Glucagon-like peptide-1 (GLP-1), immediately prior to reperfusion, decreases neutrophil activation and reduces myocardial infarct size in rodents.

Glucagon-like peptide-1 (GLP-1) is an incretin that has glucoregulatory effects as well as protective effects in a variety of tissues, including the heart. We hypothesized that GLP-1 may have a direct effect on neutrophils (PMNs) after myocardial ischemia, to ameliorate reperfusion injury. Deeply anesthetized Sprague-Dawley rats underwent 30 min of left coronary artery occlusion followed by 120 min of reperfusion. Immediately prior to reperfusion, rats were treated with either GLP-1 (human rGLP-1, 30 pM/kg/min) or PBS as placebo. GLP-1 significantly decreased myocardial infarct size [73.2±11.7% INF/AAR in PBS (n=4) vs. 15.7 ±5.52% INF/AAR in GLP-1-treated animals (n=5), p<0.05], PMN activation in blood in vivo (fMLP-stimulated CD11b surface expression: PBS 2.78±1.14 vs. GLP-1 1.7±0.21, TFI, p<0.05), and accumulation in myocardium (PBS: 6.52±0.31 vs. GLP-1: 4.78±0.90, n=4-6 animals/group, p<0.05). In addition, we found that GLP-1 mitigated PMN CD11b surface expression in whole rat blood in vitro, an effect that was abolished by GLP-1 receptor blockade (PBS 6.52±0.31 vs. GLP-1 4.78±0.90, TFI, p<0.05). These findings suggest that one mechanism by which GLP-1 decreases reperfusion injury may be the attenuation of PMN-mediated reperfusion injury.

The blood contribution to early myocardial reperfusion injury is amplified in diabetes.

Cardiovascular disease is excessive in diabetes, and blood cell function is altered. It is not clear, however, if alterations in the blood contribute to the excessive cardiovascular complications of this disease. In this study, we compared the contribution of nondiabetic and diabetic blood to myocardial reperfusion injury. The recovery of cardiac contractile function following no-flow ischemia was studied in isolated diabetic and nondiabetic rat hearts perfused with diabetic or nondiabetic diluted whole blood. Hearts were isolated from 10- to 12-week-old diabetic (streptozotocin, 65 mg/kg, i.v.) and nondiabetic rats and perfused with a Krebs-albumin-red cell solution (K2RBC, Hct 20%). After a 30-min pre-ischemic control period, during which cardiac pump function was evaluated, diabetic and nondiabetic hearts were perfused for 5 min with diluted whole blood (DWB; Hct 20%) collected from either diabetic or nondiabetic donor animals. Coronary flow was then stopped and the hearts subjected to 30 min of no-flow ischemia. Following ischemia, the hearts were reperfused with the K2RBC perfusate. Cardiac contractile function was evaluated throughout the 60-min reperfusion period. Six groups were studied: diabetic and nondiabetic hearts perfused before ischemia with either K2RBC, nondiabetic DWB (NDDWB), or diabetic DWB (DDWB). Perfusion with DWB prior to ischemia impaired the recovery of contractile function in all cases. The impairment to recovery was greater with DDWB than with NDDWB. Although diabetic hearts perfused with K2RBC throughout recovered quite well, the effect of DDWB perfusion in the diabetic hearts was dramatic. In an effort to determine why diabetic blood impaired functional recovery, measures of blood filterability and the generation of reactive oxygen species (ROS) were made. We found that diabetic blood was less filterable than nondiabetic blood; that is, the diabetic blood cells tended to plug the 5-microm filter pores more readily than the nondiabetic blood cells. Also, we found that the diabetic blood was capable of generating significantly greater ROS (oxygen free radicals) than nondiabetic blood (P < 0.05). These findings suggest that the blood contribution to myocardial reperfusion injury is amplified in diabetes. A tendency for diabetic blood cells to plug capillary-sized pores and show enhanced oxygen free radical production may account for the excessive contribution of diabetic blood to reperfusion injury in the heart.

Brief perfusion with diluted whole blood after global myocardial ischaemia increases reperfusion injury.

OBJECTIVES: In vivo studies indicate that blood components, especially leucocytes, contribute to reperfusion injury after myocardial ischaemia. This study was designed to: (1) develop a small animal heart model of ischaemia-reperfusion that demonstrates the contribution of blood to reperfusion injury; (2) determine when the presence of blood in the heart--that is, during ischaemia or during early reperfusion--caused greater dysfunction; and (3) attempt to limit the blood contribution to reperfusion injury by leucocyte depletion. METHODS: Adult rat hearts were perfused in situ with a Krebs-albumin red cell solution (K2RBC), then isolated. Cardiac pump function was assessed with an intraventricular balloon as left ventricular developed pressure and contractility (dP/dt). Group I served as a non-ischaemic control group. Group II was subjected to global, no flow ischaemia for 30 min followed by 45 min reperfusion. In group III, diluted whole blood replaced the K2RBC for five min immediately before ischaemia. In group IV, diluted whole blood was perfused during the first five min reperfusion. In group V, the hearts were reperfused with leucocyte poor diluted whole blood. RESULTS: Pre-ischaemic pump function values were similar to other blood perfused, isolated heart models. Group I showed no increase in coronary resistance or decrease in pump function with time or in response to diluted whole blood. After 35 min reperfusion, the recovery (% control) of dP/dt in group II was 56(12), in group III it was 39(15) and in group IV it was only 19(6) (p < 0.05). Large increases in coronary vascular resistance, oedema, and contracture during reperfusion were also seen in group IV. When leucocytes were depleted from the diluted whole blood (group V), the recoveries were similar to reperfusion without diluted whole blood (group II). CONCLUSIONS: Thirty min of global, normothermic ischaemia caused significant cardiac dysfunction early during reperfusion. Perfusion with unstimulated blood for a limited period further impaired the recovery of function and enhanced myocardial oedema. Dysfunction was particularly evident when diluted whole blood was perfused during the first minutes of reperfusion. The leucocyte depletion studies suggest that leucocytes are necessary, but may not be sufficient, to demonstrate the blood contribution to reperfusion injury.

Plasma lipid changes in young adult couples consuming polyunsaturated meats and dairy products.

Twenty-five young couples consumed either a saturated or polyunsaturated fat diet for a 20-week period. The polyunsaturated beef, lamb and dairy products, high in linoleic acid, were produced by feeding ruminant animals "protected lipid" feeds which prevent hydrogenation of fats in the rumen. The experimental design provided for four dietary groups: A) saturated diet for 20 weeks; B) polyunsaturated diet for 20 weeks; C) saturated diet for 10 weeks then polyunsaturated diet for 10 weeks; and D) polyunsaturated for 10 weeks then saturated diet for 10 weeks. Polyunsaturated-to-saturated ratios (linoleic: total saturated fatty acids) for the diets were: prestudy, 0.43-0.56; saturated 0.11-0.14; polyunsaturated, 0.56-0.62. Factors other than diet that appeared to affect cholesterol responses were carefully considered. During the initial 3 weeks (regimentation period) plasma cholesterol concentration decreased in all groups irrespective of diet. This was followed by two experimental periods in which the effects of the prescribed diets were readily apparent (response periods I and II). The final 4 weeks of the study were characterized by diminishing compliance with the dietary discipline (abatement period). Subjects in each group (A,B,C,D) were subdivided into high and low on a basis of each group's initial median cholesterol level. Those in the high subgroups were very responsive to dietary changes whereas those in the low subgroups were not. Combined responses of high subjects were: polyunsaturated diet, -10.7 mg/dl (P less than 0.025), saturated diet, d8 mg/dl (P less than 0.05). Combined difference between saturated and polyunsaturated diets was 18.5 mg/dl or approximately a 10% cholesterol difference between the experimental polyunsaturated and saturated diets.

Use of cold blood cardioplegia to protect against coronary microcirculatory injury due to ischemia and reperfusion.

The effect of cold blood cardioplegia in preventing microvascular injury owing to myocardial ischemia and reperfusion was studied. Two groups of eight dogs each were placed on cardiopulmonary bypass with separate coronary perfusion at 80 mm Hg. Microcirculatory function was assessed by measuring the extraction and permeability surface area product (PS) for inulin and albumin. These changes were correlated with the transport and extraction of oxygen, coronary blood flow, and morphologic studies of the microvasculature. In Group I, ischemic hearts were kept normothermic for 45 minutes. In Group II, 250 ml of cold (4 degrees C) blood cardioplegic solution (potassium chloride 30 mEq/L) was infused and the infusion repeated at 15 and 30 minutes. Reperfusion resulted in marked reactive hyperemia for Group I (p less than 0.05) but no hyperemic response in Group II. In Group I, but not II, ischemia-reperfusion caused a significant decrease in PS inulin (0.47 +/- 0.10 ml/min/gm) compared to the preischemic value (1.04 +/- 0.23) (p less than 0.05). There was a threefold decrease in the PS inulin/PS albumin ratio with reperfusion in Group I, indicating increased vascular permeability to albumin. There was also a significant decrease in myocardial oxygen consumption (from 5.1 +/- 0.7 to 3.4 +/- 0.5 ml/min/100 gm, p less than 0.05) for Group I. These did not decrease for Group II. Histologic studies showed diffused areas of no reflow in the unprotected hearts. The wet/dry weight ratio for Group I (4.97 +/- 0.09) was significantly greater than for Group II (4.49 +/- 0.07) (p less than 0.001). The results indicate that in the unprotected heart, ischemia-reperfusion caused microcirculatory injury resulting in increased permeability to albumin, edema, a reduction in surface area, and areas of no reflow. In contrast, in the hearts protected with cold blood cardioplegia, no evidence of microcirculatory injury occurred.

Improved myocardial recovery from ischemia. Treatment with low-dose adenosine triphosphate-magnesium chloride.

To evaluate the effects of adenosine 5-triphosphate-magnesium chloride (ATP-MgCl2) on myocardial function following ischemia, mongrel dogs were placed on cardiopulmonary bypass with separate coronary perfusion pressures at 80 mm Hg. An intraventricular balloon was used to assess cardiac function as the area under the pressure-volume curve (PV), compliance (C), and cardiac contractility (dP/dT). Control measurements were made of coronary flow (Q), myocardial oxygen consumption and PV, C, and dP/dT. Myocardial ischemia was then induced for 45 minutes, followed by reperfusion (R). In group 1 (n = 5), no ATP-MgCl2 was infused into the coronary perfusion line. In group 2 (n = 5), low-dose ATP-MgCl2 (0.13 mg/min/kg) was infused during the first 30 minutes of reperfusion (R0 to R30), and in group 3 (n = 5), high-dose ATP-MgCl2 (3.2 mg/min/kg) was infused from R0 to R30. Use of ATP-MgCl2 therapy produced marked coronary vasodilation. After 20 minutes of reperfusion (R20), coronary resistance was 81% +/- 12%, 55% +/- 15%, and 31% +/- 3% of control in groups 1, 2, and 3, respectively. The high-dose ATP-MgCl2 (group 3) caused a marked systemic hypotension, but the low-dose ATP-MgCl2 (group 2) did not. After 75 minutes of reperfusion (R75), compliance was decreased in all groups. In groups 1 and 3, both function (PV) and dP/dT were significantly decreased. However, for group 2 (low-dose ATP-MgCl2), function (PV), and dP/dT were not different from the control group, indicating an excellent recovery. Thus, at low doses, ATP-MgCl2 appears to be a promising adjunct to the treatment of the ischemic myocardium.

Fucoidin reduces coronary microvascular leukocyte accumulation early in reperfusion.

BACKGROUND: Leukocytes rapidly accumulate in the heart early in reperfusion after ischemia, contributing to reperfusion injury. The purpose of this study was to determine whether treatment with the selectin blocker fucoidin (FCN) would attenuate early leukocyte retention in coronary venules and capillaries during low flow reperfusion. METHODS: Isolated rat hearts subjected to 30 minutes of 37 degrees C, no-flow ischemia were initially reperfused with blood containing labeled leukocytes, followed by reperfusion with a Krebs red cell solution. The deposition of leukocytes in coronary capillaries and venules was observed using intravital microscopy. Three groups were studied: nonischemic control hearts, untreated postischemic hearts reperfused at low flow, and postischemic hearts reperfused at low flow, where both the hearts and the blood reperfusate were pretreated with FCN (0.36 mg/mL blood). RESULTS: In the ischemia-reperfusion group, we observed a rapid and significant increase in leukocyte accumulation in both capillaries and venules. Treatment with FCN significantly reduced the leukocyte accumulation in both capillaries and venules (p<0.05). In addition, FCN significantly reduced the persistence of leukostasis in both capillaries and venules, indicating that FCN affected a transient adhesion process. CONCLUSIONS: These results suggest that the selectin family of leukocyte-endothelial cell adhesion proteins mediates the initial retention of leukocytes in both coronary capillaries and venules during reperfusion. Selectin blockade may be effective in reducing the contribution of leukocytes to early reperfusion injury.

Pentoxifylline reduces coronary leukocyte accumulation early in reperfusion after cold ischemia.

BACKGROUND: Ischemia/reperfusion injury can complicate recovery in cardiac operations. Ischemia induces endothelial dysfunction, which may contribute to leukocyte accumulation during reperfusion. Leukocyte-mediated injury may then occur. Using intravital microscopy we previously reported increased leukocyte retention in coronary capillaries and venules during early reperfusion during warm ischemia/reperfusion. In this study we investigated whether cold cardioplegic protection would limit leukocyte sequestration in coronary microvessels early in reperfusion. Pentoxifylline (PTX) has antiinflammatory effects and may limit endothelial dysfunction during ischemia/reperfusion. The effect of cardioplegia modification with PTX was also examined. METHODS: Isolated rat hearts were subjected to 90 minutes of 4 degrees C ischemia after arrest with cardioplegia. Hearts were reperfused with diluted whole blood containing fluorescent-labeled leukocytes. Leukocyte retention in coronary microvessels was observed with intravital microscopy. Three groups were studied, nonischemic control, cold ischemia, and PTX-modified cold ischemia. RESULTS: In coronary capillaries, leukocyte trapping was nearly doubled in unmodified cold ischemia versus control. PTX modification significantly reduced leukocyte accumulation. In coronary venules, greater leukocyte adhesion was observed in unmodified cold ischemia compared to nonischemic controls. PTX modification significantly reduced leukocyte adhesion. CONCLUSIONS: Cold cardioplegia did not prevent leukocyte retention in the coronary microcirculation early in reperfusion. PTX modification of cardioplegia significantly reduced leukocyte sequestration in coronary capillaries and venules. Preserving endothelial function during ischemia may limit leukocyte accumulation and ischemia/reperfusion injury after cardiac operation.

Diabetes enhances leukocyte accumulation in the coronary microcirculation early in reperfusion following ischemia.

BACKGROUND: Diabetic hearts are particularly vulnerable to ischemia-reperfusion injury. For leukocytes to participate in ischemia-reperfusion injury, they must first sequester in the microcirculation. The aim of this study was to determine, by direct observation, if early leukocyte deposition was increased in the diabetic coronary microcirculation early in reperfusion following myocardial ischemia. METHODS: Non-diabetic and streptozotocin (STZ)-induced diabetic rat hearts, subjected to 30 min of 37 degrees C, no-flow ischemia, were initially reperfused with blood containing labeled leukocytes. The deposition of fluorescent leukocytes in coronary capillaries and venules was directly visualized and recorded using intravital fluorescence microscopy. In addition, flow cytometry was used to measure CD11b adhesion molecule expression on polymorphonuclear (PMN) leukocytes from non-diabetic and STZ-diabetic rats. RESULTS: In the non-diabetic, control hearts, early in reperfusion, leukocytes trapped in coronary capillaries and adhered to the walls of post-capillary venules. In the diabetic hearts, leukocyte trapping in capillaries and adhesion to venules were both significantly increased (P<0.05). PMN CD11b expression was also significantly increased in the diabetic blood compared to the non-diabetic blood (P<0.05). CONCLUSIONS: Early in reperfusion following myocardial ischemia, leukocytes rapidly accumulate in greater numbers in the coronary microcirculation of the diabetic heart by both trapping in coronary capillaries and by adhering to venules. The enhanced retention of leukocytes in the diabetic coronary microcirculation increases the likelihood of inflammation-mediated reperfusion injury and may explain, in part, the poor recovery of diabetic hearts from an ischemic event.

The microvascular pathophysiology of chronic venous insufficiency.

Severe chronic venous insufficiency (CVI) demonstrates as chronic, hard-to-heal wounds of the lower extremity. The wound is the result of poor skin perfusion due to a complex series of pathologic events, often initiated by a deep vein thrombosis (DVT). As years pass, the DVT causes venous valvular damage and incompetence. The calf muscle pump fails to augment venous return, and venous blood pressure is chronically elevated upon standing. Mechanisms that normally prevent the transmission of venous hypertension back upstream to the dermal microcirculation are lost. Early dermal microvascular responses include increased fluid filtration and edema. An inflammatory response induces white cell activation and adhesion. It is thought that activated white cells are trapped in dermal capillaries and increase microvascular permeability. Plasma proteins leak into the tissue space, increasing the edema. Ischemic damage to the epidermis leads to epithelial cell necrosis and ulceration. The ulcer is often slow to heal, due to inadequate perfusion and delivery of substrates required for proper wound healing. Current treatments aim to improve calf pump function, reduce edema, improve perfusion, and enhance wound healing.

Both protein and blood cells reduce coronary microvascular permeability to macromolecules.

A number of studies report that isolated Krebs-perfused hearts deteriorate with time, develop edema, and demonstrate a progressive increase in coronary vascular resistance. However, hearts perfused with filtered blood are more stable with regard to cardiac function and coronary resistance. The changes observed in the Krebs hearts may be due to a "permeability"-type edema. The purpose of this study was to systematically determine whether adding protein and blood cells to a Krebs perfusate affected coronary microvascular permeability to macromolecules. The rat heart preparation employed allowed direct visualization and quantification of transcoronary macromolecular leakage. We observed severe transcoronary leakage of fluorescent albumin (FITC-BSA) when FITC-BSA was later added after 20 min of perfusion with Krebs. Leakage was decreased by including 2 g/100 ml albumin (BSA) in the initial perfusate but was not further reduced by increasing the BSA concentration to 5 g/100 ml. However, adding washed blood cells to the initial perfusate did further reduce FITC-BSA leakage. The index of FITC-BSA exchange, the O/I ratio, was 0.70 +/- 0.02 (+/- SE) for Krebs perfusate, 0.55 +/- 0.03 for Krebs-BSA, and 0.45 +/- 0.02 for Krebs-BSA-blood cells, indicating significant effects for both protein and blood cells (P less than 0.05). The results suggest that both protein and blood cells are necessary to maintain the semipermeable characteristics of the coronary exchange vessels.

The role of the coronary microcirculation in myocardial recovery from ischemia.

The aim of thrombolysis, angioplasty, and coronary artery bypass surgery is to "reperfuse" ischemic myocardium; however, reperfusion can cause further cardiac damage and compromise the coronary microcirculation. Because nutrient supply and exchange and delivery of pharmacologic agents require a patent microvasculature, the coronary microcirculation plays a major role in myocardial recovery from ischemia. It is known that ischemia-reperfusion can cause an increase in coronary permeability and microvascular plugging (No-reflow). The permeability to macromolecules is increased more than the permeability to smaller molecules. The permeability increase leads to extravasation of plasma proteins and a permeability edema. Furthermore, proteins that normally remain extravascular are now free to wash out the heart. Both microvascular effects, increased coronary permeability and No-reflow, compromise cardiac function. The degree of damage depends on the nature (No-flow versus low-flow) and length of ischemia. Unfortunately, both the increase in coronary permeability and the reduction in perfused capillarity advance with time during early reperfusion. Although the increase in permeability does not require the presence of platelets or leukocytes, it is apparent that the No-reflow response does. Mechanisms that may explain the microvascular responses to ischemia include cell swelling, damage caused by oxygen free radicals, and inflammatory responses that may or may not involve granulocytes. The permeability response may involve a calcium-mediated endothelial contraction because the macromolecular leakage that follows ischemia can be prevented by pretreating hearts with the calcium blocker nisoldipine. Protection of the coronary microcirculation should be included in any attempt to improve treatment of occlusive coronary artery disease.

Platelets reduce coronary microvascular permeability to macromolecules.

Several studies in organs other than the heart suggest that platelets play a role in maintenance of microvascular integrity. In an earlier study, we reported that coronary microvascular permeability to macromolecules was reduced when blood cells were added to a Krebs-albumin perfusate. At that time, we could not differentiate the contributions made by red cells and platelets. To examine the specific role of platelets in the cell effect, isolated rat hearts were perfused with a mixture of Krebs, albumin [2 g/100 ml bovine serum albumin (BSA)], and rat plasma that was either rich in platelets (PRP) or poor in platelets (PPP). For the nine PRP hearts studied, the perfusate contained an average of 10(4) platelets/microliter. For the nine PPP hearts, the perfusate contained 5 X 10(1) platelets/microliter. The left ventricular epicardial microcirculation was observed directly using intravital fluorescence microscopy, and coronary microvascular permeability to macromolecules was assessed by monitoring the transcoronary extravasation of fluorescent albumin (FITC-BSA). We found that the measure of transcoronary FITC-BSA extravasation, the (O/I) ratio, was 0.57 +/- 0.02 (n = 70 fields) for the PPP perfused hearts and 0.47 +/- 0.02 (n = 70) for the PRP hearts (P less than 0.05). The value for the PRP group was similar to that observed earlier with the red cell perfusate (0.45 +/- 0.02). These findings support the concept that platelets help maintain the normal semipermeable membrane characteristics of the coronary exchange vessels.

The preparation and use of fluorescent-protein conjugates for microvascular research.

A procedure is described for making large quantities (100 ml) of fluorochrome-labeled albumin. Chromatographic techniques are described for the purification of commercial albumin (BSA) and the purification of albumin from serum. We report experimentally determined optimal conditions for the covalent attachment of fluorescent dyes (rhodamine isothiocyanate (RITC) and fluorescein isothiocyanate (FITC] to albumin. Subsequent removal of all unreacted fluorescent material (UFM) was achieved using charcoal adsorption. We observed no loss of protein following charcoal treatment. The final protein conjugate was analyzed by polyacrylamide gel electrophoresis, gel chromatography, and isoelectric focusing. The conjugates were determined to be free of UFM and homogeneous with respect to molecular weight. However, FITC conjugation lowered the average isoelectric point of albumin by 0.1 to 0.3 pH units. Illustrations of combining fluorescence microscopy with FITC-BSA and RITC-BSA to view microvascular phenomena in skeletal muscle and the heart are given. Knowledge of the biochemical characteristics of the fluorochrome employed is important for proper interpretation of experimental results using this technique.

Early in reperfusion, leukocytes alter perfused coronary capillarity and vascular resistance.

Myocardial no-reflow is a critical consequence of myocardial ischemia-reperfusion (I/R). Recent studies indicate that formed blood elements (e.g., leukocytes and platelets) contribute greatly to the compromise of myocardial blood flow that occurs after I/R. To assess the contributions of leukocytes and platelets to alterations in microvascular perfusion, we measured total coronary vascular resistance and perfused coronary capillary density before and after a 30-min period of no-flow ischemia in isolated rat hearts perfused with either 1) a Krebs-albumin-red cell solution [K(2)RBC]; 2) diluted whole blood (DWB) with Krebs (1:1); or 3) leukocyte-free DWB (LFB). We found that hearts perfused with K(2)RBC before ischemia demonstrated a significant decrease in perfused capillarity (-25%, P less than 0.05) after 25 min of reperfusion. Hearts perfused with LFB before ischemia exhibited a similar decrease in perfused capillarity (-33%, P less than 0.05) during reperfusion. However, in the DWB-perfused hearts, there was a 62% decrease in perfused capillarity (-62%, P less than 0.01) during reperfusion. Moreover, during reperfusion, total coronary vascular resistance was elevated significantly (+76%, P less than 0.01) in the DWB-perfused hearts but not in either the K(2)RBC or LFB groups. These results indicate that 1) platelets do not play a major role in alterations of microvascular perfusion after ischemia; 2) leukocytes are not requisite for the development of microvascular no-reflow early in reperfusion but their presence further exacerbates this deleterious effect; and 3) a relationship exists between perfused capillarity and vascular resistance in the isolated rat heart after global ischemia.

Microvascular perfusion and transport in the diabetic heart.

Diabetes is a chronic disease of metabolic dysfunction that is increasing world-wide. The hyperglycemia associated with diabetes causes significant protein alterations and an oxidative stress. In the heart, all cell types are affected by diabetes: the myocyte, the vasculature and the blood cells. Four out of five diabetics die from ischemic heart disease and stroke, suggesting that the diabetic is quite vulnerable to ischemic injury. It is important to understand the pathophysiologic challenges that occur in the diabetic heart in order to develop thoughtful treatments to limit this serious complication. This review focuses on the anatomical and functional alterations that occur in the diabetic circulation of the heart, with emphasis on the coronary microcirculation. Coronary microvascular dysfunction combined with blood cellular alterations are presented to explain the amplified oxidative stress that occurs in the diabetic heart under ischemic conditions.

Stimulated leukocyte adhesion in coronary microcirculation is reduced by a calcium antagonist.

The first step in the acute myocardial inflammatory response is leukocyte sequestration in the coronary microcirculation. To determine the location(s) of stimulated leukocyte deposition in the coronary microcirculation and the effects of the calcium antagonist, nisoldipine, on leukocyte adhesion, leukocytes were stimulated with the chemotactic peptide, N-formylmethionyl-leucyl-phenylalanine (FMLP) and blood cell adherence was evaluated using two methods. In vitro leukostasis was evaluated by measuring the extraction of white cells in nylon fiber columns. We found that diluted whole blood (DWB) demonstrated 30% granulocyte adherence. The chemotactic peptide FMLP (1 microM) significantly increased adherence to 69%. Pretreatment of the blood with nisoldipine (1 microM) immediately before FMLP significantly reduced the FMLP-induced adhesion to 47%. In the coronary microcirculation, FMLP caused a marked increase in leukocyte sequestration, primarily in coronary capillaries. The FMLP effect was somewhat transient because the washout of trapped white cells was similar in the vehicle and FMLP groups. Nisoldipine significantly reduced the FMLP-induced leukostasis in coronary capillaries (P < 0.05). The magnitude of the attenuation of leukostasis with nisoldipine was remarkably similar in both models, suggesting a direct effect of this agent on the blood rather than on the blood vessels. These findings offer another possible mechanism by which dihydropyridine calcium antagonists may be cardioprotective under pathophysiological conditions.

A comparison of capillary hydraulic conductivities in postural and locomotor muscle.

In a comparative skeletal muscle study Folkow and Halicka (Microvasc. Res. 1: 1-14, 1968) reported that the capillary filtration coefficient (CFC) of postural (red) muscle was two times the CFC of locomotor (white) muscle. It was concluded that the twofold difference in CFC was due solely to a difference in the perfused capillary surface areas (Sf) of red vs. white muscle. However, CFC is the product of capillary hydraulic conductivity (LP) and Sf. Hence their conclusion assumed that the average LP of red muscle capillaries is exactly equal to the average LP of white muscle capillaries. The following study was undertaken to test the validity of this assumption. The microocclusion procedures and analytical model described by Lee et al. (Circ. Res. 28: 358-370, 1971) and Gore [Am. J. Physiol. 242 (Heart Circ. Physiol. 11): H268-H287, 1982] were used to determine LP. Independent measurements of LP were recorded from single capillaries in red, anterior latissimus dorsi (ALD) and white, posterior latissimus dorsi (PLD) muscles of chickens anesthetized with L.A. Thesia. We found that the mean capillary hydraulic conductivity in postural muscle [(LP)ALD = 0.20 +/- 0.06 (SE) micrometers . s-1 . cmH2O-1 (n = 11)] was significantly different from the mean capillary hydraulic conductivity in locomotor muscle [(LP)PLD = 0.061 +/- 0.01 micrometers . s-1 . cmH2O-1 (n = 14)] (P less than 0.05). These results provide direct evidence that observed differences in red vs. white muscle CFC's may not be due solely to different perfused capillary surface areas but may also be due to differences in capillary hydraulic conductivity.

Platelets do not modulate leukocyte-mediated coronary microvascular damage during early reperfusion.

Several studies indicate that leukocytes and platelets exacerbate the compromise of myocardial function that occurs after ischemia-reperfusion (I/R). However, it is unclear whether both leukocytes and platelets must be present to mediate coronary microvascular damage early during reperfusion after ischemia. To examine the effects of leukocytes and platelets on microvascular damage after I/R, we measured transcoronary albumin extravasation (O/I), perfused coronary capillary density (Caps), and transcoronary albumin extravasation per perfused capillary [(O/I)/Caps] in isolated rat hearts perfused with a Krebs-albumin-red blood cell solution [K(2)RBC], whole rat blood diluted with Krebs buffer (DWB), leukocyte-free, platelet-rich DWB (LFB), or leukocyte-rich, platelet-free DWB (LRB) before and after a 30-min period of global, no-flow ischemia. We found that in isolated hearts perfused with K(2)RBC before ischemia, O/I values were significantly increased (+68%, P < 0.01) and Caps values were significantly decreased (-25%, P < 0.05) after 25 min of reperfusion. A similar pattern of O/I values (+72%, P < 0.01) and Caps values (-40%, P < 0.05) was observed in hearts perfused with LFB. These effects were exacerbated in hearts perfused with DWB or LRB. O/I values were increased 90% (P < 0.01), and Caps values were decreased 62% (P < 0.01) in the DWB-perfused hearts. Similar increases in O/I values (+82%, P < 0.01) and decreases in Caps values (-65%, P < 0.01) were measured in the LRB-perfused hearts. Additionally, (O/I)/Caps values were significantly increased in the hearts perfused with DWB (+93%, P < 0.01) and LRB (+84%, P < 0.01) compared with the hearts perfused with K(2)RBC or LFB. These results suggest that interactions between leukocytes and platelets are not requisite for the development of coronary microvascular damage early during reperfusion after ischemia.