Effect of progesterone on collagen breakdown and tissue collagenolytic activity in the involuting rat uterus.

Progestational agents were studied for their effects on collagenolytic activity and loss of collagen and wet weight from the involuting post-partum rat uterus. Administration of very large doses of progesterone (80-150 mg/day) significantly retarded uterine involution and loss of collagen. This was accompanied by a significant reduction in uterine collagenolytic activity. By 72 h post partum, uteri of rats treated with 150 mg progesterone/day had wet weights 30% above, collagen 85% above, and collagenolytic activity 45% below, those of the control uteri. Similar effects were produced by 17alpha-acetoxy-6alpha-methylprogesterone at the same dosage levels. However, the progestational agent 6-chloro-17alpha-acetoxypregna-4,6-diene-3,20-dione acetate had no effect in this system.