Relaxin and estrogen synergistically accelerate growth and development in the uterine cervix of prepubertal pigs

This study was designed to determine the developmental and growth-promoting effects of relaxin with or without estrogen on the uterine cervix of prepubertal gilts. Twenty littermate gilts of similar body weight (33 ± 3 kg; mean ± SE) at 80 days of age were randomly assigned to four treatments: Vehicle (Control, 1 ml PBS and 1 ml vegetable oil, n = 5); Relaxin (Relaxin, in PBS, 1 ml, 167 μg ml−1, n = 5); Estradiol Benzoate (EB, in vegetable oil, 1 ml, 2 mg ml−1, n = 5); and Relaxin plus EB (Relaxin + EB, at the same doses, n = 5), total six intramuscular injections for all treatments. Twenty four hours after the last injection, hysterectomy was performed, and the uterine tissues were immediately frozen at −80°C. Samples were taken from the middle portions of the cervix and the uterine horns and dried to a constant weight to determine the dry weight and water concentration. Homogenates of uterine horns and cervices were analyzed for concentrations and contents of protein, hydroxyproline (collagen index) and DNA. Relaxin alone had no significant effect on any parameters (i.e., wet weight, Relaxin vs. Control: 36 ± 5 vs. 28 ± 3 g uterus−1, dry weight 5.6 ± 0.6 vs. 4.4 ± 0.4 g uterus−1). EB alone increased significantly (P < 0.05) wet weight of the uterus (EB vs. Control: 85 ± 23 vs. 28 ± 3 g uterus−1), dry weight (EB vs. Control: 14.5 ± 3 vs. 4.4 ± 0.4 g uterus−1), and hydroxyproline content (EB vs. Control: 47.2 ± 13 vs. 12.6 ± 4 mg cervix−1). In the presence of EB, relaxin treatment increased all measurements compared with Control (i.e., wet weight, Relaxin + EB vs. EB: 136 ± 34 vs. 28 ± 3 g uterus−1). Compared with EB, Relaxin + EB significantly (P < 0.05) increased the uterine wet weight (Relaxin + EB vs. EB: 136 ± 34 vs. 85 ± 23 g uterus−1), the hydroxyproline content (Relaxin + EB vs. EB: 91 ± 29 vs. 47 ± 13 mg cervix−1), and DNA content (Relaxin + EB vs. EB: 8.1 ± 2 vs. 5.4 ± 1 mg cervix−1). These results indicate that the growth-promoting effects of relaxin on the uterus and cervix may be, at least partly, estrogen-dependent and that the growth and development of the uterus and cervix can be accelerated by a combination of relaxin and estrogen treatment.