Growth-promoting effects of relaxin and related compositional changes in the uterus, cervix, and vagina of the rat

Targeting the relaxin hormonal pathway in prostate cancer

Targeting the androgen signalling pathway has long been the hallmark of anti-hormonal therapy for prostate cancer. However, development of androgen-independent prostate cancer is an inevitable outcome to therapies targeting this pathway, in part, owing to the shift from cancer dependence on androgen signalling for growth in favor of augmentation of other cellular pathways that provide proliferation-, survival- and angiogenesis-promoting signals. This review focuses on the role of the hormone relaxin in the development and progression of prostate cancer, prior to and after the onset of androgen independence, as well as its role in cancers of other reproductive tissues. As the body of literature expands, examining relaxin expression in cancerous tissues and its role in a growing number of in vitro and in vivo cancer models, our understanding of the important involvement of this hormone in cancer biology is becoming clearer. Specifically, the pleiotropic functions of relaxin affecting cell growth, angiogenesis, blood flow, cell migration and extracellular matrix remodeling are examined in the context of cancer progression. The interactions and intercepts of the intracellular signalling pathways of relaxin with the androgen pathway are explored in the context of progression of castration-resistant and androgen-independent prostate cancers. We provide an overview of current anti-hormonal therapeutic treatment options for prostate cancer and delve into therapeutic approaches and development of agents aimed at specifically antagonizing relaxin signalling to curb tumor growth. We also discuss the rationale and challenges utilizing such agents as novel anti-hormonals in the clinic, and their potential to supplement current therapeutic modalities.

Relaxin and castration in male mice protect from, but testosterone exacerbates, age-related cardiac and renal fibrosis, whereas estrogens are an independent determinant of organ size

This study determined the effects of castration and hormone replacement therapy on the age-related cardiac and renal pathology of male relaxin gene-knockout (RlnKO) and age-matched wild-type (RlnWT) mice and that of aged male aromatase knockout (ArKO) mice, which lack estrogens and have 5-10 times the androgen levels of male wild-type mice. One-month-old RlnWT and RlnKO mice were bilaterally gonadectomized or sham operated and maintained until 12 months. Subgroups of castrated animals received testosterone or 17β-estradiol treatment from 9 to 12 months. Male ArKO mice and aromatase wild-type mice were aged to 12 months. Collected heart and kidney tissues were assessed for changes in organ size and fibrosis. Castration reduced body, heart, left ventricle, and kidney weights in both RlnKO and RlnWT mice, and the cardiac/renal fibrosis that was seen in sham RlnKO animals (all P < 0.05 vs. respective sham). Testosterone normalized organ weights and organ weight to body weight ratio of castrated animals and increased cardiac/renal collagen concentration to levels measured in or beyond that of sham RlnKO mice (all P < 0.05 vs. respective castrated mice). Furthermore, expression of TGF-β1, mothers against decapentaplegic homolog 2 (Smad2), and myofibroblast differentiation paralleled the above changes (all P < 0.05 vs. respective castrated mice), whereas matrix metalloproteinase-13 was decreased in testosterone-treated RlnKO mice. Conversely, 17β-estradiol only restored changes in organ size. Consistent with these findings, intact ArKO mice demonstrated increased cardiac/renal fibrosis in the absence of changes in organ size. These findings suggest that relaxin and castration protect, whereas androgens exacerbate, cardiac and renal fibrosis during ageing, whereas estrogens, in synergy with relaxin, regulates age-related changes in organ size.

Effect of relaxin on the decidual cell reaction in the Mongolian gerbil (Meriones unguiculatus)

Purpose

Differentiation of endometrial stromal cells into decidual cells occurs during embryo implantation and pregnancy. Recently, it has been reported that relaxin affects the decidualization of cultured human endometrial cells in vitro; however, there has been no study on the decidualization of the Mongolian gerbil (Meriones unguiculatus). The authors demonstrated artificially induced decidualization, and the effect of relaxin on decidualization in gerbils.

Methods

Ten-to-twelve-week-old female Mongolian gerbils were ovariectomized, treated with estradiol, progesterone, and relaxin, and the uterine horn was stimulated. On day 10, uterine horns were measured for weight, protein concentration, and the incorporation of ¹⁴C-methionine; tissue sections were examined. Interleukin-11 (IL-11) primers were used for RT-PCR to confirm decidualization.

Results

Decidualization can be induced artificially in gerbils. In general, the histological observations of gerbil decidual cells were very similar to those of rats. The uterine horn weight, protein content, and protein synthesis from ¹⁴C-methionine significantly increased in the relaxin-treated gerbils (P< 0.05). Mast cells in the relaxin-treated uterus had proliferated more than those of the non-relaxin-treated group, which was confirmed by IL-11 expression.

Conclusions

We conclude that decidualization can be induced artificially, and relaxin increased weight of uterine horn, protein concentration, protein synthesis and IL-11 expression in gerbils.

Relaxin treatment of solid tumors: effects on electric field-mediated gene delivery

Pulsed electric fields have been shown to enhance interstitial transport of plasmid DNA (pDNA) in solid tumors in vivo. However, the extent of enhancement is still limited partly due to the collagen component in extracellular matrix. To this end, effects of collagen remodeling on interstitial electrophoresis were investigated by pretreatment of tumor-bearing mice with a recombinant human relaxin (rh-Rlx). In the study, two tumor lines (4T1 and B16.F10) were examined and implanted s.c. to establish two murine models: dorsal skin-fold chamber (DSC) and hind leg. Effects of rh-Rlx on pDNA electrophoresis were measured either directly in the DSC model or indirectly in the hind leg model via reporter gene expression. It was observed that rh-Rlx treatment reduced collagen levels in the hind leg tumors but not in the DSC tumors. The observation correlated with the results from electromobility experiments, where rh-Rlx treatment enhanced transgene expression in 4T1 hind leg tumors but did not increase the electromobility of pDNA in the DSC tumors. In addition, it was observed that pDNA binding to collagen could block its diffusion in collagen gel in vitro. These observations showed that effects of rh-Rlx on the collagen content depended on microenvironment in solid tumors and that rh-Rlx treatment would enhance electric field-mediated gene delivery only if it could effectively reduce the collagen content in collagen-rich tumors.

Relaxin (RLX) and estrogen affect estrogen receptor α, vascular endothelial growth factor, and RLX receptor expression in the neonatal porcine uterus and cervix

The porcine female reproductive tract undergoes estrogen receptor (ER) α-dependent development after birth (postnatal day=PND 0), the course of which can determine adult uterine function. Uterotrophic effects of relaxin (RLX) in the porcine neonate are age specific and may involve ER activation. Here, objectives were to determine effects of RLX and estrogen administered from birth on uterine and cervical growth and expression of ERα, vascular endothelial growth factor (VEGF), and the RLX receptor (RXFP1). On PND 0, gilts were treated with the antiestrogen ICI 182 780 (ICI) or vehicle alone and, 2 h later, were given estradiol-17β (E) or porcine RLX for 2 days. Neither RLX nor E affected uterine wet weight or protein content on PND 2. However, RLX, but not E, increased cervical wet weight and protein content when compared with controls. Pretreatment with ICI did not inhibit RLX-stimulated cervical growth. Uterine and cervical ERα increased in response to RLX, but not E. Both RLX and E increased VEGF in the uterus and cervix on PND 2. Pretreatment with ICI increased VEGF in both tissues and increased RLX-induced cervical VEGF. In the uterus E, but not RLX, increased RXFP1 mRNA. In the cervix, E increased RXFP1 gene expression whereas RLX decreased it. Results indicate that the neonatal uterus and cervix are sensitive to E and RLX and that growth responses to RLX in these tissues differ by PND 2. Effects of RLX on uterine and cervical ERα and VEGF expression may be important for neonatal reproductive tract development.

Expression of LGR7 and LGR8 by neonatal porcine uterine tissues and transmission of milk-borne relaxin into the neonatal circulation by suckling

Estrogen receptor-dependent organizational events between birth [postnatal day (PND) 0] and PND 14 affect development and function of porcine uterine tissues. Observations that uterotrophic effects of relaxin (RLX) in neonatal gilts were inhibited by the antiestrogen ICI 182,780 suggested that a RLX signaling system, capable of cross-talk with the estrogen receptor, evolves during a critical period for uterine programming (PND 0-14). Objectives were to determine 1) effects of age and estrogen exposure from birth on porcine uterine RLX/insulin-like 3 receptor (LGR7/LGR8) expression and 2) whether milk serves as a natural source of RLX in neonatal pigs. Uterine LGR7/LGR8 expression, detected by RT-PCR and in situ hybridization on PND 0, 7, and 14, was predominantly stromal for LGR7, myometrial for LGR8, and increased with age and after treatment with estradiol valerate (50 microg/kg body weight x d) from birth. Stromal expression of LGR7 was also detected immunohistochemically. Milk RLX concentrations declined (P < 0.001) from 17.3 +/- 1.4 ng/ml (lactation d 0) to 1.7 +/- 0.3 ng/ml (lactation d 14). RLX, present in the serum of nursing pigs on PND 0 and 1, was undetectable before nursing and in neonates fed RLX-free milk replacer for 12 h. Thus, a developmentally regulated, estrogen-sensitive LGR7 and LGR8 receptor system is present in the porcine uterus at birth and may be activated by milk-borne RLX delivered into the circulation during the first 48 h of postnatal life. Maternal lactocrine contributions to the neonatal hormonal milieu could affect the developmental programming of uterine and other somatic tissues.

Uterotrophic effects of relaxin related to age and estrogen receptor activation in neonatal pigs

While uterotrophic effects of relaxin are well documented, the mechanism through which relaxin promotes uterine growth is incompletely understood. Studies in rats suggest that relaxin-stimulated uterine edema depends on estrogen receptor (ER) activation. Here, neonatal pigs were used to investigate the interaction between relaxin and ER signaling pathways. Gilts were treated either at birth (postnatal day (PND) 0) (study 1) before the onset of endometrial ERα expression, or on PND 12 (study 2) after the onset of ERα expression. In study 1, gilts were treated with estradiol-17β or porcine relaxin for two days and uteri were collected on PND 2. In study 2, PND 12 gilts were treated with a single injection of the ER antagonist ICI 182,780 (ICI) or vehicle. Two hours later, gilts were given either estradiol-17β or porcine relaxin for two days. When administered for two days from birth (study 1), neither estradiol-17β nor relaxin affected uterine weight or protein content. However, uterine luminal epithelial height was greater in relaxin- than in vehicle-treated gilts. In contrast, in study 2, both estradiol and relaxin increased uterine weight, protein content and uterine luminal epithelial height on PND 14. These effects were inhibited by pre-treatment with ICI in both estradiol- and relaxin-treated gilts. The results indicate that uterotrophic effects of relaxin in the neonatal pig are related to age and to both the relative presence and state of activation of the ER system in developing uterine tissues between birth and PND 14.

Tissue-Specific Effects of Relaxin on the Reproductive Tract of Neonatal Gilts

In the pig, relaxin treatment for 2 d from birth (postnatal day 0, PND 0) was not uterotrophic, but it increased cervical size. To understand the mechanism underlying this tissue-specific response, relaxin receptor (LGR7) expression in the neonatal uterus and cervix was investigated. At PND 2, quantitative RT-PCR analysis showed that LGR7 levels were higher in the cervix than in the uterus. Interestingly, relaxin decreased cervical LGR7 expression when compared to that of the controls. Differential expression of LGR7 between uterine and cervical tissues may contribute to tissue-specific relaxin responsiveness in the neonatal porcine reproductive tract.

Effects of Relaxin on Neonatal Porcine Uterine Growth and Development

Relaxin (RLX), a key reproductive hormone in pigs, stimulates uterine growth in pregnant and prepubertal gilts and in neonates 2 weeks after birth. The neonatal uterotrophic response to RLX is developmentally regulated and estrogen receptor dependent because RLX fails to increase uterine weight in the absence of estrogen receptor (ER)-alpha or when the ER is chemically inactivated. However, the role of RLX and insulin-like peptide-3 receptors, LGR7 and LGR8, respectively, in the neonatal uterotrophic response is unknown. Current studies focus on direct (LGR7/8-mediated) and indirect (ER-mediated) effects of RLX in the neonatal porcine uterus. Porcine LGR7 and LGR8 cDNAs were cloned and used as probes to identify uterine transcripts for LGR7 and LGR8, which increased from birth (postnatal day [PND] 0) to PND 14, a critical period for porcine uterine development. In situ hybridization showed that endometrial signals for both LGR7 and LGR8 are predominantly stromal during this period. Administration of RLX on PND 0, before onset of uterine ER expression, increased uterine luminal epithelial height (P < .05) but not uterine weight in the LGR7/8-positive uterus on PND 2. However, RLX increased both uterine weight and luminal epithelial height by PND 14 (P < .05), after overt endometrial ER expression. Aberrant ER activation between PND 0 and 14 alters the uterine organizational program and affects the function of adult porcine uterine tissues. Present data suggest that crosstalk between LGR7/8 and ER may be involved in estrogen-sensitive morphoregulatory events that are central to the development of an optimally functional adult uterus in the pig.

The extent to which relaxin promotes proliferation and inhibits apoptosis of cervical epithelial and stromal cells is greatest during late pregnancy in rats

Relaxin promotes marked growth of the cervix during the second half of rat pregnancy, and this growth is accompanied by an increase in both epithelial and stromal cells. The objective of this study was to test the hypothesis that the extent to which relaxin promotes proliferation and inhibits apoptosis of cervical cells is greatest during late pregnancy in rats. The influence of neutralization of circulating relaxin by iv injection of 5 mg monoclonal antibody against rat relaxin (MCA1) was examined at 3-d intervals throughout the second half of pregnancy. Controls were injected with either 5 mg monoclonal antibody against fluorescein or 0.5 ml PBS vehicle. To evaluate cell proliferation, 5'-bromo-2-deoxyuridine was injected sc 8 h before cervixes were collected. Terminal deoxynucleotidyl transferase-mediated deoxyuridine 5'-triphosphate nick end-labeling and electron microscopy were used to detect apoptotic cells. Neutralization of relaxin with MCA1 decreased the rate of proliferation and increased the rate of apoptosis of cervical cells by d 13. However, the extent to which relaxin influenced these processes was greatest and dramatic by late pregnancy. In MCA1-treated rats on d 22 of pregnancy, the rates of proliferation of both epithelial and stromal cells were less than 20% those in controls, and the rates of apoptosis in epithelial cells and stromal cells were more than 10- and 3-fold, respectively, greater than those in controls. In conclusion, this study provides evidence that the extent to which relaxin promotes proliferation and inhibits apoptosis of cervical epithelial and stromal cells is greatest during late pregnancy.

Cloning, characterization, and expression of the rat relaxin gene

Relaxin, a hormone in the insulin superfamily, is synthesized by the corpus luteum of the rat ovary. Expression of relaxin precursor mRNA in rats is sharply induced after day 10 of pregnancy and plateaus on days 15 to 20 (parturition occurs on day 23). In an effort to understand this induction, we cloned the gene and carried out promoter analyses by transient transfection and chromatin immunoprecipitation methods. The single gene is 2.9 kilobases and is composed of two exons and one intron. There are alternative splice acceptor sites, 3 base pairs apart, which account for the inclusion of an extra codon in about 10% of the transcripts. The induction of transcription by day 15 was observed by the binding of polymerase II and histone H3 acetylation at the promoter region. There is a functional STAT binding site, about 3.8 kb upstream from the transcriptional start site, that is occupied by STAT3 on day 6 of pregnancy, when relaxin expression is minimal; on day 15, when expression is maximal, STAT3 is replaced by STAT5a. These data are consistent with STAT5 playing a role in the induction of relaxin expression.

Cellular turnover in the rat uterine cervix and its relationship to estrogen and progesterone receptor dynamics

Histoarchitectural changes of the uterine cervix allow its successful adaptation to different physiological conditions. In this study, we evaluated cell turnover in each cellular compartment of the uterine cervix in association with steroid hormone receptor expression in order to establish the range of physiological changes. Proliferation, apoptosis, and progesterone receptor (PR) and estrogen receptor alpha (ERalpha) expression were evaluated in cycling, pregnant, and postpartum rats. In estrus and diestrus II, ERalpha and PR expression exhibited variations according to the region evaluated. Proliferation and apoptosis showed a reciprocal pattern, the epithelium being the region with higher cell turnover. High apoptotic index (AI) in estrus was associated with the lowest ERalpha and the highest PR scores. During pregnancy, proliferation of the epithelium was the predominant event and AI was low. On Postpartum Day 1 (PPD1), proliferation decreased while apoptosis increased. As described for the estrous cycle, during pregnancy and PPD1, AI and ERalpha were negatively correlated. In the fibroblastic stroma, low proliferation was observed throughout pregnancy; however, there was a net increase in cell number because very few cells underwent apoptosis. No difference in ERalpha was observed in fibroblastic cells during pregnancy and postpartum; however, a great decrease of this receptor in the epithelial compartment was observed after delivery. Unlike cervical epithelium, PR was highly expressed in stromal cells. At term, a dramatic increase in epithelial PR was observed. While epithelial PR remained high on PPD1, a decrease was observed in muscle stroma. These results show that, in all stages studied, 1) ERalpha and PR have different patterns of expression with differential responses to signals that modulate proliferation and/or apoptosis depending on the cellular compartment, and 2) even though the epithelium is the region with the highest cell turnover, the fibroblastic and muscle stroma are active regions that have their own patterns of behavior.

Relaxin increases secretion of tissue inhibitor of matrix metalloproteinase-1 and -2 during uterine and cervical growth and remodeling in the pig

Remodeling of reproductive organs during pregnancy requires degradation and resynthesis of structural barriers to cell invasion. Matrix metalloproteinases (MMPs) are enzymes that break down components of the extracellular matrix (ECM) and are essential for tissue remodeling processes. Tissue inhibitors of metalloproteinases (TIMPs) are important regulators of MMP activity. In the pig, relaxin stimulates growth and remodeling of the uterus and cervix during pregnancy, effects that include the ability to alter elements of the ECM. Therefore, the objective of this study was to determine whether relaxin alters the production and/or activity of TIMP-1 and TIMP-2 in the porcine uterus or cervix. The growth-promoting effects of relaxin were elicited by administering relaxin to prepubertal gilts every 6 h for 54 h. Expression of TIMP-1 and TIMP-2 was characterized by immunoblotting. Total enzyme activity was measured using an MMP-specific fluorescent substrate assay. TIMP-1 and TIMP-2 proteins were present in the uterus and cervix of control and relaxin-treated pigs, and both proteins were increased by relaxin in the uterine flushes and tissues (P < 0.05). Inhibitor activity in uterine tissue extracts and uterine flushes from relaxin-treated animals was greater than that in controls; however, this activity was restricted to inhibition of MMP-2. In the uterine cervix, relaxin enhanced expression of TIMP-1 and TIMP-2 (P < 0.05), whereas expression of both TIMP proteins was similar in the vaginal cervix of control and relaxin-treated animals. Likewise, inhibitor activity against MMP-2 in the uterine cervix was enhanced in response to relaxin (P < 0.05). In contrast, inhibitor activity was attenuated in extracts from the vaginal cervix (P < 0.05). This study highlights the complex nature of MMP/TIMP regulation during reproductive tissue growth and suggests that TIMP-1 and TIMP-2 may be involved in other aspects of the growth process. These data support a role for relaxin in regulating the activity of TIMPs during growth and remodeling of reproductive connective tissue.

Relaxin increases secretion of matrix metalloproteinase-2 and matrix metalloproteinase-9 during uterine and cervical growth and remodeling in the pig

Matrix metalloproteinases are proteolytic enzymes that degrade the extracellular matrix and are essential for tissue remodeling. Uterine and cervical growth require remodeling of structural barriers to cell invasion and matrix metalloproteinase-2 and -9 degrade type IV collagen, the major component of basement membranes. Relaxin stimulates uterine and cervical growth and remodeling, which includes remodeling of support elements such as basement membranes. The objective of this study was to determine whether relaxin alters the production and/or activity of matrix metalloproteinase-2 and -9 in the uterus or cervix of the pig. The growth-promoting effects of relaxin were elicited by administering relaxin to prepubertal gilts every 6 h for 54 h. The expression of matrix metalloproteinase-2 and matrix metalloproteinase-9 was characterized by gel zymography, and proteins were quantified by immunoblotting. Total enzyme activity was measured using matrix metalloproteinase-specific fluorescent substrate assays. In both uterine and cervical tissues, immunoreactive matrix metalloproteinase-2 and matrix metalloproteinase-9 protein expression was similar in relaxin-treated and control animals. However, tissue-associated gelatinase activity was attenuated by relaxin (P < 0.05). In contrast, relaxin significantly increased the secretion of active matrix metalloproteinase-2 and -9 protein into uterine fluid (P < 0.05). Given the importance of matrix metalloproteinases in extracellular matrix degradation, the observation that relaxin promotes uterine secretion of matrix metalloproteinase-2 and -9 supports the concept that relaxin facilitates the growth and remodeling of reproductive tissues by increasing extracellular proteolysis in the pig reproductive tract.

Inhibition of nitric oxide synthase activity diminishes the acute effects of relaxin on growth, but not softening, of the cervix in the rat

Relaxin promotes growth and softening of the cervix during pregnancy in the rat. This study examined the hypothesis that nitric oxide (NO) mediates the effects of relaxin on the rat cervix. To test that hypothesis, N omega-nitro-L-arginine methyl ester (L-NAME) was used to inhibit NO synthase, the enzyme that converts arginine to NO and L-citrulline. Nonpregnant rats were ovariectomized when they were 78 days old (day 1 of treatment). At ovariectomy each animal was fitted with silicon tubing implants containing progesterone (P) and estrogen (E) in doses that provide blood levels similar to those during late pregnancy. Rats were assigned to three treatment groups. The control group OPE (n = 6 rats) received 0.5 ml L-NAME vehicle (PBS) sc at 6-h intervals from 0600 h on day 7 through 1200 h on day 8 and 0.5 ml relaxin vehicle (PBS) sc at 0600 and 1200 h on day 8. Group OPER (n = 6 rats) was treated in the same way as group OPE, except that 20 microg porcine relaxin were administered. Group OPERI (n = 7 rats) was treated in the same way as group OPER, except that L-NAME was administered at a dose of 100 mg/kg x 6 h. Between 1400-1500 h on day 8, the cervices were removed and weighed. Cervical wet weight and extensibility were markedly greater (P < 0.01) in relaxin-treated group OPER rats than in group OPE controls. Treatment with L-NAME diminished relaxin's effects on cervical wet weight, but not cervical extensibility. In conclusion, this study provides evidence that NO contributes to the acute effects of relaxin on the growth, but not the softening, of the rat cervix.

Ruminant relaxin in the pregnant one-humped camel (Camelus dromedarius)

We have determined the cDNA sequence of preprorelaxin in the pregnant one-humped camel by employing reverse transcription- and rapid amplification of cDNA ends-polymerase chain reaction. Camel preprorelaxin consisted of 600 base pairs (bp) encoding a protein of 199 amino acids (aa) with a signal peptide of 25 aa (75 bp), a B domain of 28 aa (84 bp), a C domain of 121 aa (366 bp), and an A domain of 24 aa (72 bp). The N terminus of the C domain of camel prorelaxin contained the unique proline-rich repetitive sequence (-RPAP)(3)-(-K/RPAL-)(2), and within the B domain the classical -GRELVR- receptor binding motif was found. Camel preprorelaxin showed highest homology with porcine (74.6%) and equine (65.4%) relaxin. The ovary and the uteroplacental unit were a dual source of relaxin in the pregnant dromedary. Within the ovary, weak expression of relaxin was detected in large luteal cells of the mature corpus luteum. In the ovarian follicles, immunoreactive relaxin, but not relaxin mRNA, was detected in the granulosa and theca interna cell layer. Beginning at around Day 93 of gestation and coinciding with increasing interdigitation of the fetal villus with the underlying maternal endometrium, uterine luminal epithelial cells in the uteroplacental tissue expressed relaxin. Weak expression of immunoreactive relaxin, but not relaxin mRNA, was observed in villous trophoblast cells. Pseudostratified trophoblast cells at the base of the placental villi and multinucleate giant cells did not express relaxin.

Relationship of serum levels of endogenous relaxin to cervical size in the second trimester and to cervical ripening at term

OBJECTIVE

To assess whether cervical size in the early second trimester and cervical ripening at term may be related to serum levels of endogenous relaxin, 17beta-oestradiol or progesterone.

DESIGN

A cross-sectional study investigating the relationship between hormone concentrations and cervical parameters as measured by ultrasound and Bishop score, respectively.

PARTICIPANTS

Uncomplicated human pregnancies with normal fetal outcome, 72 women in the second trimester and 40 women at term.

METHODS

Vaginal ultrasound and palpation were used to estimate cervical parameters. Hormones were analysed either by dissociation-enhanced fluoroimmunoassay (relaxin) or by automated electrochemiluminescent immunoassays.

RESULTS

Cervical length and diameter correlated positively during mid-gestation and negatively at term. During mid-gestation, but not at term, relaxin was significantly associated with cervical length and volume, and with progesterone. Bishop score only correlated inversely with progesterone at term.

CONCLUSION

Corpus luteum function is reflected by progesterone and relaxin in the early second trimester. An impact of relaxin on cervical growth, previously demonstrated by animal models and in vitro experiments, was confirmed during human mid-gestation. In contrast to many other species, human cervical ripening was not associated with endogenous relaxin at term, but with decreased progesterone.

Canine preprorelaxin: nucleic acid sequence and localization within the canine placenta

Employing uteroplacental tissue at Day 35 of gestation, we determined the nucleic acid sequence of canine preprorelaxin using reverse transcription- and rapid amplification of cDNA ends-polymerase chain reaction. Canine preprorelaxin cDNA consisted of 534 base pairs encoding a protein of 177 amino acids with a signal peptide of 25 amino acids (aa), a B domain of 35 aa, a C domain of 93 aa, and an A domain of 24 aa. The putative receptor binding region in the N'-terminal part of the canine relaxin B domain GRDYVR contained two substitutions from the classical motif (E-->D and L-->Y). Canine preprorelaxin shared highest homology with porcine and equine preprorelaxin. Northern analysis revealed a 1-kilobase transcript present in total RNA of canine uteroplacental tissue but not of kidney tissue. Uteroplacental tissue from two bitches each at Days 30 and 35 of gestation were studied by in situ hybridization to localize relaxin mRNA. Immunohistochemistry for relaxin, cytokeratin, vimentin, and von Willebrand factor was performed on uteroplacental tissue at Day 30 of gestation. The basal cell layer at the core of the chorionic villi was devoid of relaxin mRNA and immunoreactive relaxin or vimentin but was immunopositive for cytokeratin and identified as cytotrophoblast cells. The cell layer surrounding the chorionic villi displayed specific hybridization signals for relaxin mRNA and immunoreactivity for relaxin and cytokeratin but not for vimentin, and was identified as syncytiotrophoblast. Those areas of the chorioallantoic tissue with most intense relaxin immunoreactivity were highly vascularized as demonstrated by immunoreactive von Willebrand factor expressed on vascular endothelium. The uterine glands and nonplacental uterine areas of the canine zonary girdle placenta were devoid of relaxin mRNA and relaxin. We conclude that the syncytiotrophoblast is the source of relaxin in the canine placenta.

Nucleic acid sequence of feline preprorelaxin and its localization within the feline placenta

The cat placenta is known to secrete large amounts of relaxin. We employed uteroplacental tissue at approximately Day 35 of gestation to determine the nucleic acid sequence of feline preprorelaxin using reverse transcription- and rapid amplification of cDNA ends-polymerase chain reaction. Feline preprorelaxin cDNA was found to consist of 540 base pairs encoding a protein of 180 amino acids (aa). We identified a signal peptide of 25 aa, a B domain of 33 aa, a C domain of 98 aa, and an A domain of 24 aa. The putative receptor binding region in the N'-terminal part of the B domain contained one substitution from the classical GRELVR motif (L-->F). Feline preprorelaxin shared highest homology with porcine and equine preprorelaxin. Northern analysis revealed a specific 1-kilobase transcript present in total RNA of feline uteroplacental tissue but not of liver tissue. Nonradioactive in situ hybridization was used to localize relaxin mRNA, and immunohistochemistry was used to localize the relaxin hormone and cytokeratin, in tissues of the feto-maternal interface recovered from two queens at Day 35 of gestation. Specific hybridization signals for relaxin mRNA were exclusively detected in cells located in the lamellar placental labyrinth but were absent from other placental and nonplacental uterine parts. The cells expressing relaxin mRNA also displayed immunoreactivity for cytokeratin and were, therefore, identified as trophoblast cells. Immunoreactive relaxin colocalized in those placental areas expressing relaxin mRNA. Trophoblast cells located at the villous chorioallantoic tips invading the endometrium and extravillous trophoblast cells in the junctional placental zone were devoid of relaxin.

Evidence that relaxin's effects on growth and softening of the cervix are not mediated through prostaglandins in the rat

Relaxin plays a major role in promoting the growth and softening of the cervix that occurs during the second half of pregnancy in the rat. There is limited evidence that prostaglandins play a role in cervical softening in mammalian species. Accordingly, this study was conducted to determine if prostaglandins mediate relaxin's effects on the rat cervix. To attain that objective, indomethacin was used to inhibit cyclooxygenase, the key enzyme in the conversion of arachidonic acid to prostaglandins. Twenty-six nonpregnant female rats were ovariectomized when they were 78 days old (day 1 of treatment). At ovariectomy (O), each rat was fitted with silicon tubing implants containing progesterone (P) and estrogen (E) in doses that provided blood levels similar to those during late pregnancy in rats. Rats were randomly assigned to three treatment groups. Group OPE controls (n = 8 rats) received 2 ml indomethacin vehicle (0.5% methyl cellulose, 0.025 Tween 80 in water) via gavage at 0900 h on days 8 and 9 and 0.5 ml relaxin vehicle (0.9% NaCl) s.c. at 6-h intervals from 1200 h on day 8 through 0600 h on day 10. Group OPER (n = 9 rats) was treated as group OPE except that 20 microg highly purified porcine relaxin was administered. Group OPERI (n = 9 rats) was treated as group OPER except that indomethacin was administered at a dose (20 mg/kg BW) that reduced cervical PGE2 levels by more than 90%. Between 0800 h and 1000 h on day 10, the cervices were removed, trimmed of fat, weighed, and placed in ice-cold Krebs-Ringer bicarbonate buffer, pH 7.5. Cervical extensibility (degree of softening) was determined within 4 h of tissue collection. Both the mean cervical wet weight and the mean cervical extensibility in the relaxin-treated group OPER rats were markedly greater (P < 0.01) than in the group OPE controls. Treatment with indomethacin did not diminish relaxin's effects on either cervical wet weight or cervical extensibility. In conclusion, this study provides evidence that relaxin's effects on cervical growth and softening in the rat are not mediated through prostaglandins.

Relaxin and estrogen synergistically accelerate growth and development in the uterine cervix of prepubertal pigs

This study was designed to determine the development and growth-promoting effects of relaxin with or without estrogen on the uterine cervix of prepubertal gilts. Twenty littermate gilts of similar body weight (33 +/- 3 kg; mean +/- SE) at 80 days of age were randomly assigned to four treatments: Vehicle (CONTROL, 1 ml PBS and 1 ml vegetable oil, n = 5); Relaxin (Relaxin, in PBS, 1 ml, 167 micrograms ml-1, n = 5); Estradiol Benzoate (EB, in vegetable oil, 1 ml, 2 mg ml-1, n = 5); and Relaxin plus EB (Relaxin + EB, at the same doses, n = 5), total six intramuscular injections for all treatments. Twenty four hours after the last injection, hysterectomy was performed, and the uterine tissues were immediately frozen at -80 degrees C. Samples were taken from the middle portions of the cervix and the uterine horns and dried to a constant weight to determine the dry weight and water concentration. Homogenates of uterine horns and cervices were analyzed for concentrations and contents of protein, hydroxyproline (collagen index) and DNA. Relaxin alone had no significant effect on any parameters (i.e., wet weight, Relaxin vs.

CONTROL

36 +/- 5 vs. 28 +/- 3 g uterus-1, dry weight 5.6 +/- 0.6 vs. 4.4 +/- 0.4 g uterus-1). EB alone increased significantly (P < 0.05) wet weight of the uterus (EB vs.

CONTROL

85 +/- 23 vs. 28 +/- 3 g uterus-1), dry weight (EB vs.

CONTROL

14.5 +/- 3 vs. 4.4 +/- 0.4 g uterus-1), and hydroxyproline content (EB vs.

CONTROL

47.2 +/- 13 vs. 12.6 +/- 4 mg cervix-1). In the presence of EB, relaxin treatment increased all measurements compared with CONTROL (i.e., wet weight, Relaxin + EB vs. EB: 136 +/- 34 vs. 28 +/- 3 g uterus-1). Compared with EB, Relaxin + EB significantly (P < 0.05) increased the uterine wet weight (Relaxin + EB vs. EB: 136 +/- 34 vs. 85 +/- 23 g uterus-1), the hydroxyproline content (Relaxin + EB vs. EB: 91 +/- 29 vs. 47 +/- 13 mg cervix-1), and DNA content (Relaxin + EB vs. EB: 8.1 +/- 2 vs. 5.4 +/- 1 mg cervix-1). These results indicate that the growth-promoting effects of relaxin on the uterus and cervix may be, at least partly, estrogen-dependent and that the growth and development of the uterus and cervix can be accelerated by a combination of relaxin and estrogen treatment.

Placental localization of relaxin in the pregnant mare

In situ hybridization employing a cRNA probe derived from a 428-bp fragment of equine relaxin was used to localize relaxin mRNA, and immunocytochemistry was used to localize relaxin itself, in tissues of the placenta-endometrium interface recovered between 33 and 153 days of gestation from mares carrying intraspecific horse, interspecific mule and extraspecific donkey conceptuses. Immunocytochemical staining was also used to localize trophoblast-specific and class I major histocompatibility complex (MHC) antigens on some specimens. Relaxin mRNA and relaxin were both present in the single-cell non-invasive trophoblast layer of the allantochorion between 45 and 153 days of gestation in all three types of equine pregnancy examined. Both, however, were absent from the invasive trophoblast cells of the progenitor chorionic girdle and the differentiated trophoblast cells of the endometrial cups throughout the latters' 60-80-day period of development and regression. Discrete and irregularly spaced clusters of elongated pseudostratified trophoblast cells on the allantochorion remained negative for relaxin mRNA and ligand, but stained strongly for equine trophoblast-specific antigens. These areolae-like structures of the mature horse placenta overlie the mouths of endometrial glands between adjacent microcotyledons and they are clearly involved with the uptake of uterine milk for fetal sustenance. It is speculated that their loose attachment to the endometrium and weak expression of class 1 MHC antigens may serve to tolerize the mother to the paternally-inherited histocompatibility antigens of the fetus.

Relaxin: a pleiotropic hormone

1. Relaxin is a peptide hormone of about 6000 Da belonging to the insulin family. Like insulin, relaxin is composed by two disulfide-linked chains, termed the A and B chains, the B chain bearing the receptor interaction site. 2. Relaxin is produced primarily by the corpus luteum, in both pregnant and nonpregnant females. It attains the highest plasma levels during pregnancy. In this condition, relaxin is also produced by the decidua and placenta. In males, relaxin is synthesized in the prostate and released in the seminal fluid. An additional source of relaxin has recently been identified in the heart atria. 3. Relaxin has a broad range of biologic activities, some of which have been known for a long time. These latter ones include: (a) the induction of collagen remodeling and consequent softening of the tissues of the birth canal in view of delivery; (b) the inhibition of uterine contractile activity; (c) the stimulation of growth and differentiation of the mammary gland. 4. In more recent years, novel sites of relaxin action have been recognized. In particular, it has been shown that relaxin: (a) regulates growth and differentiation of breast cancer cells in culture; (b) promotes dilation of blood vessels in several organs and tissues, including the uterus, the mammary gland, the lung and the heart; (c) has a chronotropic action on the heart; (d) inhibits the release of histamine by mast cells, thus being able to counteract experimental allergic asthma; (d) depresses aggregation of platelets and their release by megakaryocytes; (e) influences the secretion of hormones by the pituitary gland; and (f) contributes to the regulation of fluid balance. 5. Concerning the mechanisms of action of relaxin, stimulation of nitric oxide generation, with consequent rise in intracellular cyclic GMP levels, and stimulation of cyclic AMP production have been demonstrated to occur in the target cells and organs. 6. It may be expected that the next decade will provide answers about the utility of relaxin, in terms of insight into the actual physiologic functions of relaxin in the animal kingdom and especially in man, in view of possible therapeutic use of relaxin or relaxin-derived drugs in human disease, especially considering that human recombinant relaxin is now available for clinical experimentation.

Proteoglycans and hyaluronan in female reproductive organs

Proteoglycans and hyaluronan have been isolated from various female reproductive organs and fetal membranes. Special attention has been directed to changes in the composition of these molecules in the tissue during pregnancy and ovulation. Various chondroitin sulfate/dermatan sulfate proteoglycans, which represent extracellular matrix proteoglycans, are closely related to the organization of connective tissues. Heparan sulfate proteoglycans are widely distributed on the plasma membrane of most mammalian cells including those in the female reproductive organs. They are involved in various aspects of cell-to-cell or cell-to-extracellular matrix interactions. Although the precise biological functions of these proteoglycans are not currently clear, recent advances in biochemistry and molecular biology techniques promise an exciting new development in this area.

The disposition of a human relaxin (hRlx-2) in pregnant and nonpregnant rats

The pharmacokinetics and tissue distribution of a human relaxin were investigated after intravenous (iv) bolus administration to pregnant or nonpregnant rats. Human gene-2 relaxin (hRlx-2) serum concentrations after iv bolus administration were described as the sum of three exponentials. The pharmacokinetics were comparable in pregnant and nonpregnant rats. The serum clearance (CL) was 7.4-10.2 ml/min/kg at doses of 46-93 micrograms/kg and was linear in this range. The half-lives were 1.1-2.0, 15.1-16.4, and 53.7-67.9 min, respectively. The volume of the central compartment (Vc) was 48-79 ml/kg and the volume of distribution at steady state (Vss) was 271-336 ml/kg. Increasing the dose to 463 micrograms/kg increased the dose-corrected area under the serum concentration-time curve and significantly decreased CL and Vss. The distribution of radioactivity in the tissues of pregnant rats was followed after iv bolus dosing with hRlx-2 internally labeled with 35S-cysteine. Comparison of the extent of organ uptake of radiolabel after 35S-hRlx-2 or 35S-cysteine administration suggested that the kidneys were the principal site of uptake; the liver was of secondary importance. In perfusion experiments utilizing livers isolated from pregnant or nonpregnant rats, 36-52% of the dose of hRlx-2 was cleared from the perfusate in 2 hr. These studies showed that the pharmacokinetics of hRlx-2 in rats appeared to be unaffected by pregnancy and suggested that the kidneys and liver both play a role in the elimination of hRlx-2.

Stimulation of DNA synthesis in rat uterine cells by growth factors and uterine extracts

Replicative DNA synthesis, as measured by thymidine incorporation, has been measured in rat uterine cells in primary culture in response to growth factors. Insulin, insulin-like growth factor-I (IGF-I), multiplication-stimulating activity (MSA) and platelet-derived growth factor (PDGF) stimulated DNA synthesis, while estradiol, epidermal growth factor (EGF), transforming growth factor-beta (TGF-beta), basic fibroblast growth factor (bFGF) and relaxin did not stimulate or did so weakly and only at very high concentrations. Uterine acid extracts also stimulated DNA synthesis. IGF-I stimulated at concentrations consistent with its acting through the IGF-I receptor; however, insulin stimulated at concentrations higher than expected for its acting through its receptor and this its action may be mediated through the IGF-I receptor. IGF-I was found in uterine tissue by radioimmunoassay (RIA). There was a 5- to 10-fold increase in IGF-I in the uteri from ovariectomized rats that had been treated with estradiol 24 h earlier. This is analogous to the increase in growth factor activity found previously in rat uterus after 24-h estradiol treatment (Beck, C.A. and Garner, C.W. (1989) Mol. Cell. Endocrinol. 63, 93-101). These data are consistent with the hypothesis that estradiol effects in the uterus are in part mediated through IGF-I.

Differential regulation of insulin-like growth factor binding protein secretion from human decidual cells by IGF-I, insulin, and relaxin

Several growth hormone-independent 25-31,000 kD insulin-like growth factor binding proteins (IGF-BPs) have been identified in plasma, extravascular fluids, and various cell-conditioned media. Cultured human decidual cells release three IGF-BPs with 24,000, 30,000, and 34,000 Mr. Using ligand blot analysis and an RIA for the 30,000-Mr form (IGF-BP-1), we examined the effects of IGF-I (10-1,000 ng/ml), insulin (10-10,000 ng/ml), and relaxin (10-250 ng/ml) on decidual cell IGF-BP release after 120 h of hormone exposure. IGF-I inhibited release of both IGF-BP-1 and the 24,000 Mr form. Inhibition of IGF-BP-1 release was noted after 48 h of treatment and was progressive throughout the subsequent 120 h. Insulin stimulated a fourfold increase in release of the 24,000-Mr protein while inhibiting IGF-BP-1 release comparable to IGF-I, alpha-IR3, a monoclonal antibody to the IGF-I receptor, blocked approximately 33% of the IGF-I response but had no effect on insulin-mediated IGF-BP-1 inhibition. Relaxin stimulated a 2.4-fold increase in release of the 24,000-Mr form and a 16-fold increase in the 30,000-Mr protein after 120 h. Stimulation of the 30,000-Mr protein was inhibited by the addition of cycloheximide (50 micrograms/ml). Both IGF-I and insulin also blocked the relaxin-mediated increase in IGF-BP-1. These studies suggest that three structurally related proteins differentially regulate IGF-BP secretion possibly via activation of distinct receptor subtypes.