High-affinity LH/hCG binding sites have been characterized in bovine, lepin
e, murine, human uteri and porcine myometrium and endometrium. In the prese
nt studies we analyzed these receptors in the porcine cervix. Radioreceptor
ligand assays were performed with cell membrane preparations of the cervix
which were analyzed for binding sites specificity, capacity and affinity.
Corpus luteum and myometrium were used as positive control tissues. In the
cervix there was little competition for receptor occupancy between hCG and
porcine FSH (1.2%) or bovine TSH, porcine GH and porcine PRL (0.1%, 0.1% an
d < 0.001%; respectively) but porcine LH could completely inhibit the bindi
ng of [I-125]hCG. There was not binding for LH/hCG in crude membrane prepar
ations of kidney or skeletal muscle. The concentration (fmol/mg protein) of
cervical LH/hCG receptor did not vary significantly during particular phas
es of the estrous cycle, except the early luteal phase (Days 6-7) when the
level of LH receptors was very low (p < 0.05). The affinity of uterine LH/h
CG binding sites in the cervix and the myometrium was not different from th
e affinity of LH/hCG binding sites in luteal cells. The porcine cervix as w
ell as the myometrium contains a 75- and 48-kDa immunoreactive LH/cCG recep
tor proteins similar to corpus luteum. Southern blot of RT-PCR products per
formed to enhance the specificity and sensitivity of LH receptor transcript
s determination in uterine tissues revealed that expected fragments of 740
and 470 bp were present in myometrium and corpus luteum. The cervix showed
only 740 bp fragment. In situ hydridization showed the expression of mRNA f
or LH receptor in the epithelium of the cervix. Immunoreactive staining for
LH/hCG receptors was also observed only in epithelial cells of the cervica
l tissue. Our studies are probably the first evidence demonstrating the spe
cific LH/hCG binding sites in female cervix.