Alpha-2 adrenergic receptor localization in the rat heart and kidney using autoradiography and tritiated rauwolscine.

To study the distribution and characterization of alpha-2 adrenergic receptors in the rat heart and kidney, we used light microscopic autoradiography and a computer-based image analyzer to quantify the localization of [3H]rauwolscine (RAUW) binding. Scintillation spectrometry of frozen sections of rat kidney demonstrated rapid binding, saturability, stereospecificity and agonist and antagonist binding characteristic of an alpha-2 adrenergic receptor. For autoradiography, sections of rat kidney and heart were incubated in several concentrations of [3H]RAUW in the absence of (total binding) and in the presence of (nonspecific binding) 10(-5) M yohimbine. The sections were processed and grain density quantified using a computer-based image analyzer. The tubules in the renal cortex had significantly more specific [3H]RAUW labeling than either the renal glomeruli or the tubules in the renal medulla at all concentrations of [3H]RAUW used (P less than .0001). Nonspecific binding was significantly higher over the cortical tubules than either the glomeruli or the tubules in the renal medulla (P less than .0001). Scatchard analysis of specific grain densities determined that the tubules in the renal cortex had the highest density of any structure studied [maximum binding (Bmax) = 1182 grains/10(-2) mm2]. The glomeruli had a Bmax of 485 grains/10(-2) mm2, whereas the tubules in the renal medulla had a Bmax of 273 grains/10(-2) mm2. There were no significant differences among these three regions in the dissociation constant of the [3H]RAUW. When analyzing the heart, we found no specific [3H]RAUW labeling over either the cardiac myocytes or the myocardial arterioles.(ABSTRACT TRUNCATED AT 250 WORDS)