6-Oxo-prostaglandin F1a production by guinea-pig skeletal muscle in vitro: the effects of oestradiol and progesterone.

Fragments of guinea-pig skeletal muscle produce four times as much 6-oxo-PGF1a as PGE and PGF. This production of 6-oxo-PGF1a was unaffected by relatively high concentrations of oestradiol-17B (100 micrograms/ml) but was increased four-fold in the presence of progesterone (500 micrograms/ml). In skeletal muscle homogenates, oestradiol (100 micrograms/ml) inhibited 6-oxo-PGF1a synthesis and this inhibition was enhanced in the presence of progesterone (500 micrograms/ml); at this concentration, progesterone had no effect on its own. Tamoxifen (100 micrograms/ml), a drug with anti-oestrogenic properties in humans, enhanced the inhibition of 6-oxo-PGF1a synthesis by oestradiol and by oestradiol and progesterone together, suggesting that oestradiol and tamoxifen may exert their effect by a similar mechanism in this experimental model. The significance of these observations is discussed.