As is well known, ovulation and steroidogenesis are controlled by gonadotropins. In spite of many studies, action mechanism of gonadotropin is not yet clear. This experiment was carried out to clarify the question whether gonadotropin acts especially in the ovary simply because it is concentrated in the ovary, and the effects of HCG on the synthesis of nucleic acids and protein. [1] Disappearance of 131I-gonadotropin from blood of rabbits About 107 cpm of 131I-NIH FSH or NIH LH was injected

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... ugh ear vein of rabbits. One ml of blood sample was taken from femoral vein and counted for radioactivity by Well type gamma detector. "1I-FSH and LH were disappeared rapidly from blood in one hour after 131I-gonadotropin injection and thereafter relatively slowly diminished in 24 hours. [2] Transport of 131I-gonadotropin to ovary Immature female rats of Sprague Dowley strain, about four weeks after birth were used. Rats were injected intravenously with about 2 x 105 cpm/10 g.body weight of NIH FSH, NIH LH, HCG or NaI labelled with "'Iodine. After variable intervals, rats were sacrificed and perfused by saline solution to except blood contamination from many tissues. The tissue was counted for radioactivity by Well type gamma detecter. 131I -gonadotropins administered intravenously were transported mainly to liver and kidney. 19 -gonadotropins were transported to ovary at unexpected low level, but in ovary the one hour value was slightly higher than the value immediately after "'I injection, whereas in other tissues the value immediately after "1I-gonadotropin injection showed the highest level. This was the only difference. [3] Effects of HCG on the synthesis of nucleic acids and protein 50 iu of HCG (pregnyl) was injected to immature female rats of Sprague Dowley strain. After some intervals, "C-valine (2 pc), "C-uridine (4 pc) or "C-thymidine (4 pc) was administered intravenously. Rats were sacrificed 2 hours after "C-valine or uridine injection and 6 hours after thymidine injection. Ovaries were removed, stripped off adipose tissue, and then homogenized in saline solution. The homogenate was centrifuged at 800 g x 10 min. and the supernatant was treat-Vol. 47 No. 4 222 M. Ozaki and K. Kurachi lo83,(1968)21) Ree1,