Both dietary fish-oil supplementation and aspirin fail to inhibit atherosclerosis in long-term vein bypass grafts in moderately hypercholesterolemic nonhuman primates.

BACKGROUND: Aortocoronary vein bypass grafts are vulnerable to late atherosclerotic occlusion. Conventional platelet inhibitor therapy provides early but not persistent protection against graft failure. Evidence suggests that consumption of marine foods may reduce cardiovascular disease, possibly because of the unique long-chain unsaturated omega-3 fatty acids present in these foods. We hypothesized that dietary fish-oil supplementation would protect against atherosclerosis in vein bypass grafts. METHODS AND RESULTS: Thirty-three moderately hypercholesterolemic cynomolgus macaques were divided into four groups: control, control+aspirin, fish oil, and fish oil+aspirin. Each control group received olive oil as placebo to equalize calorie and fat consumption with that of the fish-oil groups. Both oils were in ethyl ester form, with the fish oil providing 0.88 g/d eicosapentaenoic acid. The aspirin dose was 40 mg/d. Cephalic vein grafts were interposed bilaterally in the carotid arteries and excised for analysis at 4 years. Bleeding time was significantly prolonged in all groups receiving fish oil or aspirin (P<.05). Plasma cholesterol levels were similar among groups, averaging 6.9+/-2.4 mmol/L (267+/-94 mg/dL). The extent of atherosclerosis in vein grafts did not differ among groups as evaluated both by Sudan IV staining of intimal lipid lesions (27+/-21% of total surface area, P=.89) and analysis of cholesterol content (236+/-203 nmol/mg, 9.1+/-7.8 microg/mg, P=.85). Vein graft connective tissue composition was also unaffected by treatment. CONCLUSIONS: Our findings do not support the use of concentrated dietary fish-oil supplements or aspirin for the prevention of atherosclerosis in long-term vein bypass grafts. Consumption of fish flesh or less refined oil preparations could have effects different from those of the purified fish-oil ethyl esters we used.

Dietary fish oil decreases low-density-lipoprotein clearance in nonhuman primates.

To assess whether fish oil-induced alterations in low-density-lipoprotein (LDL) composition have distinct and important effects on LDL metabolism, we evaluated LDL kinetic behavior in cynomolgus macaques fed an atherogenic diet supplemented with either fish oil (1.6 g n-3 fatty acids; n = 10) or olive oil (n = 9) for > or = 6 mo. LDL from monkeys supplemented with fish oil or olive oil was isolated, labeled with either 125I or 131I, and simultaneously reinjected so that each monkey received its own (autologous injection) and donor (homologous injection) LDL. For LDL injected autologously (monkeys that received their own LDL), the LDL fractional clearance rate (FCR) was reduced in fish oil-supplemented monkeys compared with the olive oil-supplemented controls (0.42 +/- 0.03 compared with 0.56 +/- 0.05 pools/d, P = 0.04). The cholesteryl ester content of fish oil LDL increased compared with olive oil LDL (43 +/- 2% and 36 +/- 3%, respectively, P = 0.03), and the LDL cholesteryl ester content was strongly correlated with autologous LDL clearance (r = -0.76, P = 0.0001). Compared with olive oil LDL, fish oil LDL had a reduced dissociation constant (KD) for binding to the LDL receptor in vitro (KD for fish oil LDL compared with olive oil LDL: 13.9 +/- 1.8 and 7.4 +/- 1.0 mg LDL protein/L, P = 0.03). When both fish oil LDL and olive oil LDL were simultaneously injected into fish oil-supplemented monkeys, the FCR of fish oil LDL was decreased compared with olive oil LDL (0.42 +/- 0.03 and 0.52 +/- 0.04 pools/d, P = 0.006). These data suggest that dietary supplementation with fish oil decreases LDL clearance, and that this effect is mediated, at least in part, by altering LDL structure and reducing the affinity of LDL for its receptor.

Reactivity of human saphenous veins at arterial perfusion pressures.

Vasospasm of human saphenous vein grafts has been reported after aorta-coronary bypass operations. However, it is unknown whether veno-arterial grafts are inherently responsive to vasoconstrictor stimuli after implantation into the arterial circulation or whether their vasomotion is secondary to hemodynamic changes. Thus in this study we used in vitro methods to directly evaluate whether isolated human saphenous vein segments respond to vasoconstrictor agents at arterial pressure levels. External diameter and intraluminal flow were monitored in 12 human saphenous vein segments, which were perfused at 30 ml/min with physiologic salt solution at 90, 70, and 50 mm Hg. Increasing intraluminal pressure higher than 50 mm Hg or exposing the vein to Ca(2+)-free media did not increase vessel external diameter or intraluminal flow, which suggests that human saphenous veins were fully distended at pressures of 50 mm Hg or greater. However, all human saphenous veins were activated by a 1 mumol/L dose of norepinephrine at 50 mm Hg and dilated during subsequent intraluminal infusion of a 1 mumol/L dose of acetylcholine, showing intact vascular smooth muscle and endothelial cell function. In the same vessels, a 1 mumol/L concentration of 5-hydroxytryptamine constricted human saphenous veins by 19%, 22%, and 26% at intraluminal pressures of 90, 70, and 50 mm Hg, respectively, and reduced vessel flow by 6%, 24%, and 42% at the same pressure levels. Similarly, a 1 mumol/L concentration of norepinephrine constricted vessels pressurized at 90, 70, and 50 mm Hg by 9%, 12%, and 17%, respectively, and attenuated vessel flow by as much as 32%. We conclude that human saphenous vein segments are fully distended at perfusion pressures greater than 50 mm Hg, but can dynamically constrict to vasoactive agonists and regulate graft flow at intraluminal pressures as high as 90 mm Hg. Our findings in isolated human saphenous vein segments lend support to clinical observations that human saphenous vein grafts should be regarded as vasoactive conduits after implantation at arterial pressure levels.

Tolerance of the developing heart to ischemia: impact of hypoxemia from birth.

Many infants who require cardiac surgery have cyanotic heart disease. We assessed the relative tolerances to ischemia of hearts from immature normoxemic rabbits versus hearts from immature rabbits subjected to hypoxemia since birth. Normoxemic animals were raised from birth in an environment where the inspired fractional concentration of oxygen (FIO2) was 0.21; for the hypoxemic studies FIO2 was reduced to 0.09. Hearts (n = 6/group) from normoxemic and chronically hypoxemic rabbits at 7-12, 21-28, 35-44, and 51-56 days of age underwent aerobic "working" perfusion with Krebs bicarbonate buffer, and cardiac function was measured. Hearts were then arrested by a 3-min infusion with either cold (14 degrees C) Krebs buffer (hypothermia alone group) or St. Thomas' Hospital II solution (hypothermia plus cardioplegia group) before 6 h of hypothermic (14 degrees C) global ischemia. Hearts were reperfused, and postischemic creatine kinase leakage and recovery of function were measured. For hearts protected with hypothermia alone, recovery of aortic flow was better in hearts hypoxemic from birth compared with normoxemic controls at 7-12 days (78 +/- 7 vs. 60 +/- 6%, P < 0.05) and 21-28 days old (81 +/- 12 vs. 26 +/- 28%, P < 0.05). Protection with hypothermia plus cardioplegia was also better in hearts hypoxemic from birth compared with normoxemic controls at 7-12 days (74 +/- 8 vs. 63 +/- 10%, P < 0.05) and 21-28 days old (84 +/- 3 vs. 71 +/- 5%, P < 0.05). Protection with hypothermia alone and hypothermia plus cardioplegia was no different within chronically hypoxemic age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular effects of spinal cord stimulation in the monkey.

Because of clinical reports suggesting beneficial effects of electrical stimulation in peripheral vascular disease, studies have been conducted in the monkey. Regional blood flow was measured prior to, during and following the application of electrical currents to the spinal cord. The flow measurements were made using radioactive microspheres. In addition, tissue temperatures and venous and arterial concentrations of epinephrine and norepinephrine were measured. The results show that electrical stimulation increases blood flow to the skin and muscle. It is hypothesized that the effect is due to sympathetic inactivation secondary to the application of electrical currents.

Comparison of saphenous vein graft relaxation between Plasma-Lyte solution and normal saline solution.

Venospasm of saphenous vein grafts may damage endothelial cells and compromise early and late graft performance. Hence it is desirable to identify and use storage solutions that minimize vascular spasm during vein preparation. In view of this, we initiated isometric tension-recording studies in isolated canine and human saphenous vein to evaluate the acute, vasoactive effects of two storage solutions, Plasma-Lyte solution and normal saline solution. In initial experiments, canine saphenous veins were mounted in tissue baths containing physiologic salt solution and tonically constricted by 2 x 10(-6) mol/L norepinephrine. The physiologic salt solution in the bath was then replaced by Plasma-Lyte solution or normal saline solution containing the same norepinephrine concentration, and changes in contraction amplitude were recorded for 90 minutes. Storage in Plasma-Lyte solution at 37 degrees C completely relaxed norepinephrine-activated canine saphenous vein within 20 minutes, whereas veins remained partially constricted in normal saline solution. Both Plasma-Lyte solution and normal saline solution relaxed canine saphenous vein less at room temperature (25 degrees C) than at 37 degrees C, implying that warming of storage solutions in the operating room may promote graft dilation. To identify the mechanism by which Plasma-Lyte solution induced relaxation, we replaced its putative vasodilator components of gluconate and acetate with NaCl, but this alteration did not reduce relaxation induced by Plasma-Lyte solution. However, adding 1.6 mmol/L CaCl2 to Plasma-Lyte solution completely reversed the venodilation, suggesting that the low Ca2+ content of Plasma-Lyte solution confers its relaxant action. Finally, we tested the vasoactive effect of Plasma-Lyte solution on human saphenous vein obtained by discard from coronary bypass operations. Plasma-Lyte solution at 37 degrees C effectively dilated norepinephrine-activated human saphenous vein, inducing complete relaxation within 20 minutes. On this basis, we recommend the use of Plasma-Lyte solution as a venodilating storage solution during coronary bypass operations to optimize vein graft relaxation before implantation.

Validity of cardiac output measurement by the thermodilution method in the presence of acute tricuspid regurgitation.

Evaluation of patients with acute tricuspid insufficiency may include assessment of cardiac output by the thermodilution method. The accuracy of estimates of thermodilution-derived cardiac output in the presence of tricuspid insufficiency has been questioned. This study was designed to determine the validity of the thermodilution technique in a canine model of acute reversible tricuspid insufficiency. Cardiac output as measured by thermodilution and electromagnetic flowmeter was compared at two grades of regurgitation. The relationship between these two methods (thermodilution/electromagnetic) changed significantly from a regression slope of 1.01 +/- 0.18 (mean +/- standard deviation) during control conditions to a slope of 0.86 +/- 0.23 (p < 0.02) during severe regurgitation. No significant change was observed between control and mild regurgitation or between the initial control value and a control measurement repeated after tricuspid insufficiency was reversed at the termination of the study. This study shows that in a canine model of severe acute tricuspid regurgitation the thermodilution method underestimates cardiac output by an amount that is proportional to the level of cardiac output and to the grade of regurgitation.

Protection of the ischemic immature heart--effect of perfusate reinfusion and composition.

We determined the influence of perfusate composition and reinfusion during ischemia upon myocardial protection in the immature rabbit heart. Isolated "working" hearts (n = 6 per group) from 7-10-day-old New Zealand White rabbits were perfused with Krebs bicarbonate buffer and function measured. Hearts were then arrested with 3 minutes cold (14 degrees C) perfusion with bicarbonate buffer (as hypothermia-alone group) or St. Thomas' II cardioplegic solution (as hypothermia-plus-cardioplegia group). Hearts were then subjected to hypothermic (14 degrees C) global ischemia for 2 or 6 hours, with and without multiple reinfusion of the coronary vasculature. Following 2 hours ischemia impaired recovery of aortic flow occurred after multiple reinfusion in comparison with a single infusion with the cardioplegic solution (64 +/- 3% versus 72 +/- 4%) but not with bicarbonate buffer (79 +/- 3% versus 83 +/- 4%). However after 6 hours ischemia impaired recovery of function occurred after multiple reinfusion in comparison with single infusion both with the cardioplegic solution (60 +/- 3% versus 68 +/- 3%) and with bicarbonate buffer (57 +/- 4% versus 75 +/- 5%). There were no differences in post-ischemic creatine kinase leakage or myocardial water content between groups. These results suggest (i) that reinfusion itself, regardless of the composition of the perfusate, caused decreased recovery of function after an extended period of ischemia, and (ii) protection of the ischemic immature heart with St. Thomas' II solution remains inadequate and requires improvement.

Heparinization of biological vascular graft reduces fibrin deposition.

An alternative graft is needed for coronary bypass operations in patients lacking suitable autologous vessels. We therefore studied Denaflex, a biologic graft, in a dog ex-vivo shunt model to determine whether heparin treatment makes this graft less thrombogenic. Comparison was also made to Bioflow, a nonheparinized biologic graft. Fibrinogen deposition during high flow (593 +/- 202 ml/min) decreased from 672 +/- 467 ng/mm2 in nonheparinized Denaflex grafts to 448 +/- 298 ng/mm2 (p < 0.05) in heparinized Denaflex grafts. At low flow (117 +/- 13 ml/min), heparinization of Denaflex grafts similarly decreased fibrinogen deposition from 1102 +/- 601 ng/mm2 to 703 +/- 405 ng/mm2 (p < 0.05). At both flow rates fibrinogen deposition in Bioflow grafts was less than in nonheparinized Denaflex, but was similar to heparinized Denaflex grafts. Platelet deposition was not influenced by heparinization of Denaflex grafts and was similar among Denaflex and Bioflow preparations. Whether Denaflex performs acceptably in vivo as a xenograft requires extensive study.

Age and protection of the ischemic myocardium: is alkaline cardioplegia appropriate?

Hypothermic alkaline pharmacologic cardioplegia used in pediatric cardiac surgery may be less than satisfactory despite its benefits in adults. We determined whether the pH (7.8) of standard St. Thomas' II cardioplegic solution contributes to inadequate protection of the ischemic immature heart and whether the effect is age-related. Modified hypothermic St. Thomas' II solution (pH range, 4.8 to 8.8) was compared with hypothermic bicarbonate buffer alone (pH 7.25) in protecting the ischemic immature (7 to 10 days old) and mature (12 months old) rabbit heart. Isolated hearts (n = 6 per group) were perfused with bicarbonate buffer, and aortic flow was measured before hypothermic (14 degrees C) ischemia (immature hearts: 4 hours; mature hearts: 3 hours). Hearts were reperfused, and enzyme leakage and recovery of function were measured. In the immature heart, a bell-shaped dose-response profile was observed for pH and recovery of aortic flow but not for postischemic creatine kinase leakage. Optimal recovery of aortic flow (98% +/- 3%) occurred at pH 6.8, which was greater than protection with hypothermia alone (82% +/- 4%; p < 0.05) and standard St. Thomas' II solution (72% +/- 2%; p < 0.05). In the mature heart, a bell-shaped dose-response curve existed for recovery of aortic flow and a U-shaped curve existed for creatine kinase leakage. Again, optimal recovery of aortic flow (84% +/- 5%), which was superior to that with standard St. Thomas' II solution (60% +/- 8%; p < 0.05), and minimal enzyme leakage also occurred at pH 6.8, as did the least enzyme leakage (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The lack of effect of hemodilution, myocardial water content, and increased coronary artery blood flow on integrated myocardial ultrasonic backscatter in the beating canine heart.

The effects of coronary blood flow, tissue water content and hematocrit variation on the Integrated Myocardial Backscatter Rayleigh 5 (IBR5) and Fourier coefficient of amplitude modulation (FAM, an index of cardiac cycle-dependent variation in IBR5) were measured in five open chest dogs. Data were obtained at baseline, during adenosine infusion and after two hours of crystalloid hemodilution (Hct 15%). IBR5 of -46.4 +/- .94 dB at baseline did not change significantly during adenosine infusion (-45 +/- .85 dB) and after hemodilution (-46.4 +/- 2.0 dB). FAM at baseline was (4.0 +/- 1.0 dB) (3.8 +/- -1.0 dB) during adenosine infusion and after hemodilution (5.0 +/- 1.8 dB). Myocardial water content increased significantly (p < .05) from 78 +/- .20% at baseline to 80.7 +/- .17% after hemodilution. Coronary blood flow demonstrated a three-fold increase with adenosine and two-fold increase with hemodilution. Electronmicroscopy demonstrated an increase in intracellular and extracellular water content. In conclusion, IBR5 and FAM did not change significantly despite significant increases in coronary blood flow and myocardial water content. Myocardial cellular derangements seen with nonischemic cell swelling, increased blood flow and a fall in hematocrit are insufficient to affect integrated backscatter.

The effect of ambient temperature on papaverine-induced relaxations in canine saphenous veins.

This study was designed to measure the effect of ambient temperature (25 degrees C) on papaverine-induced relaxations in canine saphenous veins. Segments of vein were suspended in water-jacketed tissue baths at 37 degrees C, and isometric tension was recorded. After equilibration, veins were preconstricted by a median effective dose of norepinephrine 2 x 10(-6) mol/L at either 25 degrees C or 37 degrees C. Consequent dose-dependent relaxations showed that papaverine (10(-7) to 10(-3) mol/L was three times more potent as a dilator at 37 degrees C than at 25 degrees C, with half-maximal relaxations occurring at 2.2 x 10(-5) mol/L and 6.4 x 10(-5) mol/L, respectively. A 10(-4) mol/L dose of papaverine completely relaxed veins at 37 degrees C, whereas veins at 25 degrees C never fully relaxed even at ten times the standard concentration. In addition, the time for half-maximal relaxation with a 10(-4) mol/L dose of papaverine averaged 40 minutes at 25 degrees C compared with 22 minutes at 37 degrees C; this is indicative of a reduced relaxation rate at the lower temperature. These data show that papaverine is a slower and less potent dilator of canine saphenous veins at 25 degrees C than at 37 degrees C. This may have implications for the use of papaverine in the operating room, where it is usually applied at ambient temperature to reduce vasospasm of the saphenous vein during coronary artery bypass procedures.

Effects of storage solutions on contraction and relaxation of isolated saphenous veins.

Saphenous veins are placed frequently in storage solutions before use as coronary bypass grafts. Controversy remains regarding which solution is optimal for the preservation of endothelium and vascular smooth muscle viability. Thus, this study measured the effect of four different storage solutions on saphenous vein smooth muscle and endothelial cell function. Saphenous vein segments from five baboons were stored for 3 h in one of four storage solutions consisting of physiological salt solution (PSS), University of Wisconsin solution (UWS), normal saline solution (NSS), or autologous whole blood (WB). Following storage, veins were suspended for isometric tension recording in tissue baths filled with PSS. Veins stored in PSS, UWS, and NSS showed similar contractile amplitude and agonist sensitivity to norepinephrine (10(-8) -10(-4) M) and KCl (20-100 mM). However, veins stored in WB contracted 31% less to KCl on average than those stored in the other three solutions (p < 0.05). The direct vascular muscle vasodilator, papaverine (10(-7) -10(-4) M), and the endothelium-dependent dilator, A23187 (10(-5) M), relaxed all vein preparations equally well. These results suggest that after storage in PSS, UWS, and NSS, contractile and relaxant vascular responses are similar in isolated saphenous veins. However, although veins stored in WB show comparable relaxation responses, they demonstrate an impaired vascular contraction immediately after storage. We conclude that storage of veins in blood may immediately modify vascular smooth muscle function.

Atherogenic effect of barotrauma on in situ saphenous veins in monkeys.

The objectives of this study were to determine whether veins subjected to barotrauma in situ undergo lipid uptake and morphologic changes to the same extent as veins grafted into the arterial circulation. Saphenous veins in seven stump-tailed macaque monkeys were exposed bilaterally and were circumferentially dissected free from surrounding tissue only at isolated sites. Segments of the veins were distended for 1 minute at hydrostatic pressures of 125 or 350 mm Hg. An undistended segment served as control. A cephalic vein graft was interposed in the femoral artery for comparison with in situ veins. The animals were fed a diet that sustains plasma cholesterol levels of approximately 225 mg/dl. Saphenous veins and the cephalic vein grafts were explanted at 3 months for biochemical and histologic analyses. Cholesterol content in undistended saphenous veins was similar to that in veins distended at 125 or 350 mm Hg--105 +/- 15, 122 +/- 14, and 109 +/- 30 micrograms/100 mg wet tissue weight, respectively. Cholesterol content in cephalic vein grafts, 473 +/- 122 micrograms/100 mg, was greater (p less than 0.001) than in saphenous veins at all distention pressures studied. There was no difference among the distention pressures in the intimal fraction of saphenous vein wall, with the pooled value being 20% +/- 12%. This contrasted with the value of 59% +/- 11% in cephalic vein grafts (p less than 0.01). Endothelial coverage of the luminal surface in saphenous veins was similar among the levels of barotrauma, with the pooled value being 83% +/- 15%. Less of the lumen was covered with endothelium in cephalic vein grafts, 46% +/- 18% (p less than 0.01). Slightly more medial fibrosis was observed in cephalic vein grafts as compared with saphenous veins (p less than 0.05). These data demonstrate that barotrauma alone does not cause veins that remain in the venous system to undergo the lipid uptake or morphologic changes that occur in veins grafted into the arterial circulation in nonhuman primates.

Acute, reversible tricuspid insufficiency: creation in canine model.

Relatively few methods have been described for the creation of valvular insufficiency in an animal model. Those presented involve limitations such as permanent destruction of the valves or lack of control over the degree of regurgitation produced. We describe a method of acute reversible tricuspid insufficiency that can be easily created and controlled in anesthetized dogs. The model employs a wire spiral that is advanced through the atrioventricular canal from the right atrium. The spiral causes regurgitation by preventing complete apposition of the valve leaflets while permitting retrograde flow to occur through the spiral lumen. The degree of regurgitation can be controlled by the use of spirals of different sizes. Creation of tricuspid insufficiency is demonstrated by the onset of right atrial pressure V waves, a "ballooning" of the right atrium during ventricular systole, palpation of an atrial thrill, or by color Doppler echocardiography. In 14 dogs, right atrial pressure increased from a control value of 9 +/- 3 (mean +/- SD) mmHg to 10 +/- 3 and 12 +/- 3 mmHg, respectively, with spirals of 1.5 and 2.2 cm in diameter (both P less than 0.05). With the 2.2-cm spiral, aortic blood pressure decreased from a control value of 104 +/- 20 to 83 +/- 17 mmHg (P less than 0.05), and cardiac output decreased from 73 +/- 26 to 59 +/- 19 ml.min-1.kg-1 (P less than 0.05). This model is reversible, allows repeated trials of various grades of regurgitation, does not require ventriculotomy, and is relatively nonarrhythmogenic.

Cardioplegia-induced damage to ischemic immature myocardium is independent of oxygen availability.

The known benefits of hypothermic pharmacological cardioplegia in protecting the ischemic adult heart may not extend to children. Protection of the ischemic immature rabbit heart with hypothermic Krebs-Henseleit bicarbonate buffer is better than with hypothermic St. Thomas' II cardioplegic solution. We investigated whether the availability of oxygen in the preischemic perfusate is responsible for the increased tolerance to ischemia of immature (7- to 10-day-old) hearts perfused with Krebs buffer in comparison with St. Thomas' II solution immediately before ischemia. After obtaining preischemic control data in the "working" mode, we perfused hearts (n = 8 per group) for 3 minutes with hypothermic (14 degrees C) Krebs buffer or hypothermic St. Thomas' II solution saturated with 0%, 25%, or 95% oxygen. This was followed by 2 hours of global ischemia at 14 degrees C. Hearts were reperfused for 15 minutes in the Langendorff mode and 35 minutes in the working mode, and recovery of function was measured. For preischemic oxygen concentrations of 0%, 25%, and 95%, recovery of aortic flow in hearts protected by hypothermia alone during ischemia was 74% +/- 9%, 82% +/- 4%, and 99% +/- 2% of preischemic values, respectively. In hearts protected by hypothermia plus cardioplegia, the values were 69% +/- 6%, 72% +/- 3%, and 86% +/- 5%, respectively. Thus, at equal oxygen concentrations, recovery of postischemic function was better in hearts protected by hypothermia alone compared with hypothermia plus cardioplegia. We conclude that factors other than oxygen availability are responsible for the damaging effect of St. Thomas' II solution on the ischemic immature rabbit heart.

Histologic, morphometric, and biochemical evolution of vein bypass grafts in a nonhuman primate model. III. Long-term changes and their modification by platelet inhibition with aspirin and dipyridamole.

The objectives of this study were to elucidate the long-term influence on vein bypass grafts of platelet inhibition and its late discontinuation. Cephalic vein grafts were interposed bilaterally in the femoral arteries of stump-tailed macaque monkeys fed a diet that sustains plasma cholesterol levels of approximately 225 mg/dl. Fifteen animals were divided into three groups of five animals each. Group I received no medications and served as a control group. Group II received for the full duration of the study a combination of aspirin, 80 mg/day, and dipyridamole, 50 mg/day. Group III received the same regimen of platelet inhibition as in group II during the first 9 months, but were not treated during the subsequent 9-month interval. Grafts were excised for analysis from groups I and II at both 9 and 18 months and from group III at 18 months. Cholesterol content in group I grafts was 470 +/- 89 micrograms/100 mg at 9 months and 388 +/- 127 micrograms/100 mg at 18 months. In group II grafts, cholesterol content was 208 +/- 72 micrograms/100 mg at 9 months (p less than 0.001 compared with group I) and 266 +/- 84 micrograms/100 mg at 18 months. In group III grafts, cholesterol content was 249 +/- 71 micrograms/100 mg at 18 months. Differences in cholesterol content among the three groups of grafts at 18 months were not found to be statistically significant. Stepwise regression analysis at 18 months showed that cholesterol content was best predicted by medial fibrosis (r2 = 0.66) followed by abundance of foam cells (increase in r2 = 0.26) in group I, by fibrin in group II (r2 = 0.63), and by prevalence of macrophages in group III (r2 = 0.74). In all groups, platelets, fibrin, and polymorphonuclear leukocytes were less abundant than they had been at 3 months. Cross-sectional area occupied by the intima was not influenced by platelet inhibition.

Is protection of ischemic neonatal myocardium by cardioplegia species dependent?

Hypothermia combined with pharmacologic cardioplegia protects the globally ischemic adult heart, but this benefit may not extend to children, resulting in poor postischemic recovery of function and increased mortality. The relative susceptibilities to ischemia modified by hypothermia alone and by hypothermia plus cardioplegia were assessed in isolated perfused neonatal (3- to 4-day-old) rabbit and pig hearts. Hearts were perfused aerobically with Krebs buffer solution in the working mode for 30 minutes and aortic flow was recorded. This was followed by 3 minutes of hypothermic (14 degrees C) coronary perfusion with either Krebs or St. Thomas' Hospital cardioplegic solution No. 2 followed by hypothermic (14 degrees C) global ischemia (rabbits 2, 4, and 6 hours; pigs 2 and 4 hours). Hearts were reperfused for 15 minutes in the Langendorff mode and 30 minutes in the working mode, and recovery of postischemic aortic flow was measured. Hypothermia alone provided excellent protection of the ischemic neonatal rabbit heart, with recovery of aortic flow after 2 and 4 hours of ischemia at 91% +/- 4% and 87% +/- 5% (mean +/- standard deviation) of its preischemic value. Recovery after 6 hours of ischemia was depressed to 58% +/- 9% of its preischemic value. Ischemic neonatal pig hearts protected with hypothermia alone recovered 94% +/- 3% of preischemic aortic flow after 2 hours; none was able to generate flow after 4 hours. St. Thomas' Hospital solution No. 2 decreased postischemic aortic flow after 4 hours of ischemia in rabbit hearts from 87% +/- 5% to 70% +/- 7% (p less than 0.05, hypothermia alone versus hypothermia plus cardioplegia) but improved postischemic recovery of aortic flow in pig hearts after 4 hours of ischemia from 0 to 73% +/- 13% (p less than 0.0001, hypothermia alone versus hypothermia plus cardioplegia). This effect was dose related in both species. We conclude that the neonatal pig heart is more susceptible to ischemia modified by hypothermia alone than the neonatal rabbit and that St. Thomas' Hospital solution No. 2 improves postischemic recovery of function in the neonatal pig but decreases it in the neonatal rabbit. This species-dependent protection of the neonatal heart may be related to differences in the extent of myocardial maturity at the time of study.

Histologic, morphometric, and biochemical evolution of vein bypass grafts in a nonhuman primate model. II. Modification of early changes by platelet inhibition with aspirin and dipyridamole.

The objective of this study was to determine the early influence of platelet inhibition on the histologic, morphometric, and biochemical evolution of vein bypass grafts in a nonhuman primate model. Cephalic vein grafts were interposed bilaterally in the femoral arteries of 15 stump-tailed macaque monkeys fed a diet that sustains plasma cholesterol levels of approximately 225 mg/dl. All animals received in combination aspirin, 80 mg/day, and dipyridamole, 50 mg/day. Grafts were excised from five animals for analysis on each of postoperative days 3, 7, 14, 30, 60, and 90. In animals subjected to platelet inhibition, cholesterol content in the graft was 170 +/- 52 micrograms/100 mg at 90 days, 205% of the level in ungrafted vein (p less than 0.01). This change was small in comparison with the increase to 686% of ungrafted vein observed in our study of control animals. In stepwise regression analysis, cholesterol content of grafts was best predicted by prevalence of foam cells (r2 = 0.82), and the proportion of intima as a fraction of total wall area was best predicted by the presence of macrophages (r2 = 0.69). Platelet inhibition did not decrease the extent of intimal hyperplasia. The prevalence of adherent platelets (r = -0.72) and the amount of fibrin (r = -0.78) correlated inversely with the amount of endothelium present during the first 14 days. The strength of these correlations declined with time, despite persistent lack of endothelium in some areas. Medial fibrosis occurred to the same extent as in control grafts, as did the early appearance of platelet factor VIII and fibronectin and the lack of vasa vasorum at 3 days followed by reappearance at 7 days. These data demonstrate that platelet inhibition dramatically reduces lipid uptake by grafts in the first 90 days but has less influence over histologic or morphometric changes.

Histologic, morphometric, and biochemical evolution of vein bypass grafts in a nonhuman primate model. I. Sequential changes within the first three months.

The objective of this study was to define the histologic and morphometric evolution that accompanies the increase in cholesterol content of vein bypass grafts in a nonhuman primate model. Cephalic vein grafts were interposed bilaterally in the femoral arteries of 15 stump-tailed macaque monkeys (Macaca arctoides), which were fed a diet that sustains plasma cholesterol levels of approximately 225 mg/dl. Grafts were excised from five animals for analysis on each of postoperative days 3, 7, 14, 30, 60, and 90. Cholesterol content increased from 69 +/- 24 micrograms/100 mg (mean +/- standard deviation) in ungrafted vein to 473 +/- 122 micrograms/100 mg in grafts 90 days after implantation (p less than 0.05). By stepwise regression analysis, cholesterol content was best predicted by abundance of foam cells (r2 = 0.82). Intima comprised 13% +/- 5% of the total cross-sectional area of the wall in ungrafted vein and 59% +/- 11% at day 90 (p less than 0.001). With cholesterol content excluded from the stepwise regression, intimal area was best predicted by the presence of foam cells (r2 = 0.39). There was consistently an increase in the prevalence of polymorphonuclear leukocytes on the luminal surface and in both the intima and media during the first 14 days after grafting. Vasa vasorum, which were always present in ungrafted vein, were sparse at 3 days but reappeared by day 7. Medial fibrosis occurred in grafts, and in the 30- to 90-day interval it was directly correlated with the number of adventitial vasa vasorum present (r = 0.64, p less than 0.05). Immunohistochemistry revealed prominent staining for both platelet factor VIII and fibronectin during the first month, with a gradual decline in staining intensity thereafter. The evolution of changes in vein bypass grafts documented in this report are in general agreement with graft changes observed in humans and support the validity of our model in evaluating the histologic correlates of increased graft cholesterol content.