G. Min et Od. Sherwood, IDENTIFICATION OF SPECIFIC RELAXIN-BINDING CELLS IN THE CERVIX, MAMMARY-GLANDS, NIPPLES, SMALL-INTESTINE, AND SKIN OF PREGNANT PIGS, Biology of reproduction, 55(6), 1996, pp. 1243-1252
We previously demonstrated that relaxin promotes growth and softening
of the cervix and development of the mammary glands in the pregnant pi
g. An important aspect of understanding relaxin's mechanism of action
in these tissues is to identify the specific cell type(s) that contain
s relaxin receptors, that is, to identify those cells that initiate re
laxin's effects. The objective of the present study was to identify re
laxin-binding cells in tissues known to respond to relaxin (cervix and
mammary gland) as well as in tissues suspected of being responsive to
relaxin (nipple, small intestine, and skin) in the pregnant pig. To a
ccomplish that objective we developed an in vitro modification of an i
mmunohistochemical technique recently developed for identification of
relaxin-binding cells. Two groups of pregnant gilts were used: intact
control (group C) and ovariectomized progesterone-treated (group OF).
Group OP was ovariectomized on Day 40 of gestation (Day 40) and treate
d with progesterone (50 mg/2 ml corn oil i.m., twice daily) until Day
110 to maintain pregnancy. On Day 110, tissues from both groups were r
emoved, cut into cubes (2-3 cm(3)), frozen in liquid nitrogen, and cry
osectioned (8 pm). Specific cell types that bind relaxin were identifi
ed by sequential application of a biotinylated relaxin probe, antibiot
in immunoglobulin G conjugated to 1 nm colloidal gold, and silver for
signal amplification. The study demonstrates for the first time that r
elaxin binds with specificity to 1) blood vessels (cervix, mammary gla
nds, nipples, small intestine); 2) smooth muscles in small intestine (
circular, longitudinal, muscularis mucosa); and 3) skin from sites oth
er than the mammary nipples (back, ear, thigh, leg). In addition, cons
istent with previous findings in the rat, prominent labeling was obser
ved in epithelial cells in the cervix, mammary glands, and nipples; in
smooth muscle cells in the cervix and mammary nipples; and in the ski
n of the nipples. There were no apparent differences in relaxin bindin
g between group C and group OF. We conclude that the specific relaxin-
binding cells in the cervix, mammary glands, nipples, small intestine,
and skin of the pregnant pig probably contain relaxin receptors and,
therefore, mediate relaxin's effects in these tissues.