Myocardial O2 consumption in porcine left ventricle is heterogeneously distributed in parallel to heterogeneous O2 delivery

Myocardial blood flow is unevenly distributed, but the cause of this heterogeneity is unknown. Heterogeneous blood flow may reflect heterogeneity of oxygen demand. The aim of the present study was to assess the relation between oxygen consumption and blood flow in small tissue regions in porcine left ventricle. In seven male, anesthetized, open-chest pigs, local oxygen consumption was quantitated by computational model analysis of the incorporation of 13C in glutamate via the tricarboxylic acid cycle during timed infusion of [13C]acetate into the left anterior descending coronary artery. Blood flow was measured with radioactive microspheres before and during acetate infusion. High-resolution nuclear magnetic resonance 13C spectra were obtained from extracts of tissue samples (159 mg mean dry wt) taken at the end of the acetate infusion. Mean regional myocardial blood flow was stable [5.0 +/- 1.6 (SD) and 5.0 +/- 1.4 ml.min(-1).g dry wt(-1) before and after 30 min of acetate infusion, respectively]. Mean left ventricular oxygen consumption measured with the NMR method was 18.6 +/- 7.7 micromol.min(-1).g dry wt(-1) and correlated well (r = 0.85, P = 0.02, n = 7) with oxygen consumption calculated from blood flow, hemoglobin, and blood gas measurements (mean 22.8 +/- 4.7 micromol.min(-1).g dry wt(-1)). Local blood flow and oxygen consumption were significantly correlated (r = 0.63 for pooled normalized data, P < 0.0001, n = 60). We calculate that, in the heart at normal workload, the variance of left ventricular oxygen delivery at submilliliter resolution is explained for 43% by heterogeneity in oxygen demand.     

31P NMR measurement of ATP synthesis rate in perfused intact rat hearts

Using 31P NMR and the saturation-transfer method, the unidirectional rate of ATP synthesis was measured in isolated, Langendorff-perfused, isovolumic rat hearts operating at a rate pressure product of 25.6 +/- 2.5 (SE) X 10(3) mmHg X min-1 and consuming O2 at a rate of 35 +/- 2 mumol O2 X min-1 X (g dry wt)-1, at 37 degrees C. This rate was 7.2 +/- 0.9 mumol X s-1 X (g dry wt)-1 and was related to the rate of oxygen atom consumption by a ratio of 6.3 +/- 0.9. These data show that in the intact heart the unidirectional rate of ATP synthesis exceeds the net rate of ATP synthesis and consumption by approximately a factor of 2.     

Muscle metabolism during heavy-intensity exercise after acute acetazolamide administration.

Carbonic anhydrase (CA) inhibition is associated with a lower plasma lactate concentration ([La(-)](pl)), but the mechanism for this association is not known. The effect of CA inhibition on muscle high-energy phosphates [ATP and phosphocreatine (PCr)], lactate ([La(-)](m)), and glycogen was examined in seven men [28 +/- 3 (SE) yr] during cycling exercise under control (Con) and acute CA inhibition with acetazolamide (Acz; 10 mg/kg body wt iv). Subjects performed 6-min step transitions in work rate from 0 W to a work rate corresponding to approximately 50% of the difference between the O(2) uptake at the ventilatory threshold and peak O(2) uptake. Muscle biopsies were taken from the vastus lateralis at rest, at 30 min postinfusion, at end exercise (EE), and at 5 and 30 min postexercise. Arterialized venous blood was sampled from a dorsal hand vein and analyzed for [La(-)](pl). ATP was unchanged from rest values; no difference between Con and Acz was observed. The fall in PCr from rest [72 +/- 3 and 73 +/- 3.6 (SE) mmol/kg dry wt for Con and Acz, respectively] to EE (51 +/- 4 and 46 +/- 5 mmol/kg dry wt for Con and Acz, respectively) was similar in Con and Acz. At EE, glycogen (mmol glucosyl units/kg dry wt) decreased to similar values in Con and Acz (307 +/- 16 and 300 +/- 19, respectively). At EE, no difference was observed in [La(-)](m) between conditions (46 +/- 6 and 43 +/- 5 mmol/kg dry wt for Con and Acz, respectively). EE [La(-)](pl) was higher during Con than during Acz (11.4 +/- 1.0 vs. 8.2 +/- 0.6 mmol/l). The similar [La(-)](m) but lower [La(-)](pl) suggests that the uptake of La(-) by other tissues is enhanced after CA inhibition.     

Hyperbaric oxygen toxicity: role of thromboxane.

Exposing rabbits for 1 h to 100% O2 at 4 atm barometric pressure markedly increases the concentration of thromboxane B2 in alveolar lavage fluid [1,809 +/- 92 vs. 99 +/- 24 (SE) pg/ml, P less than 0.001], pulmonary arterial pressure (110 +/- 17 vs. 10 +/- 1 mmHg, P less than 0.001), lung weight gain (14.6 +/- 3.7 vs. 0.6 +/- 0.4 g/20 min, P less than 0.01), and transfer rates for aerosolized 99mTc-labeled diethylenetriamine pentaacetate (500 mol wt; 40 +/- 14 vs. 3 +/- 1 x 10(-3)/min, P less than 0.01) and fluorescein isothiocyanate-labeled dextran (7,000 mol wt; 10 +/- 3 vs. 1 +/- 1 x 10(-4)/min, P less than 0.01). Pretreatment with the antioxidant butylated hydroxyanisole (BHA) entirely prevents the pulmonary hypertension and lung injury. In addition, BHA blocks the increase in alveolar thromboxane B2 caused by hyperbaric O2 (10 and 45 pg/ml lavage fluid, n = 2). Combined therapy with polyethylene glycol- (PEG) conjugated superoxide dismutase (SOD) and PEG-catalase also completely eliminates the pulmonary hypertension, pulmonary edema, and increase in transfer rate for the aerosolized compounds. In contrast, combined treatment with unconjugated SOD and catalase does not reduce the pulmonary damage. Because of the striking increase in pulmonary arterial pressure to greater than 100 mmHg, we tested the hypothesis that thromboxane causes the hypertension and thus contributes to the lung injury. Indomethacin and UK 37,248-01 (4-[2-(1H-imidazol-1-yl)-ethoxy]benzoic acid hydrochloride, an inhibitor of thromboxane synthase, completely eliminate the pulmonary hypertension and edema.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bradykinin is degraded in hypoxic lungs and does not affect epithelial permeability

To investigate the effect of intravenous infusions of bradykinin (BK) on the permeability of the hypoxic pulmonary epithelium to small solutes, experiments (n = 7) were performed in yearling sheep with chronic vascular catheters. Sheep were anesthetized, intubated, paralyzed, and ventilated. After establishing stable and normal base-line pulmonary hemodynamics and blood gas tensions, the lungs were insufflated with a submicronic aerosol of technetium-99m-labeled diethylenetriaminepentaacetate (99mTc-DTPA, mol wt = 492). Radioactivity arising from the right hemithorax was measured by an NaI probe with a parallel-holed collimator. The base-line pulmonary clearance rate (k) for 99mTc-DTPA was 0.51 +/- 0.09% (SE)/min, while the sheep were ventilated with a fractional concentration of inspired O2 (FIO2) of 0.5 [arterial partial pressure of O2 (PaO2) = 196 +/- 11.4 (SE) Torr]. Clearance of 99mTc-DTPA was unaffected by hypoxia alone or BK infusions in nonhypoxic lungs. The combination of an intravenous infusion of BK at either 1.2 (n = 3) or 2.4 micrograms . kg-1 . min-1 (n = 4) and alveolar hypoxia [FIO2 = 0.11, PaO2 = 28 +/- 1.6 (SE) Torr] did not affect pulmonary clearance of 99mTc-DTPA [k = 0.43 +/- 0.08% (SE)/min]. In contrast, a 0.05-ml/kg intravenous infusion of oleic acid increased clearance 10-fold in one sheep. During combined hypoxia and BK infusion the pulmonary arterial BK concentration (radioimmunoassay) increased from 0.82 +/- 0.16 (SE) to 7.05 +/- 1.86 ng/ml (P less than 0.001), but the systemic arterial concentrations were unchanged [0.67 +/- 0.19 (SE) to 0.66 +/- 0.09 ng/ml].(ABSTRACT TRUNCATED AT 250 WORDS)     

PDC activity and acetyl group accumulation in skeletal muscle during prolonged exercise.

Seven subjects cycled to exhaustion [58 +/- 7 (SE) min] at approximately 75% of their maximal oxygen uptake (VO2max). Needle biopsy samples were taken from the quadriceps femoris muscle at rest, after 3, 10, and 40 min of exercise, at exhaustion, and after 10 min of recovery. After 3 min of exercise, a nearly complete transformation of the pyruvate dehydrogenase complex (PDC) into active form had occurred and was maintained throughout the exercise period. The total in vitro activated PDC was unchanged during exercise. The muscle concentration of acetyl-CoA increased from a resting value of 8.4 +/- 1.0 to 31.6 +/- 3.3 mumol/kg dry wt at exhaustion and that of acetylcarnitine from 2.9 +/- 0.7 to 15.6 +/- 1.6 mmol/kg dry wt. This was accompanied by corresponding decreases in reduced CoA (CoASH) from 45.3 +/- 3.1 to 25.9 +/- 3.1 mumol/kg dry wt and in free carnitine from 18.8 +/- 0.7 to 5.7 +/- 0.5 mmol/kg dry wt. Acetyl group accumulation, in the form of acetyl-CoA and acetylcarnitine, was maintained throughout exercise to exhaustion while the glycogen content decreased by 90%. This suggests that availability of acetyl groups was not limiting to exercise performance despite the nearly total depletion of the glycogen store. The increased acetyl-CoA-to-CoASH ratio during exercise caused inhibition of neither the PDC transformation nor the calculated catalytic activity of active PDC.     

Diversity in levels of intracellular total creatine and triglycerides in human skeletal muscles observed by (1)H-MRS.

We used (1)H-magnetic resonance spectroscopy to noninvasively determine total creatine (TCr), choline-containing compounds (Cho), and intracellular (IT) and extracellular (between-muscle fibers) triglycerides (ET) in three human skeletal muscles. Subjects' (n = 15 men) TCr concentrations in soleus [Sol; 100.2 +/- 8.3 (SE) mmol/kg dry wt] were lower (P < 0.05) than those in gastrocnemius (Gast; 125.3 +/- 9.2 mmol/kg dry wt) and tibialis anterior (TA; 123. 7 +/- 8.8 mmol/kg dry wt). The Cho levels in Sol (35.8 +/- 3.6 mmol/kg dry wt) and Gast (28.5 +/- 3.5 mmol/kg dry wt) were higher (P < 0.001 and P < 0.01, respectively) compared with TA (13.6 +/- 2. 4 mmol/kg dry wt). The IT values were found to be 44.8 +/- 4.6 and 36.5 +/- 4.2 mmol/kg dry wt in Sol and Gast, respectively. The IT values of TA (24.5 +/- 4.5 mmol/kg dry wt) were lower than those of Sol (P < 0.01) and Gast (P < 0.05). There were no differences in ET [116.0 +/- 11.2 (Sol), 119.1 +/- 18.5 (Gast), and 91.4 +/- 19.2 mmol/kg dry wt (TA)]. It is proposed that the differences in metabolite levels may be due to the differences in fiber-type composition and deposition of metabolites due to the adaptation of different muscles during locomotion.     

Plasma norepinephrine and muscle sympathetic discharge during rhythmic exercise in humans

The purpose of this study was to examine the relationship between plasma norepinephrine concentrations (PNE) and efferent muscle sympathetic nerve activity to noncontracting muscle (MSNA) during graded, rhythmic exercise in humans. In the initial study, six healthy men (ages 20-30 yr) performed 2-min bouts of two-arm cycling exercise at power outputs of 0, 10, 20, 40, 60 (n = 6), and 80 (n = 3) W. Heart rate (HR) was recorded and intraneural measurements of MSNA (right peroneal nerve) were made continuously for 2 min before (control) and during exercise at each work load. At least 2 wk later, subjects performed the same exercise bouts at which time HR was measured and a venous (forearm) blood sample was obtained for the subsequent determination of PNE by high-performance liquid chromatography. During exercise, HR increased progressively from 0 to 80 W. Neither MSNA nor PNE increased above control in response to arm cycling at 0, 10, and 20 W [0-16 +/- 1% (SE) of peak work load], but both variables increased progressively at the 40-, 60-, and 80-W (33 +/- 1 to 67 +/- 2% of peak work load) levels (all P less than 0.05). The individual MSNA and PNE responses (% change from control) over the six work loads were directly related (r = 0.80, P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise.

This investigation determined the effect of different rates of dehydration, induced by ingesting different volumes of fluid during prolonged exercise, on hyperthermia, heart rate (HR), and stroke volume (SV). On four different occasions, eight endurance-trained cyclists [age 23 +/- 3 (SD) yr, body wt 71.9 +/- 11.6 kg, maximal O2 consumption 4.72 +/- 0.33 l/min] cycled at a power output equal to 62-67% maximal O2 consumption for 2 h in a warm environment (33 degrees C dry bulb, 50% relative humidity, wind speed 2.5 m/s). During exercise, they randomly received no fluid (NF) or ingested a small (SF), moderate (MF), or large (LF) volume of fluid that replaced 20 +/- 1, 48 +/- 1, and 81 +/- 2%, respectively, of the fluid lost in sweat during exercise. The protocol resulted in graded magnitudes of dehydration as body weight declined 4.2 +/- 0.1, 3.4 +/- 0.1, 2.3 +/- 0.1, and 1.1 +/- 0.1%, respectively, during NF, SF, MF, and LF. After 2 h of exercise, esophageal temperature (Tes), HR, and SV were significantly different among the four trials (P < 0.05), with the exception of NF and SF. The magnitude of dehydration accrued after 2 h of exercise in the four trials was linearly related with the increase in Tes (r = 0.98, P < 0.02), the increase in HR (r = 0.99, P < 0.01), and the decline in SV (r = 0.99, P < 0.01). LF attenuated hyperthermia, apparently because of higher skin blood flow, inasmuch as forearm blood flow was 20-22% higher than during SF and NF at 105 min (P < 0.05). There were no differences in sweat rate among the four trials. In each subject, the increase in Tes from 20 to 120 min of exercise was highly correlated to the increase in serum osmolality (r = 0.81-0.98, P < 0.02-0.19) and the increase in serum sodium concentration (r = 0.87-0.99, P < 0.01-0.13) from 5 to 120 min of exercise. In summary, the magnitude of increase in core temperature and HR and the decline in SV are graded in proportion to the amount of dehydration accrued during exercise.     

Triidothyronine and epinephrine rapidly modify myocardial substrate selection: a (13)C isotopomer analysis

Triiodothyronine (T(3)) exerts direct action on myocardial oxygen consumption (MVO(2)), although its immediate effects on substrate metabolism have not been elucidated. The hypothesis, that T(3) regulates substrate selection and flux, was tested in isovolumic rat hearts under four conditions: control, T(3) (10 nM), epinephrine (Epi), and T(3) and Epi (TE). Hearts were perfused with [1,3-(13)C]acetoacetic acid (AA, 0.17 mM), L-[3-(13)C]lactic acid (LAC, 1.2 mM), U-(13)C-labeled long-chain free fatty acids (FFA, 0.35 mM), and unlabeled D-glucose (5.5 mM) for 30 min. Fractional acetyl-CoA contribution to the tricarboxylic acid cycle (Fc) per substrate was determined using (13)C NMR and isotopomer analysis. Oxidative fluxes were calculated using Fc, the respiratory quotient, and MVO(2). T(3) increased (P < 0.05) Fc(FFA), decreased Fc(LAC), and increased absolute FFA oxidation from 0.58 +/- 0.03 to 0.68 +/- 0.03 micromol. min(-1). g dry wt(-1) (P < 0.05). Epi decreased Fc(FFA) and Fc(AA), although FFA flux increased from 0.58 +/- 0.03 to 0.75 +/- 0.09 micromol. min(-1). g dry wt(-1). T(3) moderated the change in Fc(FFA) induced by Epi. In summary, T(3) exerts direct action on substrate pathways and enhances FFA selection and oxidation, although the Epi effect dominates at a high work state.     

Impaired muscle glycogen resynthesis after eccentric exercise

Eight men performed 10 sets of 10 eccentric contractions of the knee extensor muscles with one leg [eccentrically exercised leg (EL)]. The weight used for this exercise was 120% of the maximal extension strength. After 30 min of rest the subjects performed two-legged cycling [concentrically exercised leg (CL)] at 74% of maximal O2 uptake for 1 h. In the 3 days after this exercise four subjects consumed diets containing 4.25 g CHO/kg body wt, and the remainder were fed 8.5 g CHO/kg. All subjects experienced severe muscle soreness and edema in the quadriceps muscles of the eccentrically exercised leg. Mean (+/- SE) resting serum creatine kinase increased from a preexercise level of 57 +/- 3 to 6,988 +/- 1,913 U/l on the 3rd day of recovery. The glycogen content (mmol/kg dry wt) in the vastus lateralis of CL muscles averaged 90, 395, and 592 mmol/kg dry wt at 0, 24, and 72 h of recovery. The EL muscle, on the other hand, averaged 168, 329, and 435 mmol/kg dry wt at these same intervals. Subjects receiving 8.5 g CHO/kg stored significantly more glycogen than those who were fed 4.3 g CHO/kg. In both groups, however, significantly less glycogen was stored in the EL than in the CL.     

Muscle carnitine after strenuous endurance exercise.

The effect of very long endurance exercise on muscle carnitine was studied. Eighteen cross-country skiers took part in a race in the Alps (average inspired partial pressure of O2 100-110 Torr) that lasted on average 13 h 26 min. Carnitine intake, evaluated for 2 wk before the event, was 50 +/- 4 (SE) mg/day. Muscle (vastus lateralis) total carnitine concentration, measured twice with a 2-yr interval on eight rested subjects, did not change with time (17 vs. 16 mumol/g dry wt, NS) but showed consistent interindividual differences (range 12-22, P = 0.001) with no correlation with intake. After exercise, total muscle carnitine was unaltered (from 17.9 +/- 1.0 at rest to 18.3 +/- 0.8 mumol/g dry wt postexercise in the 15 subjects who completed the race, NS), but muscle free carnitine decreased 20% (from 14.9 +/- 0.8 mumol/g, P = 0.01) and short-chain acylcarnitine increased 108% (from 3.5 +/- 0.4 mumol/g, P = 0.01). These results suggest that carnitine deficiency will probably not result from strenuous aerobic exercise in trained subjects who consume a moderate amount of carnitine in their food.     

Accelerated triacylglycerol turnover kinetics in hearts of diabetic rats include evidence for compartmented lipid storage

Triacylglycerol (TAG) storage and turnover rates in the intact, beating rat heart were determined for the first time using dynamic mode (13)C- NMR spectroscopy to elucidate profound differences between hearts from diabetic rats (DR, streptozotocin treatment) and normal rats (NR). The incorporation of [2,4,6,8,10,12,14,16-(13)C(8)]palmitate into the TAG pool was monitored in isolated hearts perfused with physiological (0.5 mM palmitate, 5 mM glucose) and elevated substrate levels (1.2 mM palmitate, 11 mM glucose) characteristic of the diabetic condition. Surprisingly, although the normal hearts were enriched at a near-linear profile for >or=2 h before exponential characterization, exponential enrichment of TAG in diabetic hearts reached steady state after only 45 min. Consequently, TAG turnover rate was determined by fitting an exponential model to enrichment data rather than conventional two-point linear analysis. In the high-substrate group, both turnover rate (DR 820+/- 330, NR 190 +/-150 nmol.min(-1).g(-1) dry wt; P< 0.001) and [TAG] content (DR 78 +/-10, NR 32+/- 4 micromol/g dry wt; P< 0.001) were greater in the diabetic group. At lower substrate concentrations, turnover was greater in diabetics (DR 530+/-300, NR 160+/- 30; P<0.05). However, this could not be explained by simple mass action, because [TAG] content was similar between groups [DR 34+/- 7, NR 39+/- 9 micromol/g dry wt; not significant (NS)]. Consistent with exponential enrichment data, (13)C fractional enrichment of TAG was lower in diabetics (low- substrate groups: DR 4+/-1%, NR 10+/- 4%, P<0.05; high-substrate groups: DR 8+/- 3%, NR 14+/- 9%, NS), thereby supporting earlier speculation that TAG is compartmentalized in the diabetic heart.     

Training at high exercise intensity promotes qualitative adaptations of mitochondrial function in human skeletal muscle

This study explored mitochondrial capacities to oxidize carbohydrate and fatty acids and functional optimization of mitochondrial respiratory chain complexes in athletes who regularly train at high exercise intensity (ATH, n = 7) compared with sedentary (SED, n = 7). Peak O(2) uptake (Vo(2max)) was measured, and muscle biopsies of vastus lateralis were collected. Maximal O(2) uptake of saponin-skinned myofibers was evaluated with several metabolic substrates [glutamate-malate (V(GM)), pyruvate (V(Pyr)), palmitoyl carnitine (V(PC))], and the activity of the mitochondrial respiratory complexes II and IV were assessed using succinate (V(s)) and N,N,N',N'-tetramethyl-p-phenylenediamine dihydrochloride (V(TMPD)), respectively. Vo(2max) was higher in ATH than in SED (57.8 +/- 2.2 vs. 31.4 +/- 1.3 ml.min(-1).kg(-1), P < 0.001). V(GM) was higher in ATH than in SED (8.6 +/- 0.5 vs. 3.3 +/- 0.3 micromol O(2).min(-1).g dry wt(-1), P < 0.001). V(Pyr) was higher in ATH than in SED (8.7 +/- 1.0 vs. 5.5 +/- 0.2 micromol O(2).min(-1).g dry wt(-1), P < 0.05), whereas V(PC) was not significantly different (5.3 +/- 0.9 vs. 4.4 +/- 0.5 micromol O(2).min(-1).g dry wt(-1)). V(S) was higher in ATH than in SED (11.0 +/- 0.6 vs. 6.0 +/- 0.3 micromol O(2).min(-1).g dry wt(-1), P < 0.001), as well as V(TMPD) (20.1 +/- 1.0 vs. 16.2 +/- 3.4 micromol O(2).min(-1).g dry wt(-1), P < 0.05). The ratios V(S)/V(GM) (1.3 +/- 0.1 vs. 2.0 +/- 0.1, P < 0.001) and V(TMPD)/V(GM) (2.4 +/- 1.0 vs. 5.2 +/- 1.8, P < 0.01) were lower in ATH than in SED. In conclusion, comparison of ATH vs. SED subjects suggests that regular endurance training at high intensity promotes the enhancement of maximal mitochondrial capacities to oxidize carbohydrate rather than fatty acid and induce specific adaptations of the mitochondrial respiratory chain at the level of complex I.     

Body-weight-support treadmill training improves blood glucose regulation in persons with incomplete spinal cord injury.

The impact of a 6-mo body-weight-supported treadmill training program on glucose homeostasis and muscle metabolic characteristics was investigated. Nine individuals (31 +/- 3 yr, 8.1 +/- 2.5 yr postinjury; means +/- SE) with incomplete spinal cord injury trained three times weekly for a total of 6 mo. Training session duration and intensity (velocity) increased by 54 +/- 10% (P < 0.01) and 135 +/- 20%, respectively. Muscle biopsies and a modified glucose tolerance test (100 g glucose with [U-(13)C]glucose) were performed before (Pre) and after training (Post). Training resulted in a reduction in area under the curve of glucose x time (-15 +/- 4%) and insulin x time (-33 +/- 8%; both P < 0.05). Oxidation of exogenous (ingested) glucose increased as a result of training (Pre = 4.4 +/- 0.7 g/h, Post = 7.4 +/- 0.6 g/h; P < 0.05), as did oxidation of endogenous (liver) glucose (Pre = 3.8 +/- 0.3 g/h, Post = 5.2 +/- 0.3 g/h; P < 0.05). Training resulted in increased muscle glycogen (80 +/- 23%; P < 0.05) and GLUT-4 content and hexokinase II enzyme activity (126 +/- 34 and 49 +/- 4%, respectively, both P < 0.01). Resting muscle phosphocreatine content also increased after training (Pre = 62.1 +/- 4.3, Post = 78.7 +/- 3.8, both mmol/kg dry wt and P < 0.05). Six months of thrice-weekly body-weight-supported treadmill training in persons with an incomplete spinal cord injury improved blood glucose regulation by increasing oxidation and storage of an oral glucose load. Increases in the capacity for transport and phosphorylation glucose in skeletal muscle likely play a role in these adaptations.     

Stimulation of vascular Na-K pump with subpressor angiotensin II in rats.

The effect of subpressor doses of angiotensin II (ANG II) on vascular Na-K pump activity and Na-H exchange, two transmembrane signals of trophic stimulation of vascular muscle, was investigated. Male Sprague-Dawley rats (350-400 g) were given subpressor doses of ANG II by osmotic minipump intraperitoneally for 24 hr or 7-10 days. Control rats received sham procedure/vehicle infusion. Na-K pump activity (86Rb uptake), total and intracellular (Li exchange at 4 degrees C) Na content, and amiloride-sensitive and -insensitive Na uptake of aortas were measured ex vivo. Ouabain-sensitive 86Rb uptake of aortas of rats receiving 80-100, 160-180, and 240-260 ng/kg.min-1 of ANG II for 24 hr was 26.6 +/- 3.5, 28.8 +/- 3.4, and 29.1 +/- 2.6 nmol/mg dry wt.15 min-1 (mean +/- SD, n = 7-12), respectively, compared with 25.2 +/- 3.8 in controls (n = 23, P less than 0.01). These increases were maintained at 7-10 days. After 24 hr and 7-10 days of ANG II treatment, the total Na content of aortas was increased by 9.2% (P less than 0.01) and 7.6% (P less than 0.02), respectively, without a change in intracellular Na content, indicating accumulation of excess extracellular Na. Total and amiloride-sensitive Na uptake of the aorta was unchanged after 24 hr or 7-10 days of ANG II administration. The dry weight of anatomically defined segments of the aorta was 40 +/- 3.8 mg/kg body wt (n = 25) after 24 hr and 42 +/- 4.4 (n = 20) after 7-10 days of ANG II administration, compared with 37 +/- 4.8 (n = 15, P less than 0.05) and 37 +/- 4.9 (n = 17, P less than 0.01) in appropriate controls. Increased Na-K pump activity may signal the onset of trophic stimulation of vascular muscle by ANG II.     

Creatine supplementation increases muscle total creatine but not maximal intermittent exercise performance.

This study investigated creatine supplementation (CrS) effects on muscle total creatine (TCr), creatine phosphate (CrP), and intermittent sprinting performance by using a design incorporating the time course of the initial increase and subsequent washout period of muscle TCr. Two groups of seven volunteers ingested either creatine [Cr; 6 x (5 g Cr-H(2)O + 5 g dextrose)/day)] or a placebo (6 x 5 g dextrose/day) over 5 days. Five 10-s maximal cycle ergometer sprints with rest intervals of 180, 50, 20, and 20 s and a resting vastus lateralis biopsy were conducted before and 0, 2, and 4 wk after placebo or CrS. Resting muscle TCr, CrP, and Cr were unchanged after the placebo but were increased (P < 0.05) at 0 [by 22.9 +/- 4.2, 8.9 +/- 1.9, and 14.0 +/- 3.3 (SE) mmol/kg dry mass, respectively] and 2 but not 4 wk after CrS. An apparent placebo main effect of increased peak power and cumulative work was found after placebo and CrS, but no treatment (CrS) main effect was found on either variable. Thus, despite the rise and washout of muscle TCr and CrP, maximal intermittent sprinting performance was unchanged by CrS.     

Manipulation of dietary carbohydrates after prolonged effort modifies muscle sarcoplasmic reticulum responses in exercising males

The hypothesis tested was that disturbances in the sarcoplasmic reticulum (SR) Ca2+-cycling responses to exercise would associate with muscle glycogen reserves. Ten untrained males [peak O2 consumption (VO2 peak) = 3.41 +/- 0.20 (SE) l/min] performed a standardized cycle test (approximately 70% VO2 peak) on two occasions, namely, following 4 days of a high (Hi CHO)- and 4 days of a low (Lo CHO)-carbohydrate diet. Both Hi CHO and Lo CHO were preceded by a session of prolonged exercise designed to deplete muscle glycogen. SR Ca2+ cycling in crude homogenates prepared from vastus lateralis samples indicated higher (P < 0.05) Ca2+ uptake (microM x g protein(-1) x min(-1)) in Hi CHO compared with Lo CHO at 30 min (2.93 +/- 0.10 vs. 2.23 +/- 0.12) and at 67 min (2.77 +/- 0.16 vs. 2.10 +/- 0.12) of exercise, the point of fatigue in Lo CHO. Similar effects (P < 0.05) were noted between conditions for maximal Ca2+-ATPase (microM x g protein(-1) x min(-1)) at 30 min (142 +/- 8.5 vs. 107 +/- 5.0) and at 67 min (130 +/- 4.5 vs. 101 +/- 4.7). Both phase 1 and phase 2 Ca2+ release were 23 and 37% higher (P < 0.05) at 30 min of exercise and 15 and 34% higher (P < 0.05), at 67 min during Hi CHO compared with Lo CHO, respectively. No differences between conditions were observed at rest for any of these SR properties. Total muscle glycogen (mmol glucosyl units/kg dry wt) was higher (P < 0.05) in Hi CHO compared with Lo CHO at rest (+36%), 30 min (+53%), and at 67 min (+44%) of cycling. These results indicate that exercise-induced reductions in SR Ca2+-cycling properties occur earlier in exercise during low glycogen states compared with high glycogen states.     

Glycogenesis in muscle and liver during exercise

We hypothesized that glycogenesis increases in muscle during exercise before significant glycogen depletion occurs. Therefore, rats ran for 15 or 90 min at speeds of 8-22 m/min. D-[5-3H]glucose (10 microCi/100 g body wt) was administered 10 min before the end of exercise. Hindlimb muscles [soleus (SOL), plantaris (PL), extensor digitorum longus (EDL), and red (RG) and white gastrocnemius (WG)] and a portion of liver were analyzed for glycogen concentrations and rates of glycogen synthesis (i.e., D-[3H]glucose incorporated into glycogen). At rest, marked differences were observed among muscles in their rates of glucose incorporation into glycogen: i.e., SOL = 24.3 +/- 3.1, RG = 5.4 +/- 1.9, PL = 2.8 +/- 1.1, EDL = 0.54 +/- 0.10, WG = 0.12 +/- 0.02 (SE) dpm.micrograms glycogen-1.10 min-1 (P less than 0.05 between respective muscles). Compared with the glucose incorporation into glycogen at rest, increments in the PL (272%), RG (189%), WG (400%), EDL (274%), and liver (175%) were observed after 90 min of exercise (P less than 0.05, all data). In contrast, a decrease in glucose incorporation into glycogen (-62%) occurred in the SOL at min 15 (P less than 0.05), but this returned to the rates observed at rest after 90 min of exercise. This measure for rates of net glycogen synthesis (dpm.microgram glycogen-1.10 min-1) was weakly related to the ambient glycogen levels in most muscles; the exception was the SOL (r = -0.79; P less than 0.05). There was up to a 50-fold difference in glycogen synthesis among muscles.(ABSTRACT TRUNCATED AT 250 WORDS)     

Issues in the culture of the extremely thermophilic methanogen, Methanothermus fervidus

Basic issues in the culture of the extremely thermophilic archaeon, Methanothermus fervidus, have been investigated, including culture medium formulation, substrate yield and product yield coefficient, growth rate and stoichiometry, and H(2) uptake kinetics. The pH optimum for growth of this organism was estimated at 6.9. Growth medium buffered with PIPES instead of bicarbonate supported both increased growth rate and maximum biomass concentration. Substitution of titanium(III) citrate for the reducing agent sodium sulfide improved culture performance as well. However, independent adjustment of iron and nickel concentrations from 11 to 111 muM, respectively, and carbon dioxide partial pressure from 5 to 20 psia did not impact the culture of M. fervidus significantly. An elemental balance approach was utilized to aid in design of a defined medium to support growth to a target maximum biomass concentration of at least 1.0 g dry wt/L. The growth of this organism was limited by H(2) availability in this reformulated culture medium. The maximum growth rate and biomass concentration achieved in anaerobic vials with the defined medium was 0.16 h(-1) and 0.74 g dry wt/L, respectively. This maximum biomass concentration was a 72% improvement over that obtained with a literature-based defined medium. The Monod parameter, K(s), with H(2) as limiting substrate, was estimated at 1.1 +/- 0.4 psia (55 +/- 20 muM in the broth), based on a H(2) consumption study. Representative values for the substrate yield, Y(X/CO(2) ), and product yield coefficient, Y(CH(4)/) (X), were determined experimentally to be 1.78 +/- 0.04 g dry wt/mol CO(2), and 0.52 +/- 0.01 mol CH(4)/g dry wt, respectively. A bench-scale fermentation system suitable for the culture of extremely thermophilic anaerobes was designed and constructed and proved effective for the culture of M. fervidus. (c) 1993 Wiley & Sons, Inc.