Effects of high-intensity sprint training on skeletal muscle blood flow in rats TIMOTHY I. MUSCH, JOHN A. TERRELL, AND MARK R. HILTY Departments of Medicine and Physiology, College of Medicine, The Pennsylvania State University, Hershey, Pennsylvania 17033 MUSCH, TIMOTHY I., JOHN A. TERRELL, AND MARK R. toward the working muscles as a whole cannot be disEffects of high-intensity sprint training on skeletal musmissed (4). cle blood flow in rats. J. Appl. Physiol. 71(4): 1387-1395,1991.The primary purpose of the present investigation was The regional blood flow response (via radioactive microto determine whether HIST would produce a significant spheres) was determined for female rats after 6 wk of high-inincrease in blood flow to the working musculature of rats tensity sprint training (HIST) or limited cage activity as the required to exercise at work loads that would elicit . animals exercised at work loads that would elicit maximal 0, vo 2 max. We were also interested in whether HIST would uptake. Blood flow to the different organs of the abdominal produce significant changes in the distribution of blood region was greatly reduced during maximal exercise conditions, flow within and among the different muscles of the rat and the magnitude of the reduction appeared to be similar for hindlimb along with changes in blood flow to the organs both the HIST group of rats and their sedentary (SED) control found in the splanchnic region. Correspondingly, we hycounterparts. Of the 20 different hindlimb muscles examined in pothesized that blood flow to the muscles classified as the present study, blood flow to the soleus, plantaris, gastrocnemius, flexor hallicus longus, vastus lateralis, rectus femoris, ankle extensors (3,4,18) would be significantly greater in biceps femoris, and adductor magnus and brevis muscles was trained rats than in their sedentary counterparts because significantly greater (P < 0.05) in the HIST rats during maxihigh-intensity training has been shown to increase the mal exercise conditions than in the SED control rats. Correvascular transport capacity of different muscles found in spondingly, blood flow to the total hindlimb during maximal this region (20,22). We also hypothesized that the reducexercise was also significantly greater in the HIST rats than in tions in blood flow to the different organs of the splanchthe SED control rats [240 t 18 vs. 192* 15 (SE) ml min-’ 100 nit region would be similar in trained and sedentary rats g-l]. These results support the contention that the increase in because previous investigations have demonstrated that maximal cardiac output that is produced by HIST in the rat is the reductions in blood flow to the organs of the splanchprimarily directed toward the working skeletal muscle and not nit region during maximal exercise conditions remain toward the organs found in the abdominal region. We conclude unaffected by training (26). from these experiments that HIST will produce significant adaptations in central cardiac function and skeletal muscle blood flow in the rat. METHODS HILTY.
l
maximal spheres
oxygen uptake; regional
blood flow; radioactive
l
micro-
RESULTS from our laboratory have shown that a program of high-intensity sprint training (HIST) will produce a significant increase in the maximal 0, uptake . WO 2,,,) of rats (14). We demonstrated in that study that the increase in VO, max was due to an increase in maximal stroke volume (SV,,,) and that the increase in SV,,, resulted in an increase in maximal cardiac output (&,,). Because a number of investigations have demonstrated that exercise training will produce an increase in the vascular transport capacity of the rat’s hindlimb (20,2l, 30), it would be logical to assume that a significant portion of the increase in SV,,, produced by HIST would be directed toward the working musculature. However, the possibility that blood flow is redistributed within and among the different muscles of the hindlimb and that a significant portion of the increase in SV,, is directed toward the organs of the splanchnic region instead of PREVIOUS
0161-7567/91
$1.50 Copyright
Animal selection, training protocol, and measurements
Female Sprague-Dawley rats (Charles River Laboratories) weighing 225-275 g were initially familiarized with running on a motor-driven treadmill (Precision Instruments). Rats were then randomly assigned to either a training (n = 25) or sedentary control group (n = 25). Rats in the training group exercised 5 min/day, 6 days/ wk on a treadmill. Training consisted of five I-min bouts of high-intensity sprinting interspersed with 90 s of rest. During the 1st wk of training the rats ran at a treadmill grade of 15% and a speed of 66 m/min. During the 2nd wk of training the treadmill speed was gradually increased from 66 to 97 m/min. The treadmill grade and speed were then held constant for the remainder of the 6-wk training period. In the sedentary control group familiarity with treadmill running was maintained by having each rat run on the treadmill every 3rd or 4th day of the training period at a grade of 0% and a speed of 24 m/min for 6-9 min/day. Before training was initiated and after training was completed, VO, m8x was determined for all rats during a of 0, uptake (VoJ.
0 1991 the American
Physiological
Society
1387
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MUSCLE
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FLOW
IN
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RATS
was being monitored. When the catheter reached the aortic valve the pressure waveform became distorted. The catheter was then retracted -3-4 mm and secured Exercise Test I Exercise Test 2 in place. The catheter that was placed in the tail artery was advanced toward the bifurcation of the descending HIST 98+1 96+1 aorta (-45 mm) and secured in place. Both catheters (69 m/min) (73 mlmin) 88&2 8922 were advanced subcutaneously to the dorsal aspect of the SED (47 m/min) (51 m/min) cervical region of the rat and exteriorized through a puncture wound made in the skin. After closure of the Values are means + SE in ml. min-’ kg-’ of 10 high-intensity sprint-trained (HIST) and 10 sedentary control (SED) rats. Values in neck and tail incisions, the rats were taken off the anesparentheses represent average speed reached during the treadmill test thesia and each animal was given a minimum of 2 h to at a 15% grade. In exercise test I maximal O2 uptake (VO,-) was recover. This period of recovery was chosen because preattained in the rat when no increases in VO, occurred with further vious studies by Flaim et al. (10) have shown that cardiac increases in external work load; in exercise test 2 iTo max was attained by or circulatory dynamics, regional blood flow, arterial having the rats exercise at work loads greater than those found in exercisetest1. blood gases, and acid-base status remain unchanged during a l- to 6-h recovery period after halothane anesprogressive exercise test. VO, and CO, production were thesia. measured according to the methods described by Brooks After instrumentation each rat was placed into a channel of the treadmill. The right carotid catheter was conand White (8) that had been adapted for use in our laboratories (23). After a 2-min warm-up on the treadmill at a nected to a pressure transducer placed at the same level grade of 0% and speed of 16 m/min, the progressive exer- as the rat. The tail artery catheter was connected to a cise test was initiated by increasing the treadmill to a 5-ml glass syringe that was connected to a Harvard withgrade of 15% and a speed of 40 m/min. Every 90 s the drawal pump (model 907). Exercise was then initiated, treadmill speed was increased 3-5 m/min. Vo2max was and the rat was given a 2-min warm-up on the treadmill at a grade of 5% and a speed of 16 m/min. After the defined as the point at which VO, did not increase with further increases in work load as the rat was running warm-up period the treadmill grade and speed were prosteadily on the treadmill. It should be noted that numergressively increased over the next minute to the last work ous attempts were made with many of the rats participatload that had elicited Vo2 maxin the rat before instrumening in the study before the strict criterion for the attaintation. After the designated work load was reached, the ment of VO, maxwas met. In this respect as many as five rat continued to exercise steadily for another 90 s before or six attempts were made before some of the animals blood withdrawal from the tail artery catheter was initiperformed adequately. ated at a rate of 0.253 ml/min. At the same time arterial Reproducibility of VO, maxvalues was ascertained in 10 blood pressures and heart rate (HR) were being recorded animals from both the trained and sedentary control from the right carotid artery catheter. After 30 s of blood groups a.fter the period of training or limited activity by withdrawal (3 min of total exercise time and 2 min of having the rats perform multiple maximal exercise tests. exercise at the designated work load), the right carotid The first vo2 maxwas attained in each rat with the use of artery catheter was disconnected from the pressure transthe progressive treadmill test, which lasted ~6-8 min. In ducer, and the injection of radioactive microspheres into the second test each rat was given a 2-min warm-up. the aortic arch of the running animal was begun. The After the warm -up each rat was gradually taken to a injection of the radioactive microspheres took -5 s and work load that was greater than the work load that elic- was followed by 0.5 ml of saline flush, which took another ited VO 2maxin the first test. The rat was then required to -5-10 s. Exercise was then terminated; however, the run freely and steadily at this work load for 3-4 min while withdrawal of blood into the tail artery catheter was conthe measurements of To2 and CO, production were per- tinued for another minute to ensure that all the microformed. Results demonstrated that the measured 60, max spheres had been cleared out of the tail artery catheter and were in the glass withdrawal syringe. On the complefrom the second maximal exercise test was in agreement with that measured in the first test (Table 1). Correspontion of the withdrawal of blood from the tail artery, both dingly, the VO, maxmeasured during the second maximal the right carotid and tail artery catheters were flushed exercise test was within t2% (SE) of the VO, m8Xvalue with heparinized saline, and the rats were given a minimeasured during the first test. Because Vo2 m8xmeasuremum of 60 min to recover. ments from both tests were similar to one another, these After this recovery period we found that a small subvalues were averaged and considered as Vo2max for the group of rats was willing to exercise at supramaximal animal. work loads. In these animals the regional blood flow reInstrumentation and final experimental protocol. After sponses to work loads that were greater than 00, maxwere the 6-wk period of training each rat was anesthetized determined with the use of the same procedures dewith halothane, and polyethylene catheters (PE-10 con- scribed above. In the remaining rats blood flow measurements were made at rest after another period of recovery. nected to PE-50) were placed into the right carotid artery and caudal (tail) artery. The catheter that was placed After the second regional blood flow determination, sointo the right carotid artery was advanced toward the each rat was killed with an overdose of pentobarbital heart and secured in a position just inside the aortic arch. dium (>50 mglkg of body wt) via the right carotid artery This was accomplished by advancing the catheter toward catheter. The thorax was opened, and the placement of the left ventricle while the arterial pressure waveform both catheters was verified by anatomic dissection. The
TABLE 1. Reproducibility of vozmcrr measurements performed in HIST and SED rats
l
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MUSCLE
BLOOD
FLOW
organs of the abdominal region and the muscles of both hindlimbs of each rat were then identified and removed. The tissues were blotted, weighed on an electrobalance (Mettler model PL 300 or Cahn Electrobalance), and placed immediately into counting vials. Between dissections, all remaining organs of the abdominal region and muscles were kept moist by covering the tissues with gauze soaked in saline to prevent evaporation. Determination of blood flow to different organs. Blood flows to the different organs of the abdominal region and the different muscles of the hindlimb were determined with the use of the radionuclide-tagged microsphere technique that has been adapted for use in the exercising rat (13, 19, 24).
Briefly, the microspheres (46Sc and 85Sr) used in the present study were 15 t 5 pm diam with specific activity of - 12 mCi/g and suspended in normal saline containing 0.01% Tween 80. Before each injection, the microspheres were thoroughly mixed and agitated by sonication (Heat Systems Ultrasonics model W2OOR) to prevent clumping. Each group of microspheres (-0.6-0.7 X lo6 total number) was injected into the ascending aorta of the rat in a 0.15 to 0.20-ml volume. The radioactivity levels of the tissues (removed after the animal completed the experimental protocol) were determined on a two-channel gamma scintillation counter (Packard Auto-Gamma Spectrometer model 5230) set to record the peak energy activity of each isotope for 5 min. The radioactivity of the tissues was then analyzed by computer, taking into account the cross-talk fraction between the different isotopes. Absolute blood flow to each tissue was calculated by the reference sample method (15) and was expressed on the basis of the measured flow per 100 g of tissue. Adequate mixing of the microspheres was verified for each injection by demonstrating a ~15% difference between blood flows to the right and left kidneys and to the total right and left hindlimb musculature. Blood flows measured during exercise were excluded from the study if the rat did not maintain a normal gait throughout the microsphere infusion and if the microsphere injection produced any noticeable effect on exercise performance. Blood flows were determined in the following organs of the abdominal region: kidneys, adrenal glands, liver, pancreas, spleen, stomach, and the small and large intestine. Blood flows were also determined for the rat’s hindlimb musculature on the basis of the fiber-type classification described by Laughlin and Armstrong (3, 18). The hindlimb muscles included thigh adductors, adductor longus, adductor magnus and brevis, gracilis, pectineus; knee flexors, biceps femoris, semitendinosus, deep red portions of the semimembranosus, superficial white portions of the semimembranosus; knee extensors, vastus intermedius, vastus medialis, the red portion of the vastus lateralis, the mixed portion of the vastus lateralis, the white portion of the vastus lateralis, the red portion of the rectus femoralis, the white portion of the rectus femoralis; ankle flexors, the deep red portion of the tibialis anterior, the superficial white portion of the tibialis anterior, extensor digitorum longus, peroneals; and ankle extensors, soleus, plantaris, the deep red portion of the lateral head of the gastrocnemius, the superficial white por-
IN
TRAINED
1389
RATS
2. v02and body weight of HIST and SED rats before and after 6 wk of HIST TABLE
Pretraining
ml
HIST SED
l
hmax, min-’
Posttraining Body
l
kg-’
wt, g
92k2
251G4
92t-2
252+7
Values are means vs. pretraining.
+ SE. * P < 0.05 HIST
ml
l
hmax, min-’
Body l
kg-’
96&l? 86+1*“r vs. SED.
wt, g
282+5 288+5 t
P < 0.05 post-
tion of the medial head of the gastrocnemius, the remainder or middle portion of the gastrocnemius, tibialis posterior, flexor digitorum longus, flexor hallicus longus. Statistical analysis. Pretraining and posttraining body weight and Tjoa maxvalues for the trained and sedentary control rats were analyzed by a two-way analysis of variance for repeated measures. Similarly, the posttraining vo 2max values measured in both the trained and sedentary control rats and the blood flows measured in the right and left hindlimbs of rats that were willing to run at work loads equal to and greater than V02max were analyzed with the use of the same statistical approach. When a significant F value was found by the analysis of variance, a Student-Newman-Keuls post hoc test was performed to detect differences between mean values. Because we were primarily interested in whether significant differences existed between the HIST and sedentary control rats regarding the regional blood flow response during exercise, posttraining blood flows measured during exercise were compared between the two groups of rats with the use of unpaired t tests. Similarly, posttraining tissue blood flows measured at rest were analyzed with the use of the same statistical approach. Statistical comparisons between the blood flows measured at rest and during exercise were not performed in the present study because the differences in blood flow to various tissues during the transition from rest to exercise have been previously described and because this response was not the primary focus of the present investigation. It should be clarified that all the blood flow comparisons performed in the present study were made a priori. In addition, all values in the present study are expressed as means t SE, and the 0.05 level of probability was used to signify statistical significance. RESULTS
Responsesof uninstrumented rats. Pretraining values were similar between the trained and sedentary control rats . with respect to iTo, max and body weight (Table 2). vo 2max increased 4% in the trained rats after the 6-wk period of HIST, whereas it decreased 7% in the sedentary control group. These changes resulted in a 12% difference between the two groups of rats in vo2mar found posttraining. Concomitant with the changes in . vo 2 maxy both groups of rats gained weight during the training period. However, the gain in body weight was similar for the trained and sedentary rats such that differences in body weight did not exist between the two groups posttraining.
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1390
MUSCLE
BLOOD
FLOW
3. Heart rates at rest and during maximal exercise conditions from instrumented HIST and SED rats TABLE
Maximal
HIST SED Values
are means
522+5 525+5
411+_16*
445k7 + SE in beatdmin.
Exercise
*
P
vozrnar = 459 t 132; blood flow to the left kidney at vo2,,, = 429 t 111, >v02max = 462 t 124 mlemin-‘0 100 g-l). DISCUSSION
The present study demonstrated that blood flow to the total hindlimb musculature of rats that completed the HIST protocol is significantly greater during maximal exercise than that in rats that are restricted to limited activity. These results agree with those of Mackie and Terjung (22), who used a similar type of sprint training paradigm consisting of running up a 15% grade at 60 m/min (total exercise time of 10 miniday) to produce significant increases in maximal blood flow to the working musculature. They also agree with previous studies where this type of training regimen has been shown to increase the vascular transport capacity of the rat’s hindlimb musculature (20, 21, 30). In toto, results from our laboratory along with the results of others (14,20-22, 30) support the conclusion that a training program consisting of high-intensity sprinting will produce significant increases in the ability to generate a greater SV,,, during exercise along with significant vascular adaptations in the working musculature. Effects of training on Vo2 mcuc and resting HR. HIST at treadmill speeds >80 m/min will not produce an increase in the oxidative enzyme capacity of the hindlimb musculature of the rat (9, 14, 28). Therefore this conventional indicator of a training effect could not be used in the present study, and alternative indicators had to be se4. Blood flow to diaphragm and different organs in abdominal region of SED and HIST instrumented rats
TABLE
Rest SED
Exercising HIST
SED
HIST
227k39 848+106 866+60 62+17 142+26 401+106 347t78 274+29
520+56 339+38 342~~38 19+3 49t7 150+47 23+5 122k14
405+62 405+59 401+51 31+4* 6OklO 157&36 27k8 106_+15
Diaphragm Left kidney Right kidney Liver? Pancreas Adrenals Spleen Small intestine Large intestine Stomach
313+94 9212103 906t94 52k6 236+64 384+94 351+34 278+26
Values sedentary.
& SE in ml min-’ 100 g? * blood flow to the liver only.
are means t Arterial
at \jo2 max
141k18
92+9
62k9
66k17
105&7
107+14
36+5
41+5
l
l
P
l
maximal spheres
oxygen uptake; regional
blood flow; radioactive
l
micro-
RESULTS from our laboratory have shown that a program of high-intensity sprint training (HIST) will produce a significant increase in the maximal 0, uptake . WO 2,,,) of rats (14). We demonstrated in that study that the increase in VO, max was due to an increase in maximal stroke volume (SV,,,) and that the increase in SV,,, resulted in an increase in maximal cardiac output (&,,). Because a number of investigations have demonstrated that exercise training will produce an increase in the vascular transport capacity of the rat’s hindlimb (20,2l, 30), it would be logical to assume that a significant portion of the increase in SV,,, produced by HIST would be directed toward the working musculature. However, the possibility that blood flow is redistributed within and among the different muscles of the hindlimb and that a significant portion of the increase in SV,, is directed toward the organs of the splanchnic region instead of PREVIOUS
0161-7567/91
$1.50 Copyright
Animal selection, training protocol, and measurements
Female Sprague-Dawley rats (Charles River Laboratories) weighing 225-275 g were initially familiarized with running on a motor-driven treadmill (Precision Instruments). Rats were then randomly assigned to either a training (n = 25) or sedentary control group (n = 25). Rats in the training group exercised 5 min/day, 6 days/ wk on a treadmill. Training consisted of five I-min bouts of high-intensity sprinting interspersed with 90 s of rest. During the 1st wk of training the rats ran at a treadmill grade of 15% and a speed of 66 m/min. During the 2nd wk of training the treadmill speed was gradually increased from 66 to 97 m/min. The treadmill grade and speed were then held constant for the remainder of the 6-wk training period. In the sedentary control group familiarity with treadmill running was maintained by having each rat run on the treadmill every 3rd or 4th day of the training period at a grade of 0% and a speed of 24 m/min for 6-9 min/day. Before training was initiated and after training was completed, VO, m8x was determined for all rats during a of 0, uptake (VoJ.
0 1991 the American
Physiological
Society
1387
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on September 6, 2018. Copyright © 1991 American Physiological Society. All rights reserved.
1388
MUSCLE
BLOOD
FLOW
IN
TRAINED
RATS
was being monitored. When the catheter reached the aortic valve the pressure waveform became distorted. The catheter was then retracted -3-4 mm and secured Exercise Test I Exercise Test 2 in place. The catheter that was placed in the tail artery was advanced toward the bifurcation of the descending HIST 98+1 96+1 aorta (-45 mm) and secured in place. Both catheters (69 m/min) (73 mlmin) 88&2 8922 were advanced subcutaneously to the dorsal aspect of the SED (47 m/min) (51 m/min) cervical region of the rat and exteriorized through a puncture wound made in the skin. After closure of the Values are means + SE in ml. min-’ kg-’ of 10 high-intensity sprint-trained (HIST) and 10 sedentary control (SED) rats. Values in neck and tail incisions, the rats were taken off the anesparentheses represent average speed reached during the treadmill test thesia and each animal was given a minimum of 2 h to at a 15% grade. In exercise test I maximal O2 uptake (VO,-) was recover. This period of recovery was chosen because preattained in the rat when no increases in VO, occurred with further vious studies by Flaim et al. (10) have shown that cardiac increases in external work load; in exercise test 2 iTo max was attained by or circulatory dynamics, regional blood flow, arterial having the rats exercise at work loads greater than those found in exercisetest1. blood gases, and acid-base status remain unchanged during a l- to 6-h recovery period after halothane anesprogressive exercise test. VO, and CO, production were thesia. measured according to the methods described by Brooks After instrumentation each rat was placed into a channel of the treadmill. The right carotid catheter was conand White (8) that had been adapted for use in our laboratories (23). After a 2-min warm-up on the treadmill at a nected to a pressure transducer placed at the same level grade of 0% and speed of 16 m/min, the progressive exer- as the rat. The tail artery catheter was connected to a cise test was initiated by increasing the treadmill to a 5-ml glass syringe that was connected to a Harvard withgrade of 15% and a speed of 40 m/min. Every 90 s the drawal pump (model 907). Exercise was then initiated, treadmill speed was increased 3-5 m/min. Vo2max was and the rat was given a 2-min warm-up on the treadmill at a grade of 5% and a speed of 16 m/min. After the defined as the point at which VO, did not increase with further increases in work load as the rat was running warm-up period the treadmill grade and speed were prosteadily on the treadmill. It should be noted that numergressively increased over the next minute to the last work ous attempts were made with many of the rats participatload that had elicited Vo2 maxin the rat before instrumening in the study before the strict criterion for the attaintation. After the designated work load was reached, the ment of VO, maxwas met. In this respect as many as five rat continued to exercise steadily for another 90 s before or six attempts were made before some of the animals blood withdrawal from the tail artery catheter was initiperformed adequately. ated at a rate of 0.253 ml/min. At the same time arterial Reproducibility of VO, maxvalues was ascertained in 10 blood pressures and heart rate (HR) were being recorded animals from both the trained and sedentary control from the right carotid artery catheter. After 30 s of blood groups a.fter the period of training or limited activity by withdrawal (3 min of total exercise time and 2 min of having the rats perform multiple maximal exercise tests. exercise at the designated work load), the right carotid The first vo2 maxwas attained in each rat with the use of artery catheter was disconnected from the pressure transthe progressive treadmill test, which lasted ~6-8 min. In ducer, and the injection of radioactive microspheres into the second test each rat was given a 2-min warm-up. the aortic arch of the running animal was begun. The After the warm -up each rat was gradually taken to a injection of the radioactive microspheres took -5 s and work load that was greater than the work load that elic- was followed by 0.5 ml of saline flush, which took another ited VO 2maxin the first test. The rat was then required to -5-10 s. Exercise was then terminated; however, the run freely and steadily at this work load for 3-4 min while withdrawal of blood into the tail artery catheter was conthe measurements of To2 and CO, production were per- tinued for another minute to ensure that all the microformed. Results demonstrated that the measured 60, max spheres had been cleared out of the tail artery catheter and were in the glass withdrawal syringe. On the complefrom the second maximal exercise test was in agreement with that measured in the first test (Table 1). Correspontion of the withdrawal of blood from the tail artery, both dingly, the VO, maxmeasured during the second maximal the right carotid and tail artery catheters were flushed exercise test was within t2% (SE) of the VO, m8Xvalue with heparinized saline, and the rats were given a minimeasured during the first test. Because Vo2 m8xmeasuremum of 60 min to recover. ments from both tests were similar to one another, these After this recovery period we found that a small subvalues were averaged and considered as Vo2max for the group of rats was willing to exercise at supramaximal animal. work loads. In these animals the regional blood flow reInstrumentation and final experimental protocol. After sponses to work loads that were greater than 00, maxwere the 6-wk period of training each rat was anesthetized determined with the use of the same procedures dewith halothane, and polyethylene catheters (PE-10 con- scribed above. In the remaining rats blood flow measurements were made at rest after another period of recovery. nected to PE-50) were placed into the right carotid artery and caudal (tail) artery. The catheter that was placed After the second regional blood flow determination, sointo the right carotid artery was advanced toward the each rat was killed with an overdose of pentobarbital heart and secured in a position just inside the aortic arch. dium (>50 mglkg of body wt) via the right carotid artery This was accomplished by advancing the catheter toward catheter. The thorax was opened, and the placement of the left ventricle while the arterial pressure waveform both catheters was verified by anatomic dissection. The
TABLE 1. Reproducibility of vozmcrr measurements performed in HIST and SED rats
l
Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (192.236.036.029) on September 6, 2018. Copyright © 1991 American Physiological Society. All rights reserved.
MUSCLE
BLOOD
FLOW
organs of the abdominal region and the muscles of both hindlimbs of each rat were then identified and removed. The tissues were blotted, weighed on an electrobalance (Mettler model PL 300 or Cahn Electrobalance), and placed immediately into counting vials. Between dissections, all remaining organs of the abdominal region and muscles were kept moist by covering the tissues with gauze soaked in saline to prevent evaporation. Determination of blood flow to different organs. Blood flows to the different organs of the abdominal region and the different muscles of the hindlimb were determined with the use of the radionuclide-tagged microsphere technique that has been adapted for use in the exercising rat (13, 19, 24).
Briefly, the microspheres (46Sc and 85Sr) used in the present study were 15 t 5 pm diam with specific activity of - 12 mCi/g and suspended in normal saline containing 0.01% Tween 80. Before each injection, the microspheres were thoroughly mixed and agitated by sonication (Heat Systems Ultrasonics model W2OOR) to prevent clumping. Each group of microspheres (-0.6-0.7 X lo6 total number) was injected into the ascending aorta of the rat in a 0.15 to 0.20-ml volume. The radioactivity levels of the tissues (removed after the animal completed the experimental protocol) were determined on a two-channel gamma scintillation counter (Packard Auto-Gamma Spectrometer model 5230) set to record the peak energy activity of each isotope for 5 min. The radioactivity of the tissues was then analyzed by computer, taking into account the cross-talk fraction between the different isotopes. Absolute blood flow to each tissue was calculated by the reference sample method (15) and was expressed on the basis of the measured flow per 100 g of tissue. Adequate mixing of the microspheres was verified for each injection by demonstrating a ~15% difference between blood flows to the right and left kidneys and to the total right and left hindlimb musculature. Blood flows measured during exercise were excluded from the study if the rat did not maintain a normal gait throughout the microsphere infusion and if the microsphere injection produced any noticeable effect on exercise performance. Blood flows were determined in the following organs of the abdominal region: kidneys, adrenal glands, liver, pancreas, spleen, stomach, and the small and large intestine. Blood flows were also determined for the rat’s hindlimb musculature on the basis of the fiber-type classification described by Laughlin and Armstrong (3, 18). The hindlimb muscles included thigh adductors, adductor longus, adductor magnus and brevis, gracilis, pectineus; knee flexors, biceps femoris, semitendinosus, deep red portions of the semimembranosus, superficial white portions of the semimembranosus; knee extensors, vastus intermedius, vastus medialis, the red portion of the vastus lateralis, the mixed portion of the vastus lateralis, the white portion of the vastus lateralis, the red portion of the rectus femoralis, the white portion of the rectus femoralis; ankle flexors, the deep red portion of the tibialis anterior, the superficial white portion of the tibialis anterior, extensor digitorum longus, peroneals; and ankle extensors, soleus, plantaris, the deep red portion of the lateral head of the gastrocnemius, the superficial white por-
IN
TRAINED
1389
RATS
2. v02and body weight of HIST and SED rats before and after 6 wk of HIST TABLE
Pretraining
ml
HIST SED
l
hmax, min-’
Posttraining Body
l
kg-’
wt, g
92k2
251G4
92t-2
252+7
Values are means vs. pretraining.
+ SE. * P < 0.05 HIST
ml
l
hmax, min-’
Body l
kg-’
96&l? 86+1*“r vs. SED.
wt, g
282+5 288+5 t
P < 0.05 post-
tion of the medial head of the gastrocnemius, the remainder or middle portion of the gastrocnemius, tibialis posterior, flexor digitorum longus, flexor hallicus longus. Statistical analysis. Pretraining and posttraining body weight and Tjoa maxvalues for the trained and sedentary control rats were analyzed by a two-way analysis of variance for repeated measures. Similarly, the posttraining vo 2max values measured in both the trained and sedentary control rats and the blood flows measured in the right and left hindlimbs of rats that were willing to run at work loads equal to and greater than V02max were analyzed with the use of the same statistical approach. When a significant F value was found by the analysis of variance, a Student-Newman-Keuls post hoc test was performed to detect differences between mean values. Because we were primarily interested in whether significant differences existed between the HIST and sedentary control rats regarding the regional blood flow response during exercise, posttraining blood flows measured during exercise were compared between the two groups of rats with the use of unpaired t tests. Similarly, posttraining tissue blood flows measured at rest were analyzed with the use of the same statistical approach. Statistical comparisons between the blood flows measured at rest and during exercise were not performed in the present study because the differences in blood flow to various tissues during the transition from rest to exercise have been previously described and because this response was not the primary focus of the present investigation. It should be clarified that all the blood flow comparisons performed in the present study were made a priori. In addition, all values in the present study are expressed as means t SE, and the 0.05 level of probability was used to signify statistical significance. RESULTS
Responsesof uninstrumented rats. Pretraining values were similar between the trained and sedentary control rats . with respect to iTo, max and body weight (Table 2). vo 2max increased 4% in the trained rats after the 6-wk period of HIST, whereas it decreased 7% in the sedentary control group. These changes resulted in a 12% difference between the two groups of rats in vo2mar found posttraining. Concomitant with the changes in . vo 2 maxy both groups of rats gained weight during the training period. However, the gain in body weight was similar for the trained and sedentary rats such that differences in body weight did not exist between the two groups posttraining.
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1390
MUSCLE
BLOOD
FLOW
3. Heart rates at rest and during maximal exercise conditions from instrumented HIST and SED rats TABLE
Maximal
HIST SED Values
are means
522+5 525+5
411+_16*
445k7 + SE in beatdmin.
Exercise
*
P
vozrnar = 459 t 132; blood flow to the left kidney at vo2,,, = 429 t 111, >v02max = 462 t 124 mlemin-‘0 100 g-l). DISCUSSION
The present study demonstrated that blood flow to the total hindlimb musculature of rats that completed the HIST protocol is significantly greater during maximal exercise than that in rats that are restricted to limited activity. These results agree with those of Mackie and Terjung (22), who used a similar type of sprint training paradigm consisting of running up a 15% grade at 60 m/min (total exercise time of 10 miniday) to produce significant increases in maximal blood flow to the working musculature. They also agree with previous studies where this type of training regimen has been shown to increase the vascular transport capacity of the rat’s hindlimb musculature (20, 21, 30). In toto, results from our laboratory along with the results of others (14,20-22, 30) support the conclusion that a training program consisting of high-intensity sprinting will produce significant increases in the ability to generate a greater SV,,, during exercise along with significant vascular adaptations in the working musculature. Effects of training on Vo2 mcuc and resting HR. HIST at treadmill speeds >80 m/min will not produce an increase in the oxidative enzyme capacity of the hindlimb musculature of the rat (9, 14, 28). Therefore this conventional indicator of a training effect could not be used in the present study, and alternative indicators had to be se4. Blood flow to diaphragm and different organs in abdominal region of SED and HIST instrumented rats
TABLE
Rest SED
Exercising HIST
SED
HIST
227k39 848+106 866+60 62+17 142+26 401+106 347t78 274+29
520+56 339+38 342~~38 19+3 49t7 150+47 23+5 122k14
405+62 405+59 401+51 31+4* 6OklO 157&36 27k8 106_+15
Diaphragm Left kidney Right kidney Liver? Pancreas Adrenals Spleen Small intestine Large intestine Stomach
313+94 9212103 906t94 52k6 236+64 384+94 351+34 278+26
Values sedentary.
& SE in ml min-’ 100 g? * blood flow to the liver only.
are means t Arterial
at \jo2 max
141k18
92+9
62k9
66k17
105&7
107+14
36+5
41+5
l
l
P
