Renal Transport of Bile Salts

Because of results (see below) suggesting an interaction of bile salts with the renal tubular mechanism for organic anion secretion, it is interesting to consider the consequences of efficient renal secretion of these substances, were it to occur. At a mean plasma level of 1 / g/ml and renal plasma flow of 700 ml/min, urinary excretion would be 1 g/day. This exceeds the daily turnover of bile salts in man and is many times greater than the highest excretory rates observed. 

Rudman and Kendall (55) were the first to appreciate that the observed 

This was confirmed in dogs (57) in a study which also demonstrated (for cholic, taurocholic, and glycocholic acids) that reabsorption occurs in the proximal tubule (Fig. 7) and that the reabsorptive process involves active transport. The latter conclusion was based on estimates of the tubular fluid/ ultrafiltrable plasma concentration ratio for taurocholate and an estimate of transtubular electrical potential taken from the literature. In addition, it was shown that the reabsorptive process for bile salts had a maximal rate (saturation kinetics) (Fig. 8). 

Although entirely consistent with the earlier clinical evidence, this work did not provide an explanation for observations which suggested (but did not require) an interaction of bile salts with a secretory process. The latter was inferred from the observation of Woo and Hong (58) that bile salts inhibit 

Values for excretion (UV) have been divided by glomerular filtration rate (GFR) to correct for differences among dogs. The dashed line depicts the idealized situation in which maximal rate of reabsorption is 20 mg/min, GFR is 100 ml/min, and reabsorption is complete until the maximal rate is attained. Obviously, the actual approach to the maximal rate is more gradual. From Weiner et al. (57). 

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