Relaxin and Estrogen Accelerate Growth of Uterine Cervix of Prepubertal Pigs
One of the primary targets for the biological actions of relaxin is the uterine cervix. The effects of relaxin on this organ include inducing growth and remodeling of connective tissue and cervical cells to accommodate pregnancy and parturition. The related physiological and clinical observations include softening, ripening, and dilating the cervix and facilitating delivery of the young. The underlying molecular and cellular mechanisms remain obscure. Collagen is the most abundant protein in the cervix and plays a key role in connective tissue remodeling. This study was designed to determine the developmental and growthpromoting effects of relaxin with or without estrogen on the uterine cervix of prepubertal gilts. Littermate gilts of 80 days old were randomly assigned to four treatments: vehicle (control, 1 milliliter [ml.] phosphate buffer saline [PBS] and 1 ml. vegetable oil, n = 5); relaxin (relaxin, in PBS, 1 ml., 167 mg. 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, the uterus was surgically removed, and the uterine tissues were immediately frozen at -80°C. Homogenates of uterine horns and cervices were analyzed for concentrations and contents of protein or hydroxyproline (collagen index) and DNA. Relaxin alone had no significant effect on wet or dry weight of the uterus. EB alone increased significantly (P<.05) wet weight of the uterus. In the presence of EB, relaxin treatment increased all measurements compared with control (i.e., wet weight). Compared with EB, Relaxin + EB significantly (P<.05) increased the uterine wet weight, the hydroxyproline content and DNA content. 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. The present results show that the growth and development of the porcine uterus and cervix can be accelerated by treatment with relaxin and estrogen. Although it is not known whether the pig at this prepubertal stage contains relaxin receptors after relaxin and estrogen stimulation, the results reported here indicate that relaxin regulates the growth and development of the uterus and cervix during pregnancy as well as during the prepubertal period.