Due to the constantly increasing hazard of styrene exposure and possible cocarcinogenesis in digestive tract with bilious acids, an experimental model of chronic exposure of stomach mucosa to styrene oxide [SO] with accompanying bilious reflux has been elaborated. In this study, 250 Buffalo rats were divided into four groups. The first experimental group E was fed with a control diet mixed with 0.25% sodium taurocholate [ST], and styrene oxide in vegetable oil, in concentration 200 mg/kg body weight. This was introduced into the stomach 3 times a week. The first control group C1 was fed with sodium taurocholate only, the second control group C2 was administered styrene oxide by gavage, and the third C3 received vegetable oil only. The experiment was carried out until natural death of the animals, and hence it has been completed after two years. The animals have been autopsied after death, and their organs have been taken for histologic examination. The results of stomach and forestomach examination have been then laid down to compare the frequency and intensity of occurring of particular features in groups, their coexistence, as well as the influence of survival upon their appearance. The results of this experiment show the potentializing effect of sodium taurocholate on the stomach carcinogenesis caused by styrene oxide. The influence of sodium taurocholate in the case of styrene oxide is not so strong as in the case of other carcinogens, what can result from the ability of styrene oxide, a non-polar compound, to penetrate the mucosa epithelium of the stomach and forestomach. In case of the carcinogens with a polar structure, occurring in the ionized form, the mucosa barrier becomes permeable only after it had been damaged by bile acids. The styrene dose, affecting dysplastic changes and carcinomas in stomach and forestomach in Buffalo rats, turned out to be a toxic dose, shortening the survival rate. The observed by us 5/138 cases of squamous carcinoma and 17/138 cases of dysplasia in the experimental group E have been accompanied by the 66/138 cases of papilla proliferation as well as by the acanthotic changes and basal layer hyperplasia in 38/138 and 52/138 cases, respectively.The results confirmed to the progression of the chemical carcinogenesis in rat's stomach, intensified by the activity of sodium taurocholate leading to carcinoma in the inflammatory changed mucosa via hyperplastic or dysplastic alterations. The results can be referred to ethiology and natural history of squamous esophageal carcinoma, and partially to Barrett esophagus with co-existing duodenal-gastro-esophageal reflux.

Keywords: styrene oxide, Bile Reflux, forestomach, carcinogenesis, Rat