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Cardiovascular Research 1998 37(1):171-178; doi:10.1016/S0008-6363(97)00213-7
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Copyright © 1998, European Society of Cardiology

Dual cardiac microdialysis to assess drug-induced changes in interstitial purine metabolites: adenosine deaminase inhibition versus adenosine kinase inhibition

Sara A Manthei, Cristine M Reiling and David G.L Van Wylen*

Department of Biology, St. Olaf College, Northfield, MN, USA

* Corresponding author. Tel. +1-507-646-3979; Fax +1-507-646-3968; E-mail: vanwylen@stolaf.edu

Received 13 August 1996; accepted 12 August 1997


   Abstract
Top
 Abstract
1 Introduction
 2 Methods
 3 Results
 4 Discussion
 References
 
Objective: The purpose of this study was: 1) to evaluate a dual microdialysis technique coupled with local drug administration in the regionally ischemic rabbit heart, and; 2) to assess the ischemia-induced changes in interstitial fluid (ISF) adenosine during inhibition of adenosine deaminase or adenosine kinase. Methods: Two microdialysis probes were implanted parallel to each other and separated by 5 mm in myocardium perfused by a branch of the left coronary artery. Probes were used to sample myocardial ISF and to deliver drugs locally to the myocardium; purine metabolite concentrations in the collected dialysate were used as indices of ISF levels. Three groups of pentobarbital-anesthetized rabbits were studied. In a control group (n = 6), both probes were perfused with Krebs-Henseleit buffer. In the second and third groups, one probe was perfused with buffer, whereas the other probe was perfused with buffer containing 1 mM erythro-2-(2-hydroxy-3-nonyl)adenine (EHNA) (n = 5), an adenosine deaminase inhibitor, or 10 µM iodotubercidin (n = 9), an adenosine kinase inhibitor. All animals were exposed to 30 min of regional myocardial ischemia followed by 60 min of reperfusion. Results: In the control group, similar increases in dialysate purine metabolites during ischemia were observed in both probes. Locally administered EHNA increased dialysate adenosine prior to ischemia and decreased dialysate inosine and hypoxanthine. During ischemia, the increase in dialysate adenosine in the EHNA-perfused probe was markedly augmented, while the increases in inosine and hypoxanthine were attenuated. In contrast, local infusion of iodotubercidin did not alter dialysate purine metabolites before ischemia, but there was a modest augmentation of adenosine during ischemia. These data illustrate the feasibility of dual microdialysis for assessing the effect of locally administered compounds on interstitial metabolite concentration in the regionally ischemic rabbit heart. Furthermore, adenosine deaminase inhibition has a more profound adenosine augmenting effect than adenosine kinase inhibition in the rabbit heart.

KEYWORDS Adenosine; Ischemia; Cardiac microdialysis; Purine metabolites; Rabbit


   1 Introduction
Top
 Abstract
 1 Introduction
2 Methods
 3 Results
 4 Discussion
 References
 
Cardiac microdialysis is a technique that has been developed to allow sampling of interstitial fluid (ISF) in the intact heart [1–8]. The essence of cardiac microdialysis is the placement within the myocardium of a hollow dialysis fiber and the continuous perfusion of the dialysis fiber with Krebs-Henseleit buffer. The buffer is pumped through the dialysis fiber, where diffusion occurs between the buffer within the fiber and the ISF surrounding the fiber. Molecules present in the ISF are therefore collected in the effluent dialysate, which can then be analyzed for their identity and concentrations.

The ability to assess ISF levels of various compounds offers two distinct advantages. First, since metabolic by-products are released into the ISF, cardiac microdialysis can provide insight into cellular metabolism. For example, in the present study, ISF levels of the by-products of ATP degradation were measured to assess adenosine metabolism. Second, many biologically active molecules, such as adenosine, norepinephrine, and acetylcholine, exert their effects via membrane-bound receptors that have their active sites facing the ISF. Thus, the ISF is the pertinent compartment to monitor when assessing the actions of compounds that act via extracellular oriented receptors.

An additional feature of cardiac microdialysis, which forms the focus of the present study, is that one is able to deliver a drug locally to the myocardium of the intact heart by inclusion of the drug in the buffer perfusing the probe. The drug diffuses out of the dialysis fiber into the surrounding myocardium, thereby exposing myocytes locally while eliminating systemic effects associated with systemic delivery. Thus, with microdialysis, one can create a microenvironment in the intact heart from which the ISF can be sampled and into which drugs can be delivered.

Although microdialysis in conjunction with local drug infusion has been used extensively in the brain (for examples, see references [9–14]), it has been used only rarely in the heart [6, 15, 16]. The primary purpose of this study, therefore, was to evaluate a dual microdialysis technique coupled with local drug administration in the regionally ischemic rabbit heart. In the present study, we chose to compare the ischemia-induced changes in ISF adenosine and the adenosine metabolites inosine and hypoxanthine during inhibition of adenosine deaminase or inhibition of adenosine kinase. Due to their proposed ability to augment endogenous adenosine, inhibitors of adenosine deaminase [17–19]and adenosine kinase [20–22]have been investigated for potential therapeutic applications. Adenosine is known to protect both heart and brain against the cellular injury which ultimately ensues from prolonged ischemia. Thus, agents which can augment the ischemia-induced accumulation of adenosine could potentially provide ‘site specific’ and ‘event specific’ protection.


   2 Methods
Top
 Abstract
 1 Introduction
 2 Methods
3 Results
 4 Discussion
 References
 
2.1 Animal preparation
All experiments were performed in accordance with the "Guide for the Care and Use of Laboratory Animals" (NIH Publication No. 85-23, revised 1996) and were approved by the Institutional Animal Care and Use Committee at St. Olaf College. Male New Zealand white rabbits weighing 2.5–3.0 kg were anesthetized with 30 mg/kg sodium pentobarbital. The animals were intubated and ventilated with a mixture of 100% oxygen and air. Tidal volume, respiratory rate, and percent oxygen in the inspired air were adjusted to maintain normal blood gas values. Core body temperature was monitored with a rectal temperature probe and maintained with a heating pad at approximately 37.5°C. The right femoral artery was cannulated for the measurement of arterial blood pressure and heart rate, as well as for the determination of arterial blood gases. The right femoral vein was cannulated for infusion of fluids and anesthetic supplement.

A thoracotomy was performed through the left fifth intercostal space and the pericardium was incised to expose the left ventricle. In preparation for the induction of regional myocardial ischemia, a suture was placed around an anterolateral branch of the left circumflex coronary artery and polyethylene tubing was placed onto the suture to be used later as an occlusion device.

The cardiac microdialysis technique, as utilized by our laboratory, has been described in detail previously [7, 8, 23]. The cardiac microdialysis probes were constructed in our laboratory using an individual dialysis fiber (Clirans TH 10 hollow fiber dialysis tubing, Terumo Corp., Tokyo, Japan; 300 µm diameter; molecular weight cutoff 5,000 atomic mass units) and hollow silica tubes (Scientific Glass Engineering, Austin, Texas; 120 µm inner diameter, 170 µm outer diameter). In each animal, two microdialysis probes, with a 5 mm window for diffusion, were placed approximately midwall within the myocardium perfused by the snared coronary artery. Placement of the probes was aided by visualization of the ischemic zone resulting by a brief (<30 s) occlusion of the coronary artery. The probes were implanted parallel to each other and separated by approximately 5 mm. After insertion of the microdialysis probes, each inflow silica tube of the microdialysis probes was connected to a separate gas-tight glass syringe filled with buffer. Each probe was perfused at 2.0 µl·min–1, allowing for diffusion between the fluid within the fiber and the surrounding ISF as the fluid passed through the dialysis fiber. The effluent from the microdialysis fiber, referred to as dialysate, was therefore representative of intramyocardial ISF concentration. The dialysate was collected from the outflow silica tube in plastic tubes and frozen until later analysis.

In a previous published study [23], the in vitro efficiency of purine metabolite recovery was determined for a microdialysis probe with a 5 mm window perfused at a flow rate of 2 µm·min–1. Percent recoveries were 27% for adenosine, 25% for inosine, and 41% for hypoxanthine, all recoveries being a percentage of external solution concentrations.

2.2 Drugs used in the study
Two drugs were utilized in this study. An adenosine deaminase inhibitor, erythro-2-(2-hydroxy-3-nonyl)adenine (EHNA, generously provided as a gift from Burroughs Wellcome Co., Research Triangle Park, NC, U.S.A.) was used at a concentration of 10–3 M in the Krebs-Henseleit buffer to block the breakdown of adenosine to inosine. An adenosine kinase inhibitor, iodotubercidin (Research Biochemicals Inc., Natick, MA, U.S.A.), was used at a concentration of 10–5 M in Krebs-Henseleit buffer to block the synthesis of AMP from adenosine. These doses were chosen based on dose response studies from a previous microdialysis study with EHNA and iodotubercidin in the brain [11].

2.3 Protocols
A minimum of 70 minutes was allowed after microdialysis probe implantation prior to initiation of the protocol. Three experimental groups were studied. In each group, dialysate sampling was collected throughout a 40 minute pre-ischemia period, a 30 minute occlusion period, and a 60 minute reperfusion period. Two 20 minute dialysate samples were collected during the baseline sampling period. During the 30 minute period of coronary artery occlusion, two 5 minute dialysate samples followed by two 10 minute dialysate samples were collected. During reperfusion, a 10 minute, 20 minute, and 30 minute dialysate sample was collected in each group. The difference between the three groups was in the buffer composition being perfused through the two probes throughout the protocol. The control group (Group 1; n = 6) had both probes perfused with drug-free buffer throughout the entire protocol. The second group (Group 2; n = 5) had both probes perfused with drug-free buffer for the first 20 minutes of baseline sampling. One of the probes was then perfused with a 10–3 M EHNA-buffer solution for the remainder of the protocol. The third group (Group 3; n = 9) had both probes perfused with drug-free buffer for the first 20 minutes of baseline sampling, upon which a probe was perfused with a 10–5 M iodotubercidin-buffer solution for the remainder of the protocol.

At the conclusion of the protocol, the coronary artery was reoccluded and a 2% Evan's blue solution was infused into the femoral vein. Upon delineation of the ischemic and non-ischemic zones, the heart was removed and frozen. Tissue slices were subsequently made in the frozen heart in order to visualize the location of the microdialysis probe in relation to the ischemic zone.

Based on later analysis after dye injection, a fourth group of rabbits (n = 6) arose from faulty probe placement within the often small ischemic area in the rabbit myocardium. In this group, one of the two buffer perfused probes was recognized, via the Evan's blue staining, to be in the border zone or not entirely within the ischemic area.

As we completed our experimental groups, we were surprised that iodotubercidin at 10–5 M in the perfusate did not alter baseline adenosine values, despite our previous observation that this dose markedly increased baseline adenosine in the rat brain [11]. Therefore, in a final group of animals (n = 6), we performed a dose response study in which iodotubercidin at successively increasing doses of 10–5 M, 10–4 M, and 10–3 M was perfused through the microdialysis probe in the presence of 10–3 M EHNA. A 20 minute dialysate sample was collected at each dose before switching to the next higher dose.

2.4 High performance liquid chromatography
Before chromatographic analysis, all dialysate samples were diluted with 0.01% sodium azide to prevent bacterial degradation. The dialysate was analyzed for adenosine, inosine, and hypoxanthine. These compounds were separated using a reverse phase column (Supelco LC-18S) and a 1% (pH 5.3) to 25% (pH 5.58) methanol in 100 mM KH2PO4 gradient (flow rate 1.3 ml/min) and detected by absorbance changes at 254 nm. The peaks of interest in the dialysate were identified and quantified by comparing retention times and peak areas to known standards.

2.5 Statistical analysis
Mean values and standard errors of the means of dialysate data at a given time point were calculated for all groups. For comparison of values between probes at corresponding times, a paired t test was used. For comparison of values during/after ischemia to pre-ischemia values, analysis of variance (ANOVA) followed by Dunnett's test for multiple comparisons to control was performed. With all statistical analyses, a p value less than 0.05 was accepted as indication of a statistically significant difference.


   3 Results
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
4 Discussion
 References
 
3.1 Hemodynamic data
Local infusion of iodotubercidin or EHNA did not alter heart rate (pre-iodotubercidin=262±7, iodotubercidin=262±6; pre-EHNA=261±14, EHNA=262±13 beats/min) or mean arterial pressure (pre-iodotubercidin=86±2, iodotubercidin=82±2; pre-EHNA=78±2, EHNA=76±3 mmHg). In all groups, however, there was a progressive decrease in heart rate throughout the period of coronary artery occlusion and reperfusion (end of ischemia: Group 1=236±8, Group 2=240±11, Group 3=246±15, and at the end of reperfusion: Group 1=231±6, Group 2=252±15, and Group 3=248±14 beats/min). Likewise, there was a progressive decrease in mean arterial pressure throughout the period of coronary artery occlusion and reperfusion in all groups (end of ischemia: Group 1=64±5, Group 2=64±3, Group 3=70±2, and at the end of reperfusion: Group 1=64±4, Group 2=65±1, and Group 3=69±3 mmHg).

3.2 Dialysate data
Fig. 1 illustrates the dialysate adenosine, inosine, and hypoxanthine profiles for both probes from the control group. Probe A (Fig. 1A) and probe B (Fig. 1B), both being perfused with drug-free buffer, show similar dialysate profiles for the three purine metabolites. In both probes, inosine and hypoxanthine increased markedly during coronary artery occlusion and returned to baseline values during reperfusion. Although dwarfed by the large increase in inosine and hypoxanthine, adenosine concentrations were similar in both probes as well, rising transiently throughout the period of ischemia and then returning to baseline values during reperfusion. Thus, it is possible to place two microdialysis probes in the ischemic zone of the rabbit and obtain similar purine metabolite profiles in both probes.


Figure 1
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  		Fig. 1 Dialysate adenosine, inosine, and hypoxanthine profiles (mean±SEM) for both probes in the control group. The shaded area represents the period of coronary artery occlusion. Where SEM bars are not seen, the SEM fell within the symbol of the given data point. ISC=ischemia.

 
However, proper probe placement is critical for a dual microdialysis technique. In several early experiments, we varied the size of the ischemic region and where the probes were placed within the ischemic zone. Fig. 2 shows data from six experiments in which, upon retrospective analysis, one of the probes was placed outside the ischemic area or in the border zone. In these experiments, dialysate concentrations from one probe (Fig. 2A) showed similar profiles in the three purine metabolites as that shown in Fig. 1. However, dialysate values from the other probe (Fig. 2B), which was likely not located entirely within the ischemic area, rose only slightly from baseline. Thus, it is crucial that the windows of both probes are placed within the core of the ischemic area.


Figure 2
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  		Fig. 2 Dialysate adenosine, inosine, and hypoxanthine profiles (mean±SEM) for both probes in the group with a probe not entirely within the ischemic area. The shaded area represents the period of coronary artery occlusion. Where SEM bars are not seen, the SEM fell within the symbol of the given datum point. ISC=ischemia.

 
Fig. 3 shows the effect of local EHNA infusion on purine metabolite levels prior to ischemia. Dialysate concentrations of adenosine, inosine, and hypoxanthine prior to the delivery of EHNA to one of the probes, when both probes were being perfused with EHNA-free buffer, were similar in both probes. As shown in Fig. 3, when the buffer containing EHNA was perfused through one of the probes, dialysate adenosine concentration increased, whereas dialysate levels of inosine and hypoxanthine decreased.


Figure 3
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  		Fig. 3 Dialysate adenosine, inosine, and hypoxanthine concentrations (mean±SEM) for both probes in the EHNA group prior to ischemia. *p<0.05 vs. untreated animals.

 
Purine metabolite values throughout the entire protocol for the EHNA group are shown in Fig. 4. The control probe (Fig. 4A), perfused with drug-free buffer throughout the entire protocol, showed profiles of adenosine, inosine, and hypoxanthine similar to those seen in Group 1. The effects of EHNA on the ischemia-induced changes in dialysate purine metabolite levels (Fig. 4B) were quite pronounced. Throughout the ischemic period, dialysate adenosine was notably increased, peaking at a value of 25 µM, whereas the increases in inosine and hypoxanthine were diminished.


Figure 4
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  		Fig. 4 Dialysate adenosine, inosine, and hypoxanthine profiles (mean±SEM) for both probes in the EHNA group. The shaded area represents the period of coronary artery occlusion. Where SEM bars are not seen, the SEM fell within the symbol of the given datum point. ISC=ischemia.

 
Data from the iodotubercidin experiments (Group 3) are illustrated in Fig. 5Fig. 6. Local iodotubercidin delivery did not significantly alter pre-ischemic dialysate purine metabolite levels. As shown in Fig. 5, dialysate inosine and hypoxanthine values were not significantly different during ischemia in the iodotubercidin perfused probes as compared to the drug-free buffer-perfused probes. Fig. 6 shows the time course of dialysate adenosine concentration in the iodotubercidin experiments. Local iodotubercidin administration produced a significant augmentation in dialysate adenosine during ischemia, although this augmentation was modest compared to that produced by EHNA.


Figure 5
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  		Fig. 5 Dialysate adenosine, inosine, and hypoxanthine profiles (mean±SEM) for both probes in the iodotubercidin (IODO) group. The shaded area represents the period of coronary artery occlusion. Where SEM bars are not seen, the SEM fell within the symbol of the given datum point. ISC=ischemia.

 

Figure 6
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  		Fig. 6 Dialysate adenosine profiles (mean±SEM) for both probes in the iodotubercidin (IODO) group. The shaded area represents the period of coronary artery occlusion. Where SEM bars are not seen, the SEM fell within the symbol of the given datum point. ISC=ischemia. *p<0.05.

 
In the presence of adenosine deaminase inhibition with EHNA, 10–5 M iodotubercidin produced a 45±18% increase in baseline adenosine, and there was no further significant increase with 10–4 M (38±21% increase) or 10–3 M iodotubercidin (72±41% increase). Therefore, it is likely that 10–5 M iodotubercidin effectively blocks adenosine kinase in this model.


   4 Discussion
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
 4 Discussion
References
 
Cardiac microdialysis is a relatively new but increasingly used technique for measuring ISF purine metabolites [7, 8, 15, 23]or other compounds [2, 4, 5]in the intact heart. However, few studies have investigated the possibility of using the cardiac microdialysis technique to deliver drugs locally to the myocardium while simultaneously measuring ISF purine metabolite values [15]. The purpose of this study, therefore, was to investigate a dual microdialysis technique which coupled local drug administration and ISF sampling in the regionally ischemic rabbit heart. We chose to examine dual microdialysis using inhibitors of two enzymes that play a role in adenosine metabolism in the myocardium: adenosine deaminase, which catalyzes the conversion of adenosine to inosine, and adenosine kinase, which catalyzes the rephosphorylation of adenosine to AMP. The major findings of this study were that: 1) a dual microdialysis technique is possible in the regionally ischemic rabbit heart, and; 2) inhibition of adenosine deaminase has a more pronounced effect on ISF adenosine and adenosine metabolite levels before and during ischemia than does inhibition of adenosine kinase.

Local drug infusion in conjunction with microdialysis is not a new experimental approach; it has been used extensively in the brain using microdialysis techniques adapted for studies on the central nervous system [9–14]. In fact, the present study was designed based on observations from a previous study from our laboratory in which EHNA and/or iodotubercidin were infused locally into the caudate nucleus of the rat brain [11]. In these studies, it was established with dose response experiments that 10–3 M EHNA or 10–5 M iodotubercidin present in the perfusate buffer effectively inhibited adenosine deaminase or adenosine kinase, respectively. With dual microdialysis in the brain, one can implant a microdialysis probe in a particular nuclei or anatomical region on each hemisphere of the brain, thereby keeping the two tissue regions sampled physically separate from each other; this obviously is not possible in the regionally ischemic rabbit heart. On one hand, the probes must both be placed within the relatively small ischemic zone of the rabbit heart that results from the occlusion of the anterolateral branch of the circumflex artery. On the other hand, the probes must be far enough away from each other in order to prevent sampling or drug delivery overlap. Studies in the brain have suggested that drugs may diffuse as far as 2.5 mm away from a microdialysis probe [24]. Based on our initial experiments in which we explored different dimensions of probe separation and area at risk, we decided to separate the probes by approximately 5 mm (many of these initial experiments contributed to the group with a probe placed not entirely within the ischemic area (Fig. 2)). This allowed the probes to be 3–5 mm within the border of the ischemic zone. With this technique, we were able to observe similar dialysate purine metabolite profiles in both probes without any evidence of overlap of drug delivery or ISF sampling areas.

Although local infusion of drugs in conjunction with microdialysis has not been investigated extensively in the heart, it has been used previously. Shindo et al. [6]infused an inhibitor of neuronal norepinephrine uptake locally into the regionally ischemic cat myocardium while measuring dialysate norepinephrine levels. However, these investigators did not use the dual microdialysis approach, but rather performed separate experiments in which the probes were perfused with the uptake inhibitor. The advantage of the dual microdialysis approach is that ischemic myocardium from the same animal is studied with and without drug. In a preliminary study from our laboratory [15], as well as in a recent study by Wilkström et al. [16], a dual microdialysis approach was utilized during occlusion of the left anterior descending coronary artery in the dog and pig heart, respectively; however, the ischemic zone in the regionally ischemic dog or pig heart is much larger than that in the rabbit. It was therefore important to first demonstrate that two probes could reliably be placed in the regionally ischemic rabbit heart. Our data indicate that with careful placement, similar dialysate purine metabolite profiles can be obtained from two probes placed within the ischemic zone of the rabbit heart. It should be noted that for investigations of metabolic changes in response to global rather than regional changes, more than two probes could be implanted in the myocardium and several drugs could be assessed at once.

Our results suggest that, in the rabbit heart, inhibition of adenosine deaminase has a more profound effect on ISF adenosine before and during ischemia than does inhibition of adenosine kinase. While this was not surprising during ischemia, when there is a large net breakdown of adenine nucleotides, this observation was somewhat surprising during pre-ischemic conditions. Several studies [25–32]have suggested that during normoxic conditions the majority (70–90%) of the adenosine that is produced is recycled via adenosine kinase to AMP, thus providing a salvage pathway for the adenosine moiety of adenine nucleotides. Consistent with this notion, it is known that adenosine kinase has a lower Km for adenosine than adenosine deaminase [27, 33, 34]. Furthermore, measurements of either ISF or coronary venous adenosine in the isolated perfused guinea pig heart [25, 26]have shown that inhibition of adenosine kinase with iodotubercidin caused a pronounced increase in adenosine. However, in these isolated perfused heart studies, inhibitors of adenosine kinase were administered only in the presence of an inhibitor of adenosine deaminase. Thus, it is not clear if an inhibitor of adenosine kinase alone would have increased adenosine prior to ischemia, although Dennis et al. [35]recently documented a negative dromotropic effect of iodotubercidin in the isolated guinea pig heart, suggesting that adenosine kinase inhibition alone does cause an increase in adenosine.

Based on the lower Km of adenosine kinase for adenosine, we do not have an explanation as to why iodotubercidin did not have an effect on ISF adenosine and adenosine metabolites prior to ischemia in the intact rabbit heart. We have shown that iodotubercidin delivered at the same dose to the normoxic rat brain via microdialysis increases ISF adenosine [11]. Since in our experiments iodotubercidin does produce a modest increase in adenosine in the presence of EHNA, it is unlikely that the failure of iodotubercidin to augment ISF purines is due to insufficient drug delivery. Furthermore, in two experiments we increased the concentration of iodotubercidin in the buffer perfusing the microdialysis probe to 10–4 M, but there was still no effect on ISF adenosine prior to ischemia. One conclusion would be that adenosine kinase is either less active or less abundant in the rabbit heart than is adenosine deaminase. However, Wagner et al. [30]have shown that 2 µM iodotubercidin increased extracellular adenosine accumulation in isolated rabbit cardiomyocytes. Whether this difference is due to differences between in vivo and in vitro preparations remains to be determined.

A comparison of the purine metabolite profiles during ischemia in rabbits obtained in the present study with that obtained in rats in a previous study [8]suggests that interstitial adenosine accumulation during ischemia is much greater in rats that in rabbits. Headrick [36]has also demonstrated this phenomenon, noting that whereas six minutes of global ischemia caused a 27-fold increase in interstitial adenosine in rats, six minutes of global ischemia in rabbits caused only a 6-fold increase in adenosine. Both our data and Headrick's data indicate that greater amounts of inosine and hypoxanthine are produced during ischemia in rats as well. This suggests that the primary difference between rats and rabbits is that the rats produce more total purine metabolites during ischemia than rabbits, rather than some difference in the way these two species metabolize purine metabolites. The NMR work of Headrick and of Matherne et al. [36, 37]indicates that rabbit hearts are bioenergetically more stable during ischemia.

In summary, this study demonstrates that, with dual cardiac microdialysis, it is possible to deliver a drug locally to one portion of the regionally ischemic rabbit myocardium while simultaneously sampling ISF in both regions. With the local delivery of EHNA, an adenosine deaminase inhibitor, or iodotubercidin, an adenosine kinase inhibitor, we have shown that inhibition of adenosine deaminase markedly alters ISF adenosine and adenosine metabolites before and during ischemia, whereas adenosine kinase inhibition only augments ISF adenosine during ischemia.

Time for primary review 21 days.


   Acknowledgements
 
This study was supported by NIH HL-46027 and was done during the tenure of an Established Investigator Award from the American Heart Association and Bristol-Myers Squibb. This work was presented at the Experimental Biology '96 conference in Washington, DC, April 14–17, 1996.


   References
Top
 Abstract
 1 Introduction
 2 Methods
 3 Results
 4 Discussion
 References
 

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