Albumin localization in the frog hepatocyte during vitellogenesis as revealed by protein A-gold immunocytochemistry.

The protein A-gold immunocytochemical technique was used to localize albumin in the hepatocyte of the normal male American bullfrog, Rana catesbeiana, and also in the hepatocyte of this animal 8 days after treatment with estradiol-71 beta. Albumin concentration in plasma also was estimated biochemically. In the normal animal, specific immunolabeling for albumin was present in the intracellular compartments involved in protein secretion, i.e., rough endoplasmic reticulum (RER), Golgi apparatus and secretory granules, and also in lysosomes. Density of labeling increased as it progressed along the secretory pathway. In the hepatocyte of the estrogen-treated frog, specific immunolabeling for albumin was also present along the entire secretory pathway and in the lysosomes. Density of labeling over the RER was similar to that seen for this organelle in normal tissue; however, no progressive increase, but rather significant decreases, in labeling density occurred further along the secretory pathway. The biochemical data demonstrated no change in the concentration of plasma albumin in the treated frog, compared with the normal one. These observations localize albumin along its secretory pathway in frog hepatocyte and demonstrate a perturbation in its secretion in response to estrogen treatment.