Overexpression of histamine H4 receptors in the kidney of diabetic rat.

OBJECTIVE AND DESIGN: The renal expression of H1 and H2 receptors has previously been demonstrated, while that of the H4 receptor has been poorly investigated, and thus the aim of this research was to investigate the expression of the H4 receptor in the kidney of diabetic rats. MATERIAL OR SUBJECTS: 24 8-week-old male Wistar rats. TREATMENT: Diabetes was induced in 12 rats by a single intravenous injection of streptozotocin, and animals were killed 6 weeks later. METHODS: Kidneys were collected and processed for quantitative PCR or immunohistochemical analyses. To ascertain the renal topology of the H4 receptor, colocalization experiments were performed with a series of markers. RESULTS: H4 receptor is expressed in healthy rats, although at a very low level, and is strongly upregulated in diabetic animals. Immunohistochemical analysis revealed the highest immune-positivity in the medulla. Colocalization experiments revealed a close overlap in expression topology of the H4 receptor and both Tamm-Horsfall glycoprotein and aquaporin 1 was observed. CONCLUSIONS: The results demonstrate, for the first time, that the H4 receptor is expressed in the kidney mainly by resident renal cells of the loop of Henlé and that this receptor is significantly overexpressed in diabetic animals, thus suggesting a possible role in the pathogenesis of diabetes-associated renal disease.

Relationships between telocytes and cardiomyocytes during pre- and post-natal life.

Evidence has been given that the adult heart contains a specific population of stromal cells lying in close spatial relationship with cardiomyocytes and with cardiac stem cells in sub-epicardial cardiogenic niches. Recently termed 'telocytes' because of their long cytoplasmic processes embracing the parenchymal cells, these cells have been postulated to be involved in heart morphogenesis. In our opinion, investigating the occurrence and morphology of telocytes during heart histogenesis may shed further light on this issue. Our findings show that typical telocytes are present in the mouse heart by early embryonic to adult life. These cells closely embrace the growing cardiomyocytes with their long, slender cytoplasmic processes. Hence, in the developing myocardium, telocytes may play nursing and guiding roles for myocardial precursors to form the correct three-dimensional tissue architectural pattern, as previously suggested.

Relaxin and nitric oxide signalling.

The peptide hormone relaxin (RLX) has been shown to exert a variety of functions in both reproductive and non-reproductive tissues. The molecular mechanism of RLX on its target cells appears to involve multiple intracellular signalling systems, including the nitric oxide (NO) pathway. NO is an ubiquitous molecule synthesised from L-arginine under the catalytic action of different nitric oxide synthase (NOS) isoforms and its altered production has been reported to be involved in several diseases. RLX has been demonstrated to promote NO biosynthesis by up-regulating NOS expression; its influence on the different NOS appears to depend on the cell type studied. In addition to its physiological roles, RLX has been postulated as a potential therapeutic agent in several diseases. In particular, based on its property to promote NO biosynthesis, RLX may be regarded as a therapeutic tool in diseases characterized pathogenically by an impaired NO production. The aim of the present mini-review is to summarize and discuss the pathophysiological actions of RLX, strictly related to its ability to activate the endogenous NO pathway in reproductive and non-reproductive target organs.

Relaxin activates AMPK-AKT signaling and increases glucose uptake by cultured cardiomyocytes.

PURPOSE: Many evidences show that the hormone relaxin plays a pivotal role in the physiology and pathology of the cardiovascular system. This pleiotropic hormone exerts regulatory functions through specific receptors in cardiovascular tissues: in experimental animal models it was shown to induce coronary vasodilation, prevent cardiac damage induced by ischemia/reperfusion and revert cardiac hypertrophy and fibrosis. A tight relationship between this hormone and important metabolic pathways has been suggested, but it is at present unknown if relaxin could regulate cardiac metabolism. Our aim was to study the possible effects of relaxin on cardiomyocyte metabolism. METHODS: Neonatal rat cardiomyocytes were treated with relaxin and (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assays (MTT) were performed to assess metabolic activity; while 2-deoxy-D-[3H] glucose and BODIPY-labelled fatty acid incorporations were analyzed to measure glucose and fatty acid uptakes, and western blot was utilized to study the intracellular signaling pathways activated by the hormone. RESULTS: We observed that relaxin at 10 ng/ml was able to increase the level of metabolic activity of cultured neonatal rat cardiomyocytes; the rate of 2-deoxy-D-[3H]glucose incorporation demonstrated that relaxin also induced an increase in glucose uptake. First evidence is also offered that relaxin can activate the master energy sensor and regulator AMPK in cardiomyocytes. Moreover, the treatment of cardiomyocytes with relaxin also induced dose-dependent increases in ERK1/2, AKT, and AS160 phosphorylation. That raise in AS160 phosphorylation induced by relaxin was prevented by the pretreatment with AMPK and AKT pathways inhibitors, indicating that both molecules play important roles in the relaxin effects reported. CONCLUSION: Relaxin can regulate cardiomyocyte metabolism and activate AMPK, the central sensor of energy status that maintains cellular energy homeostasis, and also ERK and AKT, two molecular sensing nodes that coordinate dynamic responses of the cell's metabolic responses.

Effects of relaxin on mast cells. In vitro and in vivo studies in rats and guinea pigs.

The results of the current study demonstrate that relaxin inhibits histamine release by mast cells. This effect is related to the peptide concentrations, and could be observed in both isolated rat serosal mast cells stimulated with compound 48/80 or calcium ionophore A 23187, and in serosal mast cells isolated from sensitized guinea pigs and challenged with the antigen. The morphological findings agree with the functional data, revealing that relaxin attenuates calcium ionophore-induced granule exocytosis by isolated rat serosal mast cells. Similar effects of relaxin have also been recognized in vivo by light microscopic and densitometric analysis of the mesenteric mast cells of rats which received the hormone intraperitoneally 20 min before local treatment of the mesentery with calcium ionophore. Moreover, evidence is provided that relaxin stimulates endogenous production of nitric oxide and attenuates the rise of intracellular Ca2+ concentration induced by calcium ionophore. The experiments with drugs capable of influencing nitric oxide production also provide indirect evidence that the inhibiting effect of relaxin on mast cell histamine release is related to an increased generation of nitric oxide. It is suggested that relaxin may have a physiological role in modulating mast cell function through the L-arginine-nitric oxide pathway.

Relaxin activates the L-arginine-nitric oxide pathway in human breast cancer cells.

Recently, we demonstrated that relaxin (RLX), a peptide hormone of ovarian origin, inhibits growth and promotes differentiation of MCF-7 breast adenocarcinoma cells. We also showed that RLX stimulates the production of nitric oxide (NO) in several cell types. NO has been reported to have antitumor activity by inhibiting proliferation, promoting differentiation, and reducing the metastatic spread of some tumor cell types. In this study, we aimed at evaluating whether RLX influences the L-arginine-NO pathway in MCF-7 cells. The cells were grown in the absence or presence of RLX at different concentrations, and cell proliferation, constitutive and inducible NO synthase activities, nitrite production, and intracellular levels of cyclic GMP were investigated. The results obtained indicate that RLX increases inducible NO synthase activity and potentiates NO production. This was accompanied by an elevation of intracellular cyclic GMP, which is known to mediate the cell response to NO. The RLX-induced activation of the L-arginine-NO pathway in the MCF-7 cells was inversely related to the rate of cell proliferation. These results suggest that the cytostatic effect of RLX on MCF-7 breast cancer cells may rely on its ability to stimulate endogenous production of NO.

Protection from cardiac injury by induction of heme oxygenase-1 and nitric oxide synthase in a focal ischaemia-reperfusion model.

The enzymes heme oxygenase (HO) generate carbon monoxide (CO) in living organisms during heme degradation. Carbon monoxide has recently been shown to dilate blood vessels and to possess anti-inflammatory properties. It is also known that nitric oxide (NO) donors ameliorate cardiac ischaemia-reperfusion injury in experimental models of global or focal ischaemia-reperfusion (FIR). The two gaseous mediators share the same mechanism of action via the stimulation of soluble guanylyl cyclase and the increase in cellular levels of cyclic GMP. We studied the effects of manipulating the HO system and the possible interaction between CO and NO in an experimental in vivo model of FIR in the rat heart. FIR-subjected rats had necrotic area in the left ventricle, ventricular arrhythmias and a shortening of survival time in comparison to sham-operated animals. Resident mast cells underwent a heavy degranulation, malonyldialdehyde was produced by myocardial cell membranes, and tissue calcium levels were increased. High levels of myeloperoxidase were also detected, suggesting a FIR-related inflammatory process. In animals pre-treated with the HO-1 inducer, hemin, all the biochemical and morphometric markers of FIR were minimized or fully abated. Consistently, the biochemical and morphometric markers of FIR were reversed in rats treated with the HO-1 blocker, ZnPP-IX, prior to hemin administration. Pre-treatment with hemin significantly increases the expression and activity of both cardiac HO-1 and iNOS, suggesting that CO and NO cooperate in the cardioprotective effect against FIR-induced damage, and that there is a therapeutic synergism between NO-donors and CO-releasing molecules, via the common stimulation of increase in cGMP levels and decrease in calcium overload.

Atomic force microscopy of histological sections using a chemical etching method.

Physiology and pathology have a big deal on tissue morphology, and the intrinsic spatial resolution of an atomic force microscope (AFM) is able to observe ultrastructural details. In order to investigate cellular and subcellular structures in histological sections with the AFM, we used a new simple method for sample preparation, i.e. chemical etching of semithin sections from epoxy resin-embedded specimens: such treatment appears to melt the upper layers of the embedding resin; thus, removing the superficial roughness caused by the edge of the microtome knife and bringing into high relief the biological structures hidden in the bulk. Consecutive ultrathin sections embedded in epoxy resin were observed with a transmission electron microscope (TEM) to compare the different imaging properties on the same specimen sample. In this paper we report, as an example, our AFM and TEM images of two different tissue specimens, rat pancreas and skeletal muscle fibres, showing that most of the inner details are visible with the AFM. These results suggest that chemical etching of histological sections may be a simple, fast and cost-effective method for AFM imaging with ultrastructural resolution.

A new low molecular weight, MnII-containing scavenger of superoxide anion protects cardiac muscle cells from hypoxia/reoxygenation injury.

Reperfusion injury after oxygen starvation is a key pathogenic step in ischemic diseases. It mainly consists in oxidative stress, related to mitochondrial derangement and enhanced generation of reactive oxygen species (ROS), mainly superoxide anion (O2(•2)), and peroxynitrite by cells exposed to hypoxia. This in vitro study evaluates whether Mn(II)(4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diacetate).2H2O, or Mn(II)(Me2DO2A), a new low molecular weight, Mn(II)-containing O2(•) scavenger, has a direct protective action on H9c2 rat cardiac muscle cells subjected to hypoxia and reoxygenation. Mn(II)(Me2DO2A) (1 and 10 µmol/l) was added to the culture medium at reoxygenation and maintained for 2 h. In parallel experiments, the inactive congener Zn(II)(Me2DO2A), in which Zn(II) replaced the functional Mn(II) center in the same organic scaffold, was used as negative control. Mn(II)(Me2DO2A) (10 µmol/l) significantly increased cardiac muscle cell viability (trypan blue assay), improved mitochondrial activity (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide test, membrane potential Δψ), reduced apoptosis (mitochondrial permeability transition pore opening, caspase-3, terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling assay), decreased intracellular ROS levels (2',7'-dichlorodihydrofluorescein diacetate and MitoSOX assays), and decreased protein nitroxidation (nitrotyrosine [NT] expression) and DNA oxidation (8-hydroxy-deoxyguanosine levels). Of note, Zn(II)(Me2DO2A) had no protective effect. The mechanism of Mn(II)(Me2DO2A) relies on concentration-dependent removal of harmful O2(•) generated at reoxygenation from dysfunctional mitochondria in hypoxia-induced cells, as indicated by the MitoSOX assay. This study suggests that Mn(II)(Me2DO2A) is a promising antioxidant drug capable of reducing O2(•)-mediated cell oxidative stress which occurs at reoxygenation after hypoxia. In perspective, Mn(II)(Me2DO2A) might be used to reduce ischemia-reperfusion organ damage in acute vascular diseases, as well as to extend the viability of explanted organs before transplantation.

Structural and functional analysis of two different nodD genes in Bradyrhizobium japonicum USDA110.

Bradyrhizobium japonicum has two closely linked homologs of the nodulation regulatory gene, nodD; these homologs are located upstream of and in divergent orientation to the nodYABCSUIJ gene cluster. We report here the nucleotide sequence and mutational analyses of both nodD copies. The predicted NodD1 and NodD2 proteins shared 62% identical amino acid residues at corresponding positions and exhibited different degrees of homology with NodD proteins of other Bradyrhizobium, Azorhizobium, and Rhizobium strains. Induction of the nodYABCSUIJ operon, as measured by expression of a translational nodC'-'lacZ fusion, required the nodD1 gene, but not nodD2. A B. japonicum mutant deleted for both nodD copies (strain delta 1267) still showed residual nodulation activity; however, nodulation of soybean was significantly delayed, and nodulation of mung bean and siratro resulted in strongly reduced nodule numbers. Fully efficient nodulation of mung bean and siratro by strain delta 1267 was restored by genetic complementation with the nodD1 gene, but not with nodD2. We conclude from these data that nodD1 is the critical gene that contributes to maximal nodulation efficiency, whereas the nodD2 gene does not play any obvious role in nodulation of the host plants tested.

Relaxin counteracts asthma-like reaction induced by inhaled antigen in sensitized guinea pigs.

In previous studies, the peptide hormone relaxin (RLX) was found to inhibit mast cell secretion and platelet activation. It has been established that the release of mediators from these cells plays a central pathogenic role in allergic asthma. This prompted us to ascertain whether RLX may counteract the respiratory and histopathological abnormalities of the asthma-like reaction to inhaled antigen in sensitized guinea pigs. Guinea pigs were sensitized with ovalbumin and challenged with the same antigen given by aerosol. Some animals received RLX (30 microg/kg BW, twice daily for 4 days) before antigen challenge. Other animals received inactivated RLX in place of authentic RLX. Respiratory abnormalities, such as cough and dyspnea, were analyzed as were light and electron microscopic features of lung specimens. RLX was shown to reduce the severity of respiratory abnormalities, as well as histological alterations, mast cell degranulation, and leukocyte infiltration in sensitized guinea pigs exposed to ovalbumin aerosol. RLX was also found to promote dilation of alveolar blood capillaries and to reduce the thickness of the air-blood barrier. This study provides evidence for an antiasthmatic property of RLX and raises the possibility of new therapeutic strategies for allergic asthma in humans.

Relaxin counteracts myocardial damage induced by ischemia-reperfusion in isolated guinea pig hearts: evidence for an involvement of nitric oxide.

Relaxin was previously shown to cause coronary vasodilation and to inhibit mast cell activation through a stimulation of endogenous nitric oxide production. This suggests that relaxin may have beneficial effects on ischemia-reperfusion-induced myocardial injury, which is triggered by endothelial damage and impaired nitric oxide generation. In this study, we tested the effect of relaxin on isolated and perfused guinea pig hearts subjected to ischemia and reperfusion. Ischemia was induced by ligature of the left anterior descending coronary artery; removal of the ligature induced reperfusion. Relaxin, at the concentration of 30 ng/ml of perfusion fluid, causes: a significant increase in coronary flow and in nitric oxide generation; a significant decrease in malonyldialdehyde production and in calcium overload, both markers of myocardial injury; an inhibition of mast cell granule exocytosis and histamine release, which are known to contribute to myocardial damage; a reduction of ultrastructural abnormalities of myocardial cells; an improvement of heart contractility. The beneficial effects of relaxin were blunted by the NO synthase inhibitor L-NMMA. The current study provides first experimental evidence that relaxin has a powerful protective effect on the heart undergoing ischemia and reperfusion acting through a nitric oxide-driven mechanism.

Relaxin up-regulates the nitric oxide biosynthetic pathway in the mouse uterus: involvement in the inhibition of myometrial contractility.

The uterus is a site of nitric oxide (NO) production and expresses NO synthases (NOS), which are up-regulated during pregnancy. NO induces uterine quiescence, which is deemed necessary for the maintenance of pregnancy. Relaxin is known to promote uterine quiescence. Relaxin has also been shown to stimulate NO production in several targets. In this study we investigated the effects of relaxin on the NO biosynthetic pathway of the mouse uterus. Estrogenized mice were treated with relaxin (2 microg) for 18 h, and the uterine horns were used for determination of immunoreactive endothelial-type NOS and inducible NOS. Moreover, uterine strips from estrogenized mice were placed in an organ bath, and the effect of relaxin on K+-induced contracture was evaluated in the presence or absence of the NOS inhibitor nitro-L-arginine. Relaxin increases the expression of endothelial-type NOS in surface epithelium, glands, endometrial stromal cells, and myometrium, leaving inducible NOS expression unaffected. Moreover, relaxin inhibits myometrial contractility, and this effect is blunted by nitro-L-arginine, thus indicating that the L-arginine-NO pathway is involved in the relaxant action of relaxin on the myometrium. Because relaxin is elevated during pregnancy, it is suggested that relaxin has a physiological role in the up-regulation of uterine NO biosynthesis during pregnancy.

Relaxin activates the L-arginine-nitric oxide pathway in vascular smooth muscle cells in culture.

The peptide hormone relaxin (RLX) has been shown to elicit a powerful vasodilatory response in several target organs. This response is mediated by the stimulation of intrinsic nitric oxide (NO) generation. The present study was designed to clarify whether RLX directly promotes the relaxation of vascular smooth muscle cells through stimulation of NO generation. Vascular smooth muscle cells from bovine aortas were incubated with RLX at concentrations ranging from 1 nmol/L to 1 micromol/L. The expression and activity of NO synthase, production of NO, and the intracellular levels of cGMP and Ca2+ were determined. The cell morphology and signal transduction mechanisms of these bovine aortic smooth muscle cells in response to RLX were also studied. RLX stimulated the expression of immunoreactive inducible NO synthase and increased significantly and in a concentration-related fashion inducible NO synthase activity, NO generation, and intracellular cGMP levels. Concurrently, RLX significantly decreased cytosolic Ca2+ concentrations and caused changes in cell shape and the actin cytoskeleton that were consistent with cell relaxation. The signal transduction mechanisms leading to the enhanced expression of inducible NO synthase protein and activity caused by RLX involve the activation of tyrosine kinase, phosphatidylcholine-phospholipase C, and the transcription factor nuclear factor-kappaB, similar to bacterial endotoxins and proinflammatory cytokines. This study suggests that RLX is an endogenous agent capable of regulating vascular tone by activation of the L-arginine-NO pathway in vascular smooth muscle cells.

Morphological changes in rat pancreatic acinar cells induced by long-term treatment with cyclosporine and their reversal after withdrawal.

Cyclosporine (CsA), administered to rats at daily doses of 10 and 50 mg/kg body weight, for 21 days, influenced negatively the structures involved in the synthesis, storage and secretion of digestive enzymes in pancreatic acinar cells. A dose-related, significant reduction in basophilic cell regions, secretion granule content, and overall size of acinar cells was appreciable by light microscopy and morphometry. By electron microscopy, the acinar cells of the rats given 10 mg/kg/day CsA were similar to the controls, whereas with the higher dose most cells showed reduction in the size of nucleoli, increase in the number of lysosomes, and evidence of autophagy. In only a few cells was autophagy particularly severe and involved almost the entire cytoplasm. Nine weeks after withdrawal from CsA treatment, the structural recovery of acinal cells was complete, and features indicating enhanced protein synthesis and mitochondrial multiplication were observed by electron microscopy. In conclusion, prolonged administration of CsA to rats induces changes in the acinar cells indicating a depression of their activity, without substantial impairment in the viability of the most of them, even at high doses. This accounts for complete restoration of the acinar tissue upon withdrawal.

Immunocytochemical and ultrastructural changes of islet cells in rats treated long-term with cyclosporine at immunotherapeutic doses.

Daily cyclosporine doses of 10 mg/kg body weight for 21 days in Wistar rats cause impairment in glucose homeostasis and changes in the amount of immunostainable hormones and in the ultrastructure of the cells of the pancreatic islets. CsA induces hyperglycemia and reduced glucose tolerance, and causes a decrease in immunoreactive insulin and an increase of somatostatin and pancreatic polypeptide (PP) immunoreactivities, leaving glucagon immunoreactivity unaffected. Ultrastructurally, different degrees of dilation of rough endoplasmic reticulum cisternae and enlargement of Golgi apparatus can be observed in B cells, together with a pronounced reduction in the number of secretory granules. Nevertheless, there were no apparent morphological changes of the other cytoplasmic organelles, suggesting that the drug, besides a depression of protein synthesis, as previously stated, also induces a substantial defect in granulogenesis, probably due to impairment in the intracellular transport of the hormone from the sites of synthesis to the secretory granules. The B cell alterations are not accompanied by any sign of B cell degeneration or death. Non-B cells did not show any of the ultrastructural changes found in B cells and were similar to those of the control rats. The above findings indicate that CsA at immunotherapeutic doses causes impairment in the secretory processes of B cells specifically. An hypothesis on the mode of action of CsA on B cells is drawn.

Mechanical stretch reveals different components of endothelial-mediated vascular tone in rat aortic strips.

1. Since the role of mechanical stretches in vascular tone regulation is poorly understood, we studied how stretch can influence endothelial tone. 2. Isometric contractions of isolated rat aortic helical strips were recorded. The resting tension was set at 0.7 g, 1.2 g or 2.5 g. Endothelium-preserved strips were precontracted with either phenylephrine or prostaglandin F(2 alpha) (PGF(2 alpha)). 3. In control conditions, acetylcholine (ACh) dose-dependently relaxed phenylephrine-precontracted strips independently of resting tension. 4. At 0.7 g resting tension, nitric oxide synthase (NOS) inhibitors did not reduce ACh-induced relaxation, while either a guanylyl cyclase inhibitor or a NO trapping agent prevented it. At 1.2 g and 2.5 g resting tensions, NOS inhibitors shifted the ACh dose-response curve to the right. 5. After preincubation with indomethacin (5 microM) or ibuprofen (10 and 100 microM), at 0.7 g and 1.2 g resting tensions, ACh induced an endothelium-dependent, dose-dependent contraction. ACh (10(-6) M) increased the contraction up to two times greater the phenylephrine-induced one. Lipoxygenase inhibitors prevented it. At high stretch, the ACh vasorelaxant effect was marginally influenced by cyclooxygenase (COX) inhibition. Similar results were obtained when aortic strips were precontracted with PGF(2 alpha). 6. Our data indicate that when resting tension is low, ACh mobilizes a stored NO pool that, synergistically with COX-derived metabolites, can relax precontracted strips. COX inhibition up-regulates the lipoxygenase metabolic pathway, accounting for the ACh contractile effect. At an intermediate resting tension, NO production is present, but COX inhibition reveals a lipoxygenase-dependent, ACh-induced contraction. At high resting tension, NO synthesis predominates and COX metabolites influence ACh-induced relaxation marginally.

Relaxin-induced increased coronary flow through stimulation of nitric oxide production.

1. Relaxin (RLX) is a multifunctional hormone which, besides its role in pregnancy and parturition, has also been shown to influence the cardiovascular system. In this study, we investigated the effect of RLX on coronary flow of rat and guinea-pig hearts, isolated and perfused in a Langendorff apparatus. RLX was either added to the perfusion fluid at a concentration of 5 x 10(-9) M for a 20-min perfusion, or given as a bolus into the aortic cannula at concentrations of 10(-9) M, 5 x 10(-8) M dissolved in 1 ml of perfusion fluid. 2. RLX, given either for a 20-min perfusion or as a bolus in the aortic cannula to guinea-pig and rat isolated hearts, increased the coronary flow and the amount of nitrite, a stable end-product of nitric oxide (NO) metabolism, that appeared in the perfusates in a concentration-dependent fashion. 3. The increase in coronary flow and in nitrite in the perfusates induced by RLX was significantly reduced by pretreatment with the nitric oxide synthase (NOS) inhibitor, NG-monomethyl-L-arginine (L-NMMA, 10(-4) M). 4. The effects of RLX on coronary flow and nitrite amounts in the perfusates were compared with those induced by the endothelium-dependent vasodilator agent, acetylcholine (ACh, 10(-8)-10(-7) M), and by the endothelium-independent vasodilator agent, sodium nitroprusside (SNP, 10(-7)-10(-6) M). The results obtained show that RLX is more effective than ACh and SNP in increasing coronary flow. 5 The results of this study show that RLX increases coronary flow through stimulation of NO production; hence this hormone should be regarded as a novel agent capable of improving myocardial perfusion.

Protective effect of relaxin in cardiac anaphylaxis: involvement of the nitric oxide pathway.

1 Relaxin (RLX) is a multifunctional hormone best known for its role in pregnancy and parturition, that has been also shown to influence coronary perfusion and mast cell activation through the generation of endogenous nitric oxide (NO). In this study we report on the effects of RLX on the biochemical and mechanical changes of ex vivo perfused hearts isolated from ovalbumin-sensitized guinea-pigs induced by challenge with the specific antigen. The possible involvement of NO in the RLX action has been also investigated. 2 A 30-min perfusion with RLX (30 ng ml(-1)) before ovalbumin challenge fully abated the positive chronotropic and inotropic effects evoked by anaphylactic reaction to the antigen. RLX also blunted the short-term coronary constriction following to antigen challenge. Conversely, perfusion with chemically inactivated RLX had no effect. 3 The release of histamine in the perfusate and the accumulation of calcium in heart tissue induced by antigen challenge were significantly decreased by RLX, while the amounts of nitrites in the perfusate were significantly increased, as were NO synthase activity and expression and cGMP levels in heart tissue. 4 These findings indicate that RLX has a protective effect in cardiac anaphylaxis which involves an up-regulation of the NO biosynthetic pathway.

The vasorelaxant hormone relaxin induces changes in liver sinusoid microcirculation: a morphologic study in the rat.

This study shows that specialized contractile endothelial cells exist in rat liver sinusoids which may be involved in the local control of hemodynamics and which are sensitive to vasoactive agents, including the vasorelaxant hormone relaxin. Male rats were treated with 10 microg relaxin for 4 days; phosphate-buffered saline (PBS)-treated rats were the controls. For comparison, rats treated with relaxin together with the NO-synthase inhibitor N(omega)-nitro-l -arginine methyl ester (L-NAME), and rats treated with the vasodilator taurodeoxycholic acid or the vasoconstrictor ethanol were investigated. Liver fragments were studied morphologically and morphometrically. In the control rats, peculiar contractile cells were present in the endothelial lining. These cells had abundant myofilaments and formed cytoplasmic blebs projecting into and often occluding the lumen. In the ethanol-treated rats, sinusoids were constricted and filled with cytoplasmic blebs. In the relaxin-treated rats, sinusoids were markedly dilated and the cytoplasmic blebs nearly disappeared. Similar findings were observed in the taurodeoxycholic acid-treated rats. The effects of relaxin were blunted by L-NAME, suggesting that the relaxin action involves an NO-mediated mechanism.