|Cushman, Robert - Bob|
Submitted to: Biology of Reproduction Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 4/17/2009
Publication Date: 12/1/2009
Citation: Perry, G.A., Perry, B.L., Cushman, R.A. 2009. Association Between Preovulatory Concentrations of Estradiol and Expression of Uterine Milk Protein Precursor, Inhibin Beta A, Period 1, Proenkephalin, and Receptors for Oxytocin, Progesterone, and Estradiol [abstract]. Biology of Reproduction. 2009 Supplement:117 (Abstract #308). Interpretive Summary:
Technical Abstract: Eliminating the preovulatory surge of estradiol decreased uterine weight, uterine protein, RNA to DNA ratio, rate of protein synthesis, and embryo survival following embryo transfer in sheep. Furthermore, cows that did not exhibit standing estrus (decreased preovulatory concentrations of estradiol) around the time of gonadotropin-releasing hormone (GnRH)-induced ovulation had decreased pregnancy success compared to cows having elevated preovulatory concentrations of estradiol. Thus, induction of ovulation alone may not be sufficient for maximum pregnancy success because decreased steroidogenic capacity of the follicle or induced corpus luteum may alter uterine function. Therefore, the objective of the present experiment was to characterize changes in expression of uterine milk protein precursor, inhibin beta A, proenkephalin, period 1, oxytocin receptor, progesterone receptor, and estradiol receptor alpha and beta between cows with high (highE2; n = 13) and low (lowE2; n = 19) concentrations of estradiol at time of GnRH-induced ovulation (day 0). Beef cows were treated with 100 µg GnRH on day -9, 25 mg prostaglandin F2alpha on day -2, and 100 µg GnRH on day 0. Uterine horn biopsies (collected ipsilateral to the ovulatory follicle) were collected on day 5 (n = 14) or 10 (n = 18) and blood samples were collected on days 0, 5, 10, and 16. Total cellular RNA was extracted from all biopsies and relative mRNA levels were determined by real-time RT-PCR and corrected for polyubiquitin. Concentrations of estradiol on day 0 (P < 0.001) and 5 (P = 0.01) were greater in highE2 cows compared to lowE2 cows but did not differ (P > 0.24) between treatments on days 10 and 16. Concentrations of progesterone did not differ (P > 0.32) between treatments on day 0 or 10 but tended to be (P = 0.08; day 5) and were greater (P < 0.001; day 16) in highE2 compared to lowE2 cows. Expression of progesterone receptor was greater (P < 0.001) on day 5 compared to day 10 but did not differ (P > 0.10) between treatments. Expression of estrogen receptor alpha decreased (P = 0.01) from day 5 to day 10 in highE2 cows but was similar (P = 0.30) in lowE2 cows. Expression of estrogen receptor beta did not differ (P > 0.12) between days 5 and 10 or between treatments. Oxytocin receptor expression decreased (P </= 0.01) from day 5 to 10 in both treatments. Expression was greater (P = 0.01) on day 5 in highE2 cows compared to lowE2 cows but did not differ (P = 0.22) on day 10. Expression of uterine milk protein precursor, inhibin beta A, and period 1 did not differ (P > 0.10) between treatments or between days 5 and 10. Expression of proenkephalin did not differ (P = 0.89) between treatments on day 5 but expression increased (P = 0.01) from day 5 to 10 in highE2 cows but not (P = 0.23) in lowE2 cows. In summary, preovulatory concentrations of estradiol influenced expression of oxytocin receptors and proenkephalin on days 5 and 10 of the subsequent estrous cycle. Reduced fertility among cows with decreased concentrations of estradiol prior to GnRH-induced ovulation may be associated with effects of changes in uterine protein and receptor expression on uterine environment.