Bidirectional regulation of the cyclic guanosine monophosphateadenosine monophosphate synthase-stimulator of interferon gene pathway and its impact on hepatocellular carcinoma

BACKGROUND Hepatocellular carcinoma(HCC)ranks as the fourth leading cause of cancerrelated deaths in China,and the treatment options are limited.The cyclic guanosine monophosphate-adenosine monophosphate synthase(cGAS)activates the stimulator of interferon gene(STING)signaling pathway as a crucial immune response pathway in the cytoplasm,which detects cytoplasmic DNA to regulate innate and adaptive immune responses.As a potential therapeutic target,cGASSTING pathway markedly inhibits tumor cell proliferation and metastasis,with its activation being particularly relevant in HCC.However,prolonged pathway activation may lead to an immunosuppressive tumor microenvironment,which fostering the invasion or metastasis of liver tumor cells.AIM To investigate the dual-regulation mechanism of cGAS-STING in HCC.METHODS This review was conducted according to the PRISMA guidelines.The study conducted a comprehensive search for articles related to HCC on PubMed and Web of Science databases.Through rigorous screening and meticulous analysis of the retrieved literature,the research aimed to summarize and elucidate the impact of the cGAS-STING pathway on HCC tumors.RESULTS All authors collaboratively selected studies for inclusion,extracted data,and the initial search of online databases yielded 1445 studies.After removing duplicates,remaining 964 records were screened.Ultimately,55 articles met the inclusion criteria and were included in this review.CONCLUSION Acute inflammation can have a few inhibitory effects on cancer,while chronic inflammation generally promotes its progression.Extended cGAS-STING pathway activation will result in a suppressive tumor microenvironment.

Role of cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes pathway in diabetes and its complications

Diabetes mellitus(DM)is one of the major causes of mortality worldwide,with inflammation being an important factor in its onset and development.This review summarizes the specific mechanisms of the cyclic guanosine monophosphate-adenosine monophosphate synthase(cGAS)-stimulator of interferon genes(STING)pathway in mediating inflammatory responses.Furthermore,it compre-hensively presents related research progress and the subsequent involvement of this pathway in the pathogenesis of early-stage DM,diabetic gastroenteropathy,diabetic cardiomyopathy,non-alcoholic fatty liver disease,and other complic-ations.Additionally,the role of cGAS-STING in autonomic dysfunction and intes-tinal dysregulation,which can lead to digestive complications,has been discuss-ed.Altogether,this study provides a comprehensive analysis of the research advances regarding the cGAS-STING pathway-targeted therapeutic agents and the prospects for their application in the precision treatment of DM.

Effects of plant extract neferine on cyclic adenosine monophosphate and cyclic guanosine monophosphate levels in rabbit corpus cavernosum in vitro

Aim： To further investigate the relaxation mechanism of neferine （NED, a bis-benzylisoquinoline alkaloid extracted （isolated） from the green seed embryo of Nelumbo nucifera Gaertn in China, on rabbit corpus cavernosum tissue in vitro. Methods： The effects of Nef on the concentrations of cyclic adenosine monophosphate （cAMP） and cyclic guanosine monophosphate （cGMP） in isolated and incubated rabbit corpus cavernosum tissue were recorded using ^125I radioimmunoassay. Results： The basal concentration of cAMP in corpus cavernosum tissue was 5.67 ± 0.97 pmol/mg. Nef increased the cAMP concentration in a dose-dependent manner （P 〈 0.05）, but this effect was not inhibited by an adenylate cyclase inhibitor （cis-N-[2-phenylcyclopentyl]azacyclotridec-1-en-2-amine, MDL-12, 330A） （P 〉 0.05）. The accumulation of cAMP induced by prostaglandin Et （PGEt, a stimulator of cAMP production） was also augmented by Nef in a dose-dependent manner （P 〈 0.05）. The basal concentration of cGMP in corpus cavernosum tissue is 0.44 ± 0.09 pmol/mg. Nef did not affect this concentration of cGMP, either in the presence or in the absence of a guanyl cyclase inhibitor （1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ） （P 〉 0.05）. Also, sodium nitroprusside （SNP, a stimulator of cGMP production）-induced cGMP production was not enhanced by Nef （P 〉 0.05）. Conclusion： Nef, with its relaxation mechanism, can enhance the concentration of cAMP in rabbit corpus cavernosum tissue, probably by inhibiting phosphodiesterase activity. （Asian JAndro12008 Mar; 10： 307-312）

Studies on Relationship between Serum Nitric Oxide and Plasma Cyclic Guanosine Monophosphate and Prolonged Bleeding after Medical Abortion as well as Prophylaxis and Treatment of Bleeding with Traditional Chinese Medicine

Objectives To study the relationship between serum nitric oxide (NO and plasma cyclic guanosine monophosphate (cGMP) and prolonged bleeding after medical abortion. Methods A total of 120 women having received medical abortions at random were recruited and divided into two groups: the one (Group A,n=60) taking 'Gong Fu Mixture(Uterus Recovering Mixture)' and the other (Group B,n=60) not taking it after abortion. On d 10, 20 and 30 after medical abortion, serum NO and plasma cGMP were tested before and after mifepristone administration and 10 d later by Gresis reaction method and radioimmunoassay respectively. Results NO concentration in serum and cGMP concentration in plasma decreased significantly after taking mifepristone given (P<0.05). Ten days later, the number of those with bleeding discontinuation in the group A was significantly greater than that in the group B (P<0.05). Serum NO level and plasma cGMP level in the group A decreased more significantly than those in the group B (P<0.05). Conclusion The slow decrease of serum NO and plasma cGMP is closely related to prolonged bleeding after medical abortion. “Gong Fu Mixture (uterus recovering mixture)” is effective in prevention and treatment of prolonged bleeding.

Existence of Heme Oxygenase-carbon Monoxide-cyclic Guanosine Monophosphate Pathway in Human Trabecular Meshwork Cells In Vitro

To confirm the existence of heme oxygenase (HO)-carbon monoxide (CO)- cyclic guanosine monophosphate (cGMP) pathway in the cultured human trabecular meshwork cells (HTMCs) in vitro, and to evaluate the inductive role of hemin on this pathway, HTMCs of the third to fourth generation were cultured in vitro. Reverse transcripase-polymerase chain reaction (RT-PCR) was employed for detection of HO-1 and HO-2 mRNA. Immunohistochemical staining was used to detect HO-1 and HO-2 proteins. Hemin was added into the culture solution. The HO-1 mRNA levels were quantified by RT-PCR. The relative amount of carbon monoxide released into the media was measured with the quantifying carbon monoxide hemoglobin (HbCO) by spectrophotometry. Radioimmunoassay was used to determine changes of cGMP in HTMCs. The results showed that cultured cells had the specific characteristics of HTMCs. Both HO-1 and HO-2 genes were expressed in HTMCs, as well as HO-1 and HO-2 proteins in HTMCs. Hemin induced HO-1 mRNA, HbCO and cGMP in a dose-dependent manner. In conclusion, HO-CO-cGMP pathway exists in the cultured HTMCs and can be induced by hemin. Pharmacological stimulation of HO-CO-cGMP pathway may constitute a novel therapeutic approach to rescuing glaucoma.

The cGAS-STING-interferon regulatory factor 7 pathway regulates neuroinflammation in Parkinson's disease

Interferon regulatory factor 7 plays a crucial role in the innate immune response.However,whether interferon regulatory factor 7-mediated signaling contributes to Parkinson's disease remains unknown.Here we report that interferon regulatory factor 7 is markedly up-regulated in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced mouse model of Parkinson's disease and co-localizes with microglial cells.Both the selective cyclic guanosine monophosphate adenosine monophosphate synthase inhibitor RU.521 and the stimulator of interferon genes inhibitor H151 effectively suppressed interferon regulatory factor 7 activation in BV2 microglia exposed to 1-methyl-4-phenylpyridinium and inhibited transformation of mouse BV2 microglia into the neurotoxic M1 phenotype.In addition,si RNA-mediated knockdown of interferon regulatory factor 7 expression in BV2 microglia reduced the expression of inducible nitric oxide synthase,tumor necrosis factorα,CD16,CD32,and CD86 and increased the expression of the anti-inflammatory markers ARG1 and YM1.Taken together,our findings indicate that the cyclic guanosine monophosphate adenosine monophosphate synthase-stimulator of interferon genes-interferon regulatory factor 7 pathway plays a crucial role in the pathogenesis of Parkinson's disease.

The mechanistic study on Wa medicine Niang-Mu-Liang medicinal liquor mitigating diabetes mellitus erectile dysfunction in rats by inhibiting ferroptosis

Background:This study aims to investigate the therapeutic effect of Wa medicine Niang-Mu-Liang medicinal liquor(NML)on rats with diabetes mellitus erectile dysfunction(DMED)and its impact on the ferroptosis signaling pathway.Methods:Thirty Sprague-Dawley rats were randomly divided into three groups:Control,DMED,and NML.After establishing the DMED model,treatments were administered for 8 weeks.After the administration,apomorphine hydrochloride tests were conducted to measure the mass and organ index of testes and epididymides,sperm concentration and viability in each group.Penile corpus cavernosum tissues were stained with hematoxylin and eosin.Nitric oxide and cyclic guanosine monophosphate levels in the penile corpus cavernosum tissues were determined using biochemical kits and enzyme-linked immunosorbent assay,while the expression of proteins related to the ferroptosis signaling pathway was measured by Western blot.Results:Compared to the DMED group,the DMED rats treated with NML showed significantly increased erection frequency,testicular and epididymal mass and index,sperm count and viability,along with noticeable improvement in the pathological morphology of penile corpus cavernosum.The content of nitric oxide and cyclic guanosine monophosphate,and the expression of ferritin heavy chain,ferritin light chain,and glutathione peroxidase 4 proteins in penile corpus cavernosum tissue were elevated,while the expression of transferrin and STEAP3 proteins was reduced.Conclusion:NML can improve erectile function in DMED rats by inhibiting the ferroptosis signaling pathway.

Glabridin Relaxes Vascular Smooth Muscles by Activating BK_(Ca) Channels and Inhibiting Phosphodiesterase in Human Saphenous Vein

The aim of the current study was to investigate the pharmacological activity of glabridinon the isolated human saphenous vein (SV) and explore the underlying mechanisms. Samples of patients' SVs were removed during bypass surgery, and 4-mm lengths of the vessels were placedin Krebs solution at ±4℃ and hung in an isolated organ bath to assess their contraction/relaxationresponses. The contraction/relaxation responses were recorded to observe if the cyclic guanosinemonophosphate (cGMP)/protein kinase G (PKG) pathway mediates the relaxant effect of glabridinafter treatment with blockers like ODQ (a guanylate cyclase inhibitor), KT5823 (a PKG inhibitor),isobutylmethylxanthine [IBMX, a phosphodiesterase (PDE) inhibitor], and cantharidin [Cant,a myosin light-chain phosphatase (MLCP) inhibitor]. Moreover, nitric oxide (NO), cGMP, andPKG levels in SV tissues were determined by ELISA after incubation with glabridin, N(o)-nitro-L-arginine methyl ester (L-Name, a NO synthetase inhibitor), phenylephrine (PE), ODQ, IBMX,and KT5823. The results showed that glabridin relaxed the vascular smooth muscle of humanSV pretreated with PE in a dose-dependent manner, which was independent of the endothelium.The vasorelaxant effect of glabridin was only inhibited by iberiotoxin (IbTX), Cant, and KT5823.Glabridin increased cGMP and PKG levels in SV homogenates, whereas it did not alter the NOlevel. The enhancing efects of cGMP and PKG levels by glabridin were abolished by ODQ andKT5823. In conclusion, glabridin has a vasorelaxant effect, which is associated with the activationof BKc. channels and inhibition of PDE.

Neuroprotective effects of tadalafil on gerbil dopaminergic neurons following cerebral ischemia

Impairment of dopamine function, which is known to have major effects on behaviors and cognition, is one of the main problems associated with cerebral ischemia. Tadalafil, a long-acting phosphodiesterase type-5 inhibitor, is known to ameliorate neurologic impairment induced by brain injury, but not in dopaminergic regions. We investigated the neuroprotective effects of treatment with tadalafil on cyclic guanosine monophosphate level and dopamine function following cerebral ischemia. Forty adult Mongolian gerbils were randomly and evenly divided into five groups （n = 8 in each group）： Sham-operation group, cerebral ischemia-induced and 0, 0.1, 1, and 10 mg/kg tadalafil-treated groups, respectively. Tadalafil dissolved in distilled water was administered orally for 7 consecutive days, starting 1 day after surgery. Cyclic guanosine monophosphate assay and immunohistochemistry were performed for thyrosine hydroxylase expression and western blot analysis for dopamine D2 receptor expression. A decrease in cyclic guanosine monophosphate level following cerebral ischemia was found with an increase in thyrosine hydroxylase activity and a decrease in dopamine D2 receptor expression in the striatum and substantia nigra region. However, treatment with tadalafil increased cyclic guanosine monophosphate expression, suppressed thyrosine hydroxylase expression and increased dopamine 92 receptor expression in the striatum and substantia nigra region in a dose-dependent manner. Tadalafil might ameliorate cerebral ischemia-induced dopaminergic neuron injury. Therefore, tadalafil has the potential as a new neuroprotective treatment strategy for cerebral ischemic injury.

Dendroaspis natriuretic peptide relaxes gastric antral circular smooth muscle of guinea-pig through thecGMP/cGMP-dependent protein kinase pathway

AIM: To systematically investigate if cGMP/cGMP- dependent protein kinase G (PKG) signaling pathway may participate in dendroaspis natriuretic peptide (DNP)-induced relaxation of gastric circular smooth muscle. METHODS: The content of cGMP in guinea pig gastric antral smooth muscle tissue and perfusion solution were measured using radioimmunoassay; spontaneous contraction of gastric antral circular muscles recorded using a 4-channel physiograph; and Ca2+-activated K+ currents (IK(Ca)) and spontaneous transient outward currents (STOCs) in isolated gastric antral myocytes were recorded using the whole-cell patch clamp technique. RESULTS: DNP markedly enhanced cGMP levels in gastric antral smooth muscle tissue and in the perfusion medium. DNP induced relaxation in gastricantral circular smooth muscle, which was inhibited by KT5823, a cGMP-dependent PKG inhibitor. DNP increased IK(Ca). This effect was almost completely blocked by KT5823, and partially blocked by LY83583, an inhibitor of guanylate cyclase to change the production of cGMP. DNP also increased STOCs. The effect of DNP on STOCs was abolished in the presence of KT5823, but not affected by KT-5720, a PKA-specific inhibitor. CONCLUSION: DNP activates IK(Ca) and relaxes guinea-pig gastric antral circular smooth muscle via the cGMP/PKG-dependent singling axis instead of cAMP/ PKA pathway.

Epigallocatechin-3-gallate exerts antihypertensive effects and improves endothelial function in spontaneously hypertensive rats

Objective:To investigate the effect of epigallocatechin-3-gallate(EGCG)on endothelial dysfunction in spontaneously hypertensive rats(SHR).Methods:Wistar-Kyoto(WKY)rats and SHR were divided into four groups;WKY control,SHR control and SHR treated with EGCG(50 mg/kg/day)or losartan(10 mg/kg/day).The treatment was given daily for 4 weeks by oral gavage and the blood pressure was monitored by tail-cuff method every 3 days.Acetylcholineinduced endothelium-dependent relaxations were assessed in isolated phenylephrine-precontracted aortic rings at the end of treatment.The vascular levels of reactive oxygen species,nitric oxide,tetrahydrobiopterin,and cyclic guanosine monophosphate were also measured.Moreover,the expression of angiotensinⅡtype 1(AT_(1))receptor protein was determined.Results:The systolic blood pressure was significantly decreased in SHR treated with EGCG.The impaired endothelium-dependent relaxation was significantly improved in aortic ring isolated from the EGCG-treated SHR group.EGCG also significantly increased the levels of nitric oxide,tetrahydrobiopterin,and cyclic guanosine monophosphate,while decreasing the level of reactive oxygen species and the protein expression of AT_(1)receptor in SHR.Conclusions:EGCG attenuates endothelial dysfunction in SHR by decreasing oxidative stress and increasing vascular nitric oxide bioavailability,which may be modulated partly by inhibition of vascular AT_(1)receptors.An increase in endothelium-dependent relaxation may contribute to a decrease in blood pressure in hypertensive animals.

Nitric oxide promotes survival of cerebellar granule neurons cultured in vitro through the Akt pathway

In this study, cerebellar granule neurons were used to examine the role of nitric oxide on cell survival. The N-methyI-D-aspartic acid receptor antagonist, MK-801, and the soluble guanylate cyclase antagonist, 1H-[1, 2, 4]oxadiazolo-[4, 3-a] quinoxalin-1 -one, decreased cell viability, induced caspase-3, and decreased phosphorylated-Akt levels, suggesting that blockade of nitric oxide production promotes apoptosis of differentiating cerebellar granule neurons. After administration of sodium nitroprusside, an endogenous nitric oxide donor, cell viability recovered, caspase-3 expression was decreased, and phosphorylated-Akt levels increased. This study provides direct evidence that nitric oxide can sustain the survival of developing cerebellar granule neurons in vitro through the nitric oxide-Akt pathway. Moreover, endogenous nitric oxide exerts these effects in a cyclic guanosine monophosphate-dependent manner while exogenous nitric oxide does so in a cyclic guanosine monophosphate-independent manner.

Role of the ACTH/MC2R System in the Hair Cycle in Mice

Adrenocorticotropin hormone (ACTH), which is secreted in response to psychological stress, plays an important role in the hair cycle. This study examined the mechanism by which ACTH affects the hair cycle using mice deficient in melanocortin receptor-2(MC2R-/-), which is a main receptor for ACTH. We observed the hair cycle using female MC2R-/- mice at 15 weeks old and five days old to determine whether there were any age-dependent differences. The 15-week-old MC2R-/- mice showed the anagen phase for all mice. On the other hand, all of the MC2R+/+ mice showed the telogen phase at the same age. Moreover, in the five-day-old mice, the hair growth of the MC2R-/- mice occurred earlier than in the MC2R+/+ mice. Both the 15-week-old and five-day-old MC2R-/- mice had higher levels of ACTH and alpha-melanocyte stimulating hormone in the blood than did the MC2R+/+ mice. In addition, in the 15-week-old MC2R-/- mice, the hair cycle shifted to the telogen phase following the administration of a cyclic guanosine monophosphate (cGMP) inhibitor and MC1R/MC5R inhibitor. In the five-day-old MC2R-/- mice, the hair growth was slowed by the administration of corticosterone. These results suggest that the ACTH/MC2R system has an important role in the hair cycle.

L-Arginine Supplementation and Nitric Oxide Production:No Additional Effect When Associated to Exercise

L-arginine is an amino acid semiessencial considered a precursor of nitric oxide, a gas mainly produced in endothelial cells. Nutritional supplements based on the amino acid L-arginine have been broadly marketed in order to increase vasodilation and the blood supply to muscle in order to optimize metabolic responses induced by exercise. The main objective of this study was to evaluate the effect of L-arginine supplementation on nitric oxide production in response to exercise. Furthermore, the biochemical parameters of muscle fatigue were assessed. Fourteen trained runners were divided in two groups, supplemented with L-arginine (ARG) and placebo (PLA). Blood samples were collected before supplementation (T0), immediately after the first exercise session (T1), immediately after the second exercise session (T2), and after 20 minutes of rest (T3). Plasma cyclic guanosine monophosphate was assessed as a marker of nitric oxide production. The biochemical parameters of muscle fatigue analyzed were plasma lactate and ammonia. There was significant increase in plasma cyclic guanosine monophosphate in both groups in response to exercise: ARG (T0: 3.6 ± 1.4;T1: 17.9 ± 5.8;T2: 15.9 ± 5.3;T3: 7.3 ± 2.5 pmol/mL) and PLA (T0: 4.1 ± 1.1;T1: 18.8 ± 9.9;T2: 16.1 ± 3.5;T3: 9.3 ± 3.7 pmol/mL). A significant reduction in plasma lactate and ammonia were observed in the recovery period after exercise (T3). However, no significant difference was observed between groups in the variables studied. Therefore, L-arginine supplementation was unable to increase the effects of exercise on nitric oxide production and did not improve the metabolic responses to exercise in runners.

Cyclic Nucleotide Structural Differentiation of Compounds Modulating Apoptosis and Drug Resistance

Carcinogenesis is associated with malfunction in the cGMP-mediated regulation of cytosolic Ca2+ and reactive oxygen species. Chemotherapy resistant cancer cells are re-sensitised to apoptosis by the action of a substantial number of natural compounds on cell membrane multidrug resistant proteins. Chemical structures of pro-apoptotic and anti-apoptotic compounds demonstrate relative molecular similarity to cGMP. This study uses a computational chemistry program to investigate molecular similarity within cGMP and chemo-preventative structures. Chemotherapeutic drugs and resistance modulators provide multiple fits to a nucleotide template that differ in their relationship to the cyclised ring of cGMP. The alternative fits of drug and modulator structures may relate to the development and unblocking of apoptosis and drug resistance.

Molecular Similarity within Carcinogen and Guanine Cyclic Nucleotide Structures

Tumor promoters, apoptosis and autophagy modulators, chemotherapy drugs, and endogenous steroids demonstrate molecular similarity relative to cyclic nucleotide structure. This study explores relative molecular similarity within established human carcinogen structures using computational chemistry software. Molecular structures of conventional carcinogenic drugs and industrial agents demonstrate molecular similarity with a focus on the guanine base and nucleotide cyclized ring. Structures of volatile and gaseous anesthetic carcinogens do not conform to conventional 3-point pharmacophore-based fits characteristic of receptor-binding drugs. The results of this study provide some insight into how carcinogen structures may interact with endogenous compounds to disrupt cyclic nucleotide-driven homeostatic mechanisms.

Low expression of vascular endothelial growth factor and high serum level of cyclic guanine monophosphate as the risk factors of femoral head osteonecrosis in alcohol-exposed Wistar rat

Purpose:Severe damage to the femoral head in patients with osteonecrosis has a high impact on morbidity.Despite early diagnosis,the treatment outcome is still unsatisfactory.This study aimed to explore the expression of vascular endothelial growth factor(VEGF)and cyclic guanine monophosphate(cGMP)serum level as the risk factors of femoral head osteonecrosis in alcohol-exposed Wistar rats.Methods:This was an exper imental study using randomized post-test only control group design,with samples using 10-14 weeks Wistar male rats.Rats were then divided into 6 groups:3 groups without intervention,and 3 groups with intervention using 40%alcohol given perorally.Each one group from intervention and control group was euthanized by the end of the week for 3 consecutive weeks.Proximal femurs were examined under microscope for osteonecrosis,immunohistochemically for VEGF,and blood serum for cGMP levels.Results:VEGF expression in the femoral head of alcohol-exposed Wistar rats was lower than those not exposed to alcohol(p<0.005).Blood serum cGMP levels of alcohol-exposed Wistar rats were higher than those not exposed to alcohol(p<0.005).The number of necrotic osteocytes in the femoral head of Wistar rats exposed to alcohol was greater than those not exposed to alcohol(p<0.005).There are significant differences between VEGF,cGMP levels,and number of necrotic osteocytes in the control group and treatment at 1st,2nd'and 3rd week(p<0.005).Conclusions:Based on the result of this study,VEGF and cGMP may be considered as diagnostic bio-markers for alcohol-induced femoral head osteonecrosis.

Role of nitric oxide during early phase myocardial ischemic preconditioning in rats

Background To date, there have been no reports on altered nitric oxide （NO） content in ischemia/reperfusion with regard to in vivo preconditioning procedures. These studies are important for understanding the mechanisms of NO during early myocardial ischemic preconditioning. The aim of the present study was to investigate the mechanisms of NO during early myocardial ischemic preconditioning by measuring levels of NO and cyclic guanosine monophosphate （cGMP）, as well as activity of nitric oxide synthase （NOS） in ischemia/reperfusion with respect to preconditioning in rats. Methods Sixty-six female Sprague-Dawley rats were randomly divided into four groups： ischemic preconditioning group （IP）, ischemia/reperfusion group （I/R）, control group （CON）, and preconditioning procedure group （PC）. In the PC group, rats were further divided into PC1-, PC1＋, PC2-, PC2＋, PC3-, and PC3＋ subgroups. Rats underwent left coronary artery occlusion and reperfusion, and subsequently, NOS activity and levels were assessed with spectrophotometric analysis. cGMP contents were measured with radioimmunoassay. Results The level of NO and cGMP, as well as the activity of NOS, were significantly higher in the IP group compared to the I/R and CON groups （P 〈0.05）. During preconditioning prior to prolonged ischemia, NO and cGMP levels varied markedly with ischemia and reperfusion. The levels of NO repeatedly increased when the heart was exposed to three episodes of 5-minute ischemia, and were almost completely reversed during each reperfusion period. NO and cGMP levels were significantly different between the 5-minute period of ischemia and the same period of reperfusion during preconditioning. Conclusions NO plays an important role during early phase myocardial ischemic preconditioning in rats. NO and cGMP could be triggers and mediators of early phase myocardial ischemic preconditioning. Altered NOS activity following ischemic stress could be the primary inducer of higher NO levels detected. NO and cGMP fluctuations might be the trigger for protection during early phase myocardial ischemic preconditioning.

Pancreatic kininogenase improves erectile function in streptozotocin-induced type 2 diabetic rats with erectile dysfunction

Erectile dysfunction （ED） associated with type 2 diabetes is a severe problem that requires effective treatment. Pancreatic kininogenase （PK） has the potential to improve the erectile function of ED patients. This study aims to investigate the effect of PK on erectile function in streptozotocin-induced type 2 diabetic ED rats. To achieve this goal, we divided male Sprague-Dawley rats into five groups. One group was not treated, and the other four groups were treated with saline, sildenafil, PK or sildenafil, and PK, respectively, for 4 weeks after the induction of type 2 diabetic ED. Then, intracavernous pressure under cavernous nerve stimulation was measured, and penile tissue was collected for further study. Endothelial nitric oxide synthase levels, smooth muscle content, endothelium content, cyclic guanosine monophosphate （cGMP） levels in the corpus cavernosum, and neuronal nitric oxide synthase levels in the dorsal penile nerve were measured. Improved erectile function and endothelium and smooth muscle content in the corpus cavernosum were observed in diabetic ED rats. When treating diabetic ED rats with PK and sildenafil at the same time, a better therapeutic effect was achieved. These data demonstrate that intraperitoneal injection of PK can improve erectile function in a rat model of type 2 diabetic ED. With further research on specific mechanisms of erectile function improvement, PK may become a novel treatment for diabetic ED.

Cell-specific expression and immunolocalization of nitric oxide synthase isoforms and the related nitric oxide/cyclic GMP signaling pathway in the ovaries of neonatal and immature rats

Objective: The present study is designed to investigate the cellular expressions and immunolocalizations of three different nitric oxide synthase (NOS) isoforms and the related nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) signaling pathway in the ovaries of neonatal and immature rats.Methods: The ovaries were obtained from ICR (Institute for Cancer Research) female Sprague-Dawley rats at postnatal days 1,5,7,10,and 19.Then we carried out the histologic examination,immunohistochemistry,measurement of NOS activity,and modifications within the NO/cGMP pathway.Results: During postnatal days 1,5,7,10,and 19,all three isoforms of NOS were mainly localized to the oocytes and expressed as a gradual increase in granulosa cells and theca cells within the growing follicle.The ovarian total NOS activities and NO levels were increased at postnatal days 7 and 10 compared with other days.Conclusions: Our findings suggest that the locally produced NO and the NO/NOS signaling systems are involved in the follicular development to puberty.