High-energy Phosphate Content Research Articles

Myocardial Energy Metabolism in the Newborn Lamb In Vivo during Pacing-Induced Changes in Oxygen Consumption

Myocardial energy metabolism was studied in newborn sheep to determine whether the metabolic responses to pacing-induced increases in heart rate were similar to those previously found during catecholamine stimulation. Open-chest newborn sheep, 3 to 9 d old (n = 11), underwent atrial pacing at a respiratory rate harmonic just above the intrinsic heart rate. Pacing rate was increased by 30 beats/min every 5 min until conduction block or a drop in systemic arterial pressure occurred. Phosphorous metabolites were monitored simultaneously (n = 7) using a 31P magnetic resonance surface coil over the heart within a magnet operating at 4.7 tesla. Myocardial oxygen consumption was monitoring via an extracorporeal shunt from the coronary sinus. Rate pressure product increased with heart rate and was found to relate to myocardial oxygen consumption (r = 0.75), which increased maximally by 47 +/- 9% due to increases in coronary blood flow. Phosphocreatine/ATP ratio decreased significantly, and calculated ADP increased between baseline and peak performance but returned to near baseline levels during recovery at the initial pacing rate. These findings indicate that intracellular high-energy phosphate concentrations do change with alterations in myocardial oxygen consumption induced by cardiac pacing in the newborn. These changes are similar to those found during epinephrine infusion. Furthermore, the ATP hydrolysis products probably participate in myocardial respiratory regulation in the newborn in vivo.

Blood flow of the urinary bladder: Effects of outlet obstruction and correlation with bioenergetic metabolism

This study investigated the effects of outlet obstruction on blood flow and high energy phosphates content in the rabbit urinary bladder. Mild bladder outlet obstruction was induced by placing a silicon ring (diameter 7 mm) around the bladder neck of each male New Zealand White rabbit (n = 7). Before and immediately after inducing obstruction, and 2 weeks later, the bladders were emptied and regional blood flow measured using laser Doppler flowmetry (LASERFLO BPM2, Vasamedics Inc., St. Paul, Minnesota). Six different areas of each bladder were measured, and the average blood flow calculated for each rabbit. Then, the animals were sacrificed, the bladder excised, and the tissue content of high energy phosphates determined by high performance liquid chromatography (HPLC). Six normal male New Zealand White rabbits served as controls. The results can be summarized as follows: (1) Before surgery, bladder blood flow was similar in all animals (16.3 ml/min/100 g); positioning the silicon ring around the bladder neck did not affect blood perfusion, two weeks after the induction of outlet obstruction, bladder blood flow was significantly decreased (4.9 ml/min/100 g). (2) There was no significant difference between control and obstructed bladders in NAD, AMP, or ADP content. However, the obstructed bladders contained significantly less phosphocreatine (12.0 vs 21.9 nmol/mg protein) and ATP (4.0 vs. 6.1 nmol/mg protein) than control bladders. In summary, this study showed that urinary bladder blood flow was reduced by outlet obstruction, and the reduction in blood flow was associated with decreased tissue high energy phosphates content.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes of contractile properties of extensor digitorum longus in response to creatine-analogue administration and/or hindlimb suspension in rats.

Changes of contractile properties of extensor digitorum longus in response to hindlimb suspension and/or altered high-energy phosphate contents were studied in rats. A reduction of high-energy phosphates, especially phosphocreatine, was seen in rats fed creatine analogue beta-guanidinopropionic acid (beta-GPA), but they were elevated after 10-d supplementation of creatine. The one-half relaxation time was increased by feeding beta-GPA, but was normalized by creatine supply. The fatigue resistance of creatine-depleted muscle was significantly improved, but tended to decrease by suspension and creatine supply, although it was still better than that in the control diet group. It is indicated that the contractile properties of muscle are influenced by the high-energy phosphate content. It is also suggested that the endurance capacity may be influenced by the mitochondrial respiratory capacity, but not necessarily by the levels of high-energy phosphates.

Effects of Chronic Iron Deficiency Anemia on Brain Metabolism.

The effects of chronic iron deficiency anemia on brain (cortex) metabolism were estimated by 31P-nuclear magnetic resonance spectroscopy and biochemical analyses in male Wistar rats. Iron deficiency anemia was induced by supplying diet containing either approximately 2 or approximately 6 ppm Fe. Control diet was supplemented with 100 ppm Fe as ferric citrate. After 8-9 weeks, blood hemoglobin levels were approximately 13, 5, and 3 g/100 ml in the 100 ppm, 6 ppm, and 2 ppm Fe group, respectively. The blood lactate levels at rest in these groups were approximately 3, 5, and 6 mM. The blood glucose concentration also tended to be elevated in iron-deficient rats. The high-energy phosphate contents in brain were not affected by iron deficiency. The activities of succinate dehydrogenase and cytochrome oxidase per unit protein in the 2 ppm Fe group were significantly less than in the 100 ppm Fe group, but those activities were not significantly affected by feeding diet with 6 ppm Fe. The activities of lactate dehydrogenase in iron-deficient group tended to be elevated but not significantly. The activities of non-iron containing mitochondrial enzymes, citrate synthase and beta-hydroxyacyl CoA dehydrogenase, were unchanged. It is suggested that the brain has a higher tolerance to iron deficiency than skeletal muscle in terms of the metabolic characteristics, although this may be associated with a lower level of neural activity.

The effect of load on atrophy, myosin isoform shifts and contractile function: studies in a novel rat heart transplant preparation

A novel heterotopic rat heart transplant preparation was used with the objective of investigating the effect of load on cardiac contractile function, mass, myosin and high energy phosphates over a 7-day period. Donor hearts were excised, arrested with a hypothermic (4 degrees C) cardioplegic solution and transplanted (90-min operation time) into the abdomens of recipient rats. The transplanted hearts were reperfused in situ for 7 days. Two groups of hearts (n = 14/group) were studied. Group 1: a conventional unloaded transplanted preparation in which the aorta and pulmonary artery were anastomosed to the abdominal aorta and inferior vena cava, respectively. Group 2: a novel loaded preparation in which, additionally, the left atrium was anastomosed to the inferior vena cava which was then ligated proximally so as to divert distal venous flow to the left ventricle of the transplanted heart. Non-transplanted, fresh hearts served as controls. Seven days after transplantation the hearts were excised and perfused aerobically for 20 min. Systolic and diastolic functions had deteriorated severely in Group 1: left ventricular developed pressure (LVDP) had fallen to 96 +/- 11 v 162 +/- 6 mmHg in fresh controls (at 12 mmHg of end-diastolic pressure) and left ventricular volume to 80 +/- 12 v 268 +/- 20 microliters (P < 0.05 in both instances). In Group 2, LVDP (134 +/- 6 mmHg) and left ventricular volume (144 +/- 6 microliters) were significantly higher than in Group 1 but were still significantly lower than in fresh controls. Coronary flow in absolute terms was similar in all groups; however, when expressed as ml/min/g wet wt, coronary flow tended to be greater in unloaded hearts (19.8 +/- 0.6) than in fresh hearts (15.0 +/- 0.8; P < 0.05) and loaded hearts (17.6 +/- 1.3; N.S.). Unloaded hearts exhibited a significant loss of left ventricular weight (0.40 +/- 0.02 g) when compared with fresh aerobic controls (0.57 +/- 0.02 g; P < 0.05). However, there was no significant weight loss in the loaded hearts (0.53 +/- 0.03 g). The content of V1 isoform of myosin in left ventricular muscle was 77.8 +/- 5.0% in fresh hearts; this was reduced to 60.0 +/- 3.6% in the unloaded hearts (P < 0.05). The value in the loaded hearts (73.2 +/- 3.4%) did not differ significantly from that in fresh controls. The adenine nucleotide pool was similar in all groups. In conclusion, imposing a load on the heterotopically transplanted heart prevents the loss of cardiac mass and the shift of myosin isoforms, however, it does not totally prevent the development of systolic and diastolic dysfunction. The contractile abnormalities do not appear to be related to high energy phosphate content but might well arise as a consequence of the denervation associated with transplantation or the transplantation procedure itself.

Energetic status and viability of porcine kidney cells after hypoxic, hypothermic preservation in UW solution and subsequent reoxygenation: the influence of taurine

Taurine (2-aminoethane sulfonic acid) is a physiologic compound with osmoregulative properties and presumbly an inhibitor of lipid peroxidation. The present study evaluates the effects on the viability of isolated kidney cells of the addition of various doses of taurine to the UW preservation solution. Porcine tubular cell monolayers were incubated at 4°C for 9 h in UW solution under hypoxic conditions, and subsequently reoxygenated for 30 min in Hank's balanced salt solution equilibrated with room air. Taurine was added to the preservation solution at final concentrations of 0, 1, 10 ot 20 mmol/1. Cel viability was assessed by exclusion on Trypan blue and by determination of the energetic status reoxygenation. While tuarine had no influence on the post-hypoxic vaibility according to Trypan blue exclusion, a dose-related increases in cellular content of high energy phosphates after post-hypoxic reoxygenation was observed after addition of taurine to the preservation medium. It is concluded that taurine is able to reduce tissue alterations during hypoxia and reoxygenation and that the determination of post-hypoxic recovery of energy metabolism may be a more sensitive indicator of cell viability than the morphological Trypan blue exclusion test.

The protective potency of two commonly used cardioplegic solutions on cultured endothelial cells exposed to free-oxygen radicals injury

Human umbilical vein endothelial cells were incubated with Bretschneider and St. Thomas II cardioplegic solution followed by a stimulation with cumene hydroperoxide (CHPO), which was used as an oxygen radicals generating agent. A statistically significant decrease of intracellular high energy phosphates (adenosine-5-triphosphate: ATP; creatine phosphate; CP) compared to controls was observed in response to Bretschneider cardioplegia and CHPO. Furthermore, significant rises in prostaglandin I 2 (prostacyclin; PGI 2) production and lipidperoxidation were measured. The authors failed to record such alterations of endothelial cell metabolism for the St. Thomas II cardioplegic solution. They could also demonstrate that the cellular protection against oxygen radicals exerted by the St. Thomas II solution is attributable to procaine. The enhanced cytotoxicity of CHPO observed in presence of the Bretschneider solution was found to be partially caused by its constituent L-histidine, which led to significant decreases of high energy phosphates and increased lipidperoxidation when cells were subsequently treated with CHPO. However, alterations of high energy phosphate content initiated by CHPO and amplified by the Bretschneider solution could not be inhibited by adding procaine. Simultaneous pretreatment of cells with the Bretschneider solution and procaine and stimulation with CHPO resulted in decreases of ATP and CP, as observed using the Bretschneider cardioplegia alone.

Adenosine Formation During Hypoxia in Isolated Hearts: Effect of Adrenergic Blockade

Adrenergic receptor blockade has been reported to decrease cardiac adenosine formation and release during hypoxia. We wished to determine whether this occurs by an improvement in the energy supply/demand ratio. Isolated guinea pig hearts were perfused at a constant pressure of 50 mm Hg. Hypoxia (30% O2) was maintained for 20 min while adenosine release and venous PO2 were measured in the coronary venous effluent. β-adrenergic blockade with 5 μM atenolol did not change hypoxic adenosine release (Control: 15.6 ± 2.7. Atenolol: 23.6 ± 5.7 nmol/g/20 min). Addition of 6 μm phentolamine with atenolol significantly reduced hypoxic adenosine release (4.4 ± 1.4 nmol/g/20 min, P < 0.05). Atenolol was without hemodynamic effects, but addition of phentolamine reduced left ventricular pressure development, heart rate, and oxygen consumption prior to hypoxia. Atenolol plus phentolamine did not change venous PO2 during hypoxia. Treatment with phenoxybenzamine (1 μM) plus atenolol also reduced adenosine release (7.4 ± 0.8 nmol/g/20 min). Control experiments and atenolol plus phentolamine experiments were repeated using 31 P-NMR to measure high energy phosphates. Adrenergic blockade had no effect on phosphate concentrations during normoxia, but resulted in higher [PCr], lower [Pi] and higher phosphorylation potentials during hypoxia. Adrenergic blockade also prevented the hypoxia-induced rise in intracellular [H+]. [AMP] and [ADP] seen in control hearts. The changes in phosphorylation potential are correlated with similar changes in adenosine release in adrenergically intact hearts. We conclude that the primary effect of adrenergic blockade during hypoxia is a reduction in ATP use due to α-receptor blockade. This leads to improved high energy phosphate concentrations during hypoxia and a reduction in adenosine formation.

Enhanced fatigue resistance of rat muscles with lowered contents of high-energy phosphates

Enhanced fatigue resistance of rat muscles with lowered contents of high-energy phosphates

Correlation between content of high-energy phosphates and hypoxic-ischemic damage in immature and mature astrocytes

The effect of ‘simulated ischemia’, i.e., combined anoxia and substrate deprivation, was studied in 1- and 3-week-old (i.e., immature and mature) primary cultures of mouse astrocytes. Cell survival, as indicated by retention of the high-molecular cytosolic protein lactate dehydrogenase was compared with retained high-energy phosphate compounds (ATP and phosphocreatine). A previously established longer survival of the immature cells during the metabolic insult was confirmed and found to correlate with a more complete maintenance of high-energy phosphates. However, in both the mature and immature cells, no death occurred as long as the ATP content remained at or above 25% of its control value. ATP concentrations below 10% of control were accompanied by almost complete cell death in both age groups. Thus, the better survival of immature astrocytes during simulated ischemia is correlated with better maintenance of the levels of high-energy phosphates and, regardless of age, cell death occurs only once a critically ‘low’ threshold of ATP has been reached.

Loss of relaxations, metabolic failure and increased calcium permeability of smooth muscle during chronic cerebral vasospasm

In the canine basilar artery during chronic vasospasm following subarachnoid hemorrhage, endothelium-dependent relaxations were diminished. Release of endothelium-derived relaxing factor (EDRF), as measured by a bioassay method, was unchanged. Relaxation to nitric oxide (NO) in preparations without endothelium was smaller in the spastic arteries. Production of cyclic GMP, measured by radioimmunoassay, was reduced in the spastic arteries; the impaired production was accompanied by decrease in GTP, the substrate for the production of cyclic nucleotide. The contents of other high-energy phosphates, such as creatine phosphate and ATP were also markedly reduced. Close temporal correlation between the metabolic failure and development of vasospasm was observed. Sarcolemmal regulation of intracellular calcium concentration was impaired in the pathological condition, suggesting a link between the metabolic failure and the pathological protracted contractions. Metabolic changes, and resultant affected viability of smooth muscle cells are likely to be an important factor in the pathogenesis of chronic vasospasm.

Metabolic adaptation of skeletal muscles to gravitational unloading

Responses of high-energy phosphates and metabolic properties to hindlimb suspension were studied in adult rats. The relative content of phosphocreatine (PCr) in the calf muscles was significantly higher in rats suspended for 10 days than in age-matched cage controls. The Pi PCr ratio, where Pi is inorganic phosphate, in suspended muscles was less than controls. The absolute weights of soleus and medial gastrocnemius (MG) were approximately 40% less than controls. Although the % fiber distribution in MG was unchanged, the % slow fibers decreased and the % fibers which were classified as both slow and fast was increased in soleus. The activities (per unit weight or protein) of succinate dehydrogenase and lactate dehydrogenase in soleus were unchanged but those of cytochrome oxidase, β-hydroxyacyl CoA dehydrogenase, and citrate synthase were decreased following unloading. None of these enzyme activities in MG changed. However, the total levels of all enzymes in whole muscles decreased by suspension. It is suggested that shift of slow muscle toward fast type by unloading is associated with a decrease in mitochondrial biogenesis. Further, gravitational unloading affected the levels of muscle proteins differently even in the same mitochondrial enzymes. Unloading-related atrophy is prominent in red muscle or slow-twitch fiber 1, 2. Such atrophy is accompanied by a shift of contractile properties toward fast-twitch type 2–9. Further, inhibition of mitochondrial metabolism in these muscles is also reported by some studies 10–14 suggesting a lowered mitochondrial biogenesis, although results from some studies do not necessarily agree 1, 7, 15. However, the precise mechanism responsible for such alterations of muscle properties in response to gravitational unloading is unclear. On the contrary, mitochondrial biogenesis, suggested by mitochondrial enzyme activities and/or mass, is stimulated in muscles with depleted high-energy phosphates by cold exposure 16 and/or by feeding creatine analogue β-guanidinopropionic acid 17–19. Tension production may be inhibited in unloaded antigravity muscles 20, although the muscular activity detected by electromyography is not necessarily decreased 21. Thus, the contents of high-energy phosphates or turnover rate of adenosine triphosphate (ATP), which then affect the mitochondrial energy metabolism, may be altered. Therefore, the responses of high-energy phosphates and metabolic properties of rat hindlimb muscles to gravitational unloading were investigated.

Effects of aprotinin on acute recovery of cerebral metabolism in piglets after hypothermic circulatory arrest

Brain protection during cardiopulmonary bypass and hypothermic circulatory arrest is incomplete. Activation of blood protease cascades may contribute to cellular injury under these conditions. To test this hypothesis, effects of the protease inhibitor aprotinin on recovery of brain energy metabolism after hypothermic circulatory arrest were studied in the piglet. Twenty-four 4-week-old piglets (10 aprotinin-treated and 14 control) underwent core cooling, 1 hour of circulatory arrest at 15 °C, reperfusion and rewarming (45 minutes), and normothermic perfusion (3 hours) on cardiopulmonary bypass. Cerebral high-energy phosphate concentration and intracellular pH were studied by phosphorus-31 magnetic resonance spectroscopy in 12 animals. In the remaining animals cerebral and regional blood flow were measured with radioactive microspheres and carctid artery blood flow was measured with an electromagnetic flowmeter. Cerebral oxygen and glucose extraction were measured, and vascular resistance responses to endothelium-dependent (acetylcholine) and -independent (nitroglycerin) vasodilators were calculated. Recovery of cerebral adenosine triphosphate ( p = 0.02) and intracellular pH p = 0.04) in the initial 30 minutes of reperfusion was accelerated in the aprotinin-treated piglets. These piglets showed a greater in vivo cerebral and systemic endothelium-mediated vasodilation (acetylcholine response: cerebral p < 9.01, systemic p = 0.04) after reperfusion. The response to endothelium-independent vasodilation (nitroglycerin) was the same in both groups. Carotid blood flow tended to be greater at 20 minutes of reperfusion and less during 45 to 80 minutes after reperfusion in the aprotinin-treaied animals. Brain water content postoperatively was 0.8077 in the aprotinin group and 0.8122 in control animals ( p = 0.06). Water content in the lungs, heart, kidneys, jejunum, and lower limb muscle was less in the aprotinin group p < 0.05). Aprotinin enhances recovery of cerebral energy metabolism from the deletenous effects of deep hypothermic circulatory arrest in the immature animal, possibly through mechanisms involving preservation of vascular integrity.

Exercise heat stress in rats: performance and biochemical effects

Disturbed mental status (DMS) is the most obvious sign of exertional heatstroke in humans, and is one of the main complications of severe exercise heat-stress (SHS). The cause of exertional heat-stroke has been attributed to many factors such as thermoregulatory failure or impairment of muscular function. This investigation was designed to assess muscle energy metabolism in two groups of rats running at 34 °C. One group ( n = 17) stopped because of DMS (SHS rats), while the other group (n = 21) stopped because of mild or moderate exercise heat-stress (MHS rats). SHS rats ran longer and had a higher final rectal temperature ( Tre): 66.5 ± 4.2 °C vs 47.3 ± 3.8 °C, p &lt;0.05 and 42.7 ± 0.12 °C vs42.2 ± 0.15 °C, p &lt; 0.05, respectively. SHS rats also had a slower rate of change of Tre (0.054 ± 0.007 °C min−1 vs 0.072 ± 0.008 °C min−1) and a lower mean rate of dehydration: 0.065 ± 0.006 vs 0.084 ± 0.005% bodyweight min−1, p &lt; 0.05. There were no significant differences between the two groups for skeletal muscle concentration of high energy phosphates and glycogen, but lactate was higher in SHS than in MHS rats: 25.0 ± 6.7 vs 11.8 ± 1.6 μmoles per mg protein respectively, p &lt;0.05. These data suggest that DMS may be linked to Tre and that there is muscular functional impairment caused by SHS.

Phospholipid Peroxidation in Isolated Perfused Rat Hearts Subjected to Hypothermia Followed by Rewarming: Inverse Relation to Loss of Function

In the present experimental study phospholipid peroxidation after hypothermia and rewarming was investigated in isolated buffer-perfused rat hearts. Stable normotherm perfusion (37°C) for 20 min was followed by cooling to 14°C, 4 h perfusion at 14°C, and rewarming to 37°C followed by 30 min normotherm perfusion. Seven hearts went through the whole protocol, whereas six hearts were subjected only to the initial stabilization period. Mechanical performance was measured by a balloon in the left ventricle (LV) permitting measurements of LV pressure and its derivatives. At the end of perfusion, hearts were freeze clamped in liquid nitrogen for phospholipid peroxidation measurements, phospholipid fatty acid composition, high-energy phosphate content (adenosine tri-, di-, and monophosphate and creatine phosphate), and tissue water content. After rewarming there was a significant reduction in mechanical performance and coronary flow. Tissue content of high-energy phosphates was decreased and tissue water content was increased. Levels of peroxidized polyunsaturated fatty acids (conjugated diens) in phospholipids and nonesterified fatty acids were not significantly changed (135.2 ± 31.1 vs 74.3 ± 7.6 nmol/g tissue dry wt and 1212 ± 203 and 1685 ± 197 nmol/g in control and rewarmed hearts). However, the amount of peroxidized polyunsaturated fatty acids in phospholipids expressed as a fraction of the phospholipids was significantly reduced by the cooling/rewarming procedure (1.28 ± 0.22 vs 0.61 ± 0.09 × 10-3, P < 0.05). In conclusion, membrane destabilization due to increase in phospholipid peroxidation cannot explain loss of function, loss of energy reserve, and increase in tissue water content observed after rewarming of hearts subjected to prolonged hypothermia in combination with sustained perfusion and oxygen supply.

NMR spectroscopic study of cell cultures of astrocytes and neurons exposed to hypoxia: Compartmentation of astrocyte metabolism

Primary cultures of murine cerebral cortical astrocytes or cerebellar granule neurons were exposed to 7 h of hypoxia (3 h in some cases). The culture medium was analyzed at the end of the hypoxic or normoxic period by 1H NMR spectroscopy and intracellular components were analyzed as perchloric acid extracts by 31P and 1H NMR spectroscopy. Lactate production in astrocytes increased only marginally, whereas high energy phosphate concentrations were reduced, during 7 h of hypoxia and after 17 h of reoxygenation. After 3 h of hypoxia full recovery was possible during reoxygenation. Citrate and glutamine secretion was reduced or unchanged, respectively, during 7 h of hypoxia. Succinate secretion was only observed during normoxia, whereas pyruvate was secreted during hypoxia. Cerebellar granule neurons were more efficient in increasing glycolysis and were, therefore, more resistant to the effects of hypoxia than astrocytes. In the neurons lactate production was doubled and no effects on levels of high energy phosphates were seen after 7 h of hypoxia. Astrocytes were reoxygenated for 17 h after hypoxia or normoxia in a medium containing [2- 13C]acetate in order to access if astrocytes were still capable of supplying neurons with essential precursors. The media were subsequently analyzed by 13C NMR spectroscopy. After shorter periods of hypoxia (3 h) full recovery was possible. Citrate and glutamine production remained however decreased during reoxygenation after 7 h of hypoxia. 13C incorporation into glutamine was greatly reduced but that into citrate was unchanged. These results suggest that under the present conditions, neurons are more efficient than astrocytes in switching the energy metabolism from aerobic to anaerobic glycolysis and that astrocytes may suffer long term damage to mitochondria from longer periods of hypoxia. Furthermore, evidence is presented for the existence of several TCA cycles within astrocytes based on labeling ratios. During normoxia the labeling ratios in the C-2/C-4 positions in glutamine and in the equivalent positions in citrate were 0.27 and 0.11, respectively.

Responses of beta-adrenoceptor in rat soleus to phosphorus compound levels and/or unloading

Responses of beta-adrenoceptor (beta-AR) in rat soleus to gravitational unloading and/or changes in the levels of phosphorus compounds by feeding either creatine or its analogue beta-guanidinopropionic acid (beta-GPA) were studied. A decrease in the density of beta-AR (about -35%) was induced by 10 days of hindlimb suspension, but the affinity of the receptor was unaffected. Suspension unloading tended to increase the levels of adenosine triphosphate and phosphocreatine and decrease inorganic phosphate. Even without unloading, the beta-AR density decreased after an oral creatine supplementation (about -20%), which also tended to elevate the high-energy phosphate levels in muscle. However, an elevation of beta-AR density was induced (about +36%) after chronic depletion of high-energy phosphates by feeding beta-GPA (about +125%). Data suggest that the density of beta-AR in muscle is elevated if the high-energy phosphate contents are chronically decreased and vice versa. However, it may not be directly related to the degree of muscle contractile activity.

Ryanodine and theophylline-induced depletion of energy stores in amphibian muscle

The effects of high and low levels of ryanodine on theophylline-induced energy depletion were studied in isolated frog sartorius muscle. Whereas low concentrations of ryanodine (1–10 μM) did not change high energy phosphate contents (PE) after 60 min, high levels (100 μM) reduced resting energy contents by 60% after 60 min. Subcontracture levels of theophylline (2 mM), in the presence of high ryanodine, produced an 80% PE depletion, suggesting possible additive or synergistic effects of these two agents. In contrast to theophylline-induced depletion, neither the ryanodine-induced depletion nor the theophylline-plus-ryanodine-induced depletion of PE seemed sensitive to inhibition by 1 mM procaine. This suggests that there may be differences in the mechanisms whereby methylxanthines and ryanodine deplete energy stores and evoke contractures in amphibian skeletal muscle.

Beneficial effects of iloprost on acute myocardial ischemia in dogs.

The effects of intravenous administration of iloprost, a prostacyclin analogue, on myocardial energy metabolism and myocardial blood flow (MBF) were examined in anesthetized open-chest dogs subjected to 60 min of myocardial ischemia by coronary ligation. Iloprost administration at levels of 0.1 or 0.2 micrograms/kg/min was started 30 min before the commencement of ischemia and continued throughout the 90 min observation period. Since systolic aortic pressure in the iloprost 0.2 micrograms/kg/min group showed significantly lower values than that in the control group, whereas no clear effect was observed with the lower concentration (0.1 micrograms/kg/min), this latter group was further investigated. This 0.1 microgram/kg/min dose of iloprost lacked influence on MBF in both ischemic and nonischemic areas but did result in a significantly higher value for high energy phosphate contents in the ischemic myocardium. Moreover, myocardial mitochondrial respiratory function in the ischemic area was significantly improved. These results indicate that iloprost brought about preservation of myocardial energy metabolism without alteration of coronary perfusion, suggesting that it may exert a direct cardioprotective effect.

Effects of unloaded reperfusion on mitochondrial function in the postischemic myocardium.

The effect of mechanical unloading on recovery of postischemic myocardial performance, high energy phosphate content, and mitochondrial function was tested in an isolated working rabbit heart model. After 30 min of global ischemia, prolonged unloaded reperfusion could prevent complete loss of contractility, deterioration of mitochondrial function, and depletion of the ATP pool as was found when only short-term unloading was performed. Aortic flow recovered to 21% of preischemic control, and left ventricular dP/dt max to 46% (p < 0.05 vs. short-term unloading). OPR and ADP/O stabilized at 42 and 72%, respectively (p < 0.05 vs. short-term unloading), and ATP at 33% of control (p < 0.05 vs. short-term unloading). These results show the beneficial effect of prolonged unloading in postischemic hearts.