Laser-Doppler determination of papillary blood flow in young and adult rats

Renal hemodynamics and renal blood flow autoregulatory ability differ in young (body wt 100 g) and adult (body wt 300 g) rats. Possible age-dependent changes in inner medullary hemodynamics have not been examined because it has not been possible to expose the papilla of adult rats for direct study of the vasa recta circulation. This study presents a technique for exposure of the papilla in any size rat. Seven days before an acute experiment, a small amount of cortical tissue overlying the papilla on the dorsal surface of the kidney was removed. The creation of this papillary window allowed for exposure of the papilla in adult rats after removal of the ureter. Using this preparation, we compared papillary blood flow in young and adult rats using a Periflux differential laser-Doppler flowmeter (Perimed, Stockholm, Sweden). The meter was calibrated by comparing the signal obtained from the papilla of 28 rats with papillary flow measured from the accumulation of 51Cr-labeled erythrocytes in the papilla. The l...