Rex A. Hess


Professor of Reproductive Biology
and Toxicology


B.S., University of Missouri-Columbia
M.S., University of Missouri-Columbia 
Ph.D., Clemson University


Biographical Information and HomePage

Research Interests

Estrogen in the male. My laboratory conducts research in the areas of male reproductive biology, endocrinology and toxicology, with the following specific interests: spermatogenesis, testicular growth and development, structure and function of the epididymis and the role of estrogens in male reproduction. A major discovery was published in Nature (1997) 390, 509-512, showing for the first time an important function for estrogen in the male reproductive tract. Estrogen is considered the "female" hormone, whereas testosterone is considered the "male" hormone. Both hormones, however, are present in both sexes. Thus, sexual distinctions are not qualitative differences, but rather due to quantitative divergence in hormone concentrations and differential expressions of steroid hormone receptors. In males, oestrogen is present in low concentrations in blood, but can be extraordinarily high in semen and as high as 250 pg/ml in rete testis fluids, which is higher than serum estradiol in the female. It is well known that male reproductive tissues express oestrogen receptors; yet, the role of oestrogen in male reproduction had remained an open question until now. In this paper, we were able to show that estrogen regulates reabsorption of luminal fluid in the head of the epididymis. This was the first demonstration of a physiological function for oestrogen in male reproductive organs. Disruption of this essential function causes sperm to enter the epididymis diluted, rather than concentrated, resulting in infertility.
Molecular mechanism of estrogen function in the male. We have now determined that estrogen regulates expression of the Na+/H+ exchanger-3 (NHE3) and the rate of (22)Na+ transport, sensitive to a NHE3 inhibitor. Immunohistochemical staining for NHE3, carbonic anhydrase II (CAII) and aquaporin-I (AQP1) was decreased in ERa knockout (aERKO) efferent ductules. Targeted gene deficient mice were compared to aERKO and the NHE3 knockout and CAII deficient mice showed aERKO-like fluid accumulation, but only the NHE3 knockout and aERKO mice were infertile. Northern blot analysis showed decreases in mRNA for NHE3 in aERKO and antiestrogen-treated mice. The changes in AQP1 and CAII in aERKO appeared to be secondary, due to the disruption of apical cytoarchitecture. Ductal epithelial ultrastructure was abnormal only in aERKO mice. Thus, in the male, estrogen regulates one of the most important epithelial ion transporters and maintains epithelial morphological differentiation in efferent ductules of the male, independent of its regulation of Na+ transport. Finally, these data raise the possibility of targeting ERa in developing a contraceptive for the male. Proc. Natl. Acad. Sci. USA (2001) 98:


Revised: 2013