Effects of lifestyle changes and metformin on salt sensitivity and nitric oxide metabolism in obese salt-sensitive Hispanics.

Salt sensitivity is associated with obesity, and increased cardiovascular morbidity and mortality. We investigated whether treatment of obesity and its associated metabolic abnormalities corrects salt sensitivity and restores impaired nitric oxide (NO) metabolism characteristic of salt sensitivity. Twenty, otherwise, healthy obese salt-sensitive subjects completed a 12-month program of caloric restriction, aerobic exercise and metformin. Two salt sensitivity tests were performed, that is at baseline and end of program. Lifestyle-metformin treatment decreased weight (9.8+/-0.3 kg), body mass index (3.9+/-0.2 kg/m(2)), waist (11.5+/-0.5 cm), systolic blood pressure (SBP) (8.6+/-0.4 mm Hg), diastolic blood pressure (DBP) (5.5+/-0.4 mm Hg), triglyceride (40+/-5 mg/dl), fasting (8.3+/-1 microIU/ml) and post-load (20+/-4 microIU/ml) insulin levels, and salt sensitivity. Going from a high-sodium ( approximately 300 mmol) to a low-sodium diet ( approximately 30 mmol of sodium/day) lowered SBP/DBP by 14.7+/-1.7/7.4+/-0.9 mm Hg at baseline and by 8.6+/-1.9/3.2+/-1.2 mm Hg after treatment (P<0.001). More importantly, blood pressure (BP) sensitivity to customary levels of dietary salt ( approximately 150 mmol of sodium/day) was abolished by the lifestyle-metformin treatment. Differences in SBP/DBP between usual and low salt averaged 11+/-1/8+/-1 mm Hg before treatment, and 3+/-1/1+/-0.5 mm Hg after treatment (P<0.001). At baseline, NO-metabolite excretion was inhibited during high salt; this impairment was corrected by the lifestyle-metformin treatment. In conclusion, acquired correctable factors play an important role in the pathogenesis of salt sensitivity associated with obesity. Correction of salt sensitivity may account for the BP lowering induced by weight reduction. Restoration of the inability to increase or sustain NO production in response to high salt could account for the correction of salt sensitivity induced by the lifestyle-metformin treatment.

Heterogeneous effect of leucotriene CysLT1 receptor antagonists on antigen-induced motor and inflammatory responses in guinea-pig airways.

1. The effect of montelukast or MEN91507, selective leucotriene CysLT1 receptor antagonists, on antigen-induced airway inflammation and bronchoconstriction were compared in anaesthetized guinea-pigs. 2. In sensitized animals, ovalbumin (0.3 mg kg(-1), i.v.)-induced microvascular leakage in trachea, intrapulmonary airways, total lung (parenchyma and intrapulmonary airways) and urinary bladder was reduced by MEN91507 (0.01-1 micromol kg(-1), i.v.), whereas montelukast (0.01-1 micromol kg(-1), i.v.) antagonized the effect of the antigen only in the lung and urinary bladder. 3. Ovalbumin (1 mg kg(-1), i.v.)-induced bronchoconstriction was dose dependently antagonized by MEN91507 (10-30 micromol kg(-1), i.v.), whereas the effect of montelukast (0.1-30 micromol kg(-1), i.v.) was marginal (15-30% inhibition). Neither MEN91507 nor montelukast (30 micromol kg(-1), i.v.) affected the bronchoconstrictor response induced by acetylcholine (0.3 micromol kg(-1), i.v.) in sensitized animals. 4. It is concluded that montelukast and MEN91507 display a differential activity against the effect of endogenous leucotrienes, despite the fact that both compounds show a similar antagonist profile against exogenous leucotrienes acting through CysLT1 receptors.

NAD(P)H oxidase p22phox gene C242T polymorphism, nitric oxide production, salt sensitivity and cardiovascular risk factors in Hispanics.

Mutations in the NAD(P)H oxidase gene may be associated with abnormal superoxide generation, nitric oxide (NO) availability and cardiovascular diseases. We investigated the prevalence of the NAD(P)H oxidase p22phox gene C242T polymorphism, and its possible association with blood pressure, NO production, salt sensitivity and cardiovascular risk factors in Hispanics. Genotype frequencies were as follows: CC, 52.9%; CT, 40.3%; and TT, 6.8%. There were no significant differences in systolic blood pressure, diastolic blood pressure, age, weight, fasting and post-load glucose levels, LDL and HDL cholesterol, triglyceride and urinary albumin levels in subjects with CC, CT or the TT genotypes. Presence of the T allele was associated with increased salt sensitivity in women, but not in men. NO metabolite excretion was markedly decreased both in women and men with the TT genotype (CC: 868+/-79 micromol/day; CT: 839+/-75 micromol/day; TT: 534+/-78 micromol/day; P<0.05). In conclusion, the prevalence of the NAD(P)H oxidase p22phox gene C242T polymorphism in Venezuelans was comparable to that of Caucasians, but different from that of Chinese and Japanese. Although the T allele was not associated with cardiovascular risk factors, hyperinsulinaemia or hypertension, in women, it appeared to be a genetic susceptibility factor for salt sensitivity. Both in women and men, the p22phox gene may play a role in the genetic control of NO levels.

Endothelial nitric oxide synthase polymorphism, nitric oxide production, salt sensitivity and cardiovascular risk factors in Hispanics.

Mutations in the endothelial nitric oxide synthase (eNOS) gene may be associated with abnormal nitric oxide (NO) production and cardiovascular diseases. In this study, we investigated the prevalence of two eNOS polymorphisms, the Glu298Asp variant on exon 7, and the 4a/b variable number of tandem repeats (VNTR) on intron 4, and their association with blood pressure (BP), NO production, salt sensitivity and cardiovascular risk factors in healthy Venezuelans. The prevalence of both polymorphisms in Venezuelans was comparable to that described for Caucasians, but significantly different from that known for African-Americans and Japanese. The 4a/b genotype was associated with reduced levels of NO metabolites (25% decrease), larger BP lowering in response to salt restriction (9.0 vs 4.8 mmHg, P<0.05), greater prevalence of salt sensitivity (39% in 4a/b and 27% in 4b/b; P<0.05) and with higher LDL-cholesterol levels. The Glu298T polymorphism did not affect NO production, nor it was associated with salt sensitivity. Glu298Asp polymorphism was positively associated with higher weight, triglycerides and LDL-cholesterol. Neither polymorphism was associated with changes in fasting or postload serum glucose, BP, obesity and albuminuria. In conclusion, the prevalence of eNOS polymorphisms is strongly determined by ethnic factors. The 4a/b gene polymorphism could be a genetic susceptibility factor for the BP response to salt intake and for the genetic control of NO production. The reduced NO production in subjects with the 4a/b genotype may be responsible for the increased sensitivity of their BP to salt.

Nitric oxide and salt sensitivity.

Studies in laboratory animals suggest that altered nitric oxide (NO) production may be associated with salt sensitivity. In this investigation we determined whether the endogenous NO production was altered in salt-sensitive human subjects when salt intake was changed. Salt sensitivity was assessed from the magnitude of the blood pressure (BP) lowering obtained when the salt intake was reduced from high to a low intake. The combined urinary excretion of nitrites and nitrates, the major metabolites of NO, was employed as an index of endogenous NO production. Salt-sensitive subjects (n = 23) were older, heavier, and had greater waist-to-hip ratios and higher baseline BP than salt-resistant individuals (n = 25). In salt-sensitive subjects, mean blood pressure (MBP) decreased 11.8+/-0.7 mm Hg, and NO metabolite excretion increased from 823+/-102 to 1530+/-148 mmol/24 h, when salt intake was reduced from 316 to 28 micromol/day. NO metabolite excretion was 45% lower during high salt (0.66+/-0.1 micromol/mg creatinine) than during low salt intake (1.12+/-0.1 micromol/mg creatinine) (P < .001). In contrast, when salt intake was reduced, salt-resistant subjects exhibited no significant mean changes in BP or NO metabolite excretion. During low salt intake, NO metabolite excretion (micromol/ day) was significantly higher in salt-sensitive individuals. The magnitude of decrease of systolic blood pressure, diastolic blood pressure, or MBP induced by reducing salt intake was not related to the increase in urinary excretion of NO metabolite levels (r2 = 0.009; P = .66). In summary, to the extent that urinary NO metabolite levels reflect the activity of the endogenous NO system, our results support the view that salt sensitivity may in part be determined by an inability to increase or to sustain NO production in response to high salt. Insufficient NO production during high salt may in turn lead to altered pressure-natriuresis relationships and to an increase in BP. The possibility that the increase in BP induced by high salt intake in salt-sensitive individuals could be the key factor in reducing NO metabolite levels can not be ruled out.

Effects of inhibition of serotonin synthesis on 5-hydroxyindoleacetic acid excretion, in healthy subjects.

The urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin, reflects the content and turnover of gastrointestinal (GI) serotonin. Employing longitudinal measurements of 5-HIAA, the authors investigated in healthy subjects (n = 43) how manipulations of serotonin synthesis affect GI serotonin. Under conditions of serotonin-free diets, the intersubject and intrasubject variability (coefficient of variation) for 5-HIAA excretion averaged 33% and 14%, respectively. Dietary tryptophan restrictions to 50% of minimal daily requirements (which is equivalent to a 10-fold reduction in baseline tryptophan intake) decreased by half the urinary excretion of 5-HIAA, irrespective of the caloric content of diet. Restoration to the regular tryptophan intake produced a rapid normalization of the 5-HIAA excretion. Neutral amino acids are known to compete with the intestinal transport absorption mechanisms of tryptophan. Administration of neutral amino acids (1.8 g, by mouth, three times a day, before each meal) or of carbidopa (50 mg, by mouth, three times a day for 3 days) to a normal tryptophan diet failed to alter significantly the 5-HIAA excretion. Further, neutral amino acids failed to enhance the reduction in 5-HIAA produced by the low-tryptophan diet. The failure of these treatments to reduce 5-HIAA excretion could be due to large capacity transport and decarboxylation systems for tryptophan. Other possibilities are discussed. In summary, dietary tryptophan is essential for the maintenance of GI serotonin. Reductions or increases in dietary tryptophan are the easiest and most effective method to alter GI serotonin.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of NK1 receptors on cisplatin-induced nephrotoxicity in the rat.

The role of NK1 receptors on the nephrotoxicity associated with cisplatin treatment was evaluated. Adult Sprague-Dawley male rats (300-400 g) were treated with saline (0.1 ml/100 g, i.p., every 8 h for 72 h) or the selective NK1 receptor antagonist (GR205171; 2 mg/kg, i.p., every 8 h for 72 h). Treatments were started 5 min before cisplatin (7.5 mg/kg, i.p., single dose). All evaluations were made from 72 h to 96 h after cisplatin. An oral load of 10 ml/kg of water was given at time 0 (72 h after cisplatin). Cisplatin reduced the urinary volume (-45%), creatinine clearance (>90%), lithium clearance (-76%) and urinary potassium excretion (-54%). Protein and sodium excretion was not affected by cisplatin. GR205171 prevented the reduction in urine volume induced by cisplatin. In addition, the decreases in creatinine and lithium clearances induced by cisplatin were also attenuated by the NK1 receptor antagonist. The clearance of creatinine averaged 0.57+/-0.2 ml/min in controls, 0.004+/-0.01 ml/min after cisplatin, and 0.09+/-0.02 ml/min after cisplatin + GR205171. The lithium clearance was 0.09+/-0.04 ml/min in controls, 0.02+/-0.01 ml/min after cisplatin and 0.06+/-0.01 ml/min after cisplatin + GR205171. Cisplatin induced marked necrosis, vacuolation and edema of proximal renal tubules; these changes were considerably reduced in GR205171-treated animals. These results indicate that treatment with a selective NK1 receptor antagonist ameliorated cisplatin-induced renal toxicity in rats, as evidenced by improvements in renal function and histology.

Nitric oxide synthases and cyclophosphamide-induced cystitis in rats.

The role of inducible (iNOS) and neuronal nitric oxide (nNOS) synthases and of tachykinin NK1 receptors on the pathogenesis of cyclophosphamide (CYP)-induced cystitis was investigated, in rats. CYP-induced cystitis was characterized by large increases in bladder-protein plasma extravasation (PPE), increases in the urinary excretion of nitric oxide (NO) metabolites and histological evidences of urothelial damage, edema, extensive white blood cell infiltrates and vascular congestion of the bladder. The specific iNOS inhibitor, S-methylthiourea (MITU), produced marked inhibition (>90%) of CYP-induced increases in PPE associated with amelioration of tissue inflammatory changes. Treatment with 7-nitroindazole (7-NI; 20, 40 and 80 mg/kg), a selective nNOS inhibitor, did not significantly reduce CYP-induced increases in PPE and failed to produce histological improvement. In addition, treatment with MITU, but not with 7-NI, inhibited the increases in the urinary excretion of NO metabolites induced by CYP treatment. WIN 51,708 (17-beta-hydroxy-17-alpha-ethynyl-androstano[3,2-b]pyrimido[1,2-a]benzimidazole; WIN), a selective NK1-receptor antagonist, reduced the increases in EPP and ameliorated the inflammatory changes in the bladder induced by CYP. However, the maximal degree of protection achieved with WIN was significantly less than that produced by MITU. Combined treatment with the iNOS inhibitor and the NK1 antagonist produced no greater effect than that produced by the iNOS inhibitor alone. Our results suggest that NO plays a fundamental role in the production of the cystitis associated with CYP treatment. The iNOS, and not nNOS, seems responsible for the inflammatory changes. Part of the increases in NO may due to activation of NK1 receptors by neuropeptides such as substance P possibly released from primary afferent fibers.

Treatment with para-chlorophenylalanine antagonises the emetic response and the serotonin-releasing actions of cisplatin in cancer patients.

To test the role of serotonin in chemotherapy-induced nausea and emesis, ten cancer patients were pretreated with the serotonin synthesis inhibitor para-chlorophenylalanine (PCPA). PCPA (2 g 8 hourly for 2 or 3 days prior to cisplatin) reduced the spontaneous urinary excretion of 5-hydroxyindoleacetic acid (5-HIAA), inhibited the increase in urinary 5-HIAA induced by cisplatin and markedly attenuated the acute period of nausea and vomiting associated with the cytotoxic drug. These results indicate that gastrointestinal serotonin mediates cisplatin-induced emesis and that the amount of serotonin released by cisplatin is a major factor in determining the severity of the acute period of emesis experienced by the patient.

Effects of GR203040, an NK1 antagonist, on radiation- and cisplatin-induced tissue damage in the ferret.

1. The effects of GR203040, a tachykinin neurokinin1 receptor antagonist, on tissue damage induced by X-irradiation (Rad) or cisplatin (Cisp) were investigated in ferrets. 2. GR203040 (0.3 mg/kg SC) reduced the Rad-induced plasma protein extravasation (PPE) in the duodenum and kidney by 25% in each tissue. 3. GR203040 (3 mg/kg SC, 5-min pretreatment and every 8 hr for 48 hr after Cisp) reduced the Cisp-induced PPE in the duodenum, jejunum and lung by 59, 52 and 60%, respectively. 4. Histological examination showed that GR203040 also ameliorated the Rad- and Cisp-induced tissue damage.

Comparative efficacy of a single oral dose of ondansetron and of buspirone against cisplatin-induced emesis in cancer patients.

Buspirone, an agonist of the 5-HT1A subtype of serotonin receptors, has shown antiemetic activity in animal models. However, in cancer patients treated with cisplatin, ondansetron, given either i.v. (one 8-mg dose 30 min after cisplatin) or orally (one 16-mg dose at the end of cisplatin infusion) was superior (P < 0.001) to buspirone (60 mg p.o. at the end of cisplatin and 60 mg p.o., 30 min later), in all parameters of antiemetic efficacy. These results are in favour of 5-HT3 receptors, but against the participation of 5-HT1A receptors in acute emesis associated with cisplatin chemotherapy.

Nitric oxide and NK(1)-tachykinin receptors in cyclophosphamide-induced cystitis, in rats.

The present study was conducted to investigate the role of NK(1) receptors and of nitric oxide (NO) on the pathogenesis of cyclophosphamide-induced cystitis, in rats. This bladder toxicity was characterized by marked increases in protein plasma extravasation, urothelial damage, edema, white blood cell infiltrates, and vascular congestion. These changes were associated with appearance of Ca(2+)-independent NO-synthase (NOS) activity [characteristic of inducible NOS (iNOS)] in the bladder and with increases in urinary NO metabolites. GR205171, a selective NK(1) antagonist (10-20 mg/kg, i.p.) reduced cyclophosphamide-induced increases in protein plasma extravasation and in the urinary excretion of NO metabolites. N(G)-Nitro-L-arginine (L-NNA) (10 mg/kg, i.p.), a NOS inhibitor, reduced basal and cyclophosphamide-induced increases in NO metabolites and protected against cyclophosphamide-induced protein plasma extravasation. GR205171 had no effect, whereas L-NNA reduced basal NO metabolite excretion. Combined treatment with the NK(1) antagonist and the NO-synthesis inhibitor produced comparable reduction in protein plasma extravasation than that achieved with each drug given separately. Combined drug treatment ameliorated cyclophosphamideinduced urothelial damage, and the extent of edema, vascular congestion, and white blood cell infiltrates in the bladder. In summary, NK(1) receptors and iNOS play a role in NO formation and on cyclophosphamide-induced cystitis. Activation of NK(1) receptors mainly acts through the formation of NO. It is proposed that cyclophosphamide and/or its metabolites would stimulate primary afferent capsaicin-sensitive fibers in the bladder, releasing neuropeptides, which would activate NK(1) receptors. However, additional mechanisms are involved, because neither the NK(1) receptor antagonist nor the NO synthesis inhibitor, either alone or in combination, were able to completely prevent the toxicity.

Effects of short- and long-term exercise on urinary cGMP excretion in healthy subjects and in patients with coronary artery disease.

The possibility that systemic formation of cyclic guanosine monophosphate (cGMP) could reflect the level of cardiovascular fitness was investigated. The relations between physical activity and systemic formation of cGMP were evaluated in healthy volunteers and in patients with coronary artery disease (CAD). No significant differences were observed in the basal urinary excretion of cGMP in highly trained runners, sedentary subjects, and in patients with CAD, despite the large differences in aerobic exercise training between groups. In addition, the basal levels of cGMP in CAD patients failed to increase after a 12-week cardiac rehabilitation program. Short-term exercise, on the other hand, was associated with significant increases in urinary cGMP excretion. A 42-km marathon increased urinary cGMP excretion by 272%. The 15-km race increased urinary cGMP excretion by 330%. In CAD patients, 30 min of supervised exercise on a treadmill, at 80% of patient's maximal heart rate, induced a 60% increase in urinary cGMP, which returned to preexercise levels 90 min after termination of the exercise. Completion of the 12-week cardiac rehabilitation program improved exercise capacity and the magnitude of increase in cGMP levels induced by short-term treadmill exercise. Our findings suggest that cGMP increases during and shortly after short-term exercise and that the magnitude of the increase seems dependent on the intensity of the exercise and on physical fitness. Exercise training in healthy subjects and in CAD patients enhanced the amount of cGMP produced during short-term exercise, which might be responsible for some of the protective cardiovascular actions of exercise. The short half-life of cGMP may explain why the basal resting levels of cGMP are not appropriate predictors of a subject's physical fitness.

Urinary excretion of nitric oxide metabolites in runners, sedentary individuals and patients with coronary artery disease: effects of 42 km marathon, 15 km race and a cardiac rehabilitation program.

BACKGROUND: The mechanisms by which regular exercise is associated with decreases in all-cause and cardiovascular mortality are unknown. Nitric oxide (NO) may have a role, as it is known to be an important factor in cardiovascular regulation. The relationships between physical activity and systemic formation of NO were evaluated in healthy volunteers and in patients with coronary artery disease (CAD). METHODS: Urinary excretion of NO metabolites (nitrates + nitrites) was measured in 50 men. Group 1 comprised 14 highly trained runners (90 km/week) who were tested before and after a marathon race of 42.2 km. Group 2 comprised 11 well trained men (64 km/week) who were tested before and after a 15 km race. Group 3 comprised 12 sedentary individuals who gave a single urine sample. Group 4 comprised 13 patients with CAD who were tested before and after a 6 km walk. RESULTS: Group 1 showed the highest basal levels of urinary NO metabolites: 10.10 mmol/g creatinine; they were followed by group 2, with 5.60 mmol/g creatinine, group 3 with 1.59 mmol/g creatinine and patients with CAD (group 4), who had 0.35 mmol/g creatinine. After the marathon, those in group 1 showed a significant (P=0.0001) reduction of 80% in the excretion of NO metabolites. The 15 km race (group 2 and the 6 km walk (group 4), produced nonsignificant reductions in NO excretion. Patients with CAD were prospectively evaluated before and after a 12-week cardiac rehabilitation program. Their urinary excretion of NO metabolites (mmol/g creatinine) at the end of the program was 157% higher than at baseline (P=0.034). A positive, significant correlation (P=0.006) was observed between the increases in exercise capacity [in METs (one MET is equal to the body's oxygen consumption at rest, and corresponds to 3.5 ml/Kg/min)] and in NO metabolite excretion induced by the 12-week program. CONCLUSIONS: The baseline urinary excretion of NO metabolites increases with increasing levels of physical activity (chronic aerobic exercise). Patients with CAD had lowest levels of urinary NO metabolites and these increased in direct proportion with the gain in functional capacity. These findings suggest that increased NO production may be a major adaptive mechanism by which chronic aerobic exercise training benefits the cardiovascular system. The marked increase in NO production induced by long-term, high levels of aerobic exercise may be protective in athletes undertaking strenuous levels of exercise.