Role of internalization and degradation in the removal of receptor-bound human chorionic gonadotropin in rat luteal cells in vivo.

Abstract

The subcellular and catabolic fate of [125I]iodohCG in rat luteal cells after in vivo binding was studied to determine whether internalization and degradation of bound hormone are associated with the removal of hormone-receptor complexes. Pseudopregnant rats were injected iv with [125I]iodohCG, and the ovarian uptake of radioactivity was studied over 24 h. The radioactivity disappeared from the ovarian tissue after the maximal uptake at 1.5 h in a biphasic manner, with half-lives of 1.2 and 4.8 h. The decrease in the loss of radioactivity was not due to an accumulation of hormone catabolites in the tissue. Gel filtration of the radioactivity from the ovarian tissue 2, 6, 12, or 24 h after the injection of labeled hCG displayed only one radioactive peak corresponding to the hormone-receptor complex. Electron microscopic autoradiographs showed that a majority of the silver grains were associated with microvillous projections of the luteal cell plasma membrane directed toward the capillary regions. Multiple ...