UPTAKE AND SUBCELLULAR CATABOLISM OF HUMAN CHORIO-GONADOTROPIN IN THE PROXIMAL TUBULE CELLS OF RAT-KIDNEY

To determine subcellular organelles involved in catabolism of hCG in the renal proximal tubule cells male rats were injected intravenously with 1.9 μg of human [125I]iodochoriogonadotropin (hCG) and the radioactivity was localized in the cells by electron-microscopic autoradiography at 0.5, 2 and 4 h after the injection. The degradation products of the hormone were analysed simultaneously by gel filtration. The autoradiographs showed that a majority of the silver grains was associated with the lysosomes and the large apical vesicles at each observation point. The analysis of grain distribution revealed that the lysosomes were by far the most heavily labelled organelles and also that the large apical vesicles contained radioactivity. Gel filtration of the renal extracts revealed three radioactive peaks at each observation point, identified as intact labelled hCG, α-subunit of the hormone and labelled tyrosine. Gel filtration of the extract obtained from the separated organelle pellet showed only one peak corresponding to α-subunit of hCG while the remaining cytosol showed labelled hCG, α-subunit and labelled tyrosine. The present observations suggest that the structural modifications of hCG leading to cleavage of the subunits and hydrolysis to amino acids take place in the lysosomes of the renal proximal tubule cells. © 1979.