INDIVIDUAL AND COMBINED EFFECTS OF RELAXIN, ESTROGEN, AND PROGESTERONE IN OVARIECTOMIZED GILTS .1. EFFECTS ON THE GROWTH, SOFTENING, AND HISTOLOGICAL PROPERTIES OF THE CERVIX

Marked growth and softening of the uterine portion of the cervix occur during the last third of the 115-day gestation period in the gilt. Th ese changes in the cervix are temporally correlated with elevated bloo d levels of relaxin, estrogen, and progesterone. We recently demonstra ted that relaxin plays a major role in promoting both the growth and s oftening of the cervix that occur in pregnant gilts. The roles of estr ogen and progesterone in these cervical changes remain poorly understo od. Accordingly, this study determined the influence of relaxin, estro gen, and progesterone, individually and in combination, on cervical gr owth and softening in gilts. Fifteen days after ovariectomy, six to ni ne nonpregnant, sexually mature gilts were assigned to one of the foll owing eight treatment groups: ovariectomized controls, relaxin treated , estrogen treated, progesterone treated, estrogen plus relaxin treate d, progesterone plus relaxin treated, estrogen plus progesterone treat ed, and progesterone plus estrogen plus relaxin treated. Treatment was given for 10 days, with doses of relaxin (0.5 mg, four times daily), estradiol benzoate (1 mg, twice daily), and progesterone (50 mg, twice daily) selected to provide blood levels resembling those between days 100-110 of gestation. The growth, softening, and histological charact eristics of the cervices were determined. Treatment with relaxin signi ficantly increased the growth and softening and altered the histologic al characteristics of the uterine portion of the cervix in the absence of steroid treatment. Estrogen treatment alone increased cervical gro wth, but when given in combination with relaxin, estrogen did not augm ent relaxin's ability to increase either cervical growth or softening. Progesterone alone had little or no effect on the growth or softening of the uterine portion of the cervix. Unexpectedly, when given in com bination with relaxin, progesterone augmented markedly relaxin's effec ts on softening and alteration of the histological characteristics of the cervix. In conclusion, this study is consistent with recent report s that relaxin promotes both the growth and softening of the cervix in the pig. Additionally, this study provides evidence that estrogen and relaxin act independently to promote the growth of the cervix in gilt s, whereas progesterone acts in concert with relaxin to promote soften ing of the cervix and a reduction in the organization and density of c ervical collagen fibers. This study provides evidence that relaxin, es trogen, and progesterone all very likely play important roles in the m odifications of the cervix that occur during late pregnancy in the gil t.