Intestinal transport of pyridoxine in experimental renal failure

Abstract Renal failure (RF) has been shown to alter intestinal transport of a number of nutrients. We studied jejunal absorption of pyridoxine (B 6 ) in rats rendered azotemic by subtotal nephrectomy (RF group) and compared the results with those obtained in normal rats subjected to sham operation (controls) and animals pair-fed (PF) with their RF counterparts. In vivo recirculating perfusion and in vitro everted sac techniques were employed. The in vitro experiments were repeated using sera from uremic and normal individuals to assess the possible effect of uremic chemical environment. The results showed significant reduction in B 6 absorption in vivo in the RF group as compared to the control and PF groups. Paradoxically, the rate of in vitro B 6 absorption determined for a wide range of concentrations was increased in the RF and PF groups as compared to the control group. The observed increase in B 6 absorption in vitro suggests enhanced permeability in the RF and PF groups due probably to reduced nutrient intake which was common to both groups. The disparity between the in vivo and in vitro results is indicative of some inhibitory factor(s) present in the RF animals. Sacs containing uremic serum showed significantly suppressed B 6 absorption in vitro as compared to those containing normal serum. These observations suggest that the uremic chemical environment may be, in part, responsible for the observed impairment of B 6 transport in RF animals despite in vitro evidence of hyperpermeability. Pyridoxine (B 6 ) is the major plant form of vitamin B 6 , while pyridoxamine phosphate and pyridoxal phosphate are the primary forms in animals. Consumption of a B 6 -deficient diet leads to rapid occurrence of B 6 deficiency (1) which is associated with neuromuscular irritability, central nervous system depression, convulsion, stomatitis, cheilosis, cutaneous lesions, peripheral neuropathy, disorders of oxalate metabolism, impaired immune response and anemia. (2–7) Earlier studies in our laboratory have revealed an impaired intestinal absorption of riboflavin, (8) tetrahydrofolate, (9) and vitamin D-3 (10) in experimental renal failure (RF). In addition, B 6 deficiency has been reported in patients with renal insufficiency. (11) However, the effect of RF on the intestinal absorption of B 6 has not been previously investigated. The present study was designed to determine the effect of experimental RF on the intestinal absorption of B 6 using the in vivo perfusion and in vitro everted sac techniques. (12)