Protein anabolic effects of two chemically distinct relaxins in mouse uteri

In addition to B-28 relaxin (relaxin B) and B-32 relaxin, acid-acetone extracts of porcine ovaries contain relaxin C, which differs both chemically and biologically from the others. Relaxin C contains one proline residue and a single tryptophane residue; it is about half as active as relaxin B in the guinea pig assay, is active in the motility inhibition assay, but is essentially completely inactive in the mouse pubic ligament assay. Relaxin B has been shown to exhibit protein anabolic properties in rat uteri. To compare the effects of relaxins B and C on uterine protein synthesis, ovariectomized, estrogen-primed mice were given relaxin B or C (10-100 μgm/100 gm b.w. in 1% benzopurpurine 4B) and the uptake of 3H-proline into uterine protein measured in vitro and in vivo 3-12 hours later. Both relaxins induced significant (40-100%) increases in proline incorporation rates. Maximal stimulation of soluble protein synthesis occurred 3 hr after administration of either relaxin; in contrast, peak uptake of proline into uterine collagen occurred after 6 hr. Stimulation of collagen synthesis was more pronounced as well as more prolonged than the synthesis of soluble protein. Larger doses of relaxin C (as compared to B) were required for continued enhancement of collagen synthesis