Dibutyltin dichloride (DBTC) is a chemical used as a
polyvinyl carbonate stabilizer/catalyzer,
biocide in agriculture, antifouling agent in paint and fabric. DBTC induces an
acute pancreatitis flare through generation of
reactive oxygen species. Lewis-inbred rats received a single i.v. injection with either DBTC or vehicle. Spinal cord and dorsal root ganglia (DRG) were taken at the peak of
inflammation and processed for transcriptional profiling with a
cDNA microarray biased for rat brain-specific genes. In a second study, groups of animals with DBTC-induced
pancreatitis were treated with
endothelin (ET) receptor antagonists [ET-A (
BQ123) and ET-B
BQ788)]. Spontaneous
pain related mechanical and thermal
hypersensitivity were measured. Immunohistochemical analysis was performed using anti-ET-A and ET-B
antibodies on sections from pancreatic tissues and DRG of the T10-12 spinal segments.
RESULTS: Animals developed acute pancreatic
inflammation persisting 7-10 d as confirmed by pathological studies (
edema in parenchyma, loss of pancreatic architecture and islets, infiltration of inflammatory cells, neutrophil and mononuclear cells, degeneration, vacuolization and
necrosis of acinar cells) and the
pain-related behaviors (cutaneous secondary mechanical and thermal
hypersensitivity). Gene expression profile was different in the spinal cord from animals with
pancreatitis compared to the vehicle control group. Over 260 up-regulated and 60 down-regulated unique genes could be classified into 8 functional gene families: circulatory/acute phase/immunomodulatory; extracellular matrix; structural; channel/receptor/transporter; signaling transduction; transcription/translation-related;
antioxidants/chaperones/heat shock; pancreatic and other
enzymes. ET-1 was among the 52 candidate genes up-regulated greater than 2-fold in animals with pancreatic
inflammation and
visceral pain-related behavior. Treatments with the ET-A (
BQ123) and ET-B (BQ-788) antagonists revealed significant protection against inflammatory
pain related mechanical and thermal
hypersensitivity behaviors in animals with
pancreatitis (P < 0.05). Open field spontaneous behavioral activity (at baseline, day 6 and 30 min after
drug treatments (
BQ123,
BQ788) showed overall stable activity levels indicating that the drugs produced no undesirable effects on normal exploratory behaviors, except for a trend toward reduction of the active time and increase in resting time at the highest dose (300 μmol/L). Immunocytochemical localization revealed that expression of ET-A and ET-B receptors increased in DRG from animals with
pancreatitis.
Endothelin receptor localization was combined in dual staining with neuronal marker NeuN, and glia marker,
glial fibrillary acidic protein. ET-A was expressed in the cell bodies and occasional nuclei of DRG neurons in naïve animals. However, phenotypic expression of ET-A receptor was greatly increased in neurons of all sizes in animals with
pancreatitis. Similarly, ET-B receptor was localized in neurons and in the satellite glia, as well as in the Schwann cell glial myelin sheaths surrounding the axons passing through the DRG.
CONCLUSION: