Calcium responsiveness in regional myocardial short-term hibernation and stunning in the in situ porcine heart. Inotropic responses to postextrasystolic potentiation and intracoronary calcium

BACKGROUND

We tested the hypothesis that decreased calcium responsiveness is responsible for the reduction in contractile function in regional hibernating and stunned myocardium in situ.

METHODS AND RESULTS

In 19 anesthetized swine, the left anterior descending coronary artery flow was reduced to decrease anterior myocardial work index (sonomicrometry) by approximately 60%. During 90 minutes of hypoperfusion, creatine phosphate recovered (as determined by biopsy specimens and bioluminescence) and no necrosis developed (as determined by staining with triphenyl tetrazolium chloride). In 10 swine, changes in the intracellular calcium concentration were induced by systematic variation of the postextrasystolic time interval at a constant prematurity. In 9 additional swine, a graded IC calcium infusion was performed. Under control conditions, anterior myocardial work increased with a fully compensated postextrasystolic time interval from 380+/-93 (mean+/-SD) to 523+/-98 mm Hg . mm. IC calcium infusion increased anterior myocardial work under control conditions from 356+/-85 to a maximum of 428+/-93 mm Hg . mm. Although the maximal responses were decreased during postextrasystolic potentiation (222+/-68 versus 523+/-98 mm Hg . mm) and calcium infusion (176+/-32 versus 428+/-93 mm Hg . mm) after 90 minutes of ischemia, the relationships between increases in anterior myocardial work and, respectively, postextrasystolic time interval and IC calcium were not different. The same was true after 30 minutes of reperfusion.

CONCLUSIONS

Both regional hibernating myocardium and stunned myocardium in situ are characterized by a decrease in overall myocardial calcium responsiveness; however, there appears to be no significant myocardial desensitization to calcium.

Internal resourcefulness, task demands, coping, and dysphoric affect among caregivers of the frail elderly

Internal resourcefulness is defined as the repertoire of skills and behaviors individuals employ to deal with negative affective states. The relationships among caregivers' internal resourcefulness, demands of the caregiving situation, and caregivers' self-reported coping behaviors were examined relative to changes in dysphoric affect over time. Primary caregivers of the frail elderly (N = 143) completed the following measures, at two time periods, approximately four months apart: Rosenbaum's Self Control Schedule, assessing internal resourcefulness; Poulshock and Deimling's list of tasks carried out for the frail elder; Zarit et al.'s Memory and Behavior Problem Check List assessing caregiver burden; Moos et al.'s Indices of Coping; and Beck et al.'s Depression Inventory as a means of assessing dysphoric affect. Although caregivers' reactions to the care recipients' annoying behaviors predicted negative affect at time 1 and avoidant coping behavior predicted negative affect at times 1 and 2, internal resourcefulness was the only significant predictor of changes in dysphoric affect over time. Decreased dysphoric affect among caregivers was linked to possession of a larger initial set of internal resources to deal with negative internal experiences.

Aspirin does not prevent the attenuation of myocardial stunning by the ACE inhibitor ramiprilat

The attenuation of myocardial stunning by the ACE inhibitor ramiprilat is prevented by cyclooxygenase inhibition with indomethacin. In the clinical setting of ischemia/reperfusion however, the cyclooxygenase inhibitor aspirin is widely used to prevent platelet aggregation. The present study therefore investigated whether aspirin in dosages sufficient to inhibit platelet aggregation interferes with the attenuation of myocardial stunning by ramiprilat. Fifteen dogs received either 1 mg/(kg.day) (group I, n = 7) or 10 mg/(kg.day) (group II, n = 8) aspirin orally for 1 week. Both dosages of aspirin inhibited ADP-induced platelet aggregation. The dogs were then anesthetized thoracotomized and subjected to 15 min LCx-occlusion and 4 h reperfusion. Before LCx-occlusion, groups I and II received ramiprilat (20 micrograms/kg, i.v.). Systemic hemodynamics, posterior myocardial blood flow (PMBF, colored microspheres) and wall thickening (PWT, sonomicrometry) of these groups were measured and data compared to placebo-controls (group III, n = 11) and dogs receiving only ramiprilat before LCx-occlusion (group IV, n = 11). Four dogs received 10 mg/(kg.day) aspirin without ramiprilat (group V). Mean aortic pressure was kept constant by an intra-aortic balloon, and heart rate did not change. PMBF was not different between the five groups. Under control conditions and during myocardial ischemia PWT was also not different. At 4 h reperfusion PWT was still depressed in group III (-5 +/- 20% of control) and group V (-23 +/- 6%) whereas PWT recovered to the same extent in groups I (46 +/- 23%), II (50 +/- 15%) and IV (58 +/- 18%) (all P < 0.05 v groups III and V). The attenuation of myocardial stunning by the ACE inhibitor ramiprilat is not prevented by aspirin in dosages which are nevertheless sufficient to inhibit platelet aggregation.

Crystal structures of the human p56lck SH2 domain in complex with two short phosphotyrosyl peptides at 1.0 A and 1.8 A resolution

src homology 2 (SH2) domains are modules of about 100 amino acid residues and bind to phosphotyrosine-containing motifs in a sequence-specific manner. They play important roles in intracellular signal transduction and represent potential targets for pharmacological intervention. The protein tyrosine kinase p56lck is a member of the src family and is involved in T-cell activation. The crystal structure of its SH2 domain with an 11-residue peptide showed that the phosphotyrosine and the Ile residue at the pY + 3 position are recognized by the SH2 domain. We present here the crystal structure of the SH2 domain of human p56lck in complex with the short phosphotyrosyl peptide Ac-pTyr-Glu-Glu-Ile (pYEEI peptide) at 1.0 A resolution. The structural analysis at atomic resolution reveals that residue Arg134 (alphaA2), which interacts with the phosphotyrosine side-chain, is present in two conformations in the complex. The structure at 1.8 A resolution of the complex with the phosphotyrosyl peptide Ac-pTyr-Glu-Glu-Gly (pYEEG peptide), which is 11 fold less potent, shows another binding mode for the pY + 3 residue as well as rearrangements of the side-chain of Arg196 (EF3) and one of the water molecules at the base of the pY + 3 pocket. The structure of the complex with the short pYEEI peptide at atomic resolution represents a good starting point for the design and optimization of new inhibitors. Comparative structural analysis of many different inhibitor complexes will be an important component of this drug discovery process.

Randomized, double-blind, placebo-controlled trial of intravenous ketamine in acute asthma

STUDY OBJECTIVE

To evaluate the efficacy of IV ketamine in the management of acute, severe asthma.

METHODS

This prospective, randomized, double-blind, placebo-controlled clinical trial at an urban teaching hospital emergency department involved 53 consecutive patients aged 18 to 65 with a clinical diagnosis of acute asthmatic exacerbation and a peak expiratory flow of less than 40% of the predicted value after three albuterol nebulizer treatments. All patients received oxygen, continuous nebulized albuterol, and methylprednisolone sodium succinate (Solu-Medrol). Patients then received either ketamine hydrochloride in a bolus of .2 mg/kg followed by IV infusion of .5 mg/kg per hour for 3 hours or a placebo bolus and infusion for 3 hours. Because of the occurrence of dysphoric reactions, the bolus dose was lowered to .1 mg/kg after the first 9 patients; the infusion dose was kept the same.

RESULTS

The first nine patients were eliminated from analysis. Repeated ANOVA testing on the remaining 44 patients determined significant improvements over time within each treatment group in peak flow (F=3.637, P=.004). Borg score (F=22.959, P=.001), respiratory rate (F=8.11, P=.0001). and 1-second forced expiratory volume (F=9.076, P=.001). However, no difference could be detected over time between treatment groups (power, 80%). Patients receiving ketamine gave the treatment a rating of 4.3 on a scale of 1 to 5, whereas those receiving placebo scored their treatment 3.7 (P=.0285). The hospital admission rate was not different between treatment groups (P=.1088).

CONCLUSION

IV ketamine at a dose low enough to avoid dysphoric reactions demonstrated no increased bronchodilatory effect compared with standard therapy in treating exacerbations of asthma in the ED. Although there was a slight increase in satisfaction in the ketamine group, no clinical benefit in terms of hospital admission rate was noted.

Strangulation injuries in children. Part 1. Clinical analysis

Over the past 4 years, 7.4% of deaths caused by strangulation in Peoria County, Ill., involved children under 18 years of age. Clinical review of a consecutive series of 13 children treated from 1985 through 1994 revealed an incidence of 32 of 10,000 intensive care unit admissions with a 5.5:1 male bias. Accidental causes were seen in six children, with suicide or autoerotic causes prevalent in older children and adolescents. Five children had behavioral disorders before injury. The initial Glasgow Coma Scale score was 8 or below in seven children. Cervical roentgenograms in all patients and computed tomographic examinations performed in seven children were interpreted as normal. Seven children required ventilatory assistance, and four had pneumonia or acute lung injury. Intracranial pressure monitoring in three children failed to reveal sustained elevations of pressure. Serial changes in electroencephalograms in five patients paralleled improvements in their clinical examinations. Ten children were normal on follow-up; one adolescent reported mild neurologic sequelae and one adolescent showed severe disability. One adolescent died 2 days after injury. Comparison of this series with previous reports of 26 children indicated that the extent of the initial injury and effectiveness of resuscitation were major determinates for outcome. Pulmonary complications were common, whereas the development of elevated intracranial pressure indicated a poor prognosis and suggested the use of telemetry in children, with clinical evidence of severe injury. Continued awareness of preventative measures for accidental strangulation in infants and intentional hanging in children with behavioral disorders may reduce the incidence of these injuries.

Strangulation injuries in children. Part 2. Cerebrovascular hemodynamics

The cerebrovascular hemodynamics were recorded in two children with comparable hypoxic-ischemic injuries after strangulation. Monitoring was initiated within 13 hours of injury and continued for at least 38 hours. The profile included continuous measurements of cortical regional cerebral blood flow (rCBF) with a subdural thermal diffusion probe, intracranial pressure, mean arterial pressure, and expired CO2 tension. Data sets were obtained every 15 minutes or every 5 minutes during epochs of hyperventilation and inotropic support. Arterial CO2 and oxygen content and pH and, in the second patient, cardiac output (and cardiac index) were determined every 3 to 6 hours. Both children showed cortical hyperemia with a gradual rise of rCBF during the study; neither child showed elevated intracranial pressure. Mean CO2 reactivities were 1.8 and 2.1 mL/100 g/minute/mm Hg, with gradual elevations during the study. Mean cerebrovascular resistances were 0.7 and 0.9 mL/100 g/minute/mm Hg, respectively. Dissociative vasoparalysis with loss of autoregulation and preservation of CO2 reactivity was observed in both children. In the second child, during two periods of hyperventilation, an inverse steal occurred with rCBF indirectly related to expired CO2 tension; the rCBF was not related to changes in cardiac output or cardiac index. Neurologic outcome was not related to mean levels of rCBF, CPP, and CO2 reactivity, or clinical dissociative vasoparalysis. Lower initial and mean values of rCBF and an inverse steal after hyperventilation were associated with a poor outcome in the second patient.

Effects of bilateral adrenalectomy on initiation of fur growth cycles in the deer mouse (Peromyscus maniculatus)

The objectives of this study were to determine the effects of bilateral adrenalectomy on the initiation of hair growth in the deer mouse and the duration of the actively growing phase of the hair growth cycle (anagen). Bilateral adrenalectomy plus deoxycorticosterone supplementation of adult deer mice resulted in the onset of hair growth 4 days earlier than in sham-operated mice supplemented with deoxycorticosterone. The duration of hair growth (anagen), based on guard hair measurements, was estimated to be approximately 12 days in both groups. As was expected for this species, the portion of the sheared test area in which new hair grew was incomplete in all control mice. In contrast, all adrenalectomized mice had hair growth over the entire sheared area. This suggests that normal, incomplete pelage replacement in adults was abolished and that adrenalectomy had a systemic effect, causing a greater number of hair follicles to become activated concurrently. These findings support the hypothesis that adrenal hormones exert an inhibitory effect on the induction of anagen and may be part of the mechanism controlling the onset of hair growth cycles.

Involvement of endogenous adenosine in ischaemic preconditioning in swine

Adenosine release and the subsequent activation of adenosine receptors are involved in ischaemic preconditioning in dogs and rabbits. In the present study, we investigated whether adenosine also mediates ischaemic preconditioning in swine. Swine were used since, due to the lack of an innate collateral circulation, infarct development in this species most closely resembles that observed in humans. In 36 enflurane-anaesthetized swine the impact of increased adenosine breakdown with exogenous porcine adenosine deaminase (5 IU/ml blood/min) on global and regional myocardial function (sonomicrometry), subendocardial blood flow (ENDO, microspheres) and infarct size (IS, triphenyl tetrazolium chloride staining following 90 min ischaemia and 120 min reperfusion) were analysed. Low-flow ischaemia for 90 min at an ENDO of 0.09 +/- 0.04 (mean +/- SD) ml/min/g caused an IS of 13.2 +/- 9.7% (n = 8) of the area at risk. Ischaemic preconditioning by a cycle of 10 min low-flow ischaemia followed by 15 min reperfusion prior to the 90-min ischaemic period (ENDO = 0.06 +/- 0.03 ml/min/g) reduced IS to 2.6 +/- 3.0% (n = 11, P < 0.05). The interstitial adenosine concentration (microdialysis) increased from 1.60 +/- 0.87 nmol/ml to above 10 microM during ischaemia; with intracoronary adenosine deaminase, the interstitial adenosine concentration fell from 1.65 +/- 0.23 to 0.12 +/- 0.07 nmol/ml and did not increase during ischaemia. Adenosine deaminase per se did not alter IS after 90 min ischaemia (n = 7, ENDO = 0.08 +/- 0.04 ml/min/g, IS = 12.1 +/- 6.9%) but abolished the beneficial effect of ischaemic preconditioning (n = 10, ENDO = 0.06 +/- 0.03 ml/min/g, IS = 8.8 +/- 5.8%). For any given ENDO, IS was significantly reduced in the ischaemic preconditioned group compared with the other three groups. Global and regional myocardial function were comparable among all groups of swine. We conclude that endogenous adenosine mediates ischaemic preconditioning also in swine.

Regional short-term myocardial hibernation in swine does not involve endogenous adenosine or KATP channels

Short-term hibernating myocardium is characterized by reduced contractile function during persistent ischemia, the recovery of metabolism over time, a recruitable inotropic reserve, and the lack of necrosis. The mechanisms underlying myocardial hibernation are unclear. The present study addressed the role of endogenous adenosine and that of activation of ATP-dependent potassium (KATP) channels. In 22 enflurane-anesthetized swine, coronary inflow was reduced to decrease regional myocardial work (W, measured by sonomicrometry) by 60-70% at 5 min of ischemia; this flow reduction has previously been shown to be compatible with the development of myocardial hibernation. Systemic hemodynamics, W, subendocardial blood flow (measured by microspheres), and the myocardial creatine phosphate content (measured by biopsies, mumol/g wet wt) were measured under control conditions and during 90 min of ischemia, with an intracoronary dobutamine infusion during the last 5 min of ischemia. The impact of endogenous adenosine was eliminated by infusion of intracoronary adenosine deaminase (ADA), and the impact of activation of KATP channels by glibenclamide. Creatine phosphate content recovered in the placebo-treated swine (n = 8, 3.8 +/- 1.9 to 5.8 +/- 2.0 mumol/g wet wt) as well as in swine receiving ADA (n = 7, 4.1 +/- 1.2 to 6.0 +/- 1.7 mumol/g wet wt) or glibenclamide (n = 7, 2.8 +/- 1.3 to 6.7 +/- 1.6 mumol/g wet wt) when ischemia was prolonged from 5 to 85 min. At the end of 90 min of ischemia, W increased during intracoronary dobutamine in all three groups to a comparable extent, and myocardial necrosis was absent in all three groups of swine.(ABSTRACT TRUNCATED AT 250 WORDS)

Bilateral adrenalectomy induces early onset of summer fur growth in mink (Mustela vison)

The purpose of this study was to determine the effects of bilateral adrenalectomy on the time at which growth of the summer pelage begins in mink. Bilateral adrenalectomy of adult female mink between 2 and 11 March 1991, supplemented with deoxycorticosterone (DOC) as a mineralocorticoid, resulted in the onset of the summer fur growth approximately 5 weeks earlier than the controls (P < 0.01). Mink with their adrenal glands intact and treated with DOC, exhibited summer fur growth 2 weeks earlier than the controls (P < 0.01). The duration of time between the first observed hair growth and attainment of maximal guard hair length, was approximately 10 days longer in mink with their adrenal glands intact and supplemented with DOC than the controls (P < 0.05). Adrenalectomized mink treated with DOC exhibited guard hair growth for approximately 13 days longer than controls (P < 0.05). Although exogenous DOC initiated hair growth, the rate of growth appeared to be reduced. These data suggest that adrenal hormones, of undetermined identity, exert a tonic inhibitory effect on the initiation of summer fur growth in mink and may be part of the mechanism through which changes in photoperiod regulate the onset of hair growth cycles.

Prolactin receptor concentrations in the skin of mink during the winter fur growth cycle

The objectives of this study were to determine: 1) if the skin of mink might be a target organ for prolactin (PRL) by establishing if PRL binding sites (receptors) exist in the cell membranes of skin, and 2) if PRL receptor concentrations change during the onset and progression of the winter fur growth cycle. Skin was collected on October 6, 1992 for characterization of PRL receptors and from July through December 1992 (N = 3 mink/month) to evaluate possible changes in PRL receptor concentrations during the fur growth cycle. PRL receptors were quantified using 125I-oPRL in a validated radioreceptor assay. Scatchard analysis of saturation data revealed a single class of high-affinity (Kd = 5.21 x 10(-11) +/- .84 M), low capacity (Bmax = 27.03 +/- 3.37 fmoles/mg) binding sites. Only oPRL (40% displacement) and to a lesser extent oGH (3% displacement) inhibited the binding of 125I-oPRL to mink skin cell membranes. No inhibition of 125I-oPRL binding to membranes occurred in the presence of a 500-fold excess of bTSH or oLH, indicating that the receptors were hormone specific. Concentrations of 125I-oPRL receptors during the onset and development of winter fur growth (July through November) exhibited no significant change. However, following completion of the winter fur growth cycle (December 1) PRL receptor concentration was significantly higher than all preceding months. The greater binding observed at that time may reflect a change in tissue sensitivity, in preparation for growth of the summer pelage.(ABSTRACT TRUNCATED AT 250 WORDS)

The development of PCR based assays for the detection and differentiation of simian immunodeficiency virus in vivo

Polymerase chain reaction based assays, which amplify a region of the gag gene, have been developed for the direct detection of simian immunodeficiency virus (SIV) DNA sequences in the blood of experimentally infected cynomolgus macaques. In macaques infected with a characterised virus pool (11/88 pool SIVmac 32H), an assay employing a single round of amplification was found to be highly sensitive and specific. However, in animals infected with the SIV molecular clones J5 and C8 (Rud et al., J. Gen. Virol. 75, 529-543), it was necessary to use two rounds of amplification and nested primer pairs in order to achieve sensitivity > 90%. In order to differentiate macaques infected with either of the two genetically distinct SIV clones, J5 or C8, a third PCR based assay has been developed, which amplifies a 492 bp region of the nef gene. Sequence differences between the nef genes of the two molecular clones enabled the PCR product amplified from each virus to be distinguished by restriction analysis. These sensitive and specific assays complement virological detection of SIV and enable superinfection studies to be evaluated; a prerequisite for the testing of live attenuated immunodeficiency virus vaccines.

Bradycardic agent UL-FS 49 attenuates ischemic regional myocardial dysfunction and reduces infarct size in swine: comparison with the beta-blocker atenolol

Heart rate (HR) is a major factor determining the severity of myocardial ischemia, and HR reduction is an effective therapy for myocardial ischemia. We tested the effects of HR reduction induced by either UL-FS 49 or atenolol on regional myocardial blood flow, function, and infarct size (IS) in a porcine model of 90-min low-flow ischemia and 2-h reperfusion. In 24 Göttinger miniswine, the left anterior descending coronary artery (LAD) was cannulated and hypoperfused at constant inflow to reduce anterior systolic wall thickening (AWT, sonomicrometry) by approximately 85%. Eight swine served as a placebo group, and 8 other swine received UL-FS 49 (0.60 mg/kg intravenously, i.v.) after 10-min ischemia. In the remaining 8 swine, atenolol was infused after 10-min ischemia at a dosage [mean 1.75 +/- 1.20 (SD) mg/kg i.v.] to mimic the HR reduction observed with UL-FS 49. Systemic hemodynamics, subendocardial blood flow (ENDO, microspheres) and AWT were measured under control conditions, at 10 and 90 min of ischemia. In the swine receiving UL-FS 49 or atenolol, additional measurements were made 5 min after administration of the respective drug. After 2-h reperfusion, IS (percentage of area at risk) was determined with TTC-staining. Five minutes after administration of UL-FS 49, HR was decreased from 113 +/- 9 to 83 +/- 13 beats/min (p < 0.05) and remained unchanged when ischemia was prolonged to 90 min. In the swine receiving atenolol, HR was reduced from 117 +/- 14 to 93 +/- 7 beats/min (p < 0.05) 5 min after drug administration and decreased further to 87 +/- 10 beats/min when ischemia was prolonged to 90 min. After 10 min of ischemia, AWT in the placebo, UL-FS 49, and atenolol group was decreased to 7.0 +/- 5.5, 6.4 +/- 3.5, and 6.2 +/- 3.3% (all p < 0.05 vs. control), respectively. The reduction in ENDO was also comparable among the three groups. In the placebo group, AWT remained unchanged when ischemia was prolonged to 90 min (4.4 +/- 2.6%). In swine receiving atenolol, AWT tended to increase (13.6 +/- 10.5%), whereas in swine receiving UL-FS 49, AWT was significantly increased to 21.4 +/- 7.1% (p < 0.05 vs. 10-min ischemia and vs. the placebo and atenolol groups). IS was significantly reduced in swine receiving atenolol (3.9 +/- 3.5%) or UL-FS 49 (5.8 +/- 4.6%) as compared with the placebo-group (10.4 +/- 8.9%).(ABSTRACT TRUNCATED AT 400 WORDS)

The thumb's knuckle. Flexibility in the thumb subdomain of T7 RNA polymerase is revealed by the structure of a chimeric T7/T3 RNA polymerase

We have solved the structure of a chimeric T7/T3 RNA polymerase (RNAP) in an orthorhombic crystal by molecular replacement with the T7 RNAP structure determined from a monoclinic crystal. The structure of the protruding "thumb" subdomain of the polymerase appears very different in these two crystals apparently because of differences in packing contacts made by the thumb subdomain. These observations support the proposal that the thumb subdomain is flexible and can wrap around bound template to obstruct polymerase: template dissociation during processive synthesis.

Muscle pathology and clinical measures of disability in children with cerebral palsy

We performed a histologic and morphometric study of spastic muscle from 10 children with diplegic cerebral palsy, comparing muscle structure with the gait parameters of energy expenditure index and dynamic electromyography. Variations in fiber area within and between fiber types were increased significantly in children with cerebral palsy. In each of the control subjects, the combined coefficient of variation for type-1 and type-2 fiber area was less than 25% and the average was 17%; in the subjects with cerebral palsy, the combined coefficient of variation was more than 25% and the average was 36% (p < or = 0.004). The average difference between the mean area of type-1 and type-2 fibers was 26.7 +/- 18.9% for subjects with cerebral palsy and 4.2 +/- 2.4% for control subjects (p < or = 0.004). There was a 67% predominance of one fiber type in the subjects with cerebral palsy compared with a 55% predominance in the control subjects (p < or = 0.03). The difference between the total area of type-1 and type-2 fibers was 57% in the subjects with cerebral palsy and 17% in the control subjects (p < or = 0.002). There was a significant correlation between the combined coefficient of variation of fiber area and the energy expenditure index (r = 0.77, p < or = 0.03). The difference between the mean area of type-1 and type-2 fibers correlated with prolongation of electromyographic activity (r = 0.69, p < or = 0.05). No abnormalities in fiber ultrastructure were found in the subjects with cerebral palsy. Children with cerebral palsy had abnormal variation in the size of muscle fibers and altered distribution of fiber types. The values for variation in fiber area correlated with the energy expenditure index and with prolongation of electromyographic activity during walking.

Involvement of activation of ATP-dependent potassium channels in ischemic preconditioning in swine

This study evaluated the importance of ATP-dependent potassium channels (KATP) for ischemic preconditioning (IP) in swine. Swine were studied because due to the sparsity of their innate collateral circulation infarct size (IS) development closely resembles that observed in humans. Ninety minutes of ischemia at a blood flow reduction sufficient to reduce regional myocardial work by 90% caused 13.2 +/- 8.9% (SD) IS of the area at risk. A single cycle of 10-min preconditioning ischemia followed by 15-min reperfusion reduced IS after 90 min of ischemia to 2.8 +/- 2.7%. The epicardial monophasic action potential duration at 50% repolarization (MAP50) was decreased more markedly during the initial 10 min of the prolonged ischemia than during the first 10 min of the preconditioning ischemic period (84 +/- 4 vs. 89 +/- 2%). Transmural myocardial adenosine (ADO) uptake was reversed to net release during both ischemic periods and during the initial phase of reperfusion. Glibenclamide (0.5 mg/kg, followed by 50 micrograms/min i.v.) abolished the reduction in MAP50 without altering ADO release. Glibenclamide did not alter IS per se (13.0 +/- 7.6%) but abolished the beneficial effect of IP (IS: 13.6 +/- 6.2%). Thus blockade of KATP with glibenclamide abolishes the IS-reducing effect of IP in swine but does not reduce ADO release.