Ralph E. Watson

Enteric glia mediate neuron death in colitis through purinergic pathways that require connexin-43 and nitric oxide.

Background & Aims The concept of enteric glia as regulators of intestinal homeostasis is slowly gaining acceptance as a central concept in neurogastroenterology. Yet how glia contribute to intestinal disease is still poorly understood. Purines generated during inflammation drive enteric neuron death by activating neuronal P2X7 purine receptors (P2X7R); triggering adenosine triphosphate (ATP) release via neuronal pannexin-1 channels that subsequently recruits intracellular calcium ([Ca2+]i) in surrounding enteric glia. We tested the hypothesis that the activation of enteric glia contributes to neuron death during inflammation. Methods We studied neuroinflammation in vivo using the 2,4-dinitrobenzene sulfonic acid model of colitis and in situ using whole-mount preparations of human and mouse intestine. Transgenic mice with a targeted deletion of glial connexin-43 (Cx43) [GFAP::CreERT2+/−/Cx43f/f] were used to specifically disrupt glial signaling pathways. Mice deficient in inducible nitric oxide (NO) synthase (iNOS−/−) were used to study NO production. Protein expression and oxidative stress were measured using immunohistochemistry and in situ Ca2+ and NO imaging were used to monitor glial [Ca2+]i and [NO]i. Results Purinergic activation of enteric glia drove [Ca2+]i responses and enteric neuron death through a Cx43-dependent mechanism. Neurotoxic Cx43 activity, driven by NO production from glial iNOS, was required for neuron death. Glial Cx43 opening liberated ATP and Cx43-dependent ATP release was potentiated by NO. Conclusions Our results show that the activation of glial cells in the context of neuroinflammation kills enteric neurons. Mediators of inflammation that include ATP and NO activate neurotoxic pathways that converge on glial Cx43 hemichannels. The glial response to inflammatory mediators might contribute to the development of motility disorders.

Role of sensory nervous system vasoactive peptides in hypertension

The goal of the present research was to elucidate the roles and mechanisms by which the sensory nervous system, through the actions of potent vasodilator neuropeptides, regulates cardiovascular function in both the normal state and in the pathophysiology of hypertension. The animal models of acquired hypertension studied were deoxycorticosterone-salt (DOC-salt), subtotal nephrectomy-salt (SN-salt), and Nomega-nitro-L-arginine methyl ester (L-NAME)-induced hypertension during pregnancy in rats. The genetic model was the spontaneously hypertensive rat (SHR). Calcitonin gene-related peptide (CGRP) and substance P (SP) are potent vasodilating neuropeptides. In the acquired models of hypertension, CGRP and SP play compensatory roles to buffer the blood pressure (BP) increase. Their synthesis and release are increased in the DOC-salt model but not in the SN-salt model. This suggests that the mechanism by which both models lower BP in SN-salt rats is by increased vascular sensitivity. CGRP functions in a similar manner in the L-NAME model. In the SHR, synthesis of CGRP and SP is decreased. This could contribute to the BP elevation in this model. The CGRP gene knockout mouse has increased baseline mean arterial pressure. The long-term synthesis and release of CGRP is increased by nerve growth factor, bradykinin, and prostaglandins and is decreased by alpha2-adrenoreceptor agonists and glucocorticoids. In several animal models, sensory nervous system vasoactive peptides play a role in chronic BP elevation. In the acquired models, they play a compensatory role. In the genetic model, their decreased levels may contribute to the elevated BP. The roles of CGRP and SP in human hypertension are yet to be clarified.

Do race and gender influence the use of invasive procedures

OBJECTIVE: To assess the influence of race and gender on the use of invasive procedures in patients with acute myocardial infarction (AMI) in community hospitals.DESIGN: Prospective, observational.SETTING: Five mid-Michigan community hospitals.PATIENTS: All patients (838) identified with AMI between January 1994 and April 1995 in 1 of these hospitals.MEASUREMENTS AND MAIN RESULTS: After adjusting for age, hospital of admission, insurance type, severity of AMI, and comorbidity, using white men as the reference group, the rate of being offered cardiac catheterization (CC) was 0.88 (95% confidence interval [CI], 0.60 to 1.29) for white women; 0.79 (95% CI, 0.41 to 1.50) for black men; and 1.14 (95% CI, 0.53 to 2.45) for black women. Among patients who underwent CC, after also adjusting for coronary artery anatomy, the rate of being offered angioplasty, using white men as the reference group, was 1.22 (95% CI, 0.75 to 1.98) for white women; 0.61 (95% CI, 0.29 to 1.28; P=.192) for black men; and 0.40 (95% CI, 0.14 to 1.13) for black women. The adjusted rate of being offered bypass surgery was 0.47 (95% CI, 0.24 to 0.89) for white women; 0.36 (95% CI, 0.12 to 1.06) for black men; and 0.37 (95% CI, 0.11 to 1.28) for black women.CONCLUSIONS: Our study shows that white women are less likely than white men to be offered bypass surgery after AMI. Although black men and women with AMI are less likely than white men to be offered percutaneous transluminal coronary angioplasty or coronary artery bypass grafting in both unadjusted and adjusted analyses, these findings did not reach statistical significance. Our study is limited in power due to the small number of blacks in the sample.

Experimental animal models of hypertension

Hypertension (HTN) and cardiovascular disease are the most common causes of death in developed countries. The use of experimental animal models of HTN has provided valuable information regarding many aspects of HTN, including etiology, pathophysiology, complications, and treatment. Because the etiology of HTN is heterogeneous, many experimental animal models have been developed to mimic the many facets of human HTN. The choice of animal model will be determined by the research question, monetary limitations, and technical expertise. The categories of models of HTN are: renovascular, renal parenchymal, pharmacologically induced, environmentally induced, and genetic. There are considerable differences between HTN in animals and humans, including differences in homeostatic mechanisms and pathophysiology; therefore, a thorough understanding of the animal models and rigorous analysis is required before extrapolating the finding in animals to humans.

Case Report: Transverse Colon Volvulus in a Patient With Clostridium Difficile Pseudomembranous Colitis

Sixty-eight cases of transverse colon volvulus have been reported in the literature. The authors report the first case of transverse colon volvulus in association with Clostridium difficile pseudomembranous colitis, with a review of the available literature. It is possible that the acute inflammation of the colonic mucosa, which occurred from the pseudomembranous colitis in this patient, contributed to the development of volvulus. Further studies are needed to explore the role of mucosal inflammation in the occurrence of volvulus.

Hypertension in Asian/Pacific Island Americans

Asian/Pacific Islander Americans (APIAs) are the fastest growing population in the United States by percentage. Hypertension is common and increases cardiovascular risk to a great extent in this population. The medical problems of this group are being increasingly encountered by US physicians. Many gene mutations associated with hypertension are more common in Asians. The significance of these polymorphisms in the pathogenesis of hypertension in APIAs is unclear. The percentage of APIAs who are aware, treated, and controlled is small. There may be some differences in the responses to antihypertensive medications between APIAs and whites. The results of human studies on the effect of drinking of tea on blood pressure in different groups are conflicting. Cough associated with angiotensin‐converting enzyme inhibitor therapy may be more common in APIAs than in whites. There is a need for more education of APIAs regarding hypertension and for more effective treatment of hypertension by the physicians caring for this population.

Preferential Myosin Heavy Chain Isoform B Expression May Contribute to the Faster Velocity of Contraction in Veins versus Arteries

Smooth muscle myosin heavy chains occur in 2 isoforms, SMA (slow) and SMB (fast). We hypothesized that the SMB isoform is predominant in the faster-contracting rat vena cava compared to thoracic aorta. We compared the time to half maximal contraction in response to a maximal concentration of endothelin-1 (ET-1; 100 nM), potassium chloride (KCl; 100 mM) and norepinephrine (NE; 10 µM). The time to half maximal contraction was shorter in the vena cava compared to aorta (aorta: ET-1 = 235.8 ± 13.8 s, KCl = 140.0 ± 33.3 s, NE = 19.8 ± 2.7 s; vena cava: ET-1 = 121.8 ± 15.6 s, KCl = 49.5 ± 6.7 s, NE = 9.0 ± 3.3 s). Reverse-transcription polymerase chain reaction supported the greater expression of SMB in the vena cava compared to aorta. SMB was expressed to a greater extent than SMA in the vessel wall of the vena cava. Western analysis determined that expression of SMB, relative to total smooth muscle myosin heavy chains, was 12.5 ± 4.9-fold higher in the vena cava compared to aorta, while SMA was 4.9 ± 1.2-fold higher in the aorta than vena cava. Thus, the SMB isoform is the predominant form expressed in rat veins, providing one possible mechanism for the faster response of veins to vasoconstrictors.

Changes in Rates of Beta-blocker Use in Community Hospital Patients with Acute Myocardial Infarction

OBJECTIVE: To examine changes in the rate of beta-blocker (BB) use at admission, in hospital, and at discharge between 1994 and 1995 (MICH I) and 1997 (MICH II) in patients with acute myocardial infarction (AMI).DESIGN: Comparison of two prospectively enrolled cohorts.SETTING: Five mid-Michigan community hospitals.PATIENTS: We studied 287 MICH I patients and 121 MICH II patients with AMI who had no contraindications to BB use from cohorts of consecutively admitted cases of AMI (814 in MICH I; 500 in MICH II).RESULTS: Prescription of BBs to ideal patients with AMI increased in patients with previous history of myocardial infarction on arrival at the hospital (12.5% vs 36.0%; P=.01), in hospital (47.0% vs 76%; P<.01), and at discharge (34.0% vs 61.9%; P<.01). Neither race nor gender was a predictor of BB use. Younger age predicted BB prescription at discharge (odds ratio [OR], 2.07; 95% confidence interval [CI], 1.32 to 3.23). Later study cohort was the most important predictor of BB use in hospital (OR, 3.4; 95% CI, 2.09 to 5.25).CONCLUSION: BB use improved dramatically over the study period, but additional work is needed to improve use of BB after discharge and among elderly patients with AMI.

Ammonia modifies enteric neuromuscular transmission through glial γ-aminobutyric acid signaling

Impaired gut motility may contribute, at least in part, to the development of systemic hyperammonemia and systemic neurological disorders in inherited metabolic disorders, or in severe liver and renal disease. It is not known whether enteric neurotransmission regulates intestinal luminal and hence systemic ammonia levels by induced changes in motility. Here, we propose and test the hypothesis that ammonia acts through specific enteric circuits to influence gut motility. We tested our hypothesis by recording the effects of ammonia on neuromuscular transmission in tissue samples from mice, pigs, and humans and investigated specific mechanisms using novel mutant mice, selective drugs, cellular imaging, and enzyme-linked immunosorbent assays. Exogenous ammonia increased neurogenic contractions and decreased neurogenic relaxations in segments of mouse, pig, and human intestine. Enteric glial cells responded to ammonia with intracellular Ca2+ responses. Inhibition of glutamine synthetase and the deletion of glial connexin-43 channels in hGFAP::CreERT2+/-/connexin43f/f mice potentiated the effects of ammonia on neuromuscular transmission. The effects of ammonia on neuromuscular transmission were blocked by GABAA receptor antagonists, and ammonia drove substantive GABA release as did the selective pharmacological activation of enteric glia in GFAP::hM3Dq transgenic mice. We propose a novel mechanism whereby local ammonia is operational through GABAergic glial signaling to influence enteric neuromuscular circuits that regulate intestinal motility. Therapeutic manipulation of these mechanisms may benefit a number of neurological, hepatic, and renal disorders manifesting hyperammonemia.NEW & NOTEWORTHY We propose that local circuits in the enteric nervous system sense and regulate intestinal ammonia. We show that ammonia modifies enteric neuromuscular transmission to increase motility in human, pig, and mouse intestine model systems. The mechanisms underlying the effects of ammonia on enteric neurotransmission include GABAergic pathways that are regulated by enteric glial cells. Our new data suggest that myenteric glial cells sense local ammonia and directly modify neurotransmission by releasing GABA.