Autoregulation of LH/hCG Receptors and Catabolism of hCG in Rat Testis

The number of free and occupied LH/hCG-receptors in adult rat testes after subcutaneous injections of hCG was studied. When 3–10 IU of hCG was injected, there was initially (between 6 and 16 h) a significant increase in free binding sites, without detectable occupancy of receptors. Higher doses (100 and 1000 IU) induced a drop in the amount of free receptors which was explained by simultaneous receptor occupancy. Later (between 12 and 48 h) there was a pronounced net loss of both free and occupied binding sites. Gel filtration of radioactivity extracted from testicular tissue demonstrated that following the initial uptake ¹²⁵I]hCG undergoes a cleavage to subunits and hydrolysis to peptide fragments and amino acids. The autoradiographic results suggest that the degradative processes take place in Leydig cells. The degradation of ¹²⁵I]hCG was markedly reduced by simultaneous injection of an excess of unlabelled hormone, supporting the autoradiographic evidence of the degradation site of ¹²⁵I]hCG.