Effects of the nitric oxide synthase inhibitor NG-nitro-L-arginine on the erectile response to cavernous nerve stimulation in the rabbit

Using a rabbit model, the involvement of the L-arginine/nitric oxide pathway in penile erection was investigated. The mean basal intracavernous pressure was 21 cm H₂O. Cavernous nerve stimulation (4–8 V, 20–30 Hz) increased the pressure to approximately 130 cm H₂O. This response was highly reproducible and usually associated with full penile erection. The pressure increase could be quantified in terms of: (1) the slope of the initial, ascending part of the pressure increase; (2) ΔP, which was defined as the maximal pressure obtained by the stimulation minus the basal pressure before the stimulation; (3) T₉₀, which was defined as the time to reach 90 per cent of ΔP. Intrapenile administration of the L-arginine/nitric oxide synthesis inhibitor N^G-nitro-L-arginine had no effect on systemic arterial blood pressure. However, N^G-nitro-L-arginine (0.22 and 2.19 mg), administered via the same route, abolished the erectile response induced by cavernous nerve stimulation; T₉₀ increased and slope and ΔP decreased significantly. N^G-nitro-D-arginine (2.19), on the other hand, had no inhibitory effect. L-arginine (21.07 mg), given either directly or after N^G-nitro-L-arginine had no consistent effect on the functional response to cavernous nerve stimulation. The results suggest that pharmacologically induced effects on intracavernous pressure in the rabbit can be described quantitatively, and that this model may be useful to study the mechanisms controlling penile erection in vivo. The pronounced inhibitory action of N^G-nitro-L-arginine demonstrates the important role of the arginine/nitric oxide pathway in mediating relaxation of penile smooth muscles necessary for erection.     

一氧化氮生物利用度失调与动脉粥样硬化

内皮功能障碍与动脉粥样硬化(AS)密切相关。氧化应激、脂质浸润、炎性反应因子表达及血管张力改变等涉及一氧化氮(NO)生物利用度(内源性NO的生成和利用)的降低,在内皮功能障碍中发挥重要作用。精氨酸酶活性增强、非对称性二甲基精氨酸和同型半胱氨酸增加均能使NO生物利用度下降,促进AS发生发展。糖尿病、肥胖、慢性肾病和吸烟等通过多种方式影响NO生物利用度,参与AS的发生。     

Ovary and ovulation: Cell-specific localization of nitric oxide synthases (NOS) in the rat ovary during follicular development, ovulation and luteal formation

Nitric oxide (NO) has emerged as one of several important intraovarianregulatory factors. In particular, NO has been implicated inthe processes of ovulation and atresia-related apoptosis. Theaim of the present study was to investigate the presence anddistribution of the NO-generating nitric oxide synthase (NOS)enzymes in the ovary during follicular development, ovulationand luteal formation of the equine chorionic gonadotrophin (ECG)/humanchorionic gonado-trophin (HCG)-primed rat NADPH diaphorase activitywas used as a histochemical marker for NOS within the ovary.Diaphorase reactivity was most abundant in the stroma (S) ofthe ovary and in the theca (T) layer of the follicle. In luteinizedovaries, weaker diaphorase reactivity was present within thecorpora lutea (CL). Two different isoforms of NOS, the constitutivelyexpressed endothelial NOS (eNOS) and the inducible isoform ofNOS (iNOS), were immunolocalized in ovaries of immature ratsand in ECG/HCG-primed rats during the periovulatory period fromHCG injection until 2 days after ovulation. In addition, ovarianconcentrations of eNOS and iNOS were quantified by immunoblotting.Immunoblotting with a monoclonal anti-eNOS antibody demonstratedthe presence of eNOS mainly in the residual ovary (ROV) duringthe periovulatory period. In luteinized ovaries, higher concentrationsof eNOS were seen in CL, while those in the ROV at this stagewere lower than in the periovulatory ovary. Immature ovariescontained diminutive amounts of eNOS, detectable mostly in theROV compartment. In contrast, iNOS was barely detectable duringfollicular development to the preovulatory stage. A slight elevationof iNOS was observed in the granulosa cells at 6 h after theHCG injection. The levels of iNOS during the luteal phase werealso low. Immunohistochemical analysis using polyclonal eNOSand iNOS antibodies revealed the localization of these two isoformsprimarily in the S and the T of the periovulatory ovary. Inluteinized ovaries, positive immunoreactivity was also seenwithin the CL. With a monoclonal antibody against eNOS, intenseimmunoreactivity was observed in the S, T and within CL. Therewas a particularly strong staining in blood vessels. These datademonstrate the presence of an intraovarian NO-generating system.The localization of this system to the S, T and CL suggestsa role for NO in the ovulatory process and in the regulationof CL function.     

Nitric oxide synthesis is increased in the endometrial tissue of women with endometriosis

BACKGROUND: Previous studies have shown that peritoneal macrophages from women with endometriosis produce excess nitric oxide (NO). This study was designed to quantify the amount of NO and determine the expression of endothelial (eNOS) and inducible NO synthases (iNOS) in women with and without endometriosis. METHODS: An enzyme-linked immunosorbent assay (ELISA) was performed on endometrial tissues obtained from controls (myoma, n = 30) and on eutopic/ectopic endometrial tissues from endometriosis patients (n = 34) to evaluate eNOS and iNOS protein concentrations in these endometrial tissues. A rapid-response chemiluminescence analyser was used to measure NO directly in fresh endometrial tissues. RESULTS: Mean (+/- SEM) levels of NO were significantly increased in the endometrial tissues of women with endometriosis (13.2 +/- 7.8 versus 19.8 +/- 12.6 nmol/g tissue; P = 0.016). Apparently higher levels of NO were found in ectopic compared with eutopic endometrium (P = 0.057). Endometrial tissues of women with endometriosis appeared to contain more iNOS than those of controls (3.6 +/- 2.2 versus 8.6 +/- 12.2 pg/ microg protein; P = 0.06), but no significant difference was found in eNOS levels. CONCLUSIONS: Greater amounts of NO and NOS are present in the endometrial tissues of women with endometriosis, implying a possible role for NO in the pathogenesis of endometriosis.     

罗格列酮减轻2型糖尿病大鼠血管内皮功能受损

目的观察2型糖尿病大鼠血清内皮素(ET)和一氧化氮(NO)水平、主动脉病理变化、在主动脉的内皮型一氧化氮合酶(e NOS)蛋白和mRNA表达及罗格列酮的干预作用。方法将大鼠随机分为对照组、高脂组、糖尿病组和罗格列酮组,每组20只。制备2型糖尿病大鼠模型后,罗格列酮治疗组4 mg/kg·d灌胃给药,于治疗6周和12周时检测血糖、ET、NO及光镜下主动脉的病理变化;用Western blot和real-time PCR检测主动脉的e NOS蛋白和mRNA表达。结果 1)与对照组比较,高脂组、糖尿病组及罗格列酮治疗组ET升高,NO降低(P0.01)。12周时糖尿病组较高脂组和罗格列酮治疗组ET升高,NO降低(P0.05)。糖尿病组NO水平在12周时比6周时明显下降(P0.05)。2)12周时高脂组、糖尿病组和罗格列酮组大鼠主动脉出现不同程度病理改变。3)6周和12周时,与对照组比较,高脂组、糖尿病组和罗格列酮组主动脉e NOS的蛋白和mRNA表达下调(P0.01);糖尿病组较罗格列酮组主动脉e NOS的蛋白表达下调(P0.01)。结论罗格列酮可以缓解糖尿病组大鼠血管内皮功能受损。     

Hormone replacement therapy can augment vascular relaxation in post-menopausal women with type 2 diabetes

BACKGROUND: Diabetes is a major risk factor for coronary heart disease in women and event rates increase substantially after the menopause. Observational studies have suggested that estrogens may provide cardioprotection by regulating endothelial nitric oxide synthase. METHODS: In order to examine the effect of hormone replacement therapy (HRT) on endothelium-dependent and -independent vascular relaxation in post-menopausal women with type 2 diabetes, an open study was conducted in which gluteal biopsies were collected from 17 women before and after 6 months of transdermal 17 beta-estradiol (80 microg twice weekly) in combination with oral norethisterone (1 mg daily). Small arteries (<550 microm) were dissected from fat and mounted on a wire myograph for assessment of relaxation in response to acetylcholine (ACh), bradykinin (BK) and sodium nitroprusside (SNP). RESULTS: Maximal relaxation responses to ACh, BK and SNP in women with diabetes and non-diabetic control subjects were 52 +/- 8 versus 96 +/- 2% (P < 0.05), 76 +/- 7 versus 97 +/- 1%, (P < 0.05) and 91 +/- 2 versus 98 +/- 1% (P < 0.05) respectively. After 6 months of HRT, maximal relaxation responses to ACh, BK and SNP in women with diabetes (compared with pre-HRT) were: 88 +/- 4 (P < 0.05), 93 +/- 3 (P < 0.05) and 98 +/- 1% (P < 0.05) respectively. At baseline and after HRT, EC50 (concentration required to obtain 50% of maximum response) data exhibited similar changes. CONCLUSIONS: HRT had potentially beneficial effects on vascular relaxation. Data were consistent with improvements in endothelial function, vascular smooth muscle function, or both. Controlled studies are required to confirm and extend these findings.     

Is estradiol cardioprotection a nitric oxide-mediated effect?

BACKGROUND: Estradiol exerts a number of biological effects that support extensive observational data suggesting a protective role for estrogen in cardiovascular disease prevention. These include effects on lipid and carbohydrate metabolism, coagulation/fibrinolysis as well as a possible effect on vascular reactivity. It has been proposed that this might be mediated by vascular endothelial nitric oxide (NO) production. Accordingly, we designed complementary in-vivo and in-vitro studies to investigate this hypothesis further. METHODS: Firstly, in a group of 10 healthy post-menopausal women, bilateral venous occlusion plethysmography was used to examine forearm vasoconstrictor responses to intrabrachial N(G)-monomethyl-l-arginine (l-NMMA; a substrate inhibitor of nitric oxide synthase) both before and after 4 weeks of treatment with transdermal 17beta-estradiol (E(2)) (80 microg/day). Secondly, we examined the direct effects of acute (24 h) and chronic (7 days) treatment with E(2) (10 pmol/l and 10 nmol/l) on endothelial nitric oxide synthase (eNOS) gene expression in cultured human aortic endothelial cells. RESULTS: No significant differences were observed between the vasoconstrictor responses to l-NMMA (2, 4, 8 micromol/min) before and after E(2) treatment. Comparison of E(2)-treated endothelial cells with control cells showed no significant increase in eNOS mRNA expression following either acute or chronic estradiol treatment. CONCLUSIONS: The present studies do not provide evidence for an eNOS-mediated cardioprotective response to estrogen and therefore suggest that additional mechanisms other than the endothelial NO system may have an important role in the cardiovascular effects of estrogen.     

Autonomic dysfunction and HPV immunization: an overview

This article reviews the case series reported from several countries describing patients with suspected severe side effects to the HPV vaccines. The described symptom clusters are remarkably similar and include disabling fatigue, headache, widespread pain, fainting, gastrointestinal dysmotility, limb weakness, memory impairment episodes of altered awareness, and abnormal movements. This constellation of symptoms and signs has been labeled with different diagnoses such as complex regional pain syndrome (CRPS), postural orthostatic tachycardia syndrome (POTS), small fiber neuropathy (SFN), myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), or fibromyalgia. It is known that autoimmunity and autoantibodies are present in a subset of patients with CRPS, POTS, SFN, ME/CFS, and fibromyalgia. This article proposes that vaccine-triggered, immune-mediated autonomic dysfunction could lead to the development of de novo post-HPV vaccination syndrome possibly in genetically susceptible individuals. Being cognizant that a temporal relationship between vaccination and symptom onset does not necessarily equate to causality, mounting evidence of case series calls for well-designed case-control studies to determine the prevalence and possible causation between these symptom clusters and HPV vaccines. Since personalized medicine is gaining momentum, the use of adversomics and pharmacogenetics may eventually help identify individuals who are predisposed to HPV vaccine adverse events.     

Expression of nitric oxide synthase and effect of substrate manipulation of the nitric oxide pathway in mouse ovarian follicles

BACKGROUND: Nitric oxide (NO) is a cell messenger with multiple actions in different biological systems, implicated in the control of follicle and oocyte function. NO is formed from L-arginine by isoforms of nitric oxide synthase (NOS) via NG-hydroxy-L-arginine, with L-citrulline as a byproduct. This study aimed to show how modulation of NO by manipulating NOS substrates would affect mouse follicle growth and ovulation in vitro, where vascular effects of NO are attenuated. METHODS: Immunohistochemistry [endothelial (eNOS) and inducible (iNOS)] and in situ hybridization (iNOS) were applied on mouse ovaries. Cultured follicles were also stained for iNOS by immunohistochemistry. For follicles cultured in the presence or absence of L-arginine, the ability of L-citrulline or NG-hydroxy-L-arginine to substitute for L-arginine was assessed in terms of follicle growth and ovulation. RESULTS: iNOS and eNOS were localized in oocytes and theca, with some staining in granulosa. iNOS mRNA occurred predominantly in granulosa and oocyte. Omission of L-arginine significantly reduced follicle survival and ovulation. Partial compensation for L-arginine withdrawal was achieved with L-citrulline and NG-hydroxy-L- arginine. Specific abnormalities of follicle growth were noted. CONCLUSIONS: NOS is present in mouse follicles, and its action is necessary at a local level for normal follicle development in vitro. Reduced growth, persistent basement membranes and reduced ovulation were associated with in vitro disruption of NO.     

参芪汤对糖尿病大鼠勃起功能的影响

目的　探讨参芪汤对雄性糖尿病大鼠勃起功能的作用。方法　48只Wistar大鼠随机分为正常 对照组(NC组);糖尿病组(DM组),链脲佐菌素60mg/kg腹腔注射;中药治疗组(DD组),参芪汤17.7g· kg-1·d-1灌胃。检测各组第8周的血糖、阴茎勃起潜伏期、酶组化及图象分析观察阴茎海绵体中一氧化氮合 酶(NOS)和球海绵体肌中乙酰胆碱酯酶(AchE)的活性。结果　DD组的血糖略低于DM组,无差异(P> 0.05)。DD组阴茎勃起潜伏期明显短于DM组,差异显著(P<0.05)。DD组的NOS、AchE的阳性反应显著 强于DM组,差异显著(P<0.05)。DD组的勃起潜伏期、NOS、AchE阳性反应与正常组接近。结论　参芪汤 可能通过增加NOS和AchE活性,发挥改善阴茎勃起功能的作用。     

Andrology: Effects of nitric oxide on human spermatozoa: evidence that nitric oxide decreases sperm motility and induces sperm toxicity

Endogenous nitric oxide (NO) is an important functional mediatorin several physiological systems, including the reproductivesystem. However, when generated in excessive amounts for longperiods, mainly during immunological reactions, NO is cytotoxicand cytostatic for invading microbes, as well as for the cellsgenerating it and the tissues present around it. Since infertilityassociated with urogenital tract infection in males and femalesis also accompanied by reduced sperm motility and viability,it is possible that reduced fertility in these patients is dueto NO-induced sperm toxicity. We therefore evaluated the directeffects of NO, chemically derived from S-nitroso-N-acetylpenicillamine(SNAP, 0.012–0.6 mM) and sodium nitroprusside (SNP, 0.25–2.5mM), on the motility and viability of human spermatozoa. Furthermore,we tested whether inhibition of NO synthesis prevents spermmotility and viability by incubating washed total cells presentin the semen (spermatozoa, round cells) with N-nitro-L-arginine-methyl-ester(L-NAME), a NO synthesis inhibitor. Treatment of purified spermatozoawith SNAP or SNP decreased forward progressive sperm motilityand straight line velocity, and also increased the percentageof immotile spermatozoa in a concentration-dependent manner.Furthermore, the percentage of immotile spermatozoa positivelycorrelated with the percentage of dead spermatozoa. In contrastto freshly prepared SNAP, SNAP preincubated for 48 h had noeffect on the motility and viability of the spermatozoa. Furthermore,as compared to untreated controls, a significantly higher percentageof forward progressive sperm motility as well as viability (P< 0.05) was maintained in washed semen incubated with L-NAME(0.15 mM). Seminal plasma concentrations of nitrite-nitrate(stabile metabolites of NO/10⁶ spermatozoa correlated positively(P < 0.05) with the percentage of immotile spermatozoa. Ourresults suggest that NO can cause sperm toxicity as well asinhibit sperm motility. In conclusion, excessive NO synthesisin response to infection and inflammation could be an importantfactor contributing to functional change of the spermatozoa,leading to their dysfunction and to infertility.     

Pre-eclampsia-like conditions produced by nitric oxide inhibition: effects of L-arginine, D-arginine and steroid hormones

The aim of this study was to establish that inhibiting nitricoxide (NO) production with N^G-nitro-L-arginine methyl ester(L-NAME) results in high blood pressure conditions in chronicallytreated pregnant rats. To validate the model,the effects ofL-arginine (the substrate for NO) and Darginine (the stereoisomerof L-arginine which is not substrate for NO synthesis) werestudied on blood pressure and fetal weights. The effects ofa progesterone agonist, promegestone (R5020) and 17-oestradiolwere also explored. The NO synthase inhibitor L-NAME was chronicallyinfused s.c. into pregnant rats from day 17 of gestation, eitheralone or with the simultaneous infusion of L-arginine and injectionsof sex steroid hormones (promegestone and oestradiol), compoundsthat may act in the pathogenic pathways of pre-eclampsia. Systolicblood pressure was measured daily. Weight and mortality of pupswere recorded immediately after delivery. Blood pressure waselevated significantly in rats treated with L-NAME for only1 day following infusion; there was a consistent decline duringthe next 3 days of pregnancy followed by a dramatic and significantrise just prior to delivery and post-partum. Fetal weights werereduced significantly in the L-NAMEtreated rats. Co-treatmentof L-NAME-infused rats with L-arginine reversed both the increasein blood pressure and the decrease in fetal weights observedwith L-NAME alone. R5020, but not oestradiol, also reduced bloodpressure and increased fetal weights in the L-NAME-treated animals.NO appears to play essential roles in the regulation of bloodpressure during pregnancy, as well as in fetal perfusion andfetal weights at delivery. This study also indicates that progesterone,and not oestrogen, may regulate the vascular adaptations duringnormal pregnancy. LArginine and progesterone agonists like promegestonemay have beneficial effects on the high blood pressure levelsand reduced fetal weights associated with pre-eclampsia.     

Nitric oxide in inflammatory bowel disease: a universal messenger in an unsolved puzzle

In recent years, nitric oxide (NO), a gas previously considered to be a potentially toxic chemical, has been established as a diffusible universal messenger that mediates cell-cell communication throughout the body. Constitutive and inducible NO production regulate numerous essential functions of the gastrointestinal mucosa, such as maintenance of adequate perfusion, regulation of microvascular and epithelial permeability, and regulation of the immune response. Up-regulation of the production of NO via expression of inducible nitric oxide synthase (iNOS) represents part of a prompt intestinal antibacterial response; however, NO has also been associated with the initiation and maintenance of inflammation in human inflammatory bowel disease (IBD). Recent studies on animal models of experimental IBD have shown that constitutive and inducible NO production seems to be beneficial during acute colitis, but sustained up-regulation of NO is detrimental. This fact is also supported by studies on mice genetically deficient in various NOS isoforms. However, the mechanism by which NO proceeds from being an indispensable homeostatic regulator to a harmful destructor remains unknown. Furthermore, extrapolation of data from animal colitis models to human IBD is questionable. The purpose of this review is to update our knowledge about the role of this universal mediator and the enzymes that generate it in the pathogenesis of IBD.     

Drospirenone increases endothelial nitric oxide synthesis via a combined action on progesterone and mineralocorticoid receptors

BACKGROUND: Progestins have actions on the cardiovascular system, which depend on the structure as well as on receptor binding characteristics. Drospirenone (DRSP) is a progestin that uniquely interferes with the signaling of the mineralocorticoid receptor (MR). Hormone therapy containing DRSP results in blood pressure reduction in hypertensive post-menopausal women. METHODS: We describe the effects of DRSP on endothelial nitric oxide (NO) synthesis and compare them with those of progesterone (P) and of medroxyprogesterone acetate (MPA). In addition, we herein tested the relevance of the anti-mineralocorticoid activity of DRSP for NO synthesis. RESULTS: DRSP results in rapid activation of the endothelial NO synthase (eNOS) through mitogen-activated protein kinases and phosphatidylinositol 3-kinase as well as in enhanced eNOS expression. These actions depend on P receptor. When the cells are exposed to aldosterone, a reduction of eNOS expression is found that is antagonized by DRSP. This action is not shared by P or MPA. In addition, DRSP does not interfere with the induction or activation of eNOS induced by estradiol, as opposed to MPA. CONCLUSIONS: DRSP acts on endothelial cells via a combined action through the P and MRs. These results help to interpret the anti-hypertensive effects of hormonal therapies containing DRSP.     

Endothelial nitric oxide synthase gene polymorphism in women with idiopathic recurrent miscarriage

BACKGROUND: Lack of endothelium-derived nitric oxide is associated with vasospasm and vascular infarction. We investigated the relationship between idiopathic recurrent miscarriage and a polymorphism of the gene encoding endothelial nitric oxide synthase (NOS3). METHOD: In a prospective case-control study, 105 women with idiopathic recurrent miscarriage and 91 healthy controls were investigated. We used the polymerase chain reaction to identify the different alleles of a 27 base pair tandem repeat polymorphism in intron 4 of the NOS3 gene. RESULTS: The wild type B allele was identified on 329 out of 392 chromosomes (frequency 0.84). The polymorphic A allele was present on 63 chromosomes (frequency 0.16). The genotype frequencies were as follows: 68% (B/B), 31% (A/B) and.5% (A/A). The distribution of genotype frequencies was significantly different between the study and control groups for allele A/B heterozygotes (NOS3(A/B)) (36.7 versus 23.8%, P = 0.03, OR 1.6, 95% CI 1.1--3.8). Only one individual was homozygous for the A allele (NOS3(A/A)). She was in the study group. Between women with primary and secondary recurrent miscarriages, no statistically significant difference between the distribution of NOS3(A/B) genotypes (28 versus 34%) was observed. CONCLUSIONS: These data support a role for the NOS3 gene as a genetic determinant of the risk of idiopathic recurrent miscarriage.     

Regulation of vascular adaptation during pregnancy and post-partum: effects of nitric oxide inhibition and steroid hormones

Treatment of pregnant rats with the nitric oxide synthase inhibitorNG-nitro-L-arginine methyl ester (L-NAME), has been shown toproduce symptoms similar to pre-eclampsia (i.e. elevated bloodpressure, proteinuria and fetal growth retardation). After L-NAMEinfusion is initiated on day 17 or 18 of gestation, the bloodpressure proceeds in a biphasic pattern (immediate rise, followedby a decline, then increasing again in the post-partum period).The blood pressure actually begins to rise prior to deliveryon days 21–22, i.e. after progesterone withdrawal occurs,suggesting that these responses may be regulated by changesin steroid hormone concentrations during pregnancy. Therefore,we evaluated the effects of the different steroid hormones:progestins (progesterone, promegestone, levonorgestrel), antiprogestins(mifepristone), 17-oestra-diol or androgens (testosterone, dihydrotestosterone)on systolic blood pressure in pregnant, non-pregnant femaleand normal male rats with and without L-NAME treatment and spontaneouslyhypertensive male rats. The animals received continuous infusionsof L-NAME (150 mg/kg/day) or vehicle through osmotic mini-pumpsand daily s.c. injections of steroid hormones. In pregnant ratsthe pump was inserted on day 17 or 18 of gestation and steroidhormone injections were started on the first day following deliveryat term and continued daily until post-partum day 10. In non-pregnantfemale or male rats steroid hormone injections were initiated5 days after the L-NAME pump was inserted. Systolic blood pressurewas measured daily from the tail with a pneumatic tail-cuffdevice. R5020 (1.5 mg/kg/day) significantly attenuated the bloodpressure elevation induced by L-NAME during the post-partumperiod. Similarly, it lowered blood pressure in L-NAME treatednon-pregnant female rats or male rats. R5020 also lowered bloodpressure in spontaneously hypertensive male rats. Progesterone(6 mg/kg/day) had similar effects on blood pressure in the post-partumperiod, although it also lowered the blood pressure in controlanimals. Interestingly, administration of two different dosesof Ievonorgestrel (03 and 1.5 mg/kg/day) did not decrease theblood pressure in either L-NAME-infused rats or controls. Mifepristone(RU486, 30 mg/kg/day) further increased blood pressure in L-NAME-treatedrats post-partum. 17-oestradiol (30 ng/kg/day) had no effecton blood pressure in either L-NAME infused rats in the post-partumperiod or controls, whereas both testosterone (03 mg/kg/day)and dihydrotestosterone (0.3 mg/kg/day) significantly attenuatedthe blood pressure increase after L-NAME, while raising theblood pressure in vehicle-infused animals. These results suggestthat the control of systemic blood pressure during pregnancymay be modulated by steroid hormones. Progesterone may be thesteroid hormone with the major action on vascular tension duringpregnancy.     

Pregnancy: Differential regulation of nitric oxide in the rat uterus and cervix during pregnancy and labour

The aim of this study was to determine if nitric oxide (NO)production and nitric oxide synthase (NOS) isoforms change withinthe uterus and cervix during pregnancy and labour either atterm or preterm. NO production was compared in the rat uterusand cervix of non-pregnant and pregnant rats on days 18–22prior to labour, day 22 during delivery, 1 day post-partum andafter treatment with either 10 mg onapristone or progesterone.Uterine NO synthesis, reflected in nitrite production, increasedduring gestation (194.2±22.6 nmol/g on day 19) comparedwith the non-pregnant state (76.2±18.4 nmollg, P <0.05)and decreased during term labour and post-partum. Furthermore,injection of lipopolysaccharide (LPS) (100 µg/rat i.p.)on day 20 of gestation resulted in a significant increase inNO synthesis after 6 h. Conversely, cervical NO synthesis andnitrite production was low in the non- pregnant (65.1±9.2nmol/g) and pregnant animals on days 18–22 of gestation(53.2±9.0 nmol/g on day 22, P >0.05), but markedlyincreased during term labour (139±28.6 nmollg, P <0.05).Treatment with the antiprogestin onapristone suppressed uterineNO production and increased cervical production while continuousadministration of progesterone from day 19 had the oppositeeffect. LPS produced a significant increase in cervical NO production in both the pregnant (8-fold) and non-pregnant (4-fold)states. All three known NOS isofonus (i.e. iNOS, nNOS and eNOS)were detected in the cervical samples but only two were presentin the uterus (iNOS and eNOS). An increase in the presence ofiNOS occurred during labour at term compared with cervices collectedfrom day 19. This was contrary to the measurements of the isoformin the uterus. Also, there was a similar increase of nNOS inthe cervix during labour. This isoform seemed absent in theuterus during gestation. No significant changes occurred inthe abundance of eNOS in the cervix during labour at term comparedwith day 19. During preterm labour after onapristone, 1NOS concentrationsincreased significantly in the cervix. In order to examine whetherthe NO pathway plays a role in cervical ripening, the effectsof the nitric oxide synthesis inhibitor L-nitro-arginine methylester(L-NAME) on the duration of delivery and on cervical extensibilitywere also investigated. The duration of delivery was significantlyprolonged in L-NAME.treated rats compared with the control group(2.4-fold). Moreover, cervical extens ibifity decreased significantly(1.7-fold) after in-vitro incubation with L-NAME (P <0.005).We conclude that the NO system may have an active role in thecascade of processes involved in preparing the uterus and cervixfor parturitlon.     

Nitric oxide in the endometrium

Nitric oxide (NO) is an important mediator of paracrine interactions, especially within the vascular system. It is a powerful inhibitor of platelet aggregation and a potent vasodilator. NO is also a neurotransmitter and it plays a role in cell-mediated cytotoxicity. NO-generating enzymes (nitric oxide synthases, NOS) have been described in the endometrium of a number of species, suggesting that NO might be involved in endometrial function. In human endometrium, endothelial NOS and inducible NOS have been localized to glandular epithelium in the non-pregnant uterus. Weak inducible NOS immunoreactivity has been observed in decidualized stromal cells. NO might participate in the initiation and control of menstrual bleeding. Furthermore, it may play a part in the inhibition of platelet aggregation within the endometrium, where menstrual haemostasis is thought to occur primarily by vasoconstriction rather than clot organization. Endometrially derived NO could also suppress myometrial contractility. Recent attention has focused on the part that NO might play in maintaining myometrial quiescence during pregnancy. NO also appears to relax the non-pregnant myometrium, an action which could be exploited for the medical treatment of primary dysmenorrhoea.