AUTORADIOGRAPHIC QUANTIFICATION OF ADRENERGIC-RECEPTORS IN RAT-KIDNEY

The adrenergic nervous system is active in kidney function, and the kidney has large numbers of adrenergic receptor subtypes. Because of the cellular complexity of the kidney, it is difficult to obtain direct assessments of adrenergic receptor binding characteristics over specific tissue compartments. Qualitative autoradiography allows the localization of adrenergic receptors over tissue types in the kidney, but quantitative autoradiography allows direct comparison of adrenergic receptor number over different cellular compartments. The purpose of this study was to obtain direct assessments of alpha1, alpha2, and beta adrenergic receptor numbers over different tissue compartments of the kidney using quantitative autoradiography. Sections of Sprague-Dawley rat kidney were incubated in several concentrations of 3H-dihydroalprenolol to label beta receptors, 3H-prazosin to label alpha1 receptors and 3H-rauwolscine to label the alpha2 receptors. Sections of rat heart incubated in 3H-dihydroalprenolol were included as standards. The sections were then prepared for receptor autoradiography. After processing, the grains were then quantified on an image analysis system, and binding curves constructed from the specific binding. In some animals, the proximal tubules were stained to localize the proximal convoluted tubules. Significant Scatchard analyses were obtained in the glomeruli with dihydroalprenolol (5.18 x 109 receptors/mm3) and with rauwolscine (2.48 x 109 receptors/mm3). Significant Scatchard analyses were obtained in the cortex with rauwolscine (9.47 x 109 receptors/mm3) and with prazosin (3.9 x 109). In addition, specific binding was seen with rauwolscine and prazosin to the kidney arterioles. Qualitative analysis of the alkaline phosphatase activity in sections indicated that rauwolscine and prazosin binding was associated with proximal tubules, while dihydroalprenolol binding was associated with distal convoluted tubules. Straight tubules approaching the medulla were labeled with dihydroalprenolol. These data indicate that there are approximately twice the number of beta receptors on the glomeruli as alpha2 receptors, and that the proximal convoluted tubules have approximately three times as many alpha2 receptors as alpha1 receptors. Alpha1 and alpha2 receptors are localized on arterioles, and beta receptors are associated with distal convoluted tubules and straight tubular elements in the kidney. These data demonstrate that adrenergic receptor subtype and number varies considerably among the tissue compartments of the kidney.