Local application of platelet-activating factor induces cervical ripening accompanied by infiltration of polymorphonuclear leukocytes in rats

OBJECTIVE: The purpose of this study was to determine the effect of locally applied platelet-activating factor on cervical ripening and leukocyte infiltration. STUDY DESIGN: Timed-pregnant rats were treated vaginally twice each day on days 14 and 15 of gestation with platelet-activating factor 5 × 10^-8 mol/L (low-dose), 5 × 10^-7 mol/L (high-dose), or solvent and were killed on day 16. Cervical ripening was assessed by cervical resistance-to-stretch and light-induced autofluorescence of cross-linked collagen. Longitudinal sections of the cervix were hematoxylin and eosin stained, and the number of polymorphonuclear leukocytes in eight high-power fields was determined. RESULTS: Cervical resistance-to-stretch and light-induced autofluorescence were decreased in rats that were treated with high-dose platelet-activating factor compared with controls (0.4375 ± 0.0126 N/mm vs 0.5528 ± 0.0294 N/mm, and 2.739 ± 0.150 N/mm vs 3.475 ± 0.236 N/mm; P < .05). High-dose platelet-activating factor led to infiltration with polymorphonuclear leukocytes compared with control (22.1 ± 5.2 vs 2.1 ± 1.3 cells/8 high-power fields, P < .05). CONCLUSION: Local platelet-activating factor application induces cervical ripening accompanied by stromal polymorphonuclear leukocyte infiltration. Platelet-activating factor may play a major role in parturition under physiologic and pathologic conditions.