Rln3a is a prerequisite for spermatogenesis and fertility in male fish

The essential roles of Relaxin3 (RLN3) in energy homeostasis had been well investigated, while the mechanisms of RLN3 regulating reproduction remain to be elusive in mammals. Although two rln3 paralogues have been characterized in several teleosts, their functions still remain largely unknown. In this study, two paralogous rln3 genes, represented as rln3a and rln3b, were identified from the testis of Nile tilapia (Oreochromis niloticus). Rln3a was dominantly expressed in testis, while the most abundant rln3b expression was in brain. In situ hybridization demonstrated that rln3a is abundantly expressed in the Leydig cells of the testis. To understand the role of Rln3 in the testicular development, homologous null-rln3a gene mutant line was constructed by CRISPR/Cas9 technology. Morphological observation demonstrated that null mutation of rln3a gene caused testicular hypertrophy and a significant increase of GSI. However, a significant decrease of spermatogenic cells at different phases, i.e. spermatogonia, spermatocytes, spermatids and sperms was found. Silencing of rln3a gene repressed the expression of key genes in germ cell and Leydig cell. Deficiency of Rln3a led to the significant decrease of 11-KT production, which stimulated the up-regulation of both FSH and LH production in the pituitary via a negative feedback manner possibly. Mutation of rln3a in XY fish led to the hypogonadism with sperm deformation, significant decrease of fertility, and sperm motility, revealing as the high mortality of the offspring obtained by crossing the wild type female and rln3a^-/- XY fish. Interestingly, recombinant human RLN3 injection significantly enhanced the sperm motility in rln3a^-/- XY fish. Moreover, hCG treatment stimulated the expression of steroidogenic enzyme genes and 11-KT production, which were repressed by rln3a mutation in XY fish. Taken together, this study, for the first time by using a gene knockout model, proved that Rln3a is an indispensable mediator for androgen production in testis via HPG axis, and plays an essential role in spermatogenesis, sperm motility and male fertility in fish.

USP4 promotes invasion of breast cancer cells via Relaxin/TGF-β1/Smad2/MMP-9 signal

OBJECTIVE

Ubiquitin-specific protease 4 (USP4) is a deubiquitinating enzyme with key roles in the regulation of TGF-β1 signaling, suggesting its importance in tumorigenesis. However, the underlying mechanisms causing this are not entirely clear. In the present study, we investigated the effect of USP4 on invasion and tumorigenesis of breast cancer cells, and explored its mechanism.

MATERIALS AND METHODS

Effects of USP4 overexpression or USP4 silencing by small interfering RNA (USP4 siRNA) on invasion of breast cancer MDA-MB-231 and T47D cells in vitro was detected. Using siRNAs and inhibitors to examine the USP4 signaling pathway.

RESULTS

The migration and invasion assays showed that USP4 promotes human breast cancer cell migration and invasion by USP4 overexpression, and knockdown of USP4 by siRNA inhibits human breast cancer cell migration and invasion. Treatment with RLX siRNAs, TGF-β1 siRNAs, Smad2 siRNAs or BB94 (MMPs inhibitor) to USP4-overexpressing breast cancer cells revealed that USP4- induced RLX via TGF-β1 pathway promotes the cell migration and invasion. Further studies demonstrated that USP4-mediated TGF-β1 activation not only enhances the phosphorylation of Smad2 through TGF-β, but also directly upregulate matrix metalloproteinase (MMP)-9-mediated cell migration and invasion of breast cancer cells.

CONCLUSIONS

Therapies targeting the USP4 inhibits invasion of breast cancer cells via Relaxin/TGF-β1/Smad2/MMP-9 signal. These results indicate that USP4 is an attractive target for breast cancer therapy.

RNAi-mediated knockdown of relaxin decreases in vitro proliferation and invasiveness of osteosarcoma MG-63 cells by inhibition of MMP-9

PURPOSE

The purpose of this study is to determine the role of relaxin knowdown by siRNA transfection in cellular growth and invasion of osteosarcoma MG-63 cells, and discusses the molecular mechanisms of this action.

MATERIALS AND METHODS

The expression of relaxin in MG-63 cell was examined by western blot or RT-PCR. To evaluate the biological role of relaxin, proliferation assay (MTT) and invasion assay (BD Matrigel™), apoptosis assay (TUNEL and ELISA) and cell cycle analysis (flow cytometer) were performed after silencing relaxin using siRNA. MMP-9 expressions were analyzed using RT-PCR, western blot and zymography after silencing relaxin.

RESULTS

Results showed that the downregulation of relaxin expression by siRNA in human osteosarcoma MG-63 cells significantly inhibited cell proliferation and invasion in vitro. Furthermore, relaxin knockdown led to cell arrest in the G1/G0 phase of the cell cycle, and eventual apoptosis enhancement in MG-63 cells. We provide evidence in our cell model that the relaxin siRNA down-regulated the expression of MMP-9 and the MMP-9 activity, suggesting that relaxin may promote the proliferation, invasion and metastasis of osteosarcoma cells by regulating the expression of MMP-9 and facilitating ECM degradation.

CONCLUSIONS

Therefore, siRNA-directed knockdown of relaxin may represent a viable clinical therapy for osteosarcoma.

Chronic Intracerebroventricular Administration of Relaxin-3 Increases Body Weight in Rats

Bolus-administered intracerebroventricular (ICV) relaxin-3 has been reported to increase feeding. In this study, to examine the role of relaxin-3 signaling in energy homeostasis, we studied the effects of chronically administered ICV relaxin-3 on body weight gain and locomotor activity in rats. Two groups of animals received vehicle or relaxin-3 at 600 pmol/head/day, delivered with Alzet osmotic minipumps. In animals receiving relaxin-3, food consumption and weight gain were statistically significantly higher than those in the vehicle group during the 14-day infusion. During the light phase on days 2 and 7 and the dark phase on days 3 and 8, there was no difference in locomotor activity between the two groups. Plasma concentrations of leptin and insulin in rats chronically injected with relaxin-3 were significantly higher than in the vehicle-injected controls. These results indicate that relaxin-3 up-regulates food intake, leading to an increase of body weight and that relaxin-3 antagonists might be candidate antiobesity agents.

Relaxin-3 stimulates the hypothalamic-pituitary-gonadal axis

The hypothalamus plays a key role in the regulation of both energy homeostasis and reproduction. Evidence suggests that relaxin-3, a recently discovered member of the insulin superfamily, is an orexigenic hypothalamic neuropeptide. Relaxin-3 is thought to act in the brain via the RXFP3 receptor, although the RXFP1 receptor may also play a role. Relaxin-3, RXFP3, and RXFP1 are present in the hypothalamic paraventricular nucleus, an area with a well-characterized role in the regulation of energy balance that also modulates reproductive function by providing inputs to hypothalamic gonadotropin-releasing hormone (GnRH) neurons. Other members of the relaxin family are known to play a role in the regulation of reproduction. However, the effects of relaxin-3 on reproductive function are unknown. We studied the role of relaxin-3 in the regulation of the hypothalamo-pituitary-gonadal (HPG) axis. Intracerebroventricular (5 nmol) and intraparaventricular (540-1,620 pmol) administration of human relaxin-3 (H3) in adult male Wistar rats significantly increased plasma luteinizing hormone (LH) 30 min postinjection. This effect was blocked by pretreatment with a peripheral GnRH antagonist. Central administration of human relaxin-2 showed no significant effect on plasma LH. H3 dose-dependently stimulated the release of GnRH from hypothalamic explants and GT(1)-7 cells, which express RXFP1 and RXFP3, but did not influence LH or follicle-stimulating hormone release from pituitary fragments in vitro. We have demonstrated a novel role for relaxin-3 in the stimulation of the HPG axis, putatively via hypothalamic GnRH neurons. Relaxin-3 may act as a central signal linking nutritional status and reproductive function.

Relaxin-induced matrix metalloproteinase-9 expression is associated with activation of the NF-κB pathway in human THP-1 cells

Matrix metalloproteinases (MMPs) and relaxin (RLX) are reported to play an important role in tissue remodeling and wound repair. When macrophages populate wound sites, they secrete biologically active substances, including MMPs. The transcription factor NF-kappaB is important in MMP gene regulation in macrophage cells. Thus, a monocyte/macrophage cell line, THP-1, was used to study the molecular mechanism of RLX action on MMP-2 and MMP-9 expression. After 24 h incubation with porcine RLX (100 ng/ml), conditioned media (CM) and THP-1 cells were collected. Gelatin zymography demonstrated an increase in pro-MMP-9 activity in response to RLX in CM, and no significant change in pro-MMP-2 expression was observed. Immunoblot analysis also revealed an increase in pro-MMP-9 in CM from RLX-treated THP-1 cells. Gel EMSA showed that NF-kappaB DNA-binding activity was elevated in THP-1 cells treated with RLX for 10 min and reached a peak at 30 min. The NF-kappaB DNA complex was supershifted using antibodies against NF-kappaB subunits p50 and p65. Increased expression of the p50 and p65 NF-kappaB subunits was also detected in THP-1 cells after RLX treatment. Incubation with RLX (90 min) reduced THP-1 expression of the NF-kappaB inhibitor protein, IkappaB-alpha. Using a specific NF-kappaB inhibitor, pyrrolidine dithiocarmate (PDTC) inhibited nuclear binding of NF-kappaB. Pre-exposure to PDTC suppressed pro-MMP-9 activity and protein levels in RLX-treated THP-1 cells. In conclusion, these data suggest that RLX-induced tissue remodeling through increasing MMP-9 expression is dependent on NF-kappaB activation.

LGR7-truncate is a splice variant of the relaxin receptor LGR7 and is a relaxin antagonist in vitro

The relaxin receptor (LGR7) and the insulin-like peptide 3 (INSL3) receptor (LGR8) are unique LGR family members in possessing a single, functionally important amino terminal LDL-A module.1 Mouse and rat cDNA was screened for LGR7 and LGR7 splice variant expression. A uterus-specific exon 4 deleted variant was identified and named LGR7-Truncate. Deletion of exon 4 results in a premature stop codon and a transcript that putatively encodes a secreted protein containing LGR7's LDL-A module. Expression of LGR7-Truncate with LGR7 in HEK-293T cells resulted in decreased relaxin-induced signaling of LGR7. LGR7-Truncate is potentially an endogenous regulator of LGR7 signaling.

Disparate effects of relaxin and TGFbeta1: relaxin increases, but TGFbeta1 inhibits, the relaxin receptor and the production of IGFBP-1 in human endometrial stromal/decidual cells

BACKGROUND

The purpose of this study was to determine the effect of progestin, relaxin (RLX) and transforming growth factor beta1 (TGFbeta1) on the content of relaxin receptor (LGR7) mRNA. The effect of RLX on insulin-like growth factor binding protein-1 (IGFBP-1) production was determined to evaluate the biological function of RLX/receptor in human endometrial cells.

METHODS AND RESULTS

The levels of LGR7 mRNA and the effect of hormones were determined by real-time PCR in endometrial cells. LGR7 mRNA was found to be relatively abundant in endometrial glands and decidual cells and much less in endometrial stromal cells. In stromal cells, medroxyprogesterone acetate (MPA), or MPA plus RLX, significantly increased the LGR7 mRNA and RLX alone had little effect. In decidual cells, RLX increased LGR7 mRNA in a dose- and time-dependent fashion. TGFbeta1 reduced the LGR7 mRNA. In stromal cells, MPA alone caused a slight increase (2-4-fold) of the production rate of IGFBP-1 whereas MPA plus RLX synergistically increased (>40-fold) the IGFBP-1 production. In decidual cells in which the basal production rate was already approximately 50-fold higher than in stromal cells, RLX alone caused an additional increase (>30-fold) on the production rate. TGFbeta1 inhibited the IGFBP-1 production.

CONCLUSION

The present study showed that in undifferentiated endometrial stromal cells, progestin increases the RLX receptor content to enhance the effect of RLX on the target gene (IGFBP-1). In decidual cells, RLX alone up-regulates its receptor, resulting in a large scale induction of IGFBP-1. TGFbeta1 has an inhibitory effect on LGR7 and IGFBP-1.

Relaxin signalling links tyrosine phosphorylation to phosphodiesterase and adenylyl cyclase activity

The relaxin receptor has so far avoided molecular cloning and characterization. We have therefore characterized the signalling events activated by relaxin (RLX), using two different cell culture-based bioassay systems: primary human endometrial stromal cells from the cycle (ESC) and the human monocyte cell line THP-1. Upon RLX stimulation, both cell types showed a rapid increase in cAMP accumulation, which could be inhibited by an inhibitor of G-protein activation, GDP-beta-S. However, evolutionarily one would expect the RLX receptor, like those for the structurally related hormones insulin and insulin-like growth factor-I, to involve tyrosine kinase activity. The specific tyrphostins AG 1478, AG 527 and AG 879 inhibited the RLX-stimulated cAMP response in human ESC and THP-1 cells in a dose-dependent manner, though the potent broad range tyrphostin AG 213 had no effect. Also, treatment of THP-1 cells with the potent phosphotyrosine phosphatase inhibitors bpV(phen) and mpV(pic) increased RLX-stimulated cAMP accumulation in a dose-dependent manner. The effect of the general tyrosine kinase inhibitor genistein (which can also inhibit some phosphodiesterases) on RLX-mediated cAMP accumulation strongly depended on the activity status of phosphodiesterase. In the absence of a phosphodiesterase inhibitor, genistein enhanced RLX-stimulated cAMP accumulation in both bioassays. When phosphodiesterase was inhibited by isobutylmethylxanthine, this effect was not observed. The results imply that activation of the RLX receptor uses tyrosine kinase signalling to control phosphodiesterase activity, and hence to up-regulate intracellular cAMP.

Relaxin as a relaxant of the isolated rat uterus: comparison with its mechanism of action in vivo

1. Glibenclamide, a blocker of ATP-sensitive potassium channels, has been shown to antagonize relaxin as a uterine relaxant in the rat in vivo but not in vitro. The aim, therefore, was to investigate whether the discrepancy between the two studies was a consequence of differences in (1) muscle layers, (2) hormonal conditions or (3) spasmogens utilized. Relaxin was compared with salbutamol and levcromakalim. 2. Relaxin was of similar potency as a uterine relaxant against oxytocin (0.2 mM)-induced spasm with tension measured in the circular or longitudinal muscle layers. Glibenclamide (10 microM) did not antagonize relaxin or salbutamol in these preparations but greatly antagonized levcromakalim (91-fold). Relaxin was a relaxant of tension activated by transmural electrical stimulation in uteri from rats that had been ovariectomized, although the maximal effect was only 30 +/- 15%, and in uteri from rats that had been treated with 17 beta-estradiol benzoate. Glibenclamide was not an antagonist of relaxin in the latter preparation but did antagonize levcromakalim (118-fold). Relaxin also inhibited spontaneous phasic tension development in uteri from ovariectomized rats but again was not antagonized by glibenclamide. 3. Because relaxin was not antagonized by glibenclamide under any of these various conditions, it would appear that the in vivo-in vitro discrepancy in the antagonism of relaxin by glibenclamide is not attributable to the effects of different muscle layers, hormonal conditions or spasmogens. It may be that the mechanism of action of relaxin or glibenclamide or both differs between in vivo and in vitro preparations.

The role of a cAMP-dependent pathway in the uterine relaxant action of relaxin in rats

The aim of this study was to investigate the role of the adenylyl cyclase pathway, and in particular cyclic AMP-dependent protein kinase A, in the relaxant action of relaxin in the isolated uterus of the nonpregnant rat. The purportedly selective inhibitor of cAMP-dependent protein kinase A N-[2-(methylamino) ethyl]-5-isoquinolinesulfonamide hydrochloride (H-8) (at 100 mumol l-7) antagonized relaxin, salbutamol (an agonist at beta-adrenoceptors) and levcromakalim (a K+ channel opener) to a similar extent (by factors of 3.1, 1.9 and 2.8, respectively), demonstrating that it is not a selective inhibitor. Relaxin and levcromakalim were less potent and had smaller, maximal, relaxant effects in longitudinal myometrium than in intact uterus cut in the longitudinal plane. By contrast, nifedipine (a Ca2+ channel blocker) was equipotent in the two preparations and salbutamol only slightly less potent in the longitudinal myometrium. Relaxin did not alter the cyclic AMP-dependent protein kinase A activity ratio in longitudinal myometrium, but did increase the activity ratio by a factor of 2.0 +/- 0.2 in the intact uterus. Salbutamol, the positive control, increased this activity ratio in both longitudinal myometrium (by 1.9 +/- 0.3 times) and in the intact uterus (by 3.8 +/- 0.3 times), whereas the negative control levcromakalim had no effect. Relaxin seems to act as a relaxant of longitudinal myometrium by a cyclic AMP-independent mechanism but possibly interacts with the circular myometrium or endometrium to release a relaxant factor via a cyclic-AMP-dependent mechanism.

Relaxin modulates the ovulatory process and increases secretion of different gelatinases from granulosa and theca-interstitial cells in rats

There were two related objectives in this study. The first was to determine the influence of endogenous relaxin on ovulation in rats. The second was to investigate the effect of relaxin on the secretion of gelatinases involved in extracellular matrix remodeling from rat ovarian cells. Immature rats were primed s.c. with 10 IU eCG; 51 to 52 h later, a monoclonal antibody specific for rat relaxin (MCAR), a control antibody against fluorescein (MCAF), or PBS vehicle was administered via intraovarian bursal injection under anesthesia, and 15 IU hCG was injected i.p. immediately thereafter. Rats were killed 26 h later, and oviducts were isolated and examined under the microscope to determine the number of ovulated oocytes. MCAR (0.25 and 2.5 micrograms/ovary) partially suppressed gonadotropin-induced ovulation as compared to the value for PBS controls. There was no significant difference in the number of ovulated oocytes between animals treated with MCAF and PBS controls. Also, porcine relaxin, given s.c. immediately after MCAR treatment, could reverse the inhibitory effect of MCAR on ovulation. To examine a possible mechanism for the effect of relaxin on ovulation, granulosa cells and theca-interstitial cells were obtained from ovaries of eCG-primed immature rats. The gelatinases secreted from cultured cells were analyzed using gelatin zymography and scanning densitometry. In the granulosa cell culture, relaxin increased the secretion of two major gelatinases of about 92 and 63 kDa in a dose-and time-dependent manner within 24 h of treatment. In the theca-interstitial cell culture, relaxin induced dose- and time-dependent increases in the secretion of two other major gelatinases of about 76 and 71 kDa. These gelatinases were characterized as metalloproteinases but not serine/cysteine proteinases. Furthermore, an immunoblot study demonstrated that relaxin stimulated the secretion of a 72-kDa type IV collagenase-like substance from cultured theca-interstitial cells but not from granulosa cells. This study demonstrates several original findings. First, endogenous relaxin may facilitate the ovulatory process in rats. Second, exogenous relaxin exhibits a biological effect on cultured rat theca-interstitial cells in addition to granulosa cells. Third, exogenous relaxin regulates the secretion of different major forms of gelantinases from cultured rat granulosa cells and theca-interstitial cells. The study supports the idea that relaxin may play an autocrine/paracrine role that is involved in modulating ovarian function.

Relaxin stimulates myometrial calcium-activated potassium channel activity via protein kinase A

Relaxin, a hormone that is elevated during pregnancy, can suppress myometrial contractile activity. Ca(2+)-activated K+ channels (KCa) play a role in the modulation of uterine contractions and myometrial Ca2+ homeostasis and have been implicated in the control of smooth muscle excitability. We now show that relaxin stimulates KCa channels in cell-attached patches in a cell line derived from term pregnant human myometrium. This effect was prevented by the protein kinase A (PKA) antagonist, the Rp diastereomer of adenosine 3',5'-cyclic monophosphothioate (Rp-cAMPS). After patch excision, the channel was activated by PKA and inhibited by alkaline phosphatase. These data suggest that relaxin may promote myometrial quiescence in part by stimulation of KCa channels via a PKA-mediated mechanism.

Inhibition of relaxin-induced pubic symphyseal "relaxation" in guinea pigs by glycosaminoglycan polysulfates and pentosan polysulfate

There are similarities between the actions of estrogen and relaxin on the connective tissues of the pubic symphysis and those of neutral proteases on cartilage in osteoarthritis, including cartilage hydration, proteoglycan loss, and dissolution of collagen fibers. We hypothesized that compounds known to inhibit cartilage breakdown in animal models of osteoarthritis, such as polysulfated GAGs, would also antagonize the actions of estrogen and relaxin that increase the laxity and mobility of the pubic symphyses of guinea pigs. Estrogen-primed guinea pigs were injected with relaxin or with relaxin and the test compound. The pubic symphyses were manually palpated 6 h later and the degree of mobility scored. Glycosaminoglycan polysulfates and pentosan polysulfate inhibited relaxin-induced pubic symphyseal relaxation, whereas other types of agents were without effect. The guinea pig pubic symphysis assay for relaxin may thus provide a novel rapid screening test for compounds with potential chondroprotective activity.

Antagonism of relaxin by glibenclamide in the uterus of the rat in vivo

1. The effects of glibenclamide (a blocker of adenosine triphosphate [ATP]-dependent K(+)-channels) on the inhibition of uterine contractions by relaxin, salbutamol and cromakalim were compared in vivo. 2. Glibenclamide (20 mg kg-1) did not antagonize salbutamol. Glibenclamide produced a parallel rightward shift in the dose-response curve to cromakalim with a 5.5 fold decrease in uterine sensitivity (post-vehicle log ID50, -0.87 mg kg-1; post-glibenclamide log ID50, -0.07 mg kg-1). Glibenclamide produced a non-parallel rightward shift in the dose-response curve to relaxin (post-vehicle log ID50, 0.99 microgram kg-1; post-glibenclamide log ID50, 2.28 micrograms kg-1). 3. Glibenclamide reversed established inhibition of uterine contractions by cromakalim or relaxin but not that by salbutamol. 4. Insulin produced no antagonism of relaxin on isolated uterus of the rat, demonstrating that glibenclamide antagonism of relaxin in vivo is not by released insulin. Apamin did not antagonize relaxin in vivo, suggesting that small calcium-activated K(+)-channels are not involved in the action of relaxin. 5. Comparison of the lack of antagonism of salbutamol with the non-competitive-like antagonism of relaxin by glibenclamide suggests that relaxin does not relax uterine smooth muscle predominantly by increasing intracellular adenosine 3', 5'-cyclic monophosphate concentrations. Comparison of the non-competitive-like antagonism of relaxin and the competitive-like antagonism of cromakalim by glibenclamide suggests that the two relaxants may share, in part, a common mechanism of action and that additional mechanism(s) may also be involved in the inhibitory action of relaxin.

Total synthesis of human relaxin and human relaxin derivatives by solid-phase peptide synthesis and site-directed chain combination

Human relaxin, a two-chain protein hormone, was synthesized by solid-phase peptide synthesis in combination with a novel thiol-protecting group strategy whereby the three disulfide bonds could be synthesized sequentially and without error. The final product was shown to be homogeneous by reversed-phase high performance liquid chromatography and electrophoresis and had the correct amino acid composition and sequence. Tryptic digestion and peptide mapping of the synthetic relaxin by reversed-phase high performance liquid chromatography resulted in a pattern identical with that produced by standard tryptic relaxin fragments synthetized by different methods. Three human relaxin derivatives containing oxidized methionine, formyltryptophan, and bis[B13,B17-citrulline]-relaxin, were produced and their biological activity and structural similarity to human relaxin was assessed. All derivatives, except those containing modified tryptophan residues, showed indistinguishable circular dichroic spectra, indicating that the modifications did not cause significant structural changes. However, only human relaxin and the tryptophan- and methionine-protected relaxin derivatives showed bioactivity. The derivative in which the two arginines in positions B13 and B17 had been replaced by the uncharged isosteric amino acid citrulline were biologically inactive. This observation confirms preliminary studies (Büllesbach, E. E. and Schwabe, C. (1988) Int. J. Pept. Protein Res. 32, 361-367) that suggested that these two conserved arginines located in the midregion of the relaxin B chain are essential for the function of the hormone.

Progesterone inhibits the uterotrophic effect of relaxin in immature rats

Injection of progesterone for 3 days before treatment with relaxin inhibited the trophic effect of the peptide in both estrogen-primed and unprimed uteri. The depression in collagen concentration and increase in apparent rate of proline incorporation into collagen induced by relaxin alone were also eliminated, indicating a fundamental blockade of the effect of relaxin in this experimental design as well as a close association of changes in collagen concentration with tissue hypertrophy. The effect of relaxin on incorporation of proline into soluble protein was not blocked by progesterone, however, suggesting a separate mechanism for this anabolic effect of relaxin.

Effects of chronic infusion of porcine relaxin on oxytocin release in lactating rats

The effects of chronic infusion of porcine relaxin on oxytocin release were studied in lactating rats. Infusion of relaxin (4.2 micrograms/h for either 4 or 6 days) suppressed reflex milk ejection and reduced litter weight gain for 48 h compared with saline-infused controls. After 2 days, neither the rate of growth nor the frequency of milk ejection were significantly different from controls. For 24 h after the infusion of relaxin ended, litters gained weight more quickly than controls but there was no difference seen in the frequency of milk ejection. The effects on oxytocin release of stopping an infusion of relaxin after 3 days were investigated. There was a significant (P less than 0.01) rise in plasma oxytocin (up to 90 pmol/l) 30 min after the infusion was stopped, followed by a sustained rise in intramammary pressure. Treatment of relaxin-infused rats with naloxone (0.1 mg/kg) when the infusion was halted caused a more rapid release of oxytocin (within 2 min), a greater release of oxytocin (up to 140 pmol/l) and a prolonged rise in intramammary pressure.

The effect of relaxin and prostaglandin E2 on the motility of human spermatozoa

Relaxin and prostaglandin E2 (PGE2) are present in human semen and have been shown to affect sperm motility. The authors further examined the effects of porcine relaxin and PGE2 on the motility of human spermatozoa. A dose-response study revealed that PGE2 at a concentration of 25 micrograms/ml is most effective in improving the motility of washed human sperm. Relaxin (100 ng/ml), PGE2 (25 micrograms/ml), or the two combined have no effect on the motility of spermatozoa in fresh, normal semen, suggesting that the constituents of fresh semen are optimal for motility. Relaxin and PGE2 individually improve the motility of washed spermatozoa. However, relaxin, but not PGE2, improves the motility of sperm in semen incubated at 37 degrees C for 5 hours (aged). In contrast to the individual substances, a combination of relaxin + PGE2 has no effect on the motility of washed spermatozoa or aged spermatozoa, suggesting that these two substances antagonize each other's actions on sperm motility. The presence of both relaxin and PGE2 in seminal plasma with normal motility spermatozoa suggests that other factors in seminal plasma regulate the effects of these substances on sperm motility.