THE MECHANISM OF EPINEPHRINE ACTION.

IV. THE INFLUENCE OF EPINEPHRINE ON LACTIC ACID PRO- DUCTION AND BLOOD SUGAR UTILIZATION.

BY CARL F. CORI AND GERTY T. CORI.

(From the State Institute for the Study of Malignant Disease, Buffalo.)

(Received for publication, August 13, 1929.)

It has been shown in a previous paper that subcutaneous in- jections of epinephrine lead to an increase in blood lactic acid of rabbits and cats (1). The effect was more pronounced in the former species than in the latter. This increase in blood lactic acid after epinephrine injection was also observed in men (2) and rats (3) and it seems likely therefore that it occurs in all mammals. Other experiments made it seem probable that the lactic acid which was found in increased amounts in the blood had its source in muscle glycogen, since the latter was found to diminish after epinephrine injections (4, 5). In the rat it is possible to analyze the body in toto for glycogen and not merely corresponding muscles before and after injection. Non-glycosuric doses of epinephrine caused a disappearance of muscle glycogen in fasting rats in which the glycogen remained practically constant when no injection was given (5). The animals were killed 3 hours after the injection while active absorption of epinephrine from the subcutaneous tissue was still going on. In rats in the postabsorptive state, muscle glycogen disappeared nearly twice as fast after non-glyco- suric doses of epinephrine as in uninjected controls or after insulin injections (4). Several other authors, who observed a decrease in muscle glycogen were cited in these two papers. More recently Chaikoff and Weber (6) state that they observed a decrease in muscle glycogen in the standard white rat after epinephrine. Geiger and Schmidt (7) observed mobilization of the glycogen depots of the muscles in phlorhizinized dogs, and they were able to account in this way for the extra sugar appearing in the urine. Blatherwick and Sahyun (8) noted a decrease in muscle glycogen

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Epinephrine and Lactic Acid

in rabbits, and Sahyun and Alsberg (9) made use of epinephrine to free the muscles of glycogen. Eadie (10) concludes that l+ hours after administration of epinephrine to cats under amytal anesthesia the glycogen content of the muscles is unaltered, but this contention is not borne out by the experiments. This author published two control experiments and two experiments with epinephrine. In the former the muscle glycogen rose in one case from 0.95 to 0.99 per cent and in the other it fell from 1.09 to 0.97 per cent. After epinephrine injection the muscle glycogen of one animal diminished from 0.93 to 0.9 per cent, which is a nega- tive result, but in the other it fell from 1.3 to 1.0 per cent. The author, who determined glycogen in only 10 gm. of muscle, does not seem to realize what this means when the whole muscle mass is taken into consideration. According to Best et al. (11) the muscles constitute 50 per cent of the body weight of cats. Since the animal weighed 2.93 kilos, the difference in muscle glycogen of 0.3 per cent must be multiplied by 14.65. In other words, in this experiment with epinephrine, when taken at its face value, muscle glycogen disappeared to the extent of 4.4 gm. During the same time only 0.8 to 0.9 gm. of glycogen disappeared from the liver. Hence, one is justified in concluding that the action of epinephrine on muscle glycogen is far more important from a quantitative standpoint than the action on liver glycogen, which is the opposite conclusion from that reached by Eadie. In view of this, it seems remarkable that the author did not continue his observations before publishing his results. The point is, of course, that in 13 hours epinephrine might mobilize a considerable quantity of muscle glycogen, as shown in the above calculation, without appreciably affecting the percentage of glycogen in one individual muscle or, indeed, exceeding the considerable error involved in this type of experiment. When blood lactic acid is determined under the conditions obtaining in Eadie’s experiments, definite evidence is obtained that epinephrine acts on muscle glycogen.

In the present experiments the relation between the blood sugar and lactic acid curves after epinephrine injection was studied in detail and lactic acid was also determined in arterial and venous blood of the leg. In this way it could be shown that mobilization of muscle glycogen is a constant as well as an early effect of epineph- rine injections. Since insulin in suitable doses prevents the rise

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C. F. Cori and G. T. Cori 685

in blood sugar after epinephrine injection, it seemed of interest to see whether insulin would have the same effect on blood lactic acid. Insulin alone does not lead to an appreciable increase in blood lactic acid, provided the blood sugar remains above the level at which hypoglycemic symptoms occur (1, 12). It was found that insulin has very little effect on the increase of blood lactic acid after epinephrine injection, a point which will be dis- cussed later.

EXPERIMENTAL.

Male rabbits of a quiet disposition were kept for some time in the laboratory on a diet of green vegetables, carrots, oats, and table scraps, to insure their good health. They were fasted for

Time.

9.40 a.m. 10.40 “ 11.40 “

12.40 p.m. 1.40 “

TABLE I.

Control Experiment.

Blood sugar. Bloo~iactio Remarks.

mg. pw 100 cc. “9. per 100 cc.

120 7.8 Rabbit A, weight 2300 gm. No

117 10.5 injections. 110 14.1

112 11.1 111 10.7

24 hours previous to the experiments. Dilatation of the marginal ear vein was produced by rubbing with xylene and a clean cut was made by means of a razor. The blood flowed freely, and the collection was effected in a short time and with a minimum of stasis. The bleeding was stopped by application of some cotton and a short compression. For the next bleedings it was merely necessary to tear away the cotton and rub the incision with xylene. The rabbits were sitting in boxes which afforded little opportunity for movement. While the blood was being taken, which lasted only 1 minute, the animals were perfectly quiet and showed no signs of excitement. Generally two samples of blood were re- moved before either epinephrine alone or combined with insulin was injected. The respective doses of the two hormones are given in Table II. No signs of discomfort or twitching of muscles were

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686 Epinephrine and Lactic Acid

TABLE II.

Blood Sugar and Lactic Acid Curve after Epinephrine and Insulin Plus Epinephrine.

The results are expressed in mg. per 100 cc. of blood.

-- Before. ‘I I 122 I 129 13.1 0.5 mg. epinephrine.

1 hr. 305 78.1 2 hrs. 312 73.6 3 ‘< 254 66.4 4 ‘I 198 67.9

Before. 121 7.4 “ 142 8.9

0.5 mg. epinephrine.

1 hr. 332 79.1 2 hrs. 399 50.6 3 I‘ 352 33.9 4 L‘ 244 23.4

Before. 120 “ 121 14.6

%n 0.5 mg. epinephr 1 hr. 320 2 hrs. 350 3 I( 305 4 “ 180

Before. 116 ‘I 131

0.5 mg. epinephr I

in

le. 62.5 52.4 44.1 29.5

11.1 10.6 le.

1 hr. 381 75.9 2 hrs. 417 73.7 3 ‘i 416 51.2 4 ‘I 321 28.3

Blood sugar. Blo;$ixctic

123 15.7 138 16.9

40 units insulin, 0.5 mg. epinephrine.

124 71.6 98 67.2 80 52.7 65 48.2

115 13.5 130 15.1

20 units insulin, 0.5 mg. epinephrine.

194 69.5 169 55.8 106 37.8 80 31.2

112 14.8 20 units insulin, 0.5 mg. epinephrine.

93 54.3 62 43.7 46 45.1

132 7.2 126 8.3

15 units insulin, 0.5 mg. epinephrine.

222 61.4 209 40.3 146 27.4 105 23.0

Remarks.

Rabbit 1, weight 2400 gm.

Rabbit 2, weight 2300

gm.

Rabbit 3, weight 2300 gm. Convulsions 10 min. after last blood sampling.

Rabbit 4, weight 1700 w.

observed in the rabbits after epinephrine injection. Blood sam- ples were removed every hour for 4 hours and a total quantity of 9 to 10 cc. of blood was withdrawn during that time. A con-

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C. F. Cori and G. T. Cori 687

trol experiment was performed in order to show that the removal of such quantities of blood and the handling of the rabbits are without influence on sugar and lactic acid content of the blood (Table I).

Blood sugar was determined by means of the Hagedorn and Jensen method (13) in the same Folin-Wu filtrate in which the lactic acid determination was carried out. For lactic acid the method of Friedemann and Kendall (14) was used with excellent

HOURS 0 / 2 3 4

FIG. 1. Graphic representation of the average values calculated from Table II. 0-- o represents blood sugar after epinephrine; q - q , blood lactic acid after epinephrine; A- A, blood sugar after epinephrine plus insulin; l - 0, blood lactic acid after epinephrine plus insulin.

success. The recoveries of lactic acid in pure solution and after addition to blood were very satisfa,ctory. Frequent determina- tions of the reagent blank were found essential in an effort to determine as nearly as possible true lactic acid values.

Two experiments, one with epinephrine alone and one with insulin plus epinephrine, both injected subcutaneously in different skin regions, were performed on the same rabbit. An interval of 8 to 12 days was allowed between two experiments and care was

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688 Epinephrine and Lactic Acid

taken to alternate the order in which the two experiments were made in the different rabbits. The results obtained are shown in Table II. A compound curve of the average values of Table II was drawn in Fig. 1. By way of comparison, glucose was injected intravenously into two normal rabbits, the aim being to determine at what rate glucose must be supplied in order to obtain the same blood sugar curve as after epinephrine injection (Table III). This rate was found to be greater than 2.5 gm. of glucose per kilo per

TABLE III.

Blood Sugar and Lactic Acid Curve after Glucose Injection.

bra.

Before injection. After beginning

injection.

1

2 3 4

Before injection. After beginning

injection. 1

2 3 4

-

--

I -

270 23.0

286 27.6 223 22.1 139 18.8

125 18.2

297 312 22.6

306 153 17.9

Remarks.

Rabbit B, weight 1SOOgm. 1.27 gm.

glucose intravenously every 20 min. for 3 hrs.; total injected 11.43 gm. (2.1 gm. glucose per kilo

per hr.),

Rabbit C, weight 2300 gm. 1.92 gm.

glucose intravenously every 20

min. for 3 hrs.; total injected 17.28 gm. (2.5 gm. glucose per kilo per hr.).

hour, The experiments in Table III also show that hyperglycemia as such does not lead to marked changes in blood lactic acid.

Another group of rabbits was used in experiments which were designed to show the site of lactic acid formation after epinephrine injection. For this purpose one femoral vein and carotid artery were exposed under amytal anesthesia (60 to 70 mg. per kilo intraperitoneally) with as little trauma as possible. Hinsey and Davenport (15) have shown that amytal does not cause a decrease of muscle glycogen. Anesthesia was used to insure complete mus- cular relaxation. The rabbits were not tied down during the experi-

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Before injection. 149 146 -3 14.3 12.5 -1.8 Rabbit 5, weight 3000 After injection. gm. 1 mg. epineph- 1 hr. 320 318 -241.947.1 f5.2 rine subcutane- 2 hrs. 350 351 +133.239.9 f6.7 ously. 3 cc 327 324 -327.529.1 +1.6

Before injection. After injection. 30 min. 1 hr. 2 hrs.

148 144 -424.424.0 -0.4 Rabbit 6, weight 2806 gm. 1 mg. epineph-

225 220 -557.070.7 f13.7 rine subcutane- 306 300 -676.686.9 f10.3 ously. 355 353 -250.153.7 f3.6

Before injection. After injection. 30 min. 1 hr. 2 hrs. 3 I‘

131 128 -3 13.7 13.9 +0.2 Rabbit 7, weight 2460 gm. 0.5 mg. epi-

182 178 -424.829.4 +4.6 nephrine subcuta- 225 220 -541.455.3 f13.9 neously. 268 255 -1344.855.6 +10.8 283 275 -856.158.6 f2.5

Before injection. After injection. 30 min. 1 hr. 2 hrs. 3 I‘

145 135 -10 17.8 19.9 $2.1 Rabbit 8, weight 3100 gm. 1 mg. epineph-

228 215 -1325.533.7 +8.2 rine subcutane- 258 253 -529.745.8+16.1 ously. 303 294 -951.970.3 f18.4 330 315 -1552.259.8 +7.6

Before injection. After injection. 30 min. 1 hr. 2 hrs. 3 ‘L

140 137 -3 16.9 15.4 -1.5 Rabbit 9, weight 2500 m 1.0 mg. epin-

245 240 -521.141.3 f20.2 ephrine subcutane- 298 295 -351.155.6 +4.5 ously. 368 360 -865.275.9+10.7 355 352 -357.374.3 f17.0

C. F. Cori and G. T. Cori 689

TABLE IV.

Comparison of Arterial and Venous Blood Sugar and Lactic Acid after Epinephrine.

The animals were under amytal anesthesia. The results are expressed in mg. per 100 cc. of blood.

Remarks.

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690 Epinephrine and Lactic Acid

ment. Blood was drawn from the vein without interfering in any way with the blood flow, and within 1 minute a sample of blood was taken from the carotid artery. Difficulty from bleeding was not encountered and all blood samples were removed from the same

TABLE V.

Comparison of Arterial and Venous Blood Sugar and Lactic Acid during Glucose Injection at Constant Rate.

The animals were under amytal anesthesia. The results are expressed in mg. per 100 cc. blood.

hrs.

Before injection. After beginning

injection.

1 2 3

129 129 +O 10.4 11.9 f1.5 Rabbit D, weight 2700 gm. 1.66 gm. glu- cose per kilo per hr.

349 330 -1919.820.2 $0.4 for 3 hrs. 306 289 -1723.923.1 -0.8

285 270 -1524.420.4 -4.0

Before injection. 163 160 -3 14.8 11.3 -3.5 Rabbi% E, weight 1900

After beginning gm. 1.45 gm. glucose

injection. per kilo per hr. for

1 328 315 -1316.310.4 -5.9 3 hrs. 2 330 312 -18 17.7 15.7 -2.0

3 358 344 -1426.721.1 -5.6

Before injection. After beginning

injection.

1 2

3

145 144 -1 Rabbit F, weight 2400

gm. 1.68 gm. glu- cose per kilo per hr.

322 286 -36 for 3 hrs.

351 324 -27 299 280 -19

-

Remarks.

vein. All animals survived the experiments indefinitely. Where- as before the injection of epinephrine venous blood coming from the leg contained less lactic acid than arterial blood, this was reversed after the injection. This result is shown in Table IV. It is of importance to note that the blood lactic acid increased

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C. F. Cori and G. T. Cori 691

after epinephrine in spite of the fact that the animals were at absolute rest on account of the anesthetic. Three control experi- ments were performed in which hyperglycemia was produced by means of an injection of glucose (Table V). In this case the ve- nous blood contained less lactic acid than arterial blood, and the blood lactic acid did not rise as during epinephrine hyperglycemia. Special attention is called to the arteriovenous blood sugar differ- ences. When epinephrine is injected, the differences remain small

TABLE VI.

Influence of Epinephrine on Blood Lactic Acid of Cat.

Time.

10.25 a.m. 10.50 “ 10.53 “ 11.53 “ 12.53 p.m. 1.53 “ 2.53 “

9.40 a.m. 10.40 “ 12.20 p.m. 12.42 “ 12.45 “ 1.30 “ 2.15 “ 3.15 “

God suga,

mg. per 100 cc.

111 105

232 294 320 300

91

272 260 271

BlOOdl&Cti

ng. per 100 cc.

8.6 10.7

40.6 31.8 29.1 15.5

11.2

38.3 52.2 42.7

Remarks.

July 17, 1929. Weight 3200 gm.

0.6 mg. epinephrine subcutaneously. Animal restless.

“ “

July 26, 1929. 180 mg. amytal subcutaneously. 45 “ “ ‘I 45 “ “ intraperitoneally.

3 “ epinephrine subcutaneously.

in spite of the marked hyperglycemia. In contrast to this, it can be seen in the control experiments in Table V that the muscles take up more sugar when hyperglycemia is produced by an injec- tion of glucose.

In Table VI two experiments on a cat are recorded. In a pre- liminary test 0.2 mg. of epinephrine per kilo was injected into the unnarcotized animal. This was followed by a marked rise in blood sugar and lactic acid, though the dose was 5 times smaller than the one used by Eadie. The curves for both blood sugar and

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692 Epinephrine and Lactic Acid

lactic acid resemble those obtained on rabbits with the exception that all values, especially those for lactic acid, tend to be lower. In the second test exactly the same conditions as in the experi- ments of Eadie were established, because it seemed advisable to see what effect the prolonged anesthesia has on lactic acid produc- t.ion in muscle. The cat was given 60 mg. of amytal per kilo subcutaneously, followed 30 minutes later by 15 mg. This did not prove to be sufficient anesthetic, because the animal showed violent shivering, and anot.her 15 mg. per kilo was therefore given intraperitoneally. After 3 hours of anesthesia a blood sample was removed and the dose of epinephrine that Eadie used (1 mg. per kilo) was injected subcutaneously. A marked increase in blood lact,ic acid resulted, which shows that a breakdown of muscle glycogen occurred in this experiment,

DISCUSSION OF RESULTS.

The previous observation that subcutaneous injections of epi- nephrine produce a marked rise in the lactic acid content of the blood is confirmed and amplified. The increase occurs shortly after the injection and reaches its maximum in 1 hour. In the next 4 to 5 hours the blood lactic acid gradually returns to the initial level. This is the effect to be observed in rabbits following t,he injection of 0.2 to 0.26 mg. of epinephrine per kilo (Table II, and Fig. 1). After large doses the increase in blood lactic acid is greater, the peak of the lactic acid curve occurs after 2 hours or later, and t.he return to normal is more prolonged.

The shape of the lactic acid curve depends on the rate of pro- duction of lactic acid and the rate of removal of lactic acid from the blood. Evidence is offered in the present paper that the lactic acid production occurs in muscle and that it persists for several hours; that is, as long as epinephrine is being absorbed into the blood stream. By comparing t,he lactic acid content of arterial and venous blood it was found that blood drawn at various time intervals from the femoral vein following epinephrine injections contained decidedly more lactic acid than arterial blood, while before the injection venous blood from the leg contained the same amount or less lactic acid than arterial blood (Table IV). The average differences in Table IV were as follows: Before the in- jection there was 0.3 mg. less lactic acid in venous than in a.rterial

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C. F. Cori and G. T. Cori 693

blood; 30, 60, 120, and 180 minutes after the injection there were 11.7, 10.4, 10.0, and 7.1 mg. more lactic acid in venous than in arterial blood. When hyperglycemia was produced by glucose injection, there occurred only a slight rise in blood lactic acid and venous blood contained less lactic acid than arterial blood (Table V). As regards removal of lactic acid from the blood, it was shown in a previous paper (5) that a large part of the lactic acid derived from muscle glycogen is converted into liver glycogen and it was pointed out that epinephrine, since it is responsible for this transfer of muscle glycogen to liver glycogen, makes the former available as blood sugar.

The blood sugar curve after epinephrine injection formed a more or less distinct plateau, since there was not much difference in the average blood sugar values of the 1, 2, and 3 hour periods after the injection (Fig. 1). After 4 hours the blood sugar was still markedly elevated. A point to be considered carefully is the quantitative aspect of a hyperglycemia of such magnitude and duration as occurs after epinephrine injections. It is generally accepted that liver glycogen is the immediate source of blood sugar, and it is evident therefore that mobilization of liver glyco- gen must be involved in the production of epinephrine hypergly- cemia.’ However, it can easily be shown that such quantities of glycogen as are usually present in the liver, even if they would be mobilized completely, could only lead to a hyperglycemia of short duration, provided the tissues retain their normal ability to utilize sugar. In order to arrive at a quantitative estimate it is merely necessary to determine how much glucose must be in- jected intravenously into a normal rabbit in order to produce a blood sugar curve similar to that after epinephrine injection. If this is done, one finds that more than 2.5 gm. of glucose per kilo per hour must be administered (Table III). From this it can be calculated that the liver of a rabbit of 2 kilos, containing 5 per cent glycogen (about 4 gm.), could supply such quantities of sugar not even for 1 hour, while the epinephrine hyperglycemia lasts for 5 hours or longer and leads to considerable sugar excretion

1 This has been expressed clearly on several occasions and also in a sum- marizing article (16). The fact that blood sugar is of hepatic origin does not necessarily mean that the liver and no other organ is responsible for the

epinephrine hyperglycemia.

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in the urine. What is, then, the mechanism of epinephrine hy- perglycemia? Two possibilities have to be considered. One is that the rabbit receiving epinephrine utilizes less blood sugar than the rabbit receiving an intravenous injection of 2.5 gm. of glucose per kilo per hour. In this case the supply of blood sugar by the liver could last longer and the explanation would be that a low rate of mobilization of liver glycogen leads to hyperglycemia be- cause epinephrine decreases the utilization of blood sugar in the tissues. The other possibility is that liver glycogen is being mo- bilized at a high rate (above 2.5 gm. per kilo per hour), but that new liver glycogen is being formed as fast as it disappears. In this case there would be no need for the assumption of a decreased utilization of blood sugar in the tissues. Finally a combination of both possibilities might occur.

A new formation of liver glycogen from blood lactic acid was found in previous experiments (5) but the rate of this process is too low to enable the liver to produce the required large amounts of blood sugar. On the other hand, a lowered utilization of blood sugar in the peripheral tissues was clearly observable in glucose- fed and epinephrine-injected rats (17). This low utilization was regarded as the essential factor necessary to account for the long drawn out epinephrine hyperglycemia. Obviously, some mobili- zation of liver glycogen must occur in order to raise the blood sugar level but the rate of this mobilization is not excessive after small doses of epinephrine, as was shown by the fact that in the rat under various conditions new formation of liver glycogen from blood lactic acid overbalanced the loss incurred by glycogen mo- bilization. A low utilization of blood sugar is also shown in the present experiments. The normal difference in arterial and ve- nous blood sugar of unanesthetized rabbits was the subject of a previous investigation and was found to be 7 mg. in favor of ar- terial blood as an average of 60 observations (18). In the present experiments on rabbits under amytal (Table IV) the normal aver- age difference was smaller (5 mg.). During epinephrine hypergly- cemia the arteriovenous difference was hardly increased, and it can be stated quite definitely that the peripheral tissues did not respond to the hyperglycemia with increased withdrawal of sugar from the blood. Thus 30, 60, 120, and 180 minutes after the injection, the venous blood of the leg ‘contained on an average

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C. F. Cori and G. T. Cori

7, 4, 6, and 7 mg. less glucose than arterial blood. In contrast to this, average differences of 23, 21, and 16 were found when glucose was injected intravenously for 3 hours at a constant rate into rabbits under amytal anesthesia (Table V). Amytal lowers the glucose tolerance and it is therefore of importance that a similar result was obtained in unanesthetized rabbits in which a much milder hyperglycemia was produced by feeding glucose by mouth (18). In these experiments average differences of 20.3, 16.5, 17.2, and 11.8 mg. were found for the time intervals indicated. When insulin was injected along with the glucose feeding, the average differences between arterial and venous blood sugar were 25.7, 22.4, 25.0, and 19.0 mg. (18). Insulin is thus seen to acceler- ate the disappearance of sugar from the blood, and it becomes clear how insulin antagonizes epinephrine hyperglycemia and oice versa. These two hormones are mutually antagonistic mainly because of their divergent effect on blood sugar utilization.2

2 Cannon believes that utilization of blood sugar in muscle is facilitated during epinephrine hyperglycemia and he is therefore opposed to our ex-

perimental evidence to the contrary; namely, that epinephrine decreases utilization of blood sugar. His statement (19) that emotional excitement can raise blood sugar 30 per cent and more in a few minutes and his ob-

jection that “the hyperglycemia comes too soon and is too clearly of hepatic origin to be ascribed to failure of use of glucose by peripheral tissues” are not to the point for two reasons. In the first place we ex-

plained the persistence of epinephrine hyperglycemia by a decreased utili- zation of blood sugar and not the initial rise in blood sugar. The latter has not yet been subjected to a thorough quantitative analysis. Sec-

ondly, we have repeatedly emphasized that blood sugar is of hepatic origin and a quotation (4) from one of our papers makes our stand- point clear; namely, “ . . . that other factors play a role in the pro- duction of hyperglycemia besides mobilization of liver glycogen.” Cannon

also offers as evidence against our view the observation that “dogs ex- hausted by running can be made to continue (i.e. using sugar in their muscles) and will put forth from 17 to 44 per cent additional energy if

they are given subcutaneously small doses of adrenin.” (The italics are ours.) However, Cannon offers no experimental evidence that the addi-

tional muscular work was performed at the expense of blood sugar and he also states in another paper (20) that “it is clear that adrenalin has effects on muscular fatigue quite apart from mobilizing sugar in the blood or improving circulation.” It was shown experimentally that under certain conditions epinephrine enables the muscles to utilize a greater proportion of their glycogen (4). The mobilizing action of epinephrine on muscle

glycogen is also connected with the increase in blood lactic acid. Campos,

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696 Epinephrine and Lactic Acid

In the experiments with simultaneous administration of insulin and epinephrine (Table II), the dose of the latter was so chosen that the epinephrine hyperglycemia WCM either slight or absent or there was even a hypoglycemia. In spite of this marked effect on blood sugar, insulin had only a slight effect on blood lactic acid. Thus insulin did not prevent the marked rise in the 1st hour nor did it cause a more rapid disappearance of lactic acid in the follow- ing hours. With the exception of slightly lower values, the lactic acid curve in the experiments with insulin plus epinephrine is the exact duplicate of the curve obtained in the experiments with epinephrine alone (Fig. 1). This result is of interest in two respects. In the first place insulin can have no or very little effect on lactic acid production itself; in other words, it does not prevent the breakdown of muscle glycogen which is characteristic for epineph- rine. Secondly, insulin hardly accelerates the removal of lactic acid from the blood. As has been mentioned before, the lactic acid accumulating in the blood as the result of epinephrine injec- tions is partly removed by the liver where it is converted into gly- cogen. Insulin seems to be unable to accelerate this process. Little is known concerning the disposal of blood lactic acid in muscle under normal conditions. It seems clear, however, that insulin can have no marked effect on any possible oxidation of blood lactic acid in muscle or on its conversion into muscle glyco- gen. This seems remarkable since insulin is known to accelerate

Cannon, et al. (20) confirm the increase in blood lactic acid after epinephrine injections but Cannon (19) is unwilling to accept the fact that mobilization of muscle glycogen occurs and is responsible for the increase in blood lactic

acid, because he fails to see any advantage arising to the organism from such a mobilization. The possibility must at least be taken into con- sideration that the effectiveness of epinephrine in muscle fatigue may be

due to its action on muscle glycogen. Finally, Cannon states that we “do not hint at the nature of the compensatory process” that leads to the

disappearance of liver glycogen after insulin injections, “though we report low blood sugar levels which would set in action the sympathicoadrenal apparatus.” Since we have shown that insulin injection causes a dis- appearance of liver glycogen in adrenalectomized animals (21), the adrenal

apparatus cannot be responsible for this mobilization and we have more than hinted at the fact that this experimental evidence has not been dis- proved by Cannon though it is disregarded by him. The objections raised

by Cannon in regard to the dose of epinephrine used in our experiments have been answered elsewhere (22).

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C. F. Cori and G. T. Cori 697

storage and oxidation of glucose in muscle. Indeed this is the mechanism by which insulin prevents the epinephrine hyper- glycemia. If insulin had the same effect on blood lactic acid as on glucose, it would also prevent the rise in blood lactic acid after epinephrine. The fact that insulin has such a small effect on the disposal of lactic acid casts some doubt on the assumption that lactic acid is an intermediary of glucose oxidation.

A discussion of the question of dosage will be presented in a later paper. It may be stated here that the minimal rate of in- travenous infusion of epinephrine into unnarcotized rabbits which causes a perceptible rise in blood sugar also causes an increase in blood lactic acid. This minimal effective rate of infusion was found to be 0.00005 mg. of epinephrine per kilo per minute. The larger doses used in the present paper merely serve to illus- trate better the changes that are taking place to a lesser extent with smaller doses.

SUMMARY AND CONCLUSIONS.

1. Subcutaneous injections of 0.2 mg. of epinephrine per kilo into rabbits are followed by marked changes in blood lactic acid. Starting from an average resting value of 11 mg. per cent, the lactic acid reaches a maximum value of 74 mg. per cent in 1 hour and gradually returns to the initial level in the next 5 hours. The peak of the blood sugar curve is reached in 2 hours and the hyper- glycemia persists for about the same length of time as the increase in the blood lactic acid.

2. When insulin is given along with epinephrine, the rise in blood sugar can be suppressed completely, or, with smaller doses, markedly inhibited. In either case insulin has very little effect on the lactic acid curve. On an average, the values are 14 per cent lower than those obtained when epinephrine alone is injected; otherwise the two curves have a parallel course.

3. By means of lactic acid determinations in arterial and venous blood it was found that the peripheral tissues (muscles) are the source of the increase in blood lactic acid. Under resting condi- tions the average arteriovenous difference was 0.3 mg., while 3, 1, 2, and 3 hours after the epinephrine injection the lactic acid in venous blood was 11.7, 10.4, 10.0, and 7.1 mg. per cent higher than in arterial blood.

4. The arteriovenous blood sugar difference remained at the

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Epinephrine and Lactic Acid

resting value of 5 to 7 mg. per cent throughout the course of the epinephrine hyperglycemia. When glucose was administered the difference increased threefold. This indicates that less sugar passes from the blood to the muscles during epinephrine hyper- glycemia than during the hyperglycemia produced by glucose administration.

5. More than 2.5 gm. of glucose per kilo per hour must be injected intravenously into normal rabbits in order to produce a blood sugar curve similar to that after epinephrine injection. Such quantities of sugar are not at the disposal of the liver. Since during epinephrine action the peripheral tissues do not respond with increased blood sugar utilization, even a moderate amount of sugar offered to them by the liver causes marked and prolonged hyperglycemia. The mere fact that blood sugar is of hepatic origin cannot explain the epinephrine hyperglycemia because it fails to take into account the quantitative relationship between blood sugar production and utilization.

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3. Unpublished experiments.

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Carl F. Cori and Gerty T. CoriUTILIZATION

PRODUCTION AND BLOOD SUGAR EPINEPHRINE ON LACTIC ACIDACTION: IV. THE INFLUENCE OF

THE MECHANISM OF EPINEPHRINE

1929, 84:683-698.J. Biol. Chem. 

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