Rat renal papilla: comparison of two techniques for x-ray analysis

Major differences in elemental and water content in cells of rat papillae have been reported by investigators using the frozen hydrated/frozen dried method versus that using external standards for x-ray microanalysis. These differences could not be ascribed to either cryosectioning at warmer temperatures or to the analytical algorithm used by either group. In this study, six paired left and right renal papillae were subjected to x-ray analysis. The frozen hydrated/frozen dried method was used on undipped papilla, while both methods were applied simultaneously to contralateral papillae dipped in albumin standard. No significant differences were seen between the physiologic state of the left and right kidneys prior to freezing. Our results demonstrated two major problems with application of an albumin peripheral standard: 1) albumin dipping significantly changed elemental and water content in papillary collecting duct cells, epithelial cells and interstitium, but interstitial cells were not affected; 2) the peripheral albumin standard itself also changed water and elemental content in a direction consistent with movement of Na and Cl from tissue to standard, and water from standard to tissue.