INDIVIDUAL AND COMBINED EFFECTS OF RELAXIN, ESTROGEN, AND PROGESTERONE IN OVARIECTOMIZED GILTS .1. EFFECTS ON THE GROWTH, SOFTENING, AND HISTOLOGICAL PROPERTIES OF THE CERVIX
Rj. Winn et al., INDIVIDUAL AND COMBINED EFFECTS OF RELAXIN, ESTROGEN, AND PROGESTERONE IN OVARIECTOMIZED GILTS .1. EFFECTS ON THE GROWTH, SOFTENING, AND HISTOLOGICAL PROPERTIES OF THE CERVIX, Endocrinology, 135(3), 1994, pp. 1241-1249
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.