Accumulation of cyclooxygenase-2 gene transcripts in uterine tissues of pregnant and parturient cows: Stimulation by oxytocin

Cyclooxygenase 1 and 2 (COX-1 and COX-2) mRNA were measured by ribonuclease protection assays in total RNA extracted from intercaruncular and caruncul ar endometrium, myometrium, cotyledons, and cervical mucosa of pregnant cow s. Tissues were obtained at gestational ages of 150 days and 275 days and a t term not in labor, at term in labor, and 6-12 h postpartum. Additionally, the effect of oxytocin (OT) on COX-2 expression was determined in intercar uncular endometrium of six third-trimester cows (between 230 and 270 days o f pregnancy), three of which were injected with OT (200 IU) and three with saline 2 h before tissues were harvested. Prostaglandin F-2 alpha (PGF(2 al pha)) metabolite was measured in plasma samples taken at 15-min intervals b efore and after the injections. Results showed that COX-2 mRNA was expresse d in every type of tissue examined, although in different concentrations an d beginning at different stages. Other than in seminal vesicular and prosta te glands used as positive controls, low concentrations of COX-1 mRNA were detected only in myometrium and caruncles. Cotyledons had the highest conce ntration of COX-2 transcripts at all stages studied. Caruncles had about ha lf the concentration of COX-2 transcripts that was seen in cotyledons, and on Day 150 even less. COX-2 mRNA expression in both tissues increased with advancing gestation, but there was no difference between samples from term- no-labor and term-in-labor cows. COX-2 mRNA concentrations in endometrium a nd myometrium were low; they varied randomly during pregnancy with no signi ficant increase until postpartum, when COX-2 transcripts in endometrium had increased severalfold whereas those in myometrium were similar to values b efore parturition. Cervical mucosa expressed COX-2 mRNA weakly until term b ut had increased markedly at parturition. Injection of 200 IU of OT induced a substantial increase in endometrial COX-2 mRNA concentration within 2 h; this was associated with linearly increasing plasma concentrations of 13,1 4-hydroxy-15-keto-prostaglandin F-2 alpha, which were still rising at termi nation of the experiment. The results suggest that endogenous OT is a major factor in induction of COX-2 expression and PGF(2 alpha) release at term a nd during parturition in cows.