Biomedical subjects

G K Asimakis

Publications and source records attributed to G K Asimakis.

At least 19 recordsLinked to original sources

PubMed1998

Cardioprotection by local heating: improved myocardial salvage after ischemia and reperfusion.

BACKGROUND: Previous studies have shown that expression of the inducible 70-kD heat-shock protein (HSP72) by whole-body hyperthermia is associated with protection against ischemia-reperfusion injury. To develop techniques for regional elevation of heat-shock proteins that prevent extracardiac sequelae during whole-body hyperthermia, we sought to determine if local heating of the heart in vivo provides protection against ischemia-reperfusion injury in the rat. METHODS: A thermal probe was used to locally heat rat hearts at two adjacent sites on the epicardial surface of the left ventricle. Rats were subjected to either 30 minutes of sham surgery (control; n = 10) or two local applications of the probe at 42.5 degrees to 43.5 degrees C for 15 minutes each (n = 9). After 4 hours, rats were subjected to 30 minutes of regional ischemia followed by 120 minutes of reperfusion. Hearts were removed and area at risk and infarct area were determined. RESULTS: Localized heat stress resulted in a significant limitation of infarct size in heat-treated animals versus controls (mean +/- standard error of the mean infarct area/area at risk = 4.3% +/- 0.85 versus 19.2% +/- 3.4%; p < 0.005). Western blot experiments confirmed elevated HSP72 expression in left (heated) and right (nonheated) ventricular samples from treated animals (n = 6; left ventricular = 5.5-fold; right ventricular = 3.7-fold) compared with sham-operated controls. Controls treated with the probe at 37 degrees C (n = 4) showed no increases in HSP72. CONCLUSIONS: Local heating of the heart is associated with elevated levels of HSP72 and improved myocardial salvage. The increase in expression of HSP72 is not limited to the heated region, but extends into nonheated regions of the heart as well. This may lead to the development of new techniques that improve methods of myocardial revascularization and heart transplantation procedures.

Analysis of Variance↗

PubMed1998

Heat shock improves recovery and provides protection against global ischemia after hypothermic storage.

BACKGROUND: Improved methods of donor heart preparation before preservation could allow for prolonged storage and permit remote procurement of these organs. Previous studies have shown that overexpression of heat-shock protein 72 provides protection against ischemic cardiac damage. We sought to determine whether rats subjected to heat stress with only 6-hour recovery could acquire protection to a subsequent heart storage for 12 hours at 4 degrees C. METHODS: Three groups of animals (n = 10 each) were studied: control, sham-treated, and heat-shocked rats (whole-body hyperthermia 42 degrees C for 15 minutes). After 12-hour cold ischemia hearts were reperfused on a Langendorff column. To confirm any differences in functional recovery, hearts were then subjected to an additional 15-minute period of warm global ischemia after which function and lactate dehydrogenase enzyme leakage were measured. RESULTS: Heat-shocked animals showed marked improvements compared with controls in left ventricular developed pressure (63+/-4 mm Hg versus 44+/-4 mm Hg, p<0.05) heart rate x developed pressure (13,883+/-1,174 beats per minute x mm Hg versus 8,492+/-1,564 beats per minute x mm Hg, p<0.05), rate of ventricular pressure increase (1,912+/-112 mm Hg/second versus 1,215+/-162 mm Hg/second, p<0.005), rate of ventricular pressure decrease (1,258+/-89 mm Hg/second versus 774+/-106 mm Hg/second, p<0.005). Diastolic compliance and lactate dehydrogenase release were improved in heatshocked animals compared with controls and sham-treated animals. Differences between heat-shocked animals and control or sham-treated animals were further increased after the additional 15-minute period of warm ischemia. Western blot experiments confirmed increased heat-shock protein 72 levels in heat-shocked animals (>threefold) compared with sham-treated animals and controls. CONCLUSIONS: Heat shock 6 hours before heart removal resulted in marked expression of heat-shock protein 72 and protected isolated rat hearts by increased functional recovery and decreased cellular necrosis after 12-hour cold ischemia in a protocol mimicking that of heart preservation for transplantation. Protection was further confirmed after an additional 15-minute period of warm ischemia.

Animals↗

PubMed1997

Role of low molecular weight iron in functional preconditioning of the isolated rat heart.

Post-ischemic contractile dysfunction in the heart may be due to oxygen-derived free radicals catalyzed by low molecular weight iron (lmw Fe), which is thought to accumulate during ischemia and reperfusion. We tested the hypothesis that functional preconditioning with transient ischemia in the rat heart may be due to decreasing the myocardial lmw Fe pool, and consequently free radicals during ischemia or reperfusion. Hearts were preconditioned with two 5-min episodes of ischemia followed by 5 min of reperfusion. The lmw Fe pool of pre-ischemic hearts was 172 +/- 13pmol/mg protein. After 40 min of prolonged ischemia, the lmw Fe contents were 176 +/- 25 and 127 +/- 13 pmol/mg for non-conditioned and preconditioned hearts, respectively (P=N.S.). After 10 min of reperfusion, the lmw Fe contents were 246 +/- 26 and 228 +/- 23 pmol/mg protein, respectively (P=N.S.). We next tested the ability of deferoxamine, an iron chelator, to mimic functional preconditioning. The percentage recoveries of heart rate x developed pressure after 40 min of ischemia and 30 min of reperfusion were 38 +/- 6 and 25 +/- 5 for non-conditioned and deferoxamine-treated hearts, respectively (P=N.S.). We further tested the hypothesis by determining if iron-overloading by dietary enhancement and weekly iron injections would exacerbate post-ischemic contractile dysfunction and attenuate functional preconditioning with ischemia. The total iron contents of the high iron and normal groups were 10.3 +/- 0.6 and 4.4 +/- 0.2 nmol/mg protein (P<0.001). Percentage recoveries of heart rate x developed pressure were 36 +/- 6 and 33 +/- 5 for non-conditioned hearts in the high iron and normal iron groups, respectively (P=N.S.). Percentage recoveries of heart rate x developed pressure were 58 +/- 5 and 68 +/- 6 for ischemically preconditioned hearts in the high and normal iron groups, respectively (P= N.S.). The results suggest that functional preconditioning in the rat heart is not due to attenuation lmw Fe accumulation.

Animals↗

PubMed1996

Myocardial glycogen depletion cannot explain the cardioprotective effects of ischemic preconditioning in the rat heart.

The mechanism of ischemic preconditioning remains unknown. The role of glycogen depletion prior to prolonged ischemia was examined as a potential mechanism of ischemic preconditioning. The glycogen content of the rat heart varies in a 24-h rhythm. In a retrospective study, the relationships between the time of day the animals were sacrificed, pre-ischemic myocardial glycogen content, and post-ischemic functional recovery were assessed in non-conditioned and ischemically preconditioned hearts. The analyses were performed on previously published data (Asimakis et al.. 1992, 1993). After an equilibration perfusion, isolated rat hearts were given 40 min of global ischemia followed by 30 min of reperfusion. Preconditioned hearts received 5 min of ischemia followed by a 5-min recovery period prior to the 40-min ischemic period. Some of the hearts were freeze-clamped immediately prior to the 40-min ischemic period to determine pre-ischemic glycogen content. Pre-ischemic glycogen was higher in the morning than afternoon. The time of day correlated significantly with the pre-ischemic glycogen content of non-conditioned (r = 0.67; P < 0.005) and preconditioned (r = 0.79; P < 0.001) hearts. However, time of day did not correlate significantly with post-ischemic recovery of heart rate x developed pressure (HR x DP) on end-diastolic pressure (EDP) in either the non-conditioned or preconditioned hearts. The relationships were also assessed by subdividing the groups into either morning (a.m.) or afternoon (p.m.) hearts. The pre-ischemic glycogen content was lower in the non-conditioned-p.m. (n = 5) hearts compared to the non-conditioned-a.m. (n = 10) hearts (67.6 +/- 9.0 nu 128.1 +/- 13.3 nmol glucose/mg protein P < 0.005). However, there were no significant differences between p.m. (n = 13) and a.m. (n = 9) non-conditioned hearts with respect to post-ischemic recovery of HR x DP (20.6 +/- 4 nu 12.0 +/- 4% of baseline, respectively, P = N.S.). In contrast, preconditioned-p.m. (n = 6) and -a.m. (n = 7) had pre-ischemic glycogen contents of 49.6 +/- 6 and 76.6 +/- 5.0 nmol glucose/mg protein, respectively. These glycogen values were not significantly different from the non-conditioned-p.m. hearts (67.6 nmol/mg protein). However, post-ischemic recovery of HR x DP in the preconditioned-p.m. (n = 5) and -a.m. (n = 6) hearts were 54.6 +/- 5 and 51.4 +/- 8% of baseline, respectively (these values were significantly higher (P < 0.05) than the recovery for the non-conditioned-p.m. and -a.m. hearts). The results imply that the cardioprotection of ischemic preconditioning cannot be explained solely by myocardial glycogen depletion.

Adenosine Triphosphate↗

PubMed1996

Transient ischemia cannot precondition the rabbit heart against postischemic contractile dysfunction.

BACKGROUND: The rat heart is preconditioned against postischemic contractile dysfunction by a brief period of transient ischemia before a prolonged ischemic period. However, the rabbit heart does not receive such cardio-protection from pretreatment with a single transient ischemia periods. We hypothesized that in the rabbit heart, a multiple cycle of transient ischemia is required to reach a threshold necessary to precondition against postischemic contractile dysfunction. METHODS: To test this hypothesis, we subjected isolated, perfused rabbit hearts to either one 5-minute transient ischemic period or three 5-minute transient ischemic periods followed by a 40-minute period of warm ischemia and 30 minutes of reperfusion. Control hearts (no pretreatment with transient ischemia) were examined simultaneously. Left ventricular developed pressure was measured with an intraventricular balloon. RESULTS: Postischemic recoveries (expressed as percent of preischemic values) of left ventricular developed pressure for the group with one ischemic period and the group with three ischemic periods were 43% +/- 5% (n = 5) and 38% +/- 6% (n = 6), respectively. These values were not significantly different from control values. CONCLUSIONS: Neither one nor three periods of transient ischemia protect the isolated, perfused rabbit heart from postischemic contractile dysfunction. Therefore, the rabbit heart may not have the capacity to be ischemically preconditioned against postischemic contractile dysfunction.

Animals↗

PubMed1995

Preconditioning with dobutamine in the isolated rat heart.

The ability of dobutamine to precondition the isolated rat heart against postischemic contractile dysfunction was assessed. Hearts were perfused with varying concentrations of dobutamine for 5 min followed by a 5 min "washout" period and 30 min of global ischemia. The hearts were reperfused for 30 min to assess postischemic function. Dobutamine improved postischemic developed pressure, +dp/dt, heart rate x developed pressure, end diastolic pressure, and coronary flow in a concentration-dependent manner. The concentration of dobutamine showing the maximum protective effect was 10(-6)M. Propranolol administered with dobutamine significantly attenuated the protective effect. The results indicate that transient treatment with dobutamine can precondition the rat heart against ischemia/reperfusion injury. The mechanism of protection appears to involve beta-adrenergic stimulation.

Animals↗

PubMed1994

Transient beta adrenergic stimulation can precondition the rat heart against postischaemic contractile dysfunction.

OBJECTIVE: The aim was to assess the abilities of exogenous noradrenaline, isoprenaline, and phenylephrine to precondition the isolated rat heart against ischaemic and reperfusion injury. METHODS: The isovolumetric Langendorff rat heart model was used to determine postischaemic recovery of left ventricular function. The hearts were subjected to 30 min of normothermic global ischaemia followed by 30 min reperfusion. Treated hearts were perfused with noradrenaline (10(-7) M), isoprenaline (10(-8) M), or phenylephrine (10(-6) M, 10(-5) M, and 10(-4) M) for 5 min followed by 5 min washout before the 30 min ischaemic period. RESULTS: Control hearts recovered 47.6(SEM 4.3)% of baseline heart rate x developed pressure after 30 min reperfusion, whereas noradrenaline and isoprenaline treated hearts recovered 75.1(4.6) and 76.4(4.6)%, respectively (p < 0.001 v control). Left ventricular end diastolic pressures at the end of reperfusion were 48.8(4.0), 20.0(2.4), and 21.6(2.7)mm Hg for control, noradrenaline treated (p < 0.001 v control), and isoprenaline treated (p < 0.001 v control) hearts respectively. beta Blockade with propranolol during noradrenaline treatment blocked the protective effects. No concentration of phenylephrine used was able to enhance postischaemic heart rate x developed pressure significantly, or result in improved (lower) postischaemic left ventricular end diastolic pressure. During treatment with noradrenaline and phenylephrine (10(-5) M), lactate release was 13.0(1.0) and 11.0(0.9) mumol.5 min-1, respectively (p = NS); these values were significantly (p < 0.001) greater than baseline value of 3.7(0.5) mumol.5 min-1. Immediately before the 30 min ischaemic period, control and phenylephrine treated groups had glycogen levels of 132(14) and 128(5) nmol.mg-1 protein, respectively (p = NS), whereas the glycogen content of the noradrenaline treated group was only 96(5) nmol.mg-1 protein (p < 0.05 v control and phenylephrine treated). CONCLUSIONS: Transient beta adrenergic but not alpha 1 adrenergic stimulation can precondition the isolated perfused rat heart. The mechanism of protection may, at least in part, be due to transient demand ischaemia. Partial depletion of glycogen following treatment may play a role in the observed protective effects.

Adrenergic beta-Agonists↗

PubMed1993

Attenuation of postischaemic dysfunction by ischaemic preconditioning is not mediated by adenosine in the isolated rat heart.

OBJECTIVE: The aim was to test the hypothesis that adenosine mediates the cardioprotective effects of ischaemic preconditioning in the isolated rat heart. METHODS: Transient exposure of the hearts to adenosine and the A1 selective agonist, PIA, were tested for the ability to mimic the cardioprotective effects of ischaemic preconditioning in hearts that underwent 40 min normothermic ischaemic followed by 30 min reperfusion. Treated hearts were perfused with 10 or 50 microM adenosine or 10(-7) M R-phenylisopropyladenosine (PIA) for 5 min followed by a 5 min washout period. Preconditioned hearts underwent 5 min of ischaemia and 5 min of reflow prior to the 40 min ischaemic period. The ability of the adenosine receptor antagonist, BW A1433U, to inhibit the cardioprotective effects of ischaemic preconditioning was also tested. The effects of these treatments on metabolite levels and postischaemic haemodynamic function were assessed. RESULTS: Adenosine (50 microM), but not PIA, resulted in enhanced accumulation of lactate after 40 min ischaemia: 122(SEM 8) v 96(5) nmol.mg-1 protein in control hearts (p < 0.002). Adenosine and PIA treatments did not significantly affect myocardial acidosis during ischaemia. Postischaemic contractile function (as assessed by percent recovery of the heart rate x developed pressure) was lower in 50 microM, but not 10 microM, adenosine treated hearts [8.8(2.2)] and PIA treated hearts [11.9(2.5)] than in control hearts [20.4(3.6)] (p < 0.01). Ischaemic preconditioning (1) lowered glycogen levels prior to the 40 min ischaemic period [57(6) v 110(18) nmol glucosyl units.mg-1 protein; p < 0.01]; (2) lowered lactate levels at the end of the 40 min ischaemic period [61(4) v 104(5) nmol.mg-1 protein]; (3) preserved myocardial pH during ischaemia [6.69(0.07) v 6.40(0.07); p < 0.01]; and (4) enhanced recovery of postischaemic contractile function [42.3(4.4)% v 19.7(6.0)%; p < 0.02]. BW A1433U did not prevent these effects of ischaemic preconditioning. CONCLUSIONS: The cardioprotective effects of ischaemic preconditioning are not mediated by adenosine released during the preconditioning period in the isolated rat heart. Also, transient treatment of the heart with A1 adenosine receptor agonists can exacerbate postischaemic contractile dysfunction.

Adenosine↗

PubMed1992

Ischemic preconditioning attenuates acidosis and postischemic dysfunction in isolated rat heart.

The hypothesis that brief ischemia (preconditioning) protects the isolated heart from prolonged global ischemia was tested. Isovolumic rat hearts were preconditioned with either 5 min of ischemia followed by 5 min of perfusion (P1) or two 5-min episodes of ischemia separated by 5 min of perfusion (P2). Control hearts received no preconditioning. All hearts received 40 min of sustained ischemia and 30 min of reperfusion. Preconditioning (P1 or P2) significantly (P less than 0.0005) improved recovery of the rate-pressure product; percentage recoveries were 17.8 +/- 3.2 (n = 14), 59.9 +/- 5.5 (n = 6), and 46.4 +/- 4.7 (n = 8) for control, P1, and P2, respectively. Improved functional recovery of preconditioned hearts was associated with reduced end-diastolic pressure and improved myocardial perfusion. During the 40-min ischemic period, myocardial pH decreased from approximately 7.4 to 6.3 +/- 0.1 (n = 7) in the control hearts and to 6.7 +/- 0.1 (n = 7) in the preconditioned hearts (P less than 0.01). Also during the 40-min ischemic period, myocardial lactate (expressed as nmol/mg protein) increased to 146 +/- 11 (n = 7) and 101 +/- 12 (n = 8) in control and preconditioned hearts, respectively (P less than 0.02). The results demonstrate that a brief episode of ischemia can protect the isolated rat heart from a prolonged period of ischemia. This protection is associated with decreased tissue acidosis and anaerobic glycolysis during the sustained ischemic period.

Acidosis↗

PubMed1992

Postischemic recovery of mitochondrial adenine nucleotides in the heart.

BACKGROUND: Adenine nucleotides (AdNs) are lost from the mitochondrial fraction of the heart cell during ischemia. It is unknown whether this pool of AdNs can be replenished after reperfusion. The purpose of this study was to evaluate the postischemic recovery of the mitochondrial AdN pool. METHODS AND RESULTS: The left anterior descending coronary artery (LAD) of the canine heart was occluded for 30 minutes followed by either no reflow, 30-minute reflow, 1-day reflow, or 7-day reflow. Systolic shortening in the LAD-supplied region was absent during occlusion but recovered to approximately 30% of preocclusion values during early reperfusion. Mitochondrial and tissue AdNs (ATP, ADP, and AMP) were determined in the LAD-supplied and left circumflex-supplied (control) regions of the heart. The AdN content (expressed as percent of control values) of mitochondria from the LAD region was 55 +/- 10% (p less than 0.002), 64 +/- 7% (p less than 0.001), 81 +/- 6% (p less than 0.03), and 94 +/- 8% for the no-reflow, 30-minute-reflow, 1-day-reflow, and 7-day-reflow groups, respectively. The AdN content (expressed as percent of control values) of tissue samples from the LAD region was 52 +/- 9% (p less than 0.002), 48 +/- 12% (p less than 0.02), 68 +/- 5% (p less than 0.002), and 70 +/- 9% for the no-reflow, 30-minute-reflow, 1-day-reflow, and 7-day-reflow groups, respectively. There was a good correlation between mitochondrial and tissue AdN (r = 0.95). Using initial exchange rates, adenine nucleotide translocase activities of mitochondria from the LAD and control regions were not significantly different. State 3 respiration of LAD mitochondria was depressed (approximately 25%, p less than 0.05) only in the no-reflow group. Acceptor control ratios of the LAD mitochondria were not significantly different from control values in any group. CONCLUSIONS: After 30 minutes of regional ischemia, postischemic restoration of the mitochondrial AdN pool occurs between 1 and 7 days; this restoration is preceded by recovery of respiratory and adenine nucleotide translocase functions. Although the abnormally low levels of AdN persist in the mitochondrial compartment during the early reperfusion period, postischemic contractile dysfunction cannot be explained by depressed mitochondrial respiratory activity.

Adenine Nucleotides↗

PubMed1991

Mechanism of loss of adenine nucleotides from mitochondria during myocardial ischemia.

We tested the hypothesis that loss of mitochondrial adenine nucleotides during myocardial ischemia is induced by the accumulation of inorganic phosphate (Pi) and a decrease in cytosolic ATP. In the isolated perfused rat heart, loss of mitochondrial adenine nucleotides (ATP + ADP + AMP) was preceded by the rise in tissue Pi and the loss of tissue ATP. After 30 min ischemia, the average rate of loss of mitochondrial adenine nucleotides was c. 1.5% of the initial pool/min. In isolated heart mitochondria, there are two pathways for adenine nucleotide release: a 'fast', phosphate-dependent pathway, which is inhibited by atractyloside; and a 'slow', phosphate-independent pathway, which is insensitive to atractyloside. Decreasing the pH from 7.4 to 6.5 significantly decreased the rate of release by the phosphate-dependent pathway (but not the phosphate-independent pathway). Analysis of release rates indicated that HPO4-2 is responsible for the phosphate-induced release; Vmax = 53.8% of the pool/per minute, Km = 7.5 mM. In vitro, extramitochondrial ATP inhibited adenine nucleotide release in the presence of Pi such that the rate of release was inversely proportional to the extramitochondrial [ATP]; extrapolation to zero ATP indicated a release rate of 2 to 3% of the pool/per minute, which is approximately equal to the rate of the 'slow' phosphate-independent pathway. Moreover, increasing the Pi concentration did not increase the rate of adenine nucleotide release in the presence of extramitochondrial ATP. Accumulation of mitochondrial adenine nucleotides was observed when the mitochondria were incubated in the presence of 4 mM or greater ATP. The results suggest that the rise in intracellular Pi during myocardial ischemia does not induce the loss of adenine nucleotides from the mitochondrial compartment, but rather that degradation of cytosolic ATP results in a slowing of ATP influx such that the rate of efflux (phosphate-independent) exceeds the rate of influx.

Adenine Nucleotides↗

PubMed1991

Uncoupling of oxidative phosphorylation in rat liver mitochondria by chloroethanols.

Chloroethanols are toxic chemicals used in industry and also formed as a result of the metabolism of several widely used halogenated hydrocarbons. The effect of 2-chloroethanol (CE), 2,2-dichloroethanol (DCE) and 2,2,2-trichloroethanol (TCE) on rat liver mitochondrial respiration was studied. Rat liver mitochondria were isolated in a medium consisting of 250 mM sucrose, 10mM Tris-HCl and 1 mM EDTA (pH 7.4). Mitochondrial respiration was determined with an oxygen electrode at 30 degrees C and the polarographic buffer consisted of 250 mM mannitol, 10 mM KCl, 10 mM K2HPO4, 5 mM MgCl2, 0.2 mM EDTA and 10 mM Tris-HCl (pH 7.4). With succinate as the respiratory substrate and using chloroethanols (150 mM), CE stimulated respiration by 28.2 +/- 6.5% and DCE by 202.7 +/- 8.2% while TCE inhibited mitochondrial respiration (greater than 95%). The effect of change in the concentration of chloroethanols on mitochondrial respiration was also studied. CE showed maximum stimulation at 600 mM (97.6%), DCE at 150 mM (202.6%) and TCE at 30 mM (313.6%). Respiratory stimulation was independent of mitochondrial protein concentration. Chloroethanols (optimal concentrations for respiratory stimulation with succinate) inhibited mitochondrial respiration when glutamate-malate was used as the respiratory substrate. Estimation of adenosine triphosphate (ATP) showed that chloroethanols inhibited the synthesis of ATP. These results indicate that chloroethanols stimulate mitochondrial respiration by uncoupling oxidative phosphorylation and that the uncoupling potency is proportional to the extent of chlorination at the beta-position of haloethanol.

Adenosine Triphosphate↗

PubMed1990

Intermittent ischemia produces a cumulative depletion of mitochondrial adenine nucleotides in the isolated perfused rat heart.

The purpose of the present study was to determine if repetitive myocardial ischemia would result in the cumulative loss of mitochondrial adenine nucleotides. Isolated perfused rat hearts were subjected to continuous or intermittent ischemia. A single 5-minute period of continuous ischemia did not result in a significant decrease in the mitochondrial adenine nucleotide pool; a single 10-minute period of ischemia resulted in a decrease of approximately 17%. Next, the adenine nucleotide content of mitochondria from preischemic and 30-minute continuous ischemic hearts was compared with two groups of hearts undergoing intermittent ischemia (both groups receiving a total of 30 minutes of ischemia). One group received three 10-minute episodes of ischemia interrupted by 5-minute periods of reperfusion (3 x 10-minute intermittent ischemia); the other intermittent ischemic group received six 5-minute episodes of ischemia interrupted by 5-minute periods of perfusion (6 x 5-minute intermittent ischemia). The mitochondrial adenine nucleotide content (expressed as nanomoles per nanomole cytochrome a) for the preischemic and 30-minute continuous ischemic hearts was 14.7 +/- 0.6 and 8.0 +/- 0.4, respectively. The mitochondrial adenine nucleotide content of the 3 x 10-minute intermittent ischemia group (8.5 +/- 0.5) was not significantly different from the 30-minute continuous ischemic group. The mitochondrial adenine nucleotide content of the 6 x 5-minute intermittent ischemia group (11.0 +/- 0.6) was significantly larger than that of the 30-minute continuous and the 3 x 10-minute intermittent ischemia groups (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗

PubMed1989

Hypotension and cardiac stimulation due to the parathyroid hormone-related protein, humoral hypercalcemia of malignancy factor.

Patients with humoral hypercalcemia of malignancy display markedly increased serum calcium levels, reduced blood pressure, and tachycardia. The causative agent, humoral hypercalcemia of malignancy factor [also called PTH-related protein (PTHrp)] has been shown to interact with PTH receptors in bone and kidney. We compared human PTHrp-(1-34) with rat PTH-(1-34) for the effects of each peptide on cardiovascular function in unrestrained conscious rats. Both PTHrp and PTH decreased blood pressure in a dose-dependent manner over the concentration range of 0.3-30 micrograms/kg. PTHrp was approximately 3-fold more potent than PTH, producing up to a 50 mm Hg decrease in pressure within 2 min at 10 micrograms/kg. Both peptides increased heart rate more than 70 beats/min at this dose. However, PTH appeared to exert greater efficacy and potency than PTHrp in increasing heart rate in vivo. In the isolated and perfused rat heart, PTHrp and PTH produced positive chronotropic and positive inotropic effects as well as increased coronary flow. PTHrp was more potent and more effective than PTH. The time courses of these effects in the perfused heart preparations indicated that both peptides produced maximal effects within 1 min, with all responses returning to baseline within 10 min. In isolated helical strips of rat aorta, PTHrp and PTH relaxed norepinephrine-contracted tissues in a concentration-dependent fashion. A functional endothelium was not required for the relaxing effects of either peptide. These studies indicate that PTHrp and PTH decrease blood pressure by relaxing vascular tissue in an endothelium-independent manner. Also, these peptides directly increased heart rate, contractility, and coronary flow. Since PTHrp has recently been found in normal human cells, these studies suggest the possibility of PTHrp as a regulator or modulator of cardiovascular function.

Animals↗

PubMed1987

Phosphate-induced efflux of adenine nucleotides from rat-heart mitochondria: evaluation of the roles of the phosphate/hydroxyl exchanger and the dicarboxylate carrier.

Upon the addition of inorganic phosphate, isolated rat-heart mitochondria released endogenous adenine nucleotides. To elucidate the mechanism of this phosphate-induced efflux, we evaluated the relative roles of three inner mitochondrial membrane carriers: the adenine nucleotide translocase, the phosphate/hydroxyl exchanger, and the dicarboxylate carrier. Atractyloside (a specific inhibitor of the adenine nucleotide translocase) prevented this efflux, but did not inhibit mitochondrial swelling. Inhibitors of the phosphate/hydroxyl exchanger (200 microM n-ethylmaleimide and 10 microM mersalyl) did not inhibit phosphate-induced efflux. 200 microM mersalyl (which inhibited both the phosphate/hydroxyl exchanger and the dicarboxylate carrier) inhibited the rate of efflux approx. 65% Phenylsuccinate and 2-n-butylmalonate (inhibitors of the dicarboxylate carrier) partially inhibited phosphate-induced efflux and adenine nucleotide translocase activity. Mersalyl (200 microM) had no effect on adenine nucleotide translocase activity. Partial inhibition of the adenine nucleotide translocase by phenylsuccinate and butylmalonate could not explain the extent of inhibition of phosphate-efflux by these agents. Moreover, the rates of adenine nucleotide efflux in the presence of phenylsuccinate, butylmalonate, or mersalyl correlated well with the ability of these agents to inhibit succinate-supported respiration. We conclude that phosphate-induced efflux of adenine nucleotides from rat heart mitochondria occurs over the adenine nucleotide translocase, and that the site of action of the phosphate is not the phosphate/hydroxyl exchanger, but is likely the dicarboxylate carrier.

Adenine Nucleotides↗

PubMed1987

Hemodynamic action of calcitonin gene-related peptide in the isolated rat heart.

The effects of calcitonin gene-related peptide (CGRP) on heart rate, coronary flow, pressure development, and time to ischemic contracture were studied in the isolated, perfused rat heart. A bolus of CGRP (2640 pmols) caused significant increases in heart rate and coronary flow; these effects were sustained for at least five minutes after injection. The increase in coronary flow was independent of heart rate, since CGRP caused an increase in coronary flow in non-beating (potassium-arrested) hearts. The dose-response of CGRP was studied using five doses (65, 218, 658, 1320 and 2640 pmols) given as bolus injections. Although the increase in heart rate was apparently dose-dependent, significant increases above baseline were observed only with the two highest doses. In contrast, coronary flow increased significantly above baseline with the injection of all but the lowest dose of CGRP. Ten minutes after injection of CGRP, all hearts were made ischemic. The time to onset of ischemic contracture was approximately 11 minutes for those hearts that received 65 pmols of CGRP; however, for those hearts receiving all other doses of CGRP, the time to onset of contracture was approximately 8 minutes. We conclude that CGRP significantly decreases the resistance of the coronary vascular bed, and that it may be an important regulator of regional blood flow in the heart.

Animals↗

PubMed1985

Release of AMP and adenosine from rat heart mitochondria.

Release of AMP and adenosine from rat heart mitochondria was studied. The rate of appearance of extramitochondrial adenosine was independent of the extramitochondrial phosphate concentration between 5 and 20 mM. In the absence of exogenous, respiratory substrates or in the presence of glutamate/malate plus rotenone, the rate of appearance of adenosine was relatively low when phosphate was not added. The appearance of extramitochondrial AMP + adenosine was found to be directly proportional to the extra-mitochondrial phosphate concentration. Zn2+ (10 mM) decreased the rate of adenosine appearance by 90% and increased the rate of AMP appearance 6-fold. The mitochondrial preparations dephosphorylated exogenous AMP; this activity was inhibited by 10 mM Zn2+. We conclude that the adenosine appearing in the extramitochondrial space was not due to a direct release from the matrix, but instead was due to adenine nucleotide release with subsequent conversion to adenosine in the extramitochondrial space.

5'-Nucleotidase↗

PubMed1985

Phosphate-induced efflux of adenine nucleotides from heart mitochondria.

Adenine nucleotide efflux from isolated rat heart mitochondria was studied. Inorganic phosphate induced efflux of adenine nucleotides from the mitochondria. This efflux was inhibited by carboxyatractyloside and atractyloside. The rate of efflux showed saturation kinetics with respect to extramitochondrial phosphate (Km, 9.5 mM). Lowering the pH from 7.4 to 6.8 had little or no effect on the rate of efflux. Deenergizing the mitochondria enhanced carboxyatractyloside-insensitive efflux, but it did not affect carboxyatractyloside-sensitive efflux. Extramitochondrial ATP (200 microM) or AMP (200 microM) prevented efflux when the phosphate concentration was 10 mM. AMP (200 microM) did not inhibit efflux when the phosphate concentration was 40 mM. Atractyloside inhibited efflux noncompetitively with respect to inorganic phosphate. Mersalyl (10 nmol/mg protein) did not inhibit efflux. Phenylsuccinate (20 mM) totally inhibited phosphate-induced efflux. The results of this study indicate that under conditions found in the ischemic heart cell (low ATP, high phosphate), adenine nucleotides may be lost from the mitochondria via the adenine nucleotide translocase. Phosphate does not induce this efflux by interacting with the translocase or the phosphate-hydroxyl carrier. The site of action of phosphate may be the dicarboxylate carrier.

Adenine Nucleotides↗