Habitual sleep and kidney function in chronic kidney disease: the Chronic Renal Insufficiency Cohort study.

Physiological evidence suggests that sleep modulates kidney function. Our objective was to examine the cross-sectional association between kidney function and objectively-estimated habitual sleep duration, quality and timing in a cohort of patients with mild to moderate chronic kidney disease. This study involved two US clinical centers of the Chronic Renal Insufficiency Cohort (CRIC) study, including 432 participants in a CRIC ancillary sleep study. Habitual sleep duration, quality and timing were measured using wrist actigraphy for 5-7 days. Validated sleep questionnaires assessed subjective sleep quality, daytime sleepiness and risk of sleep apnea. Kidney function was assessed with the estimated glomerular filtration rate using the Chronic Kidney Disease Epidemiology Collaboration equation, and the urinary protein to creatinine ratio. Lower estimated glomerular filtration rate was associated with shorter sleep duration (-1.1 mL min-1  1.73 m-2 per hour less sleep, P = 0.03), greater sleep fragmentation (-2.6 mL min-1  1.73 m-2 per 10% higher fragmentation, P < 0.001) and later timing of sleep (-0.9 mL min-1  1.73 m-2 per hour later, P = 0.05). Higher protein to creatinine ratio was also associated with greater sleep fragmentation (approximately 28% higher per 10% higher fragmentation, P < 0.001). Subjective sleep quality, sleepiness and persistent snoring were not associated with estimated glomerular filtration rate or protein to creatinine ratio. Thus, worse objective sleep quality was associated with lower estimated glomerular filtration rate and higher protein to creatinine ratio. Shorter sleep duration and later sleep timing were also associated with lower estimated glomerular filtration rate. Physicians treating patients with chronic kidney disease should consider inquiring about sleep and possibly sending for clinical sleep assessment. Longitudinal and interventional trials are needed to understand causal direction.

The Relationship Between Verified Organ Donor Designation and Patient Demographic and Medical Characteristics.

Previous studies on the correlates of organ donation consent have focused on self-reported willingness to donate and on self-reported medical suitability to donate. However, these may be subject to social desirability bias and inaccurate assessments of medical suitability. The authors sought to overcome these limitations by directly verifying donor designation on driver's licenses and by abstracting comorbid conditions from electronic health records. Using a cross-sectional study design, they reviewed the health records of 2070 randomly selected primary care patients at a large urban safety-net medical system to obtain demographic and medical characteristics. They also examined driver's licenses that were scanned into electronic health records as part of the patient registration process for donor designation. Overall, 943 (46%) patients were designated as a donor on their driver's license. On multivariate analysis, donor designation was positively associated with age 35-54 years, female sex, nonblack race, speaking English or Spanish, being employed, having private insurance, having an income >$45 000, and having fewer comorbid conditions. These demographic and medical characteristics resulted in patient subgroups with donor designation rates ranging from 21% to 75%. In conclusion, patient characteristics are strongly related to verified donor designation. Further work should tailor organ donation efforts to specific subgroups.

Prominent impact of community risk factors on kidney transplant candidate processes and outcomes.

Numerous factors impact patients' health beyond traditional clinical characteristics. We evaluated the association of risk factors in kidney transplant patients' communities with outcomes prior to transplantation. The primary exposure variable was a community risk score (range 0-40) derived from multiple databases and defined by factors including prevalence of comorbidities, access and quality of healthcare, self-reported physical and mental health and socioeconomic status for each U.S. county. We merged data with the Scientific Registry of Transplant Recipients (SRTR) and utilized risk-adjusted models to evaluate effects of community risk for adult candidates listed 2004-2010 (n = 209 198). Patients in highest risk communities were associated with increased mortality (adjusted hazard ratio [AHR] = 1.22, 1.16-1.28), decreased likelihood of living donor transplantation (adjusted odds ratio [AOR] = 0.90, 0.85-0.94), increased waitlist removal for health deterioration (AHR = 1.36, 1.22-1.51), decreased likelihood of preemptive listing (AOR = 0.85, 0.81-0.88), increased likelihood of inactive listing (AOR = 1.49, 1.43-1.55) and increased likelihood of listing for expanded criteria donor kidneys (AHR = 1.19, 1.15-1.24). Associations persisted with adjustment for rural-urban location; furthermore the independent effects of rural-urban location were largely eliminated with adjustment for community risk. Average community risk varied widely by region and transplant center (median = 21, range 5-37). Community risks are powerful factors associated with processes of care and outcomes for transplant candidates and may be important considerations for developing effective interventions and measuring quality of care of transplant centers.

A Standardized Donor Designation Ratio to Assess the Performance of Driver's License Agencies.

Evaluating Department of Motor Vehicles (DMV) locations based on the percent of patrons who register as donors does not account for individual characteristics that may influence willingness to donate. We reviewed the driver's licenses of 2997 randomly selected patients at an urban medical system to obtain donor designation, age, gender, and DMV location and linked patient addresses with census tract data on race, ethnicity, income, and education. We then developed a Standardized Donor Designation Ratio (SDDR) (ie, the observed number of donors at each DMV divided by the expected number of donors based on patient demographic characteristics). Overall, 1355 (45%) patients were designated as donors. Donor designation was independently associated with younger age, female gender, nonblack race, and higher income. Across 18 DMVs, the proportion of patients who were donors ranged from 30% to 68% and SDDRs ranged from 0.82 to 1.17. Among the 6 facilities in the lowest tertile by SDDR, 3 were in the lowest tertile by percent donation. In conclusion, there is a great deal of variation across DMVs in rates of organ donor designation. SDDRs that adjust for DMV patron characteristics are distinct measures that may more accurately describe the performance of DMVs in promoting organ donation.

Stability of Organ Donor Designations on Driver's Licenses.

BACKGROUND: Little is known about the stability of decisions that people make to be organ donors. We sought to determine the rate of stability of organ donor designations on driver's licenses. METHODS: With the use of a cross-sectional study design, we reviewed the health records of 2500 randomly selected primary-care patients at a large urban safety-net medical system to obtain their demographic and medical characteristics. We also examined the two most recent unique driver's licenses, state identification cards, or learner's permits that were scanned into electronic health records as part of the patient registration process. We obtained organ donor designations from these documents for each patient. RESULTS: Of all patients, 1174 (47%) had two driver's licenses, identification cards, or permits in their electronic medical records. The two documents were issued an average of 3.5 years apart. Overall, 114 (10%) patients had differing organ donor designations on their two documents. Among the 502 patients who were designated as organ donors on the first document, 32 (6%) were not designated as organ donors on the second document. Among the 672 patients who were not designated as organ donors on the first document, 82 (12%) were designated as organ donors on the second document. There was little relationship between stability of organ donor designations and patient demographic and medical characteristics. CONCLUSIONS: About 1 of every 10 patients changed their organ donor designation, but stability was not associated with any demographic or medical factors. Further work is needed to understand why individuals change their organ donor designation.

Is Signature Size Associated With Organ Donor Designation on Driver's Licenses?

INTRODUCTION: Previous studies suggest that large signature size is associated with narcissistic characteristics. By contrast, organ donation is an indicator of altruism. Because altruism and narcissism may be viewed as opposites, we sought to determine if smaller signature size is associated with willingness to be an organ donor. METHODS: Using a cross-sectional study design, we reviewed the health records of 571 randomly selected primary care patients at a large urban safety-net medical system to obtain their demographic and medical characteristics. We also examined driver's licenses that were scanned into electronic health records as part of the patient registration process. We measured signature sizes and obtained the organ donor designation from these driver's licenses. RESULTS: Overall, 256 (45%) patients were designated as donors on their driver's licenses. Signature size averaged 113.3 mm(2) but varied greatly across patients (10th percentile 49.1 mm(2), 90th percentile 226.1 mm(2)). On multivariate analysis, donor designation was positively associated with age 18-34 years, non-black race, having private insurance, and not having any comorbid conditions. However, signature size was not associated with organ donor designation. CONCLUSIONS: Signature size is not associated with verified organ donor designation. Further work is needed to understand the relationship between personality types and willingness to be an organ donor.

Extended glycoprotein structure of the seven domains in human carcinoembryonic antigen by X-ray and neutron solution scattering and an automated curve fitting procedure: implications for cellular adhesion.

Carcinoembryonic antigen (CEA) is one of the most widely used cell-surface tumour markers for tumour monitoring and for targeting by antibodies. It is heavily glycosylated (50% carbohydrate) and a monomer is constructed from one V-type and six C2-type fold domains of the immunoglobulin superfamily. The solution arrangement at low resolution of the seven domains in CEA cleaved from its membrane anchor was determined by X-ray and neutron scattering. Guinier analyses showed that the X-ray radius of gyration RG of CEA was 8.0 nm. The length of CEA was 27 to 33 nm, and is consistent with an extended arrangement of seven domains. The X-ray cross-sectional radius of gyration RXS was 2.1 nm, and is consistent with extended carbohydrate structures in CEA. The neutron data gave CEA a relative molecular mass of 150,000, in agreement with a value of 152,500 from composition data, and validated the X-ray analyses. The CEA scattering curves were analysed using an automated computer modelling procedure based on the crystal structure of CD2. The V-type and C2-type domains in CD2 were separated, and the C2-type domain was duplicated five times to create a linear seven-domain starting model for CEA. A total of 28 complex-type oligosaccharide chains in extended conformations were added to this model. By fixing the six interdomain orientations to be the same, three-parameter searches of the rotational orientations between the seven domains gave 4056 possible CEA models. The best curve fits from these corresponded to a family of zig-zag models. The long axis of each domain was set at 160(+/-25) degrees relative to its neighbour, and the two perpendicular axes were orientated at 10(+/-30) degrees and -5(+/-35) degrees. Interestingly, the curve fit from this model is within error of that calculated from a CEA model generated directly from the CD2 crystal structure by the superposition of adjacent domains. Zig-zag models of this type imply that the protein face of the GFCC' beta-sheet in neighbouring CEA domains lie on alternate sides of the CEA structure. Such a model has implications for the adhesion interactions between CEA molecules on adjacent cells or for the antibody targeting of CEA.

The protection of ischaemic preconditioning can be reinstated in the rabbit heart after the initial protection has waned.

OBJECTIVE: Preconditioning the heart with 5 min of ischaemia followed by reperfusion renders the myocardium resistant to infarction from subsequent ischaemia. This protection lasts for about 1 h. The aim of this study was to test whether the protection could be reinstated with a second episode of preconditioning after protection from an initial episode had worn off. METHODS: To induce infarction animals experienced 30 min of coronary artery occlusion and then 3 h reperfusion. Ischaemic preconditioning was accomplished with 5 min of coronary branch occlusion. In one group of rabbits the subsequent reperfusion period was prolonged to 2 h to permit protection to wear off before the 30 min coronary occlusion was initiated. In another group a second 5 min coronary occlusion was performed at the end of the 2 h reperfusion. After 10 min of reperfusion the 30 min ischaemic period began. Control animals experienced only the 30 min ischaemia and 3 h reperfusion. Infarct volume was measured with tetrazolium and expressed as a percentage of the ischaemic zone volume. RESULTS: Average infarct size in seven control rabbits [36.0 (SEM 2.0)% of the ischaemic zone] was not significantly different from that in eight rabbits with the prolonged coronary occlusion occurring 2 h after the preconditioning stimulus [28.6 (2.9)% infarction]. In contrast infarcts were significantly smaller in the re-preconditioned group of seven rabbits [8.3 (4.2)%] and comparable to those previously seen with a single preconditioning stimulus followed 10 min later by the 30 min occlusion [6.1 (1.8)%]. CONCLUSIONS: The rabbit heart can be protected with a second preconditioning stimulus after protection from an initial period of preconditioning has subsided.

Ketamine-xylazine anaesthesia permits a KATP channel antagonist to attenuate preconditioning in rabbit myocardium.

OBJECTIVE: ATP sensitive potassium (KATP) channels have been implicated in the mechanism of ischaemic preconditioning, though apparently not in the pentobarbitone anaesthetised rabbit model. The aim of this study was to test whether potassium channel activation and blockade would alter protection in ketamine-xylazine anaesthetised rabbits. METHODS: In situ rabbit hearts (n = 50) received 30 min regional ischaemia and 3 h reperfusion. Some hearts were preconditioned by 5 min regional ischaemia and 10 min reperfusion prior to the long ischaemia. Infarct size was determined by tetrazolium staining. RESULTS: In rabbits anaesthetised with ketamine-xylazine, brief preconditioning ischaemia continued to produce much smaller infarcts than in non-preconditioned animals [19(SEM 2)% v 47(3)%, p < or = 0.05]. blocking KATP channels by pretreating with glibenclamide resulted in 35(3)% infarction in non-preconditioned hearts and aborted protection in preconditioned hearts [35(4)% infarction]. Substituting the potassium channel activator pinacidil for the short ischaemia caused comparable reductions in infarct size [28(4)%, p < or = 0.05 v non-preconditioned hearts]. This protection, however, could be blocked by concomitant administration of the adenosine receptor blocker 8-(p-sulphophenyl)theophylline (SPT) [44(3)% infarction]. CONCLUSIONS: When ketamine-xylazine anaesthesia was employed, the protective effects of ischaemic preconditioning in the rabbit heart could be blocked by glibenclamide, and pinacidil could mimic the protection of ischaemic preconditioning. Because the protection afforded by pinacidil could be blocked by SPT, however, there is still some question whether the KATP channel is the end effector of preconditioning.

Intravenous co-infusion of adenosine and norepinephrine preconditions the heart without adverse hemodynamic effects.

OBJECTIVE: A simple intervention is needed that could protect the heart against infarction during limited-access coronary artery bypass grafting. Adenosine and norepinephrine can precondition the heart with resulting protection, but adverse hemodynamic effects prevent clinical application. Because heart rate, blood pressure, and contractility effects of these two drugs are diametrically opposite, a mixture might be beneficial. METHODS: A superficial branch of the left coronary artery of rabbits was surrounded with a suture. Infarction was produced in all hearts by a 30-minute coronary artery occlusion. Infarct size after reperfusion was measured and is presented as a percentage of the risk zone. The effect of 5-minute intravenous co-infusion of adenosine (20 mg/kg) and norepinephrine (0.1 mg/kg) 15 minutes before ischemia was examined. In addition, the protective effect of three sequential intravenous bolus injections of adenosine at either 0.2 or 0.4 mg/kg was evaluated. RESULTS: Thirty minutes of regional ischemia caused infarction of 40% +/- 4% of the risk zone. The combination of adenosine and norepinephrine caused no change in blood pressure but rather protected the heart, with infarction of only 9% +/- 2% of the risk zone (p = 0.0001 vs control). Adenosine-norepinephrine co-infusion still protected the heart when the interval between infusion and ischemia was extended to 60 minutes, but it did not protect with a 120-minute interval. Intravenous bolus injections of adenosine resulted in cardiac slowing and marked hypotension. Boluses of 0.2 mg/kg resulted in a minimal, but significant, reduction in infarct size, whereas the higher dose provided no protection. CONCLUSION: Adenosine-norepinephrine co-infusion provides a feasible and safe parenteral method for preconditioning the heart.

Procoagulant activity on injured arteries and associated thrombi is mediated primarily by the complex of tissue factor and factor VIIa.

BACKGROUND: Rethrombosis limits the efficacy of coronary thrombolysis and may result from surface-associated thrombin, de-novo prothrombin activation, or both. This study was designed to determine the relative roles of thrombin, factor Xa, and the complex of tissue factor and factor VIIa in the procoagulant activity on injured arteries with evolving thrombi. METHODS: Extensive vascular injury and platelet-rich thrombi were induced in the abdominal aorta of 25 anesthetized rabbits by applying anodal current through a transluminal electrode for 3 h. Injured vessel segments were excised and placed in a chamber permitting perfusion over the luminal surface and associated thrombus. RESULTS: Vessel segments perfused with recalcified, citrated human plasma induced marked increases in the concentration of fibrinopeptide A, a marker of thrombin-induced fibrin formation, in the effluent plasma after 10 min (4636 +/- 1894% of fibrinopeptide A in the nonperfused plasma, n = 5). Perfusion with plasma depleted of vitamin K-dependent coagulation factors prevented the increase in fibrinopeptide A (122 +/- 30%, n = 4), indicating the lack of preformed functional thrombin. Furthermore, appearance of fibrinopeptide A was attenuated by perfusion with plasma containing 0.1 mumol/l recombinant tick anticoagulant peptide, a specific inhibitor of factor Xa (594 +/- 320%, n = 3), and by preincubation of vessel segments with a monoclonal antibody to rabbit tissue factor (438 +/- 220%, n = 3). CONCLUSIONS: Procoagulant activity on injured vessels and associated thrombi is mediated by factor Xa, a product of the functional initiation of coagulation by factor VIIa associated with tissue factor. Accordingly, inhibition of tissue factor-mediated coagulation may be effective for attenuation of active thrombogenesis on injured vessels and during thrombolysis.

Comparison of debris extruded apically in straight canals: conventional filing versus profile .04 Taper series 29.

The purposes of this study were to determine quantitatively the amount of debris and irrigant forced in an apical direction, the frequency of apical plug development, and the time required to prepare canals when a step-back technique using K-files was compared with the .04 Taper system. Sixty-nine extracted teeth with straight canals were divided into four statistically similar groups. Two groups were instrumented either 1 mm short of the apical foramen or to the apical foramen with K-files. The other two groups were instrumented to the same levels using .04 Taper files. The extruded debris and irrigant were collected in preweighed vials. The weight of the debris and volume of irrigant extruded using both techniques were compared and analyzed using paired t test and one-way ANOVA. Tukey's Multiple Comparisons Procedure showed K-files used to the apical foramen extruded significantly more debris than the other three groups (p < 0.01). The .04 Taper files used 1 mm short extruded less debris than the other groups. Significantly more irrigant was extruded when filing was performed to the apical foramen (p < 0.007), regardless of the technique used. More apical plugs were created in teeth filed short of the apical foramen, but the difference between the two preparation techniques was not statistically significant. It took significantly less time to instrument canals with the .04 Taper system than with K-files (p < 0.002).

Hypoxia preconditions rabbit myocardium by an adenosine receptor-mediated mechanism.

OBJECTIVES: To test the ability of hypoxia without reoxygenation to precondition myocardium and to test a possible involvement of adenosine receptors in that response. DESIGN: Isolated rabbit hearts were perfused with oxygenated Krebs-Henseleit buffer. Control hearts underwent 30 min regional ischemia followed by 2 h reperfusion. A second group received 10 min global perfusion with hypoxic buffer (PO2 = 33 +/- 3 mmHg) immediately before coronary occlusion. A third group was subjected to a similar protocol as group 2, with the adenosine receptor blocker 8-(p-sulfophenyl) theophylline (SPT) (100 microM) added to the buffer immediately before and throughout hypoxia. At the end of reperfusion the area at risk for infarction was determined by fluorescent particles while infarction size was measured by triphenyltetrazolium staining. RESULTS: Hearts without hypoxic perfusion preceding ischemia experienced 38.2 +/- 2.4% infarction. The hypoxic group, despite a longer total period of oxygen deprivation, had only 21.0 +/- 4.2% infarction (P < or = 0.05). SPT blocked the protection (42.1 +/- 6.9% infarction). CONCLUSIONS: Hypoxia without subsequent reoxygenation before ischemia protected the heart from infarction, indicating that reoxygenation may not be the critical feature of reperfusion typically employed in an ischemic preconditioning protocol. Because adenosine receptor blockade abolishes the protection from hypoxic perfusion, the mechanism of this protection may be similar to that seen with ischemic preconditioning.

Pretreatment with pertussis toxin blocks the protective effects of preconditioning: evidence for a G-protein mechanism.

We tested whether a pertussis toxin-sensitive G-protein mediates the protective effects of preconditioning. Thirty-one small (1 kg) rabbits were used. All rabbits experienced 30 min regional myocardial ischaemia followed by 3 h reperfusion. Infarct size was determined by tetrazolium. The percentage of the risk zone which infarcted in controls was 37.4 +/- 4.6%. Preconditioning with a 5 min occlusion followed by 10 min reperfusion prior to the 30 min ischaemic insult protected against infarction (5.2 +/- 2.1% infarction). 25 micrograms/kg pertussis toxin, administered 48 h prior to surgery, blocked G-protein signal transduction as tested by challenge with iv acetylcholine which normally slows the heart. Pertussis toxin treatment had no effect on infarct size in non-preconditioned rabbits (37.6 +/- 4.7% infarction) but blocked protection in preconditioned rabbits (27.3 +/- 4.3% infarction). To test the involvement of G-proteins further in preconditioning, we tested the ability of the M2 agonist carbachol to substitute for ischaemic preconditioning and protect the heart from infarction. Rabbits hearts were excised and perfused with Kreb's buffer. Control animals subjected to 30 min of regional ischaemia and 2 h reperfusion yielded 29.4 +/- 2.9% infarction. Preconditioning with 5 min global ischaemia and 10 min reperfusion prior to the 30 min regional ischaemia significantly protected the isolated heart from infarction (8.41 +/- 3.26% infarction). Carbachol, infused for 5 min at 1 microM concentration, protected the hearts as well as preconditioning, yielding 8.90 +/- 2.08% infarction. We conclude that preconditioning involves a pertussis toxin-sensitive G-protein and that the same G-protein couples to muscarinic M2 receptors.

Effect of adenosine receptor blockade: preventing protective preconditioning depends on time of initiation.

Ischemic preconditioning protects the rabbit myocardium from infarction from a subsequent ischemia, and adenosine receptors appear to be involved in this protection. The present study attempts to determine when adenosine receptors must be occupied to achieve protection by infusing the adenosine receptor antagonist PD-115,199 at various time points during the study. Open-chest rabbits were subjected to 30 min of regional ischemia followed by 3 h of reperfusion and had 38 +/- 4% infarction of the risk zone. When hearts were preconditioned by 5 min of ischemia and 10 min reperfusion before the 30-min period of ischemia, only 9 +/- 2% infarction occurred. PD-115,199 given 5 min before the ischemic preconditioning episode blocked the protective effect of preconditioning (39 +/- 5% infarction). PD-115,199 also blocked the protection when given between the ischemic preconditioning episode and the 30-min period of ischemia (30 +/- 4% infarction). PD-115,199 given at the end of 30 min of ischemia did not block protection in preconditioned (PC) hearts (17 +/- 5% infarction) and had no effect on non-PC hearts (44 +/- 6% infarction). In prior studies we found that exogenous adenosine could substitute for ischemia to precondition the heart, indicating that adenosine is an initiator of preconditioning. These results, however, indicate that adenosine receptors must also be occupied during the long ischemic period for preconditioning to be protective and suggest that adenosine is a mediator of preconditioning as well.

Blockade of ATP-sensitive potassium channels increases infarct size but does not prevent preconditioning in rabbit hearts.

Ischemic preconditioning renders the heart resistant to infarction by an unknown mechanism. This study tests whether preconditioning may be working through activation of ATP-sensitive potassium channels. If that were the case, then blockade of the channels should eliminate preconditioning's protection, and activation of these channels should mimic it. Thirty minutes of regional coronary ischemia followed by 3 hours of reperfusion caused 38.0 +/- 3.7% of the risk zone to become infarcted in control rabbits. Preconditioning with 5-minute ischemia followed by a 10-minute reperfusion before the 30-minute insult caused only 8.8 +/- 2.1% infarction, which was a reduction of 29.2% in infarct size by preconditioning (p < 0.01 versus control value). Pretreatment with the potassium channel blocker glibenclamide at three different concentrations significantly elevated infarct size in the nonpreconditioned hearts at all doses. Preconditioning, however, continued to limit infarct size by an amount not different from that seen in the control group at all doses of glibenclamide. Pinacidil, a potassium channel agonist, given before a 30-minute ischemic insult resulted in infarct sizes no different from that seen in nonpreconditioned control rabbits. We conclude that ATP-sensitive potassium channels are not involved in preconditioning in the rabbit heart; however, blocking those channels does exacerbate ischemia.

Streptozotocin-induced non-insulin-dependent diabetes protects the heart from infarction.

BACKGROUND: The vulnerability of the myocardium of a diabetic animal to an ischemic insult is controversial. To address this issue, streptozotocin-induced non-insulin-dependent diabetes (NIDD) was induced in rats, and the effects of regional myocardial ischemia were assessed by measuring infarct size. METHODS AND RESULTS: Open-chest rats with NIDD and age-matched control rats underwent 30 or 45 minutes of regional ischemia and 2-hour reperfusion. Infarct size was measured by tetrazolium. Control rats had 32.0 +/- 3.3% infarction of the risk zone after a 30-minute coronary occlusion, whereas NIDD rats had significantly smaller infarcts (11.5 +/- 3.1% of the risk area, P < .005). When ischemic time was extended to 45 minutes, infarct size in control animals averaged 57.9 +/- 6.2%, whereas only 37.3 +/- 5.6% of ischemic myocardium was infarcted in NIDD rats (P < .05). In a subset NIDD group, rats experienced a period of ischemic preconditioning (three cycles of 5-minute ischemia/5-minute reperfusion) before 45-minute ischemia. Infarct size in these rats averaged only 6.9 +/- 3.0% (P < .01 vs nonpreconditioned NIDD rats with 45-minute coronary occlusions). Collateral flow was measured in NIDD rat hearts with radioactive microspheres. Collateral flow was < 1% of normal myocardial blood flow. CONCLUSIONS: We conclude that NIDD protects the heart from infarction and that this protection is not related to the development of coronary collaterals. Furthermore, preconditioning can further protect the NIDD heart.

Intravenous pretreatment with A1-selective adenosine analogues protects the heart against infarction.

BACKGROUND: Recent data from this laboratory indicate that pretreatment with adenosine can protect the heart against infarction via A1-receptors, but because of systemic hypotension, adenosine had to be given into the coronary circulation. METHODS AND RESULTS: In this study, we tested whether the protection could be achieved by intravenous administration of the A1-selective adenosine agonists N6-(phenyl-2R-isopropyl)-adenosine (PIA) and 2-chloro-N6-cyclopentyladenosine (CCPA). Nine groups of open-chest anesthetized rabbits were subjected to 30 minutes of regional coronary ischemia and 3 hours of reperfusion. Infarct size was determined by tetrazolium staining. Control hearts receiving no treatment had 38 +/- 4% of the risk zone infarcted. Preconditioning with 5 minutes of ischemia and 10 minutes of reperfusion before ischemia limited the infarct to 8 +/- 4%. Intravenous PIA 15 minutes before 30-minute ischemia also limited infarct size to 6 +/- 2% at the highest dose. CCPA offered similar protection. When the PIA was given at reperfusion, infarct size was 46 +/- 6%, indicating that receptor activation must precede ischemia to protect. Pretreatment with CGS 21680, a selective A2-receptor agonist, caused identical hypotension but failed to limit infarct size (43 +/- 3%), indicating again that the A1-receptor is involved. When rabbits pretreated with PIA were paced at 220 beats per minutes, PIA still limited infarct size (16 +/- 4%), indicating that protection was not the result of bradycardia. CONCLUSIONS: These results indicate that stimulation of adenosine A1-receptors causes the heart to become resistant to ischemia and that this protection can be achieved with intravenous administration of A1-selective agents.

Loss of myocardial protection from ischemic preconditioning following chronic exposure to R(-)-N6-(2-phenylisopropyl)adenosine is related to defect at the adenosine A1 receptor.

Exogenously administered adenosine agonist will protect myocardium against infarction during ischemia. However, long-term exposure to adenosine agonists is associated with loss of this protection. To determine why this protection is lost, isolated, perfused rabbit hearts were studied after administration of R(-)-N6-(2-phenylisopropyl)adenosine (PIA), 0.25 mg/h IP, for 3-4 days to intact animals. All hearts experienced 30 min of regional ischemia and 120 min of reperfusion. Control groups 1 and 2 were untreated. In group 1 this ischemia/reperfusion was the only intervention, whereas group 2 hearts were preconditioned with a cycle of 5 min global ischemia/10 min reperfusion preceding the 30 min regional ischemia. Groups 3-5 had been chronically exposed to PIA. Group 3 hearts had 1 preconditioning ischemia/reperfusion cycle before the prolonged ischemia. Group 4 received a 5 min infusion of 0.1 micromol/L phenylephrine in lieu of global ischemia, whereas group 5 was instead treated with 1 micromol/L carbachol. Infarct size averaged 32% of the risk zone in group 1, whereas ischemic preconditioning limited infarction to 8.2% in group 2. Prolonged exposure of group 3 hearts to PIA resulted in the inability of preconditioning with 5 min global ischemia to protect (28.7+/-4.4% infarction). However, protection was restored by either phenylephrine, an agonist of alpha1-adrenergic receptors which couple to Gq and stimulate PKC, or carbachol, an agonist of M2-muscarinic receptors which couple instead to Gi as do adenosine A1 receptors (5.2+/-1.7% and 9.2+/-2.1% infarction, resp.). Therefore, cross tolerance to ischemic preconditioning develops after chronic PIA infusion. Since both the Gi and the PKC components of the preconditioning pathway were shown to be intact, tolerance must have been related to downregulation or desensitization of the A1 adenosine receptor.