Adrenergic signaling mediates mechanical hyperalgesia through activation of P2X3 receptors in primary sensory neurons of rats with chronic pancreatitis

Abstract

. Adrenergic signaling mediates mechanical hyperalgesia through activation of P2X3 receptors in primary sensory neurons of rats with chronic pancreatitis. Am J Physiol Gastrointest Liver Physiol 308: G710 -G719, 2015. First published January 29, 2015; doi:10.1152/ajpgi.00395.2014.-The mechanism of pain in chronic pancreatitis (CP) is poorly understood. The aim of this study was designed to investigate roles of norepinephrine (NE) and P2X receptor (P2XR) signaling pathway in the pathogenesis of hyperalgesia in a rat model of CP. CP was induced in male adult rats by intraductal injection of trinitrobenzene sulfonic acid (TNBS). Mechanical hyperalgesia was assessed by referred somatic behaviors to mechanical stimulation of rat abdomen. P2XR-mediated responses of pancreatic dorsal root ganglion (DRG) neurons were measured utilizing calcium imaging and whole cell patch-clamp-recording techniques. Western blot analysis and immunofluorescence were performed to examine protein expression. TNBS injection produced a significant upregulation of P2X3R expression and an increase in ATP-evoked responses of pancreatic DRG neurons. The sensitization of P2X3Rs was reversed by administration of ␤-adrenergic receptor antagonist propranolol. Incubation of DRG neurons with NE significantly enhanced ATPinduced intracellular calcium signals, which were abolished by propranolol, and partially blocked by protein kinase A inhibitor H-89. Interestingly, TNBS injection led to a significant elevation of NE concentration in DRGs and the pancreas, an upregulation of ␤ 2-adrenergic receptor expression in DRGs, and amplification of the NE-induced potentiation of ATP responses. Importantly, pancreatic hyperalgesia was markedly attenuated by administration of purinergic receptor antagonist suramin or A317491 or ␤ 2-adrenergic receptor antagonist butoxamine. Sensitization of P2X3Rs, which was likely mediated by adrenergic signaling in primary sensory neurons, contributes to pancreatic pain, thus identifying a potential target for treating pancreatic pain caused by inflammation. chronic pancreatitis; dorsal root ganglion; purinergic receptors; norepinephrine; protein kinase A CHRONIC PANCREATITIS (CP) is a progressive inflammatory disorder characterized by repeated attacks of abdominal pain, fibrosis, and destruction of the glandular pancreas (15,29,39). Pain is a cardinal feature of CP, featured as burning, intermittent, and shooting pain (13). It is, not only the most frequent and dominant symptom of patients with CP, but also the most difficult to treat (1,3,22,35). Our lack of knowledge about what causes pain in pancreatitis has been a serious obstacle to treatment on these patients, with pain frequently relapsing or persisting (1, 31). Basic research of pancreatic nerves and experimental human pain studies have provided evidence that pain processing is abnormal in these patients and in many conditions resembles that seen in neuropathic pain disorders (34). Despite much speculation, little is known about the detailed pathophysiology of pain in ...

Differences in the Antinociceptive Effects and Binding Properties of Propranolol and Bupranolol Enantiomers

“…32 Of course, this is not the only explanation because hypersensitivity resulting from the sensitization of P2X2/3 receptors is also reversed by b-AR blockade. 63 Although propranolol and bupranolol are sympatholytic drugs, we do not believe that these drugs are important only for sympathetically maintained pain syndromes such as complex regional pain syndrome. The R-enantiomers of both compounds were associated with greater side effects and lethality.…”

Acute Effects of Transforming Growth Factor-β1 on Neuronal Excitability and Involvement in the Pain of Rats with Chronic Pancreatitis

“…19,20 Protein extracts from DRGs or pancreas were loaded onto a 15% Tris-HCl SDS-PAGE gel (Bio-Rad, Hercules, CA, USA). After electrophoresis, proteins were electrotransferred onto 0.22 μm polyvinyldifluoride membrane (Millipore, Billerica, MA, USA) at 200 mA for 2 hours at 4°C.…”

“…4,20 The filament at the force of 10 g (North Coast Medial Inc, San Jose, CA, USA) was applied to the designated abdominal area 10 times each for 1-2 seconds, with a 10-second interval between applications. A response was considered positive when the rat raised its belly.…”

“…20 Recordings were performed by the program MetaFlour (Molecular Device, Sunnyvale, CA, USA). The ratio of fluorescence signal measured at 340 nm, divided by the fluorescence signal measured at 380 nm, was used as an indicator for intracellular calcium mobilization.…”

Persistent Catechol-O-methyltransferase–dependent Pain Is Initiated by Peripheral β-Adrenergic Receptors

“…β 2 ARs are located on peripheral terminals 33-37 and cell bodies 38-40 of primary afferent nociceptors; keratinocytes; 41-43 immune cells; 44-47 and adipocytes 48 in the periphery and neurons 49,50 and glial cells 51 in the central nervous system. β 3 ARs are located on primary afferent nociceptors, 52 adipocytes 48 and immune cells 45,46 in the periphery and noradrenergic neurons in brain.…”