Preservation of Functional Corpora Lutea in the Rat by Estrogen Treatment1,2

Appropriate estrogen treatment can not only initiate, but maintain, pseudopregnancy in the rat. In a third (11/33) of estrogen treated rats studied for this length of time, vaginal signs of corpus luteum function (maintenance of diestrous smears despite the estrogen treatment) were sustained for 6-8 weeks. Most corpora degenerated after a pseudopregnancy of only 4-6 weeks, however (i.e., after a period 2-3 times the duration of a “normal” pseudopregnancy). Direct evidence that the sustained vaginal diestrus reflects preservation of a single set of corpora was provided by “tagging” 2-3 week old corpora with microinjections of India ink and allowing them to survive for an additional 17-27 days (4 rats). Possible explanations for this type of luteal longevity, and for its usual failure to persist indefinitely, are discussed. (Endocrinology79:1011,1966)