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When pseudopregnant hamsters were ovariectomized and their uteri traumatized on day 4, deciduomal growth (not significantly different from that seen in intact controls) could be maintained by daily injections of 1, 2 or 4 mg of progesterone either alone or in combination with 1, 2 or 5 μg of estrone. When ovariectomy was performed on day 1 of pseudopregnancy and uterine traumatization on day 4, induction and maintenance of a deciduomal response could be achieved with 1 or 2 mg/day of progesterone alone (or in some cases in combination with 1 μg/day of estrone) from days 1 to 3 followed by 1 or 2 mg/day of progesterone in combination with 1, 2 or 5 μg/day of estrone from days 4 to 7. The best results were obtained with progesterone alone (2 mg/day) before trauma and estrone (2 μg/day) and progesterone (2 mg/day) after trauma.

Rats were given single doses of an orally-active estrogen by mouth on days 1–5 of pregnancy. Examination of uteri on day 8 for implantations revealed that the median effective doses for preventing 50% of the eggs shed from implanting were 0.047, 0.050, 0.035, 0.145 and 0.380 mg/kg for days 1, 2, 3, 4 and 5 respectively. It was found that failure of pregnancy after treatment with the minimal 100% effective dose (ED100) on days 1, 2 or 3 was due to expulsion of eggs from the reproductive tract by day 5. Treatment of rats with the ED100 on day 4 caused expulsion of some eggs from the tract by day 5, but also had effects on the uterus: the position of the blastocysts within the lumen was abnormal and their orientation relative to the mesometrial-anti-mesometrial axis disturbed. No decidual reaction was observed on day 6 in such rats or on day 9 in pseudopregnant rats treated similarly and subjected to uterine traumatization on day 5. Treatment with ED100 on day 5 had no effect on egg transport or on the positioning of blastocysts within the lumen on day 6. A decidual reaction was seen around the blastocyst on day 6, but in pseudopregnant rats treated similarly and subjected to uterine traumatization on day 5 no decidual reaction was found on day 9. The pontamine blue reaction was negative in nearly all rats dosed on day 4 and examined on days 6–8. In rats dosed on day 5, however, the blue reaction was negative on day 6, but positive on day 7, i.e., delayed by 24 hours compared to controls and appearing later than the decidual reaction. The blastocysts were unattached in these rats on day 6, but may have attached briefly on day 7 (suggested by the positive blue reaction) and subsequently failed to develop further owing to disappearance of the decidual tissue.

The deciduomal response to uterine trauma in pesudopregnant hamsters has been studied. Trauma was effected in one uterine horn by leaving a sterile silk thread in the lumen, pulling a thread through the lumen, injecting oil or air into the lumen or crushing the horn with a hemostat. At autopsy the traumatized and untraumatized horns were weighed separately and examined histologically for a deciduomal reaction. The day of greatest uterine sensitivity was found to be day 4 of pseudopregnancy, and maximal deciduomal growth (mean uterine weight ± S.E. = 2582 ± 279 mg) occurred by day 8. No significant further increase in uterine weight was seen by day 9, and by day 10 separation of the deciduoma from the myometrium had begun. Leaving a thread in the uterine lumen produced a significantly greater uterine weight by day 8 than with any other stimulus, but good deciduomal responses (uterine weights of 1679 ± 245, 1255 ± 156 and 1192 ± 219 mg) were induced by oil injection, pulling a thead through the uterus and crushing the uterus respectively. A poor reponse was produced by air injection. At no particular time during day 4 of pseudopregnancy was it possible to demonstrate a peak of uterine sensitivity using as a traumatic stimulus either oil injection or pulling a thread through the lumen. In this respect hamsters differ from both rats and mice, which have well defined peaks of maximal uterine sensitivity.