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Modification by strychnine and d -tubocurarine of cardiac vagal inhibition in dogs
Neuroscience Letters, 23 (1981) 175-179
175
© Elsevier/North-Holland Scientific, Publishers Ltd.
M O D ~ t C A T I O N BY STRYCHNINE AND D-TUBOCURAPdNE OF CARDIAC VAGAL INHKBKTION IN DOGS
V.K. BHARGAVA*, P. BHARGAVA, D,N. SHARMA and K.D. TRIPATHI
H.P. Medical College, Simla (India) and
(D.M.S. and I(.1). T.) M.A. Medical College, l~ew Delht (India) (Received January 28th, I q81; Revised version received February 15th, 1981; Accepted February 16th, 1981)
Intravenous infusion of strychnine or ~tubocurarine chloride attenuated the cardiac depressant acuo~ ~ and fall in blood pressure produced by electrical stim~alationof the right vagus nerve in dogs anaesthetized with pentobarbitone sodium. The effects of exogenous acetylcholine on the heart and blood pressure. (B.P.) were not modified by s~rychnine or D-turbocurarine. Physostigmine sulphate potentiated the effects of injected acetylcholine without modifying the effe~xsof strychnine and D-tubocurarine on vagal transmission. Dimethylphenylpiperazinium bromide also produced ~ts characteristic effects or~ the hear~ and B.P. in the presence of strychnine and o-tubocurarine. The results indicate that strychnine and Dtubocurarine inhibition of vagal transmission is not a result of blockade of peripheral cholinerg~ receptor~ or cardiac vagal ganglia. This inhibition occurs presumably vm a preganghonic presynap~c action.
Strychnine has been reported to block cholinergic inhibition in the olivoc~hlear bundle [5, 8]7 spinal cord [6] and in the frog heart [4]. Further, we have shown tha; some central excitant effects of strychnine and curare occ~r as a result of blockade of cholinergic inhibitory mechanisms in the cerebral cortex [1, 3]. The present stud~ was designed to investigate the effects of strychnine an ~ curare on the peripheral vagal transmission in dogs. Mongrel dogs of either sex (5-15 kg) were anaesthetized with pentobarbitone sodium (30 mg/kg i.v.). Following endotracheal intubation, ~he animals were placed on positive pressure ventilation and thoracotomy was performed. Auricular and ventricular contractions were recorded with a Cushny myocardiograph and carotid pressure with a mercury manometer. The fight femoral vein was cannula~ed for
drug administration. *Present address: Division of Neurophysiology and Neu-opharmacology, National Institute fo~ Med[caE Research, Mill Hii|, London NW7 IAA, U.K.
176
After obtaining base line records, the right cervical vagus was stimulated at supramaxima~ voltage ~5-10 V, 0.1 msec, 10/sec for 15 sec) every l0 min and the corresponding changes in the heart rate, height of recorded auricular and ventricular contractions and fall in blood pressure (B.P.) were recorded. In a similar manner, the effect of injected acetylcholine (10 #g/kg) on the heart and B.P. were studied every 20 min before and after administration of drugs. The effects of vagal stimulation on the heart and B.P. were expressed as percent change in response from the baseline levels. Their modification by the drugs within a series of experiments was tested for statistical significance using a paired t-test at P < 0.05. The drugs used in the present study were strychnine sulphate (British Drug Houses); curare (D-tubocurarine chloride) (Burroughs Wellcome); physostigmine sulphate, atropine sulphate (British Drug Houses) and dimethylphenylpiperazinium bromide (DMPP) (Sigma Chemicals). Effect o f strychnine and curare on the heart and blood pressure: heart. Intravenous infusion of strychnine sulphate (0.05, 0.2, 0.6 and 1.0 mg/kg) (n = 25) and curare chloride (0.05, 0.2, 0.6 and 0.8 mg/kg) (n = 16) produced a decrease in the amplitudes of contractions of the auricles and ventricles of the dogs (Figs. 1 and 2). The depressant effect was more marked on the auricles and started within 5-7 rain of administration of the drugs and lasted for 20-30 rain. This depressant effect of strychnine sulphate or curare chloride was not modified by either atropine sulphate (n = 4) or physostigmine sulphate (n = 4). Curare was more potent than strychnine. Both drugs also caused a moderate reduction in the heart rate.
J
2
4
5
V Ac
V Ac
yen
,4°f 60 BP
aur
V
A~
S
V
Fig. 1. The effect of strychnine (S) (1.0 mg/kg) on a:etylcholine (Ac) (10 #g/kg) and vagal stimulation (V) induced depression of ventrk:les (yen), auricles ~aur) and fall in blood pressure (B.P.) in dogs. 1, control; 2, 3 and 4, 5,20 and 60 min after strychnine; 5, 30 min after physostigmine (E) (0.1 mg/kg). Note: strychnine blocked the effects of vag.1 stimul, tion on the heart and B.P. without modifying the effects of acetylcholine. Physostigmine only potenti-" ted the effects of acetylcholine.
17~
B
2
3
4
imqmm ll 100 60L BP
@
0
0
ID
oo
Ac
V
C
V
V Ac
Io.
E
V Ac
n'~n
Fig. 2. The effects o f curare (C) (0.6 mg/kg) on acetylchohne (Ac) (10 l~g/kg) and vagal-mduced (V) depression of ventricles, auricles and fall m B.P. 1, control; 2, 3 and 4, 5,20 and 69 min after curare; 5, 30 rain after physosugmme in curare-treated ammal. Note: curare, hke strychmne, only blocked the effects of vagus stimulation on the heart and B.P. The effects of exogenous acetylcholine were not modified.
Blood pressure (B.P.). Strychnine and curare consistently produced a doserelated fall in B.P. Curare was more potent in this respect. The fall in B.P. usualiy occurred within 5-7 rain of administratio~J of drugs and lasted for 20-30 mix (Figs. 1 and 2). The fall in B.P. was also not modified by either atr:)pine sulphate or physostigmine ~ulphate. Effect of strychnine and curare on vagal- and acetylchoEne-ind~ced depression of the heart and B.Po Stimulation of the right vagu~ or injection of acetylcholine (10 #g/kg) produced a decrease in the rate and force of auricula- and ventricular contractions and a fall in B.P. Pretreatment with different ¢'oncentrations of strychnine or curare partially or completely abol~.shed the vagal-irlduced depression of the heart and fall in B.P. This vagal blocking effect starte¢ 20-30 mix after administration of the drugs and lasted over 7-8 h. Table I surer ~arizes the ~'esults. Strychnine and curare blocked the effect of yoga| sti,aulatior on the heart and B.P., but did not modify the effects of injected acetytcholine (Figs. ] and 2). Furthermore, physostigmine sulphate (0.1 mg/kg) potentiated o.r~ly the effects cf injected acetylcholine on the heart and B.P., without modifying ~he strychnine- or curare-induced blockade of vagal transmission (Figs. I and 2). In order to further study if the above effects of strychnine and curare are due: to blockade of the cardiac ganglion, DMPP (25 #g/kg) was admipistered in some experiments (n = 6), to assess ganglionic transra~sion. DMPP on its own caused an initial cardiac depression and a fall in B.P., followed by cardiac e.cceleration and a rise in B.P. These effects of DMPP remained unchanged ~n the presence of strychnine or curare. Fig. 3 shows a tracing of one of the experiments wit~ cur ~re.
178 TABLE I T H E EFFECT OF STRYCHNINE AlqD CURARE ON VAGAL-INDUCED DEPRESSION O1~ AURICLES AND FALL IN B.P. CALCULATED 60-90 M I N (PEAK EFFECT) AFTER THE DRUG ADMINISTRATION *P < 0.05 No. extols.
Drug (mg/kg)
Control (vagal stimulation} Strychnine 0.05 0.2 0.6 0.8 1.0
± S.E.
% d e c r ~ s e in the amplitude o f auricular contractions, ± S.E.
30
65.8 _+ 20.2
9 8 . 6 ± 18.4
3 4 4 4 4
52.8 + 20.8 46.0 _+ 16.9 20.2 +_ 8.2* 15.2 +_ 3.3* 5.1 ± 2.1"
84.6 + 76.6 + 66.6 + 30.9 + 10.2 +
2 4 6 6
49.8 30.7 8.4 3.2
88.0 68.4 28.2 8.2
.lphate
o-Tu~ocurarine chloride 0.05 0.2 0.6 0.8
I
I00 60
% r,ai in B.P. (ram He)
2
~
± 18.9 :~ 10.6" ± 3.2* _+ 1.4"
28.3 20.3 15.8" 7.8* 3.4*
+ 15.4
± 16.2" ± 10.2" _+ 4.8*
4
f
BP
aUf
w
Dmp
c
@@
V Ac
@
@
V Ac
@
O
Dmp
V
5 rain
Fig. 3. ~" e effecls of curare (0.6 mg/kg) on the (fleets of acetylcholine (Ac), vagal stimulation (V) and DMPP (Dmp) (25 #g/kg) c,.; the auricles, ventricles and B.P. in dogs. l, comrol; 2 and 3, 20 and 60 min after curare, 4, Dmp i~ curare-treated animal. Note: curare blocked the vagal induced depression o f the heait and B.P. The effects of Dmp were not m~dified by curare.
179
The results of the present study suggests that strychnine and curare can cause impairment of vagal-induced depression of the heart and fall in BoP. in dogs. These results are consistent with our earlier findings where strychnine was shown to block the vagal-induced depression of the isolated perfused heart of frog [4]. Both strychnine and curare antagonized the depression of the heart and B.P. induced by electrical stimulation of vagus, while the effects of exogenous acetyleholir,_e were unaffected by these drugs. Further, physostigmine sulphate potentiated only the effects of injected acetylcholine on the heart and B.Po without modifying the effects of strychnine or curare on vagal transmission. This suggests that the peripheral muscarinic receptors are not the site of action of the phenomenon. Since the effect of DMPP on heart and B.P. was not modified by strychnine or curare, this also rules out the possibility of blockade of the cardiac vagal ganglion by these drugs. Although our present study is not conclusive, it does provide evidence that the modification of vagal transmission by strychnine and curare may occur at a presynaptic level in the cardiac ganglion, as has been shown in the cat's superior cervical ganglion [7] and guinea pig ileum on coaxial stimulation
[8]. In conclusion, the results of the present study clearly indicate that strychnine and curare abolish the vagal-induced inhibition of the heart and B.P. by blocking the cholinergic excitation of the autonomic ganglion. However, the exact site of action as well as the physiological signihcance ard mechanism of such blockade needs further investigations. 1 Bhargava, V.K., Effects of Drugs Modifying Synap~c Transmission on the Electrical Activity of the Cerebral Cortex, Ph.D. Thesis, Council for National Academic Awards, London, 1969. 2 Bhargava, V.K., Cholinergic inhibitory mechanism m the rerebral cortex. In P.B Bradley and B.N. Dhawan (Eds.), Drugs and Central Synaptic T;ansmissmm Umv. Park Press, London, 1976, pp 99-106. 3 Bhargava, V.K. and Meldrum, B.S., Blockade by eserine of the central cortical effects of strychmne and curare, Nature (Lond.), 230 {1971) 152. 4 Bhargava, V.K., Bhargava, P. and Tripathl, K.D., Effect of strychnine on cardiac vagal mhibmon, NeuroseL Lett., 4 (1977) 111-114. 5 Brown, R.D., Daigneault, E.A. and Prueth J.R°, The effect of selected cholinerg~c drugs and strychnine on cochlear responses and olivo~cochlear inhibition, J. Pharmacol. exp. Ther., 165 (1969) 300-309. 6 Curtis, D.R., The depression of spinal inhibition by electrophoretically admimstered strychnine, Ira. J. Neuropharmacol., I (1962) 239-250. 7 McKinstry, D.N. and Koelle, G.B., Inhibition of ~he release of acetymcho|me by strychmne and its implication regarding transmission in olivo cochlear bundle, Nature (Load.), 213 (t967) 505-506. 8 Takagi, K. and Takayanagi, |., Effects of s~rychmne derivatives of phenyl acetate and catechoiamme~ on contraction and acetylchotine output from cho|inergic nerve endings of gt ;nea pig ~teum, Jap. J. PharmacoL, 16 (1966) 211-2t6.
175
© Elsevier/North-Holland Scientific, Publishers Ltd.
M O D ~ t C A T I O N BY STRYCHNINE AND D-TUBOCURAPdNE OF CARDIAC VAGAL INHKBKTION IN DOGS
V.K. BHARGAVA*, P. BHARGAVA, D,N. SHARMA and K.D. TRIPATHI
H.P. Medical College, Simla (India) and
(D.M.S. and I(.1). T.) M.A. Medical College, l~ew Delht (India) (Received January 28th, I q81; Revised version received February 15th, 1981; Accepted February 16th, 1981)
Intravenous infusion of strychnine or ~tubocurarine chloride attenuated the cardiac depressant acuo~ ~ and fall in blood pressure produced by electrical stim~alationof the right vagus nerve in dogs anaesthetized with pentobarbitone sodium. The effects of exogenous acetylcholine on the heart and blood pressure. (B.P.) were not modified by s~rychnine or D-turbocurarine. Physostigmine sulphate potentiated the effects of injected acetylcholine without modifying the effe~xsof strychnine and D-tubocurarine on vagal transmission. Dimethylphenylpiperazinium bromide also produced ~ts characteristic effects or~ the hear~ and B.P. in the presence of strychnine and o-tubocurarine. The results indicate that strychnine and Dtubocurarine inhibition of vagal transmission is not a result of blockade of peripheral cholinerg~ receptor~ or cardiac vagal ganglia. This inhibition occurs presumably vm a preganghonic presynap~c action.
Strychnine has been reported to block cholinergic inhibition in the olivoc~hlear bundle [5, 8]7 spinal cord [6] and in the frog heart [4]. Further, we have shown tha; some central excitant effects of strychnine and curare occ~r as a result of blockade of cholinergic inhibitory mechanisms in the cerebral cortex [1, 3]. The present stud~ was designed to investigate the effects of strychnine an ~ curare on the peripheral vagal transmission in dogs. Mongrel dogs of either sex (5-15 kg) were anaesthetized with pentobarbitone sodium (30 mg/kg i.v.). Following endotracheal intubation, ~he animals were placed on positive pressure ventilation and thoracotomy was performed. Auricular and ventricular contractions were recorded with a Cushny myocardiograph and carotid pressure with a mercury manometer. The fight femoral vein was cannula~ed for
drug administration. *Present address: Division of Neurophysiology and Neu-opharmacology, National Institute fo~ Med[caE Research, Mill Hii|, London NW7 IAA, U.K.
176
After obtaining base line records, the right cervical vagus was stimulated at supramaxima~ voltage ~5-10 V, 0.1 msec, 10/sec for 15 sec) every l0 min and the corresponding changes in the heart rate, height of recorded auricular and ventricular contractions and fall in blood pressure (B.P.) were recorded. In a similar manner, the effect of injected acetylcholine (10 #g/kg) on the heart and B.P. were studied every 20 min before and after administration of drugs. The effects of vagal stimulation on the heart and B.P. were expressed as percent change in response from the baseline levels. Their modification by the drugs within a series of experiments was tested for statistical significance using a paired t-test at P < 0.05. The drugs used in the present study were strychnine sulphate (British Drug Houses); curare (D-tubocurarine chloride) (Burroughs Wellcome); physostigmine sulphate, atropine sulphate (British Drug Houses) and dimethylphenylpiperazinium bromide (DMPP) (Sigma Chemicals). Effect o f strychnine and curare on the heart and blood pressure: heart. Intravenous infusion of strychnine sulphate (0.05, 0.2, 0.6 and 1.0 mg/kg) (n = 25) and curare chloride (0.05, 0.2, 0.6 and 0.8 mg/kg) (n = 16) produced a decrease in the amplitudes of contractions of the auricles and ventricles of the dogs (Figs. 1 and 2). The depressant effect was more marked on the auricles and started within 5-7 rain of administration of the drugs and lasted for 20-30 rain. This depressant effect of strychnine sulphate or curare chloride was not modified by either atropine sulphate (n = 4) or physostigmine sulphate (n = 4). Curare was more potent than strychnine. Both drugs also caused a moderate reduction in the heart rate.
J
2
4
5
V Ac
V Ac
yen
,4°f 60 BP
aur
V
A~
S
V
Fig. 1. The effect of strychnine (S) (1.0 mg/kg) on a:etylcholine (Ac) (10 #g/kg) and vagal stimulation (V) induced depression of ventrk:les (yen), auricles ~aur) and fall in blood pressure (B.P.) in dogs. 1, control; 2, 3 and 4, 5,20 and 60 min after strychnine; 5, 30 min after physostigmine (E) (0.1 mg/kg). Note: strychnine blocked the effects of vag.1 stimul, tion on the heart and B.P. without modifying the effects of acetylcholine. Physostigmine only potenti-" ted the effects of acetylcholine.
17~
B
2
3
4
imqmm ll 100 60L BP
@
0
0
ID
oo
Ac
V
C
V
V Ac
Io.
E
V Ac
n'~n
Fig. 2. The effects o f curare (C) (0.6 mg/kg) on acetylchohne (Ac) (10 l~g/kg) and vagal-mduced (V) depression of ventricles, auricles and fall m B.P. 1, control; 2, 3 and 4, 5,20 and 69 min after curare; 5, 30 rain after physosugmme in curare-treated ammal. Note: curare, hke strychmne, only blocked the effects of vagus stimulation on the heart and B.P. The effects of exogenous acetylcholine were not modified.
Blood pressure (B.P.). Strychnine and curare consistently produced a doserelated fall in B.P. Curare was more potent in this respect. The fall in B.P. usualiy occurred within 5-7 rain of administratio~J of drugs and lasted for 20-30 mix (Figs. 1 and 2). The fall in B.P. was also not modified by either atr:)pine sulphate or physostigmine ~ulphate. Effect of strychnine and curare on vagal- and acetylchoEne-ind~ced depression of the heart and B.Po Stimulation of the right vagu~ or injection of acetylcholine (10 #g/kg) produced a decrease in the rate and force of auricula- and ventricular contractions and a fall in B.P. Pretreatment with different ¢'oncentrations of strychnine or curare partially or completely abol~.shed the vagal-irlduced depression of the heart and fall in B.P. This vagal blocking effect starte¢ 20-30 mix after administration of the drugs and lasted over 7-8 h. Table I surer ~arizes the ~'esults. Strychnine and curare blocked the effect of yoga| sti,aulatior on the heart and B.P., but did not modify the effects of injected acetytcholine (Figs. ] and 2). Furthermore, physostigmine sulphate (0.1 mg/kg) potentiated o.r~ly the effects cf injected acetylcholine on the heart and B.P., without modifying ~he strychnine- or curare-induced blockade of vagal transmission (Figs. I and 2). In order to further study if the above effects of strychnine and curare are due: to blockade of the cardiac ganglion, DMPP (25 #g/kg) was admipistered in some experiments (n = 6), to assess ganglionic transra~sion. DMPP on its own caused an initial cardiac depression and a fall in B.P., followed by cardiac e.cceleration and a rise in B.P. These effects of DMPP remained unchanged ~n the presence of strychnine or curare. Fig. 3 shows a tracing of one of the experiments wit~ cur ~re.
178 TABLE I T H E EFFECT OF STRYCHNINE AlqD CURARE ON VAGAL-INDUCED DEPRESSION O1~ AURICLES AND FALL IN B.P. CALCULATED 60-90 M I N (PEAK EFFECT) AFTER THE DRUG ADMINISTRATION *P < 0.05 No. extols.
Drug (mg/kg)
Control (vagal stimulation} Strychnine 0.05 0.2 0.6 0.8 1.0
± S.E.
% d e c r ~ s e in the amplitude o f auricular contractions, ± S.E.
30
65.8 _+ 20.2
9 8 . 6 ± 18.4
3 4 4 4 4
52.8 + 20.8 46.0 _+ 16.9 20.2 +_ 8.2* 15.2 +_ 3.3* 5.1 ± 2.1"
84.6 + 76.6 + 66.6 + 30.9 + 10.2 +
2 4 6 6
49.8 30.7 8.4 3.2
88.0 68.4 28.2 8.2
.lphate
o-Tu~ocurarine chloride 0.05 0.2 0.6 0.8
I
I00 60
% r,ai in B.P. (ram He)
2
~
± 18.9 :~ 10.6" ± 3.2* _+ 1.4"
28.3 20.3 15.8" 7.8* 3.4*
+ 15.4
± 16.2" ± 10.2" _+ 4.8*
4
f
BP
aUf
w
Dmp
c
@@
V Ac
@
@
V Ac
@
O
Dmp
V
5 rain
Fig. 3. ~" e effecls of curare (0.6 mg/kg) on the (fleets of acetylcholine (Ac), vagal stimulation (V) and DMPP (Dmp) (25 #g/kg) c,.; the auricles, ventricles and B.P. in dogs. l, comrol; 2 and 3, 20 and 60 min after curare, 4, Dmp i~ curare-treated animal. Note: curare blocked the vagal induced depression o f the heait and B.P. The effects of Dmp were not m~dified by curare.
179
The results of the present study suggests that strychnine and curare can cause impairment of vagal-induced depression of the heart and fall in BoP. in dogs. These results are consistent with our earlier findings where strychnine was shown to block the vagal-induced depression of the isolated perfused heart of frog [4]. Both strychnine and curare antagonized the depression of the heart and B.P. induced by electrical stimulation of vagus, while the effects of exogenous acetyleholir,_e were unaffected by these drugs. Further, physostigmine sulphate potentiated only the effects of injected acetylcholine on the heart and B.Po without modifying the effects of strychnine or curare on vagal transmission. This suggests that the peripheral muscarinic receptors are not the site of action of the phenomenon. Since the effect of DMPP on heart and B.P. was not modified by strychnine or curare, this also rules out the possibility of blockade of the cardiac vagal ganglion by these drugs. Although our present study is not conclusive, it does provide evidence that the modification of vagal transmission by strychnine and curare may occur at a presynaptic level in the cardiac ganglion, as has been shown in the cat's superior cervical ganglion [7] and guinea pig ileum on coaxial stimulation
[8]. In conclusion, the results of the present study clearly indicate that strychnine and curare abolish the vagal-induced inhibition of the heart and B.P. by blocking the cholinergic excitation of the autonomic ganglion. However, the exact site of action as well as the physiological signihcance ard mechanism of such blockade needs further investigations. 1 Bhargava, V.K., Effects of Drugs Modifying Synap~c Transmission on the Electrical Activity of the Cerebral Cortex, Ph.D. Thesis, Council for National Academic Awards, London, 1969. 2 Bhargava, V.K., Cholinergic inhibitory mechanism m the rerebral cortex. In P.B Bradley and B.N. Dhawan (Eds.), Drugs and Central Synaptic T;ansmissmm Umv. Park Press, London, 1976, pp 99-106. 3 Bhargava, V.K. and Meldrum, B.S., Blockade by eserine of the central cortical effects of strychmne and curare, Nature (Lond.), 230 {1971) 152. 4 Bhargava, V.K., Bhargava, P. and Tripathl, K.D., Effect of strychnine on cardiac vagal mhibmon, NeuroseL Lett., 4 (1977) 111-114. 5 Brown, R.D., Daigneault, E.A. and Prueth J.R°, The effect of selected cholinerg~c drugs and strychnine on cochlear responses and olivo~cochlear inhibition, J. Pharmacol. exp. Ther., 165 (1969) 300-309. 6 Curtis, D.R., The depression of spinal inhibition by electrophoretically admimstered strychnine, Ira. J. Neuropharmacol., I (1962) 239-250. 7 McKinstry, D.N. and Koelle, G.B., Inhibition of ~he release of acetymcho|me by strychmne and its implication regarding transmission in olivo cochlear bundle, Nature (Load.), 213 (t967) 505-506. 8 Takagi, K. and Takayanagi, |., Effects of s~rychmne derivatives of phenyl acetate and catechoiamme~ on contraction and acetylchotine output from cho|inergic nerve endings of gt ;nea pig ~teum, Jap. J. PharmacoL, 16 (1966) 211-2t6.