Metabolism of collagen types I, III, and V in the estradiol-stimulated uterus.

The synthesis and deposition of collagen in uterine tissues stimulated with 17 beta-estradiol was studied in ovariectomized nulliparous rats. Eight days after ovariectomy 200-g rats were given a single intraperitoneal injection of 100 micrograms of estradiol. [14C]Glycine, 1.5 mCi. was administered intraperitoneally 40 h later and the animals were killed between 0.5-6 h following isotope injection. Radiolabeled proteins were extracted from uterine tissues sequentially with 0.45 and 1.0 M neutral salt, 0.5 M acetic acid, 0.1 M penicillamine, and 4 M guanidine hydrochloride or pepsin digestion. The radiolabeled collagens from each pool were analyzed by a combination of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. Types I, III, and V collagens were identified in uterine pools. In the salt-soluble pool, each collagen type underwent rapid maturation into salt-insoluble collagen, although the initial appearance of type V collagen was delayed in both salt-soluble and insoluble pools. Type I procollagens were rapidly converted to alpha-chains through pc-intermediates. At 0.5 h, 28% of the type I collagen was already in a alpha-chain form. Type II procollagen was also rapidly converted but to a more stable intermediate designated p alpha 1 (III). Radiolabeled procollagens were also observed in the acetic acid, penicillamine, and guanidine hydrochloride pools suggesting that collagen precursor molecules complex through covalent and noncovalent interactions with other connective tissue macromolecules. These results indicate that both procollagen conversion and collagen assembly can follow different pathways depending upon the nature of the collagen and the tissue studied.