Disappearance of Radioactive Iron from Plasma by Day and by Night

Abstract

Conclusion

These findings provide support for the hypothesis that the plasma iron level rises by night because of diminished utilization of iron for hemoglobin synthesis during sleep in the individual with normal erythropoietic activity. The conclusion is inferential in that no actual measurement of the newly formed hemoglobin was made but is clearly suggested by the findings of Wasserman and others(5) who interpret rate of removal of iron from the plasma as providing an index of erythropoietic activity. Bothwell and Mallett(9) found that plasma iron turnover varied throughout the day and was significantly affected by the plasma iron level. It is probable that an important consideration in assessing the findings of these authors concerns the state of the plasma iron level, i.e., whether it is rising or falling at the time of plasma iron turnover determination. An interesting finding by Bothwell and Mallett was that the fraction of iron removed per hour from the plasma was uniformly large in both morning and evening determinations in anemic subjects.

The plasma iron reaches its lowest level just after sleep begins and rises during sleep (10). This diurnal pattern is reversed in night-workers who sleep by day(10–13). The usual rhythm, with morning levels higher than evening levels, is found only if the subject has slept during the night(13). The diminished plasma iron turnover and increased T 1/2 by night suggest that diurnal variation of the plasma iron level is secondary to a diurnal variation in the rate of hemoglobin synthesis, which in turn is dependent upon the sleep rhythm. The high morning level of bilirubin in the plasma may be considered due to diurnal fluctuation in liver function rather than to increased hemolysis by night, as was held by Laurell(4).