Hormonal regulation of the reproductive tract in female mammals.

This review covers only a small part of what has recently become an enormous literature on hormonal regulation of the female reproductive tract. We used the following guidelines in selecting papers for review: 1. The reproductive tract is exposed to varying levels of sex steroids during the menstrual and estrous cycles. With the advent of radioimmunoassay techniques, these patterns are now known more precisely than at any previous time. 2. The steroids are concentrated in the target cells of the tract by mechanisms that. because of recent findings in steroid­ receptor interactions, are more fully understood than ever before. Here we pay particular attention to reports of fluctuations in receptor levels during reproductive cycles and pregnancy and to the correlation between such changes and the fluctuat­ ing levels of steroids in plasma. 3. Within the target cells, the steroids interact with the cell machinery to produce multiple effects. This is the frontier of the modern research effort on hormone actions; the potential for future success here is enor­ mous. So far, however, species and organ differences have thwarted attempts to define any universal principles of hormone action, although evidence is accumulat­ ing in favor of the idea that one of the key endpoints of steroid hormone action is the production of specific RNA molecules. As to our method of selecting reports to review, we have chosen those that illustrate the interactions between estrogens and progestins in regulating the growth and function of the tract, that point to the complexity of these interactions, and that serve as guidelines for future study. No attempt was made to be comprehensive. Some emphasis has been placed on the reproductive tract of primates because of our special interests.