Department of Legal Medicine, Hyogo College of Medicine, 1-1, Mukogawa-cho, Nishinomiya, Hyogo, 663-8501 and
1 Department of Forensic Medicine, Kagawa Medical University, 1750-1, Miki, Kita, Kagawa, 761-0793, Japan
Received 15 March 2000; in revised form 5 March 2001; accepted 31 March 2001
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The aim of the present study was to investigate the effects of cholinergic blocking and stimulating agents on intestinal EtOH absorption. Using rats with high AcH concentrations induced by cyanamide (CY; a potent ALDH inhibitor) pretreatment, we compared the values of the EtOH absorption rate constant (Ka) in the investigation of involvement of cholinergic nerves in the reduction of EtOH absorption by high AcH concentrations.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
This study was approved by the Kagawa Medical University Animal Investigation Committee.
Experiment 1
Rats were divided into 10 experimental groups (five or six rats each), as follows: pretreatment saline (control), atropine sulphate (AT; a parasympatholytic muscarinic antagonist), atropine methylbromide (ATMB; a peripherally acting anti-cholinergic agent), pirenzepine dihydrochloride (PI; a muscarinic receptor antagonist with a high affinity for M1 receptors) and bethanechol chloride (BE; a choline ester with muscarinic actions mainly on smooth muscles of the gastrointestinal tract) with or without CY. The amounts of CY, AT, ATMB, PI and BE used in pretreatment were 50, 0.5, 0.5, 1.0 and 0.1 mg/kg respectively. Pretreatment of CY was performed 60 min before EtOH perfusion, whereas AT, ATMB, PI or BE treatments were performed 10 min before EtOH perfusion.
Experiment 2
To investigate the participation of the muscarinic receptor, additional experimental groups, such as pilocarpine hydrochloride (PL: a cholinomimetic agent which has a dominant muscarinic action) alone, PL + CY and PL + ATMB + CY, were tested. The doses of PL and ATMB were 5 and 20 mg/kg, respectively. The dose of ATMB was determined according to the previous report (Proctor et al., 1966). ATMB and PL pretreatments were performed 40 and 5 min before EtOH perfusion, respectively, and pretreatment of CY was the same as in Experiment 1. All reagents were purchased from Sigma Chemical Co. (St Louis, MO, USA).
Statistics
Data are expressed as means ± SD. Statistical analysis of the data was performed using Student's t-test. Values of P < 0.05 were accepted as representing significant differences.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Since cholinergic stimuli generally reduce gut absorption (Hubel, 1976), we postulated that a high AcH concentration has the possibility to act as an inhibitor of intestinal EtOH absorption through cholinergic nerves. Our hypothesis was supported by AT, one of the parasympatholytic drugs which acts through a non-selective blocking action of the muscarinic receptor in the gastrointestinal tract (Brown, 1990
), which was demonstrated to block entirely the inhibition of intestinal EtOH absorption, with Ka values remaining at control levels. A similar inhibition of intestinal EtOH absorption was induced by BE-alone, which is a choline ester with muscarinic actions mainly on the smooth muscles of the gastrointestinal tract (Taylor, 1990a
). There was no evidence of Ka level inhibition in combination with a high AcH concentration. This regulation may therefore be controlled by peripheral nerves because the value of Ka did not decline in the ATMB + CY pretreatment group, similar to the AT pretreatment in our study. ATMB, an anticholinergic agent, which is unable to cross the bloodbrain barrier, acts mainly through the peripheral nerves. As observed in Experiment 2, both Ka values of PL-alone and when combined with CY were significantly lower than that of CY, but there was no significant difference in Ka values between PL-alone and PL + CY. PL itself, which acts at both the central and peripheral nervous systems as a muscarinic receptor stimulant, has a potent inhibitory action of EtOH absorption. Therefore, additional inhibition on EtOH absorption induced by a high AcH level may be masked by PL. The decline in Ka after PL + CY was partially overcome by pretreatment with ATMB, which has peripheral effects alone. These results thus suggest that a high AcH level reduces the intestinal EtOH absorption through peripheral cholinergic nerves via muscarinic receptors.
It has been known that muscarinic receptors may be divided into five subtypes including M1, M2, M3, M4 and M5 (Lefkowitz et al., 1990). PI has a high affinity for the M1 receptor and acts as a muscarinic M1-receptor-selective blocking agent. This has similar pharmacological actions to AT, including reduced motility and inhibition of intestinal secretion (Brown, 1990
). PI pretreatment, however, had no effect on the reduction of intestinal EtOH absorption by high AcH concentrations and there was also no increase in intestinal EtOH absorption in the PI-alone-treated group.
In the intestine, activation of cholinergic nerves, which is a powerful vasodilator as well as a stimulator of intestinal constriction, acts dominantly, but a decrease of intestinal blood flow is observed. The reason for this is that intestinal blood flow is regulated, not only by vascular tone, but also by spontaneous intestinal contraction (Ching, 1989). This agrees with our previous observation that a high AcH concentration reduces portal blood flow in canines (Shinohara et al., 1993
). AT has the effect of increasing the absorptive site blood flow following intravenous administration (Mailman, 1984
). In our studies, Ka did not fall when CY was employed with AT and this may account for an increase of intestinal blood flow. In the gastrointestinal tract, AT acts to decrease secretion and BE or PL act to increase secretion via respectively a blocking or stimulating action of the muscarinic receptor. Less secretion in AT + CY group and more secretion in the BE or PL group, which are capable of affecting intestinal absorption, may have occurred (Shinohara et al., 1993
).
Alternatively, it has been reported that EtOH absorption in humans following oral ingestion is retarded by AT. One explanation is that AT acts to delay the stomach emptying time (Rinkel and Myerson, 1941). In our experiments, however, AT pretreatment alone induced neither an increase nor a decrease in intestinal EtOH absorption, presumably because EtOH was directly administered into the intestinal segment.
In conclusion, these observations clearly indicate that a high AcH concentration in blood stimulates cholinergic nerves via peripheral muscarinic receptors and we further speculate that the peripheral M1 receptor has little effect compared to other subtypes of muscarinic receptors.
![]() |
FOOTNOTES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Beck, I. T. and Dinda, P. K. (1981) Acute exposure of small intestine to ethanol. Digestive Diseases and Sciences 26, 817838.[ISI][Medline]
Brien, J. F. and Loomis, C. W. (1983) Pharmacology of acetaldehyde. Canadian Journal of Physiology and Pharmacology 61, 122.[ISI][Medline]
Brown, J. H. (1990) Atropine, scopolamine, and related antimuscarinic drugs. In Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th edn, Gilman, A. G., Rall, T. W., Nies, A. S. and Taylor, P. eds, pp. 150165. Pergamon Press, New York.
Brunsson, I., Eklund, S., Jodal, M., Lundgren, O. and Sjovall, H. (1979) The effects of vasodilatation and sympathetic nerve activation on net water absorption in the cat's small intestine. Acta Physiologica Scandinavica 106, 6168.[ISI][Medline]
Ching, C. C. (1989) Gastrointestinal circulation and motor function. In Handbook of Physiology, Section 6, The Gastrointestinal System, Volume 1, Motility and Circulation, Part 2, Stanley, G. S., Jackie, D. W. and Brenda, B. B. eds, pp. 14751518. American Physiological Society, Bethesda.
Enomoto, N., Takase, S., Yasuhara, M. and Takada, A. (1991) Acetaldehyde metabolism in different aldehyde dehydrogenase-2 genotypes. Alcoholism: Clinical and Experimental Research 15, 141144.[ISI][Medline]
Field, M. and McColl, I. (1973) Ion transport in rabbit ileal mucosa III. Effects of catecholamines. American Journal of Physiology 225, 852857.
Hubel, K. A. (1976) Intestinal ion transport: effects of norepinephrine, pilocarpine, and atropine. American Journal of Physiology 231, 252257.
Jones, A. W. (1991) Forensic science aspects of ethanol metabolism. In Forensic Science Progress, Vol. 5, Maehly, A. and Williams, R. L. eds, pp. 3189. Springer-Verlag, Berlin.
Kinoshita, H., Ijiri, I., Ameno, S., Fuke, C. and Ameno, K. (1995) Additional proof of reduction of ethanol absorption from in vivo rat intestine by high acetaldehyde concentrations. Alcohol and Alcoholism 30, 419421.[Abstract]
Kinoshita, H., Ijiri, I., Ameno, S., Fuke, C., Fujisawa Y. and Ameno, K. (1996) Inhibitory mechanism of intestinal ethanol absorption induced by high acetaldehyde concentrations: effects of intestinal blood flow and substance specificity. Alcoholism: Clinical and Experimental Research 20, 510513.[ISI][Medline]
Kricka, L. J. and Clark, P. M. S. (1979) Absorption, excretion and metabolism of ethanol. In Biochemistry of Alcohol and Alcoholism, pp. 3046. Ellis Horwood, New York.
Lefkowitz, R. J., Hoffman, B. B. and Taylor, P. (1990) Neurohumoral transmission: the autonomic and somatic motor nervous systems. In Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th edn, Gilman, A. G., Rall, T. W., Nies, A. S. and Taylor, P. eds, pp. 84121. Pergamon Press, New York.
Mailman, D. (1984) Effects of atropine and guanethidine on canine intestinal absorption and blood flow. Life Sciences 34, 13091315.[ISI][Medline]
Okada, T. and Mizoi, Y. (1982) Studies on the problem of blood acetaldehyde determination in man and its level after alcohol intake. Japanese Journal of Alcohol Studies and Drug Dependence 17, 141159.
Proctor, C. D., Denefield, B. A., Ashley, L. G. and Potts, J. L. (1966) Extension of ethyl alcohol action by pilocarpine. Brain Research 3, 217220.[Medline]
Rinkel, M. and Myerson, A. (1941) Pharmacological studies in experimental alcoholism, 1. The effect of sympathomimetic substances on the blood-alcohol level in man. Journal of Pharmacology and Experimental Therapeutics 71, 7586.
Shinohara, T., Ijiri, I., Fuke, C., Kiriu, T. and Ameno, K. (1992) Effect of acetaldehyde on ethanol absorption in the canine jejunum. Japanese Journal of Alcohol Studies and Drug Dependence 27, 519527.
Shinohara, T., Ijiri, I., Ameno, S., Fuke, C. and Ameno, K. (1993) A comparative study of ethanol absorption in the canine jejunum after pretreatment with cyanamide or pyrazole. Alcohol and Alcoholism 28, 423429.[Abstract]
Taylor, P. (1990a) Cholinergic agonists. In Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th edn, Gilman, A. G., Rall, T. W., Nies, A. S. and Taylor, P. eds, pp. 122130. Pergamon Press, New York.
Taylor, P. (1990b) Agents acting at the neuromuscular junction and autonomic ganglia. In Goodman and Gilman's The Pharmacological Basis of Therapeutics, 8th edn, Gilman, A. G., Rall, T. W., Nies, A. S. and Taylor, P. eds, pp. 166186. Pergamon Press, New York.
Yada, N. and Hayashi, M. (1985) Experimental procedures of drug absorption. In Applied Pharmacokinetics Theory and Experiments, Hanano, M., Umemura, K. and Iga, T. eds, pp. 159199. Soft Science Inc., Tokyo.