| Abstract|| |
Background/Aims: Paraoxon, an organophosphate metabolite of the insecticide parathion inhibits the enzyme, acetylcholinesterase (Achase). Organophosphates affect the heart, visual system, nervous system and muscles. In this present study, we investigate the effects of the chronic consumption of paraoxon on gastric acid and pepsin secretion in N-mari rats. Materials and Methods: This study was performed from April 2003 to May 2004 in the Physiology department of Baghiatalah University of Medical Sciences, Tehran, Iran. It was performed on three groups of female N-mari rats (10 /group) each weighing 200-250 g. The first group received 0.05 mg/kg/day paraoxon subcutaneously for one month. The second group received the same chronic doses of ethyl alcohol (96%) (solvent of paraoxon) and the third group (control) received no drugs. After tracheostomy and laparatomy, gastric secretions were collected with a tube via the duodenum. Pentagastrin (25 µg/kg, i.p.) was used as a gastric stimulator. Acid and pepsin secretions were measured by titration and the Anson method, respectively. The stages of the measurements were basal (first and second), stimulated and returned-basal. Results: Basal acid secretion in the paraoxon group was greater than those in the alcohol and control groups (14.61 ± 1.46, 7.18 ± 0.28 and 7.88 ± 0.26 µmol/15 min, respectively, P < 0.001)). Although pentagastrin-stimulated acid secretion in all the three groups was greater than that of the basal state, there were no significant differences among the three groups. Basal pepsin secretions in the paraoxon group were greater than those in the alcohol and control groups (2.97 ± 0.32, 1.19 ± 0.25 and 0.55 ± 0.06 µg/15 min, respectively). Pentagastrin-stimulated pepsin secretion in the paraoxon group was significantly greater than those in the alcohol and control groups (3.22 ± 0.38, 2.22 ± 0.46 and 1.09 ± 0.66 µg/15 min, respectively, P < 0.001). Conclusion: Chronic exposure to paraoxon results in the increased secretion of gastric acid and pepsin.
Keywords: Pepsin, gastric secretion, paraoxon, organophosphate
|How to cite this article:|
Rafsanjani FN, Ardakani ZV, Vahedian J, Moradi M, Attar AF. The effect of chronic consumption of paraoxon on basal and pentagastrin-stimulated gastric acid and pepsin secretion in rats. Saudi J Gastroenterol 2007;13:172-5
|How to cite this URL:|
Rafsanjani FN, Ardakani ZV, Vahedian J, Moradi M, Attar AF. The effect of chronic consumption of paraoxon on basal and pentagastrin-stimulated gastric acid and pepsin secretion in rats. Saudi J Gastroenterol [serial online] 2007 [cited 2019 Aug 21];13:172-5. Available from: http://www.saudijgastro.com/text.asp?2007/13/4/172/36747
While paraoxon inhibits acetylcholine (ACh)-induced nicotinic receptor stimulation, it acts as an agonist at the human M3 muscaranic receptor. Many insecticides, pesticides and nerve agents are organophosphates that are toxic esters of phosphoric acid.  After absorption through the skin, mucosal membranes, respiratory or digestive systems and reaching the bloodstream, organophosphates are distributed throughout the body.  Due to the effects on nicotinic and muscarinic receptors, organophosphates inhibit the enzyme, acetylcholinesterase and cause salivation, lacrimation, vomiting, urinary and fecal incontinence, severe muscle pain, neurological and respiratory disorders.  Previous studies examining the effects of organophosphates on the heart and visual system have shown that they decrease the acetylcholine receptors in the heart and disturb the visual system. ,
Moreover, it has been observed that organophosphates poisoning leads to acute pancreatitis and delayed neuropathy. , There are no reports in literature describing the effects of organophosphates on the digestive system, except for the superficial reports on the occurrence of nausea and vomiting after exposure to organophosphates.  However, our clinical experiences showed that gastrointestinal (GI)-related symptoms such as heartburn and maldigestion occurred more frequently in the users of organophosphate insecticides and pesticides. The dearth of information regarding organophosphate toxicity as well as the common use of organophosphate pesticides and insecticides in Iran prompted us to conduct this preliminary study to examine the effects of paraoxon toxicity on the digestive system in N-mari rats.
| Materials and Methods|| |
This study was conducted on female N-mari rats, each weighing 200-250 g, and subjected to 12 h dark / 12 h light cycles and a temperature of 25 ± 2ºC. All the procedures were approved by the Institutional Animal Care and Research Committee at the Baghiatalah University of Medical Sciences. The animals were fed with standard food and were classified into the following three groups ( n = 10):
- Experimental (paraoxon group): This group received 0.5 mg/kg paraoxon subcutaneously daily for one month. 
- Alcohol group: This group received 0.05 mg/kg ethyl alcohol (96%; solvent for paraoxon) subcutaneously daily for one month.
- Control group: This group did not receiving any drugs.
The rats were fasted for 24 h before the experiments, but had free access to water. , They were anaesthetized by an intraperitoneal injection of sodium thiopental (50 mg/kg b.w.) before performing tracheostomy wherein the cervical esophagus was ligated using a tie . , Subsequently, laparatomy was performed via a midline abdominal incision and a silicon tube with an external diameter of 2.5 mm was introduced into the stomach via the duodenum and was fixed with a tie.
Residual gastric secretions were removed by performing cleansing lavage several times with 1 ml of normal saline (T = 37ºC) and allowed to stay for 30 min to reach a steady state. , Basal gastric secretions were collected twice at a 15-min intervals by using the washout technique. , The washout technique consisted of introducing the first 1 ml of normal saline solution into the stomach and then another 1 ml of normal saline after 15 min to remove all of the gastric contents.
About 25 µg/kg of pentagastrin (Sigma Co.) was administered intraperitoneally as a stimulant so that gastric secretions could be collected after 15 min in the presence of pentagastrin. After stimulant withdrawal and return to the basal state, gastric secretions were collected twice, at an interval of 15 min. In all the states (basal, stimulated and returning to the basal), 1 ml of sample was used for acid output determination by the titrator instrument (DIN, Germany, 0.02 ml) using sodium hydroxide 0.01 N. Another 1 ml of sample was used for pepsin determination by the modified Anson method using hemoglobin as substrate. , Rats were euthanized by administering high doses of an anesthetic. All the data are expressed as the mean ± SE and ANOVA was utilized for the statistical analysis. Multiple comparisons were made using Tukey's procedure (post hoc analysis) considering P < 0.05 to be statistically significant.
| Results|| |
The first and second basal acid secretions (collected at 15-min intervals) were significantly higher in the rats in the paraoxon group (14.61 ± 1.46 and 13.5 ± 1.85 µmol/15 min) than those in the alcohol (7.18 ± 0.28 and 6.3 ± 0.32 µmol/15 min) and control (7.88 ± 0.26 and 7.26 ± 0.26 µmol/15 min) groups; P < 0.001 [Figure - 1]. Fifteen minutes after the administration of pentagastrin, acid secretions in the rats in the paraoxon, alcohol and control groups were 16.55 ± 0.52, 14.53 ± 0.64 and 16.48 ± 0.53 µmol/ 15 min, respectively. Although these were higher than the basal state, there were no significant differences in the pentagastrin-stimulated acid secretions in the rats of the paraoxon, alcohol and control groups [Figure - 1].
In the first 15 min of returning to the basal state, there were no significant differences in the acid secretions in the rats of the control, paraoxon and alcohol groups. However, after 30 min of returning to the basal state, acid secretions in the rats of the paraoxon group were found to be significantly greater than those in the rats of the control and alcohol groups ( P < 0.05), although the acid secretions in the control and alcohol-treated rats were not significantly different at this time,. The pepsin secretion was significantly greater in the basal state in rats of the paraoxon group (2.97 ± 0.32 µg/15 min) than in the rats of the alcohol (1.19 ± 0.25 µg/ 15 min) and control groups, (0.55 ± 0.06 µg/15 min), P < 0.001 [Figure - 2]. After the administration of pentagastrin, pepsin secretions in the rats of the paraoxon, alcohol and control groups were 3.22 ± 0.38, 2.22 ± 0.46 and 1.09 ± 0.06 µg/15 min, respectively. Although the increase was significantly more evident in the paraoxon group than in the control group ( P = 0.001), there were no significant differences in the pentagastrin-induced secretions in rats of the control and alcohol groups and also the alcohol and paraoxon groups [Figure - 2]. After 15 and 30 min of returning to the basal state, pepsin secretions in rats of the paraoxon group were higher than those in the control group ( P < 0.05 and P < 0.05 ). However, there was no significant difference between the returned-to-basal pepsin secretions in the rats of the paraoxon and alcohol groups [Figure - 2].
| Discussion|| |
This study sought to examine the effects of paraoxon toxicity on the digestive system in N-mari rats. To achieve this, gastric acid and pepsin secretions with and without stimulation by pentagastrin were measured in rats receiving nothing (control), paraoxon or alcohol. It was found that gastric secretions (acid and pepsin) in rats exposed to paraoxon were higher than those in alcohol-treated and control rats; there was no difference in the secretions in the rats of the last two groups.
A possible mechanism that could explain the increased gastric secretions is that the consumption of paraoxon can either alter the number, activity and sensitivity of parietal and chief cells in the stomach or increase the number, activity or sensitivity of acetylcholine receptors in parietal and chief cells. Another explanation is that paraoxon may decrease the amount and activity of acetyl cholinesterase and consequently the acid and pepsin secretion. Previous studies have shown that in some tissues such as the heart tissue organophosphates lead to various disorders by decreasing the number of ACh receptors,  On the other hand, our findings suggest that paraoxon may increase the activity and number of ACh receptors in the stomach. This contradiction may be explained by considering the fact that the heart is a skeletal muscle, whereas acid and pepsin secretions are released from gastric epithelial cells, which have different receptor types.
After the use of pentagastrin, acid and pepsin secretions showed a significant increase in paraoxon-treated rats as compared with those in the alcohol and control groups. Pentagastrin is a pentapeptide and its synthetic form being similar to gastrin, it can bind to the gastrin receptor (CCK-B) in parietal and enterochromaffin cells in the stomach and initiate subsequent effects. ,, Moreover, it is known that gastrin can bind to its receptors to increase the acid/pepsin secretion by increasing the Ca ++ concentrations in the parietal and acid-producing cells. ,, After stimulation with pentagastrin, the acid secretions did not increase in the paraoxon-treated rats as much as they did in the rats of the alcohol and control groups.
After the administration of pentagastrin, pepsin secretion in the paraoxon group was significantly greater than that in the control group. However, there were no significant differences between the pepsin secretions in the rats of the paraoxon and alcohol groups and also between those in the alcohol and control groups. As stated above, since the pepsin secretion was already high in paraoxon-treated rats, its further increase due to pentagastrin stimulation may have plateaued off in rats of the paraoxon group in comparison to the alcohol and control groups. In conclusion, chronic exposure to paraoxon results in increased gastric acid and pepsin secretions. Further studies are warranted in order to clarify the involved mechanisms underlying the increase in gastric secretions due to chronic paraoxon exposure. Moreover, this study has highlighted the need for extreme care in those whose jobs necessitate chronic exposure to pesticides and insecticides containing organophosphates (for example, farmers).
| Acknowledgments|| |
We would like to thank the Physiology Department of Baghiatalah University of Medical Sciences. We are indebted to Dr. Ali Khoshbaten and Hasan Ghoshuni for their cooperation in this research.
| References|| |
|1.||Gunderson CH, Lehmann CR, Sidell FR, Jabbari B. Nerve agents: A review. Neurology 1992;42:946-50. [PUBMED] |
|2.||Cynthia KA. Organophosphates and carbamates. In : Ford, Delaney, Ling, Erikson editors. Clinical toxicology. W.B. Saunders Co: Philadelphia; 2001. p. 819-21. |
|3.||Kubinec J, Vrana KE, Roskoski R Jr. Paraoxon-induced decrease in the muscarinic acetylcholine receptor content in rat heart. Eur J Pharmacol 1987;136:295-301. [PUBMED] |
|4.||Boyes WK, Tandon P, Barone SJ, Padilla S. Effects of organophosphates on the visual system of rats. J Appl Toxial 1994;14:135-43. |
|5.||Hsiao CT, Rang CC, Deng JF, Bullard MJ, Liaw SJ. Acute pancreatitis following organophosphate in toxication. J Toxicol Clin Toxicol 1996;34:343-7. |
|6.||Carr RL, Chambers JE. Acute effects of the organophosphate Paraoxon on Schdule-controlled behavior and esterase activity in rats: Dose-response relationships. Pharmacol Biochem Behav 1991;40:929-36. [PUBMED] |
|7.||Wecker L, Stouse M. Effects of chronic paraoxon administration on skeletal muscle fiber integrity. Res Commun Chem Pathol Pharmacol 1985;49:203-13. [PUBMED] |
|8.||Debase HT, Cavijial SH. Vagal regulation of acid secretion. Yale J Biol Med 1994;67:145-51. |
|9.||Yang H, Tache Y. PYY in brain nuclei induces vagal stimulation of gastric acid secretion in rats. Am J Physiol 1995;268:G943-8. |
|10.||Niida H, Takeuchi K, Okabe S. Role of thyrotropin-releasing hormone in acid secretary response induced by lowering of body temperature in the rat. Eur J Pharmacol 1991;198:137-42. [PUBMED] |
|11.||Salim AS. Gastric diversion: A method for H output estimation in the rat. Digestion 1988;39:47-51. [PUBMED] |
|12.||Rafsanjani FN, Maghouli F, Vahedian J, Esmaeili F. The effect of chronic consumption of heroin on basal and vagal electrical-stimulated gastric acid and pepsin secretion in rat. Saudi Med J 2004;25:1356-9. [PUBMED] |
|13.||Berstad A. A modified hemoglobin substrate method for estimation of pepsin in gastric juice. Scand J Gastroentreol 1970;5:343-8. |
|14.||Nabavizadeh Rafsanjani F, Vahedian J. The effect of insulin-dependent diabetes mellitus on basal and distention-induced gastric acid and pepsin secretion in rat. Diabetes Res Clin Pract 2004;66:1-6. [PUBMED] [FULLTEXT]|
|15.||Berne RM, Levy MN, Koeppen BM, Stanton BA. Physiology. 5 th ed. Mosby Co: 2003. p. 576. |
|16.||Friis-Hansen L, Sundler F, Li Y, Gillespie PJ, Saunders TL, Greenson JK, et al . Impaired gastric acid secretion in gastrin-deficient mice. Am J Physiol 1998;274:G561-8. |
|17.||Hills DM, Gerskowitch VP, Roberts SP, Welsh NJ, Shankley NP, Black JW. Pharmacological analysis of the CCK/gastrin receptors mediating pentagastrin-stimulated gastric acid secretion in the isolated stomach of the immature rat. Br J Pharmacol 1996;119:1401-10. |
|18.||Ganong WF. Review of medical physiology. 21 st ed. Appletonand Lange: Norwalk; 2003. p. 497-9. |
|19.||Kato S, Kitamura M, Korolkiewicz RP, Takeuchi K. Role of nitric oxide in regulation of gastric acid secretion in rats: Effects of No donors and No synthesis inhibitor. Br J Phamacol 1998;123:839-46. |
Fatemeh N Rafsanjani
16 Azar Street, Tehran University of Medical Sciences and Health Services, Tehran
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2]