Cytoplasmic estrogen and progesterone receptors in canine endometrium during the estrous cycle
Johnston, S.D.; Kiang, D.T.; Seguin, B.E.; Hegstad, R.L.
American Journal of Veterinary Research 46(8): 1653-1658
1985
ISSN/ISBN: 0002-9645 PMID: 4041148 Document Number: 250191
Estradiol and progesterone receptors (ER, PR) were characterized and measured in cytosols from canine endometrium, using saturation and sucrose-gradient centrifugation radioassays. Both receptors were demonstrated to be steroid- and tissue-specific saturable proteins which bound the respective steroids with high affinity () serum estradiol concentrations were 17.0 .+-. 2.2 (A), 55.4, .+-. 5.0 (P3), 89.4 .+-. 24.9 (E3), 41.0 .+-. 5.9 (E12), and 50.6 .+-. 3.9 (E28) pg/ml. Mean (.+-. SEM) serum progesterone concentrations were 0.4 .+-. 0.1 (A), 1.5 .+-. 0.2 (P3), 17.3 .+-. 7.5 (E3), 41.6 .+-. 9.5 (E12), and 25.8 .+-. 3.2 (E28) ng/ml. Concentrations of ER increased significantly from 1.06 pmol/g of uterus during stage A to a peak concentration of 6.18 pmol/g of uterus at E12, followed by a gradual decrease to 0.69 pmol/g of uterus by E28. The PR concentrations increased from 3.01 pmol/g of uterus in stage A to 17.32 pmol/g of uterus at P3; PR concentrations, thereafter, decreased gradually to 1.85 pmol/g of uterus by E28. Dissociation constants were significantly higher at E12 for the ER (Kd = 2.6645 .times. 10-9 M) and at P3 for the PR (Kd = 5.8282 .times. 10-9 M) than at the other stages examined, indicating a decrease in receptor affinity during the periods of high receptor concentrations. Follicular estrogen induces ER and PR formation in the dog as it does in other species. Second, decreases in serum estradiol concentrations and increases in serum progesterone concentrations are associated with decreases in receptor concentration.