An ultrasensitive method for the simultaneous determination of cyclic AMP and cyclic GMP in small-volume samples from blood and tissue

Changes in Bradykinin and Prostaglandins Plasma Levels during Dextran-sulfate Low-density-lipoprotein Apheresis

The negative charges of dextran-sulfate (DS) used for low-density-lipoprotein (LDL) apheresis initiate the intrinsic coagulation pathway in which plasma kallikrein acts on the high-molecular-weight kininogen to produce large amounts of bradykinin. This study was undertaken to assess whether bradykinin generated during DS LDL apheresis has any physiologic effects in vivo. The plasma levels of bradykinin, prostaglandins and cyclic guanosine monophosphate (cGMP) were compared, when either of two anticoagulants, heparin or nafamostat mesilate (NM), was used during DS LDL apheresis. Although anticoagulative action by NM depends on the inhibition of thrombin activity, this substance also inhibits the activity of plasma kallikrein. During apheresis using heparin, the plasma levels of prostaglandin E2 (PGE2) increased significantly (5.6 ± 1.2 (mean ± SE, n=4) pg/ml before apheresis and 33.4 ± 13.2 after apheresis, p < 0.05) in association with an increase in bradykinin levels (17.9 ± 2.6 pg/ml before apheresis and 470 ± 135 after apheresis, p < 0.01). Interestingly, these changes were suppressed during apheresis using NM. There were no appreciable changes in cGMP during DS LDL apheresis with either of the anticoagulants. This finding suggests that bradykinin generated during apheresis has some pathophysiological effects via activation of the prostaglandin system. Our results support the view that in patients taking angiotensin-convertingenzyme inhibitors, the anaphylactoid reaction occurring during apheresis may be caused by an excessive rise in the bradykinin levels.

[Liposome modified with VIP-lipopeptide as a new drug delivery system]

We have designed a novel lipid analog (lipopeptide) that mimics the structural features of modified phospholipids. This lipopeptide is easily synthesized using a peptide synthesizer and has been shown to be useful for the modification of liposomes, which are used as an active targeted drug delivery system (DDS). Vasoactive intestinal peptide (VIP) has high homology with pituitary adenylate cyclase activating peptide (PACAP). There are three major PACAP receptors: PAC1R, VPAC1R, and VPAC2R. PAC1R has affinity only for PACAP, whereas VPAC1R and VPAC2R have the same affinity for both VIP and PACAP. In the present study, we synthesized several lipopeptides conjugated with VIP through different linkers and found that liposomes modified with these lipopeptides (VIP-Lips) selectively recognized the PACAP/VIP receptors. The anti-cancer activity of these VIP-Lips was evaluated by encapsulation of an antitumor drug, doxorubicin (DOX), into the modified liposomes (VIP-Lips-DOX) against the human osteosarcoma cell line, Saos-2, which highly expresses the VIP receptor. cAMP production was then measured to determine how well the VIP-Lips were able to recognize VPAC2R. The results clearly indicate that the proposed lipopeptide methodology holds promise as a DDS for cancer therapy.

Carperitide induces coronary vasodilation and limits infarct size in canine ischemic hearts: role of NO

Carperitide is effective for heart failure (HF) owing to its diuretic and vasodilatory effects. This recombinant peptide may also have direct cardioprotective effects because carperitide reduces the severity of heart failure and limits infarct size. Because coronary vasodilation is an important cardioprotective treatment modality, we investigated whether carperitide increased coronary blood flow (CBF) and improved myocardial metabolic and contractile dysfunction during ischemia in canine hearts. We also tested whether carperitide is directly responsible for limiting the infarct size. We infused carperitide at 0.025-0.2 μg kg(-1) min(-1) into the canine coronary artery. A minimum dose of 0.1 μg kg(-1) min(-1) was required to obtain maximal vasodilation. To test the effects of carperitide on ischemic hearts, we reduced perfusion pressure in the left anterior descending coronary artery such that CBF decreased to one-third of the baseline value. At 10 min after carperitide was infused at a dose of 0.1 μg kg(-1) min(-1), we observed increases in CBF, fractional shortening (FS) and pH levels in coronary venous blood without concomitant increases in cardiac nitric oxide (NO) levels; these changes were attenuated using either the atrial natriuretic peptide receptor antagonist HS-142-1 or the NO synthase inhibitor L(ω)-nitroarginine methyl ester (L-NAME). Cyclic guanosine monophosphate (GMP) levels in the coronary artery were elevated in response to carperitide that also limited the infarct size after 90 min of ischemia and subsequent reperfusion. Again, these effects were blunted by L-NAME. Carperitide increases CBF, reduces myocardial contractile and metabolic dysfunction and limits infarct size. In addition, NO is necessary for carperitide-induced vasodilation and cardioprotection in ischemic hearts.

Neurochemical and morphological studies on differentiation of NG108-15 cells by phorbol ester and forskolin

12-O-tetradecanoylphorbol 13-acetate (TPA), forskolin or dibutyryl cAMP induced neurite outgrowth and inhibition of cell growth in NG108-15 cells. TPA, forskolin and dibutyryl cAMP significantly increased specific activity of choline acetyltransferase. Forskolin markedly stimulated cAMP accumulation, but not TPA, suggesting that forskolin could induce differentiation by increasing the cAMP content via adenylate cyclase activation, but TPA-induced differentiation seems not to be due to the raise of the cAMP level. Incubation of the cells with TPA, forskolin or dibutyryl cAMP for 24 h resulted in enhancement of 50 mM K(+)-evoked Ca(2+) influx and neurite elongation, although incubation with these agents for 1 h didn't affect these events. From these results, it is suggested that TPA and forskolin induce differentiation of NG108-15 cells to acetylcholine neurons via different mechanisms: protein kinase C activation by TPA and cAMP-dependent protein kinase activation by forskolin. In addition, it is likely that Ca(2+) channels in cells differentiated by TPA, forskolin or dibutyryl cAMP become sensitive to depolarization.

Platelet nitric oxide signaling system in patients with coronary artery disease

BACKGROUND

Coronary artery disease (CAD) is the leading cause of death worldwide, and the major cause of hospital admissions in the Western countries. The pathogenesis of CAD is closely related to nitric oxide release and formation. The purpose of this study was to investigate the status of platelets nitric oxide in patients with coronary artery disease.

METHODS

We measured platelets aggregation, cGMP, NO (nitrite/nitrate level), NO synthase activity, plasma NO, and ionized Ca(2+) in 40 healthy volunteers and 120 patients with myocardial infarction, unstable and stable angina, with 40 subjects in each group. The subjects' age mean range was from 40-51 years.

RESULTS

Platelets aggregation, NO, cGMP, NO synthase activity, plasma NO and ionized Ca(2+) have increased significantly (P <0.001) across the patients groups compared to controls. Platelets NO synthase activity (mean ± SD / U / 10(9) platelets) in healthy controls, MI, unstable angina and stable angina patients were 1.19 ± 0.56, 1.21 ± 0.64, 1.64 ± 0.98 and 1.57 ± 0.81 respectively. The cGMP (mean ± SD / pmole / 10(9) platelets) levels were 0.95 ± 0.41, 1.53 ± 0.64, 3.18 ± 0.77, and 5.12 ± 1.5 respectively.

CONCLUSIONS

The present study demonstrated that platelets aggregation, NO, cGMP, NO synthase activity, plasma NO, and ionized Ca(2+) profoundly increased in CAD. The increases in NO-cGMP components may have resulted as a compensatory response to ameliorate platelet activity and Ca(2+) levels in CAD patients.

Torasemide, but not frusemide, increases intracellular cAMP and cGMP content in the aorta of the renal hypertensive rat

Repeated oral administration of the novel loop diuretic torasemide (3 mg kg−1) and frusemide (30 mg kg−1) for 7 days, elicited a significant fall in the systolic blood pressure in the one-kidney, one-clip Goldblatt renal hypertensive rat (RHR). The hypotensive action was greater in the torasemide group than in the frusemide group. Furthermore torasemide increased intracellular cAMP and cGMP content in aorta of RHR. Frusemide caused no effect. It is hypothesized that the increase in adenosine- or guanosine-nucleotides is involved in the antihypertensive action of torasemide, but not in that of frusemide.

Properties of hydrogen peroxide-induced histamine release from rat mast cells

Incubation of rat peritoneal mast cells with hydrogen peroxide results in a marked release of histamine. Maximal release is observed with 0.05-0.1 mM H(2)O(2), but higher concentrations of H(2)O(2) instead suppresses the release. Histamine release starts after about 2 min of lag time and reaches a plateau in about 10 min. Hydrogen peroxide-induced release does not exceed 50-60 per cent of total histamine if the incubations are prolonged or additional H(2)O(2) is given at 10 min. This would be explained by the fact that H(2)O(2) causes impairment of the histamine releasing system of mast cells simultaneously with the release of histamine. Hydrogen peroxide-induced release is not due to nonspecific lysis of the cells because lactate dehydrogenase, a cytoplasmic enzyme, is not liberated during the reaction. The reaction requires the presence of Ca(2+), is enhanced by D(2)O and suppressed by colchicine. It is not, however, affected by dibutyryl cAMP or dibutyryl cGMP. No significant alteration of intracellular levels of cyclic AMP and cyclic GMP is observed during the incubation of mast cells with 0.1 mM H(2)O(2). These results indicate that microtubular functions would be involved in the releasing reaction although they are not under the control of cyclic nucleotides. Microscopic observation shows that H(2)O(2)-induced release is accompanied by degranulation.

Clinical trial to assess the effect of physical exercise on endothelial function and insulin resistance in pregnant women

Background

Preeclampsia (PE) is a common maternal disease that complicates 5 to 10% of pregnancies and remains as the major cause of maternal and neonatal mortality. Cost-effective interventions aimed at preventing the development of preeclampsia are urgently needed. However, the pathogenesis of PE is not well known. Multiple mechanisms such as oxidative stress, endothelial dysfunction and insulin resistance may contribute to its development. Regular aerobic exercise recovers endothelial function; improves insulin resistance and decreases oxidative stress. Therefore the purpose of this clinical trial is to determine the effect of regular aerobic exercise on endothelial function, on insulin resistance and on pregnancy outcome.

Methods and design

64 pregnant women will be included in a blind, randomized clinical trial, and parallel assignment. The exercise group will do regular aerobic physical exercise: walking (10 minutes), aerobic exercise (30 minutes), stretching (10 minutes) and relaxation exercise (10 minutes) in three sessions per week. Control group will do the activities of daily living (bathing, dressing, eating, and walking) without counselling from a physical therapist.

Trial registration

NCT00741312.

Sildenafil citrate (Viagra) enhances vasodilatation by atrial natriuretic peptide in normal dogs

BACKGROUND

Sildenafil citrate (Viagra) is a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5, which might enhance the vasorelaxant and natriuretic actions of atrial natriuretic peptide (ANP) in patients with heart failure. The objective of this study was to examine the combined effect of Viagra on hemodynamic changes during infusion of exogenous ANP.

METHODS AND RESULTS

Healthy male beagles were used to assess systemic blood pressure, pulmonary artery pressure (PAP), and plasma levels of cGMP. After hemodynamic variables were measured, 0.1 microg.kg(-1).min(-1) of ANP was given during this study. One hour after initiating infusion of ANP, 2 mg/kg of sildenafil citrate or vehicle was given orally via a nasogastric tube. Hemodynamic changes were measured before and 1 h after these administrations. Mean systemic and PAP decreased during infusion of ANP, and further decreased after sildenafil citrate administration, however, mean systemic blood pressure decreased within 10 mmHg. Plasma levels of cGMP also increased after sildenafil citrate administration.

CONCLUSION

In normal dogs, sildenafil citrate enhances the vasodilator effect of ANP by increasing the cGMP level, however, the concomitant use of sildenafil citrate with ANP will not induce severe hypotension.

Possible role of exogenous cAMP to improve vascular endothelial dysfunction in hypertensive rats

The study has been designed to investigate the effect of 8-Br-cAMP, an activator of protein kinase A, in hypertension-induced vascular endothelial dysfunction. Rats were uninephroctomized and desoxycortisone acetate (DOCA) (40 mg/kg, s.c.) was administered to rats to produce hypertension (mean arterial blood pressure > 140 mmHg). Vascular endothelial dysfunction was assessed using isolated aortic ring preparation, electron microscopy of thoracic aorta and serum concentration of nitrite/nitrate. The expression of mRNA for p22phox and eNOS was assessed by using reverse transcriptase-polymerase chain reaction. Serum thiobarbituric acid reactive substances concentration and aortic superoxide anion concentration were estimated to assess oxidative stress. 8-Br-cAMP (5 mg/kg, i.p.) or atorvastatin (30 mg/kg, p.o.) prevented hypertension-induced attenuation of acetylcholine-induced endothelium-dependent relaxation, impairment of vascular endothelial lining, decrease in expression of mRNA for endothelial nitric oxide synthase (eNOS), serum nitrite/nitrate concentration and increase in expression of mRNA for p22phox, superoxide anion and serum TBARS. The ameliorative effect of 8-Br-cAMP was prevented by N-nitro-L-arginine methyl ester (25 mg/kg, i.p.) and glibenclamide (30 mg/kg, i.p.). It may be concluded that 8-Br-cAMP may stimulate expression and activity of eNOS and suppress expression of p22phox subunit of NADPH oxidase to reduce oxidative stress and subsequently improve vascular endothelial dysfunction.

MELAS and l-arginine therapy

We investigated the endothelial function in MELAS patients and also evaluated the therapeutic effects of L-arginine. Concentrations of L-arginine during the acute phase of MELAS were significantly lower than in control subjects. L-arginine infusions significantly improved all symptoms suggesting stroke within 30 min, and oral administration significantly decreased frequency and severity of stroke-like episodes. Flow-mediated dilation (FMD) in patients showed a significant decrease than those in the controls. Two years of oral supplementation of L-arginine significantly improved endothelial function to the control levels and was harmonized with the normalized plasma levels of L-arginine in patients. L-arginine therapy showed promise in treating stroke-like episodes in MELAS.

Nitric oxide modifies the sarcoplasmic reticular calcium release channel in endotoxemia by both guanosine-3',5' (cyclic) phosphate-dependent and independent pathways

OBJECTIVES

a) To determine whether decreased sarcoplasmic calcium release channel (CRC) activity is a mechanism by which myocardial contractility is reduced in endotoxemia; b) to determine whether nitric oxide modulates CRC activity in endotoxemia; and c) to examine two nitric oxide signaling pathways in relation to CRC function in endotoxemia.

DESIGN

Randomized, prospective using a rat model of endotoxemia.

SETTING

: Research laboratory.

SUBJECTS

Sprague-Dawley rats.

INTERVENTIONS

Endotoxemia was induced by lipopolysaccharide administration. The effects of nitric oxide were studied using the highly selective inducible nitric oxide synthase inhibitor N-(3-(aminomethyl)benzyl)acetamidine dihydrochloride (1400W) and the specific guanylyl cyclase inhibitor 1-H (1, 2, 4)oxadiazolo[4,3-a]quinoxalin-1-one (ODQ).

MEASUREMENTS AND MAIN RESULTS

We assessed myocardial contractility, myocardial nitric oxide content, and guanosine-3',5' (cyclic) phosphate (cGMP) content. We determined CRC activity by calcium release and ryanodine binding assays. We followed these variables at four time points through the course of endotoxemia. We found that myocardial contractility and CRC activity were decreased in late but not in early endotoxemia. Furthermore, inducible nitric oxide synthase inhibition with 1400W restored contractility and CRC activity in late endotoxemia but paradoxically worsened these variables in early endotoxemia. Through the use of the guanylyl cyclase inhibitor ODQ, we demonstrate that nitric oxide acts through cGMP-mediated mechanisms in early and late endotoxemia. We investigated cGMP-independent pathways by assessing the oxidative status of the CRC. We found that in late endotoxemia, nitric oxide decreased the number of free thiols, demonstrating that nitric oxide also acts through cGMP-independent pathways.

CONCLUSIONS

Nitric oxide has a dual effect on the CRC in endotoxemia. At low concentrations, as measured in early endotoxemia, nitric oxide stabilizes the CRC through cGMP-mediated mechanisms. In late endotoxemia, high nitric oxide concentrations decrease channel activity through both cGMP-dependent and cGMP-independent mechanisms.

An attempt to integrate Western and Chinese medicine: rationale for applying Chinese medicine as chronotherapy against cancer

Current Western medical treatment lays its main emphasis on evidence-based medicine (EBM) and cure is assessed by quantifying the effects of treatment statistically. In contrast, in Chinese medicine, cure is generally assessed by evaluating the patient's "pattern" (Zheng) [cf. Glossary] and medicines are prescribed according to this. We believe that traditional Chinese medicine (TCM) cannot be evaluated precisely according to Western principles, in which a constant amount of the same medicine is given to a group of patients to be evaluated. When assessing cure using TCM, Zheng is more important than the determination of medical effects. This means that quantitative evaluation of TCM treatment can be very difficult. In this paper, we focused on the Yin-Yang [cf. Glossary]balance to determine Zheng, and at the same time attempted to determine the treatment effects by applying the concept of regulation of Yin-Yang according to chronotherapeutic principles. According to Zheng, advanced cancer patients generally lack both Yin and Yang. Chinese medical treatment therefore seeks to supplement both Yin and Yang. However, we divided patients into two groups and compared them with respect to survival. One group was administered a predominantly Yang (Qi) [cf. Glossary] tonic herbal treatment during the daytime, while the other group was administered Yin (Blood) [cf. Glossary] tonics during night time. A comparison of the results of treatment showed that the patients in the group receiving Yang (Qi) replenishment during the daytime lived longer than patients receiving Yin (Blood) nourishment during the night. Moreover, the patients in the daytime Yang (Qi) replenishment group also fared significantly better than patients treated solely by Western methods.

Moderate regular exercise increases basal production of nitric oxide in elderly women

Vascular endothelial cells produce nitric oxide (NO), which is a potent vasodilator substance and is thought to have antiatherosclerotic properties. Therefore, it has also been proposed that NO may be useful to regulate vascular tonus and prevent progression of atherosclerosis. On the other hand, NO activity reduces with aging. We previously reported that the plasma nitrite/nitrate (NOx: the stable end product of NO) concentration was significantly increased by intense aerobic exercise training in healthy young humans. We hypothesized that lifestyle modification (e.g., even mild regular exercise training) can increase NO production in previously sedentary older humans. We measured the plasma NOx concentration before and after a mild aerobic exercise training regimen (cycling on a leg ergometer at 80% ventilatory threshold for 30 min, 5 days/week) for 3 months in elderly women. In addition, we assessed the plasma concentration of cyclic guanosine monophosphate (cGMP), a second messenger of NO, in the same samples. The individual ventilatory threshold increased significantly after the 3-month exercise training. The blood pressure at rest significantly decreased after exercise training. These results suggest that the 3-month exercise training in the older women produced favorable physiological effects. The plasma concentration of NOx significantly increased by the exercise training, and the plasma concentration of cGMP also increased by the exercise training. The present study suggests that even a mild regular aerobic-endurance exercise increases NO production in previously sedentary older humans, which may have beneficial effects (i.e., antihypertensive and antiatherosclerotic effects by endogenous NO) on the cardiovascular system.

Cytokine-induced nitric oxide inhibits mitochondrial energy production and induces myocardial dysfunction in endotoxin-treated rat hearts

The mechanism responsible for cardiac depression in septic shock remains unknown. The present study examined whether nitric oxide (NO) overproduced by inducible NO synthase (iNOS) can inhibit aerobic energy metabolism and impair the myocardial function in endotoxin-treated rat hearts. Lipopolysaccharide (LPS) significantly decreased systolic blood pressure (BP) to 44% of control during the 48 h treatment. Hearts from control and LPS-treated rats were perfused in a Langendorff apparatus. After LPS injection, left ventricular (LV) developed pressure (LVDP) was significantly depressed, plasma NO2-/NO3- (NO(x)) concentration was markedly increased, and myocardial adenosine 5'-triphosphate (ATP), creatine phosphate (CrP), and the ratio of ATP/adenosine 5'-diphosphate were progressively decreased with time. Immunological examination showed a significant expression of iNOS protein in the LPS-treated myocytes. Aminoguanidine, an inhibitor of iNOS, significantly attenuated these LPS-induced functional and metabolic changes. Myocardial cyclic guanosine 3',5'-monophosphate (cGMP) content was significantly increased after LPS injection. Methylene blue, an inhibitor of soluble guanylate cyclase, blunted this increase in cGMP and significantly restored the LPS-induced contractile dysfunction 6 h after LPS injection. In addition, there was a significant negative correlation between LVDP and myocardial cGMP levels as well as a significant negative correlation between LVDP and plasma NO(x) levels. In contrast, 48 h after LPS injection, methylene blue no longer affected cardiac performance, and there was a significant positive correlation between LVDP and myocardial ATP content. Furthermore, the normalized activities (as a ratio of the citrate synthase activity) of mitochondrial NADH-CoQ reductase, succinate-CoQ reductase, and ATPase, were significantly inhibited, and the swelling or disruption of mitochondria cristae was seen in the 48 h LPS treatment. These LPS-induced functional and morphological disorders in the mitochondria were significantly improved by aminoguanidine. The findings suggest that sustained production of NO by iNOS leads to contractile dysfunction via cGMP in the early stage, but that it can directly impair the mitochondrial function, lower myocardial energy production, and contribute significantly to the myocardial dysfunction in the later stage of septic shock.

Reduced flow-mediated vasodilation is not due to a decrease in production of nitric oxide in preeclampsia

OBJECTIVE

Our aim was to determine the reduced function of endothelial nitric oxide in preeclampsia by use of noninvasive techniques in vivo.

STUDY DESIGN

With the use of a high-resolution ultrasound transducer, diameters of brachial artery were measured after reactive hyperemia in 20 nonpregnant women, 20 normotensive pregnant women, and 15 women with preeclampsia. The concentrations of cyclic guanosine monophosphate were measured in samples of platelets from all groups.

RESULTS

Flow-mediated vasodilation at 1 minute after deflation was higher in the normotensive pregnant women (115.1% +/- 6.5%) than in the nonpregnant women (108.7% +/- 3.9%); flow-mediated vasodilation was lower in women with preeclampsia (106.8% +/- 2.7%) than in the normotensive pregnant women. The concentration of platelet cyclic guanosine monophosphate was higher in the normotensive pregnant women than in the nonpregnant women (2.21 +/- 1.10 pmol/mL/10(8) cells vs 0.746 +/- 0.381 pmol/mL/10(8) cells). There was no difference between the normotensive pregnant and the preeclamptic group (2.81 +/- 1.82 pmol/mL/10(8) cells). Furthermore, the increase in cyclic guanosine monophosphate by sodium nitroprusside in platelet samples that were obtained from the normotensive pregnant women was larger than the samples from the nonpregnant women (6.20 +/- 4.2 pmol/mL/10(8) cells vs 1.62 +/- 0.81 pmol/mL/10(8) cells). The increase in cyclic guanosine monophosphate from the women with preeclampsia did not differ from that in the normotensive pregnant women (5.84 +/- 3.73 pmol/ml/10(8) cells).

CONCLUSION

These results indicate that reduced endothelial nitric oxide activity might be due to a reduction of nitric oxide-cyclic guanosine monophosphate activity rather than its production in preeclampsia.

Characterization of mexiletine as an antagonist of beta-adrenoceptor in Chinese hamster ovary cells expressing cloned human beta-adrenoceptors

We characterized the beta-adrenoceptor-blocking property of mexiletine, a class Ib antiarrhythmic drug, on Chinese hamster ovary (CHO) cells stably expressing cloned human beta1-, beta2-, and beta3-adrenoceptors. In radioligand binding experiments, mexiletine (10 microM-1 mM) concentration-dependently displaced the specific binding of [125I]cyanopindolol to human beta1- and beta2-adrenoceptors in the membrane fraction of the cells. High concentration (100 microM-1 mM) of mexiletine partially displaced the specific binding of [125I]cyanopindolol to human beta3-adrenoceptor. On the other hand, high concentration (300 microM and 1 mM) of lidocaine, another class Ib antiarrhythmic drug, partially displaced the specific binding of [125I]cyanopindolol to human beta1-adrenoceptor, whereas it did not affect the specific binding of [125I]cyanopindolol to human beta2- and beta3-adrenoceptors. Mexiletine (5, 50, and 500 microM) reduces basal adenosine 3',5'-cyclic monophosphate (cAMP) level and isoprenaline-induced cAMP accumulation on CHO cells stably expressing cloned human beta1- and beta2-adrenoceptors. Lidocaine (10 and 100 microM and 1 mM) tend to reduce basal cAMP level on CHO cells stably expressing cloned human beta1-adrenoceptors, whereas the drug did not reduce the isoprenaline-induced cAMP accumulation on CHO cells stably expressing cloned human beta1-, beta2-, and beta3-adrenoceptors. Mexiletine and lidocaine have no effect on forskolin (0.1, 1, and 3 microM)-induced cAMP accumulation. These results demonstrate that mexiletine blocks the binding of agonists to beta1- and beta2-adrenoceptors, and thereby attenuates the agonist-induced cAMP accumulation, and that the action of mexiletine as an antagonist of beta1- and beta2-adrenoceptors is independent of its antiarrhythmic property.

A benzimidazole fungicide, benomyl, and its metabolite, carbendazim, induce aromatase activity in a human ovarian granulose-like tumor cell line (KGN)

Endocrine disruptor chemicals are known to cause a range of abnormalities in sexual differentiation and reproduction. One mechanism underlying such effects may be via alteration of aromatase activity, which is responsible for estrogen production. A good screening system for identifying endocrine disruptors has long been desired. We have recently established a human ovarian granulosa-like tumor cell line, KGN, which possesses a relatively high level of aromatase expression and is considered a useful mammalian model for investigating the in vitro effects of various chemicals on aromatase activity. In this study we screened 55 different candidate chemicals for endocrine disruptors by assaying aromatase activity. Only benomyl, known as both a benzimidazole fungicide and a microtubule-interfering agent, was found to induce aromatase activity in association with increased levels of aromatase mRNA in KGN cells. The effect of benomyl was presumed to be mediated by its metabolite carbendazim, because it produced an effect equivalent to that of benomyl. The mechanism underlying the benomyl-induced increase in aromatase activity appears independent of the cAMP-protein kinase A pathway. Treatment with taxol, another class of microtubule-interfering agents, also caused induction of aromatase in KGN cells. Both benomyl and taxol changed KGN cell morphology, including the development of cell roundness and a disorganized network of microtubules. These results indicate that benomyl is a potential endocrine disruptor that provides a novel estrogenicity and operates through a microtubule-interfering mechanism.

Attenuation of biologic compensatory action of cardiac natriuretic peptide system with aging

Although plasma B-type natriuretic peptide (BNP) levels increase with age, the mechanisms responsible for this increase are unknown. We investigated the predictors of elevated BNP in older subjects without cardiac systolic dysfunction and overt renal dysfunction. Furthermore, we analyzed the relations between BNP and its second messenger, cyclic guanosine monophosphate (cGMP), to aging. In 252 subjects (mean age 69 +/- 12 years) with left ventricular ejection fraction >/=50% and creatinine levels <==1.5 mg/dl, plasma levels of BNP, cGMP, blood urea nitrogen, creatinine, and beta2-microglobulin (an endogenous marker of renal function), estimated glomerular filtration rate, and echocardiographic data were prospectively evaluated. Plasma BNP levels increased with age (r = 0.4, p <0.0001). With use of multivariate analysis, predictors of elevated BNP levels were age, use of beta blockers, and serum beta2-microglobulin levels. The molar ratio of cGMP to BNP significantly decreased with aging (r = 0.55, p <0.0001). Elevated BNP in older subjects with normal cardiac systolic function may be due in part to renal impairment. With aging, biologic compensation of the cardiac natriuretic peptide system may be attenuated.

A Combination of Oral Sildenafil and Beraprost Ameliorates Pulmonary Hypertension in Rats

Sildenafil, an oral phosphodiesterase type-5 inhibitor, has vasodilatory effects through a cyclic guanosine 3', 5'-monophosphate-dependent mechanism, whereas beraprost, an oral prostacyclin analog, induces vasorelaxation through a cAMP-dependent mechanism. We investigated whether the combination of oral sildenafil and beraprost is superior to each drug alone in the treatment of pulmonary hypertension. Rats were randomized to receive repeated administration of saline, sildenafil, beraprost, or both of these drugs twice a day for 3 weeks. Three weeks after monocrotaline (MCT) injection, there was significant development of pulmonary hypertension. The increases in right ventricular systolic pressure and ratio of right ventricular weight to body weight were significantly attenuated in the Sildenafil and Beraprost groups. Combination therapy with sildenafil and beraprost had additive effects on increases in plasma cAMP and cyclic guanosine 3', 5'-monophosphate levels, resulting in further improvement in pulmonary hemodynamics compared with treatment with each drug alone. Unlike MCT rats given saline, sildenafil, or beraprost alone, all rats treated with both drugs remained alive during 6-week follow-up. These results suggest that combination therapy with oral sildenafil and beraprost attenuates the development of MCT-induced pulmonary hypertension compared with treatment with each drug alone.

Development of antibodies for the detection of N-acetyl-glufosinate

Glufosinate is a widely used herbicide, which is difficult to detect by conventional analytical techniques. For many other herbicides, suitable antibodies have been raised for immunoassay development. Unfortunately, glufosinate is a very small molecule and difficult to immunize with. Thus, a derivatization-assisted immunoassay (DAIA) using the target analyte N-acetyl-glufosinate (NAG) was constructed. The activated hapten was synthesized by a new approach, using a homobifunctional cross-linker suberic acid bis(N-hydroxysuccinimide ester). The preparation of a suitable conjugate, the immunization, and the characterization of polyclonal antibodies are shown. The determination of the conjugation density (hapten density) of the immunogens was performed by four different methods (high-performance liquid chromatography with a refractive index detector, total reflection X-ray fluorescence, inductively coupled plasma mass spectrometry, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry), which gave similar results. The limit of detection was 17 mug/L NAG in water for the direct competitive enzyme immunoassay. NAG is also a main metabolite of glufosinate in resistant transgenic plants. The antibodies might be useful for the selective detection of NAG in the presence of the parent compound glufosinate (cross-reactivity 0.13%) and other metabolites.

Nitric oxide-cGMP pathway is involved in endotoxin-induced contractile dysfunction in rat hearts

The mechanisms by which endotoxemia causes cardiac depression have not been fully elucidated. The present study examined the involvement of nitric oxide (NO) in this pathology. Rats were infused with lipopolysaccharide (LPS) or saline, and the plasma and myocardial NO(2)(-) and NO(3)(-) (NOx) concentrations were measured before or 3, 6, and 24 h after treatment. The hearts were then immediately isolated and mounted in a Langendorff apparatus, and left ventricular developed pressure (LVDP) was determined before biochemical analysis of the myocardium. LPS injection effected the expression of inducible NO synthase (iNOS) in the myocardium, a marked increase in plasma and myocardial NOx levels, and a significant decline in LVDP compared with saline controls. The LPS-induced NO production and concomitant cardiac depression were most pronounced 6 h after LPS injection and were accompanied by a significant increase in myocardial cGMP content. Myocardial ATP levels were not significantly altered after LPS injection. Significant negative correlation was observed between LVDP and myocardial cGMP content, as well as between LVDP and plasma NOx levels. Aminoguanidine, an inhibitor of iNOS, significantly attenuated the LPS-induced NOx production and contractile dysfunction. Furthermore, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase, significantly decreased myocardial cGMP content and attenuated the contractile depression, although aminoguanidine or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one was not able to completely reverse myocardial dysfunction. Our data suggest that endotoxin-induced contractile dysfunction in rat hearts is associated with NO production by myocardial iNOS and a concomitant increase in myocardial cGMP.

Pulmonary vasodilator response to adrenomedullin in patients with pulmonary hypertension

This study sought to investigate pulmonary vasodilator responses to intrapulmonary and intravenous infusion of adrenomedullin (AM) in patients with pulmonary hypertension. In 10 patients with pulmonary hypertension, blood flow velocity in a segmental pulmonary artery was measured using a Doppler flow wire during intrapulmonary infusion of AM, acetylcholine (ACh), and adenosine triphosphate (ATP). The hemodynamic effects of intravenously administered AM (0.05 microg/kg/min) were examined in another 5 patients with primary pulmonary hypertension. Intrapulmonary infusion of AM, ACh or ATP caused a significant dose-dependent increase in blood flow velocity in a segmental pulmonary artery, respectively. The increase in flow velocity with AM at 10(-8) mol/l (41 +/- 6% of the baseline value) was comparable to that with ACh at 10(-4) mol/l (39 +/- 11%) and that with ATP at 10(-5) mol/l (36 +/- 14%), suggesting a strong pulmonary vasodilator activity of AM. Intravenous infusion of AM produced a 41% increase in cardiac index (p < 0.05) and a 30% decrease in pulmonary vascular resistance (p < 0.05) with a 3% reduction in mean pulmonary arterial pressure (p = NS). These results suggest that, on a molar basis, AM may have much more potent pulmonary vasodilator activity than ACh and ATP, and thus may have beneficial hemodynamic effects in patients with pulmonary hypertension.

Intravenous adrenomedullin in myocardial function and energy metabolism in patients after myocardial infarction

This study investigated the effects of adrenomedullin on left ventricular myocardial contraction and relaxation, coronary blood flow, and myocardial oxygen consumption in comparison with those of atrial natriuretic peptide (ANP). Fourteen patients who had had myocardial infarctions were randomly assigned to receive IV infusion of adrenomedullin (0.05 microg/kg/min) or ANP (0.05 microg/kg/min). Both adrenomedullin and ANP significantly decreased left ventricular systolic pressure (-17 mm Hg, -13 mm Hg, respectively, both p < 0.05). The increase in cardiac index by adrenomedullin (+31%) was significantly greater than that by ANP (+16%). Adrenomedullin significantly increased an index of myocardial contractility, Emax (2.5 +/- 0.3 mm Hg-3.7 +/- 0.3 mm Hg/ml, p < 0.05) and shortened an index of myocardial relaxation, Tau (52 +/- 5 ms-48 +/- 4 ms, p < 0.05). In contrast, ANP did not significantly alter either parameter. In addition, adrenomedullin, but not ANP, significantly increased coronary sinus blood flow (73 +/- 10 ml/min-86 +/- 10 ml/min, p < 0.05). Adrenomedullin did not increase myocardial oxygen consumption. Unlike ANP, IV administration of adrenomedullin enhanced left ventricular myocardial contraction and improved left ventricular relaxation without increasing myocardial oxygen consumption in patients who had had a myocardial infarction.

Interactions of sildenafil with various coronary vasodilators in isolated porcine coronary artery

There are reports of serious hypotension or circulatory shock when sildenafil citrate, a selective cyclic nucleotide phosphodiesterase type 5 inhibitor, which was developed for the treatment of erectile dysfunction, is given to patients taking certain coronary vasodilators. We thus examined the interaction of sildenafil with various coronary vasodilators including nitric oxide (NO) donors in isolated porcine coronary artery. Sildenafil caused concentration-dependent relaxations of the artery precontracted with U46619 (9,11-dideoxy-9 alpha,11 alpha-methanoepoxy-prostaglandin F(2alpha)). Incubation with the NO synthase inhibitor NG-nitro-L-arginine or the soluble guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one) significantly shifted the concentration-response curve for sildenafil to the right without affecting the maximum response, indicating that some part of the relaxant response to sildenafil may be the result of the inhibition of phosphodiestrase type 5-induced degradation of cyclic GMP (cGMP) that is produced through guanylate cyclase activation by NO released spontaneously. The relaxant effects of the vasodilators with an NO donor property, isosorbide dinitrate, sodium nitroprusside, nicorandil and nipradilol, were significantly enhanced by sildenafil, as shown by a significant leftward shift of their concentration-response curves. In contrast, the relaxant responses to the drugs without a property as an NO donor, diltiazem, celiprolol and pinacidil, were not affected by sildenafil. The cGMP level of the tissue was elevated after adding sildenafil, and the cGMP-generating effect of a combination of sildenafil and sodium nitroprusside was higher than that of each drug alone. The cyclic AMP level determined simultaneously was not changed by sildenafil. These results suggest that sildenafil potentiates specifically the relaxant responses of porcine coronary artery to the drugs which behave as an NO donor, providing basic evidence that the benefit of sildenafil in the treatment of erectile dysfunction can be limited by a risk of marked vasodilation when used together with NO-related coronary vasodilators.

Systemic administration of histamine reduces reovirus type 2-induced insulitis in suckling DBA/1 mice

Previously we suggested that reovirus type 2 (Reo-2) infection induced autoimmune insulitis, resulting in mild diabetes in suckling mice. The effect of histamine (a lymphocyte function suppressor) on Reo-2-induced insulitis was examined. Systemic histamine administration reduced the development of insulitis and blood glucose elevation. Endogenous interleukin-2 (IL-2) activity by splenic cells and the production of antibodies to pancreatic islet cells were reduced by histamine treatment. In addition, histamine treatment increased cyclic adenosine monophosphate (cAMP) concentrations in the plasma. These results further suggest that the insulitis seen in Reo-2 infection in suckling mice is induced by an immune reaction.

Role of aquaporin-2 gene expression in hyponatremic rats with chronic vasopressin-induced antidiuresis

BACKGROUND

In a state of chronic arginine vasopressin (AVP) excess, the action of antidiuresis has been attenuated, resulting in some water diuresis. This state has been termed an "AVP escape" phenomenon. The present study was designed to determine what mechanisms underlie this attenuation in renal concentrating ability, which is found in chronic AVP excess, both in the presence and absence of volume expansion.

METHODS

Two groups of experimental rats were established. One group received solid chow with water ad libitum. The second group received chow, which was offered as a liquid diet. Both groups received subcutaneous administration of 1-deamino-8-D-arginine vasopressin (dDAVP) at 5 ng/h for the entire observation period of one week. Over the course of the observation period, tissue levels of aquaporin-2 (AQP-2) mRNA and protein were measured. Levels of AVP V2 receptor were monitored, both by measuring mRNA levels and by ligand-binding studies using [3H]AVP. Tissue levels of cAMP also were determined.

RESULTS

Experimental rats with the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) had severe hyponatremia below 120 mmol/L, and impaired urinary concentrating ability, during the seven-day observation period. In contrast, the dDAVP-excess rats, given solid chow, maintained maximally concentrated urine and normal levels of serum sodium. The down-regulation of AVP V2 receptor function was comparable in the two groups. The maximal binding capacity (Bmax) fell to the nadir on day 2 and was thereafter suppressed at approximately 60% of control rats during the experiment. Up-regulation of AQP-2 mRNA expression was found, but this up-regulation was significantly less in the SIADH rats compared with the dDAVP-excess rats (153.5 +/- 29.8% vs. 323.7 +/- 23.8% on day 7, P < 0.05). This differential response between these two groups was affirmed by measured differences in AQP-2 protein levels, both in tissue and in urinary excretion.

CONCLUSIONS

These results indicate that the attenuated regulation of the AQP-2 gene leads to the decrease in urinary concentrating ability in the experimental SIADH rats, suffering from hypervolemic state, compared with the normonatremic rats receiving AVP. Either hypervolemia or hypotonicity may diminish the post-receptor signaling of AVP in renal collecting duct cells, under the chronic AVP excess state found in SIADH.

Role of cellular acidosis in production of nitric oxide in canine ischemic myocardium

We tested the hypothesis that cellular acidosis modulates the production of nitric oxide (NO) in ischemic hearts. In canine hearts, we decreased coronary blood flow (CBF) to one third of the control by reduction of coronary perfusion pressure (105+/-3 to 41+/-5 mmHg), and thereafter we maintained CBF constant (89.8+/-1.6 to 30.0+/-0.5 ml/100 g/min) with an intracoronary administration of either saline, atropine, rauwolscine, HOE140, 8-sulfophenyltheophylline (8SPT), NaHCO3, or HOE642 (the inhibitor of Na+/H+ exchange). The cardiac NO levels defined as the differences of the nitrate and nitrite levels between coronary venous and arterial blood increased in the saline administration (2.9+/-0.2 to 12.7+/-1.7 micromol/l), and the extents of increases were identical in the condition of either saline, atropine, rauwolscine, HOE140 or 8SPT administration. In the condition with either NaHCO3 or HOE642, the increases in the cardiac NO levels were blunted (4.5+/-0.7 and 4.8+/-0.4 micromol/l, respectively). Cyclic GMP content of epicardial coronary artery in the ischemic area increased, which was also attenuated by either NaHCO3 or HOE642. We confirmed the acidosis-induced NO production in a more severe ischemic myocardium, and also showed that cellular acidosis produced by infusion of HCl increased NO production in non-ischemic myocardium. We conclude that cellular acidosis and subsequent activation of Na+/H+ exchanges modulate production of endogenous NO in canine ischemic myocardium.

Heart rate and plasma cyclic AMP responses to isoproterenol infusion and effect of beta-adrenergic blockade in patients with postural orthostatic tachycardia syndrome

To clarify the pathophysiological mechanism of postural orthostatic tachycardia syndrome (POTS). the responses of heart rate and the plasma cyclic AMP (cAMP) level to isoproterenol infusion in the supine position were evaluated in 10 POTS patients and 10 age-matched controls. Also, the effect of beta-adrenergic blockade on POTS was assessed using the headup tilt test. The POTS patients consisted of two men and eight women, with a mean age of 19.7 years (range. 15-28 years). An exaggerated increase of both heart rate and the plasma cAMP concentration after isoproterenol infusion at a low dose (1 microg/min) was observed in the POTS patients, but not in control subjects. Seven POTS patients received oral beta-blocker therapy. In five of these, symptoms were abolished and there was a smaller heart rate increase during the head-up tilt test. These data suggest that POTS may be more prevalent in young women and that beta-adrenergic hypersensitivity may play a role in the mechanisms of this syndrome. However, a larger series of patients need to be studied in the future.

Haemodynamic and hormonal effects of adrenomedullin in patients with pulmonary hypertension

OBJECTIVE

To investigate whether infusion of adrenomedullin, a potent vasorelaxant peptide, has beneficial haemodynamic and hormonal effects in patients with pulmonary hypertension.

PATIENTS AND DESIGN

The haemodynamic and hormonal responses to intravenous infusion of adrenomedullin (0.05 microgram/kg/min) or placebo were examined in 13 patients with precapillary pulmonary hypertension.

RESULTS

Infusion of adrenomedullin produced a 44% increase in cardiac index (mean (SD) 1.8 (0.2) to 2.6 (0.3) l/min/m(2), p < 0. 05) and a 32% decrease in pulmonary vascular resistance (19.7 (1.4) to 13.4 (1.3) units, p < 0.05), with a 4% reduction in mean pulmonary arterial pressure (62 (4) to 59 (4) mm Hg, NS). Adrenomedullin also decreased mean systemic arterial pressure (81 (3) to 72 (4) mm Hg, p < 0.05) and increased heart rate (73 (4) to 79 (4) beats/min, p < 0.05). Adrenomedullin decreased plasma aldosterone (9.8 (2.5) to 7.1 (1.5) ng/dl, p < 0.05) without significant changes in plasma renin activity. Plasma atrial and brain natriuretic peptides tended to decrease with adrenomedullin, although these changes did not reach significance. The haemodynamic and hormonal variables remained unchanged during placebo infusion.

CONCLUSIONS

Intravenous adrenomedullin has beneficial haemodynamic and hormonal effects in patients with precapillary pulmonary hypertension.

Enhancement of the cAMP-induced apolipoprotein-mediated cellular lipid release by calmodulin inhibitors W7 and W5 from RAW 264 mouse macrophage cell line cells

Apolipoprotein (apo) A-I generates high-density lipoprotein (HDL) by removing cellular cholesterol and phospholipid on the interaction with cells as a main source of plasma HDL. The reaction is induced by dibutylyl cyclic (dbc) adenosine monophosphate (AMP) in RAW 264, mouse macrophage cell line cells, and we investigated its pharmacologic modulation using this cell model. Release of cellular cholesterol and choline phospholipid by apoA-I was increased 9.9 and 4.2 times, respectively, by pretreatment of the cells with 300 microM dbcAMP for 24 h. Calmodulin inhibitors, W7 (N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide) and W5 (N(6-aminohexyl)-1-naphthalenesulfonamide), increased the apoA-I-mediated lipid release by 3 times from the dbcAMP-treated cells. The optimal drug concentrations (80 and 160 microM for W7 and W5, respectively) were not parallel with those reported for in vitro calmodulin inhibition (IC50, 28 and 240 microM for W7 and W5, respectively, toward phosphodiesterase activity), and in fact 40 microM W7 showed much stronger intracellular calmodulin inhibition than did 300 microM W5 using S7AAS2, a fluorescent peptide probe. Other calmodulin inhibitors such as amitriptyline, chlorpromazine, and trifluoperazine showed no effect on the apoA-I-mediated cholesterol release. In contrast to these results, neither dbcAMP nor W7 influenced the diffusion-mediated nonspecific cholesterol efflux to lipid microemulsion. We concluded that W7 and W5 increased the interaction of apoA-I with RAW 264 cells to generate more HDL. The effect did not seem directly correlated to their cal modulin inhibition or modulation of cAMP and protein kinase C.

Multiple signal transduction pathways through two prostaglandin E receptor EP3 subtype isoforms expressed in human uterus

PGE2 is known to induce uterine contraction by increasing intracellular Ca2+. In the present study, to investigate other functions of PGE2 in human uterus, two EP3 isoforms were isolated by the RT-PCR method using human uterus polyadenylated ribonucleic acid (RNA). These EP3 isoforms, named EP3-V and EP3-VI, are composed of 402 and 393 amino acid residues, respectively, which are unique compared with EP3 isoforms of other species. Their N-terminal 359 amino acid residues are identical to those of previously reported human EP3 isoforms, whereas the two isoforms contained a novel amino acid sequence in their C-terminal tails. The dissociation constant values of EP3-V and EP3-VI for PGE2 were 3.9 and 1.4 nmol/L, respectively, which were consistent with those of previously reported EP3 isoforms. Signaling experiments revealed that M&B28767, an EP3 agonist, not only inhibited forskolin-induced cAMP concentrations, but also activated mitogen-activated protein kinase in Chinese hamster ovary cells stably expressing EP3-V and EP3-VI. These responses were abolished by treatment with pertussis toxin. In addition, M&B28767 increased cAMP concentrations in EP3-VI-expressing cells, whereas it did not in EP3-V-expressing cells. M&B28767 did not stimulate phosphoinositide turnover in EP3-V or EP3-VI-expressing cells. EP3-V and EP3-VI messenger RNAs (mRNAs) were detected abundantly in human uterus, whereas weak, but substantial, bands were detected in the lung and kidney in RT-PCR specific for each mRNA. In situ hybridization revealed EP3-V and EP3-VI mRNAs in the human myometrium, but not in the endometrium. The present study suggests that EP3-V and EP3-VI are possibly involved in the proliferation of cells in human myometrium.

Inward current responses to urinary substances in rat vomeronasal sensory neurons

No study has yet demonstrated an inward current in response to pheromonal substances in vomeronasal sensory neurons. Using female rat vomeronasal sensory neurons, we here successfully recorded inward currents in response to urine from various sources. Of the neurons that responded to urine, 77% responded to only one type of urine. Male Wistar urine induced responses preferentially in the apical layer of the sensory epithelium, whilst male Donryu and female Wistar urine induced responses mainly in the basal layer of the epithelium. The amplitude of inward currents induced by application of male Wistar urine was voltage-dependent with average amplitude of -47.1+/-6.2 pA at -74 mV. The average reversal potential for male Wistar urine was -9.3 +/-6.1 mV, which was not apparently different from the reversal potentials for urine from different species. It is likely that the urine-induced inward currents in response to different types of urine are mediated via a similar channel. The simultaneous removal of Na+ and Ca2+ from extracellular solution eliminated the response. The magnitude of the urine-induced inward current in Cl--free external solution was similar to that in normal solution, suggesting that the urine-induced current is cation selective. Removal of external Ca2+ enhanced the amplitude of the urine-induced current and prolonged the response. Application of the constant-field equation indicated a very high permeability coefficient for Ca2+. This study first demonstrated that substances contained in urine elicited inward currents, which induce an excitatory response in vomeronasal sensory neurons, through cation-selective channels.

Hemodynamic, renal, and hormonal effects of adrenomedullin infusion in patients with congestive heart failure

BACKGROUND

Experimental studies have shown that adrenomedullin (AM) causes vasodilatation, diuresis, and a positive inotropic effect. In humans, however, whether infusion of AM has beneficial effects in congestive heart failure (CHF) remains unknown.

METHODS AND RESULTS

Hemodynamic, renal, and hormonal responses to intravenous infusion of human AM (0.05 microg. kg(-1). min(-1)) were examined in 7 patients with CHF and 7 normal healthy subjects (NL). In NL group, AM significantly decreased mean arterial pressure (-16 mm Hg, P<0. 05) and increased heart rate (+12 bpm, P<0.05). In CHF group, AM also decreased mean arterial pressure (-8 mm Hg, P<0.05) and increased heart rate (+5 bpm, P<0.05), but to a much lesser degree (P<0.05 versus NL). AM markedly increased cardiac index (CHF, +49%; NL, +39%, P<0.05) while decreasing pulmonary capillary wedge pressure (CHF, -4 mm Hg; NL, -2 mm Hg, P<0.05). AM significantly decreased mean pulmonary arterial pressure only in CHF (-4 mm Hg, P<0.05). AM increased urine volume (CHF, +48%; NL, +62%, P<0.05) and urinary sodium excretion (CHF, +42%; NL, +75%, P<0.05). Only in CHF, plasma aldosterone significantly decreased during (-28%, P<0.05) and after (-36%, P<0.05) AM infusion. These parameters remained unchanged in 7 patients with CHF and 6 healthy subjects who received placebo.

CONCLUSIONS

Intravenous infusion of AM has beneficial hemodynamic and renal effects in patients with CHF.

Nifedipine-induced coronary vasodilation in ischemic hearts is attributable to bradykinin- and NO-dependent mechanisms in dogs

BACKGROUND

Dihydropyridine calcium channel blockers protect endothelial cells against ischemia and reperfusion injury, suggesting that nifedipine may increase the in vivo cardiac NO level and thus coronary blood flow (CBF) in ischemic hearts. We tested this hypothesis.

METHODS AND RESULTS

In open-chest dogs, coronary perfusion pressure (CPP) was reduced in the left anterior descending coronary artery so that CBF decreased to one third of the control level, and thereafter CPP was maintained constant (103+/-8 to 43+/-3 mm Hg, n=9). We obtained fractional shortening (FS) and lactate extraction ratio (LER) as indices of regional myocardial contraction and metabolism. Both FS (26.4+/-2.1% to 6.7+/-2.0%, n=9, P<0.001) and LER (32+/-6% to -37+/-5%, n=9, P<0.001) showed a decrease when CPP was reduced. After intracoronary infusion of nifedipine (4 microgram. kg(-1). min(-1)), CBF increased from 30+/-1 to 48+/-4 mL. 100 g(-1). min(-1) (P<0.01) without a change of CPP (n=9). Both FS (14.0+/-1.9%, n=9) and LER (-9+/-7%, n=9) also increased (P<0.01). Nifedipine increased the difference in the level of metabolites of NO (nitrate+nitrite; 9+/-3 to 25+/-5 nmol/mL, n=9, P<0.01) and bradykinin (22+/-5 to 58+/-4 pmol/mL, n=9, P<0.01) between coronary venous and arterial blood. L-NAME (an NO synthase inhibitor) or HOE-140 (a bradykinin receptor antagonist) attenuated (P<0.05) the increase in CBF (29+/-3 and 35+/-2 mL. 100 g(-1). min(-1), n=5 each), FS (4.8+/-0.6% and 6.9+/-1.7%, n=5 each), LER (-47+/-8% and -35+/-9%, n=5 each), and nitrate+nitrite (3+/-2 and 8+/-4 nmol/mL, n=5 each) due to nifedipine infusion.

CONCLUSIONS

These results indicate that the calcium channel blocker nifedipine mediates coronary vasodilation and improves myocardial ischemia through both bradykinin/NO-dependent and -independent mechanisms.

Transforming growth factor-beta1 inhibits the growth of primary adult rat hepatocyte cultures by increasing cAMP levels

We investigated the mechanisms of transforming growth factor-beta1 (TGF-beta1) inhibition on transforming growth factor-alpha (TGF-alpha)-induced DNA synthesis and proliferation in primary cultures of adult rat hepatocytes. TGF-alpha (1.0 ng/ml) produced a 4.2-fold elevation of DNA synthesis during 3 h of culture and a 1. 2-fold increase in nucleus number (proliferation) during 4 h of culture. TGF-beta1 dose dependently inhibited the TGF-alpha-induced hepatocyte DNA synthesis and proliferation: half-maximal inhibition occurred at a TGF-beta1 concentration of 0.08 ng/ml. The inhibitory effects of 1.0 ng/ml TGF-beta1 were almost completely reversed by adenylate cyclase inhibitors, 2,4-dideoxyadenosine (10(-6) M), and somatostatin (3 x 10(-7) M), or by a specific inhibitor of protein kinase A, H-89 (N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride; 10(-7) M). In addition, while TGF-alpha did not affect the basal cellular adenosine 3',5'-monophosphate (cAMP) levels, TGF-beta1 was found to produce dose-dependent increases in cellular cAMP levels. The cAMP-elevating effects of TGF-beta1 were also reversed by 2,4-dideoxyadenosine (10(-6) M), and somatostatin (3 x 10(-7) M), but not by H-89 (10(-7) M). The present results suggest that the specific mechanisms involved in the growth inhibitory effect of TGF-beta1 on TGF-alpha-induced hepatocyte DNA synthesis and proliferation are via stimulation of adenylate cyclase, which increases intracellular cAMP and subsequently activates protein kinase A.

Cilostazol, a cyclic AMP phosphodiesterase inhibitor, stimulates nitric oxide production and sodium potassium adenosine triphosphatase activity in SH-SY5Y human neuroblastoma cells

Deficiencies in cellular cyclic AMP (cAMP) and nitric oxide (NO) production are thought to be involved in the pathogenesis of diabetic neuropathy. We used a human neuroblastoma cell line, SH-SY5Y, to investigate the effect of cilostazol, a specific cAMP phosphodiesterase inhibitor, on NO production and Na+, K+-ATPase activity. SH-SY5Y cells were cultured under 5 or 50 mM glucose for 5-6 days, the cells were then exposed to cilostazol or other chemicals and nitrite, cAMP and Na+, K+-ATPase activity were measured. In cells grown in 50 mM glucose, cilostazol was observed to increase significantly both NO production and cellular cAMP accumulation in a time- and dose-dependent manner. Cilostazol also significantly recovered reduced levels of protein kinase A activity (PKA) in 50 mM glucose. Furthermore, a PKA inhibitor, H-89 significantly suppressed the increase in NO production stimulated by cilostazol, suggesting that cilostazol stimulates NO production by activating PKA. Cilostazol did not affect either sorbitol or myo-inositol concentrations. Dexamethasone, which is known to induce inducible NO synthase, had no effect on NO production stimulated by cilostazol, suggesting that cilostazol stimulates NO production catalyzed by neuronal constitutive NO synthase (ncNOS) in SH-SY5Y cells. L-arginine, which is an NO agonist enhanced Na+, K+-ATPase activity in cells grown in 50 mM glucose, NG-nitro-L-arginine methyl ester (L-NAME), which is an NOS inhibitor inhibited basal Na+, K+-ATPase activity in 5 mM glucose and suppressed the increased enzyme activity induced by cilostazol in 50 mM glucose. The above results confirmed our previous observation that NO regulates Na+, K+-ATPase activity in SH-SY5Y cells and suggest that cilostazol increases Na+, K+-ATPase activity, at least in part, by stimulating NO production. The present results also suggest that cilostazol has a beneficial effect on diabetic neuropathy by improving Na+, K+-ATPase activity via directly increasing cAMP and NO production in nerves.

Reduced nitric oxide production by L-arginine deficiency in lysinuric protein intolerance exacerbates intravascular coagulation

Lysinuric protein intolerance (LPI) results in low serum L-arginine, hyperammonemia, mental retardation, thrombocytopenia, and an increased frequency of bowel movements. Our objective was to evaluate the effects of low serum L-arginine, the essential substrate for reactions catalyzed by nitric oxide synthetase (NOS), on the serum nitric oxide (NO) level and coagulation activity in a patient with LPI. A 37-year-old Japanese man who presented with abdominal pain and subnormal fasting levels of serum L-arginine and L-lysine was found to have LPI. The result of oral administration of diamino acids was an increased in urine and a decrease in serum, thus confirming the diagnosis. A decrease in the platelet count and an increase in the plasma levels of thrombin-antithrombin III complex (TAT) and fibrin degradation products (FDPs) indicated the presence of subclinical intravascular coagulation. Serum levels of NO derivatives and L-arginine were determined after intravenous administration of L-arginine. The effects of intravenous L-arginine or transdermal nitroglycerin on the plasma level of TAT were also investigated. Serum levels of NO derivatives were significantly reduced in the LPI patient versus the healthy control group (n = 5). Intravenous administration of L-arginine increased the serum level of NO derivatives and the platelet count and reduced plasma TAT and FDP levels. The plasma level of TAT was also reduced by transdermal nitroglycerin. A decrease in the serum level of L-arginine in patients with LPI appears to result in a decrease in NO production. The improvement in plasma TAT levels produced by administration of intravenous L-arginine or transdermal nitroglycerin suggests that intravascular coagulation is exacerbated by the decrease of NO production in patients with LPI.

Enhancement by adenosine of insulin-induced activation of phosphoinositide 3-kinase and protein kinase B in rat adipocytes

The role of adenosine receptor in regulation of insulin-induced activation of phosphoinositide 3-kinase (PI 3-kinase) and protein kinase B was studied in isolated rat adipocytes. Rat adipocytes are known to spontaneously release adenosine, which in turn binds and stimulates the adenosine A1 receptors on the cells. In the present study, we observed that degradation of this adenosine by adenosine deaminase attenuated markedly the insulin-induced accumulation of phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3), a product of PI 3-kinase. p-Aminophenylacetyl xanthine amine congener (PAPA-XAC), an inhibitor of the adenosine A1 receptor, also inhibited the insulin-induced PtdIns(3,4,5)P3 accumulation. When extracellular adenosine was inactivated by adenosine deaminase, phenylisopropyladenosine, an adenosine A1 receptor agonist, potentiated the insulin-induced accumulation of PtdIns(3,4,5)P3. Insulin-induced activation of protein kinase B, the activity of which is controlled by the lipid products of PI 3-kinase, was also potentiated by adenosine. Prostaglandin E2, another activator of a pertussis toxin-sensitive GTP-binding protein in these cells, potentiated the insulin actions. Thus, the receptors coupling to the GTP-binding protein were found to positively regulate the production of PtdIns(3,4,5)P3, a putative second messenger for insulin actions, in physiological target cells of insulin.

Laminar distribution of pheromone-receptive neurons in rat vomeronasal epithelium

1. Responses of vomeronasal sensory neurons to urine excreted from rats, mice and hamsters were studied by the on-cell patch clamp method in slices of sensory epithelium from female Wistar rats. 2. The urine excreted from male and female Wistar rats, male Donryu rats and male C57BL/6 mice induced relatively large responses, while urine from male Sprague-Dawley rats and male Syrian hamsters induced small responses. 3. Of the 62 neurons responding to urine, 57 responded to only one of the urine preparations. 4. The sensory neurons that responded to the male Wistar urine were localized in the apical position of the epithelium where one type of GTP-binding protein, Gi2alpha, is selectively expressed. The neurons in the basal position of the epithelium, which express Goalpha, responded to urine from the other animals. 5. This study demonstrates that sensory neurons responsive to different urinary pheromones are localized in a segregated layer in the rat vomeronasal sensory epithelium.

The effect of papaverine on morphologic differentiation, proliferation and invasive potential of human prostatic cancer LNCaP cells

BACKGROUND

Intracellular cyclic adenosine monophosphate (AMP) level changes are thought to play an important role in inhibiting cell proliferation and inducing differentiation in several types of cells. It has been reported that cyclic AMP analogs induce terminal differentiation in human prostate cancer cells. Consequently, phosphodiesterase inhibitors may be useful in delineating the role of cyclic AMP in the differentiation of these cells. Therefore, the effect of phosphodiesterase inhibitors on morphologic differentiation, proliferation and invasive potential of human prostate cancer cells was investigated.

METHODS

Three human prostate cancer cell lines PC-3, DU145 and LNCaP were treated with one of the phosphodiesterase inhibitors, papaverine, 3-isobutyl-1-methylxanthine (IBMX) or theophylline, for 6 days. Morphologic changes of these cells induced by phosphodiesterase inhibitors were observed by microscopy. Intracellular cyclic AMP levels in LNCaP cells were measured by radioimmunoassay using a cyclic AMP assay kit. The effect of papaverine on the proliferation and invasive potential of LNCaP cells were measured by cell counting and the Matrigel invasion chamber assay.

RESULTS

Of the three agents, examined papaverine (10(-5) mol/L) is the most effective inducer of morphologic change and also raised intracellular cyclic AMP levels in LNCaP cells. However, unlike LNCaP cells, PC-3 and DU145 cells treated with phosphodiesterase inhibitors, including papaverine, showed little change in morphology. Additionally, proliferation and invasive potential of LNCaP cells were significantly inhibited by papaverine.

CONCLUSION

The results suggest that papaverine induces terminal differentiation in LNCaP cells, which is correlated with an intracellular cyclic AMP-mediated pathway.

Pharmacological comparison between the nitrergic responses produced by intramural nerve stimulation and exogenous NO-donors in rat gastric fundus

To investigate whether the nitrergic nerve-mediated smooth muscle relaxation is caused by authentic nitric oxide (NO) and is mediated via guanosine 3':5'-cyclic monophosphate (cyclic GMP), we compared the response to electrical field stimulation of nitrergic nerve (EFS) with other NO-related responses in rat gastric fundus strips. EFS, sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), and acidified NaNO2 and inducible NO synthase (iNOS)-mediated NO all produced relaxation and elevated cyclic GMP level in rat fundus strips. However, the basal and stimulated cyclic GMP levels were significantly lower than the basal level in aorta (40+/-4 pmol/g wet tissue). Methylene blue and 6-anilino-5,8-quinolinedione (LY83583), both known as soluble guanylyl cyclase inhibitors and O2- generators that scavenge NO, reduced the elevation of cyclic GMP level by all stimuli and inhibited the relaxations only in response to NaNO2 and iNOS-mediated NO but not to the other stimuli. These results suggest that in the rat gastric fundus strips the relaxations induced by not only nitrergic nerve but also SNP and SNAP are not associated with cyclic GMP production, in contrast to the relaxations mediated by authentic NO.

Long-term vascular effects of Nomega-nitro-L-arginine methyl ester are not soley mediated by inhibition of endothelial nitric oxide synthesis in the rat mesenteric artery

Nomega-nitro-L-arginine methyl ester (L-NAME), one of the synthetic L-arginine analogues with inhibitory effects of nitric oxide (NO) synthesis, is now widely used to examine the role of NO in various organs. We and others demonstrated that long-term treatment with L-NAME causes hypertension and cardiovascular lesions (perivascular fibrosis and medial thickening), especially at microvascular levels. However, convincing evidence is still lacking that these long-term cardiovascular effects of L-NAME are solely mediated by the inhibition of the synthesis of endothelium-derived NO (EDNO). This study was thus designed to better understand the effects of long-term treatment with L-NAME with special reference to EDNO synthesis. Male Wister-Kyoto rats were orally administered L-NAME for 8 weeks. Blood pressure significantly increased at 3 days and 1 and 8 weeks of the treatment. Endothelium-dependent relaxations to acetylcholine (ACh) of the aorta were reduced 3 days after the treatment, recovered at 1 week, and again reduced at 8 weeks, whereas the relaxations of the small mesenteric artery were unaltered throughout the experimental periods. At 8 weeks, indomethacin-sensitive, endothelium-dependent contractions to ACh were noted. The relative contributions of NO and endothelium-derived hyperpolarizing factor also were unchanged. Citrulline assay demonstrated that substantial levels of constitutive NO synthase activity remained in the aorta during the experiments. The long-term treatment with L-NAME caused perivascular fibrosis and medial thickening, not only in the aorta but also in the mesenteric artery. These results suggest that mechanism(s) other than simple inhibition of EDNO synthesis is involved in the long-term cardiovascular effects of L-NAME in the rat mesenteric artery.

Inositol-1,4,5-trisphosphate accumulation induced by urinary pheromones in female rat vomeronasal epithelium

The mechanisms involved in pheromone-induced responses in the vomeronasal neurons, especially in mammals, are still unclear. In the present study, we examined the effects of rat urine samples containing various types of pheromones regulating gonadal functions on the accumulation of cAMP and inositol 1,4,5-trisphosphate (IP3) in a vomeronasal membrane preparation from the female Wistar rat. Stimulation of the preparation with forskolin induced cAMP accumulation, but stimulation with urine samples excreted from the male Wistar rat, the female Wistar rat, and the male Donryu rat did not change cAMP levels. These results were consistent with the electrophysiological results showing that dialysis of a high concentration of cAMP into the vomeronasal neuron does not induce currents. Stimulation with the three urine samples induced the accumulation of IP3 in the membrane preparation. These results are consistent with previous electrophysiological results [K. Inamura, M. Kashiwayanagi, K. Kurihara, Inositol-1,4,5-trisphosphate induces responses in receptor neurons in rat vomeronasal sensory slices, Chem. Senses 22 (1997) 93-103; K. Inamura, M. Kashiwayanagi, K. Kurihara, Blockage of urinary responses by inhibitors for IP3-mediated pathway in rat vomeronasal sensory neurons, Neurosci. Lett. 233 (1997) 129-132]. After the treatment with Pertussis toxin (PTX), the male Wistar urine did not induce IP3 accumulation significantly. Application of the male Wistar urine decreased ADP-ribosylation of Gi with PTX, while that of the male Donryu urine decreased ADP-ribosylation of Go. Thus, the present results support a mechanism by which the responses of the rat vomeronasal neurons to urinary pheromones are mediated by IP3, Gi and/or Go.

Cardioprotective effect of angiotensin-converting enzyme inhibition against hypoxia/reoxygenation injury in cultured rat cardiac myocytes

BACKGROUND

Although ACE inhibitors can protect myocardium against ischemia/reperfusion injury, the mechanisms of this effect have not yet been characterized at the cellular level. The present study was designed to examine whether an ACE inhibitor, cilazaprilat, directly protects cardiac myocytes against hypoxia/reoxygenation (H/R) injury.

METHODS AND RESULTS

Neonatal rat cardiac myocytes in primary culture were exposed to hypoxia for 5.5 hours and subsequently reoxygenated for 1 hour. Myocyte injury was determined by the release of creatine kinase (CK). Both cilazaprilat and bradykinin significantly inhibited CK release after H/R in a dose-dependent fashion and preserved myocyte ATP content during H/R, whereas CV-11974, an angiotensin II receptor antagonist, and angiotensin II did not. The protective effect of cilazaprilat was significantly inhibited by Hoe 140 (a bradykinin B2 receptor antagonist), NG-monomethyl-L-arginine monoacetate (L-NMMA) (an NO synthase inhibitor), and methylene blue (a soluble guanylate cyclase inhibitor) but not by staurosporine (a protein kinase C inhibitor), aminoguanidine (an inhibitor of inducible NO synthase), or indomethacin (a cyclooxygenase inhibitor). Cilazaprilat significantly enhanced bradykinin production in the culture media of myocytes after 5.5 hours of hypoxia but not in that of nonmyocytes. In addition, cilazaprilat markedly enhanced the cGMP content in myocytes during hypoxia, and this augmentation in cGMP could be blunted by L-NMMA and methylene blue but not by aminoguanidine.

CONCLUSIONS

The present study demonstrates that cilazaprilat can directly protect myocytes against H/R injury, primarily as a result of an accumulation of bradykinin and the attendant production of NO induced by constitutive NO synthase in hypoxic myocytes in an autocrine/paracrine fashion. NO modulates guanylate cyclase and cGMP synthesis in myocytes, which may contribute to the preservation of energy metabolism and cardioprotection against H/R injury.

Exogenous nitric oxide inhibits platelet activation in whole blood

We examined the effect of NO on collagen-induced whole blood aggregation and platelet activation in whole blood by using impedance aggregometry and flow cytometry. For the extracellular generation of NO, we chose sodium nitroprusside dihydrate (SNP), and as intracellular generators of NO, L-arginine and isosorbide dinitrate (ISDN). The latter two significantly inhibited whole blood aggregation, whereas SNP had no such effect. The inhibitory effect of ISDN was diminished by addition of methylene blue (MB) or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl 3-oxide (carboxyl-PTIO), and the inhibitory effect of L-arginine was diminished by addition of N(G)-monomethyl-L-arginine monoacetate (L-NMMA). Although the addition of ISDN increased the cyclic guanosine monophosphate (cGMP) level in whole blood and in the suspension of platelets and white blood cells (PLTs + WBCs), no increase was found in platelet-rich plasma (PRP). The P-selectin expression on the platelet surface in whole blood was reduced by ISDN and L-arginine. These findings suggest that the intracellular generation of NO inhibits whole blood aggregation, and this mechanism may play an important role in its antithrombotic effect in whole blood.

A Ca channel blocker, benidipine, increases coronary blood flow and attenuates the severity of myocardial ischemia via NO-dependent mechanisms in dogs

OBJECTIVES

This study was undertaken to examine whether a dihydropyridine Ca channel blocker, benidipine, increases cardiac NO levels, and thus coronary blood flow (CBF) in ischemic hearts.

BACKGROUND

Benidipine protects endothelial cells against ischemia and reperfusion injury in hearts.

METHODS AND RESULTS

In open chest dogs, coronary perfusion pressure (CPP) of the left anterior descending coronary artery was reduced so that CBF decreased to one-third of the control CBF, and thereafter CPP was maintained constant (103+/-8 to 42+/-1 mmHg). Both fractional shortening (FS: 6.1+/-1.0%) and lactate extraction ratio (LER: -41+/-4%) decreased. Ten minutes after the onset of an intracoronary infusion of benidipine (100 ng/kg/min), CBF increased from 32+/-1 to 48+/-4 ml/100g/ min during 20 min without changing CPP (42+/-2 mmHg). Both FS (10.7+/-1.2%) and LER (-16+/-4%) also increased. Benidipine increased cardiac NO levels (11+/-2 to 17+/-3 nmol/ml). The increases in CBF, FS, LER and cardiac NO levels due to benidipine were blunted by L-NAME. Benidipine increased cyclic GMP contents of the coronary artery of ischemic myocardium (139+/-13 to 208+/-15 fmol/mg protein), which was blunted by L-NAME.

CONCLUSION

Thus, we conclude that benidipine mediates coronary vasodilation and improves myocardial ischemia through NO-cyclic GMP-dependent mechanisms.

Cardiovascular and renal effects of adrenomedullin in rats with heart failure

Plasma adrenomedullin (AM), a novel hypotensive peptide, has been shown to increase in heart failure (HF). This study sought to examine the cardiovascular and renal effects of intravenous infusion of AM in HF rats and sham-operated rats (control) using two doses of AM that would not induce hypotension. Rat AM-(1-50) was intravenously administered at rates of 0.01 (low) and 0.05 (high) microg. kg body wt-1. min-1. Low-dose AM increased urine flow (+21% in HF, +29% in control) and urinary sodium excretion (+109% in HF, +123% in control) without changes in any hemodynamic variables. In contrast, high-dose AM slightly decreased mean arterial pressure (-3% in HF, -5% in control) and significantly increased cardiac output (+20% in HF, +12% in control). Infusion of high-dose AM resulted in significant decreases in right ventricular systolic pressure (-11%) and right atrial pressure (-28%) only in HF rats. High-dose AM significantly increased glomerular filtration rate (+10% in HF, +16% in control) and effective renal plasma flow (+25% in HF, +46% in control) as well as urine flow and urinary sodium excretion. In summary, intravenous infusion of AM exerted diuresis and natriuresis without inducing hypotension and, in the higher dose, produced beneficial hemodynamic and renal vasodilator effects in rats with compensated HF.

Randomized, double-blind, placebo-controlled study of carvedilol on the prevention of nitrate tolerance in patients with chronic heart failure

OBJECTIVES

This study was designed to evaluate the effect of carvedilol on nitrate tolerance in patients with chronic heart failure.

BACKGROUND

The attenuation of cyclic guanosine 5'-monophosphate (cGMP) production due to inactivation of guanylate cyclase by increased superoxide has been reported as a mechanism of nitrate tolerance. Carvedilol has been known to combine alpha/beta-blockade with antioxidant properties.

METHODS

To evaluate the effect of carvedilol on nitrate tolerance, 40 patients with chronic heart failure were randomized to four groups that received either carvedilol (2.5 mg once a day [carvedilol group, n=10]), metoprolol (30 mg once a day [metoprolol group, n=10]), doxazosin (0.5 mg once a day [doxazosin group, n=10]) or placebo (placebo group, n=10). Vasodilatory response to nitroglycerin (NTG) was assessed with forearm plethysmography by measuring the change in forearm blood flow (FBF) before and 5 min after sublingual administration of 0.3 mg NTG, and at the same time blood samples were taken from veins on the opposite side to measure platelet cGMP. Plethysmography and blood sampling were obtained serially at baseline (day 0); 3 days after carvedilol, metoprolol, doxazosin or placebo administration (day 3); and 3 days after application of a 10-mg/24-h NTG tape concomitantly with carvedilol, metoprolol, doxazosin or placebo (day 6).

RESULTS

There was no significant difference in the response of FBF (%FBF) and cGMP (%cGMP) to sublingual NTG on day 0 and day 3 among the four groups. On day 6, %FBF and %cGMP were significantly lower in the metoprolol, doxazosin and placebo groups than on day 0 and day 3, but these parameters in the carvedilol group were maintained.

CONCLUSIONS

These results indicated that carvedilol may prevent nitrate tolerance in patients with chronic heart failure during continuous therapy with NTG.