A stimulatory effect of the fluid from preimplantation rabbit blastocysts upon luteinization of monkey granulosa cell cultures

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Abstract
Blastocyst fluid was aspirated from day 6 1/2-7 rabbit blastocysts and was added to cultures of granulosa cells obtained from preovulatory follicles of untreated rhesus monkeys or from follicles of monkeys treated with PMSG [pregnant mare serum gonadotropin]. The stimulation of progesterone secretion was measured and equated with that produced by hCG [human chorionic gonadotropin]. The hCG-like activity was also measured in a radioreceptor assay using 125I-labeled hCG and porcine granulosa cells. In 8 out of 10 experiments with cultured cells from untreated monkeys, addition of 20% blastocyst fluid from days 6-9 of culture stimulated progesterone secretion by 2-to 6-fold. Similar findings were obtained in 5 experiments with cultures from PMSG-treated monkeys except that the blastocyst fluid was added from days 0-6 of culture. The granulosa cells in such cultures underwent morphological luteinization. Compared to a standard of purified hCG the blastocyst fluid contained about 0.76-2.5 ng hCG-like activity/ml which was non-dialyzable. The radioreceptor assay indicated the presence of 0.5-2.5 ng hCG-like material/ml.