Evidence for the Presence of Luteinizing Hormone/ Human Chorionic Gonadotropin-Binding Sites in the Porcine Uterus

Abstract

LH/hCG-binding sites were measured in crude membrane fractions of porcine uteri. Specific high affinity and low capacity receptors for LH/hCG were found in all (n = 17) membrane preparations of myometrium but in only 5 of 17 crude membrane fractions of endometrium of porcine uteri. There was very little competition between hCG and porcine GH (pGH), bovine TSH, pFSH, and pPRL (0.5%, 0.3%, 0.2%, and less than 0.005%, respectively). Specificity of [125I]hCG binding to other tissues was determined by incubating crude membrane preparations of heart, skeletal muscle, liver, and kidney. Numbers and affinities of available LH/hCG-binding sites were characterized in all samples of myometrium and 5 endometrium membrane preparations that were positive for LH/hCG receptors. The results indicate that the number of uterine LH-binding sites in myometrium (0.66 +/- 0.17 fmol/mg) is 10 times less than the receptor capacity in porcine corpora lutea (7.46 +/- 0.54 fmol/mg) when expressed per mg protein of crude membrane preparation. However, it is approximately 60 times less when expressed per mg DNA equivalent of initial homogenate (1.31 +/- 0.28 vs. 81.18 +/- 3.64 fmol/mg, respectively). Receptor affinities of uterine LH/hCG-binding sites remained comparable to those of corpora lutea receptors (Ka = 7.8 X 10(10) M-1). Concentrations of LH/hCG-binding sites in myometrium taken from gilts in the late follicular phase of the estrous cycle (0.13 +/- 0.06 fmol/mg protein; n = 5) were significantly less (P less than 0.05 and P less than 0.01) compared to those in myometrium from luteal phase (0.85 +/- 0.22 fmol/mg protein; n = 6) or early pregnancy (1.03 +/- 0.15 fmol/mg protein; n = 6), respectively. This is probably the first evidence demonstrating specific binding of [125I]hCG by LH receptors in female uterine tissue.

Downregulation of LH receptor mRNA in the rat uterus

“…These data showed that the LHR expressed in the uterus has a function, although the biological effect on the uterus is not clear and the physiological role of LH/hCG binding sites in the uterus remains to be elucidated. Ziecik et al (1) and Angioni et al (20) postulated the role of LH in the relaxation of the myometrium; these findings are in agreement with results that preferentially locate LH/hCG binding sites in this uterine compartment. It has been reported that transgenic mice with chronically elevated LH are infertile due to anovulation and defects in uterine receptivity (11).…”

Is human chorionic gonadotropin directly involved in the regulation of human implantation?

“…Several groups have demonstrated the presence of hCG/LH-binding sites and receptor-like immunoreactivity in the porcine, rabbit, rat, mouse, bovine and human endometrium (Bernardini et al 1995;Bhattacharya et al 1993;Bonnamy et al 1993;Fazleabas et al 1999;Freidman et al 1995;Jensen and Odell 1988;Lin et al 1994;Reshef et al 1990;Ziecik et al 1986) . Receptor expression seems to be cycle dependent with secretory endometria expressing higher levels as compared to proliferative or postmenopausal samples.…”

Luteinising hormone receptor kinetic and LH-induced prostaglandin production throughout the oestrous cycle in porcine endometrium

“…[42] reported for the first time the presence of uterine gonadotropin receptors in female mammals, using pigs as a model, it was not known whether the endometrium contained LH/hCG receptors for only a specific short period of the oestrous cycle. Our recent results obtained using a ligand radioreceptor assay revealed that endometrial LH/hCG receptors, contrary to the myometrium [42], appear temporarily during the oestrous cycle in pigs. We found these receptors in preparations from days 12 to 14 (pre-luteolysis) and 15 to 16 (luteolysis) but not in preparations from other stages -from days 18 to 20 (prooestrus) and 6 to 7 (early luteal phase).…”