THE MEASUREMENT OF SYNTHESIS RATES OF ALBUMIN AND FIBRINOGEN IN RABBITS

Abstract

A formula is proposed for calculating fractional synthesis rates of liver-produced plasma proteins that dispenses with urinary information or information about the size of the urea pool in the body or the fraction of urea that is endogenously catabolized. Synthesis rates obtained for albumin and fibrinogen agreed well with corresponding catabolic rates for the I131-labelled proteins except in 2 of the fibrinogen measurements. Significant reutilization of C14 occurs in some animals after [C14]carbonate injections, thus giving rise to errors in the calculation of protein synthesis rates. These can best be avoided by using results obtained by injecting [Cl3]urea simultaneously. [Nl5]Urea was not satisfactory for this purpose.