The renal clearance (in dogs) of taurocholate, after correction for plasma-protein binding, is less than the glomerular filtration rate. Clearance increases toward, but does not attain, the filtration rate as filtered load is increased. Clearance is not influenced by changes in urinary pH or flow, nor by administration of probenecid or benzmalecene (20–25 mg/kg). The site of reabsorption demonstrated in stop-flow studies is the proximal tubule. Tubular fluid-to-plasma ultrafiltrate ratios less than unity were observed. The results are interpreted as indicating active reabsorptive transport. Glycocholate and cholate are handled in a similar manner. Possible mechanisms of interaction of this reabsorptive system with the organic acid secretory system are considered.

Active transport of sodium taurocholate was demonstrated in the following species: albino mouse, golden hamster, squirrel monkey, king pigeon, and Leghorn chicken. The criterion for active transport was the ability of everted gut sacs to establish serosal: mucosal concentration gradients greater than unity In all cases, this activity was limited to the distal half of the small intestine. 2,4-Dinitrophenol inhibited taurocholate transport. These results are similar to those previously reported for tissue from rats and guinea pigs. In vivo studies were performed by introducing solutions of radioactive taurocholate into tied-off portions of the small intestine of anesthetized animals and determining the rate of appearance of the radioactivity in the bile collected from the common duct. The following species were studied: white rat, mongrel dog, spider monkey, and rabbit. In all cases the major transport activity was in the ileum.

In four groups of subjects free of thyroid disease, the following determinations were made: serum concentrations of thyroxine (T4), triiodothyronine (T3), reverse T3(rT3) and diiodothyronine (T2), and calculated indices of free thyroxine (FT4) and free triiodothyronine (FT3). Group A comprised healthy subjects aged 16-64; Group B, 24 healthy elderly subjects aged 68-95; Group C, 23 elderly patients with mild well-controlled chronic illnesses, aged 70-85; Group D, 40 nursing home residents aged 66-100. Serum T4 and T2 concentrations and the FT4 index were not affected by age; the rT3 concentration was slightly but significantly elevated only in Group D patients. Serum T3 concentration was significantly lower in all groups of elderly subjects and decreased FT3 index measurements were detected after age 75. It was concluded that old age, without complicating illness, is accompanied only by a decrease in the serum level of T3 and the FT3 index; values for other iodothyronines are unchanged. Clinicians should consider the age-related changes in T3 and FT3 values when interpreting thyroid function tests.