9Nagoya J. med. Sci. 39: 9-14, 1976STUDIES ON ADENYL CYCLASE SYSTEM IN
MYOCARDIUM (PART II)
ADENYL CYCLASE SYSTEM IN MYOCARDIAL
INFRACTION OF DOGSKAZUSHIGE MORI

2nd Department of Internal Medicine, Nagoya University School of Medicine(Director: Prof Tatsuo Satake)

Many reports agree on the increase of CA concentration in blood and urine of patients
just after acute myocardial infarction,l) - 6) especially in cases of complications such as
arrhythmia, shock and congestive heart failure. Physiological actions of CA on the heartsuch as inotropic and chronotropic action are mediated by cyclic AMP. It is believed thatthe level of myocardial cyclic AMP is a result of a balance between its rate of synthesis, catalyzed by adenyl cyClase, and that of hydrolysis, catalyzed by phosphodiesterase.
In the present paper, myocardial CA, adenyl cyclase and phosphodiesterase activity in theinfarcted area and the non-infarcted area were measured after the ligation of left anterior
descending coronary artery of mongrel dogs to search for the role of CA and adenyl cyclasecyclic AMP system in acute myocardial infarction.

MATERIALS AND METHODS

1. Production of myocardial infarction
Fourty four mongrel dogs, weighing 9 - 15 kg, were used. The thorax of mongrel dogs
were opened under anesthesia induced by intravenous injection of 30 mg/kg of sodium
hexobarbital. Under artificial respiration, myocardial infarction was produced by the ligation of the proximal part of the left anterior descending coronary artery. Myocardialischemia was ascertained by ST segment elevation of ECG monitoring by direct epicardial
leads. (Fig. 1) Free walls of the left ventricle were removed directly from the open thorax
and used for each assay. The dogs were divided into six groups: Nine dogs of 15 minutes
after ligation of the left anterior descending coronary artery are abbreviated by MI I5 " six of60 minutes by MI 60" six of 2 days to MI 2 , seven of 7 days by MI 7 and six of 30 days by
MI 30 .
2. Preparation of samples and determination of myocardial CA, adenyl cyclase activity andphosphodiesterase activity were described in part I. The result were analyzed using
student's "t" test.

This study was presented at the 35th Annual Meeting of Japanese Circulation Society in Tokyo, April 4,1971.
~-IllZ

Received for publication December 22, 1975

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RESULTS
1. CA concentration in the left ventricle
Mean concentration of CA of the left ventricle of 10 normal dogs was 1.00 ±0.081 Jlgjg(±S.E.M.). In the infarcted area it was 0.77 ±0.077 Jlgjg in MILS' and 0.80 ±0.077 Jlgjg inMI 60., and both showed a slight reduction when compared with normal. The CA concentration of the infarcted area of MI 2 , MI 7 and MI 30 groups showed significant reduction. In
the marginal area and non-infarcted area, the ventricular CA concentration showed slight decrease at 15 minutes and 60 minutes after the ligation and the most pronounced reduction
was observed 2 days after, which averaged 0.39 ±0.056 Jlgjg in marginal area and 0.51
±0.081 Jlgjg in non-infarcted area of MI 2 respectively. This reduction recovered fairly after
7 days and almost to normal 30 days after. (Fig. 2)_I'IW

infarcted area... .-!..!..-,f....;.,.:..j marginal area

1.0. , non-infarcted area**,---,

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60min

2days

7days

30daysFig. 2. CA concentration in the left ventricle of dogs in six groups.
**: p < 0.01

2. Adenyl cyclase activity in the left ventricle
The adenyl cyclase activity in the left ventricle of 6 normal dogs averaged 0.975 ±O.l ~mJlmolejhjmg (±S.E.M.). The activity of infarcted area in MILS' was higher than that of normal

ADENYL CYCLASE SYSTEM IN MYOCARDIUM (2)IIdogs, and averaged I. I 7 ±O. I 5mj1 mole/h/mg, which was significantly elevated comparedwith non-infarcted area in MIlS" (0.77 ±0.08mj1 mole/h/mg) (p < 0.05). The adenyl cyclase
activity of MI 60., MI 7 and MI 30 groups were lower than that of normal dogs. In MI 60., itaveraged 0.57 ±0.084mj1 mole/h/mg, which was still higher than that of non-infarcted area,(0.21 ±0.05mJI mole/h/mg). But after 2 days and 7 days, the adenyl cyclase activity of theinfarcted area which had been lower than that of non-infarcted area, gradually decreased,
and averaged 0.29 ±0.05mj1 mole/h/mg in MI 2 , 0.22 ±0.08mj1 mole/h/mg in MI 7 and 0.15
±0.04mj1 mole/h/mg respectively. (Fig. 3)_m... nde/h/mgo1.0

infarcted are"marginal area

&11 non-infarcted area~

Cont15m;n60 min

2 days

7days

30daysFig. 3. Adenyl cyclase activity in the left ventricle of dogs in six groups.
*: p <0.05

3. Phosphodiesterase activity in the left ventricle
The phosphodiesterase activity in the ventricle of 6 normal dogs averaged 140 ±7.45mll
mole/h/mg (±S.E.M.). There were no significant differences in activity between infarcted,
marginal and non-infarcted areas, each of which averaged about I 35mll mole/h/mg. The activity showed a little reduction in MI 60" But on 2 days and thereafter, the activity of infarcted area was gradually reduced, and averaged 72.23 ±7. I I mj1 mole/h/mg in MI 2 , 5 1.8±9.24mj1 mole/h/mg in MI 7 and 34.35 ±3.2~mj1 mole/h/mg in MI 30 respectively. In noninfarcted area, the activity was reduced a little compared with normal and remained almost
constan 1. (Fig. 4)_om... mo~h!mg

infarcted area
marginal area

&11 non-infarcted area>. 150

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15 min60min

2 days7 days30daysFig. 4. Phosphodiesterase activity in the left ventricle of dogs in six groups.
*: p < 0.05**: p < 0.01

12K. MORIDISCUSSION
The present experiment showed a slight decrease of CA concentration in the infarcted
and non-infarcted areas of the left ventricle after 15 and 60 minutes of ligation comparedwith normal without statistical significance. Many reports showed the depletion of myocardial CA in acute myocardial infarction,?) - 8) and the present study showed the sametendency. The mechanism of myocardial CA depletion in acute myocardial ischemia isconsidered chiefly to be due to accelerated excretion of CA from the myocardium. On theother hand, blood CA is known to increase in myocardial infarction.t), 4) It is consideredthat the elevated blood CA is not only caused by the excretion of myocardial CA into thecirculation due to the ischemia, but also by the sympathetic nervous system and adrenals·due to stress such as pain or of the lung edema. 2) Moreover, a remarkable diminution of CA
in the infarcted area on 2, 7 and 30 days after ligation was due to the development ofmyocardial necrosis. As already described, inotropic and chronotropic responses of CA to
myocardium is considered to be mediated by myocardial cyclic AMP. So, the investigationof myocardial adenyl cyclase-cyclic AMP system in myocardial ischemia seemed to be very
important to understand the pathobiochemical changes of acute myocardial ischemia. At
present, there are a few studies in this field. In the present experiment, adenyl cyclase
activity in the infarcted area of the left ventricle was increased compared to that of thenon-infarcted area after 15 minutes of the ligation. Sixty minutes after the ligation, allmyocardial adenyl cyclase activity showed depressions due to development of myocardial
necrosis.
But adenyl cyclase activity in the infarcted area continued to be relatively higher thanthat of the non-infarcted area at 60 minutes after the ligation. Phosphodiesterase activity inthe ventricle showed no significant change in infarcted and non-infarcted areas at 15 and 60
minutes after the ligation. Phosphodiesterase activity on 2, 7, and 30 days after ligation
showed significant depression such as adenyl cyclase activity.
Wollenberger9) reported that myocardial cyclic AMP began to be elevated 5 seconds after
coronary occlusion and reached maximum values after 10 to 15 seconds. The elevatedlevel was then maintained for at least 10 minutes. He pointed ou t that the rapid initial risein cardiac cyclic AMP within 1 minute following the arrest of blood flow was due to increase of adenyl cyclase activity by excreted noradrenaline and that the prolonged main tenance of the elevated cyclic AMP level in the ischemic tissue may conceivably, and at leastin part, have the consequence of an accumulation of acid products of glycolysis, causing adecrease in the activity of cyclic nucleotide phosphodiesterase. But he did not measure thecardiac phosphodiesterase activity. In this study, the cardiac phosphodiesterase activity wasmeasured and showed no significant changes, and only adenyl cyclase activity was elevatedsignificantly. The mechanism of elevated cardiac adenyl cyclase activity in the early stage of
myocardial ischemia is not fully clear, but it is not a secondary phenomenon due to thechanges of myocardial CA, because CA in infarcted area is not decreased. The change ofadenyl cyclase activity could be due to the removal of certain inhibitors of this enzyme
from the cell membrane as McNamara 10) had pointed out. Of course, the possibility ofblood CA elevation in early stage of myocardial ischemia is not neglectable.
The transient elevation of myocardial adenyl cyclase activity in the early stage of acute
myocardial infarction is not fully concluded from present results. In addition to the rise ofblood CA in the early stage of myocardial infarction, myocardial adenyl cyclase activity waselevated and unequal adenyl cyclase activity in parts of infarcted and non-infarcted areas

ADENYL CYCLASE SYSTEM IN MYOCARDIUM (2)13

was noticed. This indicates that the cyclic AMP production would be unequal in the earlystage of myocardial infarction. At present, the mechanism of arrhythmias with acute
myocardial infarction has been chiefly studied electrophisiologically, and not frombiochemical standpoints such as myocardial CA and cyclic AMP. The elevation of
myocardial adenyl cyclase activity and the unequal distribution of cyclic AMP production
were notable facts in relation to the occurrence of arrhythmias at the early stage of
myocardial infarction. Adenyl cyclase activity in the infarcted area was gradually decreased
2, 7, and 30 days after ligation of the coronary artery.
In the non-infarcted area, adenyl cyclase activity showed recovery in 60 minutes and after,
but still was lower compared with normal. The reason for these drops of adenyl cyclase
activity in non-infarcted area is considered to be due to hyperfunction to compensate forthe dysfunction of infarcted area. Adenyl cyclase activity in non-infarcted area is considered primarily depressed in the same manner in cardiac hypertrophy and impending heart
failure described in part I, and the decrease of its activity may playa role in the mechanismof cardiac failure after myocardial infarction.

SUMMARY
In order to study the pathophysiological role of CA and adenyl cyclase-cyclic AMP
system in the early stage of myocardial infarction, CA, adenyl cyclase activity and phosphodiesterase activity in the infarcted and non-infarcted areas in experimental infarction ofdogs were measured.
1. CA concentration in the infarcted area showed little change compared to non-infarcted
area 15 minutes and 60 minutes after coronary artery ligation, but significant was reduced after 2 days and thereafter.
2. Adenyl cyclase activity in the infarcted area was significantly increased compared to
the non-infarcted area at 15 minutes, and this tendency had continued while 60
minutes after, but decreased after 2 days and thereafter.
3. Phosphodiesterase activity in the infarcted area was not significantly changed in theearly stage of myocardial infarction, and there had been gradual diminution after 2days and later.
ACKNOWLEDGEMENT
The author expresses deep gratitude to Prof. T. Satake for his encouragement andguidance. The author is also grateful to Dr. N. Yamazaki and Dr. K. Ogawa for their precious advances and suggestions. Thanks are also extended to Dr. H. Yamamoto, Dr. Y.
Naito, Dr. H. Sassa, Dr. Y. Suzuki, Dr. K. Mizutani, Dr. Y. Miyagishima, Dr. M. Sugiura, Dr.
N. Kakizawa, Dr. M. Okubo and Dr. M. Yoshida.

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14

K. MORl

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