MONOCLONAL-ANTIBODIES SPECIFIC FOR RAT RELAXIN .6. PASSIVE-IMMUNIZATION WITH MONOCLONAL-ANTIBODIES THROUGHOUT THE 2ND-HALF OF PREGNANCY DISRUPTS HISTOLOGICAL-CHANGES ASSOCIATED WITH CERVICAL SOFTENING AT PARTURITION IN RATS

Relaxin, which is secreted by the corpora lutea throughout the second half of rat pregnancy, promotes the growth and softening of the cervix . The mechanisms at both the cellular and molecular levels by which re laxin brings about these effects remain to be determined. The present study examined the influence of endogenous relaxin on the histological changes associated with cervical softening. A monoclonal antibody for rat relaxin, designated MCA1, was injected iv daily on days 12-22 of gestation. Cervices were removed on day 22, fixed in 10% buffered form alin, embedded in paraffin, and processed for histological staining. T issue sections (5-mu-m thick) were stained with Gomori's trichrome sta in (collagen), Orcein stain (elastin), or periodic acid-Schiff (polysa ccharide). Qualitative and quantitative analyses identified several hi stological parameters in MCA1-treated rats that differed markedly from those in control rats. Cervices obtained from MCA1-treated rats conta ined collagen fiber bundles with greater compactness; elastin fibers w ith greater density, length and interdigitation; arteries with smaller cross-sectional areas; and luminal involutions with smaller areas tha n controls. The cervices of MCA1-treated rats appeared to contain fewe r vacuolated epithelial cells, which secrete polysaccharide-rich mater ial, than did cervices obtained from controls. It seems plausible that most, if not all, of these relaxin-induced modifications of the histo logical characteristics of the cervix facilitate birth.