CHANGES WITH AGE OF THE RAT FETUIN CONCENTRATION IN SERUM AND ITS MESSENGER-RNA EXPRESSION

Rat fetuin, a counterpart of human alpha(2)-HS glycoprotein and bovine fetuin, shows strong intermolecular binding and association with Othe r serum proteins, Therefore, to measure its concentration in rat serum , we pretreated serum samples with 1% SDS plus 5% (ca. 0.7 M) 2-mercap toethanol at 100 degrees C for 3 min, and then subjected them to SDS-P AGE under reducing conditions followed by Western blotting. We found t hat the fetuin concentrations in normal rat serum determined by Wester n blotting were 2.5-4.5 mg/ml, These concentrations were three orders of magnitude higher than the previously reported concentrations, We al so tried to measure the fetuin concentration in rat serum by means of an enzyme-linked immunosorbent assay after treatment of the samples wi th 0.1% sodium dodecyl sulfate (SDS) plus 10 mM 2-mercaptoethylamine a t 100 degrees C for 3 min, but it gave a value of about 1/4 of that on Western blotting. Rat fetuin is expressed mainly in the liver, with a peak 2-4 weeks after birth, as determined by Northern blot analysis. The fetuin mRNA level in the liver changes almost in parallel with its serum concentration. The tibia also expresses fetuin, but much less t han the liver.