Effects of dexamethasone administration to diestrus cows on systemic progesterone, estrogen and uterine cyclooxygenase production

• Published in: Animal reproduction science 1997-07, Vol.47 (4), p.263-271
• Main Authors: Broussard, J.R., Rocha, A., Sirois, J., Roussel, J.D., Thibodeaux, J.K., Godke, R.A., Hansel, W.
• Format: Article
• Language: English
• Subjects: Animals; Biopsy; Blotting, Western; Cattle; Cattle-endocrinology; Cohort Studies; Cyclooxygenase; Cyclooxygenase 1; Dexamethasone - administration & dosage; Dexamethasone - pharmacology; Diestrus - blood; Diestrus - drug effects; Diestrus - metabolism; Endometrium - drug effects; Endometrium - enzymology; Endometrium - pathology; Estradiol - blood; Estradiol - metabolism; Estrogen; Female; Injections, Intramuscular; Isoenzymes - biosynthesis; Isoenzymes - drug effects; Progesterone; Progesterone - blood; Progesterone - metabolism; Prostaglandin-Endoperoxide Synthases - biosynthesis; Prostaglandin-Endoperoxide Synthases - drug effects; Random Allocation; Time Factors
• ISSN: 0378-4320; 1873-2232
• DOI: 10.1016/S0378-4320(97)00026-2

Parenteral administration of dexamethasone to diestrus cattle can extend the length of the natural estrous cycle. In mice, dexamethasone has been shown to inhibit production of the second isozyme of the cyclooxygenase (COX) enzyme (a rate limiting enzyme in prostaglandin formation). Therefore, the purpose of this study was to determine the effect of dexamethasone on estrous cycle length and COX-1 and -2 production by the uterine endometrium of cyclic cattle. Nine crossbred beef cows that exhibited two previous normal estrous cycles were randomly assigned to two treatments; a control group administered intramuscular injections of vehicle, and a dexamethasone group administered 8 mg of dexamethasone (Azium ®, Schering Corp., Kenilworth, NJ). Both groups received twice daily injections on day 13–22 of the treatment cycle. Uterine endometrial biopsies were collected on days 16, 19 and 22 of the treatment cycle. Blood samples were collected daily on day 13–22 of the treatment cycle for plasma progesterone and estradiol concentrations. The mean treatment cycle length was extended ( P < 0.05) in the dexamethasone group (31 d) compared with the control group (24 d). However, no difference was noted in the time to progesterone decline between treatments. In contrast, estradiol levels were lower in the dexamethasone treated animals compared with the control group on day 19 to 22 of treatment. A western blot analysis revealed no COX-2 in the uterine samples of either treatment. The COX-1 isoform was found on all days examined, but no treatment effect was detected. These results suggest that dexamethasone extends the cycle length by inhibiting follicle growth, and that COX-2 may not be involved in prostaglandin formation by the uterus during luteolysis.