Mechanisms of Urine Concentration

In this issue of “The Forum” we make a modest departure from our usual, case-oriented discussion. Because basic scientific principles form the backbone of all pathophysiologic reasoning, we present here a strictly physiologic discussion of the development of the countercurrent hypothesis of urine concentration and dilution. The way in which this theory developed exemplifies several recurrent themes in the history of science; valid hypotheses ignored for years, new observations forced into an outmoded theoretical framework, false pathways traversed because of erroneous experimental data, clinical acceptance of a new hypothesis, and lingering doubts that motivate additional studies forcing refinement of existing “truths.”