Evidence for the coupling of biosynthesis and secretion of serum albumin in the rat. The effect of colchicine on albumin production

Abstract

1. By using isotopic-dilution techniques it was found that colchicine causes a slight increase in the proalbumin content of liver, from 0.63+/-0.06 to 0.83+/-0.10mg/g of liver, but has no effect on albumin content (0.50+/-0.05mg/g of liver). All the proalbumin and 67% of the albumin is found in vesicles from which they are liberated by detergents. 2. Colchicine inhibits secretion of albumin, decreases the rate of conversion of proalbumin into albumin and decreases the rate of incorporation of l-[1-(14)C]leucine into proalbumin. 3. Balance studies in vivo show that all the (14)C appearing in serum albumin can be accounted for by the flow of (14)C through the proalbumin, in the presence or absence of colchicine. 4. When cycloheximide is given to the rats, 2min after [(14)C]leucine, further synthesis of protein stops. The label in proalbumin disappears and the proalbumin content of the liver falls, so as to account for the albumin appearing in the plasma. This occurs both in the presence and in the absence of colchicine. By contrast, there is little change in liver albumin. Studies with isolated perfused livers are in agreement with the above. Lumicolchicine has no effect on any of these systems at doses at which colchicine exerts its action. 5. These results suggest that biosynthesis and conversion of proalbumin into albumin, and secretion of serum albumin are controlled at each step.

A colchicine-sensitive uptake system in Morris hepatomas.

“…A preferential uptake of colchicine into hepatomas could be excluded. Furthermore, the opposite effects of colchicine on amino acid uptake in liver and hepatoma cannot be explained by changes in amino acid pool size; the increase by colchicine in the intracellular level of some amino acids, including L-leucine but not methionine, in host liver (26,27) also occurs in hepatomas. The increased amino acid concentrations (e.g., of leucine) in colchicine-treated hepatomas despite the blockage of uptake indicate that the size of a given amino acid pool is presumably ruled not only by the rate of transport of the amino acid but also by its metabolism to other products and the overall rates of protein synthesis and degradation.…”

Pathogenesis of alcohol-induced accumulation of protein in the liver.

“…Total liver immunoreactive albumin was also calculated from thle isotopic dilution of labeled serum albumin in the acid ethanol extracts of the immunoprecipitates, as described by Gordon and Humphrey (7). Hepatic proalbumin was determined by isotopic dilution according to the method of Dorling et al (22). Liver ferritin was measured by radial immunodiffusion using horse spleen ferritin as standard, according to the method of Bj0rklid and Helgeland (23).…”

Synthesis and secretion of albumin in rats during treatment with a carcinogenic dose of N-2-acetylaminofluorene

“…The change in differentiation of smooth endoplasmic reticulum caused by N-2-AAF is a long-term effect, in contrast to the reversible short-term effect reported for colchicine and fibrinogen. Colchicine causes a decrease in secretion of albumin accompanied by an accumulation in the Golgi apparatus (Dorling et al, 1975;Redman et al, 1975), while fibrinogen causes a decrease in secretion of albumin which is accompanied by an accumulation initially in the rough microsomes, but subsequently in the Golgi apparatus (Feldmann et al, 1975).…”

“…Albumin and proalbumin purification.-Albumin was putified from serum by the method of Debro et at. (1957) followed by ionexchange chromatography (Dorling et al, 1975). 3H-carrier albumin was prepared by the same procedure, after incorporation of lmCi L-4,5[3H]leucine per rat for 70 min.…”

“…was 25,000-30,000 ct/min/mg. Estimation of intracellular albumin and proalbumin involved isotopic dilution with 3H-carrier albumin, followed by purification by precipitation with anti-rat serum albumin and ion-exchange chromatography (Dorling et al, 1975). Precipitation of samples for scintillation counting was carried out as below.…”