Novel drug development opportunity for relaxin in acute myocardial infarction: evidences from a swine model.

The hormone relaxin has been shown to cause coronary vasodilation and to prevent ischemia/reperfusion-induced cardiac injury in rodents. This study provides evidence that relaxin, used as an adjunctive drug to coronary reperfusion, reduces the functional, biochemical, and histopathological signs of myocardial injury in an in vivo swine model of heart ischemia/reperfusion, currently used to test cardiotropic drugs for myocardial infarction. Human recombinant relaxin, given at reperfusion at doses of 1.25, 2.5, and 5 microg/kg b.wt. after a 30-min ischemia, caused a dose-related reduction of key markers of myocardial damage (serum myoglobin, CK-MB, troponin T) and cardiomyocyte apoptosis (caspase 3, TUNEL assay), as well as of cardiomyocyte contractile dysfunction (myofibril hypercontraction). Compared with the controls, relaxin also increased the uptake of the viability tracer 201Thallium and improved ventricular performance (cardiac index). Relaxin likely acts by reducing oxygen free radical-induced myocardial injury (malondialdehyde, tissue calcium overload) and inflammatory leukocyte recruitment (myeloperoxidase). The present findings show that human relaxin, given as a drug to counteract reperfusion-induced cardiac injury, affords a clear-cut protection to the heart of swine with induced myocardial infarction. The findings also provide background to future clinical trials with relaxin as adjunctive therapy to catheter-based coronary angioplasty in patients with acute myocardial infarction.

Human recombinant relaxin reduces heart injury and improves ventricular performance in a swine model of acute myocardial infarction.

This study shows that relaxin can be effective in the treatment of acute myocardial infarction. In a swine model of heart ischemia-reperfusion currently used to test cardiotropic drugs because of its similarities with human myocardial infarction, human recombinant relaxin (2.5 and 5 microg/kg body weight), given at reperfusion after a 30-min ischemia, markedly reduced the main serum markers of myocardial damage (myoglobin, CK-MB, and troponin T) and the metabolic and histopathologic parameters of myocardial inflammation and cardiomyocyte injury, resulting in overall improvement of ventricular performance (increased cardiac index) compared to the controls. These results provide a background for future clinical trials with human relaxin as adjunctive therapy to catheter-based coronary angioplasty in patients with acute myocardial infarction.

Relaxin inhibits the activation of human neutrophils: involvement of the nitric oxide pathway.

In animal models of inflammation, the pregnancy hormone relaxin was shown to reduce the recruitment of leukocytes, especially neutrophils, in inflamed tissues. The current study was designed to clarify whether relaxin could inhibit activation of isolated human neutrophils and, if so, whether the nitric oxide (NO) biosynthetic pathway was involved, as occurs in other relaxin targets. Human neutrophils were preincubated with 1, 10, and 100 nmol/liter porcine relaxin for 1 h before activation with N-formyl-Met-Leu-Phe (10 micromol/liter) or phorbol-12-myristate-13-acetate (0.1 micromol/liter). In selected experiments, the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA, 100 micromol/liter) was added to the samples 30 min before relaxin. In other experiments, chemically inactivated relaxin (10 nmol/liter) was substituted for authentic relaxin. Untreated, nonactivated neutrophils were the controls. Relaxin reduced significantly and in a concentration-dependent fashion the expression of the surface activation marker CD11b, as well as the generation of superoxide anion, the rise of intracellular Ca(2+), the release of cytoplasmic granules, and the chemotactic migration. These effects of relaxin were blunted by N(G)-monomethyl-L-arginine and could not be reproduced by inactivated relaxin. Relaxin also increased neutrophil inducible NO synthase expression and NO generation. This study provides evidence that relaxin inhibits the activation of human neutrophils stimulated by different proinflammatory agents. This novel property of relaxin could be of relevance in toning down maternal neutrophil activation during pregnancy, thereby counteracting the occurrence of pregnancy-related disorders such as preeclampsia, which is regarded as an excess maternal inflammatory response to pregnancy.

Relaxin depresses small bowel motility through a nitric oxide-mediated mechanism. Studies in mice.

Gastrointestinal motility is reduced and the incidence of functional gastrointestinal disorders is increased in pregnancy, possibly due to hormonal influences. This study aims to clarify whether the hormone relaxin, which attains high circulating levels during pregnancy and has a nitric oxide-mediated relaxant action on vascular and uterine smooth muscle, also reduces bowel motility and, if it does, whether nitric oxide is involved. Female mice in proestrous or estrous were treated for 18 h with relaxin (1 microg s.c.) or vehicle (controls). Isolated ileal preparations from both groups were used to record contractile activity, either basal or after acute administration of relaxin (5 x 10(-8) M). Drugs inhibiting nitric oxide biosynthesis or neurotransmission were used in combination with relaxin. Expression of nitric oxide synthase isoforms by the ileum was assessed by immunocytochemistry and Western blot analysis. Relaxin caused a clear-cut decay of muscle tension and a reduction in amplitude of spontaneous contractions upon either chronic administration to mice or acute addition to isolated ileal preparations. These effects were significantly blunted by N(G)-nitro-L-arginine, but not by the neural blockers we used. Moreover, relaxin increased the expression of nitric oxide synthases II and III, but not synthase I. Relaxin markedly inhibits ileal motility in mice by exerting a direct action on smooth muscle through the activation of intrinsic nitric oxide biosynthesis.

Depression by relaxin of neurally induced contractile responses in the mouse gastric fundus.

The peptide hormone relaxin, which attains high circulating levels during pregnancy, has been shown to depress small-bowel motility through a nitric oxide (NO)-mediated mechanism. In the present study we investigated whether relaxin also influences gastric contractile responses in mice. Female mice in proestrus or estrus were treated for 18 h with relaxin (1 microg s.c.) or vehicle (controls). Mechanical responses of gastric fundal strips were recorded via force-displacement transducers. Evaluation of the expression of nitric oxide synthase (NOS) isoforms was performed by immunohistochemistry and Western blot. In control mice, neurally induced contractile responses elicited by electrical field stimulation (EFS) were reduced in amplitude by addition of relaxin to the organ bath medium. In the presence of the NO synthesis inhibitor l-NNA, relaxin was ineffective. Direct smooth muscle contractile responses were not influenced by relaxin or l-NNA. In strips from relaxin-pretreated mice, the amplitude of neurally induced contractile responses was also reduced in respect to the controls, while that of direct smooth muscle contractions was not. Further addition of relaxin to the bath medium did not influence EFS-induced responses, whereas l-NNA did. An increased expression of NOS I and NOS III was observed in gastric tissues from relaxin-pretreated mice. In conclusion, the peptide hormone relaxin depresses cholinergic contractile responses in the mouse gastric fundus by up-regulating NO biosynthesis at the neural level.