Long-term antihypertensive therapy with beta-blockers: submaximal exercise capacity and metabolic effects during exercise

The effects of long-term (6 months) antihypertensive treatment with three different types of beta-blockers (propranolol, nonselective without ISA; pindolol, nonselective with ISA; metoprolol, beta 1-selective without ISA) on submaximal exercise capacity and metabolic variables during submaximal endurance exercise were studied in seven subjects with essential hypertension. Exercise tests were performed on a bicycle ergometer at 70% of estimated VO2 max. Similar reductions of resting and exercise blood pressure and exercise heart rate were obtained with the three beta-blockers. Exercise time was significantly reduced by all three beta-blockers during chronic antihypertensive therapy. The reduction tended to be more pronounced after 5-6 months of treatment than after 1 week (P = 0.06). During exercise, the plasma glycerol and nonesterified fatty acid concentrations were reduced. Plasma glucose concentration was reduced at the end of the exercise test during propranolol treatment only. Plasma lactate concentrations tended to be increased, but the difference was significant during pindolol treatment only. Oxygen uptake tended to decrease and respiratory exchange ratio to increase. Plasma potassium concentrations during exercise were significantly increased with all three beta-blockers. The effects on the metabolic variables during exercise were similar after 1 week and during long-term (20/24 weeks) beta-blocker treatment. The study shows that submaximal endurance exercise capacity is impaired in patients with essential hypertension on beta-blocker therapy and that the impairment is maintained during long-term antihypertensive beta-blocker treatment.     

Dietary manipulation and exercise in the heat: thermoregulatory and metabolic effects in rats

To determine the effects of dietary manipulation on the metabolic, physical, and physiological responses to exercise in the heat, adult male rats (n 5 16/group) were food deprived for 72 h followed by ad lib consumption of a high protein (HIPROT) or high carbohydrate (HICARB) diet for 96 h. Each dietary regimen was followed immediately by exercise (9.14 m . min-1) in the heat (35.58C) to hyperthermic exhaustion (TCO approximately 43 8C). Animals consuming the HICARB or HIPROT diet had an increased mean TCO prior to the acute heat/exercise protocol when compared with a control (CONT) group with uninterrupted access to a normal rodent diet; the HICARB rats also manifested a decreased endurance when compared with the CONT group. Plasma levels of urea nitrogen, lactate, and potassium were increased following exercise in the heat in all groups, but greatly exacerbated increments in urea nitrogen occurred in the HIPROT group. Following exercise, significant increments occurred in circulating levels of glucose and insulin in the HIPROT and HICARB groups. Plasma triglycerides were decreased by the exercise/heat regimen but increased by both diets. Thus, these dietary manipulations elicited a variety of metabolic responses which did not markedly alter the physiological and physical effects of work in the heat.     

Beta-endorphin, catecholamines, and cortisol during exhaustive endurance exercise

To assess changes of beta-endorphin during intense endurance exercise, ten nonspecifically trained volunteers (aged 25.7 +/- 2.9 years) were subjected to an exhaustive endurance test on a cycle ergometer at the work load of the individual anaerobic threshold (IAT) determined in a preparatory graded exercise test. Prior to, in 25-min intervals during, and repeatedly subsequent to exercise venous blood samples were drawn to measure the levels of beta-endorphin (beta-E), cortisol (C), adrenaline (A), and noradrenaline (NA). In addition, lactate, heart rate, and rate of perceived exertion were determined. The levels of beta-E remained unchanged during the first 50 min; between the 50th and 75th min beta-E increased by 82% (p less than 0.01). At the end of the exercise (mean exercise time: 89 min), a beta-E level three times the resting level was measured. The maximum exercise-induced increase of beta-E showed a positive correlation to endurance capacity (W.kg-1 of IAT): r = 0.74; p less than 0.05. C exhibited similar changes to beta-E, but the onset of increase was delayed if compared with beta-E; there was a close correlation between these two stress hormones (75th min of exercise: r = 0.91; p less than 0.001). The catecholamines A and NA increased linearly during exercise, without a correlation with the behavior of beta-E being established.     

A high carbohydrate diet negates the metabolic effects of caffeine during exercise

We tested the hypothesis that unrecognized nutritional factors might influence the serum free fatty acid response to caffeine. The time course and extent of the serum free fatty acid response to a fatty meal alone, to caffeine ingestion after a high carbohydrate meal, or to caffeine in combination with either a fatty meal or a high carbohydrate meal (the latter following 3 d of a high carbohydrate diet) were studied in six trained runners. The metabolic response to 120 min of exercise at 75% of maximum oxygen consumption after caffeine ingestion was also studied in runners after a high carbohydrate diet and ingestion of a high carbohydrate meal. Serum free fatty acid levels were highest 3 h after caffeine ingestion alone and were lower following a fatty meal with or without caffeine ingestion (P less than 0.05). The high carbohydrate diet combined with the ingestion of a high carbohydrate meal prevented the expected rise in serum free fatty acid levels following caffeine ingestion. The metabolic response to prolonged submaximal exercise was also not influenced by the ingestion of caffeine by subjects who had eaten a high carbohydrate diet. Nutritional factors, in particular the state of the body carbohydrate stores and the simultaneous ingestion of carbohydrate, influence the response of serum free fatty acid levels to caffeine ingestion.     

Naloxone does not affect muscle blood flow during low intensity exercise in rats

The purpose of this study was to determine whether endogenous opioids are involved in the control of skeletal muscle blood flow during locomotory exercise in rats. The radiolabeled miscrosphere technique was used to measure total and regional muscle blood flow. We first determined whether methionine enkephalin (1,000 micrograms.kg-1 I.V.) would produce vasodilation in muscle vascular beds. We found that methionine enkephalin produced a 36 mm Hg (range of 20-50 mm Hg) drop in mean arterial pressure (Pa), which was associated with decreases in calculated skeletal muscle vascular resistance in anesthetized rats, and that these effects on arterial pressure and skeletal muscle vascular resistance were blocked by the infusion of naloxone (10 micrograms.kg-1). Measurements were then made at 5 min of treadmill exercise at 15 m.min-1 (0 degree incline) and following exercise in both saline-treated (controls) and naloxone (10 micrograms.kg-1)-treated conscious rats. There were no differences between the heart rates, blood pressures, or total muscle blood flows of the two groups. There were also no significant differences between the blood flows to 32 hind limb muscle samples composed of various muscle fiber types. Since naloxone blockade did not affect total or regional muscle blood flow during low intensity exercise, it appears that the endogenous opioids are not required for the normal exercise hyperemia of skeletal muscles.     

Food deprivation and exercise in the heat: thermoregulatory and metabolic effects

To determine the effects of food deprivation on the physical, physiological, and metabolic responses to exercise in the heat, adult, male rats (330-360g, N = 16/group) were food-deprived for 24, 48, or 72 h. They were then exercised (9.14m X min-1) in the heat (35.5 degrees C) to hyperthermic exhaustion (Tco approximately 43 degrees C). Food deprivation had no effects on endurance, but ad lib fed controls manifested significantly (p less than 0.05) increased Tco and Tsk during the latter portion of the treadmill interval. While plasma osmolality was significantly (p less than 0.01) increased in all groups as a result of the heat/exercise contingency, hematocrit ratios were elevated (p less than 0.01) as a result of 48 and 72 h of food deprivation. Food deprivation resulted in severe hypoglycemia following exercise (p less than 0.01), and these decrements were accompanied by marked (p less than 0.01) reductions in circulating insulin levels. Prolonged food deprivation (48 and 72 h) resulted in significant (p less than 0.01) hypertriglyceridemia and hyperlactacidemia subsequent to exercise. Levels of sodium, potassium, urea nitrogen, and creatine phosphokinase were unaffected by the food deprivation intervals. We have concluded from these studies that while several thermoregulatory and metabolic responses to exercise in the heat can be significantly affected by food deprivation, short-term endurance capacity was unaltered.     

RPE, blood glucose, and carbohydrate oxidation during exercise: effects of glucose feedings

This study examined the effects of glucose ingestion on differentiated and undifferentiated ratings of perceived exertion (RPE) during prolonged cycling exercise. On two occasions, seven trained males cycled for 180 min on a Monark cycle ergometer at 70% peak VO2 (VO2peak). Subjects consumed an 8% glucose/electrolyte drink (G) or a flavored water placebo (P) every 15 min throughout exercise. Measurement of RPE, ventilation (VE), oxygen uptake (VO2), respiration rate (RR), respiratory exchange ratio (RER), heart rate (HR), and venous blood sample collection preceded ingestion of the drink. Subjects were homogenous with respect to height, weight, and VO2peak. RPE for the legs and overall body were significantly attenuated (P less than 0.05) during the last 45 min of exercise. Plasma glucose and insulin were higher (P less than 0.05) in G than in P at virtually all time points. CHO oxidation and work rate were maintained throughout exercise in G but not during the last 30 min of exercise in P (P less than 0.05). Percent changes in plasma volume, plasma lactate, HR, VE, RR, and RPE for the chest were not different between conditions (P greater than 0.05). The data suggest that ingestion of carbohydrate beverages during endurance cycling can maintain plasma glucose and CHO oxidation during the latter stages of prolonged exercise. As a result, it appears that a relationship exists between attenuation of ratings of perceived exertion (especially in the legs), blood glucose, and CHO oxidation late in prolonged exercise. The mechanism for this probably involves the increased availability of blood-borne glucose to serve as substrate for brain and/or muscle energy metabolism during a time when endogenous stores of carbohydrate are low.     

Beta-endorphin time course response to intensity of exercise: effect of training status

The concentration of beta-endorphin (B-EP) was measured in 6 trained and 6 untrained cyclists during three intensities of exercise to determine the time course changes of B-EP. B-EP was determined by radioimmunoassay with less than 5% cross reactivity with beta-lipotrophin. A counter-balanced design was used to avoid an order effect from exercise intensity. Resting B-EP values were similar across visits. There were no differences in resting B-EP values comparing the trained (4.61 +/- 0.25 pmol.l-1) to the untrained (4.03 +/- 0.23 pmol.l-1) group. Cycling at 60% VO2max did not increase B-EP in either group at any time measured. Cycling at 70% VO2max increased B-EP by 10 min in both groups p less than 0.05. The rate and magnitude of increase of B-EP were similar for both groups. B-EP changes at 80% VO2max were significantly greater that at 70% VO2max and were identical for the two groups. Both groups demonstrated increases by 5 min and further increases at 30 min of exercise p less than 0.01. These changes occurred despite the fact that lactate levels were lower in the trained group at both 70 and 80% VO2max intensities. It is concluded that the time course change for B-EP is similar for trained and untrained individuals working at the same relative intensity of exercise and does not seem to be related to plasma lactate concentrations.     

Automated blood pressure measurements during exercise

One of the critical parameters measured during exercise is blood pressure. However, the accurate measurement of systolic and diastolic blood pressure during exercise is difficult with auscultation and impractical with direct arterial techniques. The purpose of this study was to compare an automated system (Colin, Inc. STBP-680) with auscultation in humans during rest and exercise and to compare the automated system with direct arterial blood pressure measurement in a canine model during pharmacological challenges that resulted in a wide range of blood pressure values. Compared with direct arterial blood pressure taken in the canine model, the STBP-680 gave good estimates of diastolic blood pressure and adequately monitored relative changes in systolic blood pressure, diastolic blood pressure, and mean arterial pressure (mean arterial pressures in all instances were calculated as one-third systolic plus two-thirds diastolic blood pressures). Compared with auscultation methods in humans, the STBP-680 gave similar estimates of resting diastolic blood pressure and monitored relative changes in resting systolic blood pressures, diastolic blood pressures, and mean arterial pressures. During both treadmill and cycle ergometer exercise in humans, the STBP-680 monitored changes in systolic blood pressure, phase IV diastolic blood pressure, and mean arterial pressure. Further, the STBP-680 estimated exactly and noted relative changes in heart rate in every test. However, during exercise, quantitative estimations of systolic blood pressure by the STBP-680 were higher than those found using auscultation. Where exact, quantitative measures of blood pressure are needed, direct arterial measurement continues to be the most accurate method. However, where indirect methods can be used, the STBP-680 may provide a suitable alternative that reduces many of the technical concerns of auscultation in young, healthy individuals.     

Autologous red blood cell reinfusion: effects on stress and fluid regulatory hormones during exercise in the heat

This study assessed the effects of induced erythrocythemia on stress and fluid regulatory hormones during walking exercise in the heat. Six unacclimated male subjects received approximately 600 ml of a sterile saline solution containing 50% volume-to-volume of autologous erythrocytes. Three heat stress tests (HSTs) were attempted: one approximately 2 weeks prior to the reinfusion procedure, a second 48 h after the reinfusion procedure, and a third 1 week later, corresponding to 9 d subsequent to reinfusion. Each HST comprised three consecutive 45-min exercise and 15-min rest intervals (VO2 approximately 2.0 L.min-1, 1.56 m.s-1, 6% incline, 35 degrees C, 45% rh). Blood was withdrawn before the HST and 30 min into each exercise (EX) bout. In all three HST's plasma cortisol (PC) levels were significantly (p less than 0.01) reduced during the first EX bout compared to preexercise levels, and then progressively increased during the second and third EX intervals during HST 1. During HST 2 (48 h postinfusion), however, PC levels were significantly (p less than 0.05) reduced in two blood samples (EX 2, 3) compared to the same blood samples from HST-1 (preinfusion). Plasma renin activity (PRA) and aldosterone (ALD) were significantly (p less than 0.01) increased by the exercise/heat stress, but were unaffected by erythrocythemia either 48 h or 9 d subsequent to reinfusion. PRA and ALD were correlated (r = 0.84, p less than 0.001) under all conditions. We concluded from this study that acutely induced erythrocythemia reduced the stress response to consecutive exercise/heat intervals as manifested in PC responses during HST 2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Voluntary exercise during chronic renal failure in rats

PURPOSE: Chronic renal failure (CRF) patients often experience a significant degradation in quality of life that is associated with decreased physical fitness. Previous animal studies have used forced running or swimming as modalities to investigate the interactions between exercise and CRF. These modalities generally include stress responses unrelated to the exercise itself. The purpose of the current work was to determine whether, and to what extent, rats experiencing the onset of CRF would participate in voluntary wheel running exercise. An additional objective was to examine physiological parameters related to skeletal muscle and cardiovascular adaptation in the context of CRF and exercise. METHODS: Groups of rats were assigned to sham-operated or 5/6 nephrectomy groups, and further divided into running or nonrunning subgroups. Blood, heart, and muscle tissues were collected 30 d after the exercise groups were returned to running wheel-equipped cages. RESULTS: The results demonstrated that rats experiencing the early stages of CRF will voluntarily exercise to the same extent as sham-operated animals (e.g., sham, 7.2+/-0.8 vs CRF, 6.8+/-0.7 km.d). CRF resulted in increased systolic blood pressure that was not normalized by exercise. CRF induced a decrease in hemoglobin concentration that was prevented by exercise. Voluntary running resulted in an apparently nonpathological left ventricular hypertrophy in both the sham-operated and CRF rats. In locomotor skeletal muscles, CRF resulted in a 31% decrease in citrate synthase activity that was completely blunted by voluntary running activity. CONCLUSION: Rats experiencing the onset of CRF will run voluntarily. This exercise appears to provide some potentially palliative effects on the skeletal muscle and cardiovascular responses to CRF.     

Acute metabolic effects of exercise in bodybuilders using anabolic steroids.

Four male bodybuilders who had started taking anabolic steroids were monitored during exercise. Most metabolic indicators were similar to bodybuilders not taking steroids; i.e. metabolic acidosis with little change in glucose. However, there is a marked elevation of creatine kinase.     

Control of coronary blood flow during exercise

During exercise, coronary blood flow increases to match the augmented myocardial oxygen demand because of tachycardia. Coronary vasodilation during exercise is via a combination of feedforward and feedback control mechanisms. Feedforward control is mediated by sympathetic β-adrenoceptor vasodilation. Feedback vasodilator control is via a novel hypothesis where adenine nucleotides released from red blood cells act on endothelial purinergic receptors.     

Gender differences in the progression of metabolic responses during incremental exercise

AIM: The present investigation was undertaken to elucidate the differences in the progression of metabolic responses during incremental exercise between men and women of similar maximal aerobic capacity. METHODS: Twenty males and 20 females served as subjects for the study. Each subject was randomly assigned to perform a graded exercise test on either a cycle ergometer or a treadmill. Of the 20 subjects within each gender, 10 were tested on the cycle ergometer, whereas the other half was tested on the treadmill. During each test, absolute VO2, relative VO2, and HR were recorded during the last 15 seconds of every minute throughout the test. These variables were then plotted separately as a function of work rate so that a best-fit linear regression equation was generated for each of the three plots. RESULTS: Under the cycle condition, we found no difference in slope of increment in absolute VO2 between genders. However, the slope of increment in relative VO2 and HR was greater (P<0.05) in women than men. A negative correlation (r=-0.858, P<0.05) was found between body mass and slope of increment in relative VO2 in men and women combined. Under the treadmill condition, the slope for absolute VO2 were greater (P<0.05) in men than women. However, in terms of relative VO2 and HR, no between-gender differences were observed in the slope of increment. A positive correlation (r=0.769, P<0.05) was found between body mass and slope of increment in absolute VO2 in men and women combined. CONCLUSIONS: These results indicate that the progression of metabolic responses during incremental exercise differs between men and women despite a similar fitness. These gender differences may be further attributed to body mass that seems to play a distinctive role when the incremental exercise is conducted on a cycle ergometer and treadmill.     

Lactate threshold does not influence metabolic responses during exercise in cyclists

The purpose of this study was to compare plasma markers of metabolic stress and other physiological parameters during prolonged endurance exercise of different intensity in trained subjects possessing a "high" or "low" lactate threshold (LT) expressed as a percentage (%) of peak power output (PPO). Fifteen trained male cyclists completed an incremental exercise test for determination of PPO and the LT (% PPO). Each subject then completed a 90-min and 20-min exercise trial at an intensity representing 75 and 85 % of PPO, respectively. Blood lactate (La), as well as plasma hypoxanthine (Hx) and uric acid (UA) were measured during each exercise trial. The responses in two groups, one (n = 8) with a LT approximately 65 % PPO (LT (low)), the other group (n = 7) with a LT approximately 75 % (LT (high)) (p < 0.01), were then compared. With the exception of UA, La and Hx increased significantly (p < 0.01) throughout each exercise trial compared to rest. However, there were no significant differences in each trial between the two groups of cyclists. There were also no significant differences in the other physiological parameters in each exercise trial between the subjects in LT (low) and LT (high). This study demonstrates that in trained cyclists homogeneous in terms of PPO, plasma markers of metabolic demand during prolonged exercise are not influenced by the LT when measured in an incremental exercise test.     

Regulation of cerebral blood flow during exercise

Constant cerebral blood flow (CBF) is vital to human survival. Originally thought to receive steady blood flow, the brain has shown to experience increases in blood flow during exercise. Although increases have not consistently been documented, the overwhelming evidence supporting an increase may be a result of an increase in brain metabolism. While an increase in metabolism may be the underlying causative factor for the increase in CBF during exercise, there are many modulating variables. Arterial blood gas tensions, most specifically the partial pressure of carbon dioxide, strongly regulate CBF by affecting cerebral vessel diameter through changes in pH, while carbon dioxide reactivity increases from rest to exercise. Muscle mechanoreceptors may contribute to the initial increase in CBF at the onset of exercise, after which exercise-induced hyperventilation tends to decrease flow by pial vessel vasoconstriction. Although elite athletes may benefit from hyperoxia during intense exercise, cerebral tissue is well protected during exercise, and cerebral oxygenation does not appear to pose a limiting factor to exercise performance. The role of arterial blood pressure is important to the increase in CBF during exercise; however, during times of acute hypotension such as during diastole at high-intensity exercise or post-exercise hypotension, cerebral autoregulation may be impaired. The impairment of an increase in cardiac output during exercise with a large muscle mass similarly impairs the increase in CBF velocity, suggesting that cardiac output may play a key role in the CBF response to exercise. Glucose uptake and CBF do not appear to be related; however, there is growing evidence to suggest that lactate is used as a substrate when glucose levels are low. Traditionally thought to have no influence, neural innervation appears to be a protective mechanism to large increases in cardiac output. Changes in middle cerebral arterial velocity are independent of changes in muscle sympathetic nerve activity, suggesting that sympathetic activity does not alter medium-sized arteries (middle cerebral artery).CBF does not remain steady, as seen by apparent increases during exercise, which is accomplished by a multi-factorial system, operating in a way that does not pose any clear danger to cerebral tissue during exercise under normal circumstances.     

Effect of hand-arm exercise on venous blood constituents during leg exercise

To test the hypothesis that ancillary arm and hand exercise would change the values of antecubital blood constituents during leg exercise, seven healthy men (19-27 yrs) performed static (10% of a maximal voluntary contraction) or dynamic (60 finger flexions/min) hand-arm exercise with one hand during submaximal leg exercise (50% V2 max) in the supine position. Venous blood was analyzed for serum Na+, K+, osmolality, albumin, total Ca2+, and glucose; blood hemoglobin, hematocrit, and lactic acid; and change in plasma volume. During leg exercise there were no significant differences in these blood constituents between right and left arms at rest. Only glucose and lactate were affected by additional arm exercise. Compared with resting arm values during leg exercise, glucose decreased from 4.7 to 4.5 mmol/l (delta = 4%, P less than 0.05) and lactate increased from 2.0 to 2.4 mmol/l (delta = 20%, P less than 0.05) during static arm exercise. With dynamic arm exercise, glucose decreased from a resting level of 4.8 to 4.7 mmol/l (delta = 2%, P less than 0.05). We conclude that additional static or dynamic hand-forearm exercise accompanying leg exercise could introduce significant errors in glucose (2%-4%) and lactic acid (6%-20%) concentrations measured in venous blood.     

The cardiovascular and metabolic effects of bench stepping exercise in females.

The purpose of this investigation was to measure cardiovascular and metabolic responses to 20 min continuous bouts of "choreographed" bench stepping exercise in healthy females. Four frequently used bench heights were employed in a cross-over design: 15.2 cm (6 inches, B-6), 20.3 cm (8 inches, B-8), 25.4 cm (10 inches, B-10), and 30.5 cm (12 inches, B-12). Oxygen uptake (VO2) responses were significantly more pronounced in direct relationship to the bench height: B-12 greater than B-10 greater than B-8 greater than B-6 (P less than 0.05). Mean responses for VO2 ranged from 28.4 ml.kg-1.min-1 for B-6 to 37.3 ml.kg-1.min-1 for B-12. Interestingly, no difference was revealed for heart rate and the respiratory exchange ratio between B-12 and B-10 despite a higher VO2 for B-12 (B-12, B-10 greater than B-8 greater than B-6, P less than 0.05). The incorporation of 0.91 kg (2 lb) hand weights with exercise on the 20.3 cm bench elicited a modest but statistically significant increase in VO2 compared with no hand weights. No significant increase in VO2 was revealed for conditions that employed 0.45 kg (1 lb) hand weights. The results demonstrate that aerobic bench stepping is an exercise modality that provides sufficient cardiorespiratory demand for enhancing aerobic fitness and promoting weight loss in females.