but that the section when the lumbar sympathetic had been

Transcription

1 THE OXYGEN USE OF MUSCLE AND THE EFFECT OF SYMPATHETIC NERVES ON IT. -By HIROMU NAKAMURA, M.D. (JAPAN). (From the Physiological Laboratory, Cambridge.) MANSFELD and LuKIcs have recently given an account of some experiments which, they hold, confirm the theory of de Boer that the sympathetic nervous sytem exercises a tonic action on striated muscles. They estimated the respiratory exchange in the dog, as shown by analyses of the respired air. Curari was given in quantity just sufficient to paralyse the sciatic nerve. They found that section of the sciatic when the sympathetic was intact caused a decrease of respiratory exchange, but that the section when the lumbar sympathetic had been cut, had no effect on respiratory exchange. They concluded that the intact sympathetic increased the oxygen use of the muscles. There is, however, another possible explanation of the result. If, on cutting the sympathetic nerves, there was dilatation of the blood vessels of the limb, there would be transference of blood from the viscera to the limbs, i.e. from a region of more active metabolism to one of less active metabolism and a decrease of respiratory exchange would naturally follow. It is clear that in order to decide whether the sympathetic affects the oxygen use of the muscles, direct determination of the oxygen in the blood flowing to and from the muscles is required. On the data given by Mansfeld and LukAcs, the change in the oxygen consumption by the muscles.would be completely outside the limits of experimental error. They found that the respiratory exchange of the respired air decreased 1 to 15 p.c. on section of the sciatic with its sympathetic fibres, and attributed the whole of this decrease in oxygen use to a decrease in the oxygen use of the muscles of the limbs. My experiments were begun at Professor Langley's suggestion from this point of view, and in the course of them I have made observations on the oxygen use of skeletal muscle in other conditions than section of the sympathetic. The experiments were made on cats. The animals were either anasthetised with urethane (1.5 to grms. per kilo body

2 OXYGEN USE AND MUSCLE TONE. 11 weight given subcutaneously) and then if necessary with A.C.E. mixture, or they were anwsthetised with chloroform, decerebrated by Sherrington's method, tracheotomy performed, curari given and the anesthetics discontinued. In order to obtain blood coming exclusively, or almost exclusively, from the muscles, the following procedure was adopted:-the cord extending the limb was drawn tight around the ankle so as to exclude the blood coming from the foot. The veins in the popliteal space were exposed, the small saphenous (ext. saph.) vein was tied a little below its junction with the popliteal, a cut made in the vein near the junction, and a clamp placed on the vein above the cut. A woollen thread was passed under the popliteal vein. The venous blood was collected in the manner introduced by Barcroft and Kato (cp. their Fig., op. cit. p. 15) by inserting the neck of a graduated pipette through the cut in the small saphenous vein past the valve at its popliteal junction. The blood was diverted from the popliteal into the small saphenous by an assistant pulling up the thread lying under the popliteal as given by Langley and I tagaki. By this method the gastrocnemius is very little exposed, and venous blood is obtained from extensor and flexor muscles of the leg and from the bones but not from the skin. It is possible that some blood may have passed to the popliteal vein from the foot, but I found no colour in the foot (or skin of the leg) on forcibly injecting p.c. methylene blue after death into the lower end of the small saphenous vein, though the muscle-veins of the lower leg were well injected. The same pipette was used throughout; p.c. potassium oxalate was passed through it before the first sample of blood was taken, it was washed after each sample, and again rinsed with potassium oxalate, thus differences in the rate of flow caused by a different diameter of the nozzle of the pipette were avoided. After each sample of blood, care was taken to see that the thread under the popliteal vein caused no obstruction to the blood flow. The rate of flow of each *1 c.c. was recorded on a kymograph. A few minutes after collecting the venous blood, a sample of arterial blood was taken from the carotid artery by a hypodermic syringe and the oxygen use of the blood determined by Barcroft's differential method. The preliminary operation took 1 to 1l hours; an interval of about mins. was then allowed before taking the first blood sample. The animal was kept warm throughout. As the protracted nature of the experiment and the withdrawal of a number of samples of blood might cause a decrease in oxygen use, it was necessary in the first place to determine the course of events

3 1 H. NAKAMURA. when the nerves were left intact. given in Table I. Exp Wt. -7 kgm The results of such experiments are TABLE I. Cats. Urethane, nerves untouched. Exp. 1. Wt. -6 kgm. Exp. 3. Wt. -5 kgm. Blood flow use per mi. per min. Blood pr.* Hrs. mins. c.c. c.c. Hra mins. in mm * * Exp Temp ' Blood flow per min. c.c Wt. 1-9 kgm use per min. c.c * -14 * *13 * * The blood pressure, except the first, was that immediately after the sample of blood was taken. The temperature was taken hn the anus. It will be seen that the rate of blood flow declined fairly steadily, but that the rate of oxygen use did not decline with it. Naturally when the decrease of oxygen supply is sufficiently great a decrease in oxygen use must occur, but the ouly experiment in which this occurred to any marked extent was Exp.. The obvious deduction from the results is that in quiescent muscle, the oxygen use is within wide limits independent of the oxygen supply. Barcroft and Muller found in the sub-maxillary gland that increase of oxygen supply did not cause an increase of oxygen use, and VerzAr that decrease of oxygen supply did not cauase decrease of oxygen use. The condition in the muscle seems then to be the same as in the submaxillary gland. This conclusion is contrary to that arrived at by Verzfir. He found, in the few experiments made on muscle that decrease of oxygen supply (by decreasing the percentage of oxygen in the inspired air) decreased the oxygen use. His results pointed to a close dependence of the oxygen use of the muscle on the

4 OXYGEN USE AND MUSCLE TONE. 13 oxygen brought to it. If the rate of blood flow in my experiments had been much greater than in his, the difference in result might be partially reconciled since he did not investigate the effect of increased blood supply. The rate however was not very different. In Verzar's experiments the rate of blood flow from the gastrocnemius varied from *6 to 6 c.c. a minute. The gastrocnemius (triceps surae) forms not quite half the area from which the blood was collected in my experiments, so that if the rate of flow were the same as in his, the flow per min. would have varied from a little less than 1 to nearly 1 c.c. a min. In my experiments the blood flow was well within these limits, but decrease of oxygen supply by reduced blood flow caused no decrease in oxygen use. Further in Verzar's mode of experiment the muscle is necessarily much exposed. In mine, most of the muscles were not exposed at all, and the gastrocnemius but little. It is reasonable then to hold that my experiments represent the normal conditions -more nearly than do those of Verzar. The great variation in the rate of blood flow found in different experiments in cats of the same weight makes estimation of the normal rate in quiescent muscle extremely uncertain. There are a number of obvious factors-unnecessary to recount-which cause a variation in it. It may be doubted whether in waking life the blood flow can ever be as low as that giving only the minimal oxygen requirement of muscle nqt engaged in replacing lost substance. In experiments, new factors causing either an increase or decrease are introduced. An estimate of the average rate of circulation per gram of soft tissue in the body per minute can be made roughly from the data that the blood is 5 p.c. of the body weight and the circulation time sees. Allowing for the absence of circulation in epidermis and cartilage, and the weight of bone in the body, the average circulation rate in soft tissues could hardly be less than - c.c. per gram per minute. If this had been the rate in my experiments (reckoning bone as having the sp. gr. of muscle), the rate of blood flow, calculated on the ratio of muscle to body weight given by Langley and Hashimoto (This Journ. 5. p. 15, 1918), would have been about 5 c.c. a minute for cats of kgm. and about 8 c.c. a minute for cats of 3 kgms. As will be seen from the tables the rate was generally but not always less than this. In Langley and Itagaki's experiments, in which the blood flow was taken from about the same area as in mine, the lowest rate of flow was 3 93 c.c. a minute. The effect of section of the sympathetic and of the sciatic nerves was next tried. The sympathetic was dissected from the back so as to avoid exposure of the viscera. The incision w4s made about cm. from the mid-line at the level of the 6th lumbar vertebra, and extended upwards 6-8 cm. The aponeurosis was cut, and the muscles separated from the transverse process of the 6th lumbar vertebra. The transverse process was cut away. The sympathetic trunk was then isolated from the 5th to the 7th transverse process, care being taken not to puncture the peritoneum. In small cats, the transverse process of the 5th lumbar

5 14 H. NAKAMURA. vertebra was also removed, a loose ligature was put round the sympathetic between the 5th and 6th lumbar ganglia so that when required it could be gently pulled away from the surrounding tissue and cut. In cutting it during an experiment, the viscera were not disturbed. The place of section was confirmed by post-mortem examination. TABLE II. Cats. Urethane. Sympathetic and sciatic cut. Exp. 1. Wt. -4 kgm. Exp. 3. Wt. '3 kgm. Blood flow use per Blood flow use per Hrs. mins. per min. c.c. min. c.c. Hrs. mins. per min. c.c. min. c.c.. '94 *41 3- * *41 1'86 Both symp. cut '59 3 '44 *46 4 Symp. cut 38 '46 ' *6 4 Sciatic cut 1 1 '58 * * '63 ' '4 *4 1 5 Sciatic cut 5-61 *69-4 *63 Exp.. Wt. ' kgm. Exp. 4. Wt. '9 kgm. -48 *71 9'14 *13 1 '5 '7 1 6'3 *98 3 Symp. cut 6'46 * '3 *63 3 Both symp. cut 1 '98 * Sciatic cut 1 1 Sciatic cut 1 6 4'47 ' '95 * ' '54 * '86 '97 Opposite side 9 3'4 * '43 *6 17 '39 *98 1 '55 ' * '31 ' '98 *19 Exp. 5. Wt. -7 kgm. 1st blood sample; blood flow 1 c.c., use '155, there was movement during the collection of one, and only one, sample. This caused an increase of blood flow from 5'95 c.c. to 7'9 c.c., and of use from '151 c.c. to 4 c.c. Exp. 6. Wt. '5 kgm. 1st blood sample; blood flow 5-33, use '13. Exp. 7. Wt. - kgm.,,,,,, 3'5, use '9. it 1( 3(C P TABLE IIL Decerebrated and lightly curarised. Exp. 1. VVt.. kgm. Exp.. Wt. 1'7 kgm. 7 c. c. Ringer's fluid in- 7 c.c. Ringer's fluid in- into jugular vein jected into jugular vein jectebd 1'31 * *13 Synnp. cut 5'14 *13 1'14 *63 5 Both symp. cut 1-13 ' Scia,tic cut 31 3' '135 1'11 * * ' *133 4 Sciatic cut 45-3 * * *13

6 OXYGEN USE AND MUSCLE TONE. 15 Seven experiments were made on cats anaesthetised with urethane. The results are given in Table II, but the details of Exps. 5-7 which were similar to those of Exps. 1-4 are omitted. Two experiments were made on decerebrated cats to which after decerebration curari was given in about the amount required to paralyse somatic motor nerves (Table III). Exp. 1 in this table is inconclusive since the rate of blood flow was slow, but in Exp. the result seems decisive. In none of the experiments did section of the sympathetic or subsequent section of the sciatic have any appreciable effect either on blood flow or on oxygen use. In these experiments there was the possibility that during the time taken to dissect the sympathetic, the tone.of the muscles had been abolished. Experiments were then made on simple section of the sciatic, which in numerous cases has been shown to cause rise of temperature in the leg and flushing of the skin. The results are given in Table IV. The large increase of blood flow caused by the section indicates that the muscle was in an approximately normal state. The important result from my point of view was that the section did not decrease the oxygen use. In Exp. 1 a temporary increase was caused by contraction before the sciatic was cut, otherwise the oxygen use ran much the same course as in the experiments in Table I in which no nerves were cut. We may, I think, conclude that if the sympathetic has any tonic action on muscle, the tone does not lead to oxygen use. We may conclude also that the ordinary extensor tone kept up by the somatic nerves does not affect oxygen use. The latter conclusion is in harmony with the results obtained by Frank and Voit and by Roaf. Frank and Voit compared the total CO production in dogs in a quiet state with that after giving curari in sufficient amount to paralyse somatic motor nerves, and found that the C production was either not appreciably affected, or was slightly increased by the paralysis. Roaf found that the C production in the extensor tone of decerebrate cats was not certainly greater than that after curari had been given. And H. Meyer and Frohlich state that the strong tonic contraction caused in cats by tetanus toxin is accompanied by very slight muscular metabolism. The fact that in Exp. 1, Table IV, and in one of the experiments of Table II, a movement of inconsiderable extent during the time of collecting a blood sample caused a definite increase of blood flow and of oxygen use, made it advisable to determine the extent of the increase in the conditions of the experiment, when the sciatic was stimulated. That stimulation of the sciatic causes, after a brief slowing, increase of blood flow was shown by Gaskell, the increase in oxygen use by

7 16 H. NAKAMURA. TABLE IV. Urethane. Sciatic cut. Exp. 1. Wt. '4 kgm. Exp.. Blood flow use per Hrs mine. per min. c.c. min. c.c. Hrs. mins *133 5 movement 4'49 *3 1 5 mine. after 4 a movement 3'5 ' Sciatic cut * * ' * * '9 * Wt. 1*9 kgm. Blood flow () use per min. c.c. *99 *1 *9 per min. c.c. '87 '4-87 Sciatic cut 5-1 '75-4 1*41 1X13 89 TABLE V. Urethane. Sciatic stimulation. Exp. 1. Wt. 3' kgm. Exp.. Wt. -6 kgm. 9 *118 5' * Sciatic stim. 5 sece. Sciatic cut * * Sciatic stim. 1 Sciatic stim. 3 mine. 13'5 *938 8 mine. 7'65 1- * '91 *36 18 '43 *18 *91 *96 *1 *85 *7 *6 * * *7 *7 1*1 *46 *53 Verzar, and its long duration by Barcroft and Kato. The experiments in Table V show the very great effect caused by stimulating the sciatic for a few minutes in the conditions of my experiments, and Exp. shows the contrast between the effect on oxygen use of the increase of blood flow caused by cutting the sciatic, and that caused by stimulating it. Having failed to obtain any effect on section of the sympathetic, I tried the effect of stimulating it. The results are given in Table VI. It will be seen that in each case the stimulation caused marked decrease both in rate of blood flow and in oxygen use. In most cases the decrease in blood flow seems an adequate explanation of the decrease in oxygen use, for, as said above, if the oxygen supply falls below a certain point a decrease in oxygen use must occur. The results in Exp. 1 are less certainly explained in this way, they suggest a direct inhibitory action, but as the rate of blood flow was small for 'a cat weighing 3 kgm. it is probable that the rate had fallen considerably during the preliminary operation, and that the oxygen supply at the time of stimulation was close to the limit required for the ordinary needs of the muscles. It is I think clear that no metabolic change in the muscles leading to increased oxygen use is caused by stimulating the sympathetic. As the effect of

8 OXYGEN USE AND MUSCLE TONE. 17 the sympathetic on the blood flow passes off there is a tendency for the oxygen use to become a trifle greater than it was before the stimulation, but the increase is not out of the range of experimental error, and the decrease of oxygen use caused by the stimulation is certainly not compensated by after increase. Hrs. mini /35 TABLE VI. Urethane. Exp. 1. Wt. 3-1 kgm. Blood flow use per min. per mmn. c.c. c.c. 3- *169 *87 *167 Symp. cut 3.77 *16 3*3 *16 1 min. -4 *131 S5rMP. stim. I n. 1-6 *68 1 min min. 1*36 *45 Exp.. Wt. -7 kgm. 11* 9- Symp. Cut mins min *14 *13 *131 *135 *46 *66 *13 *136 Sympathetic stimulation. Exp. 3. Wt. -1 kgm. Blood flow per min. Hrs. mins. C.C Symp. cut min * mins * 45 1* I Exp. 4. Wt. 3 kgm Symp. cut 1 4 mins. X8 1 min. X96 1X *4 9 use per mm. c.c. *9 *88 *35 *64.44 *86 *9 *74 *58 *55 *53 *154 l159 *158 *15 *71 *8 *144 *159 *154 *13 *83 The results given in the preceding account as regards the rate of blood flow before and after nerve section leave some doubt as to their meaning. Section of the sciatic caused increase of blood flow when the sympathetic was intact but not when it had been cut. This suggested that the increased blood flow in the former case was due to cutting off tonic impulses passing by the sympathetic fibres of the sciatic-the usual explanation given of the rise of temperature and flushing caused by sciatic section. In favour of this suggestion were the facts (a) that the increased blood flow caused by sciatic section with intact sympathetic was not accompanied by increased oxygen use, so that it was not due to

9 18 1H. NAKAMURA. contraction of the muscles, and (b) that after the sympathetic had been cut, the sciatic section did not cause increased blood flow so that it was not due to antidromic action. On the other hand section of the sympathetic itself did not cause increase of blood flow-this suggested that the sympathetic had no tonic action on the vessels of the muscles. The results would be harmonised if the increased blood flow caused by section of the sciatic were a reflex by way of the sympathetic, but it is difficult to see how this could be brought about. The only other explanation seems to be that the sympathetic tone was lost in the time taken to dissect the sympathetic, although the tonic action of the sympathetic on the blood vessels is generally held to be very persistent. Two experiments were made on decerebrate and lightly curarised animals to see if the mechanical stimulation caused by cutting the sciatic, or the stronger stimulus caused by pinching, would cause increase of blood flow. Section of the sciatic caused no increase in blood flow. After cutting the sciatic, it was cut again lower down, and after this pinched once firmly with forceps. No effect was found, i.e. no evidence of antidromic action was obtained, but the experiments were not very satisfactory since the blood flow was slow, and the blood pressure was not taken. A few experiments were made in which the venous blood was collected from the femoral vein, the pipette being inserted into the large saphenous vein (ext. saph.), so that part of the blood came from the skin. The oxygen use in these was not determined. In a urethanised animal, after the rate of flow had sunk from 6-5 c.c. to -6 a minute, stimulation of the central end of the sciatic of the opposite side caused a rise of blood pressure from 89 to 15, and a decrease of blood flow from *6 to 19 c.c. a minute. Section of the sciatic with the blood pressure at 94 caused an increase of blood flow to 7* c.c. a minute. In another experiment (rate of blood flow at the start 1-6 c.c.) section of the sympathetic had little if any effect; stimulation of the sympathetic caused a great decrease and stimulation of the sciatic a great increase of blood flow. In an experiment on a decerebrate curarised cat, section of the sciatic caused an increase of blood flow from 3 c.c. to 6 c.c. a minute; on pinching it later the blood flow fell from -3 c.c. to 1-36 c.c. a minute. The chief difference in the results of these experiments from those given previously is that section of the sciatic in the decerebrate-curarised animal caused increased blood flow. The time at my disposal did not allow me to arrive at a definite conclusion as to the exact causes of the variation in the effect of nerve

10 OXYGEN USE AND MUSCLE TONE. 19 section on blood flow. The central sympathetic tone is dependent on a good supply of oxygen to the central nervous system, and it is probable that the effect of nerve section is greatly influenced by the degree of local tone. It is known that when the skin is cold, section of the sympathetic may cause little if any flushing. With regard to the main object of the experiments, I base my conclusion that the tonic action of the sympathetic on muscle, if it exists, does not cause an increase of oxygen use, mainly on the observations that oxygen was found to vary little with great variation in rate of blood flow, that section of the sciatic in the anasthetised cat did not cause decrease of oyxgen use (Table IV) and that stimulation of the sympathetic caused decrease and not increase of oxygen use (Table VI). SUMMARY. The results refer to the rate of blood flow, and oxvygen exchange in the muscles and bones of the lower leg of the cat. 1. The rate of blood flow makes no difference to the rate of oxygen use except when the flow becomes very small.. Section of the sciatic when the sympathetic is intact causes in anesthetised animals, in harmony with the experiments of others, an increase in rate of blood flow. The section does not cause decrease in oxygen use. 3. Stimulation of the peripheral end of the lumbar sympathetic causes great decrease both in rate of blood flow and in oxygen use; the latter is probably a consequence of the former. 4. I conclude that the sympathetic does not increase the oxygen use of the muscles, and, in agreement with Frank and Voit, that the ordinary (extensor) muscular tone kept up by somatic nerves does not increase oxygen use. 5. The rate of blood frow and oxygen use, both in ansesthetised and in decerebrate-curarised animals was found to be unaffected by section of the sympathetic nerves, and by section of the sciatic after the sympathetic nerves have been cut. The exact cause of the absence of effect in blood flow was not determined. In conclusion I wish to express my thanks to Prof. Langley for his help in considering the results of the experiments, and to Mr B arcroft for his aid in the technique of oxygen estimation.

11 11 H. NAKAMURA. REFERENCES. Barcroft and Kato. Phil. Trans. Roy. Soc. B. 7. p Barcroft and Muller. This Journ. 44. p Frank and Voit. Ztsch. f. Biol. 4. p Langley and Itagaki. Journ. PhysioL 51. p Mansfeld and Luk&cs. Arch f. d. ges. Physiol p Meyer, H. and Frohlich. Zntrlb. f. Physiol. 6. p Roaf. Quart. Journ. exp. Pbysiol. 5. p Verzar. Journ. Physiol. 44. p