Effect of thyroid hormones on basal and stimulated gastric acid secretion due to histamine, carbachol, and pentagastrin in rat (an in vitro study)

Although thyroid hormones are known to influence acid secretion, but exact mechanisms are not fully understood. So, in this experimental study carbachol, histamine, and pentagastrin were used to stimulate acid secretion in isolated stomach of hypo- and hyperthyroid rats and data were compared with controls. Each group consisted of 8 N-Mari rats from both sexes weighing 246 ± 5 g. Hypo- and hyperthyroid states were induced by administration of methimazole (500 mg/l) thyroxine (500 µg/l) in drinking water respectively. All animals were deprived of food 24 h before the experiments, but they accessed to water ad libitum. After general anesthesia with sodium thiopental (50 mg/kg of body weight, i.p.), celiotomy was done immediately. The end of esophagus was tied and a silicon tube (2-2.5 mm) was entered the stomach via a hole in the second portion of the duodenum. Then, it was tied in the pyloric region. After these procedures, the esophagus was cut proximal to the tied portion and the second part of duodenum was also cut. Then, the stomach was removed and put in a cold serous solution. After washing the serosal and mucosal surfaces by serous and mucosal solutions respectively, the stomach was transferred to a tissue bath containing warm serous solution (40 ml, 37 °C). Acid secretion following carbachol, histamine, and pentagastrin administration was measured by washout technique and automatic titrator in the hypo- and hyperthyroid and control groups. Furthermore, some dose-response experiments with different doses of pentagastrin (30, 60, 90, and 120 µg/kg), histamine (50, 100, 150, and 200 µM), and carbachol (50, l00, and 200 µM) were performed to clarify the mechanism of thyroid hormones effect on acid secretion. The results showed that basal and histamine (100 µM)-stimulated secretion in hypo and hyperthyroid groups significantly decreased and increased respectively compared to control ones (p<0.0001). Basal and carbachol (100 µM)-stimulated acid secretion significantly decreased in hypothyroid group, while the secretion showed a significant increase in hyperthyroid group compared to control group (p<0.0001). The results of TSH and T4 measurement showed that increased or decreased thyroid function can significantly affect gastric acid secretion following histamine, carbachol, and pentagastrin in rats. Taken together, it can be concluded that effects of thyroid hormones may not be mediated through changing cholinergic, gastrin, and histamine receptors. It is also possible that thyroid hormones exert their effects on the number or size of the secretory cells of the stomach.