“…Since an inverse relationship presumably exists between medullary blood flow and the hypertonicity of the medullary interstitium (33), a "wash-out" effect could reduce TCH2o/GFR and counteract the factors mentioned above. The administration of aminophylline, which increases renal blood flow (34), is accompanied by an increase in CH2o/ GFR (35) and a reduction of TCn2o/GFR (36).…”