Catabolism of Human [125I]Iodochorionic Gonadotropin in Rat Testis*

Publisher Website
Google Scholar
Abstract
The catabolic fate of [125I]iodo-hCG in rat testicular tissue after in vivo binding was studied to determine whether degradation of bound hormone is associated with the removal of hormone-receptor complexes. Male rats were injected iv with [125I]iodo-hCG, and the testicular uptake of radioactivity was studied over 24 h. The half-life of the radioactivity in testicular tissue after the maximal uptake at 6 h was calculated o be 10 h. Gel filtration of the radioactivity extracted at 6 and 24 h after the injection of labeled hormone disclosed that hCG in the rat testis undergoes catabolic modifications, including cleavage of peptide fragments identical to hormone subunits and hydrolysis to amino acids. The simultaneous injection of an excess (1500 IU) of unlabeled hCG with labeled hormone prevented the appearance of the degradation products. Autoradiography showed a distinct uptake of radioactivity in Leydig cells. Gel filtration of the radioactivity extracted from the isolated Leydig cells, prelabeled in vivo with radiolabeled hormone, displayed that the cells contain free hormone and hormone subunits in addition to hormone-receptor complexes. The homogenate prepared from isolated Leydig cells was also found to be capable of degrading hCG to subunits and amino acids. These observations suggest that the degradation of hCG observed in vivo takes place in the Leydig cells. The results of the present study indicate that the removal of receptor-bound hCG from testicular tissue in vivo is associated with degradation of the hormone molecules to peptide fragments, similar to hormone subunits, and free amino acids. This evidence supports the current view that the removal of receptor-bound hormone from target cells proceeds by the internalization and subsequent degradation of the hormone-receptor complexes.

This publication has 0 references indexed in Scilit: