Evidence that relaxin inhibits apoptosis in the cervix and the vagina during the second half of pregnancy in the rat

The growth of the cervix and vagina that occurs during the second half of r at pregnancy is accompanied by an increase in both epithelial and stromal c ells. Neither the mechanism(s) that regulates this accumulation of cells no r its hormonal control is known. To test the hypothesis that the rate of ap optosis declines during the second half of pregnancy, cervices and vaginas were collected on days 5, 10, 15, 18, and 21 of pregnancy. Terminal deoxynu cleotidyl transferase-mediated deoxyuridine 5'-triphosphate nick end-labeli ng was used to detect apoptotic cells. The rate of apoptosis declined (P < 0.05) in epithelial and stromal cells in both the cervix and vagina during the second half of pregnancy, when blood levels of relaxin are increasing. To test the hypothesis that relaxin inhibits apoptosis, cervices and vagina s were collected 6, 12, 24, 48, and 72 h after the neutralization of endoge nous relaxin, on days 19-21 of pregnancy, with a monoclonal antibody for ra t relaxin. Both the terminal deoxynucleotidyl transferase-mediated deoxyuri dine 5'-triphosphate nick end-labeling method and electron microscopy were used to detect apoptotic cells. Withdrawal of relaxin caused an increase in the rate of apoptosis in both the cervix and the vagina (P < 0.05). It is concluded that the rate of apoptosis declines in the cervix and the vagina during the second half of rat pregnancy, and that relaxin likely contribute s to this process.