Effect of oestradiol on the post-partum rat uterus: peroxidase activity and collagen breakdown

Treatment of parturient rats with 100 micrograms oestradiol/day caused a significant retardation of uterine involution and collagen breakdown. The post-partum uterus had a peroxidase activity of 180 mumol H2O2 reduced/min per uterus. Treatment with oestradiol caused an eight- to tenfold increase in this activity within 3--4 days. Treatment of rats with 4 mg cortisol/day commencing 3 days prepartum had no effect on uterine peroxidase acitvity but it blocked the oestradiol-induced increase in peroxidase. Cortisol had no effect on collagen breakdown and did not reverse the inhibition of collagen breakdown produced by oestradiol. It is postulated that the effects of oestradiol on peroxidase activity are mediated by uterine epithelial cells but that oestradiol effects on collagen breakdown may be mediated by another cell type.