Gastric distension causes changes in heart rate and arterial blood pressure by affecting the crosstalk between vagal and splanchnic systems in anesthetised rats

The role of amygdala neuropsin/serpinb6 pathway in the regulation of gastric hypersensitivity and anxiety by electroacupuncture

OBJECTIVE

To investigate whether the neuropsin pathway in the amygdala and stomach may participate in the development of anxiety-related gastric hypersensitivity, and whether electroacupuncture (EA) at the Zusanli acupoint could improve this condition by regulating such pathway in the rat model of functional dyspepsia (FD).

METHODS

A total of 48 SD rats were randomly divided into the control group, FD model group and FD + EA group (stimulation at Zusanli acupoint for 30 min daily for 7 consecutive days). Abdominal withdrawal reflex (AWR) score and open field test were used to evaluate visceral hypersensitivity and anxiety-like disorder, respectively. Electrical activity in the amygdala nucleus in each group was recorded by extracellular electrophysiology. Neuropsin and serpinb6 protein expressions in the amygdala and stomach were detected by Western blot.

RESULTS

AWR score in the FD group increased but did not differ after EA therapy than that in the contro group. Both the center square entries and center entries ratio in the FD group were lower than those in the control and FD + EA groups. The total number and frequency of amygdala nucleus discharges induced by gastric distension in the FD group were significantly higher than those in the control and FD + EA groups. Expression of neuropsin increased and that of serpinb6 decreased in the gastric mucosa and amygdale in the FD group, while no change was observed in gastric mucosa after EA therapy.

CONCLUSION

EA stimulation at the Zusanli acupoint may improve visceral hypersensitivity and anxiety in FD rats through the neuropsin/serpinb6 pathway.

Electrocardiographic changes in the acute hyperkalaemia produced by intragastric KCl load in rats

NEW FINDINGS

What is the central question of this study? This study presents a new model for studying the rapid onset of severe, acute hyperkalaemia in rats with intact kidney function by administering an intragastric KCl load. What is the main finding and its importance? This new model of intragastric KCl load produces a reliable and reproducible model for studying the rapid onset of severe, acute hyperkalaemia in rats with intact kidney function. We report unprecedented rapid changes (30 min) in ECG, blood pressure and various arterial blood analyses with this new model, providing a solid foundation for future experiments in this field.

ABSTRACT

A variety of animal models have been proposed to study hyperkalaemia, but most of them have meaningful limitations when the goal is to study the effect of potassium overload on healthy kidneys. In this study, we aimed to introduce a new approach for induction of hyperkalaemia in a reliable and reproducible animal model. We used intragastric administration of potassium chloride [KCl 2.3 M, 10 ml/(kg body weight)] to male Holtzman rats (300-350 g) to induce hyperkalaemia. The results showed that this potassium load can temporarily overwhelm the renal and extrarenal handling of this ion, causing an acute and severe hyperkalaemia that can be useful to study the effect of potassium imbalance in a variety of scenarios. Severe hyperkalaemia (>8 meqiv/l) and very profound ECG alterations, characterized by lengthening waves and intervals, were seen as early as 30 min after intragastric administration of KCl in rats. In addition, a transient increase in arterial blood pressure and time-dependent bradycardia were also seen after the KCl administration. No metabolic acidosis was present in the animals, and the potassium ion did not increase proportionally to chloride ion in the blood, leading to an increased anion gap. In conclusion, the results suggest that intragastric KCl loading is a reliable model to promote rapid and severe hyperkalaemia that can be used for further research on this topic.

The Phantom Satiation Hypothesis of Bariatric Surgery

The excitation of vagal mechanoreceptors located in the stomach wall directly contributes to satiation. Thus, a loss of gastric innervation would normally be expected to result in abrogated satiation, hyperphagia, and unwanted weight gain. While Roux-en-Y-gastric bypass (RYGB) inevitably results in gastric denervation, paradoxically, bypassed subjects continue to experience satiation. Inspired by the literature in neurology on phantom limbs, I propose a new hypothesis in which damage to the stomach innervation during RYGB, including its vagal supply, leads to large-scale maladaptive changes in viscerosensory nerves and connected brain circuits. As a result, satiation may continue to arise, sometimes at exaggerated levels, even in subjects with a denervated or truncated stomach. The same maladaptive changes may also contribute to dysautonomia, unexplained pain, and new emotional responses to eating. I further revisit the metabolic benefits of bariatric surgery, with an emphasis on RYGB, in the light of this phantom satiation hypothesis.

Ghrelin inhibits autonomic response to gastric distension in rats by acting on vagal pathway

Ghrelin is the only orexigenic peptide currently known and a potent prokinetic by promoting gastric motility but novel insights suggest that its role extends beyond satiety regulation. Whereas ghrelin was shown to provide somatic and colonic antinociception, its impact on gastric sensitivity is unknown even though stomach is a major ghrelin secreting tissue. Autonomic response to gastric mechanosensitivity was estimated by measuring blood pressure variation as a surrogate marker in response to gastric distension (GD) before and after ghrelin (or vehicle) administration. Involvement of spinal and vagal pathways in the ghrelin effect was studied by performing celiac ganglionectomy and subdiaphragmatic vagotomy respectively and by evaluating the expression of phosphorylated extracellular-regulated kinase 1/2 (p-ERK1/2) in dorsal root and nodose ganglia. Finally the phenotype of Ghrelin receptor expressing neurons within the nodose ganglia was determined by in situ hybridization and immunofluorescence. Ghrelin reduced blood pressure variation in response to GD except in vagotomized rats. Phosphorylated-ERK1/2 levels indicated that ghrelin reduced neuronal activation induced by GD in nodose ganglion. The effect of ghrelin on gastric mechanosensitivity was abolished by pre-treatment with antagonist [D-Lys³]-GHRP-6 (0.3 mg/kg i.v.). Immunofluorescence staining highlights the colocalization of Ghrelin receptor with ASIC3 and TRPV1 within gastric neurons of nodose ganglion. Ghrelin administration reduced autonomic response to gastric distension. This effect likely involved the Ghrelin receptor and vagal pathways.

Portal vein innervation underlying the pressor effect of water ingestion with and without cold stress

Water-induced pressor response appears mediated through the activation of transient receptor potential channel TRPV4 on hepatic portal circulation in animals. We sought to elucidate the mechanism of portal vein signaling in this response. Forty-five rats were divided into four groups: control rats without water ingestion (WI), control rats with WI, portal vein denervation rats with WI (PVDWI), and TRPV4 antagonist-treated rats with WI (anti-TRPV4WI). Cardiovascular responses were monitored throughout the experiments. Data analysis was performed using descriptive methods and spectral and cross-spectral analysis of blood pressure variability (BPV) and heart rate variability (HRV). Key results showed that at baseline (PreCS) before cold stress trial (CS), WI elicited robust pressor and tachycardia responses accompanied by spectral power changes, in particular, increases of low-frequency BPV (LFBPV) and very-LFBPV (VLFBPV), but decrease of very-low-frequency HRV. PVDWI, likewise, elicited pressor and tachycardia responses accompanied by increases of high-frequency BPV, high-frequency HRV, LFBPV, low-frequency HRV, and VLFBPV. When compared with WI at PreCS, WI at CS elicited pressor and tachycardia responses accompanied by increases of high-frequency BPV, LFBPV, and VLFBPV, whereas in WI, the CS-evoked pressor response and the accompanied LFBPV and VLFBPV increases were all tended augmented by PVDWI. When compared with WI and PVDWI at both PreCS and CS, however, anti-TRPV4WI attenuated their pressor responses and attenuated their increased LFBPV, VLFBPV, and very-low-frequency HRV. The results indicate that the portal vein innervation is critical for a buffering mechanism in splanchnic sympathetic activation and water-induced pressor response.

Laparoscopic fundoplication and new aspects of neural anatomy at the oesophagogastric junction

Background

In fundoplication, mobilization of the distal oesophagus and proximal stomach is essential to obtain a sufficient tension‐free intra‐abdominal oesophageal length for creation of an efficient antireflux barrier. Most surgical literature and anatomical illustrations do not describe nerve branches running from the diaphragm to the stomach. After observing small nerve branches at laparoscopic fundoplication, penetrating the left crus of the diaphragm lateral to the hiatus and apparently running into the stomach, an anatomical cadaver study was undertaken to identify the origin and target organ of these nerves.

Methods

Fifty‐three human cadavers (23 men, 30 women; age range 35–103 years) were dissected with special attention to the nerves that penetrate the left crus of the diaphragm. The entire course of these nerves was documented with standardized drawings and photos.

Results

Small nerve branches penetrating the diaphragm lateral to the left crus of the hiatus were found in 17 (32 per cent) of the 53 cadavers. In 14 of these 17 cadavers, one or two splanchnic nerve branches were identified, and in ten of the 17 the nerve branches were found to be phrenic nerves. In seven of these 17 cadavers, two different nerve branches were found and assigned to both splanchnic and phrenic nerves.

Conclusion

Nerves penetrating the left crus with splanchnic origin or phrenic origin have been identified. Their function remains unclear and their relationship to postfundoplication symptoms remains to be determined.

Hypertension as a Metabolic Disorder and the Novel Role of the Gut

Purpose of Review

Hypertension is related to impaired metabolic homeostasis and can be regarded as a metabolic disorder. This review presents possible mechanisms by which metabolic disorders increase blood pressure (BP) and discusses the importance of the gut as a novel modulator of BP.

Recent Findings

Obesity and high salt intake are major risk factors for hypertension. There is a hypothesis of “salt-induced obesity”; i.e., high salt intake may tie to obesity. Heightened sympathetic nervous system (SNS) activity, especially in the kidney and brain, increases BP in obese patients. Adipokines, including adiponectin and leptin, and renin-angiotensin-aldosterone system (RAAS) contribute to hypertension. Adiponectin induced by a high-salt diet may decrease sodium/glucose cotransporter (SGLT) 2 expression in the kidney, which results in reducing BP. High salt can change secretions of adipokines and RAAS-related components. Evidence has been accumulating linking the gastrointestinal tract to BP. Glucagon-like peptide-1 (GLP-1) and ghrelin decrease BP in both rodents and humans. The sweet taste receptor in enteroendocrine cells increases SGLT1 expression and stimulates sodium/glucose absorption. Roux-en-Y gastric bypass improves glycemic and BP control due to reducing the activity of SGLT1. Na/H exchanger isoform 3 (NHE3) increases BP by stimulating the intestinal absorption of sodium. Gastrin functions as an intestinal sodium taste sensor and inhibits NHE3 activity. Intestinal mineralocorticoid receptors also regulate sodium absorption and BP due to changing ENaC activity. Gastric sensing of sodium induces natriuresis, and gastric distension increases BP. Changes in the composition and function of gut microbiota contribute to hypertension. A high-salt/fat diet may disrupt the gut barrier, which results in systemic inflammation, insulin resistance, and increased BP. Gut microbiota regulates BP by secreting vasoactive hormones and short-chain fatty acids. BP-lowering effects of probiotics and antibiotics have been reported. Bariatric surgery improves metabolic disorders and hypertension due to increasing GLP-1 secretion, decreasing leptin secretion and SNS activity, and changing gut microbiome composition. Strategies targeting the gastrointestinal system may be therapeutic options for improving metabolic abnormalities and reducing BP in humans.

Summary

SNS, brain, adipocytes, RAAS, the kidney, the gastrointestinal tract, and microbiota play important roles in regulating BP. Most notably, the gut could be a novel target for treatment of hypertension as a metabolic disorder.

Vagal afferent activation suppresses systemic inflammation via the splanchnic anti-inflammatory pathway

Electrical stimulation of the vagus nerve (VNS) is a novel strategy used to treat inflammatory conditions. Therapeutic VNS activates both efferent and afferent fibers; however, the effects attributable to vagal afferent stimulation are unclear. Here, we tested if selective activation of afferent fibers in the abdominal vagus suppresses systemic inflammation. In urethane-anesthetized rats challenged with lipopolysaccharide (LPS, 60 µg/kg, i.v.), abdominal afferent VNS (2 Hz for 20 min) reduced plasma tumor necrosis factor alpha (TNF) levels 90 min later by 88% compared with unmanipulated animals. Pre-cutting the cervical vagi blocked this anti-inflammatory action. Interestingly, the surgical procedure to expose and prepare the abdominal vagus for afferent stimulation ('vagal manipulation') also had an anti-inflammatory action. Levels of the anti-inflammatory cytokine IL-10 were inversely related to those of TNF. Prior bilateral section of the splanchnic sympathetic nerves reversed the anti-inflammatory actions of afferent VNS and vagal manipulation. Sympathetic efferent activity in the splanchnic nerve was shown to respond reflexly to abdominal vagal afferent stimulation. These data demonstrate that experimentally activating abdominal vagal afferent fibers suppresses systemic inflammation, and that the efferent neural pathway for this action is in the splanchnic sympathetic nerves.

Gastric cooling and menthol cause an increase in cardiac parasympathetic efferent activity in healthy adult human volunteers

NEW FINDINGS

What is the central question of this study? How do gastric stretch and gastric cooling stimuli affect cardiac autonomic control? What is the main finding and its importance? Gastric stretch causes an increase in cardiac sympathetic activity. Stretch combined with cold stimulation result in an elimination of the sympathetic response to stretch and an increase in cardiac parasympathetic activity, in turn resulting in a reduction in heart rate. Gastric cold stimulation causes a shift in sympathovagal balance towards parasympathetic dominance. The cold-induced bradycardia has the potential to decrease cardiac workload, which might be significant in individuals with cardiovascular pathologies.

ABSTRACT

Gastric distension increases blood pressure and heart rate in young, healthy humans, but little is known about the effect of gastric stretch combined with cooling. We used a randomized crossover study to assess the cardiovascular responses to drinking 300 ml of ispaghula husk solution at either 6 or 37°C in nine healthy humans (age 24.08 ± 9.36 years) to establish the effect of gastric stretch with and without cooling. The effect of consuming peppermint oil capsules to activate cold thermoreceptors was also investigated. The ECG, respiratory movements and continuous blood pressure were recorded during a 5 min baseline period, followed by a 115 min post-drink period, during which 5 min epochs of data were recorded. Cardiac autonomic activity was assessed using time and frequency domain analyses of respiratory sinus arrhythmia to quantify parasympathetic autonomic activity, and corrected QT (QTc) interval analysis to quantify sympathetic autonomic activity. Gastric stretch only caused a significant reduction in QTc interval lasting up to 15 min, with a concomitant but non-significant increase in heart rate, indicating an increased sympathetic cardiac tone. The additional effect of gastric cold stimulation was significantly to reduce heart rate for up to 15 min, elevate indicators of cardiac parasympathetic tone and eliminate the reduction in QTc interval seen with gastric stretch only. Stimulation of gastric cold thermoreceptors with menthol also caused a significant reduction in heart rate and concomitant increase in the root mean square of successive differences. These findings indicate that gastric cold stimulation causes a shift in the sympathovagal balance of cardiac control towards a more parasympathetic dominant pattern.