Influence of tissue fixation on the binding of (125)I-angiotensin receptor ligands in the rat,mouse and rabbit kidney

Aldehyde fixatives are often used to preserve tissue morphology and thereby aid in the identification of cellular structures expressing a target of interest. However, the effect of fixatives on target detection methods is unpredictable and it is currently unknown whether tissue fixation would allow the accurate detection of angiotensin AT(4) receptors in the kidney. In vitro receptor autoradiography on tissues fixed with 4% paraformaldehyde and 0.5% glutaraldehyde (+/-20% sucrose) had differing effects on the density of (125)I-AT(4) receptor ligand binding without affecting the tissue distribution of ligand binding in the rat and mouse kidney, whereas an increased expression of specific (125)I-AT(4) receptor ligand binding was found in the medulla region of the rabbit kidney. In contrast, such tissue fixation conditions dramatically decreased the renal binding of (125)I-angiotensin II receptor ligands, and altered the distribution of such ligand binding, in all three species. These results suggest that the method of tissue fixation and processing should be used cautiously in angiotensin receptor density measurements but can provide an accurate representation of kidney AT(4) receptor distribution only in the rat and mouse.