The aim of this study was to identify a low molecular weight chromium-binding substance (LMW Cr) in the organs of mammals and to clarify the substance's significant role in the detoxication and excretion of absorbed chromium.
The results obtained were as follows:
1. LMW Cr was purified from the livers of dogs. Two subfractions were obtained and labelled LMW Cr I and II. Their total molecular weight was estimated at approximately 1, 500. Fine crystals of the two subfractions were obtained by repeated recrystallization.
2. The two-weeks LD50 value of LMW Cr I in mice (i.p.) was 134.9mg/kg. This value was much higher than those of K2Cr(VI)2O7 and Cr(III)Cl3⋅6H2O.
3. Urinary excretion rates of K2Cr2O7 and CrCl3⋅6H2O in rabbits 380min after i.v. injection of a single dose (200μg chromium/kg body weight) were 14.49% and 23.63%, respectively. Whereas the rate of LMW Cr was 64.44%
4. Renal clearance rates of LMW Cr were remarkably high when compared with those of K2Cr2O7 and CrCl3⋅6H2O.
5. Chromium in the forms of K2Cr2O7 and CrCl3⋅6H2O was almost completely reabsorbed from renal tubules, whereas the tubular reabsorption rate of LMW Cr was calculated at 23.54%.
6. Concentrations of chromium in the tissues of mice after i.p. injection of a single dose of LMW Cr (500μg chromium/kg body weight) were lower than those of K2Cr2O7 and CrCl3⋅6H2O.
These findings indicate that there exists a low molecular weight chromium-binding substance in the tissues of mammals which binds absorbed chromium in a specific chemical form, and that this substance plays an important role in the detoxication and excretion of chromium.