Relaxin bioactivity and immunoactivity in human corpora lutea

Relaxin family peptides and their receptors

There are seven relaxin family peptides that are all structurally related to insulin. Relaxin has many roles in female and male reproduction, as a neuropeptide in the central nervous system, as a vasodilator and cardiac stimulant in the cardiovascular system, and as an antifibrotic agent. Insulin-like peptide-3 (INSL3) has clearly defined specialist roles in male and female reproduction, relaxin-3 is primarily a neuropeptide involved in stress and metabolic control, and INSL5 is widely distributed particularly in the gastrointestinal tract. Although they are structurally related to insulin, the relaxin family peptides produce their physiological effects by activating a group of four G protein-coupled receptors (GPCRs), relaxin family peptide receptors 1-4 (RXFP1-4). Relaxin and INSL3 are the cognate ligands for RXFP1 and RXFP2, respectively, that are leucine-rich repeat containing GPCRs. RXFP1 activates a wide spectrum of signaling pathways to generate second messengers that include cAMP and nitric oxide, whereas RXFP2 activates a subset of these pathways. Relaxin-3 and INSL5 are the cognate ligands for RXFP3 and RXFP4 that are closely related to small peptide receptors that when activated inhibit cAMP production and activate MAP kinases. Although there are still many unanswered questions regarding the mode of action of relaxin family peptides, it is clear that they have important physiological roles that could be exploited for therapeutic benefit.

Immunohistochemical detection of relaxin binding to the volar oblique ligament

PURPOSE

Excess laxity in the volar oblique ligament may predispose the thumb to trapeziometacarpal joint osteoarthritis. A greater prevalence of trapeziometacarpal joint osteoarthritis in women suggests a hormonal cause and relaxin is a hormone that may have some involvement. This conclusion emerges from relaxin's diverse tissue tropism, stimulation of collagenase production in cultured fibroblasts, and reports of increased joint laxity during pregnancy. We used immunohistochemistry to assess the potential of the volar oblique ligament to bind relaxin.

METHODS

Eight volar oblique ligaments were obtained intraoperatively from perimenopausal women having basal joint arthroplasty with ligament reconstruction using the flexor carpi radialis tendon. Tissue specimens were snap-frozen in liquid nitrogen and stored at -80 degrees C until processing. Specimens then were cryosectioned, treated with a chelating rinse, incubated overnight with recombinant human relaxin, fixed, blocked, and exposed to antirelaxin antibody. Treatment with a universal aminoethylcarbizole staining kit was used to visualize areas of ligament-ligand binding. Both tissue and procedural controls served to establish binding specificity.

RESULTS

Abundant staining was observed with the positive control (cervix) and all 8 volar oblique ligaments. Little or no staining was present in fibrocartilage (negative control) or procedural controls.

CONCLUSIONS

Relaxin binds to the volar oblique ligament with specificity, implying a receptor-mediated process. Limitations of the procedure could not confirm binding saturability, necessitating additional study.

Elevated Concentrations of Serum Relaxin are Associated with Metastatic Disease in Breast Cancer Patients

Relaxin (RLX) is known to induce remodeling of benign stromal tissues through upregulation of matrix metalloproteases (MMPs). Recently, we could show that RLX also induces MMPs in breast cancer cells and enhances in vitro invasiveness. To investigate its potential role for progression of breast cancer in vivo, RLX serum concentrations were determined in 160 breast cancer patients during post-surgical follow-up. RLX concentrations in cancer patients were significantly higher than in a control population of healthy blood donors and patients with various other diseases (0.47 versus 0.29 ng/ml, p < 0.0001). There was a significant difference between patients with metastases (0.62 ng/ml) and those without (0.38 ng/ml, p < 0.0001). Overall survival was shorter in RLX-positive ( > 0.4 ng/ml) than in RLX-negative patients (p = 0.016). Cox regression analysis showed that RLX was not an independent variable, in contrast to metastatic disease and primary lymph node involvement. Taken together, the detection of elevated RLX concentrations especially in patients with metastases supports the assumption that there is a role for RLX in tissue remodeling during breast cancer progression.

The localization of cholecystokinin immunoreactivity in the rat ovary and uterine tube

The presence of cholecystokinin (CCK) immunoreactive nerve fibres in the rat ovary and uterine tubes was detected using the peroxidase antiperoxidase (PAP) technique. The antibody used was anti CCK 4562 which reacts with CCK-4, CCK-8, CCK-12 and CCK-33 (Larsson and Rehfeld, 1977). CCK-immunoreactive nerve fibres were found between the interstitial cells of the ovary, along blood vessels, and close to smooth muscle fibres in the ovary and tubal wall. A possible role of CCK-nerves in modulation of the sensitivity of the ovarian components to other humoral and nervous stimuli is discussed. The possible control of CCK over smooth muscle fibres in the ovary and the uterine tube and its role in ovulation is a matter of further studies.

Cyclic AMP response to recombinant human relaxin by cultured human endometrial cells--a specific and high throughput in vitro bioassay

A specific and high throughput 96-well format bioassay for recombinant human relaxin (rhRLX) has been developed using human endometrial cells (NHE cells). rhRLX caused a time- and dose-dependent stimulation of cyclic AMP (cAMP) with 1/2 maximal activity of 3.56 +/- 0.65 ng/ml (n = 30). The range of the standard curve was 0.39 to 25 ng/ml with interplate precision of 17 and 22% CV for high and low controls respectively. The cAMP response requires forskolin and 3-isobutyl-1-methylxanthine, and is enhanced by prostaglandin E2 and F2 alpha. The NHE cells do not respond to A or B chains of rhRLX, or a whole array of hormones. Preincubation of rhRLX with specific monoclonal antibody completely abolished the cAMP response. This bioassay has been used to determine the biological activity of several manufactured lots of recombinant human relaxin.

Progesterone and relaxin secretion in relation to the ultrastructure of human luteal cells in culture: effects of human chorionic gonadotropin

This report describes the first study to correlate the ultrastructure of long-term monolayer cultures of human luteal cells with their secretion of relaxin and progesterone under basal and human chorionic gonadotropin-stimulated conditions. In culture from 14 to 28 days, cells from both corpora lutea of the menstrual cycle and corpora lutea of pregnancy took on characteristics of granulosa luteal cells, particularly after exposure to human chorionic gonadotropin. Relaxin was detectable in the luteal cell cultures only at early time points. The effect of human chorionic gonadotropin on media relaxin levels differed in cells of the cycle and cells of pregnancy. In the cells of the cycle, relaxin was detectable only on day 2 and was decreased by human chorionic gonadotropin (p less than 0.01). In cells of pregnancy, relaxin was detectable for the first 4 days of culture and was not affected by human chorionic gonadotropin. Progesterone was detectable in all the luteal cell cultures and was enhanced by human chorionic gonadotropin (10 and 50 IU/ml) after 24 days of exposure. At earlier time points in both the luteal cells of the cycle and the luteal cells of pregnancy, the human chorionic gonadotropin-induced increases in progesterone levels were not as consistent. However, in all cases of progesterone enhancement, smooth-surfaced endoplasmic reticulum was increased in the human chorionic gonadotropin-treated cells compared with corresponding controls, consistent with more active steroid production. In addition, gap junctions, considered to be responsive to trophic hormones, were increased in the treated cells. In conclusion, this long-term monolayer culture of human luteal cells, as monitored by ultrastructural and hormonal changes, retained the differentiated function of progesterone secretion and exhibited responsiveness to human chorionic gonadotropin. Therefore, morphologic and functional aspects of progesterone secretion may be investigated more closely with use of this long-term luteal cell culture system.

Immunoreactive relaxin surge in the peritoneal fluid of women during the midluteal phase

Relaxin was assayed in the peritoneal fluid (PF) of 176 women with normal ovulatory cycles. Validation of the assay in this fluid was carefully established. Relaxin was rarely detected before day 20 of the cycle. From days 21 to 24, all samples contained detectable concentrations of the peptide, ranging between 75 and 775 pg/ml. Apparition of relaxin in the PF was not directly related to the ovulatory follicular rupture. It was also delayed, compared with the postovulatory rise of plasma and peritoneal progesterone. Relaxin is thus present in the PF only during the period propitious to human embryo implantation.

The occurrence of relaxin in hyperstimulated human preovulatory follicles collected in an in vitro fertilization program

The avidin-biotin immunoperoxidase method and antisera against highly purified porcine relaxin were utilized to localize relaxin-like immunoreactivity in biopsied specimens from six preovulatory follicles from four women undergoing laparoscopy for oocyte retrieval in an in vitro fertilization program. By histological criteria, three of the follicles were luteinized and three were not. Relaxin was found in the granulosa cells of those cells which showed histological luteinization, whereas no relaxin was found in the nonluteinized preovulatory follicles. Our results show, for the first time, the occurrence of relaxin in the human ovary before ovulation and they suggest that the appearance of relaxin is related to the luteinization process.

Relaxin in human decidua and term placenta

Using both a homologous porcine RIA and 3 bioassays, we investigated the relaxin content of human decidua from first trimester and term gestations and of placentas at term. Aqueous extracts of these tissues yielded only between 211 and 1090 pg immunoreactive relaxin/g fresh tissue. Neither acetonehexane extraction, octadecylsilica cartridge elution nor molecular sieve chromatography increased these relaxin levels. Compared with term decidua, first trimester decidua contained significantly higher levels of immunoreactive relaxin. In vitro studies did not evidence significant relaxin production by either decidual or placental tissues, even in the presence of decidual prolactin production. These results are in direct contrast to earlier reports of high concentrations of relaxin in decidua and placenta.

Immunoreactive beta-endorphin in sheep ovary

Although the ovarian production of sex steroids is of obvious physiological importance, recent studies suggest that peptides such as oxytocin, relaxin and inhibin are also synthesized in the ovary. We report here the presence of immunoreactive (ir) beta-endorphin, ir-adrenocorticotropic hormone (ACTH) and presumptive high molecular weight forms of both in extracts of sheep ovary, consistent with ovarian production from a common precursor. Our findings suggest that beta-endorphin and ACTH are produced and secreted by the follicular cells, and that their production may be related to the oestrous cycle.

Synergistic effect of human relaxin and progesterone on human myometrial contractions

In an in vitro human myometrial strip system, both relaxin and progesterone can independently decrease the amplitude of spontaneous myometrial contractions. However, progesterone and relaxin synergize in this action. Doses of relaxin and progesterone which independently are ineffective, together inhibit myometrial contraction amplitude. Relaxin and progesterone are both products of the corpus luteum, a structure necessary for early pregnancy maintenance. The synergistic action of relaxin and progesterone in vitro suggests a similar in vivo physiologic effect in establishing uterine quiescence.

Myometrial inhibiting activity of relaxin-containing extracts of human corpora lutea of pregnancy

Relaxin is a peptide hormone secreted by the human corpus luteum of pregnancy . Aqueous extracts of relaxin-rich pregnancy corpora lutea decreased the amplitude of spontaneous human myometrial strip contractions in vitro. Relaxin-poor extracts of menstrual cycle corpora lutea did not affect contractions. Antibody precipitation of relaxin from pregnancy luteal extracts eliminated the effect on myometrial strips. Relaxin removal was confirmed by bioassay. This demonstrates an inhibiting action of human relaxin on human myometrial tissue in vitro. This action suggests a mechanism for maintaining uterine quiesence in early pregnancy.