Gen. Pharmac. Vol. 15, No. 6, 523-528, 1984 Printed in Great Britain. All rights reserved
0306-3623/84 $3.00+0.00 Copyright © 1984 Pergamon Press Ltd
EFFECTS OF CHLORPROMAZINE ON THE ISOLATED PERFUSED G U I N E A PIG HEART* CARL E. ARONSONI, RONALD C. WEST I a n d JOSEPH F . SPEAR 2 ~Laboratories of Pharmacology & Toxicology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104, U.S.A. 2Laboratory of Physiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104, U.S.A. (Received 25 April 1984) Abstraet-- I. Chlorpromazine altered the mechanical and electrical activity of the isolated perfused guinea pig heart. 2. While its effects on coronary flow were variable, chlorpromazine increased resting diastolic isometric tension and decreased the isometric systolic tension developed by spontaneously beating hearts. 3. Heart rate was also decreased. 4. The drug depressed conduction through the His-Purkinje system and ventricular muscle to a greater extent than it did atrial conduction time and AV nodal conduction time. 5. From our data, we concluded that the greatest depressant action of chlorpromazine on the electrical activity of the isolated perfused guinea pig heart occurred within the specialized ventricular conduction system and ventricular muscle.
INTRODUCTION C h i o r p r o m a z i n e a n d related p h e n o t h i a z i n e drugs have been s h o w n to alter the electrical activity of hearts from several species, including man, a n d such changes occurred u n d e r b o t h in vivo a n d in vitro conditions (Ban a n d St. Jean, 1964; Langslet, 1969, 1970; Arita a n d Imanishi, 1970; A r i t a a n d Surawicz, 1973; A r o n s o n a n d Serlick, 1977; Sugiyama a n d Ozawa, 1979). While m o s t of the electrocardiographic changes p r o d u c e d by phenothiazine-type agents in vivo a p p e a r to be reversible following d i s c o n t i n u a t i o n of the drug, reports o f sudden d e a t h have a p p e a r e d in the literature (Kelly et al., 1963; Leestma a n d Koenic, 1968). While A r i t a a n d Imanishi (1970) studied the effects of c h l o r p r o m a z i n e o n the isolated right atrium, strips of left a t r i u m a n d the papillary muscle o f the left ventricle from guinea pig hearts, o u r experiments were designed to investigate the effects of chlorpromazine o n electrical c o n d u c t i o n in a whole o r g a n preparation, the isolated guinea pig heart perfused by the L a n g e n d o r f f m e t h o d . U s i n g this technique, o u r intent was to determine the drug's action simultaneously on various parts o f the c o n d u c t i n g system, a n d to ascertain w h e t h e r c h l o r p r o m a z i n e selectively acted at specific sites within the c o n d u c t i o n pathways. MATERIALS AND METHODS
Surgical and perfusion methods Albino male guinea pigs (West Jersey Biological Supply Co., Wenonah, N.J., 450-550g) given a standard diet of Agway Guinea Pig Chow and water ad libitum were sacririced by decapitation. Using techniques and a perfusion *This work was supported in part by a Research Grant from the National Heart, Lung & Blood Institute (1 ROIHL-19045-05).
system described previously, the heart was removed from each animal, placed on a Langendorff-type apparatus and perfused with Krebs-Ringer bicarbonate buffer (K-R buffer) at 37.5°C (Aronson and Serlick, 1976, 1977). Mechanical activity was recorded by placing a Palmer frog heart clip on the apex of the heart and connecting it to a Grass force displacement transducer (Model FT-0.03) with No. 4-0 nylon suture material and a ball bearing pulley system. The output signal from the transducer was fed through a Sanborn carrier preamplifier (Model 350-i 100) to a 4-channel Mingograf high speed, ink-writing recorder (Model 30). Recordings from which measurements were taken were made at paper speeds of 100 and 500 mm/sec. One group of hearts was allowed to beat spontaneously while a second group was driven electrically through silver bipolar electrodes placed on the left atrium. The region of right atrial tissue containing the Sino atrial node (SA node) was dissected free and discarded prior to beginning stimulation. Hearts were paced at predetermined rates using a Grass stimulator (Model S-44) set as follows: Frequency, 1.9-3.3 Hz; Duration, 2.0 msec; Voltage, 4-9 V d.c. All hearts were allowed to equilibrate for a period of 30 min prior to beginning the prescribed experimental protocol. During this stabilization interval, hearts were perfused with only drug-free K - R buffer. At the conclusion of the 30min equilibration period, control (0-time) measurements were made before switching the spontaneously beating hearts to drug-containing K - R buffer or continuing the perfusion, in the case of control hearts, on drug-free K - R buffer. The total period of perfusion for each heart was 90 min, including the initial stabilization period. Only one drug concentration was used for each heart. Measurements of electrical and mechanical activity were taken at 1 min intervals for the first 10 min and at 5 min intervals thereafter for the duration of the 60 min postequilibration period. Coronary flow was determined at 5 min intervals throughout the course of each experiment. Data were pooled according to the drug concentration used. In those hearts that were driven electrically, a 30 min equilibration period was also observed, but at the end of that period, the hearts were paced over a specified frequency range (1.9-3.3 Hz). Since we wished to determine whether heart rate influenced the specific conduction intervals that 523
524
C. E. ARONSON et al. ,
we were measuring and to enable us to establish and apply appropriate correction factors, when indicated, to data from the spontaneously beating hearts, measurements of electrical activity were made at each of 8 frequencies within the range stated above. The electrically-driven hearts were perfused with only drug-free K - R buffer.
Electrocardiographic recording techniques Electrical recordings were obtained by placing electrodes at several different locations on the myocardium. Wick-type electrodes (Aronson and Serlick, 1977), placed on the heart's surface, and connected to the ECG amplifier of the Mingograf recorder, were used to obtain an electrocardiogram, while one set of silver bipolar electrodes was placed in proximity to the bundle of His, at the junction of the ascending aorta and the tricuspid valve, through an opening cut in the right atrium. A second set of silver bipolar electrodes was positioned on the upper right section of the outer atrial wall. The electrodes used to record electrical activity from the bundle of His were connected to the Mingograf recorder through a World Precision Instruments Inc. (W.P.I. Model DAM-5A) differential preamplifier set as follows: Filters, I00 Hz, wide band; Gain, 10(~500, depending on electrode placement. Advancement of the gain control was minimized by adjusting electrode position for an optimal signal. A second W.P.I. preamplifier with the same approximate settings was connected to the set of electrodes located on the wall of the atrium. The intervals that were determined from the recordings and measured are defined below and illustrated schematically in Fig. 1.
interval was used to give an indication of the conduction time in the atrial muscle. A h: Interval from the highest point of the P-wave on the electrocardiogram to the point of greatest slope of the h-wave on the His bundle recording. The measurement provides an index of the conduction time through the AV node. h-Q: Interval from the point of greatest slope of the hwave on the His bundle recording to the beginning of the Q-wave on the electrocardiogram. This interval indicates His-Purkinje conduction time. Q-v: The interval between the beginning of the Q-wave and the stimulated point of greatest slope of the vwave on the QRS complex on the His bundle recording. Since the His electrogram records a ventricular component from the high ventricular system, which is the latest ventricular site to be activated, the Qv interval gives an index of total ventricular activation.
Statistical methods The data were examined by analysis of variance (Snedecor and Cochran, 1967; Sokal and Rohlf, 1969; Winer, 1962).
Drugs The chlorpromazine hydrochloride (Thorazine" used in these studies) was a gift from Smith, Kline and French Laboratories, Philadelphia, Pennsylvania. The concentrations of chlorpromazine hydrochloride specified in this study were calculated as the free base and are expressed as such. Under the conditions of our perfusion experiments, the drug was considered to be stable (Aronson and Serlick, 1977). RESULTS
Mechanicol ,some t r p c ~ contrGctio n I-- I
High right Gtriurn
Bundle
of
v
His
~h h_O~s E lectrocordiogram P-R
I
k QRS
I
I
A l t h o u g h all the s p o n t a n e o u s l y beating control a n d c h l o r p r o m a z i n e - t r e a t e d hearts were perfused for 6 0 m i n following the equilibration period, we are reporting only the d a t a for the first 30 min for purposes of u n i f o r m c o m p a r i s o n . M o s t drug-induced effects occurred relatively soon after the hearts were perfused with c h l o r p r o m a z i n e - c o n t a i n i n g medium, a n d after 30 min, it was n o t always possible to o b t a i n a complete set o f mechanical a n d electrical measurem e n t s from each heart, especially at the highest dosage. N o statistical difference between the (~30 a n d 0-60 m i n d a t a was observed w h e n it was e x a m i n e d by analysis o f variance.
Q-T
Fig. 1. This schematic drawing shows the relationship between the electrical and mechanical recordings obtained simultaneously from isolated perfused guinea pig hearts. The tracing illustrated represents a typical control heart perfused with drug-free K - R buffer. Electrical intervals were measured using standardized reference points as shown above. P-R: Interval from the beginning of the P-wave to the first upward deflection of the Q-wave on the electrocardiogram. QRS: Interval from the beginning of the Q-wave to the point where the S-wave begins to flatten out on the electrocardiogram. Q-T: Interval from the beginning of the Q-wave to the midpoint of the upper and lower peaks of the Twave on the electrocardiogram. P-A: The interval between the beginning of atrial depolarization in the high right atrial recording to the latest A-wave in the His bundle electrogram. This
Mechanical activity In s p o n t a n e o u s l y beating hearts, c h l o r p r o m a z i n e p r o d u c e d dose d e p e n d e n t alterations in c o r o n a r y flow (Table 1). A t low concentrations, flow appeared to decrease, whereas at 5000 ng/ml, it increased a n d r e m a i n e d elevated. Time, however, was not a significant factor a n d there was n o t a statistically significant interaction between the dose employed a n d the time d u r i n g which the hearts were exposed to the drug (Table 1). Resting diastolic isometric tension was increased significantly by c h l o r p r o m a z i n e as a consequence of the dose c o n t a i n e d in the perfusion medium, b u t time was n o t a significant factor (Table 2). There was n o statistically significant interaction between dosage a n d time o f perfusion with c h l o r p r o m a z i n e - c o n t a i n ing K - R buffer. The isometric systolic tension developed by spontaneously beating hearts decreased significantly as a
525
Cardiac actions o f chlorpromazine Table 1. Effects of chlorpromazine on coronary flow~ Time (min)c DoseD (ng/ml)
0
4
I0
15
20
25
30
0
9.26 4-3.61 (7)
8.44 4-3.61 (7)
8.31 q-3.66 (7)
8.17 4-3.44 (7)
8.09 4-3.50 (7)
8.36 4-3.56 (7)
8.33 a:3.99 (7)
50
9.92 + 1.53 (6)
9.77 4-2.62 (6)
9.40 4-2.34 (6)
9.05 4-2.13 (6)
8.73 4-2.08 (6)
8.57 4-2.22 (6)
8.40 4-2.27 (6)
500
9.92 +2.25 (6)
9.60 4- 1.39 (6)
9.10 4- 1.02 (6)
9.00 4-1.26 (6)
8.83 4-1.32 (6)
8.63 4-1.44 (6)
8.40 4-1.72 (6)
5000
10.22 q- 1.52 (6)
18.00 4-2.85 (6)
17.37 q-2.90 (6)
16.45 4-2.77 (6)
15.62 4-3.08 (6)
15.00 4-3.00 (6)
14.23 4-3.04 (6)
"Hearts were obtained from normal albino male guinea pigs (450-500 g). Figures in parentheses indicate the number of hearts in each group. Values are ml/min q-SDM. bChlorpromazine hydrochloride calculated and expressed as the free base. CData for the 0-30 min period were examined by a two-way analysis of variance and the dose factor was significant (P< 0.001).
Table 2. Effects of chlorpromazine on diastolic and systolic isometric tensiona Systolic isometric tension a
Diastolic isometric tension~ Doseb (ng/ml) 0 50 500 5000
0
30 min
5.04-0.0 (7) 5.04-0.0 (6) 5.0±0.0 (6) 5.0±0.0 (6)
4.74-0.6 (7) 4.94-0.2 (6) 5.4±1.32 (6) 5.64-2.1 (6)
0 12.6~2.4 (7) 12.04-2.2 (6) 12.04-2.2 (6) 11.3±3.4 (6)
30 min 11.54-2.4 (7) 10.8&2.0 (6) 7.54-2.6 (6) 0.04-0.0 (6)
aHearts were obtained from normal albino male guinea pigs (450-440 g). Figures in parentheses indicate the number of hearts in each group. Values are grams 4-SDM. bChlorpromazine hydrochloride calculated and expressed as the free base. CData for the 0-30 min period were examined by a two-way analysis of variance and the dose factor was significant (P < 0.001). dData for the 0-30 min period were examined by a two-way analysis of variance and the dose and time factors were significant (P < 0.001) as was the interaction between these factors (P < 0.001).
f u n c t i o n o f b o t h the d o s a g e o f c h l o r p r o m a z i n e used a n d the time d u r i n g w h i c h t h e h e a r t w a s e x p o s e d to it (Table 2). T h e r e was also a statistically significant i n t e r a c t i o n b e t w e e n d o s a g e a n d p e r f u s i o n time (Table 2).
Electrical activity S p o n t a n e o u s h e a r t rate d e c r e a s e d in h e a r t s perfused w i t h c h l o r p r o m a z i n e c o n t a i n i n g K - R buffer as a f u n c t i o n o f c h l o r p r o m a z i n e d o s a g e , b u t t h e time f a c t o r was n o t significant over 30 min. T h e r e was n o significant i n t e r a c t i o n b e t w e e n time a n d d o s a g e (Table 3). In o r d e r to ascertain w h e t h e r h e a r t rate h a d a significant influence o n the c o n d u c t i o n intervals t h a t we were d e t e r m i n i n g , we p a c e d a s e p a r a t e series o f h e a r t s over a f r e q u e n c y r a n g e o f 1.9-3.2 H z a n d m e a s u r e d each interval at 8 different p o i n t s w i t h i n this range. A l t h o u g h the d a t a for each interval m e a s u r e d are n o t p r e s e n t e d , we f o u n d t h a t o f the intervals r e p o r t e d in this p a p e r , only the P - R a n d Q - T inter-
vals were influenced significantly by c h a n g e s in rate (Table 4). F r o m plots o f t h e d a t a for t h e s e intervals, we d e t e r m i n e d a c o r r e c t i o n f a c t o r w h i c h was the slope o f t h e line (Table 4) in e a c h case. T h e s e c o r r e c t i o n f a c t o r s for t h e rate were t h e n a p p l i e d to t h e values obtained from each of the spontaneously beating h e a r t s for t h e P R a n d Q T intervals (Table 3). A s p r e v i o u s l y d e s c r i b e d for t h e rat h e a r t ( A r o n s o n a n d Serlick, 1977), in t h e p r e s e n t e x p e r i m e n t s c h l o r o p r o m a z i n e significantly d e c r e a s e d h e a r t rate a n d p r o l o n g e d t h e P R interval, Q R S d u r a t i o n a n d Q T interval (Table 3). H o w e v e r , the p r o l o n g a t i o n in these e l e c t r o c a r d i o g r a p h i c intervals w a s n o t d u e to a generalized d e p r e s s i o n in c a r d i a c c o n d u c t i o n . T a b l e 5 d e m o n s t r a t e s t h a t c h l o r p r o m a z i n e ' s g r e a t e s t effect was o n v e n t r i c u l a r c o n d u c t i o n . W h i l e t h e atrial c o n d u c t i o n time ( P - A ) a n d t h e A V n o d a l c o n d u c t i o n time ( A - h ) were i n c r e a s e d b y 5 8 % a n d 19%, respectively, at 5000 m g / m l . T h e c o n d u c t i o n t i m e t h r o u g h t h e His-Purkinje system (h-Q) and ventricular muscle ( Q - v ) were i n c r e a s e d by 2 5 5 % a n d 3 3 0 % at this dose.
526
C. E. ARONSON et al. Table 3. Effects of chlorpromazine on the electrocardiogram~ Heart rate~
Dose b (ng/ml) 0 50 500 5000
~ R intervald
QRS duration ~
Q T intervald
0
30 min
0
30 min
0
30 min
0
30 min
147.1±25.6 (7) 170.7±24.4 (6) 158.5±25.4
139.6 ± 32.7 (7) 163.2 ± 20.9 (6) 145.8±22.4
66.3±8.6 (7) 69.3±4.9 (6) 72.5±7.6
67.6±9.05 (7) 68.6±4.4 (6) 72.2±8.8
30.5±7.7 (7) 30.5±8.0 (6) 33.1±7.5
30.3 ± 6.9 (7) 28.5±5.8 (6) 28.4± 1 h3
197.5±33.0 (7) 173.0±12.0 (6) 181.5±24.6
(6)
(6)
(6)
(6)
(6)
(6)
(6)
168.5±14.1 (6)
126.4±30.2 (6)
67.9±6.0 (6)
114.5±31.5 (3)
38.5±11.5 (6)
83.4±45.9 (3)
179.3±10.9 (6)
204.9±40.1 (7) 179.7±14.9 (6) 200.2±17.7
(6) 321.7±0.0 ( 1)
aHearts were obtained from normal albino male guinea pigs (450-550 g). Figures in parentheses indicate the number of hearts in each group. bChlorpromazine hydrochloride calculated and expressed as the free base. CValues are beats/min± SDM. Data for the 0-30 min period were examined by a two-way analysis of variance and the dose factor was significant (P < 0.001). dValues are milliseconds ± SDM corrected for heart rate. Data for the 0-30 min period were examined by a two-way analysis of variance and the dose and time factors were significant (P < 0.001) as was the interaction between these factors (P < 0.001). ¢Values are milliseconds ± SDM. Data for the 0-30 min period were examined by a two-way analysis of variance and the dose and time factors were significant (P < 0.001) as was the interaction between these factors (P < 0.001).
Table 4. Effects of heart rate on the electrocardiograma Heart rate (beats/rain)
Interval (msec)
P-R b
Q-T~
188
123
135
146
160
172
184
198
63.5 ±5.3 (5) 189.8 ±10.3 (5)
65.6 ±4.4 (6) 185.0 ±8.6 (6)
65.6 ±4.4 (6) 180.2 ±8.0 (6)
67.t ±4.3 (6) 175.6 ±9.1 (6)
69.5 ±4.6 (6) 169.8 ±8.8 (6)
70.8 ±4.7 (6) 166.1 ±7.7 (6)
72.7 ±4.9 (6) 161.3 ±5.9 (6)
73.7 ±5.1 (5) 154.2 ±3.7 (5)
aHearts were obtained from normal albino male guinea pigs (450-550 g). Figures in parentheses indicate the number of hearts in each group. Values are expressed in milliseconds + SDM. bThe data were examined by a one-way analysis of variance and found to be significant, P = 0.002. When plotted, the slope of the line was 0.136 and r 2= 0.9962. CThe data were examined by a one-way analysis of variance and found to be significant, P~<0.001. When plotted, the slope of the line was -0.418 and r2 = 0.9933.
Thus, the greatest part of the P - R prolongation (Table 3) was due to a depression in His-Purkinje conduction and not slowing of AV nodal conduction. DISCUSSION
The concentrations of chlorpromazine utilized in our perfusion experiments were selected because they are in the same approximate range as those that caused alterations in mechanical, electrical and biochemical activity in the rat heart in vitro (Aronson and Serlick, 1977), and concentrations from 2000-50 000 ng/mi were found to decrease pacemaker activity, decrease excitability, and decrease the rate of rise of the action potential in the preparations of isolated guinea pig heart tissue studied by Arita and Imanishi (1970). The changes in mechanical activity that were observed illustrate that the guinea pig heart responds to chlorpromazine in a manner similar to that of the rat heart (Aronson and Serlick, 1977). The effects on coronary flow, for example, were most dramatic at the highest dose (5000 ng/ml), which caused a transient but significant increase in flow by 4 min, after
which flow subsequently returned toward normal (Table 1). Diastolic tension increased as a function of dose (Table 2), but isometric systolic tension was markedly depressed (Table 2), a finding consistent with data obtained by Arita and Imanishi (1970) in strips of left ventricular papillary muscle. In our experiments with the isolated, but intact, guinea pig heart, the depressant action on the preparation's contractile response was related not only to the concentration of chlorpromazine in the perfusion medium, but also to the time during which the heart was exposed to the drug. The interaction relationship between these factors was also statistically significant (Table 3). Heart rate is a rather variable factor in perfused rat heart preparations (Aronson and Serlick, 1976, 1977), but chlorpromazine clearly decreased spontaneous heart rate, in a dose dependent manner, in our experiments (Table 3). By recording electrical activity simultaneously from selected sites, we were able to measure chlorpromazine's effects on different parts of the heart's specialized conduction pathways. The effect of chlorpromazine on ventricular conduction in our experiments can be explained by a
527
Cardiac actions of chlorpromazine Table 5. Effectsof chlorpromazine on conduction intervalsa p_A~ Doseb (ng/ml) 0 50 500 5000
0 20.4±4.3 (7) 21.3±6.9 (6) 16.4~2.5 (6) 24.2±3.9 (6)
A-h~
30 min 19.1±4.9 (7) 23.4±10.7 (6) 17.6±3.6 (6) 38.0± 16.4 (5)
0 42.3±5.2 (7) 45.3±3.7 (6) 42.2±7.2 (6) 39.8±4.1 (6)
Conduction interval
30 min
h-Qd
0
44.1±6.3 (7) 45.2±3.2 (6) 42.8±8.6 (6) 47.6± 10.5 (3)
14.6±2.2 (7) 15.3±0.9 (6) 18.6±1.0 (6) 18.1 ±1.8 (6)
Q-vd
30 min 14.6~2.2 (7) 16.0±1.9 (6) 20.9±2.1 (6) 64.3±17.1 (3)
0 16.3±3.2 (7) 20.4±4.1 (6) 12.9±3.3 (6) 12.2±2.4 (6)
30 min 16.1±4.0 (7) 23.7±3.5 (6) 12.5±5.9 (6) 52.5±34.5 (3)
aHearts were obtained from normal albino male guinea pigs (450-550 g). Figures in parentheses indicate the number of hearts in each group. Values are milliseconds+ SDM. bChlorpromazine hydrochloride calculated and expressed as the free base. CData for the 0-30 min period were examined by a two-way analysis of variance and the dose factor was significant(P < 0.001). dData for the 0-30 min period were examined by a two-wayanalysis of variance and the dose and time factors were significant(P<0.001) as was the interaction between these factors (P < 0.00I).
depression in the maximum rate of rise and overshoot of action potential. Arita and Surawicz (1973) reported a significant depression in these parameters with chlorpromazine at 500 and 3000 ng/mi in isolated canine ventricular tissue. The effects were cycle length dependent and more pronounced in the isolated Purkinje fibers than in ventricular muscle. Their results indicate the mechanism of action involved a retardation of the reactivation of the rapid sodiumcarrying system and a decrease in the maximum available sodium conductance. This effect on the sodium current and mechanical function may ultimately be related to chlorpromazine's depression of mitochondrial function. Examination of the A - h interval (Table 5) showed that the time required for conduction between the low right atrium and the His bundle, AV nodal conduction, was increased by chlorpromazine. At this site, dosage was the significant factor and the time of exposure did not show statistical significance. His-Purkinje conduction, the time interval for conduction between the His bundle and earliest ventricular activation increased to a greater degree than the atrial parameters following perfusion with chlorpromazine-containing medium (Table 5). The concentration of drug and the duration of exposure were significant factors, and there was an interaction between them. The same greater effect was observed on conduction through ventricular muscle, the Q--v interval, as measured by the time difference between earliest and latest ventricular activation (Table 5). When Langslet (1969) measured chlorpromazineinduced electrical changes in the isolated rat heart, he found that the PR, Q R S and Q T intervals were all prolonged. Our findings, both in the rat heart (Aronson and Serlick, 1977) and in the guinea pig heart (Table 3) show similar electrocardiographic changes, and in the guinea pig heart, the dosage o f chlorpromazine and the time of exposure were statistically significant, as was the interaction between these factors. Our data indicate the greatest depressant action of chtorpromazine is on the specialized ventricular conduction system and ventricular muscle of the isolated perfused guinea pig heart.
Chlorpromazine altered the function of atrial muscle and it slowed conduction through that tissue. The data in Table 5 show that, as a function of dose, it lengthened the time interval between the beginning of the high right atrial wave and the latest A-wave on the His bundle electrogram. Sugiyama and Ozawa (1979) have shown that flavin-adenine-dinucleotide (FAD) antagonized chlorpromazine-induced ventricular arrhythmias in canine hearts. They postulated that F A D counteracted the adverse effects of chlorpromazine on heart mitochondria and that impaired mitochondrial function was the underlying biochemical cause for such arrhythmias. Subsequently, Pinto et al. (1982) have presented evidence that chlorpromazine and related phenothiazines with structural similarities to riboflavin inhibited the formation of F A D from riboflavin in rat hearts. In their experiments, tranquillizers without structural similarities had no inhibitory effect of F A D formation. In future experiments, we plan to study the reversibility of chlorpromazine-induced conduction alterations in our system and to investigate the action of antagonists like F A D and its precursors on conduction pathways in such preparations. REFERENCES
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