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R. K. MEYER
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R. L. COCHRANE
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SUMMARY

The daily administration of 1 mg. cortisone did not induce ovo-implantation in rats ovariectomized or ovariectomized and adrenalectomized on the 3rd day of pregnancy and injected with 4 mg. progesterone each day. Oestrone administered in daily doses of 1 μg./animal, however, did induce nidation in ovariectomized progesterone-treated rats deprived of their adrenal glands.

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R. K. MEYER
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C. E. McCORMACK
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SUMMARY

Ovulation in immature rats induced by daily subcutaneous administration of sheep follicle-stimulating hormone (FSH) was prevented by appropriately timed injection of phenobarbitone or by exposure to continuous light. Progesterone produced ovulation in light-blocked rats and in rats kept in standard lighting which had received a non-ovulatory dose of FSH.

These findings are interpreted to mean that ovulation produced by these preparations of FSH was due to a release of ovulating hormone from the pituitary gland. It is suggested that slight luteinizing hormone activity in an FSH preparation produces ovulation by causing the secretion of progesterone which then facilitates the release of ovulating hormone from the pituitary gland.

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R. K. MEYER
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E. F. NUTTING
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SUMMARY

One hundred and twenty inseminated rats were ovariectomized 3 days after coitus and assigned to twelve treatment groups. Eleven groups were injected subcutaneously daily from day 3 to day 8 with 250, 1000 or 4000μg. progesterone alone and in combination with 0·01 or 0·1 μg. oestrone. The remaining group was injected with corn oil. All animals were injected daily with 4000 μg. progesterone and 1 μg. oestrone from day 9 to day 24 after coitus. Implantation was usually prevented permanently when animals were injected with oestrone or corn oil only from day 3 to day 8. The remaining treatments caused delayed implantation of ova. The numbers of implantation sites in groups treated with progesterone alone or in combination with oestrone were compared. Differences between groups were due to the dose of progesterone, the number of implantation sites increasing with the dose of the steroid. Addition of 0·01 or 0·1 μg. oestrone had no significant effect on the implantation site response. Survival of embryos after implantation decreased with increasing pre-nidation doses of progesterone in the absence of oestrone. In general, addition of oestrone to progesterone increased survival when oestrone was combined with the high dose of progesterone and decreased survival with the low dose of progesterone. Oestrone (0·01 μg.) given with progesterone produced consistently more frequent embryonic survival than addition of 0·1 μg. oestrone, regardless of the amount of progesterone given.

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W. F. WARD
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R. K. MEYER
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R. C. WOLF
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SUMMARY

Rats were exposed to either 300 or 500 röntgen (R) acute whole-body X-irradiation on the 5th day of delayed pregnancy induced by ovariectomy. From 0 to 8 days after irradiation, implantation was induced by the administration of oestrogen. Foetal survival to the 20th day of development was used as an index of radiation effect.

If oestrogen was given immediately after exposure to 300 R, or 12 h later, only 30–35% of the embryos survived, significantly less (P < 0·01) than the non-irradiated control values of 74–79%. When implantation was postponed for 24 h or more, embryonic survival ranged from 57 to 64% and was not significantly different from that of controls.

After exposure to 500 R X-irradiation, embryonic survival increased linearly from 2% to a maximum of 41% as the interval between irradiation and oestrogen administration increased from 0 to 48 h. Embryonic survival never reached control levels after 500 R, regardless of the interval between irradiation and implantation. The irradiation regimens also induced developmental abnormalities, doubled the incidence of dead foetuses (death at a late stage of development), and significantly reduced foetal and placental weights at autopsy.

The results confirm that recovery from potentially lethal X-irradiation damage can occur during delayed implantation, and demonstrate that both the extent and the rate of recovery are functions of the radiation dose.

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