Effects on the duration of pseudopregnancy (PSP) of prolactin, LH, FSH, or various combinations of those hormones were studied in female rats. Hormones were implanted in the ovarian bursae on day 4, 7, or 9 of PSP or consecutively on days 4, 5, and 6. Prolactin, in doses ranging from 3 to 642 μg, and LH or FSH, at 3 μg, had no effect on PSP. However, 17 μg or more of LH implanted on day 4 or 7 significantly (p < 0.01) prolonged PSP to 16 and 18 days, respectively. High doses of FSH (>80 μg) likewise prolonged PSP, but lower doses (17 or 56 μg) implanted on day 7 were less effective. The effect of consecutive (days 4-6) implantation of LH or FSH was similar to that of a single (day 4) LH or FSH implant. There was no synergism among prolactin, LH, and⁄or FSH when equal amounts of those hormones were implanted simultaneously on day 7 or 9. Neither LH nor FSH, when implanted on day 9, affected PSP. Ova were not found in 15 rats 24 hr after implantation on day 7 of 17 μg or 68 μg of LH or 17 μg of FSH, suggesting that LH- or FSH-induced prolongation of PSP was not due to the formation of corpora lutea. Results of this study show that LH or FSH, but not prolactin, when implanted in the ovarian bursae, prolongs pseudopregnancy. (Endocrinology95: 1234, 1974)

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