Interstitial Fluid Adenosine Concentration Research Articles

Interstitial adenosine concentration during norepinephrine infusion in isolated guinea pig hearts

This study determined the effect of norepinephrine (NE) on cardiac interstitial fluid adenosine concentration [( ADO]isf). Isolated guinea pig hearts were perfused with a Krebs-Henseleit buffer solution. Radiolabeled albumin, sucrose, and adenosine were injected under control conditions and after 3 and 20 min of NE infusion to obtain multiple indicator dilution curves that were used to determine capillary transport parameters for adenosine. These parameters together with venous adenosine concentrations were used in a mathematical model to a calculate [ADO]isf. Capillary transport parameters were not changed significantly by NE infusion. Because of uncertainty regarding two model parameters, two sets of [ADO]isf values were calculated. One set used best-fit values obtained from indicator dilution curves, and a second set used parameters chosen to provide the highest [ADO]isf values consistent with indicator dilution curves. Venous adenosine concentrations were 1.9 +/- 0.4 nM under control conditions and 243 +/- 110 and 45 +/- 25 nM after 3 and 20 min of NE infusion, respectively. Calculated [ADO]isf was 2.6-9.4, 591-1,288, and 166-324 nM, respectively, under these same conditions. We conclude that NE infusion greatly increases [ADO]isf, and adenosine is responsible for most of the vasodilation at 3 min. The subsequent fall in venous concentration is due to a fall in [ADO]isf rather than to decreased capillary permeability. Vascular resistance remained low while [ADO]isf fell, which suggests that additional vasodilators are important during maintained NE infusion.

Cardiac microdialysis to estimate interstitial adenosine and coronary blood flow

The purpose of this study was twofold: 1) to investigate the feasibility and usefulness of cardiac microdialysis for the simultaneous estimation of regional cardiac interstitial fluid (ISF) adenosine (ADO) concentration and coronary blood flow (CBF); and 2) to determine the changes in the ISF levels of ADO and CBF during cardiac stimulation or regional myocardial ischemia. Cardiac microdialysis probes were implanted in the left ventricular myocardium of chloralose-urethan-anesthetized dogs and perfused with Krebs-Henseleit buffer. The concentration of ADO in the effluent dialysate was used as an index of intramyocardial ISF ADO concentration while local CBF was measured by H2 clearance via a platinum wire within the dialysis fiber. Dialysate ADO was elevated immediately after insertion of the microdialysis probe, declined rapidly in the first 20 min, stabilized by 60 min, and remained constant for 2 h. Based on the relationship in vitro and in vivo between microdialysis probe perfusion rate and dialysate ADO concentration, ISF ADO concentration within the left ventricular myocardium was estimated to be 0.9-1.3 microM. Dobutamine (10 micrograms.kg-1.min-1) infusion resulted in a 36% increase in CBF and a 2.5-fold increase in dialysate ADO (n = 9; P less than 0.05). Regional myocardial ischemia, induced by occlusion of the left anterior descending artery (LAD), caused a 13-fold increase in dialysate ADO in the LAD perfused myocardium (n = 9; P less than 0.05). These results are consistent with the ADO hypothesis and suggest that cardiac microdialysis provides a reliable technique for the sampling of regional intramyocardial ISF.

P-11 - Changes in cardiac interstitial fluid adenosine concentration during hypoxia, ischemia, and dipyridamole in the intact dog heart

P-11 - Changes in cardiac interstitial fluid adenosine concentration during hypoxia, ischemia, and dipyridamole in the intact dog heart

Interstitial fluid adenosine and sagittal sinus blood flow during bicuculline-seizures in newborn piglets.

Changes of interstitial fluid adenosine concentrations and effects of O2 supply on interstitial fluid adenosine were studied by the brain dialysis technique in the frontal cortex of newborn piglets subjected to bicuculline-induced seizures. The O2 supply was changed globally by changing MABP and locally by varying PO2 in the artificial CSF perfusing the dialysis cannula. Sagittal sinus blood flow (SSBF), cerebrovascular resistance (CVR), and CMRO2 were also examined in the same animals. Seizures increased interstitial fluid adenosine 7.9-fold (p less than 0.05) when ictal MABP was maintained at preictal level and perfusate PO2 was 24 mm Hg (group 1, n = 6). Interstitial fluid adenosine increased 11.8-fold (p less than 0.05) during seizures associated with moderate systemic hypotension and the low perfusate PO2 (group 2, n = 6). By contrast, seizures increased interstitial fluid adenosine three-fold (p less than 0.05) when perfusate PO2 was increased to 182 mm Hg and ictal MABP was maintained at preictal level (group 3, n = 8). When ictal MABP was elevated from the preictal level and the perfusate was rich in oxygen, seizures failed to increase interstitial fluid adenosine (group 4, n = 7). In groups 1 and 3, the increase in interstitial fluid adenosine during seizures was associated with significant increases in SSBF and CMRO2, as well as significant decreases in CVR. These data suggest that the increase in O2 supply during seizures in piglets did not match completely the increase in O2 demand and resulted in enhanced release of adenosine into the interstitial space.

Increased brain interstitial fluid adenosine concentration during hypoxia in newborn piglet.

The effects of arterial hypoxia on interstitial fluid adenosine concentrations were studied in the frontal cortex and thalamus by the brain dialysis technique and in CSF from the cisterna magna of the newborn piglet. Acute hypoxia (PaO2 = 20 +/- 1 mm Hg) increased the interstitial fluid adenosine concentrations significantly from 0.68 +/- 0.29 (SEM) to 1.60 +/- 0.35 microM in the frontal cortex and from 1.03 +/- 0.32 to 2.60 +/- 0.86 microM in the thalamus (n = 8). Interstitial fluid inosine and hypoxanthine also increased significantly during hypoxia. In separate groups of piglets, the adenosine concentration in the cisterna magna CSF under normoxic conditions was 0.04 +/- 0.01 microM (n = 5), which increased significantly to 0.17 +/- 0.04 microM (n = 6) with hypoxia (PaO2 = 4.7 +/- 1.2 mm Hg). Cisterna magna CSF inosine levels did not change significantly during the severe hypoxia. Adenosine concentrations found in the interstitial space and CSF of newborn piglets under normoxic and hypoxic conditions are within the vasodilator range. These results thus suggest that in the neonatal brain adenosine may play a role in regulating blood flow during hypoxia.

Aminophylline and interstitial adenosine during sustained exercise hyperemia.

We tested the hypothesis that an increase in interstitial fluid (ISF) adenosine concentration contributes to vasodilation of high oxidative skeletal muscle during sustained free-flow exercise. Canine calf muscles were stimulated at 3 Hz for 10 min before and after the infusion of the adenosine receptor antagonist aminophylline (10 mg/kg). The vasodilation that occurred during aminophylline infusion was allowed to decay before the postaminophylline exercise period was begun. This dose of aminophylline shifted the response to infused adenosine 20-fold during rest and reduced the response to a standard dose by 90% during exercise. Aminophylline had no significant effect on blood flow or on O2 consumption at rest or during exercise. Adenosine release (venous minus arterial plasma concentration times plasma flow) increased during 3-Hz exercise both before and after aminophylline infusion, but venous plasma adenosine concentration did not increase in either case. We developed a mathematical model of adenosine movement between ISF and plasma to help us judge whether to use adenosine release or venous concentration as an index of ISF adenosine and decided that venous concentration should be used. We conclude that aminophylline has no effect on sustained 3-Hz exercise hyperemia because under these conditions ISF adenosine concentration does not increase.

Increases in cerebral interstitial fluid adenosine concentration during hypoxia, local potassium infusion, and ischemia.

This study used the brain dialysis technique to test the hypothesis that the adenosine concentration of cerebral interstitial fluid increases during situations in which cerebral oxygen supply is inadequate for oxygen demand. Sealed 300-micron hollow dialysis fibers were implanted in the caudate nucleus of pentobarbital-anesthetized rats and perfused at 2 microliter/min with artificial cerebrospinal fluid. In vitro tests indicated the recovery of adenosine, inosine, and hypoxanthine from the external medium to be approximately 20% at 2 microliter/min and close to 100% at 0.1 microliter/min. Three in vivo interventions were tested: hypoxia/hypotension (PaO2 = 41.9 mm Hg; MABP = 42.8 mm Hg; n = 9), local potassium infusion (n = 4), and cerebral anoxia/ischemia (n = 10). These interventions produced 10-, 4-, and 30-fold increases in perfusate adenosine concentration, respectively, as well as increases in perfusate concentrations of inosine and hypoxanthine. A separate group of rats (n = 9) perfused at 0.1 microliter/min yielded estimates of cerebral interstitial fluid adenosine, inosine, and hypoxanthine concentrations of 1.26, 3.30, and 7.19 microM, respectively. These results are consistent with the adenosine hypothesis for the regulation of CBF.

How does dipyridamole elevate extracellular adenosine concentration? Predictions from a three-compartment model of adenosine formation and inactivation.

Steady-state mathematical models are developed according to which adenosine is formed in the cytoplasm of a group of cells, arises in the extracellular space via the symmetric nucleoside transporter and is inactivated in the adenosine forming cells and after rate-limiting transport into other cell-types. Dipyridamole increases the Km and Vmax. of the transporter symmetrically with respect to influx and efflux. Models incorporating differing degrees of compartmentation are used to predict intracellular and extracellular adenosine concentration as a function of dipyridamole concentration and adenosine formation rate. The vasodilator action of dipyridamole is explained since it is predicted to elevate interstitial fluid adenosine concentrations at all rates of adenosine formation provided that washout of the interstitial compartment is restricted.

Consistent parallel relationships among myocardial oxygen consumption, coronary blood flow, and pericardial infusate adenosine concentration with various interventions and beta-blockade in the dog.

Coronary blood flow responds uniquely to changes in myocardial demand, regardless of the stimulus. If adenosine mediates this response, interstitial fluid adenosine concentration should also change in parallel with myocardial oxygen consumption and coronary blood flow during alterations of cardiac work. We tested this hypothesis by measuring coronary blood flow, myocardial oxygen consumption, and the concentration of adenosine in pericardial infusates, an index of interstitial fluid adenosine concentration, during six experimental conditions and control states in anesthetized, open-chest dogs. Significant alterations of myocardial oxygen consumption and coronary blood flow during aortic constriction, vagal stimulation, atrial pacing, or intravenous infusion of calcium chloride, norepinephrine, or isoproterenol were accompanied by significant alterations in pericardial infusate adenosine concentration. Significant linear relationships were determined among myocardial oxygen consumption, coronary blood flow, and pericardial infusate adenosine concentration for each of the experimental stimuli and their paired control values. There were no significant differences among the six different conditions for any of these relationships. In addition, these relationships were not altered by beta-blockade in five dogs subjected to aortic constriction and calcium infusion. Although beta-blockade may alter the effects of a stimulus, myocardial oxygen consumption, coronary blood flow, and adenosine all are affected proportionately. The results suggest that adenosine production responds to alterations of myocardial oxygen consumption independently of the stimulus which produces the change in oxygen demand, and the resultant change in interstitial fluid adenosine concentration may initiate the change in coronary blood flow to maintain the balance between oxygen supply and demand.

Role of adenine nucleotides, adenosine, and inorganic phosphate in the regulation of skeletal muscle blood flow.

Experiments were performed on isolated frog sartorius muscle and in situ dog skeletal muscle to determine whether adenine nucleotides and their degradation products are released during contraction in concentrations capable of producing arteriolar dilation ATP was not detectable (>10 -8 M) in the bathing solution of the resting or contracting frog sartorius muscle. Inorganic phosphate (P 1 ) in the muscle bath increased from 9 x 10 -5 M to 28 x 10 -5 M with 30 minutes of contraction (2 Hz) or with rest. With the dog hindlirnb preparation, ATP, ADP, and AMP were not detectable (>5 x 10 ⊟8 M in the venous blood collected after 5 minutes of ischemic contraction whereas P 1 was present at a concentration of 3.7 x 10 x8 M. Arterial blood levels required to elicit detectable vasodilation for ATP, ADP, AMP, and P 1 were 28.7 x 10 -8 M, 27.1 x 10 -8 M 31.4 x 10 -8 M and 7.2 ⊠ 10 -4 M respectively. The adenosine concentration in dog muscle increased from 0.7 to 1.5 nmole/g with ischemic contraction, and hypoxanthine and inosine increased from 4.5 to 8.5 nmole/g and 2.0 to 5.5 nmole/g, respectively. The adenosine concentration in venous plasma collected from the hiodlimb immediately after termination of the irchemic contraction period was 2.2 x 10 -7 MM as compared to 0.4 x 10 -7 M in control venous and arterial blood samples. Hypoxanthine and inosine concentrations in venous blood increased 22- and 270-fold, respectively, foflowing ischemic contraction. The calculated interstitial fluid adenosine concentration was twice the arterial concentration of adenosine required to elicit maximal arteriolar dilation. These findings suggest that adenosine may play a role in the metabolic regulation of skeletal muscle blood flow, whereas ATP, ADP, AMP, and P 1 may not.