Prostaglandin-E2 receptors in the rat kidney: biochemical characterization and localization

A radiohistochemical technique yielding data on the distribution and characteristics of PGE2-receptor binding in tissue sections is described. The binding of tritiated PGE2 (3H-PGE2) to slide-mounted tissue sections had all the characteristics associated with ligand-receptor interactions: it was saturable, of high affinity and displayed high specificity for PGE2 binding. From the binding curves a Hill coefficient of 1.1 was calculated which suggests the presence of a homogeneous receptor population. Pretreatment with indomethacin for four days resulted in a 66% increase in maximal binding capacity (Bmax) without any change in affinity. The distribution of receptor was mapped in rats with and without indomethacin pretreatment and compared to the distribution of Tamm-Horsfall glycoprotein, a specific marker for the thick ascending limb of Henle. In both groups the PGE2 receptor showed striking regional variation. In the untreated group the distribution of PGE2 receptors was similar to that of the thick ascending limb of Henle, with maximal density in the outer medullary zone. After indomethacin pretreatment, however, a striking increase in inner medullary binding was observed together with increased binding in the cortex. Thus, in accordance with the main action of PGE2 being regulation of renal water and sodium excretion, we found the highest receptor density in areas of the kidney dominated by the thick ascending limb of Henle and collecting tubules, and much less binding to glomeruli and cortical vessels. In order to investigate characteristics and distribution of PGE2 receptor binding, however, it was mandatory that endogenous prostanoid synthesis is blocked.