Plasma Levels of Estradiol and Progesterone in the Cat During Polyestrus, Pregnancy and Pseudopregnancy

The levels of estradiol and progesterone in the systemic plasma of four domestic cats during pregnancy, pseudopregnancy and polyestrus were determined by radioimmunoassay. During polyestrus, estradiol values fluctuated between peaks (59.5 ± 13.4 (SD) pg/mi; n = 13) and troughs (8.1 ± 3.8 (SD) pg/mi; n=12) with an interpeak period of 15.8 ± 3.8 days (n=9). After the animals had been mated to either intact or vasectomized males, their estradiol levels declined sharply from peak values and remained low (6-12 pg/mi) during pseudopregnancy and pregnancy except for a slight rise just before parturition. Essentially no progesterone could be detected during polyestrus and for 2 to 3 days after copulation with either intact or vasectomized males, but by Day 21 of pregnancy or pseudopregnancy progesterone rose to a peak of either “-.35 or “-.24 ng/ml respectively. After Day 21 of pregnancy, progesterone gradually declined to “-.10 ng/ml by Day 60, ‘\�5 ng/ml just before parturition, and <1 ng/ml just after parturition. After Day 21 of pseudopregnancy, progesterone levels declined rapidly to “-.4 ng/ml by Day 40, “-.2 ng/ml by Day 50 and <1 ng/ml by Day 63-65. Estrone was measured throughout pregnancy, pseudopregnancy and polyestrusin one animals; no major elevations were detected.