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