Reproductive Hormones Directly Influence Embryo Development

A group of Dutch researchers reported evidence that the equine conceptus (i.e., the embryo and associated membranes) might be directly responsive to the reproductive hormones progesterone and estrogen, which could therefore play a more direct role in embryonic development and pregnancy maintenance than previously imagined.

Progesterone and estrogen are known to play important roles in the development of the conceptus by binding to hormone receptors in or on cells of the reproductive tract.

"It has long been thought that the reproductive hormones exerted their effects on the equine conceptus entirely indirectly, by binding to hormone receptors located in the inner lining of the uterus, also known as the endometrium," said Tom Stout, DVM, PhD, professor in the Department of Equine Sciences at Utrecht University, The Netherlands, and a co-author of this study.

Conceptuses from a small number of other mammalian species have previously been found to express steroid hormone receptors, and the purpose of this study was to determine if equine conceptuses had the capacity to respond directly to progesterone and/or estrogen.

The researchers found that receptors for progesterone and one type of estrogen were present in the conceptus' membranes in Days 7 to 19, the period of rapid conceptus growth and maternal recognition.

According to Stout, "The results of this study demonstrate that systems are in place for reproductive hormones to directly influence early development of the horse embryo."

These results suggests that researchers need to carefully examine the potential effects of either a deficiency or, in the case of unwarranted supplementation, an excess of progesterone and estrogen on the development of the delicate conceptus. This is particularly true during the period when the conceptus is most prone to early embryonic death.

"Expression of progesterone and oestrogen receptors by early intrauterine equine conceptuses," was published in the journal Theriogenology in February, 2008.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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