DELAYED HEALING OF ACETIC ACID-INDUCED ULCERATION IN THE STOMACH OF LEAD-EXPOSED RATS

Abstract

Reported cases of environmental lead exposure and its effects on the health of humans and livestock are on the increase globally. Lead affects many biological systems leading to death if it is beyond acceptable limits. Previous reports have shown that experimental lead exposure predisposes the stomach to gastric ulceration. However, there is paucity of information on whether lead will interfere with the healing of ulcers in the gastrointestinal tract. In this study, the effects of chronic lead exposure on healing of gastric ulceration in rats were investigated. Two hundred and forty male albino Wistar rats (80-100 g) were randomly divided into control (tap water), low and high dose lead acetate (100 ppm and 5,000 ppm respectively, p.o.) groups of 80 rats each. Twenty weeks post- treatment, the plasma levels of lead were estimated by atomic absorption spectrophotometry. Ulcers were induced in the stomach of rats by serosal application of 60% acetic acid solution. The following indices of ulcer healing were determined in five rats per group on days 7, 14 and 21 post–induction: ulcer area by planimetry, ulcer depth and width by histomorphometry, tissue regeneration and Goblet Cell Count (GCC) by histology and gastric acid secretion by continuous perfusion method. Lipid peroxidation and white blood cell counts were determined by spectrophotometry and haemocytometry respectively. Apoptotic cells of gastric epithelium in ulcer margins were detected by Terminal deoxynucleotidyl-transferase-mediated dUTP Nick-End Labeling (TUNEL) assay. Data were analysed using descriptive statistics and Student’s t-test at p=0.05. In the control animals, the ulcer area was 7.9±0.1mm² by day 7 and 4.8±0.1 mm² by day 14. Lead exposure significantly increased ulcer area for low (10.0±0.4mm² and 8.0±0.4mm²) and high (14.4±0.2mm² and 10.5±0.3mm²) doses respectively. Histomorphometry revealed increased ulcer width (120.8%) in the high lead group when compared with control (100%) on day 14. Histology revealed gastric ulceration in all groups on day 7 with presence of inflammatory cells at ulcer bed. By day 14, marked reduction in the inflammatory cells and greater fibroblast proliferation were observed in control compared with the treated groups. Basal acid secretion reduced over the healing period at a lower rate in the treated groups (30.4% for low, 40.0% for high lead groups) when compared with control (60.5%). Compared with control (44.2±2.0 and 55.2±1.8/unit area on days 7 and 14), lead exposure decreased GCC during healing in treated groups (32.8±0.9 and 33.2±0.9 for low lead and 33.8±1.2 and 35.6±1.2 for high lead) for the same days. The reduction in neutrophil/lymphocyte ratio accompanying healing was highest in the control (39.0%) and lowest in high lead dose (2.7%). Lipid peroxidation was significantly higher in high lead exposed rats (20.5±0.3 µmol/mg protein) compared with control (5.4±0.2 µmol/mg protein) on day 21. Apoptotic cell counts were increased in the low (112.3% and 53.8%) and high lead exposed rats (349.3% and 143.6%) compared with control values on days 7 and 14 respectively. Exposure of rats to lead delayed ulcer healing via increased gastric acidity, oxidative stress, gastric epithelial cell apoptosis and decreased mucus production. Keywords: Lead exposure, acetic acid-induced ulcer, gastric epithelial cell apoptosis, gastrointestinal inflammation. Word count: 499