbit interlobular arteries

There is controversy concerning the localization of α2-adrenoceptors in the renal vasculature. Thus, studies using antisera with specificities for rat RG20α2A, RNGα2B and RG10α2C adrenoceptors were conducted to detect the distribution of α2-adrenoceptors in two small intrarenal arteries of rabbit kidney: arcuate artery (ARC) and interlobular artery (ILUA). A newly developed immunostaining procedure (Gu et al., Cell Vision 2: 52-60, 1995) was employed which allowed specific detection of rabbit antigens with rabbit antisera. Our current functional studies indicate that norepinephrine (NE)-induced vasoconstriction is predominantly mediated by α1-adrenoceptors in the larger, more proximal ARC, but by α1-adrenoceptors as well as α1-adrenoceptora in the ILUA. In ILUA sections, immunohistochemical staining revealed RGSOofex-like immunoreactivity in the outermost smooth muscle and adventitial and connective tissue layers, RNGα2B-like iraraunoreactivity in the endothelium and RG10α2c-like immunoreactivity in the innermost smooth muscle and adventitial and connective tissue layers. No immunoreactivity for the RG20α2A, RNGα2B and RG10α2c was observed on the smooth muscle and endothelium of the ARC. Only RG10α2c-like immunoreactivity was observed in the adventitial and connective tissue layers of the ARC. These results suggest that e%-adrenoceptors are located in the ILUA, but not in the ARC. Furthermore, varying subtypes of α2-adrenoceptora are located in different regions of ILUA. [We would iike to acknowledge the gift of subtype-specific antibodies from Dr. R. J. Lefkowitz (Kurose et al., Mol. Pharmacol. 43: 444-450, 1993)]