Abstract
Abstract A sensitive, specific, and rapid immunochemical method for the measurement of the synthesis of lipoproteins in rooster liver is described. Incubation of liver slices with [3H]leucine resulted in the incorporation of radioactivity into protein material that could be precipitated from crude extracts by a monospecific antibody directed against the antigen common to plasma very low density and low density lipoproteins (very low density lipoprotein antigen). Use of this assay permitted the demonstration of a 4-fold increase in the rate of hepatic synthesis of the very low density lipoprotein antigen occurring 16 hours after the administration of estrogen to roosters. Since under these conditions as much as 18% of the total protein synthesized by the rooster liver represented very low density lipoprotein antigen, this system may provide a model for studying not only the effect of a steroid hormone on specific gene expression but also the mechanism of regulation of very low density lipoprotein synthesis in higher animals.
Highlights
The dramatic elevation in plasma very low density lipoproteins that occurs in chickens after the administration of estrogen (l-3) is an important biological phenomenon for at least two reasons: (a) it represents a major effect of a steroid hormone on specific gene expression and (b) it may provide a model system for the study of the mechanism of regulation of VLDLi synthesis in higher animals
By analogy with a similar phenomenon in Xenopus laevis in which production of the plasma egg yolk protein vitellogenin has been shown to be due to a specific effect of estrogen on hepatic protein synthesis [4,5,6], it has generally been assumed that in chickens estrogen acts on liver to induce specific lipoprotein synthesis
Plasma Lipoproteins in Control and Estradiol-treated RoostersIn the plasma of the untreated rooster, the predominant lipoproteins were relatively rich in protein and cholesterol, poor in triglyceride, and had a buoyant density between 1.063 and 1.215 (Fig. 1)
Summary
A sensitive, specific, and rapid immunochemical method for the measurement of the synthesis of lipoproteins in rooster liver is described. Incubation of liver slices with [aH]leucine resulted in the incorporation of radioactivity into protein material that could be precipitated from crude extracts by a monospecific antibody directed against the antigen common to plasma very low density and low density lipoproteins (very low density lipoprotein antigen) Use of this assay permitted the demonstration of a a-fold increase in the rate of hepatic synthesis of the very low density lipoprotein antigen occurring 16 hours after the administration of estrogen to roosters. Since under these conditions as much as 18% of the total protein synthesized by the rooster liver represented very low density lipoprotein antigen, this system may provide a model for studying the effect of a steroid hormone on specific gene expression and the mechanism of regulation of very low density lipoprotein synthesis in higher animals.
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