MONOCLONAL-ANTIBODIES SPECIFIC FOR RAT RELAXIN .9. EVIDENCE THAT ENDOGENOUS RELAXIN PROMOTES GROWTH OF THE VAGINA DURING THE 2ND HALF OF PREGNANCY IN RATS

It is established that endogenous relaxin promotes the growth and deve lopment of the cervix, mammary glands, and nipples in pregnant rats. A dditionally, the observation that porcine relaxin promotes growth of t he vagina in both nonpregnant and pregnant rats provides indirect evid ence that endogenous relaxin may effect growth of the vagina during ra t pregnancy. The purpose of this study was to determine whether endoge nous relaxin promotes growth of the vagina in pregnant rats. To that e nd, a monoclonal antibody, specific for rat relaxin, designated MCA1, was used to passively neutralize endogenous relaxin throughout the sec ond half of pregnancy in intact rats. Five milligrams of highly purifi ed MCA1 were injected iv to rats daily from days 12-22 of pregnancy. C ontrols received either a monoclonal antibody for fluorescein or PBS. The vaginal wet weight, dry weight, length, diameter, inner surface ar ea, DNA content, and percent water content were determined. No differe nces were found between monoclonal antibody for fluorescein and PBS co ntrols for any of the measured vaginal parameters. In contrast, values for all physical parameters, except percent water content, were signi ficantly lower in MCA1-treated rats than in controls. Vaginal DNA cont ent was also lower in MCA1-treated rats than in controls; and this obs ervation supports the view that relaxin induces vaginal growth at leas t in part by promoting cell proliferation. To examine the mechanism of relaxin's apparent action on the vagina, specific relaxin-binding sit es were localized immunohistochemically. Relaxin-binding sites were fo und in epithelial and smooth muscle cells, and the binding was specifi c for relaxin. We conclude that endogenous relaxin promotes growth of the vagina in pregnant rats.