Nitric oxide synthase inhibition results in immediate postoperative recovery of gastric, small intestinal and colonic motility in awake rats

Background Nitric oxide (NO) is known to inhibit gastrointestinal motility. However, no detailed analysis of gastric, small intestinal and colonic motor effects, including effects on contraction frequency, has, as yet, been reported after NO inhibition in awake rats. We therefore investigated the effects of NO synthase inhibition on gastric, small intestinal and colonic motility in awake rats under baseline conditions and in a postoperative ileus model.Methods In Sprague–Dawley rats, strain gauge transducers were sutured either to the gastric corpus, the small intestine or the colon. After 3 days, l-NMMA (NO synthase inhibitor), d-NMMA or vehicle was given i.v., while the motility was recorded continuously. In addition, postoperative gastric, small intestinal or colonic motility was investigated after l-NMMA or vehicle treatment prior to abdominal surgery. The motility index, the contraction amplitude, the area under the contraction amplitude and the contraction frequency were analysed.Results l-NMMA decreased gastric motility to 60±8% for about 15 min, but continuously increased small intestinal motility to 221±22% and colonic motility to 125±7% compared to baseline (baseline=100%; p<0.01 for all comparisons). l-NMMA increased the contraction frequency throughout the gastrointestinal tract (stomach, 13±2%; small intestine, 8±1%; colon, 16±5%; p<0.01 vs. baseline for all comparisons). l-NMMA injection prior to surgery did not prohibit intraoperative inhibition of gastrointestinal motility, but did result in immediate recovery of gastric, small intestinal and colonic motility postoperatively (l-NMMA vs. vehicle, 0–60 min postoperatively; stomach, 90±9% vs. 53±3%; small intestine, 101±5% vs. 57±3%; colon, 134±6% vs. 60±5%; p<0.01 for all comparisons; no significant difference between preoperative baseline motility and l-NMMA treated rats postoperatively).Conclusions Under baseline conditions, endogenous NO inhibits small intestinal and colonic motility and gastric, small intestinal and colonic contraction frequency in awake rats. In the early postoperative period, endogenous NO is a major inhibitory component that seems to constitute the common final pathway of mediators and the neural pathways inhibiting gastrointestinal motility in rats.     

Nitric oxide plays an insignificant role in direct vasodilator effects of calcium channel blockers in healthy humans

Several experimental studies have suggested that the vasodilatory effects of calcium channel blockers (CCBs) are due in part to an endothelium-dependent mechanism. However, it remains unknown whether CCBs directly augment liberation of endothelium-derived dilator substances such as nitric oxide (NO) in the human vasculature. The aim of this study was to examine whether CCBs of several kinds directly increase the bioavailability of NO in forearm resistance vessels. Twenty-four healthy men (mean age 30 ± 2 years) were randomly assigned to three study groups (n = 8 in each), and each group was assigned one of three first-generation CCBs (nifedipine, nicardipine, diltiazem). Subdepressor doses of CCBs [4, 8, 16, 24, and 36 (diltiazem only) nmol/min; for 2 min in each dose] were infused intra-arterially, and forearm blood flow (FBF) was determined plethysmographically. After control FBF responses to CCBs had been measured, a NO synthase inhibitor (N ^G-monomethyl-l-arginine: l-NMMA) was infused intra-arterially, and the FBF response to CCBs was again determined. Further, as a positive control for NO stimulation, acetylcholine (ACh) was also examined before and after l-NMMA in each group. Systemic blood pressure and heart rate did not change significantly during the study protocol. The FBF responses to these CCBs did not differ before and after NO synthase inhibition by l-NMMA (FBF at maximum doses: nifedipine, 8.0 ± 0.8 vs 7.3 ± 0.7; nicardipine, 7.3 ± 1.5 vs 6.5 ± 1.3; diltiazem, 5.7 ± 0.7 vs 4.2 ± 0.7 ml/min per 100 ml: all not significant), although FBF responses to ACh were significantly reduced by l-NMMA. In conclusion, direct NO liberation does not make a significant contribution to the vasodilation associated with first-generation CCBs in healthy human resistance vessels. Received: July 12, 2001 / Accepted: October 19, 2001     

Insulin increases cyclic nucleotide content in human vascular smooth muscle cells: a mechanism potentially involved in insulin-induced modulation of vascular tone

Summary It has been suggested that insulin exerts a vasodilating effect, but the mechanisms involved are not completely understood. Since cyclic nucleotides mediate the vasodilation induced by endogenous substances, such as prostacyclin and nitric oxide, we aimed to investigate the influence of insulin (concentration range 240–960 pmol/l) on both cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) content in human vascular smooth muscle cells. Insulin dose-dependently increased both nucleotides (cAMP: from 0.7±0.1 to 2.6±0.4 pmol/10⁶ cells, p=0.0001; cGMP: from 1.3±0.2 to 3.4±0.7 pmol/10⁶ cells, p=0.033). This increase is receptor-mediated, since it was blunted when cells were preincubated with the tyrosine kinase inhibitor genistein. The effect of insulin remained significant (p=0.0001) when preincubation with the phosphodiesterase inhibitor theophylline prevented cyclic nucleotide catabolism. The increase of cGMP was blunted when the cells were preincubated with the guanylate cyclase inhibitor methylene blue, and with the nitric oxide-synthase inhibitor N^G-monomethyl-l-arginine. At all the concentrations tested, insulin potentiated the increase of cAMP induced by the stable prostacyclin analogue Iloprost (p=0.0001), whereas only at 1920 pmol/l did it potentiate the cGMP increase induced by glyceryltrinitrate (p=0.05). This study demonstrates that the vasodilating effects exerted by insulin may at least in part be attributable to an increase of both cGMP and cAMP via a receptor-mediated activation of adenylate and guanylate cyclases in human vascular smooth muscle cells and that the insulin effect on cGMP is mediated by nitric oxide.Abbreviations cAMP cyclic adenosine monophosphate - cGMP cyclic guanosine monophosphate - PDE phosphodiesterases - NO nitric oxide - hVSMC human vascular smooth muscle cells - l-NMMA N^G-monomethyl-l-arginine - GTN glyceryltrinitrate - BSA bovine serum albumin - NIDDM non-insulin-dependent diabetes mellitus - MEM minimal essential medium - RIA radioimmunoassay     

Contribution of endogenous nitric oxide to basal vasomotor tone of peripheral vessels and plasma B-type natriuretic peptide levels in patients with congestive heart failure

OBJECTIVES: We examined whether a relationship exists between the vasoconstrictive response to endogenous nitric oxide (NO) synthesis inhibition and the severity of heart failure in patients with congestive heart failure (CHF). BACKGROUND: Controversy exists as to whether the vasoconstrictive response to NO synthesis inhibition in patients with CHF is comparable to that in normal subjects or is enhanced. METHODS: Forearm blood flow (FBF) and calculated forearm vascular conductance (FVC) were obtained using plethysmography before and after administration of the NO synthesis inhibitor L-NMMA (NG-monomethyl-L-arginine) in 40 patients with CHF due to dilated cardiomyopathy and in 16 normal control subjects. Basal plasma B-type natriuretic peptide (BNP) and nitric oxide concentrations were measured in all subjects. RESULTS: Plasma BNP and nitrite/nitrate (NOx) levels in the patients group were significantly greater and baseline FBF was significantly less. Administration of L-NMMA significantly decreased FBF and FVC in both groups. The percent changes in FBF (%FBF) and FVC (%FVC) from the baseline after L-NMMA correlated significantly with plasma BNP level (%FBF: r = 0.72; %FVC: r = 0.76; both p < 0.001). Percent changes in both FBF and FVC were greater in patients with BNP > or = 100 pg/ml than in normal subjects; however, in patients with BNP < 100 pg/ml they were comparable to those in normal subjects. CONCLUSIONS: Vasoconstrictive response to L-NMMA in patients with CHF was preserved or enhanced in proportion to the basal plasma BNP level, indicating a close relationship between the contribution of endogenous NO to basal vasomotor tone and the severity of heart failure.     

Nitric oxide in ischaemic acute renal failure of streptozotocin diabetic rats

Summary Changes in nitric oxide (NO) levels were determined in ischaemic acute renal failure in streptozotocin-induced diabetes mellitus rats. Two weeks after streptozotocin administration and immediately after right nephrectomy, the left renal artery was occluded for 60 min. Similar procedures were carried out in non-diabetic rats. The nitrite (NO₂) + nitrate (NO₃) levels were measured in plasma and urine. The effects of chronic oral supplementation with l-arginine and an NO synthase inhibitor (N-omega-nitro-l-arginine) were also studied in both diabetic and non-diabetic rats before and after renal artery clamping. The rats with diabetic acute renal failure had a much lower creatinine clearance (90±22 l · min^–1 · 100 g body weight^–1, p<0.005), and higher fractional excretion of sodium (FENa)% (10.90±4.2, p<0.001) and protein excretion (2078±69 g/ml creatinine clearance, p<0.001) compared with the respective values in the non-diabetic groups (163±30; 1.46±86; 453.3±31). The plasma and urine NO₂ + NO₃ levels were significantly higher in the untreated diabetic rats compared with the untreated normal rats before ischaemia (p<0.001). The ischaemic acute renal failure in non-diabetic rats increased the plasma and urinary NO₂ + NO₃ excretion after ischaemia. The urinary excretion of these metabolites decreased significantly and their plasma levels remained unchanged in the ischaemic diabetic rats. The l-arginine administration resulted in a small but significantly higher creatinine clearance after clamping in the non-diabetic rats. The NO synthase inhibitor caused deterioration in renal function in all ischaemic and non-ischaemic groups. In summary, the greater vulnerability to ischaemia of the diabetic kidney seems to be associated with both impaired response to and impaired production of NO.Abbreviations IARF Ischaemic acute renal failure - STZ streptozotocin - NOSi nitric oxide synthase inhibitor - ARF acute renal failure - Ccr creatinine clearance - FENa% fractional excretion of sodium     

Inhibition of endogenous nitric oxide reduces basal mesenteric vascular tone but does not alter intraduodenal hydrochloric acid-induced intestinal hyperemia in rats

There are conflicting reports on the role of endogenous nitric oxide (NO) in the regulation of basal intestinal blood flow. The effect of inhibition of NO on intraduodenal hydrochloric acid (HCl) induced intestinal hyperemia remains to be confirmed. We investigated the effect of inhibition of endogenous NO on basal intestinal blood flow, HCl-induced intestinal hyperemia, and duodenal villous injury. Superior mesenteric artery blood flow in rats was measured by pulsed Doppler flowmetry and duodenal villous injury evaluated by histology. Intravenous N^G-nitro-l-arginine methyl ester (l-NAME), orl-arginine ord-arginine followed byl-NAME, was given to show inhibition, reversal of inhibition of endogenous NO synthase, and stereospecificity, respectively. An intraduodenal 2 ml/kg bolus or perfusion for 30 min of 0.1 N HCl was given 15 min afterl-NAME or vehicle. Mean arterial blood pressure was increased byl-NAME, which also significantly reduced intestinal blood flow under basal condition and after intraduodenal HCl. Basal mesenteric blood flow was not altered byl- ord-arginine. Thel-NAME-induced increase in blood pressure and decrease in basal blood flow was attenuated byl- but notd-arginine. The villous damage and the magnitude of the peak hyperemia was unchanged byl-NAME,l- ord-arginine. Inhibition of endogenous NO byl-NAME is suggested by the significant rise in blood pressure. The rise in blood pressure and reduction in blood flow are attenuated byl- but notd-arginine, indicating stereospecificity. Inhibition of endogenous NO reduces basal mesenteric vascular tone but does not alter intraduodenal HCl-induced intestinal hyperemia. The increase in blood flow after intraduodenal HCl predicts the absence of exacerbation of HCl-induced duodenal villous damage.     

Effect of insulin on renal sodium handling in hyperinsulinaemic Type 2 (non-insulin-dependent) diabetic patients with peripheral insulin resistance

Summary The sodium retaining effect of insulin was studied in ten Type 2 (non-insulin-dependent) diabetic patients (mean age 56 (43–73) years, mean body mass index 29.5 (24.2–33.7) kg/m²) and eight age-matched control subjects (mean age 57 (43–68) years, mean body mass index 23.4 (20.8–26.6) kg/m²). The renal clearances of ^99mTc-DTPA, lithium, sodium and potassium were measured over a basal period of 90 min. Then insulin was infused at a rate of 40 mU·mirr^–1·m^–2. After an equilibration period of 90 min, the clearance measurements were repeated during a new 90 min period. Blood glucose was clamped at the basal level (diabetic patients: 9.9±3.5, control subjects: 5.3±0.5 mmol/l) by a variable glucose infusion. Basal plasma insulin concentration was elevated in the diabetic patients (0.12±0.05 vs 0.05±0.02 pmol/ml, p<0.01). Insulin infusion resulted in comparable absolute increments in plasma insulin concentrations in the diabetic group and in the control group (0.44±0.13 vs 0.36±0.07 pmol/ml, NS). The metabolic clearance rate of glucose during the last 30 min of insulin infusion was lower in the diabetic patients (155±62 vs 320±69 ml·min^–1·m², p<0.01), reflecting peripheral insulin resistance. The decline in sodium clearance during insulin infusion was similar in diabetic subjects (1.8±1.1 vs 0.7±0.4 ml·min^–1·1.73 m^–2, p< 0.01) and in control subjects (1.7±0.3 vs 0.8±0.3 ml · min^–1 · 1.73 m^–2, p<0.01). The glomerular filtration rate and lithium clearance was unchanged, consequently calculated distal tubular fractional sodium reabsorption increased (diabetic patients: 92.9±4.1 vs 97.1±1.5, p<0.01, control subjects: 93.1±1.1 vs 96.5±0.6%, p< 0.01). Estimated extracellular fluid volume was 10% higher in the diabetic subjects (16.3±2.1 vs 14.8±2.01·1.73 m^–2, NS). In conclusion, the sodium retaining effect of insulin is preserved in Type 2 diabetic patients with peripheral insulin resistance. Insulin may contribute to sodium and fluid retention and thus to the increased frequency of hypertension in hyperinsulinaemic Type 2 diabetic patients.     

Nitric oxide is involved in the insulin release in rats byl-arginine

The insulinogenic effect ofl-arginine has been demonstrated bothin vivo andin vitro, but the mechanism by which this amino acid stimulates the pancreatic B-cells to release insulin is not entirely clear. Recently it was shown thatl-arginine-derived nitric oxide may mediatel-arginine-induced insulin release, and data were also provided to suggest that nitric oxide (NO) has no part in this process. To further investigate whether NO is involved in the release of insulin induced byl-arginine, we infused different doses ofl- andd-arginine in rats. L-Arginine (25 and 100 mg/kg/minute) elicited dose-dependent increases of the plasma insulin levels by up to 18.65±2.13 and 48.6±6.6 U/L, respectively, and increased the plasma glucose levels by up to 1.18±0.13 and 1.43±0.1 mmol/L, respectively. D-Arginine (25 and 100 mg/kg/minute) also elicited dose-dependent increases of the plasma insulin levels by up to 9.08±1.23 and 23.33±2.33 U/L, and increased the plasma glucose levels by up to 0.32±0.09 and 0.46±0.08 mmol/L. Thus, the increases in plasma insulin and glucose levels were significantly smaller during infusion ofd-arginine. We conclude that the plasma insulin response to i.v. infusion ofl-arginine is at least partly mediated by augmented NO synthesis by the pancreatic islets, althoughl-arginine-derived NO is not an obligatory stimulus for insulin release.     

Acetylcholine causes dose dependent increase in pulmonary flow in patients with chronic heart failure and elevated pulmonary vascular resistance

Elevated pulmonary vascular resistances occur to a variable degree in patients with chronic congestive heart failure (CHF). These might be caused by increased levels of endogenous vasoconstrictors, defective endothelial vasodilatory mechanisms or structural vascular abnormalities. To determine the contribution of defective endothelial mediated vasodilation, we tested 10 patients with CHF due to coronary artery disease (n=4) or dilated cardiomyopathy (n=5), and congenital corrected transposition of the great arteries (n=1) (median pulmonary artery pressure 36 mmHg, range of pulmonary vascular resistance 0.94–10.7 WE). Patients were in median functional class NYHA III, median left ventricular ejection fraction was 21%, median oxygen uptake at the anaerobic threshhold was 8.25 ml/kg/min.Flow was measured by a flow wire (0.018 inch) positioned in a pulmonary artery branch with a diameter of 3–8 mm determined by intravascular ultrasound before. Acetylcholine infusion was adjusted to 10^–6, 10^–5 and 10^–4 molar concentrations in the pulmonary artery branch. A dose dependent increase in flow between 64 to 140% was seen in 8 out of 10 patients. We conclude: Acetylcholine mediated vasodilation is found in patients with CHF and elevated pulmonary vascular resistances.     

Effects of nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester on duodenal alkaline secretory and ulcerogenic responses induced by mepirizole in rats

The inhibition of nitric oxide (NO) production by NO synthase inhibitors stimulates HCO ₃ ^– secretion in the rat duodenal mucosa. Therefore, we examined the effects of N^G-nitro-l-arginine methyl ester (l-NAME, the NO synthase inhibitor) and nitroprusside (the exogenous NO donor) on the duodenal HCO ₃ ^– and ulcerogenic responses in anesthetized rats. Animals were administered mepirizole (200 mg/kg, subcutaneously) for induction of duodenal ulcers, and gastric acid and duodenal HCO ₃ ^– secretions were measured with or without pretreatment withl-NAME (5 mg/kg, intravenously) or nitroprusside (4 mg/kg, intravenously). Mepirizole increased acid secretion, decreased the acid-induced duodenal HCO ₃ ^– secretion, and induced hemorrhagic lesions in the proximal duodenum. The inhibition of NO production byl-NAME potentiated the acid secretory response, increased the duodenal HCO ₃ ^– secretion, and prevented the duodenal lesions, and these changes were all antagonized by simultaneous administration ofl-arginine (200 mg/kg, intravenously) but notd-arginine. On the other hand, nitroprusside slightly reduced the acid response but further decreased the HCO ₃ ^– output, resulting in aggravation of duodenal lesions induced by mepirizole. These data suggest that the inhibition of endogenous NO production by the NO synthase inhibitorl-NAME increases duodenal HCO ₃ ^– secretion and protects the duodenal mucosa against acid injury.     

Augmented vasodilator response to L-arginine after coronary angioplasty may attenuate restenosis

 Nitric oxide (NO) plays an important role in the control of vascular tone as well as structure. This study examined the possibility that the extent of restenosis 3 months after percutaneous transluminal coronary angioplasty (PTCA) might be correlated with the magnitude of NO production at the PTCA sites on the day following PTCA. In 23 consecutive patients who underwent PTCA, we examined the coronary artery diameter response to intracoronary administration of l-arginine (1 μg/kg) and isosorbide dinitrate (ISDN, 40 μg/kg) at the sites of PTCA (n= 25) and at untreated sites distal to the PTCA sites approximately 18 h after PTCA. The coronary artery diameter at the PTCA site was determined 3 months after PTCA in all patients. Normalized vasodilator responses to l-arginine (responses to l-arginine ÷ those to ISDN) were greater at the PTCA sites than at the untreated sites (P= 0.05), whereas vasodilator responses to ISDN did not differ between the PTCA and untreated sites. These results suggest a greater production of NO at the PTCA sites despite presumable loss of the endothelium due to the PTCA. Furthermore, the magnitude of normalized vasodilator responses to l-arginine examined at 18 h after PTCA correlated with the coronary artery diameter 3 months after PTCA (r= 0.592, P= 0.002). These results suggest that augmented NO production after PTCA may protect against the development of coronary restenosis. Treatment that enhances local NO production may be clinically useful in preventing restenosis after PTCA. Received: December 24, 1999 / Accepted: February 16, 2002     

Regulation of regional norepinephrine spillover in heart failure: The effect of angiotensin ii and β-adrenergic agonists in the forearm circulation

Background: Prejunctional receptors for angiotensin II (A-II) and norepinephrine (NE) have been reported to facilitate NE release. If operative in patients with congestive heart failure (CHF), such receptors could participate in positive feedback cycles amplifying sympathoactivation.Methods and Results: A-II and isoproterenol (ISO) would increase regional NE spillover via facilitation of presynaptic release of NE in the forearm circulation of patients with chronic stable CHF. A-II, ISO, and nitroprusside (NP) were sequentially infused into the brachial arteries of 10 patients with chronic stable CHF, which was attributed to dilated cardiomyopathy. Forearm blood flow (FBF) was measured via plethysmography and regional spillover of NE was measured by using the isotope dilution method of Esler. A-II (5 ng/min) produced a nonsignificant decline in FBF (1.87 ± 0.14 to 1.46 ± 0.1 mL/100 g/min, P = .07) and did not change regional NE spillover (418 ± 128 to 409 ± 121 ng/min). ISO increased FBF from 1.6 ± 0.12 to 4.3 ± 0.7 mg/100 g/min (P < .001). Regional NE spillover increased from 337 ± 86 to 856 ± 300 ng/min (P < .001). Venous NE and regional extraction of NE did not change. NP increased FBF from 2.0 ± 0.3 to 6.3 ± 1.2 mL/100 g/min (P < .001; P = NS v change with ISO) and also increased regional NE spillover (301 ± 99 to 712 ± 288 ng/min, P < .001; P = NS v change with ISO). As with ISO, venous NE and extraction of NE were not altered.Conclusions: Mild vasoconstrictor infusions of A-II do not increase regional NE spillover in the forearm circulation of patients with CHF. The β-adrenergic agonist ISO does increase regional spillover, but the effect seems to be primarily related to flow rather than presynaptic stimulation of NE release. These data argue against an important positive feedback loop involving A-II and NE on sympathoactivation, at least with the dosages of the agonists studied and in the limb circulation in chronic stable CHF.     

Nitric oxide effects depend on different mechanisms in different regions of the rat heart

The important role of nitric oxide (NO) in regulating cardiac functions has been investigated in prior research. However, NO-induced signaling mechanisms in the different regions of the heart have not been explored until now. In this study, the mechanism of NO effects on the spontaneously beating right atrium and left papillary muscle isolated from the rat heart was examined. The NO donor diethylamine NONOate (DEA/NO) (0.1–100 μM) depressed the resting and developed tensions, as well as the sinus rate, of the right atrium. The effect of DEA/NO on contractions of the right atrium was blocked by the soluble guanylate cyclase (sGC) inhibitor, ODQ (1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one) (10 μM). The ATP-sensitive potassium channel (K_ATP) blocker glyburide (3 μM) reversed DEA/NO-induced decreases in the resting tension. The suppressor effect of DEA/NO on the sinus rate was inhibited only by the superoxide radical scavenger superoxide dismutase (25 U/ml). Neither the cGMP-dependent protein kinase (PKG) inhibitor KT5823 (0.1 μM) nor the cAMP-dependent protein kinase (PKA) inhibitor KT5720 (1 μM) changed DEA/NO responses in the right atrium. While the resting tension of the right atrium was decreased by the NO precursor l-arginine (1–100 μM), it was increased by the nitric oxide synthase inhibitor l-NMMA (0.1–100 μM). The sinus rate was not affected by l-arginine or l-NMMA. The left papillary muscle contraction was not influenced by any of these NO-related agents. These results show that high concentration NO-induced depression of the contraction of the right atrium is due to sGC and K_ATP channel activation, but suppression of the sinus rate depends on redox regulation. Our results may have important implications for the region-dependent functional disability of cardiac myocytes, as well as the regulation of heart performance in high NO-induced pathological conditions.     

Abnormal peripheral vasodilatory reserve without endothelial dysfunction in patients with aortic dissection

Structural changes in the aortic wall have been reported to be present in aortic dissection (AD), while there have been no investigations concerning peripheral vasomotion characteristics. Peripheral arterial stiffness is an important factor in the regulation of the central aortic pressure because it produces excessive wave reflection. The present study investigated in AD patients endothelium-dependent peripheral vasodilation and the reactive hyperemic response which is considered to be altered by the structural abnormality of the peripheral resistance artery. Forearm blood flow (FBF) changes induced by intra-arterial infusion of acetylcholine (ACh), sodium nitroprusside (SNP), and by occlusion-induced reactive hyperemia (RH) were measured plethysmographically in 10 AD patients, 7 healthy volunteers, and 7 patients with uncomplicated hypertension (UHT). There were no significant differences in the peak FBF response to ACh and SNP infusion for the three groups (ACh, 14.2±1.8 vs 17.2±4.5 vs 15.7±2.3 ml/min/dl tissue, NS; SNP 9.5±1.3 vs 10.6±1.7 vs 11.9±0.8 vs ml/min/dl tissue, NS). In the case of RH, however, peak FBF and maximum conductance were significantly lower in AD patients than in healthy volunteers and UHT patients (21.1±2.6 vs 36.1±4.7 and 32.4±2.6 ml/min/dl tissue volume,p<0.01, and 0.25±0.03 vs 0.46±0.06 and 0.37±0.03 ml/min/dl per mmHg,p<0.05, respectively). Peripheral vasodilatory function depending on the endothelium and smooth muscle in AD patients was not significantly different from that in healthy volunteers and UHT patients. However, reactive hyperemic vasodilatory reserve, which is a well-established, noninvasive measure of arterial structure, was significantly impaired in AD. These findings indicate that arterial structural abnormalities rather than systemic atherosclerotic changes represented by endothelial dysfunction may be present. We speculated that this aspect of peripheral resistance artery might possibly have an unfavorable effect on the postonset aortic conditions in AD patients.     

Circulating endothelial cells are elevated in patients with type 2 diabetes mellitus independently of HbA1c

Aims/hypothesis Patients with diabetes mellitus are well known to be at high risk for vascular disease. Circulating endothelial cells (CECs) have been reported to be an ex vivo indicator of vascular injury. We investigated the presence of CECs in the peripheral blood of 25 patients with diabetes mellitus and in nine non-diabetic control donors.Methods Endothelial cells were isolated from peripheral blood with anti-CD-146–coated immunomagnetic Dynabeads, and were stained with acridine orange dye and counted by fluorescence microscopy. The cells were also stained for von Willebrand factor and Ulex europaeus lectin 1.Results Patients with diabetes mellitus had an elevated number of CECs (mean 69±30 cells/ml, range 35–126) compared with healthy controls (mean 10±5 cells/ml, range 3–18) (p<0.001). The increase in CECs did not correlate with the levels of HbA₁c. Circulating endothelial cell numbers were elevated regardless of glucose levels, suggesting that, even with control of glucose levels, there is increased endothelial cell sloughing.Conclusions Our study suggests that the higher number of CECs in patients with type 2 diabetes may reflect ongoing vascular injury that is not directly dependent on glucose control.     

Renal and splanchnic exchange of human biosynthetic C-peptide in Type 1 (insulin-dependent) diabetes mellitus

Summary Biosynthetic human C-peptide or NaCl (154 mmol·l^–1) was given intravenously to 13 Type 1 (insulin-dependent) diabetic patients to determine the renal and splanchnic exchange of C-peptide. Catheters were inserted percutaneously into an artery and a renal and hepatic vein. Infusions of C-peptide were given for 60 min at two dose levels (5 and 30 pmol·kg^–1·min^–1). Insulin was infused throughout the study (0.5 mU·kg^–1·min^–1) and plasma glucose was kept constant by a variable glucose infusion. The regional blood flows were measured by indicator dilution techniques. In 11 of the 13 patients basal C-peptide levels were not detectable. The arterial steady-state C-peptide concentration was 0.81±0.10 nmol·l^–1 and 2.33±0.30 nmol·l^–1 at the low and high rate infusions, respectively. Renal uptake was 124±18 pmol·min^–1 at the low infusion corresponding to 39% of the infused amount. At the higher dose C-peptide infusion renal uptake increased to 155±21 pmol·min^–1 (p<0.05). Urinary excretion of C-peptide was 7±2 pmol·min^–1 at the low dose infusion and increased to 34±6 pmol·min^–1 at the high dose infusion (p<0.01). The proportions of infused amount excreted were fairly constant and between 2% and 3%. No net exchange of C-peptide was found across the splanchnic vascular bed. The rate of glucose infusion had to be increased by 35% during the low dose C-peptide, but not during NaCl infusion in order to maintain a constant plasma glucose concentration. Arterial plasma concentrations of noradrenaline increased by 15–25% during both C-peptide and NaCl infusions. It is concluded that in patients with Type 1 diabetes (a) the kidney is the primary site of C-peptide removal, (b) renal metabolism rather than urinary excretion is the dominating process for C-peptide elimination (c) the excreted proportions of an infused amount of C-peptide were fairly constant between 2% and 3% and (d) no hepatic C-peptide catabolism could be detected.     

Nitric oxide in gastroprotection by sucralfate,mild irritant,and nocloprost

Pretreatment with sucralfate is known to protect gastric mucosa against the damaging effect of strong irritants, and this protection is accompanied by an increase in mucosal blood flow but the mechanisms underlying these effects have not been elucidated. Similar gastroprotective and hyperemic effects can be obtained with exogenous prostaglandins (PG), mild irritants such as dilute ethanol, and by capsaicin. In this study we investigated the role of nitric oxide (NO) in the prevention of ethanol-induced gastric damage and gastric blood flow by sucralfate, mild irritant such as 20% ethanol, capsaicin, and nocloprost, a stable PGE₂ analog. Pretreatment withN ^G-nitro-l-arginine (l-NNA), an inhibitor of NO synthase, enhanced ethanol-induced mucosal damage and reduced dose-dependently the gastroprotective and hyperemic effects of sucralfate, dilute ethanol, and capsaicin. The doses ofl-NNA attenuating significantly the protective effects of sucralfate or 20% ethanol were 25–50 mg/kg, while those reducing the protection by capsaicin were 6.2–12.5 mg/kg. The attenuating effect ofl-NNA on gastroprotection was reversed byl-arginine but notd-arginine. For comparison, the gastroprotective (but not hyperemic) effect of nocloprost was not affected by the pretreatment withl-NNA and/or arginine. We conclude that sucralfate, mild irritant, and capsaicin activate the NO system that may contribute to their gastroprotective effect through enhancing mucosal circulation but that NO is not essential for the mucosal protection by PGE₂ analog.     

Cross-sectional study of peripheral microcirculation in diabetic patients with microangiopathy: influence of pancreatic and kidney transplantation

Diabetic vascular lesions and peripheral autonomic neuropathy are both closely linked to long-term metabolic control of diabetes. Transcutaneous oxygen tension (P _tcO₂) measurements were made to elucidate whether autonomic neuropathy disturbs the cutaneous microciculatory blood flow, and whether long-term glucose normalization ameliorates such impairment. Twenty-eight type 1 (insulin-dependent) diabetic patients in whom clinically significant macroangiopathy had been excluded by angiography were studied, subdivided into group An=14; before simultaneous pancreas/kidney transplantation (SPKT); mean age 35 years, range 22–51 years; mean duration of diabetes 24 years, (range 15–32) years and group B (n=14; mean 31 months, range 2–101 months, after successful SPKT; mean age 35 years, range 19–56 years; mean duration of diabetes 22 years, range 14–29 years). On addition there was a group (group C) of age-and sex-matched healthy control subjects (n=14; mean age 35 years, range 23–62 years).P _tcO₂ measurements included basal recordings at 44°C on the leg and the foot, functional recordings at 44°C after arterial occlusion of the limb for 4 min, measurements during breathing 5 l oxygen per minute and finally while standing up (stand up dP ₅₀/dt). All subjects underwent extensive cardiac autonomic testing. In this cross-sectional study the recordings of basal values and of the functional parameters after arterial occlusion and during breathing oxygen did not differ significantly between groups A, B and C. The stand-up dP ₅₀/dt values were not significantly different between groups A and B (0.43±0.02 vs 0.47±0.03 mmHg/s, mean ± SEM); but A+B values were significantly higher than in C (0.22±0.01 mmHg/s;P<0.001). These values were correlated significantly with all parameters of cardiac autonomic neuropathy (r range–0.56 to –0.88;P<0.001). It may be concluded that normalization of blood glucose by pancreatic transplantation is not able to ameliorate peripheral microcirculation, but that measurement of transcutaneous oxygen tension is a possible new technique for quantifying alterations in the venoarteriolar reflex in peripheral diabetic autonomic neuropathy that lead to disturbed peripheral microcirculation in diabetic patients.     

The activity of the renin-angiotensin-aldosterone system before and during submaximal bicycle exercise in relation to circulatory catecholamines in patients with Type 1 (insulin-dependent) diabetes mellitus

Summary To evaluate the renin-angiotensin-aldosterone system in relation to circulatory catecholamines, we determined renin activity, angiotensin II, aldosterone, adrenaline, and noradrenaline in plasma before and during a submaximal bicycle exercise test in 23 Type 1 (insulin-dependent) diabetic patients (aged 19–57 years, mean 37; duration of diabetes 2–32 years, mean 16), 17 with signs of cardiac autonomic neuropathy, and in 18 healthy non-diabetic subjects (aged 24–41 years, mean 29). At rest, Type 1 diabetic patients showed significantly lower aldosterone values than control subjects (0.14±0.02 nmol/l and 0.22±0.02 nmol/l; p<0.01) while renin activity (1.0±0.1 nmol·l^–1·h^–1 and 0.9±0.1 nmol·l^–1·h^–1) and angiotensin II (14±1 nmol/l and 18±2 nmol/l) did not differ significantly between patients and control subjects. During exercise, increments (increase from the resting value to the value at 80% of maximal working capacity) in renin (1.5±0.4 nmol·l^–1·h^–1 and 3.7±0.5 nmol·l^–1 ·h^–1; p<0.001), angiotensin II (28±8 nmol/l and 60±8 nmol/l; p<0.01), aldosterone (0.16±0.04 nmol/l and 0.25±0.05 nmol/l; p<0.05), adrenaline (1.96±0.49 nmol/l and 2.92±0.51 nmol/l; ps<0.05), and noradrenaline (12.01±1.25 nmol/l and 18.74±1.45 nmol/l; p<0.01) were significantly lower in the patients than in control subjects. There was no difference in the renin-angiotensin-aldosterone response to exercise between patients with and without cardiac autonomic neuropathy but the impaired catecholamine reaction was confined to patients with cardiac autonomic neuropathy. In conclusion, Type 1 diabetic patients demonstrated low resting plasma aldosterone and reduced increments in renin activity, angiotensin II, aldosterone, and catecholamines during exercise. The low aldosterone values might be related to dysfunction of adrenal zona glomerulosa cells while it is unlikely that the reduced response to exercise of the renin-angiotensin-aldosterone system simply reflects sympathetic nerve failure.