INTERACTIONS OF COBALT AND IRON IN ABSORPTION AND RETENTION

The effects of supplementary oral cobalt and iron, as well as the inte raction between both at the absorption site, fecal and urinary excreti on as well as the retention of these trace elements were determined by using four diets containing either 9 or 63 mu g/kg of Co and 48 or 44 6 mg/kg of Fe over a period of 19 days in a total of 24 rats. Retentio n was calculated by the balance technique and by the comparative slaug hter technique. After one day, fecal as well as urinary excretion of b oth elements had already responded to the dietary treatments, with con stant values being reached after approximately three days. Cobalt excr etion was enhanced by suplementary cobalt; fecal excretion, too, was i ncreased by supplementary iron; whereas urinary excretion was decrease d in both cases. Additional iron significantly inhibited the absorptio n of cobalt in both dietary cobalt treatments. The lower rate of absor ption in the groups receiving 446 mg Fe instead of 48 mg of Fe per kg diet resulted in a decreased renal excretion of cobalt. Consequently, the effect of iron on the retention of cobalt was lower than on absorp tion. This suggests that interactions between the two elements only ta ke place at the site of absorption. Because of the low dietary cobalt concentration as compared to the iron contents of the diets, no effect of cobalt on iron absorption and excretion occurred. Differences in i ron balance were only observed between both dietary iron concentration s, showing a higher absolute but a lower relative absorption as well a s retention in the groups fed further Fe. The group differences in ret ention as obtained by the two different techniques were consistent; ho wever, the levels of retention differed greatly.