Biosynthesis of nitric oxide and citrulline from L-arginine by constitutive nitric oxide synthase present in rabbit corpus cavernosum

Impact of preovulatory follicle maturity on oocyte metabolism and embryo development

Improved oocyte competence for embryo development and pregnancy was observed following ovulation of preovulatory follicles with greater physiological maturity, as indicated by estradiol production, prior to the gonadotropin-releasing hormone (GnRH)-induced luteinizing hormone (LH) surge. It was hypothesized that follicular fluid from preovulatory follicles of greater maturity better supports the maturing oocyte's metabolic requirements and improves embryo development. The objective was to determine if differences in preovulatory follicular fluid due to follicle maturity influence oocyte metabolism during in vitro maturation (IVM) and affect embryo development. Bovine preovulatory follicular fluid was collected 18 h after a GnRH-induced LH surge. Serum estradiol concentration at GnRH administration categorized follicles as greater or lesser maturity. Immature bovine oocytes were submitted to 24 h IVM in medium supplemented with 20% follicular fluid from preovulatory follicles of greater or lesser maturity. Embryo development was recorded. Oocyte maturation media and media conditioned by developing embryos were submitted for metabolomics. A randomized block design was utilized to determine differences in embryo development and media metabolites (P ≤ 0.05). Blastocysts from oocytes matured in greater vs. lesser maturity follicular fluid had a more moderate rate of development (P = 0.01). At the conclusion of 24 h IVM, abundance of 66 metabolites differed between greater and lesser follicle maturity treatments. Nine metabolites differed in media conditioned by developing embryos. Metabolome results suggest improved amino acid, purine, and glucose metabolism, followed by a more efficient rate of embryo development, in oocytes matured in greater vs lesser maturity follicular fluid.

Exogenous l-ARGININE does not stimulate production OF NO or cGMP within the rat corporal smooth muscle cells in culture

BACKGROUND AND AIM

Nitric oxide (NO) is the intracellular chemical responsible for initiating a penile erection. Despite conflicting clinical data, it continues to be publicized and promoted that orally administered l-arginine, the putative substrate for NO, enhances the erectile response presumably by stimulating NO production by the corporal tissues resulting in an increase in cGMP production. To shed light on this issue, an in vitro study was conducted to explore the effect of direct exogenous administration of l-arginine as well as its precursor and metabolite, l-citrulline, on the NO-cGMP pathway within the cavernosal smooth muscle (CSM) cell.

MATERIALS AND METHODS

CSM cells obtained from 8 to 10 week old Sprague-Dawley rats were grown in Dulbecco media with 20% fetal calf serum and then incubated with or without l-arginine (L-ARG) or l-citrulline (L-CIT) in a time course and dose-response manner. Sildenafil (0.4 mM), IBMX (1 mM), l-NAME (3 μM), ODQ (5 μM) and Deta Nonoate (10 μM) were used as either inhibitors or stimulators of the NO-cGMP pathway. mRNA and protein were extracted and used for the determination of the phosphodiesterase 5 (PDE5). PDE5 activity was determined by luminometry. cGMP content was determined by ELISA. Nitrite formation, an indicator of NO production, was measured in the cell culture media by a colorimetric assay. The cationic (CAT-1) and neutral (SNAT-1) amino acid transporters for L-ARG and L-CIT, respectively, were determined by Western blot.

RESULTS

When compared to untreated CSM cells, incubation with 0.25-4.0 mM of L-ARG or 0.3-4.8 mM of L-CIT anywhere between 3 and 24 h did not result in any additional nitrite or cGMP production. The addition of l-NAME, IBMX or ODQ to these L-ARG and L-CIT treated cells did not alter these results. L-CIT but not L-ARG increased PDE5 mRNA and protein content as well as the activity of the PDE5 enzyme. Both CAT-1 and SNAT-1 were expressed in the CSM cells.

CONCLUSIONS

This in vitro study demonstrates that exogenous administration of L-ARG or L-CIT failed to stimulate production of either NO or cGMP by the corporal CSM cells. A re-evaluation of the presumptive role of the exogenous administration of L-ARG in improving the synthesis of NO at least at the level of the CSM cells appears warranted.

Stereoselective effects of ibuprofen in adult zebrafish (Danio rerio) using UPLC-TOF/MS-based metabolomics

Ibuprofen (IBU), as a commonly used non-steroidal anti-inflammatory drug (NSAID) and pharmaceutical and personal care product (PPCP), is frequently prescribed by doctors to relieve pain. It is widely released into environmental water and soil in the form of chiral enantiomers by the urination and defecation of humans or animals and by sewage discharge from wastewater treatment plants. This study focused on the alteration of metabolism in the adult zebrafish (Danio rerio) brain after exposure to R-(-)-/S-(+)-/rac-IBU at 5 μg L^-1 for 28 days. A total of 45 potential biomarkers and related pathways, including amino acids and their derivatives, purine and its derivatives, nucleotides and other metabolites, were observed with untargeted metabolomics. To validate the metabolic disorders induced by IBU, 22 amino acids and 3 antioxidant enzymes were selected to be quantitated and determined using targeted metabolomics and enzyme assay. Stereoselective changes were observed in the 45 identified biomarkers from the untargeted metabolomics analysis. The 22 amino acids quantitated in targeted metabolomics and 3 antioxidant enzymes determined in enzyme assay also showed stereoselective changes after R-(-)-/S-(+)-/rac-IBU exposure. Results showed that even at a low concentration of R-(-)-/S-(+)-/rac-IBU, disorders in metabolism and antioxidant defense systems were still induced with stereoselectivity. Our study may enable a better understanding of the risks of chiral PPCPs in aquatic organisms in the environment.

Rosiglitazone preserves pulmonary vascular function in lambs with increased pulmonary blood flow

BACKGROUND

Pulmonary vascular function is impaired with increased pulmonary blood flow (PBF). We hypothesized that a peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist would mitigate this effect.

METHODS

An aorta-to-pulmonary-artery shunt was placed in 11 fetal lambs. Lambs received the PPAR-γ agonist rosiglitazone (RG, 3 mg/kg/d, n = 6) or vehicle (n = 5) for 4 wk. Lung tissue from five normal 4-wk-old lambs was used for comparisons.

RESULTS

At 4 wk, pulmonary artery pressure (PAP) and vascular resistance (PVR) decreased with inhaled nitric oxide (NO) in RG- and vehicle-treated shunt lambs. PAP and PVR decreased with acetylcholine (Ach) in RG-treated, but not vehicle-treated, shunt lambs. In vehicle-treated shunt lambs, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, rac1, superoxide, and 3-nitrotyrosine (3-NT) levels were increased, and Ser1177 endothelial NO synthase (eNOS) protein was decreased as compared with normal lambs. In RG-treated shunt lambs, NOx, Ser1177 eNOS protein, and eNOS activity were increased, and NADPH activity, rac1, superoxide levels, and 3-NT levels were decreased, as compared with vehicle-treated shunt lambs. PPAR-γ protein expression was lower in vehicle-treated shunt lambs than in normal and RG-treated shunt lambs.

CONCLUSION

The PPAR-γ agonist RG prevents the loss of agonist-induced endothelium-dependent pulmonary vascular relaxation in lambs with increased PBF, in part, due to decreased oxidative stress and/or increased NO production.

Tetrahydrobiopterin (BH4), a cofactor for nNOS, restores gastric emptying and nNOS expression in female diabetic rats

Gastroparesis is a debilitating disease predominantly affecting young women. Recently, dysregulation of neuronal nitric oxide synthase (nNOS) in myenteric plexus neurons has been implicated for delayed solid gastric emptying/gastroparesis in diabetic patients. In this study, we have explored the role of tetrahydrobiopterin (BH4), a major cofactor for nNOS activity and NO synthesis in diabetic gastroparesis. Diabetes was induced with single injection of streptozotocin (55 mg/kg body wt, ip) in female rats, with experiments performed on week 3 or 9 following induction, with or without 3-wk BH4 supplementation. Gastric pyloric BH4 levels were significantly decreased in diabetic female rats compared with control (18.6 +/- 1.45 vs. 31.0 +/- 2.31 pmol/mg protein). In vitro studies showed that 2,4-diamino-6-hydroxypyrimidine (DAHP), an inhibitor of BH4 synthesis, significantly decreased gastric NO release and nitrergic relaxation. Three-week dietary supplementation of BH4 either from day 1 or week 6 significantly attenuated diabetes-induced delayed gastric emptying for solids (3 wk: BH4, 67 +/- 6.7 vs. diabetic, 36.05 +/- 7.09; 9 wk: BH4, 57 +/- 8.45 vs. diabetic, 33 +/- 9.91) and diabetes-induced reduction in pyloric nNOS-alpha protein expression in female rats. Supplementation of BH4 significantly restored gastric nNOS-alpha dimerization in 9-wk-old diabetic female rats. In addition, BH4 treatment reversed (17.23 +/- 5.81 vs. 42.0 +/- 2.70 mmHg x s) the diabetes-induced changes in intragastric pressures (IGP) and gastric pyloric nitrergic relaxation (-0.62 +/- 0.01 vs. -0.22 +/- 0.07). BH4 deficiency plays a critical role in diabetes-induced alterations including delayed solid gastric emptying, increased IGP, reduced pyloric nitrergic relaxation, and nNOS-alpha expression in female rats. Supplementation of BH4 accelerates gastric emptying by restoring nitrergic system in diabetic female rats. Therefore, BH4 supplementation is a potential therapeutic option for female patients of diabetic gastroparesis.

Nitric oxide alterations following acute ductal constriction in the fetal lamb: a role for superoxide

Acute partial compression of the fetal ductus arteriosus (DA) results in an initial abrupt increase in pulmonary blood flow (PBF), which is followed by a significant reduction in PBF to baseline values over the ensuing 2-4 h. We have previously demonstrated that this potent vasoconstricting response is due, in part, to an endothelin-1 (ET-1)-mediated decrease in nitric oxide synthase (NOS) activity. In addition, in vitro data demonstrate that ET-1 increases superoxide levels in pulmonary arterial smooth muscle cells and that oxidative stress alters NOS activity. Therefore, the objectives of this study were to determine the potential role of superoxide in the alterations of hemodynamics and NOS activity following acute ductal constriction in the late-gestation fetal lamb. Eighteen anesthetized near-term fetal lambs were instrumented, and a lung biopsy was performed. After a 48-h recovery, acute constriction of the DA was performed by inflating a vascular occluder. Polyethylene glycol-superoxide dismutase (PEG-SOD; 1,000-1,500 units/kg, n = 7) or PEG-alone (vehicle control group, n = 5) was injected into the pulmonary artery before ductal constriction. Six animals had a sham operation. In PEG-alone-treated lambs, acute ductal constriction rapidly decreased pulmonary vascular resistance (PVR) by 88%. However, by 4 h, PVR returned to preconstriction baseline. This vasoconstriction was associated with an increase in lung superoxide levels (82%), a decrease in total NOS activity (50%), and an increase in P-eNOS-Thr495 (52%) (P < 0.05). PEG-SOD prevented the increase of superoxide after ductal constriction, attenuated the vasoconstriction, preserved NOS activity, and increased P-eNOS Ser1177 (307%, P < 0.05). Sham procedure induced no changes. These data suggest that an acute decrease in NOS activity that is mediated, in part, by increased superoxide levels, and alterations in the phosphorylation status of the endothelial NOS isoform, underlie the pulmonary vascular response to acute ductal constriction.

Progressive dysfunction of nitric oxide synthase in a lamb model of chronically increased pulmonary blood flow: a role for oxidative stress

Cardiac defects associated with increased pulmonary blood flow result in pulmonary vascular dysfunction that may relate to a decrease in bioavailable nitric oxide (NO). An 8-mm graft (shunt) was placed between the aorta and pulmonary artery in 30 late gestation fetal lambs; 27 fetal lambs underwent a sham procedure. Hemodynamic responses to ACh (1 microg/kg) and inhaled NO (40 ppm) were assessed at 2, 4, and 8 wk of age. Lung tissue nitric oxide synthase (NOS) activity, endothelial NOS (eNOS), neuronal NOS (nNOS), inducible NOS (iNOS), and heat shock protein 90 (HSP90), lung tissue and plasma nitrate and nitrite (NO(x)), and lung tissue superoxide anion and nitrated eNOS levels were determined. In shunted lambs, ACh decreased pulmonary artery pressure at 2 wk (P < 0.05) but not at 4 and 8 wk. Inhaled NO decreased pulmonary artery pressure at each age (P < 0.05). In control lambs, ACh and inhaled NO decreased pulmonary artery pressure at each age (P < 0.05). Total NOS activity did not change from 2 to 8 wk in control lambs but increased in shunted lambs (ANOVA, P < 0.05). Conversely, NO(x) levels relative to NOS activity were lower in shunted lambs than controls at 4 and 8 wk (P < 0.05). eNOS protein levels were greater in shunted lambs than controls at 4 wk of age (P < 0.05). Superoxide levels increased from 2 to 8 wk in control and shunted lambs (ANOVA, P < 0.05) and were greater in shunted lambs than controls at all ages (P < 0.05). Nitrated eNOS levels were greater in shunted lambs than controls at each age (P < 0.05). We conclude that increased pulmonary blood flow results in progressive impairment of basal and agonist-induced NOS function, in part secondary to oxidative stress that decreases bioavailable NO.

Does tourniquet application alter the nitrergic responses of rabbit corpus cavernosum penis? A functional study

OBJECTIVE

To investigate the effects of short and long periods of tourniquet application on corporal nerves, endothelium and smooth muscle responses.

METHODS

After the rabbits were anesthetized with xylazine (5 mg/kg) and ketamine hydrochloride (35 mg/kg), a standard rubber circular band was applied to the base of the penis. After waiting for 20, 40 and 60 min, the tourniquets were removed and the penil tissue was reperfused for 5 min. In all groups, relaxation [carbachol, sodium nitroprusside (SNP) and electrical field stimulation (EFS) and contraction (phenylephrine and EFS)] responses were examined. In another set of experiments, the rabbits were killed 24 h after the tourniquet period of 60 min and carbachol-induced relaxation responses were obtained.

RESULTS

SNP- and EFS-induced relaxation responses were similar in all groups. Carbachol-induced relaxation responses were not altered in tissues from 20 min tourniquet group, but they were significantly reduced in tissues from 40 and 60 min tourniquet group compared to that from control group. The impaired endothelium-mediated relaxation responses did not return to control levels after 24 h of reperfusion period. Neither phenylephrine nor EFS-mediated contraction responses were altered with tourniquet application.

CONCLUSIONS

The results suggest that long period of tourniquet application altered endothelium-dependent muscarinic receptor-mediated relaxation responses. This is the first functional study that examined the effects of tourniquet application on corpus cavernosum tissue. In conclusion, it can be suggested that if tourniquet is necessary in penile surgery the application time of up to 20 min is more appropriate instead of prolonged usage.

Neurophysiological basis of penile erection

Penile erection involves a complex interaction between the central nervous system and local factors. It is a neurovascular event modulated by psychological and hormonal factors. The discovery of nitric oxide (NO) as an intercellular messenger or neurotransmitter paved the way for identifying important mechanisms underlying physiological and pathophysiological events in the penis, in addition to providing the knowledge for the development of new therapeutics based on a novel concept of molecule and cell interaction. Despite the fact that sinusoidal endothelial cells also produce and release NO in response to chemical and possibly physical stimuli, roles of neurogenic NO in penile erection appear to be more attractive and convincing, since the pharmacological neuromodulation represents an essential step to attaining penile erection. Erectile dysfunction (ED) is caused by a variety of pathogenic factors, particularly impaired formation and action of NO. Hence, a thorough knowledge of the physiology of erection is essential for future pharmacological innovations in the field of male ED, particularly targeting NO or intracellular cyclic GMP, which represent the most promising therapeutic approach to treat patients with ED.

Nicotine potentiates the nitrergic relaxation responses of rabbit corpus cavernosum tissue via nicotinic acetylcholine receptors

The presence of neuronal nicotinic acetylcholine receptors in rabbit corpus cavernosum tissue and possible mechanisms underlying the potentiation of electrical field stimulation induced relaxation by nicotine were analyzed. In corpus cavernosum tissue strips nicotine (3 x 10(-5) M) and acetylcholine (10(-3) M) produced potentiation on electrical field stimulation (amplitude 50 V; frequency 4 Hz; width 0.8 ms) induced relaxation responses. This nicotine-induced potentiation was not altered by atropine (10(-6) M), guanethidine (5 x 10(-6) M) and indomethacin (10(-5) M), but abolished by hexamethonium chloride (10(-5) M) and L-nitro arginine methyl ester (10(-5) M). Nicotine did not cause any alteration on a single dose of carbachol (3 x 10(-5) M) and sodium nitroprusside (10(-5) M) induced relaxation responses. The results suggest that, nicotine-induced potentiation is NO and nicotinic acetylcholine receptor dependent but independent from prostaglandin synthesis, activation of muscarinic receptors and does not require intact adrenergic neurons. Nicotine did not affect smooth muscle and endothelium directly. In conclusion, in this study we showed for the first time that, nicotine acts on the nicotinic acetylcholine receptors located on the nitrergic nerves, thereby evoking the release of NO from these nerve terminals inducing relaxation response in rabbit corpus cavernosum tissue.

Impairment of endothelium- and nerve-mediated relaxation responses in the cavernosal smooth muscle of experimentally diabetic rabbits: role of weight loss and duration of diabetes

The effects of short- and long-term experimental diabetes on corporal nerve, endothelium and smooth-muscle responses were investigated, and the reasons for possible alterations in corporal smooth muscle responses such as hyperglycaemia, duration of experimental diabetes and/or altered tissue weight were evaluated. Rabbits were injected with alloxan (125 mg/kg) to induce diabetes. Age-matched non-diabetic and diabetic (3 and 9 weeks) and weight-matched non-diabetic groups (9 weeks) were used as control. In all groups, relaxation (carbachol, electrical field stimulation and sodiumnitroprusside) responses were examined. The relaxation responses were expressed as percentage of the precontraction to phenylephrine and as g response/g tissue weight. The effects of elevated glucose were also examined by incubating cavernosal strips in Krebs-Henseleit solution containing 44.4 mM glucose for 6 h. Cavernosal tissues of non-diabetic and 9-week diabetic rabbits were evaluated histologically. Sodiumnitroprusside (10(-7)-10(-4) M) responses were similar in all groups. Relaxation responses to electrical field stimulation (10 s train; amplitude 50 V; frequency 0.5-32 Hz; width 0.8 ms) were only attenuated in the 9-week diabetic group compared to the non-diabetic group. Carbachol (10(-8)-3 x 10(-5) M) responses were attenuated in both diabetic groups. When the relaxation responses expressed as g response/g tissue weight were evaluated, results were similar compared to those expressed as percentage of phenylephrine (10(-5) M). Neither carbachol nor electrical field stimulation mediated responses were impaired with glucose incubation. No morphological degenerations were observed in the endothelium. Diabetes may interfere with the synthesis and/or release of nitric oxide from both nerves and endothelium in corpus cavernosum, and alterations in endothelium-derived responses occur earlier than neurological disturbances. The sensitivity of cavernosal smooth muscle to nitric oxide did not alter in diabetes. Attenuation of responses was not due to decreased tissue weight caused by diabetes.

Nitric oxide-endothelin-1 interactions after surgically induced acute increases in pulmonary blood flow in intact lambs

Several congenital heart defects require surgery that acutely increases pulmonary blood flow (PBF). This can lead to dynamic alterations in postoperative pulmonary vascular resistance (PVR) and can contribute to morbidity and mortality. Thus the objective of this study was to determine the role of nitric oxide (NO), endothelin (ET)-1, and their interactions in the alterations of PVR after surgically induced increases in PBF. Twenty lambs underwent placement of an aortopulmonary vascular graft. Lambs were instrumented to measure vascular pressures and PBF and studied for 4 h. Before and after shunt opening, lambs received an infusion of saline (n = 9), tezosentan, an ETA- and ETB -receptor antagonist (n = 6), or Nomega-nitro-L-arginine (L-NNA), a NO synthase (NOS) inhibitor (n = 5). In control lambs, shunt opening increased PBF by 117.8% and decreased PVR by 40.7% (P < 0.05) by 15 min, without further changes thereafter. Plasma ET-1 levels increased 17.6% (P < 0.05), and total NOS activity decreased 61.1% (P < 0.05) at 4 h. ET-receptor blockade (tezosentan) prevented the plateau of PBF and PVR, such that PBF was increased and PVR was decreased compared with controls at 3 and 4 h (P < 0.05). These changes were associated with an increase in total NOS activity (+61.4%; P < 0.05) at 4 h. NOS inhibition (L-NNA) after shunt placement prevented the sustained decrease in PVR seen in control lambs. In these lambs, PVR decreased by 15 min (P < 0.05) but returned to baseline by 2 h. Together, these data suggest that surgically induced increases in PBF are limited by vasoconstriction, at least in part by an ET-receptor-mediated decrease in lung NOS activity. Thus NO appears to be important in maintaining a reduction in PVR after acutely increased PBF.

Inhaled nitric oxide induced NOS inhibition and rebound pulmonary hypertension: a role for superoxide and peroxynitrite in the intact lamb

Previous in vivo studies indicate that inhaled nitric oxide (NO) decreases nitric oxide synthase (NOS) activity and that this decrease is associated with significant increases in pulmonary vascular resistance (PVR) upon the acute withdrawal of inhaled NO (rebound pulmonary hypertension). In vitro studies suggest that superoxide and peroxynitrite production during inhaled NO therapy may mediate these effects, but in vivo data are lacking. The objective of this study was to determine the role of superoxide in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy in vivo. In control lambs, 24 h of inhaled NO (40 ppm) decreased NOS activity by 40% (P<0.05) and increased endothelin-1 levels by 64% (P<0.05). Withdrawal of NO resulted in an acute increase in PVR (60.7%, P<0.05). Associated with these changes, superoxide and peroxynitrite levels increased more than twofold (P<0.05) following 24 h of inhaled NO therapy. However, in lambs treated with polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) during inhaled NO therapy, there was no change in NOS activity, no increase in superoxide or peroxynitrite levels, and no increase in PVR upon the withdrawal of inhaled NO. In addition, endothelial NOS nitration was 18-fold higher (P<0.05) in control lambs than in PEG-SOD-treated lambs following 24 h of inhaled NO. These data suggest that superoxide and peroxynitrite participate in the decrease in NOS activity and rebound pulmonary hypertension associated with inhaled NO therapy. Reactive oxygen species scavenging may be a useful therapeutic strategy to ameliorate alterations in endogenous NO signaling during inhaled NO therapy.

Nerve-induced release of nitric oxide from the rabbit corpus cavernosum is modulated by cyclic guanosine 3',5'-monophosphate

Nitric oxide (NO) is a neurotransmitter of the autonomic nerves in the urogenital tract, in particular the release of NO in the cavernous tissue is of importance for maintaining erection. However, the regulation of NO formation in neurons of the corpus cavernosum is poorly understood. Here, we report, that upon electrical stimulation of isolated rabbit corpus cavernosum, NO/NO(2-) was formed and released in a reproducible fashion. The NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester decreased the amount of NO/NO(2-) released to 50+/-18% (P<0.05). The neurotoxin tetrodotoxin diminished the nerve-induced release of NO/NO(2-), to 35+/-10% (P<0.001). Blockage of the cholinergic and noradrenergic pathways by application of scopolamine and guanethidin (both 10(-5) M) did not alter the basal or nerve-evoked formation of NO/NO(2-). We also applied modulators of the soluble guanylate cyclase (sGC)/cyclic guanosine 3',5'-monophosphate (cGMP) pathway to study if and to what extent cGMP might affect the release of NO from the erectile tissue. In the presence of the cGMP analog 8-Br-cGMP (10(-4) M), and, the sGC stimulator 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (10(-4) M), the release of NO/NO(2-) was increased to 385+/-120% (P<0.05) and 282+/-78% (P<0.05), respectively. The effect of the phosphodiesterase inhibitor zaprinast (10(-4) M), was not significant (209+/-53%, n.s). In contrast, inhibition of sGC by 1-H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (10(-5) M) decreased the release of NO/NO(2-) to 64+/-14% (P<0.05). Our results suggest that NO/NO(2-) is released by nitrergic neurons within the rabbit corpus cavernosum and that the release is subject to modulation by the sGC/cGMP pathway, but not to modulation by acetylcholine or noradrenaline.

Elevated plasma viscosity in extreme hemodilution increases perivascular nitric oxide concentration and microvascular perfusion

We tested the hypothesis that high-viscosity (HV) plasma in extreme hemodilution causes wall shear stress to be greater than low-viscosity (LV) plasma, leading to enhanced production of nitric oxide (NO). The perivascular concentration of NO was measured in arterioles and venules and the tissue of the hamster chamber window model, subjected to acute extreme hemodilution, with a hematocrit (Hct) of 11% using Dextran 500 ( n = 6) or Dextran 70 ( n = 5) with final plasma viscosities of 1.99 ± 0.11 and 1.33 ± 0.04 cp, respectively. HV plasma significantly increased the periarteriolar, perivenular, and tissue NO concentration by 2.0, 1.9, and 1.4 times the control ( n = 7). The NO concentration with LV plasma was not statistically different from control. Arteriolar shear stress was significantly increased in HV plasma relative to LV plasma in arterioles but not in venules. Aortic endothelial NO synthase (eNOS) protein expression was increased with HV plasma but not with LV plasma. There was a weak correlation between perivascular NO concentration and the locally calculated shear stress induced by the procedures, when blood viscosity was corrected according to Hct values previously determined in studies of microvascular Hct distribution. The finding that the periarteriolar and venular NO concentration in HV plasma was the same although arteriolar shear stress was significantly greater than venular shear stress maybe be due to differences in vessel wall metabolism between arterioles and venules and the presence of NO transport through the blood stream in the microcirculation. Results support the concept that in extreme hemodilution HV plasma maintains functional capillary density through a NO-mediated vasodilatation.

Changes of tissue endothelin-1 and nitric oxide synthase in a sheep model of large intestinal obstruction

Large intestinal obstruction (LIO) in farm animals can cause a ischaemic necrosis of intestinal tissue, eventually leading to death. The roles of endothelin-1 (ET-1) and nitric oxide (NO) are not well understood in the process of LIO, but evidence suggests that endothelial-derived mediators may participate. In the present study, ET-1 concentration and total nitric oxide synthase (NOS) activity were measured in heart, liver, pancreas, lung and kidney in a model of LIO in sheep. Our data demonstrated that ET-1 concentration and NOS activity were altered, with significant increases of ET-1 in heart, lung and kidney and of NOS activity in pancreas and kidney, but a marked decline of NOS activity in liver (p < 0.05). It is postulated that these alterations in NOS activity and ET-1 concentration may contribute to the progressive loss of organ function, and finally lead to death in LIO in sheep.

Endothelial alterations during inhaled NO in lambs with pulmonary hypertension: implications for rebound hypertension

Clinically significant increases in pulmonary vascular resistance (PVR) have been noted upon acute withdrawal of inhaled nitric oxide (iNO). Previous studies in the normal pulmonary circulation demonstrate that iNO increases endothelin-1 (ET-1) levels and decreases endogenous nitric oxide synthase (NOS) activity, implicating an endothelial etiology for the increase in resistance upon iNO withdrawal. However, the effect of iNO on endogenous endothelial function in the clinically relevant pulmonary hypertensive circulation is unknown. The objective of this study was to determine the effects of iNO on endogenous NO-cGMP and ET-1 signaling in lambs with preexisting pulmonary hypertension secondary to increased pulmonary blood flow. Eight fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt lambs). After delivery (4 wk), the shunt lambs were mechanically ventilated with iNO (40 ppm) for 24 h. After 24 h of inhaled NO, plasma ET-1 levels increased by 34.8% independently of changes in protein levels (P < 0.05). Contrary to findings in normal lambs, total NOS activity did not decrease during iNO. In fact, Western blot analysis demonstrated that tissue endothelial NOS protein levels decreased by 43% such that NOS activity relative to protein levels actually increased during iNO (P < 0.05). In addition, the beta-subunit of soluble guanylate cyclase decreased by 70%, whereas phosphodiesterase 5 levels were unchanged (P < 0.05). Withdrawal of iNO was associated with an acute increase in PVR, which exceeded baseline PVR by 45%, and a decrease in cGMP concentrations to levels that were below baseline. These data suggest that the endothelial response to iNO and the potential mechanisms of rebound pulmonary hypertension are dependent upon the underlying pulmonary vasculature.

Chronic endothelin A receptor blockade in lambs with increased pulmonary blood flow and pressure

Endothelin receptor blockade is an emerging therapy for pulmonary hypertension. However, hemodynamic and structural effects and potential changes in endogenous nitric oxide (NO)-cGMP and endothelin-1 signaling of chronic endothelin A receptor blockade in pulmonary hypertension secondary to congenital heart disease are unknown. Therefore, the objectives of this study were to determine hemodynamic and structural effects and potential changes in endogenous NO-cGMP and endothelin-1 signaling of chronic endothelin A receptor blockade in a lamb model of increased pulmonary blood flow following in utero placement of an aortopulmonary shunt. Immediately after spontaneous birth, shunt lambs were treated lifelong with either an endothelin A receptor antagonist (PD-156707) or placebo. At 4 wk of age, PD-156707-treated shunt lambs (n = 6) had lower pulmonary vascular resistance and right atrial pressure than placebo-treated shunt lambs (n = 8, P < 0.05). Smooth muscle thickness or arterial number per unit area was not different between the two groups. However, the number of alveolar profiles per unit area was increased in the PD-156707-treated shunt lambs (190.7 +/- 5.6 vs. 132.9 +/- 10.0, P < 0.05). Plasma endothelin-1 and cGMP levels and lung NOS activity, cGMP, eNOS, preproendothelin-1, endothelin-converting enzyme-1, endothelin A, and endothelin B receptor protein levels were similar in both groups. We conclude that chronic endothelin A receptor blockade attenuates the progression of pulmonary hypertension and augments alveolar growth in lambs with increased pulmonary blood flow.

S-nitrosylation of endothelial nitric oxide synthase is associated with monomerization and decreased enzyme activity

Endothelial nitric oxide synthase (eNOS) is active only as a homodimer. Recent data has demonstrated that exogenous NO can act as an inhibitor of eNOS activity both in intact animals and vascular endothelial cells. However, the exact mechanism by which NO exerts its inhibitory action is unclear. Our initial experiments in bovine aortic endothelial cells indicated that exogenous NO decreased NOS activity with an associated decrease in eNOS dimer levels. We then undertook a series of studies to investigate the mechanism of dimer disruption. Exposure of purified human eNOS protein to NO donors or calcium-mediated activation of the enzyme resulted in a shift in eNOS from a predominantly dimeric to a predominantly monomeric enzyme. Further studies indicated that endogenous NOS activity or NO exposure caused S-nitrosylation of eNOS and that the presence of the thioredoxin and thioredoxin reductase system could significantly protect eNOS dimer levels and prevent the resultant monomerization and loss of activity. Further, exogenous NO treatment caused zinc tetrathiolate cluster destruction at the dimer interface. To further determine whether S-nitrosylation within this region could explain the effect of NO on eNOS, we purified a C99A eNOS mutant enzyme lacking the tetrathiolate cluster and analyzed its oligomeric state. This enzyme was predominantly monomeric, implicating a role for the tetrathiolate cluster in dimer maintenance and stability. Therefore, this study links the inhibitory action of NO with the destruction of zinc tetrathiolate cluster at the dimeric interface through S-nitrosylation of the cysteine residues.

Cavernosal tissue nitrite, nitrate, malondialdehyde and glutathione levels in diabetic and non-diabetic erectile dysfunction

The aim of this study is to investigate the role of nitric oxide (NO) stabile end products, membrane lipid peroxidation and antioxidant defensive mechanism in diabetic erectile dysfunction (ED) and compare these parameters with non-diabetic ED groups. We examined the penile cavernosal tissues, obtained from 22 patients who had undergone surgery of penile prostheses implantation, for the nitrite, nitrate, malondialdehyde (MDA) and glutathione (GSH) levels. Eight patients were suffering from diabetic erectile dysfunction (ED) and 14 patients had non-diabetic ED. Nitrite and nitrate levels were lower; MDA and GSH levels were higher in the diabetic group. There were statistically significant differences between diabetic and non-diabetic groups amongst the nitrite (p<0.001), nitrate (p<0.01), MDA (p<0.001) and GSH (p<0.01) levels. Our data provide evidence that NO deficiency, possibly due to the membrane lipid peroxidation and defective antioxidant defensive mechanism, may contribute to the development of diabetic ED and thus is involved in the pathogenesis of ED in diabetic patients.

Modulation of baroreceptor activity by gene transfer of nitric oxide synthase to carotid sinus adventitia

Administration of nitric oxide (NO) or NO donors to isolated carotid sinus and carotid bodies inhibits the activity of baroreceptor and chemoreceptor afferent nerves. Furthermore, NO synthase (NOS) is present in endothelial cells and in sensory nerves innervating the carotid sinus region. The major goal of this study was to determine whether overexpression of NOS in carotid sinus modulates baroreceptor activity. Rabbits were anesthetized, and adenoviral vectors (5 x 10(8) plaque-forming units) encoding genes for either beta-galactosidase (beta-Gal) or endothelial type III NOS (eNOS) were applied topically to the adventitial surface of one carotid sinus. In some experiments, the NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) was applied to the carotid sinus immediately after the vector. Four to five days later, baroreceptor activity and carotid sinus diameter were measured from the vascularly isolated carotid sinus of the anesthetized rabbits. Transgene expression was confirmed by X-Gal staining of beta-Gal and measurement of NOS activity by citrulline assay. The expression was restricted to the carotid sinus adventitia. Baroreceptor activity was decreased significantly, and the pressure-activity curve was shifted to higher pressures in eNOS-transduced (n = 5) compared with beta-Gal-transduced (n = 5) carotid sinuses. The pressure corresponding to 50% of maximum activity averaged 55 +/- 6 and 76 +/- 7 mmHg in beta-Gal- and eNOS-transduced carotid sinuses, respectively (P < 0.05). Decreased baroreceptor activity was accompanied by a significant increase in carotid diameter in the eNOS-transduced carotid sinuses (n = 5). l-NAME prevented the inhibition of baroreceptor activity and the increase in carotid diameter in eNOS-transduced carotid sinuses (n = 5). We conclude that adenoviral-mediated gene transfer of eNOS to carotid sinus adventitia causes sustained, NO-dependent inhibition of baroreceptor activity and resetting of the baroreceptor function curve to higher pressures.

Alterations in ET-1, not nitric oxide, in 1-week-old lambs with increased pulmonary blood flow

Altered pulmonary vascular reactivity is a source of morbidity and mortality for children with congenital heart disease and increased pulmonary blood flow. Nitric oxide (NO) and endothelin (ET)-1 are important mediators of pulmonary vascular reactivity. We hypothesize that early alterations in endothelial function contribute to the altered vascular reactivity associated with congenital heart disease. The objective of this study was to characterize endothelial function in our lamb model of increased pulmonary blood flow at 1 wk of life. Eleven fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt) and were studied 7 days after delivery. The pulmonary vasodilator response to both intravenous ACh (endothelium dependent) and inhaled NO (endothelium independent) was similar in shunted and control lambs. In addition, tissue NO(x), NO synthase (NOS) activity, and endothelial NOS protein levels were similar. Conversely, the vasodilator response to both ET-1 and 4Ala-ET-1 (an ET(B) receptor agonist) were attenuated in shunted lambs, and tissue ET-1 concentrations were increased (P < 0.05). Associated with these changes were an increase in ET-converting enzyme-1 protein and a decrease in ET(B) receptor protein levels (P < 0.05). These data demonstrate that increased pulmonary blood flow induces alterations in ET-1 signaling before NO signaling and suggest an early role for ET-1 in the altered vascular reactivity associated with increased pulmonary blood flow.

Nebivolol: a selective beta(1)-adrenergic receptor antagonist that relaxes vascular smooth muscle by nitric oxide- and cyclic GMP-dependent mechanisms

Nebivolol is a highly selective beta(1)-adrenergic receptor antagonist that also possesses vasodilator properties that are attributed largely to nitric oxide (NO). The objective of the present study was to elucidate in more detail the mechanisms by which nebivolol relaxes vascular smooth muscle. In the canine species, nebivolol caused relaxation of isolated precontracted rings of coronary artery and pulmonary artery largely by endothelium-dependent, NO-dependent, and cyclic GMP-dependent mechanisms. Vasorelaxation was inhibited by N(G)-methylarginine, and this inhibition was reversed by addition of excess L-arginine. Moreover, the vasorelaxant responses to nebivolol were markedly inhibited by oxyhemoglobin, methylene blue, and 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ), whereas vasorelaxation was enhanced by zaprinast. Rat aortic ring preparations, however, relaxed in response to nebivolol by both endothelium-dependent and endothelium-independent mechanisms, both involving NO, and cyclic GMP. Endothelium-dependent and endothelium-independent vasorelaxation were inhibited by oxyhemoglobin, methylene blue, and ODQ. However, only endothelium-dependent vasorelaxation in response to nebivolol was inhibited by N(G)-methylarginine. Additional experiments ruled out other endothelium-independent vasorelaxant mechanisms. In conclusion, the vasodilator responses to nebivolol involve NO and cyclic GMP in both vascular endothelial and smooth muscle cells.

The pathophysiology of erectile dysfunction related to endothelial dysfunction and mediators of vascular function

The incidence of erectile dysfunction increases with diabetes, hypertension, hypercholesterolaemia, cardiovascular disease and renal failure. All these conditions are associated with endothelial dysfunction. This review addresses the pathophysiology of erectile dysfunction with a special focus on new insights into nitric oxide (NO)-mediated pathways, oxidative stress and parallels to endothelial dysfunction. NO appears to be the key mediator promoting endothelium-derived vasodilation and penile erection. The possibility is discussed that elevated plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, may provide an additional pathomechanism for various forms of erectile dysfunction associated with cardiovascular risk factors and disease. Likewise, the role of endothelium-derived factors mediating NO-independent pathways is evaluated.

Alterations in nitric oxide production in 8-week-old lambs with increased pulmonary blood flow

Nitric oxide (NO) is an important mediator of pulmonary vascular reactivity, and decreased NO synthase expression has been demonstrated in children with advanced pulmonary hypertension secondary to congenital heart disease and increased pulmonary blood flow. Using aortopulmonary vascular graft placement in the fetal lamb, we have established a unique animal model of pulmonary hypertension with increased pulmonary blood flow. At 4 wk of age, these lambs display an early, selective impairment in agonist-induced NO responses, but an up-regulation of basal NO activity and gene expression. We hypothesized that further exposure to increased flow and/or pressure results in progressive endothelial dysfunction and a subsequent decrease in basal NO production. The objective of this study was to characterize potential later alterations in agonist-induced NO responses and basal NO activity and gene expression induced by 8 wk of increased pulmonary blood flow and pulmonary hypertension. Twenty-two fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt), and were studied 8 wk after delivery. Both in vivo and in isolated pulmonary arteries, the pulmonary vasodilating response to endothelium-dependent agents was attenuated in shunted lambs (p < 0.05), whereas the response to endothelium-independent agents was unchanged. The pulmonary vasoconstricting responses to Nomega-nitro-L-arginine, and lung tissue endothelial NO synthase mRNA, endothelial NO synthase protein, NO synthase activity, and NO(X) levels were all unchanged. These data suggest that the increase in basal NO activity demonstrated after 4 wk of increased pulmonary blood flow is lost by 8 wk of age, whereas the attenuation of agonist-induced responses persists. We speculate that the progressive decrease in basal NO activity participates in the development of pulmonary hypertension secondary to increased pulmonary blood flow.

Wei Lun Visiting Professorial Lecture: Nitric oxide in the regulation of vascular function: an historical overview

The field of nitric oxide (NO) research has developed in explosive proportions since the discovery of endogenous NO in 1986. The biological importance of NO was first shown by the findings that nitroglycerin causes vasodilation by liberating NO in the smooth muscle, and activating guanylate cyclase to raise smooth muscle levels of cyclic GMP. NO also inhibits platelet aggregation by cyclic GMP mechanisms. NO activates guanylate cyclase by heme dependent mechanisms involving the formation of a nitrosyl-heme complex. The high pharmacological potency of NO was finally understood when NO was shown to be formed endogenously, and to be the same as EDRF. Based on these properties of NO, new drugs can be developed as vasodilators and antiplatelet agents for the treatment of a variety of vascular disorders including impotency. NO elicits many other actions in mammalian systems including inhibition of cell proliferation, airway bronchodilation, antimicrobial effects, other host defense effects, and also modulates learning and memory as well as other central functions. This allows for an extensive opportunity to develop novel drugs for the diagnosis, prevention, and treatment of a number of different diseases, many of which are vascular in origin.

Involvement of L-arginine/nitric oxide pathway at the paraventricular nucleus of hypothalamus in central neural regulation of penile erection in the rat

The objective of this study is to investigate whether the L-arginine/nitric oxide pathway is involved in the neurotransmission of paraventricular nucleus of hypothalamus (PVN) activation-induced penile erection in the rat. Male adult Sprague-Dawley rats anesthetized with pentobarbital were used. The femoral artery was cannulated to measure systemic and mean arterial pressure (SAP and MAP), and heart rate (HR). A 26-gauge needle was inserted into corpus cavernosum to measure the intracavernous pressure (ICP) simultaneously with SAP, MAP and HR on a polygraph. Four groups of study were arranged: (1) stereotaxically delivery of L-arginine (500 nmol/500 nl) into PVN; (2) administration of a mixture (1 microl) containing N(G)-Nitro-L-arginine methyl ester (L-NAME) 500 nmol and L-arginine 500 nmol into PVN; (3) microinjection of saline 500 nl into PVN as a vehicle control; and (4) intracavernous injection of L-arginine (100 nmol/50 microl). The ICP, SAP, MAP and HR were monitored for at least 2 h after each administration of the experimental agents. Upon administration of L-arginine into PVN, there was a significant increase of ICP from resting 9.6+/-2.5 mmHg to peaked at 64.4+/-9.8 mmHg after a latency of 3016.0+/-1749.7 s and with a duration of 27.6+/-15.8 min. There was no change of resting ICP after administration of the mixture of L-NAME and L-arginine into PVN. Application of saline to PVN and intracavernous injection of L-arginine failed to increase ICP. Based on elicitation of penile erection upon administration of L-arginine into PVN, and elimination of this L-arginine induced penile erection by co-administration of L-NAME with L-arginine, the results of this study suggest that L-arginine/nitric oxide pathway may be involved in the neurotransmission of PVN activation-induced penile erection in the rat.

Nitric oxide-endothelin-1 interactions after acute ductal constriction in fetal lambs

Acute partial compression of the fetal ductus arteriosus (DA) results in an initial increase in pulmonary blood flow (PBF) that is followed by acute vasoconstriction. The objective of the present study was to determine the role of nitric oxide (NO)-endothelin-1 (ET-1) interactions in the acute changes in pulmonary vascular tone after in utero partial constriction of the DA. Twelve late-gestation fetal lambs (132-140 days) were instrumented to measure vascular pressures and left PBF. After a 24-h recovery period, acute constriction of the DA was performed by partially inflating a vascular occluder, and the hemodynamic variables were observed for 4 h. In control lambs (n = 7), acute ductal constriction initially increased PBF by 627% (P < 0.05). However, this was followed by active vasoconstriction, such that PBF was restored to preconstriction values by 4 h. This was associated with a 43% decrease in total NO synthase (NOS) activity (P < 0.05) and a 106% increase in plasma ET-1 levels (P < 0.05). Western blot analysis demonstrated no changes in lung tissue endothelial NOS, preproET-1, endothelin-converting enzyme-1, or ET(B) receptor protein levels. The infusion of PD-156707 (an ET(A) receptor antagonist, n = 5) completely blocked the vasoconstriction and preserved NOS activity. These data suggest that the fetal pulmonary vasoconstriction after acute constriction of the DA is mediated by NO-ET-1 interactions. These include an increase in ET(A) receptor-mediated vasoconstriction and an ET(A) receptor-mediated decrease in NOS activity. The mechanisms of these NO-ET-1 interactions, and their role in mediating acute changes in PBF, warrant further studies.

Uterine molecular responses to bisphenol A treatment before and after decidual induction in pseudopregnant rats

The results of the study demonstrate that the weak estrogenic action of bisphenol A (a daily subcutaneous dose of 200 mg/kg on 4 consecutive days, administered before or after decidual induction that occurs on day 4 of pseudopregnancy) on deciduoma growth in pseudopregnant Sprague-Dawley rats, was functionally associated with the hormonal status of the uterus. Whereas bisphenol A displayed uterotrophic action during the pre-decidual, estrogen related period, it inhibited decidual growth and progesterone secretion during the post-decidual, progesterone-dominated period. The estrogenic action of bisphenol A on uterine decidual growth was not correlated with the reduced levels of estrogen receptor binding sites and mRNA expression, nor the unchanged serum estradiol concentrations. BPA action appeared to be antagonized by progesterone.

K(Ca) channel-opening activity of Ginkgo Biloba extracts and ginsenosides in cultured endothelial cells

1. Extracts of Ginkgo biloba (EGb) and ginsenosides (GS) have been reported to induce vasorelaxation. In the present study, the role of K+ channels in the action of EGb and GS to activate nitric oxide synthase (NOS) activity was investigated in cultured endothelial cells. 2. Nitric oxide synthase activity of cultured endothelial cells detected by the reduced nicotinamide adenine dinucleotide phosphate (NADPH) histochemistry method was significantly increased after treatment with 20 microg/mL EGb or 40 microg/mL GS plus 10 mmol/L L-arginine. The effect was completely abolished by the addition of 0.5 micromol/L Nomega-nitro-L-arginine, an inhibitor of NOS, to the incubation medium and partially inhibited by 10 micromol/L tetraethylammonium (TEA), an inhibitor of Ca2+-activated K+ (KCa) channels. 3. Application of EGb to the intracellular surface of excised inside-out patches activated K+ channels in a concentration-dependent manner in the concentration range 1-100 microg/mL. Channel activity was also activated by application of GS at concentrations ranging from 1 to 300 microg/mL. The modulation of channel activity was inhibited by 0.5 mmol/L TEA but not by 0.5 mmol/L glibenclamide, an inhibitor of ATP-sensitive K+ channels. 4. Thus, in cultured endothelial cells, the increase in NOS activity induced by EGb or GS depends on the activity of KCa channels. These compounds may regulate nitric oxide release by changing the cell membrane potential in vascular endothelial cells.

Intracavernosal injection and intraurethral therapy for erectile dysfunction

Although the search for newer and more effective oral therapies is continually expanding, intracavernosal and intraurethral treatments continue to keep pace and are expected to remain in the clinician's armamentarium in the years to come. Unless there are contraindications, oral therapies are effective, have minimal side effects, and are first-line treatment. Some patients who have failed intraurethral and intracavernosal injection therapies previously have been shown to have successful outcomes with oral sildenafil in 56% to 57% of cases. If oral therapies are ineffective or have undesirable side effects, the intraurethral or intracavernosal routes are the next approach that should be prescribed.

The pathophysiological role of prostaglandins in penile erection

Penile erection is a complex haemodynamic event and relaxation of the vascular smooth muscle of the penis is fundamental to this process. This is primarily mediated by nitric oxide (NO) produced from non-adrenergic non-cholinergic (NANC) nerves and the endothelium surrounding the corporal sinusoids. However, corporal tissue has been shown to produce a number of other vasoactive factors, including prostaglandins (PGs), which appear to not only have diverse physiological effects, but are also able to modulate the effects of other neurotransmitters, including NO.

A mechanistic assessment of 1,3-butadiene diepoxide-induced inhibition of uterine deciduoma proliferation in pseudopregnant rats

Butadiene diepoxide (BDE), a reactive metabolite of 1,3-butadiene that is an important industrial chemical used in synthetic rubber production causes a dose-dependent inhibition of deciduoma development in pseudopregnant Sprague-Dawley rats. This study used 4 daily i.p. BDE doses of 0.20, 0.25, 0.30, 0.35, or 0.40 to characterize mechanisms that may be responsible for the antideciduoma effect. Pseudopregnant rats were treated either before (pseudopregnancy [PPG] days 1-4) or after (PPG days 5-9) deciduoma induction by endometrial trauma with a blunt needle. Animals were killed on PPG day 9 and evaluated for serum progesterone and endometrial protein and DNA. RT-PCR was used to measure message for estrogen receptor (ER) alpha and pituitary adenylate cyclase-activating polypeptide (PACAP). Substrate zymography and Western blotting were used respectively to measure matrix metalloproteinase (MMP)-9 and inducible nitric oxide synthase. The antideciduoma effects of BDE were associated with decreases in endometrial weight, protein, and DNA, with decreases in serum progesterone, and with decreases in PACAP message and MMP-9. A reduction in NOS was identified at the highest dose of BDE. Message for estrogen receptor (ER) alpha was not affected at any dose. We conclude that the reduction in decidual proliferation was direct and appeared to be associated with either 1) a decrease in the effectiveness of the deciduogenic stimulation and/or a weakened endometrial sensitivity to the stimulus; or 2) an effect on deciduoma development. Molecular mechanisms that apparently contributed to BDE inhibition of decidual metabolism included the synthesis of protein and DNA involved in decidual growth, the synthesis and activation of a matrix metalloproteinase for degradation of the extracellular matrix that is essential for tissue remodeling during deciduoma development, and the nitric oxide/nitric oxide synthase and pituitary adenylate cyclase-activating peptide systems that are involved in promoting vasodilation and increased vascular permeability to enhance the availability of substrates for maximal deciduoma growth. The ovotoxicity of BDE, which has previously been established, may indirectly affect decidual proliferation by reducing progesterone, the preeminent endocrine regulator of deciduoma development. The findings also suggest that BDE may possess no estrogenic action since it was associated with endometrial weight loss and unaltered levels of the estrogen receptor alpha mRNA expression.

Nonadrenergic, noncholinergic relaxation of human isolated corpus cavernosum induced by scorpion venom

OBJECTIVES

To examine the effects of Tityus serrulatus scorpion venom (TSV) on human corpus cavernosum (HCC) using a bioassay cascade. Priapism is occasionally observed in scorpion envenomation, mostly in children.

METHODS

HCC strips were suspended in a cascade system and superfused with aerated and warmed Krebs' solution at 5 mL/min. Noradrenaline (3 micromol/L) was infused to induce a submaximal contraction of the HCC strips. The release of cyclooxygenase products was prevented by infusing indomethacin (6 micromol/L).

RESULTS

N(omega)-nitro-L-arginine methyl ester (10 micromol/L; n = 10) increased the tone of the preparations and significantly reduced (P <0.01) the acetylcholine (ACh) and TSV-induced relaxations. Subsequent infusion of L-arginine (300 micromol/L) partially reversed the increased tone and significantly restored the relaxations induced by TSV and ACh (P <0.01). The soluble guanylyl cyclase inhibitor ODQ (10 micromol/L; n = 8) markedly reduced (P <0.01) the relaxations induced by TSV, ACh, glyceryl trinitrate, and bradykinin. 7-Nitroindazole (10 micromol/L; n = 8) inhibited the relaxations induced by TSV by 84% (P <0.01) and also caused small, but significant, reductions in the ACh and bradykinin-induced HCC relaxations (P <0.05). Atropine (1 micromol/L; n = 6) abolished the relaxations evoked by ACh (P <0.01), but had no effect on those elicited by TSV. Tetrodotoxin (1 micromol/L; n = 6) abolished the relaxations induced by TSV (P <0.01) and also reversed the established TSV-induced relaxation (n = 4).

CONCLUSIONS

Our results indicate that TSV relaxes HCC through the release of nitric oxide from nonadrenergic, noncholinergic (NANC) nerves. The elucidation of the mechanism responsible for the TSV-induced relaxations might be useful for a better understanding of the development of priapism in cases of scorpion envenomation.

Hydroxyurea inhibition of cellular and developmental activities in the decidualized and pregnant uteri of rats

The cytotoxicity of hydroxyurea (HU), currently used to combat various cancers, sickle cell anemia and human immunodeficiency infection, was assessed by exposing decidualized and pregnant uteri of Sprague-Dawley rats to this drug. Consecutive daily doses of HU (500 mg/kg(-1)) for 4 days were injected subcutaneously during decidualization when proliferation of the deciduoma was biochemically analyzed on pseudopregnancy day 9, or injected intraperitoneally during pregnancy when uterine developmental processes were evaluated on gestation day 16. Hydroxyurea displayed prominent antiproliferative effects on decidual growth. These actions were comparable to significantly impaired (P<0.001) developmental responses (increases in post-implantation losses, in resorbed fetuses and in reduced fetal and placental weights) during pregnancy. The cellular components inhibited by HU were DNA, protein, nitric oxide synthase, a matrix metalloproteinase and decidual prolactin-related protein mRNA (P<0.05). Steroid-related endocrine events (serum progesterone concentrations, estrogen receptor and mRNA levels) were unaffected by HU, implying direct cellular action by the drug. Interestingly, endometrial alkaline phosphatase bioactivity was enhanced by HU (P<0.05). Subsequently, the reproductive toxicity of HU was apparently related to mitogenic and differentiation-induced endometrial cellular activities.

The role of prostaglandins in penile erection

The balance of penile smooth muscle tone is finely controlled, with contractile factors acting in opposition to relaxant factors. The principal agents in this process are undoubtedly noradrenaline and nitric oxide. Prostaglandins probably have a crucial role in the 'fine tuning' of corporal smooth muscle tone. Their effects on control mechanisms in the healthy penis are more likely to be modulatory rather than direct.

The molecular basis of penile erection

Over the past two decades our understanding of the physiology and the various mediators involved in the pathway of penile erection has greatly increased. This has enabled us to develop effective pharmacological treatments for ED.

Possible involvement of nitric oxide in pilocarpine induced seminal emission in rats

Intraperitoneal injection of pilocarpine (0.75-3.0 mg/kg) caused a dose-related seminal emission in adult male rats. The seminal emission response to 3 mg/kg of pilocarpine was greatly reduced in atropinized (5 and 10 mg/kg, SC) animals, suggesting a cholinomimetic effect. Nw-nitro-L-arginine methyl ester (5, 10, and 20 mg/kg, SC), a nitric oxide synthesis inhibitor, also inhibited the pilocarpine-induced seminal emission, which was reversed by L-arginine (600 mg/kg, SC) or by coinjection of sodium nitroprusside (0.5 mg/kg, SC). Urine analysis for levels of nitric oxide metabolites, nitrate/nitrite (NO3-/NO2-), showed marked alterations in accordance with the drug treatments. The results suggest that nitric oxide mediates the inhibitory neurotransmission responsible for seminal emission in pilocarpine stimulated rats.

Nitric oxide as a signaling molecule in the vascular system: an overview

In retrospect, basic research in the fields of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) during the past two decades appears to have followed a logical course, beginning with the findings that NO and cGMP are vascular smooth muscle relaxants, that nitroglycerin relaxes smooth muscle by metabolism to NO, progressing to the discovery that mammalian cells synthesize NO, and finally the revelation that NO is a neurotransmitter mediating vasodilation in specialized vascular beds. A great deal of basic and clinical research on the physiologic and pathophysiologic roles of NO in cardiovascular function has been conducted since the discovery that endothelium-derived relaxing factor (EDRF) is NO. The new knowledge on NO should enable investigators in this field to develop novel and more effective therapeutic strategies for the prevention, diagnosis, and treatment of numerous cardiovascular disorders. The goal of this review was to highlight the early research that led to our current understanding of the pathophysiologic role of NO in cardiovascular medicine. Furthermore, we discussed the possible mechanism of some drugs interfering with NO signaling cascade.

Chimeric forms of neuronal nitric oxide synthase identify different regions of the reductase domain that are essential for dimerization and activity

Nitric oxide synthase (NOS) is the enzyme responsible for the conversion of L-arginine to L-citrulline and nitric oxide. Dimerization of the enzyme is an absolute requirement for catalytic activity. Each NOS monomer contains an N-terminal heme-binding domain and a C-terminal reductase domain. It is unclear how the reductase domain is involved in controlling dimerization and whether dimer formation alone controls enzyme activity. Our initial studies demonstrated that no dimerization or activity could be detected when the reductase domain of rat neuronal NOS (nNOS) was expressed either separately or in combination with the heme domain. To further evaluate the reductase domain, a set of expression plasmids was created by replacing the reductase domain of nNOS with other electron-transport proteins, thereby creating nNOS chimeric fusion proteins. The rat nNOS heme domain was linked with either cytochrome P450 reductase, adrenodoxin reductase, or the reductase domain from Bacillus megaterium cytochrome P450, BM-3. All the chimeric enzymes retained the ability to dimerize but were unable to metabolize L-arginine (<8% of wildtype activity levels), indicating that dimerization alone is insufficient to produce an active enzyme. Because the greatest regions of homology between electron-transport proteins are in the flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), and nicotinamide adenine dinucleotide phosphate (NADPH) binding regions, we produced truncation mutants within the nNOS reductase domain to investigate the role of these sequences in the ability of nNOS to dimerize and to metabolize L-arginine. The results demonstrated that the deletion of the final 56 amino acids or the NADPH-binding region had no effect on dimerization but produced an inactive enzyme. However, when the FAD-binding site (located between amino acids 920 and 1161) was deleted, both activity and dimerization were abolished. These results implicate sequences within the FAD-binding site as essential for nNOS dimerization but sequences within amino acids 1373 to 1429 as essential for activity.

NOS gene transfer inhibits expression of cell cycle regulatory molecules in vascular smooth muscle cells

The mechanisms of nitric oxide (NO)-mediated inhibition of vascular smooth muscle (VSM) cell proliferation are still obscure. Cyclins A and E in association with cyclin-dependent kinase 2 (cdk2) serve as positive regulators for mammalian cell cycle progression through the G1/S checkpoint of the cell cycle and subsequent cell proliferation. Therefore, we have tested the effect of adenovirus-mediated transfection of the endothelial nitric oxide synthase (eNOS) gene into guinea pig coronary VSM cells on platelet-derived growth factor (BB homodimer) (PDGF-BB)-stimulated cell proliferation and the expression of cell cycle regulatory molecules. Transfection of the eNOS gene (eNOS) into VSM cells significantly inhibited (P < 0.05) [3H]thymidine incorporation into the DNA in response to PDGF-BB stimulation compared with lacZ-transfected control cells. The eNOS transfer significantly inhibited (P < 0.05) PDGF-BB-induced proliferating cell nuclear antigen (PCNA) and cyclin A expression in VSM cells compared with cells transfected with the control vector. The time course of cyclin E expression in response to PDGF-BB stimulation was delayed in eNOS-transfected cells. Levels of cyclin-dependent kinase inhibitors p21 and p27 were not significantly affected by eNOS transfer. eNOS transfer did not decrease PDGF-beta receptor number, affinity, and autophosphorylation measured by radioreceptor assay and Western analysis. These results suggest that inhibition of PDGF-stimulated expression of cyclin A, cyclin E, and PCNA is the target of NO action. These findings could explain, at least in part, NO-mediated inhibition of VSM cell proliferation.

Enhanced recovery of injury-caused downregulation of paxillin protein by eNOS gene expression in rat carotid artery. Mechanism of NO inhibition of intimal hyperplasia?

Injury-caused dedifferentiation accompanied by proliferation and migration of smooth muscle cells (SMCs) is an important process in the development of the neointima. Nitric oxide (NO) stimulates differentiation and inhibits proliferation and migration of SMCs. Paxillin has been found to play an important role in cell differentiation, and its phosphorylation is regulated by NO in cultured SMCs. However, the regulation of paxillin by NO in the injured artery has not been investigated. Therefore, the aim of this study was to study the effects of in vivo endothelial NO synthase (eNOS) gene transfection on paxillin expression and intimal hyperplasia. A catheter balloon-denuded rat carotid artery was transfected in vivo with the replication-deficient adenovirus Ad5/RSVeNOS or with Ad5/RSVLacZ as the control. Transfected eNOS gene expression was determined by immunostaining, Western blot analysis, and citrulline assay. The expression of paxillin and its associated proteins was determined in injured arteries by Western blot analysis. The area of the intima and the ratio of intima to media were examined on cross sections by morphometry. The data showed that the expression of paxillin was significantly downregulated after injury. eNOS gene transfer showed no effect on paxillin downregulation 2 days after injury but significantly enhanced the recovery of paxillin protein 5 days and 2 weeks after injury. Vinculin, a paxillin-binding protein, was not altered by vascular injury or by eNOS gene transfer. eNOS gene transfer significantly inhibited intimal hyperplasia for up to 4 weeks. These results suggest that NO inhibition of intimal hyperplasia may be mediated by enhancing the recovery of injury-caused downregulation of paxillin.

G protein-dependent activation of smooth muscle eNOS via natriuretic peptide clearance receptor

In gastrointestinal smooth muscle, the neuropeptides vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) induce relaxation by interacting with VIP2/PACAP3 receptors coupled via Gs to adenylyl cyclase and with distinct receptors coupled via Gi1 and/or Gi2 to a smooth muscle endothelial nitric oxide synthase (eNOS). The present study identifies the receptor as the single-transmembrane natriuretic peptide clearance receptor (NPR-C). RT-PCR and Northern analysis demonstrated expression of the natriuretic peptide receptors NPR-C and NPR-B but not NPR-A in rabbit gastric muscle cells. In binding studies using 125I-labeled atrial natriuretic peptide (125I-ANP) and 125I-VIP as radioligands, VIP, ANP, and the selective NPR-C ligand cANP(4-23) bound with high affinity to NPR-C. ANP, cANP-(4-23), and VIP initiated identical signaling cascades consisting of Ca2+ influx, activation of eNOS via Gi1 and Gi2, stimulation of cGMP formation, and muscle relaxation. NOS activity and cGMP formation were abolished (93 +/- 3 to 96 +/- 2% inhibition) by nifedipine, pertussis toxin, the NOS inhibitor, NG-nitro-L-arginine, and the antagonists ANP-(1-11) and VIP-(10-28). NOS activity stimulated by all three ligands in muscle membranes was additively inhibited by Gi1 and Gi2 antibodies (82 +/- 2 to 84 +/- 1%). In reconstitution studies, VIP, cANP-(4-23), and guanosine 5'-O-(3-thiotriphosphate) stimulated NOS activity in membranes of COS-1 cells cotransfected with NPR-C and eNOS. The results establish a unique mechanism for G protein-dependent activation of a constitutive NOS expressed in gastrointestinal smooth muscle involving interaction of the relaxant neuropeptides VIP and PACAP with a single-transmembrane natriuretic peptide receptor, NPR-C.

Increased endothelial NOS in lambs with increased pulmonary blood flow and pulmonary hypertension

Altered pulmonary vascular reactivity is a source of morbidity and mortality for children with congenital heart defects and increased pulmonary blood flow. Nitric oxide (NO) is an important mediator of pulmonary vascular reactivity. The objective of this study was to characterize potential early alterations in expression, localization, and activity of endothelial NO synthase (eNOS) induced by increased pulmonary blood flow and pulmonary hypertension. Utilizing aortopulmonary vascular graft placement in the fetal lamb, we have established a unique animal model of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. Ten fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt). RNase protection assays and Western blotting were performed on lung tissue prepared from 4-wk-old shunt lambs and age-matched controls. eNOS mRNA (2.4:1, P < 0.05) and protein (2. 08:1, P < 0.05) were increased in lungs of shunt lambs. In situ hybridization and immunohistochemistry revealed that the increase was confined to the endothelium of pulmonary arteries. eNOS protein (1.55:1, P < 0.05) and tissue cGMP concentrations (2.1:1, P < 0.05) were also increased in isolated fifth-generation pulmonary arteries of shunt lambs. In addition, total lung eNOS activity was increased (2.9:1, P < 0.05). Thus we report a previously undescribed, early upregulation of eNOS gene expression and activity in lambs with increased pulmonary blood flow and pulmonary hypertension.

Dexamethasone-induced changes in endometrial growth and inducible nitric oxide synthase during decidualization in rats

1. The present study investigated the time-dependent inhibitory responses of endometrial growth and inducible nitric oxide synthase (iNOS) to dexamethasone during deciduoma development that was surgically induced on day 4 of pseudopregnancy (PG). 2. Groups of rats (n = 6) were subcutaneously injected with dexamethasone (1.5 mg/rat per day) for 3 days (PG days 1-3, 4-6, 7-9, 10-12 and 12-15). Rats in each group were killed on the last injection day. 3. Dexamethasone produced comparable temporal inhibitory changes in endometrial growth (wet weight, protein and DNA concentrations; P<0.0001) and in iNOS activity (130 kDa protein band), which peaked after PG days 4-6 and 7-9 pretreatments. 4. Endometrial matrix metalloproteinases (72 and 92 kDa) activity profiles displayed maximal reductions (36 and 53%, respectively) following PG days 4-6 pretreatment. Serum progesterone levels were equally (P<0.0001) but asynchronously inhibited by dexamethasone on PG days 9 and 12. 5. Dexamethasone inhibition of endometrial growth and in situ iNOS was most pronounced during decidual development (PG days 4-9). Minor reductions in these endometrial parameters occurred before deciduoma induction (PG days 1-3) and during deciduoma regression (PG days 10-15). 6. These results indicate that, in the endometrium, the iNOS/endogenous nitric oxide system may be linked to the biochemical and metabolic mechanisms responsible for the developmental responsiveness of the deciduoma to dexamethasone exposure. These time-dependent changes in endometrial growth and iNOS apparently were not mediated by progesterone.

Pharmacological characterization of kinin-induced relaxation of human corpus cavernosum

OBJECTIVE

To characterize the kinin receptor subtype involved in the relaxation of human isolated corpus cavernosum (HCC) induced by bradykinin (BK), Lys-bradykinin (Lys-BK), Met-Lys-bradykinin (Met-Lys-BK) and des-Arg9-bradykinin, and to investigate whether the kinin-induced relaxation of HCC results from the stimulation of nonadrenergic, noncholinergic (NANC) neurons supplying the cavernosal tissue.

MATERIALS AND METHODS

Excised HCC tissues were immediately placed in Krebs solution and kept at 4 degrees C until use (never > 24 h after removal). HCC was cut in strips of approximately 2 cm, suspended in a cascade system and superfused with oxygenated and warmed Krebs solution at 5 mL/min. After equilibration for approximately 90 min, noradrenaline (3 micromol/L) was infused to induce a submaximal contraction of the HCC strips. The release of cyclo-oxygenase products was prevented by infusing indomethacin (6 micromol/L). HCC strips were calibrated by injecting a single bolus of the nitrovasodilator glyceryl trinitrate (GTN) and the sensitivity of the tissues adjusted electronically to be similar. The agonists (kinins, histamine and acetylcholine) were injected as a single bolus (up to 100 microL) and the relaxation of HCC expressed as a percentage of the submaximal relaxation induced by GTN.

RESULTS

Bradykinin, Lys-BK and Met-Lys-BK significantly relaxed the HCC tissues; on a molar basis, there was no statistical difference among the degrees of relaxation induced by these peptides. The B1 kinin receptor agonist des-Arg9-bradykinin had no effect on the HCC. The infusion of the B2 kinin receptor antagonist Hoe 140 (50 nmol/L) virtually abolished the relaxation induced by BK, Lys-BK and Met-Lys-BK without affecting those induced by acetylcholine and histamine. The infusion of the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester increased the tone of the HCC tissues and significantly reduced (P < 0.01) the relaxation induced by BK (74%), Lys-BK (90%), Met-Lys-BK (87%) and acetylcholine (89%) without affecting those induced by GTN. The subsequent infusion of L-arginine (300 micromol/L) partially reversed the increased tone and significantly (P < 0.01) restored the relaxation induced by BK, Lys-BK and Met-Lys-BK. The results were similar with the novel guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,3,-alquinoxalin-1-one] which reduced by > 95% (P < 0.01) the relaxation induced by BK, Lys-BK, Met-Lys-BK, acetylcholine and GTN. The infusion of the sodium-channel blocker tetrodotoxin had no significant effect on the BK-, GTN- and acetylcholine-induced relaxation of HCC.

CONCLUSION

This study clearly showed the existence of functional B2 kinin receptors in human erectile tissues that when activated lead to the release of NO and hence relaxation of the HCC tissues. As tetrodotoxin failed to affect the kinin-induced relaxation of HCC strips, it is likely that these peptides release NO from the endothelium of sinusoidal capillaries rather than from neuronal sources supplying the cavernosal tissue. Although tissue kallikreins and their components have been found in the male reproductive system, the physiopathological importance of these findings has yet to be elucidated.