Neuronal nitric oxide synthase and splanchnic blood flow in anaesthetized rats

Mycotoxins and the Enteric Nervous System

Mycotoxins are secondary metabolites produced by various fungal species. They are commonly found in a wide range of agricultural products. Mycotoxins contained in food enter living organisms and may have harmful effects on many internal organs and systems. The gastrointestinal tract, which first comes into contact with mycotoxins present in food, is particularly vulnerable to the harmful effects of these toxins. One of the lesser-known aspects of the impact of mycotoxins on the gastrointestinal tract is the influence of these substances on gastrointestinal innervation. Therefore, the present study is the first review of current knowledge concerning the influence of mycotoxins on the enteric nervous system, which plays an important role, not only in almost all regulatory processes within the gastrointestinal tract, but also in adaptive and protective reactions in response to pathological and toxic factors in food.

Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans

The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.

Neuronal nitric oxide synthase regulation of skeletal muscle functional hyperemia: exercise training and moderate compensated heart failure

Nitric oxide (NO) modulates oxygen delivery-utilization matching in resting and contracting skeletal muscle. Recent reports indicate that neuronal NO synthase (nNOS)-mediated vasoregulation during contractions is enhanced with exercise training and impaired with chronic heart failure (HF). Consequently, we tested the hypothesis that selective nNOS inhibition (S-methyl-l-thiocitrulline; SMTC, 2.1 μmol/kg) would produce attenuated reductions in muscle blood flow during moderate/heavy submaximal exercise in sedentary HF rats compared to their healthy counterparts. In addition, SMTC was expected to evoke greater reductions in exercising muscle blood flow in trained compared to sedentary healthy and HF rats. Blood flow during submaximal treadmill running (20 min/m, 5% grade) was determined via radiolabeled microspheres pre- and post-SMTC administration in healthy sedentary (Healthy + Sed, n = 8), healthy exercise trained (Healthy + ExT, n = 8), HF sedentary (HF + Sed, left ventricular end-diastolic pressure (LVEDP) = 12 ± 1 mmHg, n = 8), and HF exercise trained (HF + ExT, LVEDP = 16 ± 2 mmHg, n = 7) rats. nNOS contribution to exercising total hindlimb blood flow (ml/min/100 g) was not increased by training in either healthy or HF groups (Healthy + Sed: 105 ± 11 vs. 108 ± 16; Healthy + ExT: 96 ± 9 vs. 91 ± 7; HF + Sed: 124 ± 6 vs. 110 ± 12; HF + ExT: 107 ± 13 vs. 101 ± 8; control vs. SMTC, respectively; p > .05 for all). Similarly, SMTC did not reduce exercising blood flow in the majority of individual hindlimb muscles in any group (p > .05 for all, except for the semitendinosus and adductor longus in HF + Sed and the adductor longus in HF + ExT; p < .05). Contrary to our hypothesis, we find no support for either upregulation of nNOS function contributing to exercise hyperemia after training or its dysregulation with chronic HF.

Octreotide improves early dumping syndrome potentially through incretins: a case report

Dumping syndrome, or rapid gastric emptying, is a frequent complication after gastric surgery. In this case, the patient was a 47-year-old woman who 10 years previously had undergone distal gastrectomy with Billroth I reconstruction for early-stage gastric cancer. She presented with symptoms of weakness, headache, palpitation, sweating, dizziness and significant fatigue between one and two hours after a meal. Because a 75 g oral glucose tolerance test (75 g-OGTT) induced both acute postprandial tachycardia (within 1 hour) and postprandial hypoglycemia, we diagnosed this patient with early and late dumping syndrome. Dietary measures and acarbose improved symptoms of late dumping syndrome but did not prevent the symptoms of early dumping syndrome such as postprandial tachycardia, weakness, headache, palpitation, and dizziness. We therefore used the somatostatin analogue octreotide, which has been reported as an effective therapy for early dumping syndrome. Octreotide prevented the symptoms of early dumping syndrome, especially postprandial tachycardia, but caused postprandial hyperglycemia. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) were completely suppressed during the 75 g-OGTT following subcutaneous injection of octreotide. No change was observed in vasoactive intestinal polypeptide (VIP), which is the gastrointestinal peptide hormone generally responsible for early dumping syndrome, suggesting possible contribution of incretins in early dumping syndrome of this patient.

Effects of neuronal nitric oxide synthase inhibition on microvascular and contractile function in skeletal muscle of aged rats

Advanced age is associated with derangements in skeletal muscle microvascular function during the transition from rest to contractions. We tested the hypothesis that, contrary to what was reported previously in young rats, selective neuronal nitric oxide (NO) synthase (nNOS) inhibition would result in attenuated or absent alterations in skeletal muscle microvascular oxygenation (Po(2)(mv)), which reflects the matching between muscle O(2) delivery and utilization, following the onset of contractions in old rats. Spinotrapezius muscle blood flow (radiolabeled microspheres), Po(2)(mv) (phosphorescence quenching), O(2) utilization (Vo(2); Fick calculation), and submaximal force production were measured at rest and following the onset of contractions in anesthetized old male Fischer 344 × Brown Norway rats (27 to 28 mo) pre- and postselective nNOS inhibition (2.1 μmol/kg S-methyl-l-thiocitrulline; SMTC). At rest, SMTC had no effects on muscle blood flow (P > 0.05) but reduced Vo(2) by ∼23% (P < 0.05), which elevated basal Po(2)(mv) by ∼18% (P < 0.05). During contractions, steady-state muscle blood flow, Vo(2), Po(2)(mv), and force production were not altered after SMTC (P > 0.05 for all). The overall Po(2)(mv) dynamics following onset of contractions was also unaffected by SMTC (mean response time: pre, 19.7 ± 1.5; and post, 20.0 ± 2.0 s; P > 0.05). These results indicate that the locus of nNOS-derived NO control in skeletal muscle depends on age and metabolic rate (i.e., rest vs. contractions). Alterations in nNOS-mediated regulation of contracting skeletal muscle microvascular function with aging may contribute to poor exercise capacity in this population.

Caffeic Acid Phenylethyl Amide Protects against the Metabolic Consequences in Diabetes Mellitus Induced by Diet and Streptozocin

Caffeic acid phenyl ester is distributed wildly in nature and has antidiabetic and cardiovascular protective effects. However, rapid decomposition by esterase leads to its low bioavailability in vivo. In this study, chronic metabolic and cardiovascular effects of oral caffeic acid phenylethyl amide, whose structure is similar to caffeic acid phenyl ester and resveratrol, were investigated in ICR mice. We found that caffeic acid phenylethyl amide protected against diet or streptozocin-induced metabolic changes increased coronary flow and decreased infarct size after global ischemia-reperfusion in Langendorff perfused heart. Further study indicated that at least two pathways might be involved in such beneficial effects: the induction of the antioxidant protein MnSOD and the decrease of the proinflammatory cytokine TNFα and NFκB in the liver. However, the detailed mechanisms of caffeic acid phenylethyl amide need further studies. In summary, this study demonstrated the protective potential of chronic treatment of caffeic acid phenylethyl amide against the metabolic consequences in diabetes mellitus.

Cutaneous constitutive nitric oxide synthase activation in postural tachycardia syndrome with splanchnic hyperemia

Models of microgravity are linked to excessive constitutive nitric oxide (NO) synthase (NOS), splanchnic vasodilation, and orthostatic intolerance. Normal-flow postural tachycardia syndrome (POTS) is a form of chronic orthostatic intolerance associated with splanchnic hyperemia. To test the hypothesis that there is excessive constitutive NOS in POTS, we determined whether cutaneous microvascular neuronal NO and endothelial NO are increased. We performed two sets of experiments in POTS and control subjects aged 21.4 ± 2 yr. We used laser-Doppler flowmetry to measure the cutaneous response to local heating as an indicator of bioavailable neuronal NO. To test for bioavailable endothelial NO, we infused intradermal acetylcholine through intradermal microdialysis catheters and used the selective neuronal NOS inhibitor l-N(ω)-nitroarginine-2,4-L-diamino-butyric amide (N(ω), 10 mM), the selective inducible NOS inhibitor aminoguanidine (10 mM), the nonspecific NOS inhibitor nitro-l-arginine (NLA, 10 mM), or Ringer solution. The acetylcholine dose response and the NO-dependent plateau of the local heating response were increased in POTS compared with those in control subjects. The local heating plateau was significantly higher, 98 ± 1%maximum cutaneous vascular conductance (%CVC(max)) in POTS compared with 88 ± 2%CVC(max) in control subjects but decreased to the same level with N(ω) (46 ± 5%CVC(max) in POTS compared with 49 ± 4%CVC(max) in control) or with NLA (45 ± 3%CVC(max) in POTS compared with 47 ± 4%CVC(max) in control). Only NLA blunted the acetylcholine dose response, indicating that NO produced by endothelial NOS was released by acetylcholine. Aminoguanidine was without effect. This is consistent with increased endothelial and neuronal NOS activity in normal-flow POTS.

Tacrolimus modulates liver and pancreas nitric oxide synthetase and heme-oxygenase isoforms and cytokine production after endotoxemia

Cytoprotective effects of tacrolimus are due to its unspecific anti-inflammatory and anti-oxidant properties. Neither the exact mechanisms nor if there is any organ-specificity or dose-dependent response have not been yet elucidated. Our aim was to evaluate the effect of tacrolimus on oxidative stress and mediator production in liver and pancreatic tissue secondary to endotoxemia. Wistar rats were pretreated with intraperitoneal injection of tacrolimus (0.07, 0.15, and 0.3mg/kg) 24h before Escherichia coli LPS was administrated. Animals were sacrificed 24h after LPS administration and iNOS, eNOS, and nNOS and type 1 and 2 heme-oxygenase (HO) expression were measured. TNF-α and IL-1 tissue expression and plasmatic NO, CO, TNF-α, and IL-1 were also determined. LPS exposure increased iNOS expression in both organs, eNOS did not show variations and liver nNOS expression was significantly lower. Tacrolimus diminished both pancreas and liver iNOS and nNOS expression. Both liver and pancreatic eNOS expression augmented when tacrolimus was administrated. High doses of tacrolimus were correlated with ameliorated liver HO-1 plus HO-2 and pancreas HO-1 expression after LPS stimulation. Tacrolimus treatment diminished TNF-α but not IL-1 expression increase after LPS challenge in hepatic tissue. Pancreatic TNF-α and IL-1 values diminished partially when high doses were employed. Plasmatic NO, CO, TNF-α, and IL-1 concentrations increase after LPS challenge was diminished when highest doses of tacrolimus were given. In conclusion, tacrolimus exerts a protective effect on commonly observed harmful phenomena after LPS stimulation by modulating liver and pancreas oxidative enzyme expression and cytokine production.

Antihyperglycemic effect of a caffeamide derivative, KS370G, in normal and diabetic mice

The antihyperglycemic actions of caffeamide derivatives, especially KS370G, in normal ICR, streptozotocin-induced diabetic (T1DM) and diet-induced diabetic (T2DM) mice were investigated in this study. Oral administration of the compound decreased the plasma glucose levels in both normal and diabetic mice, and appeared to be in a dose-dependent manner in normal and diet-induced type 2 diabetic mice. It was found that KS370G could stimulate the release of insulin in both normal and T2DM mice, and a dose of 1 mg per kg KS370G could significantly attenuate the increase of plasma glucose induced by an intraperitoneal glucose challenge test in normal and diabetic mice. Similar treatment with KS370G significantly increased glycogen content in both liver and skeletal muscle. Hence, the hypoglycemic effect of KS370G in normal and diabetic mice could be attributed to the stimulation of insulin release and the increase of glucose utilization.

Effects of neuronal nitric oxide synthase inhibition on resting and exercising hindlimb muscle blood flow in the rat

Nitric oxide (NO) derived from endothelial NO synthase (eNOS) is an integral mediator of vascular control during muscle contractions. However, it is not known whether neuronal NOS (nNOS)-derived NO regulates tissue hyperaemia in healthy subjects, particularly during exercise. We tested the hypothesis that selective nNOS inhibition would reduce blood flow and vascular conductance (VC) in rat hindlimb locomotor muscle(s), kidneys and splanchnic organs at rest and during dynamic treadmill exercise (20 m min(-1), 10% grade). Nineteen male Sprague-Dawley rats (555 +/- 23 g) were assigned to either rest (n = 9) or exercise (n = 10) groups. Blood flow and VC were determined via radiolabelled microspheres before and after the intra-arterial administration of the selective nNOS inhibitor S-methyl-L-thiocitrulline (SMTC, 2.1 +/- 0.1 micromol kg(-1)). Total hindlimb muscle blood flow (control: 20 +/- 2 ml min(-1) 100g(-1), SMTC: 12 +/- 2 ml min(-1) 100g(-1), P < 0.05) and VC (control: 0.16 +/- 0.02 ml min(-1) 100 g(-1) mmHg(1), SMTC: 0.09 +/- 0.01 ml min(-1) 100 g(-1) mmHg(-1), P < 0.05) were reduced substantially at rest. Moreover, the magnitude of the absolute reduction in blood flow and VC correlated (P < 0.05) with the proportion of oxidative muscle fibres found in the individual muscles or muscle parts of the hindlimb. During exercise, total hindlimb blood flow (control: 108 +/- 7 ml min(-1) 100 g(-1), SMTC: 105 +/- 8 ml min(-1) 100 g(-1)) and VC (control: 0.77 +/- 0.06 ml min(-1) 100g(-1) mmHg(-1); SMTC: 0.70 +/- 0.05 ml min(-1) 100g(-1) mmHg(-1)) were not different (P > 0.05) between control and SMTC conditions. SMTC reduced (P < 0.05) blood flow and VC at rest and during exercise in the kidneys, adrenals and liver. These results enhance our understanding of the role of NO-mediated circulatory control by demonstrating that nNOS does not appear to subserve an obligatory role in the exercising muscle hyperaemic response in the rat.

Centrally evoked increase in adrenal sympathetic outflow elicits immediate secretion of adrenaline in anaesthetized rats

To examine whether feedforward control by central command activates preganglionic adrenal sympathetic nerve activity (AdSNA) and releases catecholamines from the adrenal medulla, we investigated the effects of electrical stimulation of the hypothalamic locomotor region on preganglionic AdSNA and secretion rate of adrenal catecholamines in anaesthetized rats. Pre- or postganglionic AdSNA was verified by temporary sympathetic ganglionic blockade with trimethaphan. Adrenal venous blood was collected every 30 s to determine adrenal catecholamine output and blood flow. Hypothalamic stimulation for 30 s (50 Hz, 100-200 microA) induced rapid activation of preganglionic AdSNA by 83-181% depending on current intensity, which was followed by an immediate increase of 123-233% in adrenal adrenaline output. Hypothalamic stimulation also increased postganglionic AdSNA by 42-113% and renal sympathetic nerve activity by 94-171%. Hypothalamic stimulation induced preferential secretion of adrenal adrenaline compared with noradrenaline, because the ratio of adrenaline to noradrenaline increased greatly during hypothalamic stimulation. As soon as the hypothalamic stimulation was terminated, preganglionic AdSNA returned to the prestimulation level in a few seconds, and the elevated catecholamine output decayed within 30-60 s. Adrenal blood flow and vascular resistance were not affected or slightly decreased by hypothalamic stimulation. Thus, it is likely that feedforward control of catecholamine secretion from the adrenal medulla plays a role in conducting rapid hormonal control of the cardiovascular system at the beginning of exercise.

Moderate hypothermia induces a preferential increase in pancreatic islet blood flow in anesthetized rats

The aim of the study was to characterize the effects of induced moderate hypothermia on splanchnic blood flow, with particular reference to that of the pancreas and the islets of Langerhans. We also investigated how interference with the autonomic nervous system at different levels influenced the blood perfusion during hypothermia. For this purpose, hypothermia (body temperature of 28°C) was induced by external cooling, whereas normothermic (37.5°C) anesthetized Sprague-Dawley rats were used as controls. Some rats were pretreated with either propranolol, yohimbine, atropine, hexamethonium, or a bilateral abdominal vagotomy. Our findings suggest that moderate hypothermia elicits complex, organ-specific circulatory changes, with increased perfusion noted in the pylorus, as well as the whole pancreas and the pancreatic islets. The pancreatic islets maintain their high blood perfusion through mechanisms involving both sympathetic and parasympathetic mediators, whereas the increased pyloric blood flow is mediated through parasympathetic mechanisms. Renal blood flow was decreased, and this can be prevented by ganglionic blockade and is also influenced by β-adrenoceptors.