There are two human relaxin genes: H1 is likely to be a pseudogene. Research
conducted since the early 1980s has established that the hormone relaxin is
essential during pregnancy . Two vital
roles for relaxin during pregnancy have been identified. Relaxin promotes
growth and softening of the uterine cervix and thereby enables rapid and safe
delivery in both rats and pigs. Relaxin also promotes growth and
development of the mammary apparatus. Hsu SY, t al 2002 reported the activation of orphan receptors by the hormone relaxin.
Relaxin is a hormone important for the growth and remodeling of reproductive and
other tissues during pregnancy. Although binding sites for relaxin are widely
distributed, the nature of its receptor has been elusive. Here, we demonstrate that two
orphan heterotrimeric guanine nucleotide binding protein (G protein)-coupled
receptors, LGR7 and LGR8, are capable of mediating the action of relaxin through an
adenosine 3',5'-monophosphate (cAMP)-dependent pathway distinct from that of the
structurally related insulin and insulin-like growth factor family ligand. Treatment of
antepartum mice with the soluble ligand-binding region of LGR7 caused parturition
delay. The wide and divergent distribution of the two relaxin receptors implicates
their roles in reproductive, brain, renal, cardiovascular, and other functions.
Sherwood OD 2004 reviewerd Relaxin's Physiological Roles and Other Diverse Actions.
Endocr Rev.
NCBI Summary:
This gene encodes a member of the relaxin subfamily and insulin superfamily of peptide hormones. In humans there are three non-allelic relaxin genes. This gene encodes multiple protein isoforms, at least one of which undergoes proteolytic processing. This processing generates relaxin A and B chains that are linked by disulfide bonds to form the mature peptide hormone. This hormone plays a role in the male and female reproductive systems and was initially noted for its role in pregnancy. This protein also plays broader roles in the cardiovascular system, including in the regulation of blood pressure and control of heart rate, and data from animal models shows that this protein may have anti-fibrotic and cardioprotective effects. [provided by RefSeq, Jul 2016]
General function
Ligand, Hormone
Comment
Serelaxin, recombinant human relaxin-2, for treatment of acute heart failure (RELAX-AHF): a randomised, placebo-controlled trial. Teerlink JR et al. BACKGROUND: Serelaxin, recombinant human relaxin-2, is a vasoactive peptide hormone with many biological and haemodynamic effects. In a pilot study, serelaxin was safe and well tolerated with positive clinical outcome signals in patients with acute heart failure. The RELAX-AHF trial tested the hypothesis that serelaxin-treated patients would have greater dyspnoea relief compared with patients treated with standard care and placebo. METHODS: RELAX-AHF was an international, double-blind, placebo-controlled trial, enrolling patients admitted to hospital for acute heart failure who were randomly assigned (1:1) via a central randomisation scheme blocked by study centre to standard care plus 48-h intravenous infusions of placebo or serelaxin (30 ?g/kg per day) within 16 h from presentation. All patients had dyspnoea, congestion on chest radiograph, increased brain natriuretic peptide (BNP) or N-terminal prohormone of BNP, mild-to-moderate renal insufficiency, and systolic blood pressure greater than 125 mm Hg. Patients, personnel administering study drug, and those undertaking study-related assessments were masked to treatment assignment. The primary endpoints evaluating dyspnoea improvement were change from baseline in the visual analogue scale area under the curve (VAS AUC) to day 5 and the proportion of patients with moderate or marked dyspnoea improvement measured by Likert scale during the first 24 h, both analysed by intention to treat. This trial is registered at ClinicalTrials.gov, NCT00520806. FINDINGS: 1161 patients were randomly assigned to serelaxin (n=581) or placebo (n=580). Serelaxin improved the VAS AUC primary dyspnoea endpoint (448 mm??h, 95% CI 120-775; p=0?007) compared with placebo, but had no significant effect on the other primary endpoint (Likert scale; placebo, 150 patients [26%]; serelaxin, 156 [27%]; p=0?70). No significant effects were recorded for the secondary endpoints of cardiovascular death or readmission to hospital for heart failure or renal failure (placebo, 75 events [60-day Kaplan-Meier estimate, 13?0%]; serelaxin, 76 events [13?2%]; hazard ratio [HR] 1?02 [0?74-1?41], p=0?89] or days alive out of the hospital up to day 60 (placebo, 47?7 [SD 12?1] days; serelaxin, 48?3 [11?6]; p=0?37). Serelaxin treatment was associated with significant reductions of other prespecified additional endpoints, including fewer deaths at day 180 (placebo, 65 deaths; serelaxin, 42; HR 0?63, 95% CI 0?42-0?93; p=0?019). INTERPRETATION: Treatment of acute heart failure with serelaxin was associated with dyspnoea relief and improvement in other clinical outcomes, but had no effect on readmission to hospital. Serelaxin treatment was well tolerated and safe, supported by the reduced 180-day mortality. FUNDING: Corthera, a Novartis affiliate company.
Cellular localization
Secreted
Comment
Serelaxin as a potential treatment for renal dysfunction in cirrhosis: Preclinical evaluation and results of a randomized phase 2 trial. Snowdon VK et al. (2017) Chronic liver scarring from any cause leads to cirrhosis, portal hypertension, and a progressive decline in renal blood flow and renal function. Extreme renal vasoconstriction characterizes hepatorenal syndrome, a functional and potentially reversible form of acute kidney injury in patients with advanced cirrhosis, but current therapy with systemic vasoconstrictors is ineffective in a substantial proportion of patients and is limited by ischemic adverse events. Serelaxin (recombinant human relaxin-2) is a peptide molecule with anti-fibrotic and vasoprotective properties that binds to relaxin family peptide receptor-1 (RXFP1) and has been shown to increase renal perfusion in healthy human volunteers. We hypothesized that serelaxin could ameliorate renal vasoconstriction and renal dysfunction in patients with cirrhosis and portal hypertension. To establish preclinical proof of concept, we developed two independent rat models of cirrhosis that were characterized by progressive reduction in renal blood flow and glomerular filtration rate and showed evidence of renal endothelial dysfunction. We then set out to further explore and validate our hypothesis in a phase 2 randomized open-label parallel-group study in male and female patients with alcohol-related cirrhosis and portal hypertension. Forty patients were randomized 1:1 to treatment with serelaxin intravenous (i.v.) infusion (for 60 min at 80 μg/kg/d and then 60 min at 30 μg/kg/d) or terlipressin (single 2-mg i.v. bolus), and the regional hemodynamic effects were quantified by phase contrast magnetic resonance angiography at baseline and after 120 min. The primary endpoint was the change from baseline in total renal artery blood flow. Therapeutic targeting of renal vasoconstriction with serelaxin in the rat models increased kidney perfusion, oxygenation, and function through reduction in renal vascular resistance, reversal of endothelial dysfunction, and increased activation of the AKT/eNOS/NO signaling pathway in the kidney. In the randomized clinical study, infusion of serelaxin for 120 min increased total renal arterial blood flow by 65% (95% CI 40%, 95%; p < 0.001) from baseline. Administration of serelaxin was safe and well tolerated, with no detrimental effect on systemic blood pressure or hepatic perfusion. The clinical study's main limitations were the relatively small sample size and stable, well-compensated population. Our mechanistic findings in rat models and exploratory study in human cirrhosis suggest the therapeutic potential of selective renal vasodilation using serelaxin as a new treatment for renal dysfunction in cirrhosis, although further validation in patients with more advanced cirrhosis and renal dysfunction is required. ClinicalTrials.gov NCT01640964.//////////////////
Ovarian function
Follicle development, Primary follicle growth, Ovulation, Follicle rupture, Early embryo development
Comment
In vitro effects of relaxin on gene expression in porcine cumulus-oocyte complexes and developing embryos. Feugang JM et al. ABSTRACT: BACKGROUND: Relaxin hormone peptide is found in porcine follicular and utero-tubal fluids, but its possible actions during early embryo development are still undetermined. Here, we investigated the effects of porcine relaxin during oocyte maturation and embryo development, and gene expression in the pig. METHODS: Immature cumulus-oocyte complexes (COCs) were obtained from ovarian follicles of sows. In experiment 1, COCs were matured in the presence of 0, 20, or 40 ng relaxin/ml, or 10% (v/v) porcine follicular fluid. In experiment 2, COCs were in vitro matured, fertilized and resulting embryos were cultured in the presence of 0, 20, or 40 ng relaxin/ml. In experiment 3, COCs were matured in the presence of 40 ng relaxin/ml, fertilized and zygotes were cultured as indicated in experiment 2. We evaluated the proportions of matured oocytes in experiment 1, cleaved and blastocysts on Day 2 and Day 7 post insemination in all experiments. The total cell number of blastocysts was also evaluated. In parallel, transcription levels of both relaxin and its receptors (RXFP1 and RXFP2), as well as a pro- (Bax) and anti- (Bcl2-like 1) apoptotic-related genes were determined. All data were analyzed by ANOVA and significant differences were fixed for P<0.05. RESULTS: In experiment 1, relaxin significantly increased the proportions of matured oocytes and cleaved embryos, as well as the expression level of RXFP2 mRNA compared to RXFP1 (P<0.05). There was no effect on endogenous expression of relaxin and Bcl2-like1/Bax ratios. In all experiments, relaxin did not affect the proportions of blastocysts, but did significantly increase their total cell numbers (P<0.05). Furthermore, no effect of relaxin was observed on Bcl2-like1/Bax expression ratios, which were similar between groups. CONCLUSIONS: Exogenous relaxin influences its own receptors expression, improves oocyte nuclear maturation. Its beneficial effect on total cell number of blastocysts appears to be through a Bcl2-like1/Bax-independent mechanism.////////////The effect of relaxin supplementation of in vitro maturation medium on the development of cat oocytes obtained from ovaries stored at 4C. Luu VV et al. Relaxin is a member of the insulin-like family of hormones that promotes growth in a number of reproductive tissues, including the granulosa and theca cells. Cat oocytes collected from cold-stored ovaries remain capable of maturing in vitro, but the developmental ability of the oocytes decreases after 24h of cold storage. To improve the developmental ability of cat oocytes from cold-stored ovaries, we investigated the effect of relaxin supplementation of maturation medium on their meiotic ability and subsequent development. Cat oocytes were collected from ovaries stored at 4C for one day and cultured in maturation medium supplemented with different concentrations (0, 10, 20, and 40ng/ml) of relaxin for 24h. They were then fertilized in vitro for 12h with frozen-thawed spermatozoa. After in vitro fertilization, the zygotes were cultured in synthetic oviduct fluid medium for 8 days. There were no significant differences in the maturation rates and glutathione contents of oocytes among the groups, irrespective of relaxin supplementation. The rate of blastocyst formation from oocytes matured with 10ng/ml relaxin (16.0%) was higher (p<0.05) than that from oocytes matured without relaxin (5.9%). Our findings indicate that supplementation of 10ng/ml relaxin into maturation medium may improve blastocyst formation of cat oocytes after in vitro fertilization.
Effects of Recombinant Relaxin on In Vitro Maturation of Porcine Oocytes. Kim HS et al. Relaxin, a member of the insulin superfamily, has diverse functions in both reproductive and nonreproductive tissues. The aim of the present study was to evaluate the effects of recombinant relaxin on the in vitro maturation of porcine oocytes and their subsequent embryonic development following in vitro fertilization. Three concentrations of relaxin (1, 10, and 100 ng/ml) were used in the in vitro maturation (IVM) medium ;TCM supplemented with 10% (v/v) porcine follicular fluid, 10 ng/ml of epidermal growth factor, 4 IU/ml of pregnant mare serum gonadotropin, and (only for the first 22 hr) 4 IU/ml of hCG. Relaxin was used during the entire IVM period. Nuclear maturation of oocytes was examined under ultraviolet light following staining with bisbenzimide (Hoechst 33342) for 5 min and mounted on a glass slide. The glutathione (GSH) content in oocytes, an important indicator of cytoplasmic maturity, was measured using a micro-glutathione assay. Cryopreserved boar semen was used for in vitro fertilization. Embryos were cultured in modified NCSU-23 medium supplemented with 0.5 mM pyruvate and 5 mM lactate. Although nuclear maturation of oocytes did not vary, the GSH content in oocytes was significantly higher when cultured with 1 ng/ml (7.9 pmol/oocyte) and 10 ng/ml (8.47 pmol/oocyte) compared to a control group. However, no additional beneficial effect was observed when 100 ng/ml of relaxin was added to the IVM medium. A significantly higher rate of blastocyst formation was observed with 10 ng of relaxin (32.4%) compared to the control (14.4%) or 100 ng of relaxin (21.4%). No difference between 1 ng and 10 ng was observed in terms of the blastocyst production rate. The inner cell mass cell numbers in relaxin-treated groups were significantly higher than control, and trophectoderm cell number was the highest in the 10 ng relaxin group. Relaxin (10 ng/ml) can be supplemented in IVM medium to support the maturation of porcine oocytes. Too CK, et al reported that relaxin increases the release of plasminogen activator,
collagenase, and proteoglycanase from rat granulosa cells
in vitro.
Relaxin (Rlx) is shown in vitro to increase the release of plasminogen
activator (PA) activity from granulosa cells obtained from 28-day-old rats
after priming 48 h before with PMSG. Priming with PMSG was essential for
the subsequent marked increase in PA by the addition of Rlx to these cells in
vitro. Under the same conditions Rlx also increased the release of both total
collagenase and total proteoglycanase activities but not of beta-glucuronidase
activity. The total collagenase and proteoglycanase activities of control cells
are made up of essentially equal amounts of their respective active and latent
enzymes. Rlx stimulation increases the amounts of the respective active
enzymes while the latent collagenase and proteoglycanase activities are
unchanged or decreased, respectively. The enzyme beta-glucuronidase was
not stimulated by Rlx and appears not to be involved in follicular
proteoglycan degradation. The
PA response to FSH is lost by 60 h after PMSG at the same time that the
response to prostaglandin E1 is maintained at the same level, whereas that to
Rlx and LH, although still significantly higher than controls, were decreased.
By 70 h after PMSG, postovulatory, the responses to all hormones studied
were lost. Thus, the involvement of PA in ovarian connective tissue alterations
appears to be greatest in the period of follicular antrum formation rather than
just before ovulation. Rlx is one of a number of hormones involved in the
sequence of events culminating in follicle connective tissue remodeling as
shown by its action on the release of three intrafollicular enzymes.
Norstrom A et al reported hormonal effects on collagenolytic activity in the isolated
human ovarian follicular wall.
Tissue pieces from the wall (i.e. tunica albuginea with adjacent theca externa)
of human follicles were incubated with and without various hormones and
their potential influence upon the collagenolytic activity was evaluated.
Following incubation the collagenase activity was determined in the incubation
medium by measurement of the hydrolytic activity against the synthetic
peptide 2,4-dinitrophenyl-Pro-Gln-Gly-Ile-Ala-Gly-Gln-D-Arg-OH.
Stimulated collagenolytic activity was seen in the presence of relaxin and
oxytocin whereas prostaglandin E2, prostaglandin F2 alpha, progesterone
and 17 beta-estradiol were without effect. It is concluded that the stimulated
collagenolytic activity induced by relaxin and oxytocin may be of importance
for the degradation of collagen which occurs prior to follicular rupture.
Expression regulated by
LH
Comment
Gagliardi CL, et al 1992 reported that human chorionic gonadotropin stimulation of relaxin
secretion by luteinized human granulosa cells.
Luteinized human GC obtained at the time of oocyte retrieval secrete relaxin
in response to hCG stimulation and secrete P under both basal and
hCG-stimulated conditions, thereby serving as a model to explore luteal
function and control.
Brannstrom M, et al 1993 reported that relaxin induces ovulations in the in-vitro perfused rat ovary.
The effects of human recombinant relaxin on ovulation and ovarian steroidogenesis
were investigated in vitro using a perfused rat ovary model. Ovaries of equine
chorionic gonadotrophin (ECG; 20 IU)-primed Sprague-Dawley rats were perfused
for 21 h. Ovarian release of oestradiol and progesterone was measured during the
perfusion period and the number of ovulations was estimated by counting the released
oocytes at termination of the experiment. Non-treated control ovaries did not ovulate
whereas addition of ovine luteinizing hormone (LH; 100 ng/ml) resulted in a mean
(+/- SEM) number of ovulations of 3.0 +/- 0.8 from all treated ovaries. Relaxin (10
micrograms/ml) induced mean (+/- SEM) number of ovulations at 2.4 +/- 0.2 in all
treated ovaries but did not further increase the ovulation rate when combined with LH
(mean +/- SEM 3.2 +/- 0.4). All ovulated oocytes in the groups stimulated by LH
showed signs of nuclear maturation (germinal vesicle breakdown) when harvested, in
contrast to ovulated oocytes in the relaxin group, which were immature (presence of
germinal vesicle). Progesterone and oestradiol release was significantly increased in
the LH-stimulated groups but not in the group treated only with relaxin, in comparison to the untreated control group. These results demonstrate that relaxin may have a
paracrine role within the ovary and may facilitate ovulation, possibly by promoting
connective tissue remodelling of the follicle wall.
The association between follicular fluid levels of cathepsin B, relaxin or AMH with clinical pregnancy rates in infertile patients. Bastu E et al. (2015) The aim of this study was to investigate the relationship of cathepsin B, relaxin and anti-Mullerian hormone (AMH) in follicular fluid (FF) with pregnancy rates in infertility patients. Seventy-nine infertile couples who underwent ICSI were included in the study. The FF levels of cathepsin B, relaxin and AMH were measured using ELISA kits. The FF cathepsin B levels were statistically higher in pregnant patients compared with non-pregnant patients (0.20±0.13 versus 0.13±0.03; P<0.001). There were statistically significant differences in the total number of oocytes (10.00±6.85 versus 5.96±3.94); the mean number of M2 oocytes (8.65±5.63 versus 4.58±3.36) between the pregnant and non-pregnant patients (P<0.05). There were no significant correlations between pregnancy rates and relaxin and AMH (P>0.05). The area under the curve of cathepsin B for prediction of pregnancy was 0.662 (p=0.024, 95% Confidence Interval 0.528-0.797). This study demonstrated that increased level of cathepsin B in FF significantly correlates with a better chance of clinical pregnancy. Further studies are needed to clarify the role of cathepsin B in the reproductive process of humans.//////////////////
O'Byrne EM, et al 1978 reported relaxin bioactivity and immunoactivity in human corpora lutea.
Bagnell CA, et al 1987 reported localization of relaxin in the pig follicle during preovulatory development
The avidin-biotin immunoperoxidase method and antisera to purified porcine relaxin were used to localize relaxin in sections of follicles from pregnant mare's serum gonadotropin (PMSG)/human chorionic gonadotropin (hCG)-primed pigs during preovulatory development. Prepubertal pigs were treated i.m. with PMSG (750 IU) and 72 h later with hCG (500 IU) to induce follicular development and ovulation. Follicles were collected from untreated gilts or from gilts 24, 48, 60, 72, 84, 96, or 108 h after PMSG treatment. Light immunostaining in the theca interna was observed early in follicular development, at 48 and 60 h post-PMSG. At 72 h post-PMSG, relaxin immunostaining in the theca interna of the preovulatory follicle was more intense. After hCG treatment, the intense thecal immunostaining persisted and was apparent 84 and 96 h after PMSG. At about 6 h prior to expected ovulation (108 h post-PMSG), there was thinning of the follicle wall and a reduction in relaxin immunostaining in the theca interna. Immunoactive relaxin was not detected in follicles from untreated gilts, follicles 24 h post-PMSG, small healthy or atretic follicles, or in granulosa cells, theca externa or ovarian stroma, at any of the time points studied. These studies support the hypothesis that the theca interna is the primary source of follicular relaxin and provide further evidence for a paracrine role for relaxin in the ovulatory process.
Follicle stages
Primordial, Primary, Secondary, Corpus luteum
Comment
Stewart DR, et al 1990 reported that
relaxin in peripheral blood was determined in
conceptive and non-conceptive cycles using a sensitive and specific
double-antibody enzyme-linked immunoassay for human relaxin. In three
conceptive cycles, relaxin was significantly elevated over baseline 9-10 days
following the LH peak. Relaxin concentrations quickly rose over the next 15
days of observation to over 800 pg/ml. Relaxin was observed to increase 1
to 2 days prior to the first detectable increase in plasma hCG as measured by
enzyme-linked immunosorbent assay. To compare the relaxin profile in
conceptive cycles with normal luteal phase concentrations, relaxin was also
measured in daily plasma samples collected from women contracepting with
barrier methods, bilateral tubal ligation, or abstinence. A small but consistent
rise in relaxin in the late luteal phase was observed in nine of eleven women,
which began 6-9 days after the LH peak, averaged approximately 50 pg/ml,
and was declining by the next menses. It is concluded that a small but
measurable rise in plasma relaxin is associated with the normal luteal phase
and that relaxin secretion is accelerated around the time that hCG is first
detected in conceptive cycles.
Early Human Preantral Follicles Have Relaxin and Relaxin Receptor (LGR7) and Relaxin Promotes their Development.
Shirota K, et al .
The regulatory mechanisms of early follicle development are not clearly understood. Although relaxin is a peptide that controls cell proliferation and differentiation in many tissues, its role in human follicular development is unclear. In this study we cultured slices of human ovarian cortical tissue in the presence and absence of recombinant human relaxin. Ovarian tissue was obtained by biopsy during gynecological laparotomy or laparoscopy (14 women, mean age +/- SEM: 29.0 +/- 6.1 yr, range: 17-37 yr). A significantly higher proportion of secondary follicles (14.5% vs. 5.0% in the control group, P < 0.01) and a significantly decreased proportion of primordial follicles (30.1% vs. 47.4% in the control group, P < 0.05) were found in tissues cultured with relaxin for 7 days. Immunocytochemical studies with the anti-C-peptide of prorelaxin and anti-relaxin antibodies revealed the localization of relaxin in the oocyte, flat pre-granulosa and granulosa cells of primordial, primary and secondary follicles. The presence of the relaxin receptor LGR7 was observed in flat pre-granulosa and granulosa cells of primordial, primary and secondary follicles by immunocytochemical and in situ hybridization analyses. These results suggest that relaxin plays a role through its receptor during the early stage of follicle development.
Phenotypes
Mutations
1 mutations
Species: mouse
Mutation name: relaxin knockout mouse
type: null mutation fertility: fertile Comment: The majority of relaxin null mice are fertile and produce normal litters. However their mammary development is deficient; pups are unable to suckle and die within 24 h of birth (Zhao et al., 1999).