Prostaglandin G/H synthase (PGHS)-2 expression in bovine myometrium: Influence of steroid hormones and PGHS inhibitors

Prostaglandins (PGs) are important mediators regulating uterine functions d uring the reproductive process. The objective of this study was to examine, in myocytes from the circular and longitudinal layers of bovine myometrium , the relative levels of mRNA and proteins corresponding to the gene expres sion of key enzymes (phospholipase A(2); prostaglandin G/H synthase-1 [PGHS -1]; prostaglandin G/H synthase-2 [PGHS-2]; prostaglandin I-2 synthase) inv olved in PC biosynthesis. We examined the influence of estradiol-17 beta and progesterone on the expr ession and activity of these enzymes. Treatment of myocytes with progestero ne (P-4: 10 nM, 24 h) in the absence or presence of estradiol-17 beta (E-2: 1 nM, 72 h) suppressed PG biosynthesis by approximately 60% in both myomet rial layers. No significant effect was observed after E-2 treatment. The co mbined effect of E-2 and P-4 on PG accumulation was correlated with the mod ulation of PGHS-2 protein and mRNA levels in the two myometrial layers with out affecting other enzymes of the PG cascade. Selective or nonselective in hibition of PGHS activity with CGP 28238 (PGHS-2-specific; a product from C iba-Geigy: 6-[2,4-difluorophenoxy]-5-methyl-sulfonylamino-1-indanone) or in domethacin (PGHS-1 and -2) reduced prostacyclin accumulation (measured as 6 -keto-PGF(1 alpha) in the culture medium) in a dose-dependent manner in the two myometrial layers. A significant inhibitory effect was obtained at a l ow concentration of indomethacin (1 nM, p < 0.05) compared to CGP 28238 (10 nM, p < 0.05). In both myometrial layers, the maximal effect of indomethac in and/or CGP 28238 on PG accumulation was observed at 100 nM and represent ed 85% and 65% inhibition, respectively. In the presence of phorbol 12-myri state (100 nM), CGP 28238 (10 nM) significantly suppressed PGHS-2 mRNA leve l by 44.80 +/- 7.67% (p < 0.01) and 27.83 +/- 7.62% (p < 0.05) in the longi tudinal and circular layer, respectively. In contrast, indomethacin did not have any significant effect. These data constitute the first quantitative analysis of key enzymes involved in PG biosynthesis in separated myometrial layers. Furthermore, the results provide interesting information on the CG P 28238 drug modulating both enzymatic activity and mRNA expression of PGHS -2.