Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:4.6.1.2 (guanylate cyclase)
 8,497 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the course of our studies on the local blood flow modulation in the NMRI-mouse placenta we have focussed on regulatory pathways involving recently appreciated gaseous messenger molecules nitric oxide (NO) and carbon monoxide (CO), which are generated by NO synthase (NOS) and heme oxygenase (HO)-2, respectively. The distribution of NOS was investigated by immunohistochemistry using an antiserum to the neuronal isoform (NOS-I) and by NADPH diaphorase (NADPHd) histochemistry, supplemented with procedures (permanganate and formaldehyde method) serving to enhance the specificity of the enzyme histochemical method for NOS visualization. HO-2 was demonstrated immunohistochemically. In addition, cyclic guanosine monophosphate (cGMP)-forming soluble guanylate cyclase (sGC) and dehydrogenases generating the NOS co-substrate NADPH were analysed either by immunohistochemistry or enzyme histochemistry. NOS-I immunostaining was observed in the intraplacental visceral yolk sac epithelial cells but not in the placenta and extraplacental visceral epithelial yolk sac cells. Co-localization of NOS-I immunolabeling and NOS-associated NADPHd was exclusively found in the intraplacental visceral epithelial cells, while NADPHd activity not associated to NOS was present in other placental and extraplacental cells additionally analysed for control reasons. HO-2 and sGC immunoreactivity could not be detected in the placenta including the intraplacental visceral epithelial cells but were expressed in several extraplacental cells. Dehydrogenases producing the NOS co-substrate NADPH were present in the intraplacental visceral epithelium as well as in other placental and extraplacental cells. Since the intraplacental visceral epithelial yolk sac layer closely accompanies large fetal blood vessels entering the placental labyrinth from the chorionic plate it may be assumed that NO, generated by the NADPH-consuming NOS-I in the intraplacental yolk sac epithelium, acts to regulate the blood flow by relaxing smooth muscle cells in the wall of these fetal vessels. The lack of immunoreactivity to the NO-effector molecule sGC may be due to methodological reasons. The absence of the HO-2/CO system suggests its insignificant role as a potential gas signaling pathway in the vascular smooth muscle system of the intraplacental visceral yolk sac of mice.
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PMID:Nitric oxide synthase I immunoreactivity and NOS-associated NADPHd histochemistry in the visceral epithelial cells of the intraplacental mouse yolk sac. 873 2

Microsomal heme oxygenase (HO) is a cytochrome P-450-assisted oxidoreductase, which catalyzes the NADPH-dependent decomposition of heme to carbon monoxide (CO), biliverdin, and iron. Recent evidence suggests that CO, similar to nitric oxide (NO), may serve as gaseous biological signalling molecule, which acts by stimulating soluble guanylate cyclase in target cells. In the present investigation, we report the HO-like immunoreactivity (LIR) pattern of the constitutive HO isozyme, HO-2, and compare the results with recently published data on constitutive NO-producing nitric oxide synthase (NOS) in rat tissues. HO-2-LIR was most consistently observed in connective tissue elements (fibrocytes/-blasts and fibroblast-like cells, such as interstitial cells in the bowel), blood vessel wall constituents (arterial and venous endothelial cells, vascular smooth muscle cells), visceral smooth muscle cells (airway musculature, myometrium, muscularis mucosae of the small intestine), mesothelial cells of serous membranes and in select epithelial cell populations. HO-2-LIR was absent from the striated (skeletal and cardiac) musculature. HO-2 had a more widespread distribution and its expression largely differs from that of NOS. HO-2-LIR and NOS appear to be co-expressed in vascular endothelial cells and in selected nerve cell populations of certain parasympathetic and probably sensory ganglia. Our data suggest potential CO and NO systems as interrelated regulatory pathways in the local paracrine and autocrine control of diverse functional systems.
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PMID:Expression of heme oxygenase-2 (HO-2)-like immunoreactivity in rat tissues. 873 5

1. The distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)-1 and -2 was studied by immunohistochemistry in the pig's lower urinary tract, including bladder extramural arteries, and the oesophagogastric junction (OGJ). In isolated smooth muscle from the urethra and the OGJ, the mechanisms for CO-induced relaxations were characterized by measurement of cyclic nucleotide levels and by responses to the guanylate cyclase inhibitor methylene blue and some K+ channel inhibitors. 2. HO-2 immunoreactivity was observed in coarse nerve trunks within the smooth muscle of the urethra and OGJ, and in nerve cell bodies of the enteric plexuses of the OGJ. Furthermore, the vascular endothelium of the intramural vessels of the urethra, bladder and OGJ, and the extramural vessels of the bladder, displayed HO-2 immunoreactivity. Two different antisera against HO-1 were used, but only one displayed immunoreactivity in neuronal structures. HO-1 immunoreactivity, as displayed by this antiserum, was seen in nerve cells, coarse nerve trunks and varicose nerve fibres in the smooth muscle of the urethra and OGJ. Some HO-2 and/or HO-1 (as displayed by both HO-1 antisera) immunoreactive cells with a non-neuronal appearance were observed within the smooth muscle of the OGJ, bladder and urethra. 3. In the urethral preparations, exogenously applied CO (72 microM) evoked a relaxation amounting to 76 +/- 6%. The relaxation was associated with an increase in cyclic GMP, but not cyclic AMP, content. CO-evoked relaxations were not significantly reduced by treatment with methylene blue, or by inhibitors of voltage-dependent (4-aminopyridine), high (iberiotoxin, charybdotoxin) and low (apamin) conductance Ca(2+)-activated, and ATP-sensitive (glibenclamide) K+ channels. Bladder strips, and ring preparations from the extramural arteries of the bladder, did not respond to exogenously administered CO (12-72 microM). 4. In the OGJ, exogenously applied CO evoked a relaxation of 86 +/- 6%, which was associated with an increase in cyclic GMP, but not cyclic AMP, content. Treatment with 30 microM methylene blue raised the spontaneously developed muscle tone, and reduced the maximum relaxation evoked by CO to 33 +/- 9%. Addition of 4-aminopyridine, apamin, glibenclamide, iberiotoxin, charybdotoxin or glibenclamide had no effect on the relaxations. 4-aminopyridine (0.1-1 mM), iberiotoxin (0.1 microM) and charybdotoxin (0.1 microM) increased the spontaneously developed tone, and a combination of charybdotoxin and apamin reduced CO-induced (24 microM CO) relaxations. 5. The present findings demonstrate the presence of HO in both neuronal and non-neuronal cells in the pig OGJ and lower urinary tract. CO produces relaxation of the smooth muscle in the OGJ and urethra, associated with a small increase in cyclic GMP concentration in both regions. Relaxations evoked by CO in the urethra do not seem to involve voltage-dependent, low and high conductance, or ATP-dependent K+ channels. However, in the OGJ relaxations evoked by CO can be attenuated by methylene blue and a combination of charybdotoxin and apamin.
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PMID:Carbon monoxide-induced relaxation and distribution of haem oxygenase isoenzymes in the pig urethra and lower oesophagogastric junction. 911 25

Recent studies indicate that vascular smooth muscle cells generate carbon monoxide (CO) via the action of heme oxygenase (HO). Because adenosine 3',5'-cyclic monophosphate (cAMP) is an important intracellular signaling molecule in the regulation of vascular cell function, we examined whether this second messenger modulates the expression of HO and the production of CO by rat aortic smooth muscle cells. Treatment of smooth muscle cells with the membrane-permeable cAMP derivative dibutyryl cAMP or with compounds that increase intracellular cAMP levels (isoproterenol and forskolin) resulted in a concentration- and time-dependent increase in the levels of HO-1 mRNA and protein, whereas the expression of HO-2 remained unchanged. Both actinomycin D and cycloheximide blocked the basal expression of HO-1 mRNA and protein and prevented the cAMP-mediated induction of HO-1. Incubation of platelets with cAMP-treated smooth muscle cells resulted in a significant increase in platelet cGMP concentration that was partially reversed by treatment of smooth muscle cells with the nitric oxide synthase inhibitor NG-monomethyl-L-arginine or the HO blocker zinc protoporphyrin-IX. However, the combined addition of these two inhibitors to cAMP-treated smooth muscle cells or the addition of the CO and NO scavenger hemoglobin to platelets completely blocked the stimulatory effect on platelet cGMP levels. These results demonstrate that cAMP induces the expression of the HO-1 gene and stimulates the formation of CO and NO in vascular smooth muscle cells. The capacity of cAMP to induce the synthesis of guanylate cyclase-stimulatory CO from smooth muscle cells may represent a novel mechanism by which this nucleotide regulates vascular tone.
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PMID:cAMP induces heme oxygenase-1 gene expression and carbon monoxide production in vascular smooth muscle. 924 6

Heme oxygenase (HO) proteins are members of the HSP30 family and consist of 2 isozymes identified to date, termed HO-1 and HO-2. Separate genes encode the isozymes and protein products which are immunochemically distinct, share less than 50% similarity at the amino acid sequence level. Each form, however, shows greater than 90% similarity among species, including human and the rat (reviewed in ref.). Furthermore, these isozymes function in a well-defined role to carry out oxidation of the heme molecule (Fe-protoporphyrin IX) in concert with NADPH-cytochrome P450 reductase. The oxidation of heme is isomer specific and results in the formation of bile pigments, carbon monoxide, and iron. The heme molecule constitutes the prosthetic moiety of hemoproteins, such as hemoglobin, myoglobin, catalase, soluble guanylate cyclase, cytochrome b5, cytochromes P450 and NO synthase. HO-1 also known as heat shock protein (HSP) 32 is encoded by a gene which is exquisitely stress-responsive and a host of stimuli that mediate oxidative stress cause induction of the protein both in vivo and in vitro. The HO-2 form shows a unique pattern of regulation from that of HO-1. HO-2 is a constitutive protein and its expression is not affected by the inducers of HO-1 tested to date; rather, the only known regulator of HO-2 yet identified is adrenal glucocorticoids. The two isozymes display vast differences in tissue distribution and under normal conditions HO-1 is present in the whole brain at the limit of immunodetection and is discreetly localized in select neuronal populations. HO-1 protein (approximately 32 kDa) and its approximately 1.8 kb transcript are increased, however, in response to stressful stimuli primarily in non-neuronal cell populations. The heme oxygenase system serves in both a catabolic and anabolic capacity in the cell. In the former capacity, it down-regulates cellular heme and hemoprotein levels. And, as such it inactivates the most effective catalyst for formation of free radicals, the heme molecule. In its anabolic role, as noted above, heme oxygenase produces bile pigments, carbon monoxide, and iron, all of which are biologically active: bile pigments function as antioxidants; the carbon monoxide generated by HO activity has been correlated with the generation of cGMP; and iron regulates expression of various genes, including that of HO-1 itself, as well as transferrin receptors, ferritin, and NO synthase. We used rabbit anti-rat HO-2 polyclonal antibody and HO-2 cDNA to localize HO-2 immunoreactive protein and the 1.3- and 1.9 kb homologous transcripts, respectively, in rodent brain as visualized by histochemical staining procedures. These protocols provide the first detailed description of methodologies successfully used to define the pattern of HO-2 expression at the transcriptional and translational levels in the adult rat brain and glucocorticoid-treated newborn rats. The procedures described herein have the virtue of being non-radioactive, as well as applicability to the systemic organs, such as the cardiovascular system and the male reproductive organs. Visualization of cellular HO-2 expression aids in assessment of potential sites of carbon monoxide, iron, and bilirubin production within the nervous system.
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PMID:Histochemical localization of heme oxygenase-2 protein and mRNA expression in rat brain. 938 81

Carbon monoxide (CO) is an endogenously produced gas sharing many properties with nitric oxide (NO), notably activating soluble guanylate cyclase and relaxing blood vessels. The brain can generate high quantities of CO from a constitutive enzyme, haem oxygenase (HO-2). To determine whether CO is involved in the regulatory mechanisms of cerebral blood flow (CBF), two conditions associated with a reproducible CBF increase were studied in rats: epileptic seizures induced by kainate, and hypercapnia. The HO inhibitor tin protoporphyrin (Sn-PP) did not modify the basal level of CBF, significantly reduced the increase in CBF during status epilepticus, and did not affect the cerebrovascular response to hypercapnia. It is concluded that CO participates in the regulation of CBF in specific conditions, notably those associated with glutamate release.
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PMID:Carbon monoxide regulates cerebral blood flow in epileptic seizures but not in hypercapnia. 969 25

Carbon monoxide (CO) is an endogenously generated gas that may play an important physiological role in the circulation. CO is generated by vascular cells as a byproduct of heme catabolism, in which heme oxygenase (HO) catalyzes the degradation of heme to biliverdin, iron and CO. Two distinct isoforms of HO have been identified in vascular tissue. The HO-2 isoform is constitutively expressed and likely mediates the release of CO under normal physiologic conditions. In contrast, the HO-1 isoform is strongly induced in vascular cells by various stress-associated agents and markedly increases CO synthesis during pathological conditions. The release of CO by vascular cells exerts both paracrine and autocrine effects on vascular smooth muscle cells (SMC) and circulating blood cells. CO regulates blood flow and blood fluidity by inhibiting vasomotor tone, SMC proliferation, and platelet aggregation. These vascular effects of CO are mediated via the activation of soluble guanylate cyclase and the consequent rise in intracellular guanosine 3',5'-cyclic monophosphate levels in target tissues. CO may also play a role in various cardiovascular disorders, including endotoxin shock, ischemia-reperfusion, hypertension, and subarachnoid hemorrhage. This review will focus on the recent progress made in understanding the regulation and function of CO in the vasculature.
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PMID:Carbon monoxide and vascular cell function (review). 985 96

The inhibitory innervation of guinea-pig urethral smooth muscle was investigated histochemically and functionally. The distribution of immunoreactivities to haem oxygenases (HO), neuronal NO synthase (nNOS), and vasoactive intestinal polypeptide (VIP) was studied, and the functional effects of the corresponding putative transmitters, CO, NO, and VIP, were assessed. HO-2 immunoreactivity was found in all nerve cell bodies of intramural ganglia, localized between smooth muscle bundles in the detrusor, bladder base and proximal urethra. About 70% of the ganglionic cell bodies were also NOS-immunoreactive (IR), whereas a minor part was VIP-IR. Some ganglion cells exhibiting tyrosine hydroxylase (TH) activity were demonstrated. Rich numbers of NOS-IR varicose nerve terminals could be found innervating the smooth muscle of the urethra, whereas VIP-IR terminals were less numerous. A rich number of TH-IR terminals were observed. The bladder showed a similar distribution of nerves, although only a few number of TH-IR nerves could be found. In bladder preparations exposed to sodium nitroprusside, cGMP-IR cells could be seen, forming an interconnecting network with long spindle-shaped processes. The cGMP-IR cells were especially abundant in the outer smooth muscle layers of the bladder, but less numerous in the urethra. In urethral strip preparations, electrical field stimulation evoked long-lasting frequency-dependent relaxations. The relaxations were not inhibited by the NO-synthesis inhibitor, L-NOARG, or enhanced by the NO-precursor, L-arginine. The haem precursor, 5-aminolevulinic acid (5-ALA), or the inhibitor of guanylate cyclase, ODQ, did not affect the urethral relaxations. Exogenously applied NO, SIN-1, and VIP relaxed the preparations by approximately 50%, whereas the relaxation evoked by exogenous CO was minor. These results suggest that CO probably is not involved in non-adrenergic, non-cholinergic inhibitory control of the guinea-pig urethra, where a non-NO/cGMP mediated relaxation seems to be predominant.
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PMID:Inhibitory innervation of the guinea-pig urethra; roles of CO, NO and VIP. 985 22

Carbon monoxide (CO) has been suggested as a novel messenger molecule in the brain. We now report on the cellular localization and hormone secretory function of a CO-producing constitutive heme oxygenase (HO-2) in mouse islets. Islet homogenates produced large amounts of CO which were suppressed dose-dependently by the HO inhibitor zincprotoporphyrin-IX (ZnPP-IX). We also show, for the first time, that glucose markedly stimulates the HO activity (CO production) in intact islets. A further potentiation was induced by the HO substrate hemin. Western blot showed that islet tissue expressed HO-2, and confocal microscopy revealed that HO-2 resided in insulin, glucagon, somatostatin, and pancreatic polypeptide cells. ZnPP-IX dose-dependently inhibited, whereas hemin enhanced, both insulin and glucagon secretion from glucose-stimulated islets. Stimulation or inhibition of CO production was accompanied by corresponding changes in islet cGMP levels. Exogenously applied CO stimulated insulin and glucagon release from isolated islets, whereas exogenous nitric oxide (NO) inhibited insulin and stimulated glucagon release. Islets stimulated by glucose or L-arginine displayed a marked increase in their NO-synthase (NOS) activity. Such an increase was suppressed by hemin, conceivably because NOS activity was inhibited by hemin-derived CO. Consequently, hemin enhanced L-arginine-induced insulin secretion. Insulin release stimulated by either hemin-derived CO or exogenous CO was strongly inhibited by the guanylate cyclase inhibitor ODQ, but it was unaffected by ZnPP-IX. Glucagon release induced by CO (but not by hemin) was inhibited by ODQ and partly inhibited by ZnPP-IX. We propose that the islets of Langerhans are equipped with a heme oxygenase-carbon monoxide pathway, which constitutes a novel regulatory system of physiological importance for the stimulation of insulin and glucagon release. This pathway is stimulated by glucose, is at least partly dependent on the cGMP system, and displays interaction with islet NOS activity.
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PMID:Heme oxygenase and carbon monoxide: regulatory roles in islet hormone release: a biochemical, immunohistochemical, and confocal microscopic study. 989 24

The nitric oxide (NO)-cGMP pathway has been proposed as a mechanism for relaxation of myometrium during pregnancy and as a modulator of labor. Carbon monoxide (CO), produced by hemeoxygenases (HO-1 and HO-2), also activates soluble guanylate cyclase to increase cGMP. A recent study reported a large increase in HO-1 and HO-2 proteins during pregnancy, suggesting that the HO-CO pathway may be important in the maintenance of uterine quiescence during pregnancy. In this study we used Western blotting, reverse transcription-polymerase chain reaction, and immunohistochemistry to determine HO-1 and HO-2 expression in nonpregnant, pregnant, and laboring myometrium. Immunolocalization of HO was also compared with endothelial and inducible nitric oxide synthases (eNOS and iNOS). In contrast to HO-1 protein, which was not detected in myometrium, HO-2 protein and mRNA were constitutively expressed, although there were no differences in expression between the groups. eNOS was expressed in endothelial cells but not in myometrial smooth muscle. iNOS protein was not detected in myometrium. These data do not support an up-regulation of HO-1 and HO-2 during pregnancy and are not consistent with a role for NO or a major role for CO in human myometrial quiescence. Our results are also in keeping with HO-2 being an noninducible protein.
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PMID:Hemoxygenase and nitric oxide synthase do not maintain human uterine quiescence during pregnancy. 1048 41


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