Effect of human chorionic gonadotropin on myometrial electrical activity in the pig

In vitro activity of human chorionic gonadotropin (hCG) on myometrium contractility

LH/hCG receptor has been found in extragonadal tissues in human and animals. The myometrium presents such receptors but their functional role is still not clear. Aim of our study was to test the activity of human chorionic gonadotropin (hCG) on bovine uterine contractility. Uterine strips from cows both during follicular and luteal phases were mounted in an organ bath and then exposed to increased doses of hCG. The amplitude of the myometrium contractions were significantly decreased in the follicular and luteal phase but the frequency was not affected. These findings prove a relaxing effect of hCG in the bovine uterus, as already shown in the sow and human, and its possible functional role in modulating uterine contractility.

Nongonadal LH receptors, their involvement in female reproductive function and a new applicable approach

Luteinising hormone (LH) and human chorionic gonadotropin (hCG) share a common receptor in gonadal cells. The receptors have also been detected in several nongonadal but reproduction-associated tissues of pigs, cattle, and other species including the uterus (myometrium, endometrium), oviduct, cervix, blood vessels, mammary gland and other tissues. The main role of LH/hCG receptors in the myometrium is stimulation of growth and hyperplasia, and relaxation of uterine motility; hCG also boosts blood flow in the uterine artery. LH and hCG can increase production of prostaglandins in the endometrium, oviduct, and blood vessels. We suggest that the preovulatory surge of LH plays an important role in controlling oviductal contractions. Awareness of LH binding to many tissues of the female reproductive tract and integration with embryonic factors may lead to the elaboration of new strategies for improved reproductive efficiency in domestic species. Mammary glands also possess LH/hCG receptors through which gonadotropins can affect the metabolism of steroid hormones and could play an inhibitory role in mammary carcinogenesis and in the growth of breast tumours. A novel approach to target and ablate carcinoma cells through LH receptors is described.

Extragonadal Luteinizing Hormone Receptors in the Reproductive Tract of Domestic Animals1

Binding sites for LH/hCG and/or its mRNA are found in the uterus of several species, including human, primate, pig, cow, and turkey. Activation of LH receptors around Day 15 of the estrous cycle is associated with increased prostaglandin F(2alpha) production in the bovine, porcine, and ovine uterus. Activation of uterine LH receptors is also associated with increased levels of prostaglandins in human and primate. The presence of gonadotropin receptors with a dynamic pattern in the oviduct, endometrium, myometrium, and cervix of different species provides evidence that gonadotropins play a substantial role in molecular autocrine-paracrine regulation of the estrous cycle and implantation.

Second messenger systems in the action of LH and oxytocin on porcine endometrial cells in vitro

LH/hCG as well as oxytocin receptors are present in the porcine endometrium. Oxytocin increases phosphatidylinositol hydrolysis in this tissue, but its action on adenylate cyclase activity is disputed. The second messenger system responding to LH/hCG in endometrial cells has not been established. In this study, we investigated the involvement of protein kinase A and C signaling mechanisms in the action of LH on porcine endometrial cells in vitro. The possibility of cAMP accumulation after treatment of endometrial cells with oxytocin was also investigated. Endometrial tissue was obtained from gilts during Days 12-15 of the estrous cycle. To study the adenylate cyclase system, endometrial cells were cultured for 48 h and then incubated with different doses of LH or oxytocin for 15, 30, 60, and 180 min. To study the phospholipase C system, dispersed cells were first labeled with myo-[3H]inositol and then treated with increasing doses of LH or 100 nM of oxytocin for 30 min. Time- and dose-dependent effect of LH and oxytocin on cAMP concentration was observed. After 30 min of incubation only the highest dose of LH (100 ng/ml) was able to increase cAMP concentration in medium (P < 0.05). Longer periods (1 and 3 h) caused increased cAMP accumulation after treatment with 10 and 100 ng/ml of LH (P < 0.001). Oxytocin-stimulated cAMP concentration was observed after 1 h when only the highest dose (1000 nM) of hormone was used (P < 0.01) and after 3 h of incubation with doses of 10-1000 nM (P < 0.01). LH (10 and 100 ng/ml) increased inositol phosphates (IPs) accumulation in endometrial cells after 30 min of incubation (P < 0.01). Oxytocin involvement in IPs synthesis was more apparent than was LH (P < 0.001 versus P < 0.01). This is the first demonstration that LH receptor signaling leads to increased cAMP generation as well as IPs turnover in porcine endometrium. Oxytocin-dependent cAMP production in endometrial cells of swine was found after longer periods (3 h) of incubation. Our observations lead to the conclusion that both protein kinase A and C second messenger systems are involved in LH action and that oxytocin is able to stimulate adenylate cyclase activity in porcine endometrial cells.

Effect of estradiol and progesterone on oviductal LH-receptors and LH-dependent relaxation of the porcine oviduct

We have previously shown that the porcine oviduct possesses immunoreactive and functional LH receptors and that LH causes relaxation of the oviduct, especially during the periovulatory stage of estrous cycle. The current studies were undertaken to investigate the effects of estradiol and progesterone on LH receptor protein and LH-stimulated motility of the oviduct in steroid-primed ovariectomized gilts. Twenty-one cross-bred gilts were ovariectomized at 6 m.o. of age. Four weeks later gilts received daily intramuscular injection of either 2 mL corn oil (control n = 4), estradiol benzoate (EB) 1.5 mg (n = 6), progesterone 50 mg (n = 5), or 1.5 mg EB plus 50 mg progesterone (n = 6) for 4 consecutive days. The gilts were slaughtered on Day 5 after the first injection of steroids or vehicle. Rings of isthmus and ampulla were collected from each oviduct and placed in a tissue chamber perfused with Kreb's solution for 60 min. The mechanical activity was recorded for 30 min after LH treatment. Immunoreactivity of LHR in the Fallopian tube sections were detected in the epithelium of the tubal mucosa, smooth muscle cells and the blood vessel endothelium. Western blotting showed that porcine oviducts contain 75, 48 and 45 kDa immunoreactive LH receptor proteins, like the corpus luteum (CL). The lowest receptor expression was found in controls and in gilts treated with estradiol or progesterone. Combined treatment with estradiol and progesterone resulted in a significant increase of LH receptor protein concentrations when compared with control animals. In vitro LH treatment affected oviduct contractility of combined estradiol and progesterone treated gilts but not the oviduct of the remaining groups. It also caused a decrease in amplitude, frequency and areas under the curve (AUC) of ampulla (P < 0.05) and the amplitude and AUC of isthmus (P < 0.001) in combined estradiol and progesterone-primed gilts. These results indicate that estradiol and progesterone together, but not separately, increase LH receptor protein in the porcine oviduct and that combined estradiol and progesterone priming is necessary for LH-induced relaxation of the porcine oviduct.

Myometrial LH/hCG receptors during the estrous cycle and pregnancy in pigs

Receptors for luteinizing hormone/human chorionic gonadotropin (LH/hCG) have been identified in porcine, rabbit, rat, and human myometrium. To determine the estrous cycle and pregnancy related changes in the receptor capacity and affinity, radioreceptor assays were performed with membrane homogenates of porcine uterine tissues. Cycling gilts were divided into four experimental groups: I (n = 6), day 1-2; II (n = 5), day 6-7; III (n = 5), day 11-12; and IV (n = 6), day 18-20 of the estrous cycle. Pregnant pigs were divided into three experimental groups: I (n = 5), day 35-40; II (n = 5), day 65-70; and III (n = 4), day 95-105 of pregnancy. The concentrations [femtomoles/mg protein (fmol/mg protein)] and affinities of unoccupied LH/hCG binding sites were characterized in all samples of myometrium. Receptor concentrations were highest (P < 0.01) in groups II and III (19.3 +/- 2.5 and 35.8 +/- 2.1 fmol/mg protein, respectively), and was lowest in groups I and IV (5.3 +/- 1.4 and 7.5 +/- 0.7 fmol/mg protein, respectively). Receptor affinity constants (Ka) were consistent (P > 0.05) throughout the estrous cycle [I, (5.1 +/- 1.5) x 10(9); II, (3.0 +/- 0.8) x 10(9); III, (3.2 +/- 0.9) x 10(9); IV, 5.5 +/- 0.7 x 10(9) 1m-1]. Plasma hormone concentrations of progesterone, estrogen and LH were typical of values noted at these times. During pregnancy, receptor concentrations were greatest (P < 0.05) in group II (85.4 +/- 18.5 fmol/mg protein). In groups I and III receptor numbers were 10.8 +/- 2.3 and 26.7 +/- 6.6 fmol/mg protein, respectively. The Ka in group I was 10 times greater (P < 0.05) than Ka in groups II and III, (I, 3.1 +/- 0.9 x 10(10) lm-1; II, 3.4 +/- 0.3 x 10(9) lm-1; III, 3.3 +/- 1.1 x 10(9) lm-1). Plasma hormone concentrations typically found during pregnancy were noted. The function of these LH/hCG binding sites remains unknown; however, changes in receptor capacity during the estrous cycle and pregnancy support a role for modulation of the receptor by hormonal factors.