Biology of Reproduction, Vol 21, 657-666, Copyright © 1979 by Society for the Study of Reproduction

Uterine Growth and Differentiation in Response to Ovarian Steroids in the Hamster

¹ Marshall Laboratory, Physiological Laboratory, University of Cambridge, Cambridge CB2 3EG, U.K.

Uterine response to progesterone and estradiol was examined in spayed hamsters and compared with that in intact hamsters. Estradiol was uterotropic whereas progesterone was relatively less so. The greatest increase in uterine dry weight was observed when the 2 hormones were given simultaneously. Stromal edema and mitoses were evident whenever progesterone was included in the hormonal regimen. Luminal closure was also observed under these conditions and was especially pronounced when estradiol was given as well and uterine morphology was similar to that observed during pregnancy. In the hamster receiving estradiol alone, the glands were abundant and epithelial mitoses were also observed but luminal closure did not occur. This condition resembled the uterine appearance at proestrus. The incorporation of [³H]-leucine in uterine luminal proteins was 40-fold greater when estradiol was injected compared with the values obtained after progesterone was given; progesterone given with estradiol dampened the incorporation nearer the level obtained with progesterone alone. The incorporation was also substantially greater during proestrus compared with the levels during pregnancy. Two groups of labeled proteins with mol 5.5 x 10⁴ and 10 x 10⁴ were detected during proestrus. However, only the former was prominent whenever progesterone was included in the hormonal regimen and during pregnancy and only the latter was detected in females receiving estradiol alone. In comparison with the condition in the rat, estradiol was substantially less uterotropic in the hamster and progesterone also potentiated rather than antagonized the uterine growth response to estradiol. The difference in the uterine response to estradiol may explain why the blastocyst cannot enter into diapause in the hamster under endocrine conditions similar to those in the rat.

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ACKNOWLEDGMENTS We thank the MRC for a project grant in support of this work and Simon Fishel and Sheila Barton for helpful suggestions.