Disappearance of Human [125I]Iodochorionic Gonadotropin from the Circulation in the Rat: Tissue Uptake and Degradation*

Abstract

125I-labeled hCG (human [125I]iodoCG) was injected iv into male and female rats, and the disappearance of the hormone from the circulation was studied. Also, the uptake of the hormone by different tissues, as well as its catabolic fate after the initial uptake were analyzed. The disappearance curve of human [125I]iodoCG consisted of two exponential components with apparent half-lives of 30 min and 4.8 h in both sexes. Two hours after the hormone injection, the uptake of radioactivity was 10.5% of the injected radioactivity in the kidneys, 2.2% in the liver, and 1.9% in the ovaries. A considerable amount of radioactivity, (1.5% of the total injected radioactivity) was also excreted in urine. Autoradiographs prepared from the kidney cortex and ovaries showed that renal uptake of the hormone took place mainly in the proximal tubule cells, and the ovarian uptake took place in the corpora lutea and theca cells. Gel filtration analyses of the radioactivity extracted with 0.5% Triton X-100 from the kidneys and l...