Homer W. Smith: The nephrologist

Abstract

If there is any group of people who do not need me to tell them about Homer Smith's contributions to renal physiology, this must certainly be it. We who tried to build on the foundation that he laid for us can be pleased to meet to honor his memory and also be happy that he chose to do at least some of his work in such an attractive spot for a summer interlude. Since I know that it is unlikely that I will tell you anything you do not already know, I shall be mercifully brief. If, in my brevity, I should seem to fall short of justice to Smith's contributions, I can refer you to my somewhat more extended tribute in a current issue of the Journal of the American Society of Nephrology [1]. For two decades it was clearance methods that provided the major tool for the progress that was achieved in understanding how the kidney works. I do not mean to underestimate the contribution of micropuncture of the laboratory of A.N. Richards, but, until its revival and widespread propagation in the late 1950's, it had provided only a few fixed points from which studies in intact animals could provide a broader and more detailed map of the field. It was Smith who recognized the full potential of clearances as a tool for the quantitative assessment of many aspects of kidney function. Of course it is well known that van Slyke, not Smith, invented the term clearance [2]. But van Slyke conceived it only as an overall index of renal function and not as a specific identifiable volume. Also, Rehberg [3] recognized that the clearance of an appropriate substance could provide the value of the rate of glomerular filtration. But, unfortunately, he chose the wrong substance to measure glomerular filtration in humans, and, after comparing the excretion of urea and chloride with the clearance of exogenous creatinine, did not press the technique further. It seems appropriate on this occasion to note that the idea of using non-metabolized sugars for measuring glomerular filtration had its origin here, or should I say down the road, in Saisbury Cove where E.K. Marshall, Smith's friend and early mentor, found that no sugars appeared in the urine of aglomerular fish. The fact that sugars were not secreted by the renal tubules of course did not prove that they were not reabsorbed. The latter, unfortunately, led to a number of studies in Smith's lab in which the clearance of xylose was assumed to be equal to glomerular filtration rate, until roughly simultaneously in Smith's lab and that of Richards, inulin was found to be the right one to use. From that time the use of inulin made it possible to measure precisely the rate of transport of various other substances and to