Plasma Glycoprotein Synthesis in Alloxan-Diabetic Rats

Abstract

Experiments were carried out to determine whether alloxan diabetes in rats altered:(1) the level of plasma seromucoid (a small carbohydrate-rich fraction), (2) the perchloric acid (PCA)-insoluble protein, making up the remainder of the plasma protein, and (3) the ability of the animal to incorporate [14C]glucosamine and [14C]leucine into these plasma fractions.Diabetes was produced in 20 male Wistar rats (250-275 g) by the following procedure. Rats, fasted for 16 h, were lightly anaesthetized with ether and injected i.v. with alloxan (70 mg/kg) in 0\m=.\9 % NaCl solution acidified to pH 3\m=.\5. They were then given protamine zinc insulin s.c. at a daily dose of 2 u. for 7 days, 1 u. for 5 days and 0\m=.\5 u. for 5 days. Experiments were carried out 3 days after the last dose of insulin. In the 24 h preceding the experiments, urinary output of glucose per rat was 667 \ m=+-\ 46 (S.E.M.) mg. Control Wistar rats were matched by weight.Ten diabetic and ten control rats were injected i.v. with 5 /tCi [l-14C]glucosamine/ 220 g body weight. The remaining ten diabetic and ten control rats were similarly injected with 10/iCi [14C]leucine/220 g body weight. Blood (1 ml) was withdrawn from the jugular vein every hour for 4 h after the injection. Seromucoid and PCAinsoluble protein were separated (Winzler, Devor, Mehl & Smyth, 1948) and the pro¬ tein of each fraction assayed (Lowry, Rosebrough, Farr & Randall, 1951). Radio¬ activity of each of these fractions and of the protein-free supernatant was measured on a Nuclear Chicago gas-flow low-background counter. Specific activity was calculated on each sample of protein. The values obtained at 4 h were analysed statistically because they had reached a plateau by this time.Total plasma protein levels in the diabetic rats were not changed significantly but a significant depression (P < 0-001) occurred in the PCA-insoluble fraction (19494 + 414 v. 22 843 + 363 µg|mí blood in the controls). The seromucoid levels in the dia¬ betic rats, normally 1/43 of the total plasma protein of the normal rat, remained un¬ changed (564 + 20 v. 529 + 20 /ig/ml blood in the control animals). One hour after the injection of isotope, less than 0-2 % of the injected radioactivity was left in the cir¬ culation in any experiment, indicating rapid incorporation and/or excretion of both glucosamine and leucine.Four hours after the injection of [l-14C]glucosamine the specific activity of the seromucoid in the diabetic rats exceeded that of the control group (P < 0-025). The