Relationship between steroid levels in peripheral serum and uterine tissue during pseudopregnancy in rabbit

Determination of the main C21, C19 and C18 steroids in peripheral serum and uterine tissue was made to study the relationships of the steroids during pseudopregnancy in the rabbit. Tissue and serum progesterone levels rose significantly (P < 0.01) from estrus to Day 9 and then decreased by 81% (tissue) and 57% (serum) at Day 15, while pregnenolone levels in uterine tissue and serum remained unaffected. Estradiol serum levels remained fairly stable, whereas its concentration in uterine tissue decreased after estrus by 85%, followed by a significant (P < 0.05) increase from Day 9. Most of the C19 steroid values in the uterine tissue and in the serum were generally at levels below or near the limit of detection and did not vary significantly. Since progesterone and estradiol levels were high and/or varied significantly in tissue throughout pseudopregnancy, and since androgens were produced in small amounts, it is suggested that androgens might not play a significant role in uterine tissue during pseudopregnancy.