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Physiol Scand 1990, 139, 391-392
Differential motor effects of lidocaine on the circular muscle of proximal and distal rat colon L. G. N I K L A S S O N * t , S. FASTHt, L. H U L T E N t a n d D . S. DELBRO" Departments of
* Physiology
and
t Surgery, University
The proximal and distal mammalian colon exhibit considerable functional differences which may partly be due to a non-uniform density, and/or the level of activity, of the neuronal supply (see Christensen 1987, Snape et ul. 1989, for references). Such a heterogeneity could explain the differential effect of some drugs (cholinergic agonists and antagonists, 5-hydroxytryptamine) on these parts of the gut (Fink & Friedman 1960). One approach to elucidating the importance of neurogenic control mechanisms for various gastrointestinal segments is to investigate the effect of nerveblocking chemical compounds. Accordingly, local anaesthetics, such as lidocaine, procaine or similar substances, as well as the specific nerve-blocking agent tetrodotoxin (TTX), cause excitation of the muscle from small intestine, both in vitro (Wood 1972, Bortoff & Muller 1975) and in viva (Biber & Fara 1973). It is generally agreed that T T X elicits this effect by causing a removal of tonically active, enteric inhibitory motor neurons, and, according to Wood (1972), local anaesthetics have the same mechanism of action. With respect to the rut colon, T T X seems to excite the proximal and distal circular muscle in a differential manner. The proximal colon response to T T X is minor and short-lasting (Ek et al. 1986, Maggi er al. 1987), while the distal colon, on the other hand, is markedly affected (Niklasson et al., in preparation). This finding could be due to different neural influences on the two parts. In this study we utilized liducazne (administered at the same dosage as in the study by Wood [ 19721) as a tool to investigate further possible differences between proximal and distal rat colon with regard to the activity of the circular muscle. A total of 25 colonic muscle preparations was taken from six male Sprague-Dawley rats (32C350 g body wt) which had been fasted for 18-24 h (tap water ad lib.) prior to the experiments. T h e animals were killed by cervical dislocation. The large intestine was dissected free and sectioned 1 cm aboral to the caecal Received 13 February 1990, accepted 19 March 1990. Key words :colon, enteric nervous system, lidocaine, smooth muscle. Correspondence : L.-G. Niklasson MD, Department of Physiology, PO Box 33031, s-400 33 Goteborg, Sweden.
of Goteborg, Sweden
junction, and 4 cm oral to the anal orifice. The colon was then removed and placed in chilled oxygenated (957/, O,, 5% CO,) Krebs solution, containing (mM) NaCl 115.5, KCI 4.6, KH,PO, 1.2, NaHCO, 21.9, MgSO, 1.2, glucose 11.5, and CaCI, 2.5. The colon was opened longitudinally, and 2 4 transverse strips (representing mainly the circular muscle ; length 6-10 mm, width 2-3 mm) were taken from both the proximal and distal 2 cm, and were used either immediately or after 4-7 h refrigeration (1-2 "C). T h e tissues were mounted vertically in 15-ml organ bath chambers, and were bathed in gassed Krebs solution (above). Isometric conpactions were recorded using a Grass FT 03 transducer on a Grass polygraph. T h e preparations were allowed to equilibrate under a resting tension of 2.5-5 m N for 60 min, with a washout every 15 min. Twenty minutes after the last washout, lidocaine hydrochloride (Xylocaine, Astra, Sweden, 10 mg mlF', 150 p l ) was administered to the tissues, giving a final concentration in the medium of 0.38 mM. The effect of this compound on the colonic muscle was monitored for another 20 min. Two parameters of motor activity were estimated, tone being calculated as baseline tension (mN) and phasic actzuzty as the area under the response curve (mN min) using a computerized planimetric analysis. Means were calculated for the data from the proximal and distal tissues from each animal. The results from all animals (n = 6) are given as means fSEM. Statistical analyses of the results (after logarithmic transformation of the motility data) were done using Student's t-test for paired or unpaired data, or by analyses of variance, followed by the Fisher's LSD test for multiple comparisons (Milliken & Johnson 1984), when relevant. A P-value of less than 0.05 was considered significant. The colonic circular muscle activity of the rat is characterized by regular phasic contractions. The time (min) that elapsed between the first washout and the appearance of the subsequent fifth contraction ( 2 2.5 mN) was significantly shorter in the proximal (18.7k6.3) than the distal (46.5k7.1) colon (P < 0.02. n = 6). This observation could indicate that there is a higher degree of spontaneous activity in the proximal colon than the distal colon. In the proximal colon, tone (mN) was 1.61 k0.50 immediately prior to the administration of lidocaine.
39 1
392
L . G.Niklusson et al.
Thereafter, tone increased significantly ( P < 0.05, n = 6) to 5.93k2.26, but returned to 2.26k0.50 by the end of the observation period. Phasic activity (mN min), estimated during the 5 min immediately prior to, and 15 min after, the administration of lidocaine, did not change significantly (21.12 4.28, 25.11 f6.50, P > 0.1, n = 6). In the distal colon, tone increased significantly ( P < 0.05,n = 5)from2.18_t0.56to 14.44+5.56,and returned to 4.41 _+ 1.47 by the end of the observation period. Phasic activity also increased significantly (P
Physiol Scand 1990, 139, 391-392
Differential motor effects of lidocaine on the circular muscle of proximal and distal rat colon L. G. N I K L A S S O N * t , S. FASTHt, L. H U L T E N t a n d D . S. DELBRO" Departments of
* Physiology
and
t Surgery, University
The proximal and distal mammalian colon exhibit considerable functional differences which may partly be due to a non-uniform density, and/or the level of activity, of the neuronal supply (see Christensen 1987, Snape et ul. 1989, for references). Such a heterogeneity could explain the differential effect of some drugs (cholinergic agonists and antagonists, 5-hydroxytryptamine) on these parts of the gut (Fink & Friedman 1960). One approach to elucidating the importance of neurogenic control mechanisms for various gastrointestinal segments is to investigate the effect of nerveblocking chemical compounds. Accordingly, local anaesthetics, such as lidocaine, procaine or similar substances, as well as the specific nerve-blocking agent tetrodotoxin (TTX), cause excitation of the muscle from small intestine, both in vitro (Wood 1972, Bortoff & Muller 1975) and in viva (Biber & Fara 1973). It is generally agreed that T T X elicits this effect by causing a removal of tonically active, enteric inhibitory motor neurons, and, according to Wood (1972), local anaesthetics have the same mechanism of action. With respect to the rut colon, T T X seems to excite the proximal and distal circular muscle in a differential manner. The proximal colon response to T T X is minor and short-lasting (Ek et al. 1986, Maggi er al. 1987), while the distal colon, on the other hand, is markedly affected (Niklasson et al., in preparation). This finding could be due to different neural influences on the two parts. In this study we utilized liducazne (administered at the same dosage as in the study by Wood [ 19721) as a tool to investigate further possible differences between proximal and distal rat colon with regard to the activity of the circular muscle. A total of 25 colonic muscle preparations was taken from six male Sprague-Dawley rats (32C350 g body wt) which had been fasted for 18-24 h (tap water ad lib.) prior to the experiments. T h e animals were killed by cervical dislocation. The large intestine was dissected free and sectioned 1 cm aboral to the caecal Received 13 February 1990, accepted 19 March 1990. Key words :colon, enteric nervous system, lidocaine, smooth muscle. Correspondence : L.-G. Niklasson MD, Department of Physiology, PO Box 33031, s-400 33 Goteborg, Sweden.
of Goteborg, Sweden
junction, and 4 cm oral to the anal orifice. The colon was then removed and placed in chilled oxygenated (957/, O,, 5% CO,) Krebs solution, containing (mM) NaCl 115.5, KCI 4.6, KH,PO, 1.2, NaHCO, 21.9, MgSO, 1.2, glucose 11.5, and CaCI, 2.5. The colon was opened longitudinally, and 2 4 transverse strips (representing mainly the circular muscle ; length 6-10 mm, width 2-3 mm) were taken from both the proximal and distal 2 cm, and were used either immediately or after 4-7 h refrigeration (1-2 "C). T h e tissues were mounted vertically in 15-ml organ bath chambers, and were bathed in gassed Krebs solution (above). Isometric conpactions were recorded using a Grass FT 03 transducer on a Grass polygraph. T h e preparations were allowed to equilibrate under a resting tension of 2.5-5 m N for 60 min, with a washout every 15 min. Twenty minutes after the last washout, lidocaine hydrochloride (Xylocaine, Astra, Sweden, 10 mg mlF', 150 p l ) was administered to the tissues, giving a final concentration in the medium of 0.38 mM. The effect of this compound on the colonic muscle was monitored for another 20 min. Two parameters of motor activity were estimated, tone being calculated as baseline tension (mN) and phasic actzuzty as the area under the response curve (mN min) using a computerized planimetric analysis. Means were calculated for the data from the proximal and distal tissues from each animal. The results from all animals (n = 6) are given as means fSEM. Statistical analyses of the results (after logarithmic transformation of the motility data) were done using Student's t-test for paired or unpaired data, or by analyses of variance, followed by the Fisher's LSD test for multiple comparisons (Milliken & Johnson 1984), when relevant. A P-value of less than 0.05 was considered significant. The colonic circular muscle activity of the rat is characterized by regular phasic contractions. The time (min) that elapsed between the first washout and the appearance of the subsequent fifth contraction ( 2 2.5 mN) was significantly shorter in the proximal (18.7k6.3) than the distal (46.5k7.1) colon (P < 0.02. n = 6). This observation could indicate that there is a higher degree of spontaneous activity in the proximal colon than the distal colon. In the proximal colon, tone (mN) was 1.61 k0.50 immediately prior to the administration of lidocaine.
39 1
392
L . G.Niklusson et al.
Thereafter, tone increased significantly ( P < 0.05, n = 6) to 5.93k2.26, but returned to 2.26k0.50 by the end of the observation period. Phasic activity (mN min), estimated during the 5 min immediately prior to, and 15 min after, the administration of lidocaine, did not change significantly (21.12 4.28, 25.11 f6.50, P > 0.1, n = 6). In the distal colon, tone increased significantly ( P < 0.05,n = 5)from2.18_t0.56to 14.44+5.56,and returned to 4.41 _+ 1.47 by the end of the observation period. Phasic activity also increased significantly (P
