INFLUENCE OF OVARIAN-STEROIDS ON RELAXIN-INDUCED DISTENSIBILITY AND COMPOSITIONAL CHANGES IN THE PORCINE CERVIX

A study was conducted to examine the influence of ovarian steroids on relaxin-induced changes in distensibility and composition of the uterine cervix in gilts. Ovariectomized, prepubertal gilts received (i.m.) either 1) 0.5 ml com oil (CO) for 16 days; 2) 0.5 ml CO for 16 days and estradiol benzoate (EB; 200 mug) twice daily on Days 13-14; 3) EB on Days 0-1 followed by CO on Days 3-16 (EB + CO); 4) EB on Days 0-1 followed by CO on Day 2 and twice daily injections of 100 mg progesterone (P) on Days 3-16 (EB + P); or 5) EB on Days 0-1 followed by CO on Day 2 and P on Days 3-16 with additional EB treatment on Days 13-14 (EB + P + EB). One half of each group also received (i.m.) 0.5 ml 0.1 M PBS or 0.5 mg relaxin (RLX) every 6 h for 54 h coinciding with the final 2 days of the experimental period. Administration of RLX increased (p < 0.05) cervical distensibility compared to PBS treatment, with the response being greater (p < 0.05) in EB-, EB + CO-, and EB + P + EB-treated gilts compared to CO- or EB + P-treated gilts. Water content of cervical tissue was greater (p < 0.05) in EB-, EB + P-, and EB + P + EB-treated gilts compared to CO- or EB + CO-treated gilts; and in all treatments, RLX enhanced (p < 0.05) imbibition of water by cervical tissues compared to that in PBS-treated gilts. Compared to administration of CO and EB + CO, administration of steroids reduced (p < 0.05) the cervical concentrations of glycosaminoglycans (GAG) in EB- and EB + P-treated gilts and those of collagen in EB- and EB + P + EB-treated gilts. Co-administration of RLX depressed (p < 0.05) the concentration of GAGs in cervical tissues from gilts in all steroid treatments except EB + P + EB. Additionally, administration of RLX reduced (p < 0.05) concentrations of collagen in CO- and EB + CO-treated gilts but did not affect concentrations of collagen in those treated with EB, EB + P, or EB + P + EB. These data demonstrate that RLX stimulates cervical dilation in gilts, a response augmented by exposure to estrogen. RLX-induced compositional changes in cervical tissues associated with increased distensibility included the enhanced imbibition of water and reduced concentrations of GAGs and collagen. To a lesser extent, administration of EB or P increased water content and reduced the concentrations of GAGs and collagen in cervical tissues, but these compositional changes were not associated with changes in cervical distensibility.