Myocardial VEGF expression after cardiopulmonary bypass and cardioplegia

BACKGROUND

Vascular endothelial growth factor (VEGF) is a heparin-binding glycoprotein that plays a critical role in angiogenesis, vascular remodeling, and regulation of vascular tone and permeability. Because myocardial and peripheral edema and systemic hypotension occur frequently after cardiac operations, we examined the effects of cardiopulmonary bypass (CPB) and cardioplegia on gene expressions of VEGF protein and the VEGF tyrosine kinase receptor flk-1 and coronary vascular responses to VEGF.

METHODS AND RESULTS

Pigs (n = 6) were placed on normothermic CPB and hearts were arrested for 1 hour with a hyperkalemic, cold blood cardioplegic solution. Pigs were then separated from CPB and perfused off CPB for an additional 2 hours. Myocardial and skeletal muscle specimens were obtained for Northern analysis of VEGF protein, flk-1 receptor, and basic fibroblast growth factor (bFGF) mRNA before CPB and after 2 hours of reperfusion. Isolated, precontracted coronary arterioles in pre-CPB dilated potently to exogenous VEGF (dilation = 26 +/- 4% of precontraction at 10(-12) mol/L VEGF). Cardioplegia-reperfusion was associated with a 4 +/- 2-fold (P < 0.05 vs pre-CPB) increase in myocardial VEGF protein mRNA, whereas no similar increase was observed in the skeletal muscle. Flk-1 mRNA was increased 6 +/- 3-fold (P < 0.05 vs pre-CPB) after reperfusion, whereas it was unchanged in the skeletal muscle. Relaxations of precontracted coronary arterioles to VEGF were significantly increased (40 +/- 6% at 10(-12) mol/L, P < 0.05 vs pre-CPB) after 2 hours of reperfusion, but those to the endothelium-dependent vasodilator ADP and the endothelium-independent vasodilator nitroprusside were not changed, suggesting that the VEGF receptors remain intact and function is selectively upregulated. In contrast, relaxation responses of microvessels to bFGF were not altered after cardioplegia-reperfusion, and there was no increase in bFGF mRNA in either myocardium or skeletal muscle.

CONCLUSIONS

This study shows that VEGF protein and its flk-1 receptor gene expressions are selectively increased and the potent VEGF-induced vascular responses are enhanced in the coronary microcirculation after blood cardioplegia. The respective parameters are unchanged in the skeletal muscle after normothermic CPB. These findings may have important implications regarding postoperative coronary blood flow regulation, increases in myocardial edema, and vascular remodeling after cardioplegia-reperfusion.

Effects of ischemic preconditioning on myocardial perfusion, function, and microvascular regulation

BACKGROUND

Ischemic preconditioning (PC) has been advocated as a method to preserve myocardial function and perfusion during minimally invasive direct coronary bypass (MIDCAB). We examined the effects of PC on indexes of myocardial function, perfusion, and endothelial and beta-adrenergic coronary regulation after 30 minutes of ischemia and 60 minutes of reperfusion (IR).

METHODS AND RESULTS

Five groups of pigs were studied: (1) PC-IR: PC by 3 cycles of 5-minute left anterior descending coronary artery occlusion (CO) and 5-minute reperfusion (Rep) + 30 minutes of CO + 60 minutes of Rep; (2) IR alone: 30 minutes of CO + 60 minutes of Rep; (3) PC alone; (4) PC-IR-glibenclamide (GLIB): PC-IR + infusion of GLIB; (5) control: noninstrumented. Reactivity (in vitro) of coronary arterioles (70 to 150 microns) from the myocardial area at risk was examined with video microscopy. beta-Adrenergic microvascular relaxations to isoproterenol, forskolin, and 8-bromo-cAMP were significantly reduced after IR alone (P < 0.05 versus control, 2-way ANOVA). PC before IR restored these responses to normal (P < 0.05 PC-IR versus IR alone), and GLIB abolished this effect of PC. Subepicardial endothelium-dependent microvascular relaxation to ADP was significantly reduced after IR alone (P < 0.01 versus control) but was preserved in both the PC-IR and PC-IR-GLIB groups (P < 0.05 versus IR alone). The response of vessels to ADP from the subendocardium was significantly reduced in all groups compared with the control response (all P < 0.05 versus control). Nitroprusside elicited a similar response in vessels from all groups. PC before IR did not affect the reduced myocardial percent segmental shortening or left ventricular maximal dP/dt, did not affect myocardial perfusion in the subepicardium or subendocardium, and did not change expression of the inducible or the constitutively expressed isoforms of nitric oxide synthase.

CONCLUSIONS

PC before IR preserves beta-adrenergic signal transduction in coronary smooth muscle through a KATP channel mechanism, whereas PC preserves endothelium-dependent relaxation in the subepicardium through a mechanism not related to KATP channels or the enhanced expression of nitric oxide synthase. Nevertheless, PC does not improve short-term myocardial function or baseline myocardial perfusion after IR. Thus, the short-term beneficial role of PC in myocardial protection during MIDCAB may be limited.

VEGF administration in chronic myocardial ischemia in pigs

OBJECTIVE

Previous investigations have shown the effectiveness of sustained intra- or extravascular administration of vascular endothelial growth factor (VEGF) in chronic myocardial ischemia in improvement of left ventricular function. The present investigations were undertaken in order to evaluate efficacy of a single bolus or local intracoronary delivery.

METHODS

Yorkshire pigs underwent placement of a left circumflex artery ameroid occluder. Three weeks later the animals were randomized to treatment with VEGF (20 micrograms) accomplished by local intracoronary delivery system (InfusaSleeve, n = 10), intracoronary bolus infusion (n = 7) or by epicardial implantation of an osmotic delivery system (n = 7). An additional group of animals received intracoronary administration of saline and served as a control (n = 9). Three weeks after initiation of therapy, the animals were evaluated with regard to myocardial perfusion and global as well as regional ventricular function.

RESULTS

All three VEGF treatment groups but not the control animals demonstrated a significant increase in the left-to-left (but not right-to-left) collateral index, myocardial blood flow (pre-therapy LCX vs. LAD (average of all groups): 0.76 +/- 0.35 vs. 0.96 +/- 0.38 ml*min-1*g-1, p = 0.03; post-therapy: LCX vs. LAD: 1.16 +/- 0.39 vs. 1.15 +/- 0.28 ml*min-1*g-1, p = NS) and coronary vasodilatory reserve 3 weeks after growth factor administration. The observed increase in VEGF-induced perfusion correlated with improvement in regional ventricular function in all VEGF-treated groups (pre-therapy vs. post-therapy: i.c. VEGF 20 +/- 5.1 vs. 33 +/- 4.8; local VEGF 16 +/- 2.8 vs. 33.6; pump VEGF 17 +/- 3.8 vs. 34 +/- 4.9 p < 0.05 for all) but not control animals (21 +/- 3.3 vs. 27 +/- 5.8, p = NS).

CONCLUSION

Single intracoronary delivery (intravascular bolus or local delivery) of VEGF is effective in stimulating physiologically significant angiogenesis in porcine model of chronic myocardial ischemia.

Effects of coronary artery disease on expression and microvascular response to VEGF

The effects of coronary artery disease (CAD) on human coronary microvascular responses to vascular endothelial growth factor (VEGF) and the alterations of the myocardial expressions of VEGF and its flk-1 and flt-1 receptors were examined in 48 patients. Microvascular studies were performed in vitro with video microscopy. The expressions of VEGF and its receptors were examined using Northern analysis of total mRNA, and the expressions of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) were examined by RT-PCR. VEGF and hepatocyte growth factor (HGF) caused potent relaxations of microvessels. These responses were reduced in the presence of NG-nitro-L-arginine and the tyrosine kinase inhibitor genistein or in microvessels from patients with CAD. Relaxations to substance P and sodium nitroprusside were similar in both groups. The substance P response was abolished in the presence of NG-nitro-L-arginine. The expression of VEGF and its receptors and the expression of cNOS and iNOS were not altered in patients with CAD. In conclusion, VEGF and HGF elicit the release of nitric oxide through activation of tyrosine kinase receptors. CAD is associated with reduced vascular responses to both VEGF and HGF; this is not likely due to a reduced expression of VEGF or flt-1 or flk-1 receptors and not due to a generalized endothelium dysfunction despite the presence of mild hypercholesterolemia in these patients with CAD. These findings may have important implications regarding the efficacy of endogenous and exogenous VEGF in patients with risk factor for CAD.

Flow-induced dilation of rat coronary microvessels is attenuated by isoflurane but enhanced by halothane

BACKGROUND

Volatile anesthetics attenuate agonist-induced endothelium-dependent vasodilation of coronary arteries. This study considered the hypothesis that the anesthetics may also attenuate flow-induced endothelium-dependent vasodilation.

METHODS

Rat subepicardial arteries of approximately 100 microm were monitored for diameter changes in vitro by a video detection system, with the midpoint luminal pressure held constant at 40 mmHg but the pressure gradient (and therefore flow) across each vessel increased from 0 to 80 mmHg, in the presence or absence of 1 or 2 minimum alveolar concentration (MAC) isoflurane or 1 or 2 MAC halothane, with or without 10 microM of the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) or 10 microM of the cyclooxygenase inhibitor indomethacin.

RESULTS

Flow-induced dilation was attenuated by L-NNA or indomethacin (p < 0.001 each). It was attenuated by isoflurane in a concentration-dependent manner (P < 0.001). Attenuation by 2 MAC isoflurane persisted even in the presence of L-NNA (P < 0.01) or indomethacin (P < 0.05). On the other hand, flow-induced dilation was enhanced by 2 MAC halothane (P < 0.05). Halothane at 1 MAC had no significant effect. Enhancement by 2 MAC halothane was evident in the presence of indomethacin (P < 0.05) but not L-NNA (P = 0.40).

CONCLUSIONS

In rat subepicardial arteries, flow-induced dilation is endothelium-dependent and mediated by both NO and a prostanoid. Isoflurane attenuates flow-induced dilation, possibly by decreasing synthesis, the action of NO and a prostanoid, or both, whereas halothane enhances it, possibly by increasing synthesis, the action of NO, or both.

Chronic atrial lead explantation using a staged percutaneous laser and open surgical approach

We report a staged approach to the explantation of a passive fixation atrial lead 4 years after implantation in a patient with extracardiac J wire protrusion. The body of the lead, from the venous entry site to the proximal electrode, was freed from extensive fibrous binding using an investigational Excimer laser lead extraction sheath. The distal end and J wire were freed and the lead was removed at thoracotomy. This staged approach offered a safe and effective method for the removal of a heavily fibrosed chronic endocardial lead.

Therapeutic angiogenesis with basic fibroblast growth factor: technique and early results

BACKGROUND

Patients not amenable to complete myocardial revascularization by conventional methods present a difficult clinical problem. Here we present the early results and technical considerations of the administration of basic fibroblast growth factor for the induction of collateral growth using heparin-alginate slow-release devices in patients undergoing coronary artery bypass grafting.

METHODS

Eight patients were enrolled. Patients were candidates if they had at least one graftable obstructed coronary artery and at least one major arterial distribution not amenable to revascularization, a serum creatinine level less than 3 mg/dL, ejection fraction greater than 0.20, and estimated operative mortality of less than 25%. During conventional coronary artery bypass grafting, 10 heparin-alginate devices, each containing either 1 microg or 10 microg of basic fibroblast growth factor, were implanted in the epicardial fat in multiple regions of the unrevascularizable territory and also in the distal distribution of a grafted or patent artery.

RESULTS

There was no mortality and no evidence of renal, hematologic, or hepatic toxicity during follow-up. Three months after the operation, all patients remain free of angina. Seven patients were examined with stress perfusion scans. Three patients had clear enhancement of perfusion to the unrevascularized myocardium, 1 patient had a new fixed defect, and 3 had minimal overall change but had evidence of new small, fixed perfusion defects. Seven patients had improved or similar myocardial contractile function (ejection fraction at 3-month follow-up = 0.53 +/- 0.22 versus 0.47 +/- 0.14 preoperatively). One patient suffered a perioperative myocardial infarction in the area of basic fibroblast growth factor administration.

CONCLUSIONS

This preliminary study demonstrates the safety and technical feasibility of therapeutic angiogenesis with basic fibroblast growth factor delivered by heparin-alginate slow-release devices. Further studies examining the safety, clinical efficacy, and long-term results are ongoing.

Clotrimazole is a potent vasodilator of the rat coronary microcirculation

Clotrimazole (CLT), used in the treatment of patients with sickle cell disease, directly blocks Ca2+-activated K+ (K+<INF POS="STACK">Ca) channels in red cells and in portal vein smooth muscle cells by a cytochrome P450(cyt P450)-independent mechanism. Therefore, we examined the effects of CLT on vasomotor tone of coronary arterioles. Rat coronary arterioles (80-180 micro(m) in diameter) were studied in vitro in a pressurized no-flow state with a video microscopy. CLT (0.1 micromol/L) elicited in nonprecontracted vessels a small contraction (<10% baseline diameter, P < 0.05 vs time control), consistent with blockade of a hyperpolarizing K+ channel. However, similar contraction was produced by the cyt P450 blocker 17-octadecynoic acid (17-ODYA, 100 micromol/L), suggesting possible involvement of arachidonate metabolites of cyt P450. In contrast, microvessels precontracted with the thromboxane A2 analog U46619 dilated in response to CLT [>90% relaxation of the U46619-induced precontraction at 100 micromol/L (P < 0.01 vs time control)] and its structural analogs flutrimazole (FLT), UR-4055, UR4057, UR-4058, and UR-4059. This relaxation was cyt P450-independent, since the in vivo CLT metabolite (CLT-carbinol) was equipotent with CLT, and 17-ODYA did not promote relaxation. CLT-induced dilation was not inhibited by the nitric oxide synthase inhibitor NGnitro-l-arginine (100 micromol/L, P > 0.5) or affected by endothelial denudation (P > 0.5). Thus, CLT at concentrations >1 micromol/L is a potent vasodilator of rat coronary arterioles. This dilation is likely mediated through a vascular smooth muscle mechanism independent of cyt P450 and is not modulated by nitric oxide or by the endothelium. This effect may arise from CLT's reported ability to inhibit voltage-gated Ca2+ channels or to inhibit, in some tissues, Ca2+ release from intracellular stores. The CLT- and FLT-induced relaxation may be a property common to this class of drugs and have clinical applicability.

Angiogenic potential of perivascularly delivered aFGF in a porcine model of chronic myocardial ischemia

A number of heparin-binding growth factors, including basic (bFGF) and acidic (aFGF) fibroblast growth factors have been shown to promote angiogenesis in vivo. In this study, we employed a sustained-release polymer extravascular delivery system to evaluate the angiogenic efficacy of a novel form of genetically modified aFGF in the setting of chronic myocardial ischemia. Fifteen Yorkshire pigs subjected to Ameroid occluder placement on the left circumflex (LCX) artery were treated with perivascularly administered aFGF in ethylene vinyl acetate (EVAc) polymer (10 micrograms, n = 7) or EVAc alone (controls, n = 8). Seven to nine weeks later, after coronary angiography to document Ameroid-induced coronary occlusion, all animals underwent studies of coronary flow and global and regional left ventricular function. Microsphere-determined coronary flow in the Ameroid-compromised territory was significantly increased in aFGF-treated compared with control animals, and this improvement in perfusion was maintained during ventricular pacing. Left ventricular function studies demonstrated improved global and regional function in aFGF-treated animals. We conclude that local perivascular delivery of genetically modified aFGF results in significant improvement in myocardial flow and regional and global left ventricular function.

Mesenteric and skeletal muscle microvascular responsiveness in subacute sepsis

This study was performed to assess the effects of subacute sepsis in rats on the in vitro reactivity of arterioles (internal diameter, 100-150 microm) to alpha1- and alpha2-adrenergic stimulation and to angiotensin II. Male Sprague-Dawley rats were rendered septic by intraperitoneal implantation of a gelatin capsule containing sterile rat feces and 1 x 10(6) viable colony forming units of Escherichia coli. Control rats underwent sham laparotomy and implantation of a gelatin capsule containing only sterile feces. In vitro reactivity of arterioles from mesentery and skeletal muscle were studied 48 h later in a pressurized (50 mmHg) no flow state using videomicroscopy. Subacute sepsis decreased the contractile response of nonprecontracted microvessels from both anatomical sites to phenylephrine (both p < .01 versus control) and blunted the relaxation response to staurosporine (both p < .01), an inhibitor of protein kinase C. The small contraction to angiotensin II of mesenteric vessels was inhibited by sepsis (p < .05) but was unaltered in the skeletal muscle microcirculation. In the precontracted mesenteric microvessels from septic rats, endothelium-dependent relaxation to clonidine and to adenosine 5'-diphosphate were decreased (both p < .01 versus control), whereas in skeletal muscle microvessels, clonidine and adenosine 5'-diphosphate elicited constriction (both p < .01). Relaxation to the endothelium independent vasodilators sodium nitroprusside and pinacidil was preserved across all vessels. In conclusion, mesenteric and skeletal muscle microvascular responses to angiotensin II and alpha1- and alpha2-adrenergic stimulation are altered in subacute sepsis. This may in part lead to systemic hypotension and altered organ perfusion during states of chronic sepsis.

Epithelial dependence of the bronchodilatory effect of sevoflurane and desflurane in rat distal bronchi

The bronchial epithelium releases substances that enhance bronchodilation in response to certain bronchodilators. We examined the hypothesis that the bronchodilatory effect of desflurane and sevoflurane depends on the epithelium in rat distal bronchial segments. Wistar rat subsegmental bronchial segments (diameter approximately 100 microm) were dissected. After preconstriction with 5-hydroxytryptamine, each segment was exposed to increasing concentrations of desflurane 0%-12% or sevoflurane 0%-4.8% under four conditions: after epithelial rubbing, after pretreatment with the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (L-NNA), after pretreatment with the cyclooxygenase inhibitor indomethacin, or with no preintervention (control). Changes in bronchial diameter were monitored using an in vitro video detection system. Both desflurane and sevoflurane produced concentration-dependent bronchodilation (P < 0.001 for either anesthetic; 54% +/- 8% [mean +/- SD] dilation for 12% desflurane and 48% +/- 14% dilation for 4.8% sevoflurane). For both anesthetics, bronchodilation was significantly attenuated by epithelial rubbing (15% +/- 4% dilation for 12% desflurane and 13% +/- 10% dilation for 4.8% sevoflurane; P < 0.001 each), by pretreatment with indomethacin (12% +/- 3% dilation for 12% desflurane and 9% +/- 5% dilation for 4.8% sevoflurane; P < 0.001 each), and by L-NNA (24% +/- 8% dilation for 12% desflurane, P < 0.001; and 17% +/- 10% dilation for 4.8% sevoflurane, P < 0.01). Desflurane- and sevoflurane-mediated bronchodilation depends at least partially on the epithelium, and may involve both a prostanoid and NO in rat distal bronchi.

IMPLICATIONS

Bronchodilation by the volatile anesthetics desflurane and sevoflurane is at least partially epithelium-dependent and may be attenuated in diseases affecting the epithelium, such as asthma.

Beta-adrenergic regulation of the cerebral microcirculation after hypothermic cardiopulmonary bypass

BACKGROUND

The beta-adrenergic-cAMP pathway importantly regulates cerebral blood flow. Previous studies have found that normothermic cardiopulmonary bypass (CPB) is associated with reduced cerebral beta-adrenoceptor-mediated relaxation.

METHODS AND RESULTS

In order to examine the effects of hypothermic CPB on regulation of perfusion by the beta-adrenergic-cAMP pathway, pigs were placed on moderately (25 degrees C) or profoundly hypothermic (16 degrees C with 1 hour of circulatory arrest) or normothermic (37 degrees C) CPB for 2 hours. After normothermic perfusion for 15 minutes and separation from CPB, cerebral microvascular responses to the beta-adrenoceptor agonist isoproterenol (ISO), the adenylate cyclase activator forskolin, and the stable cAMP analogue 8-bromo-cAMP were examined in vitro in a pressurized, no-flow state. Baseline internal carotid artery blood flow was similar and unchanged after rewarming in the three experimental groups. However, ISO (100 micromol/L) elicited less relaxation after moderately hypothermic CPB (75+/-6%, P<.05 versus control, percent of U46619 induced precontraction) and profoundly hypothermic circulatory arrest (42+/-5%, P<.05) than in vessels from uninstrumented controls (91+/-2%) or after normothermic CPB (84+/-4%). The relaxation to forskolin was reduced after profoundly hypothermic circulatory arrest (83+/-3%, P<.05), but was similar in the other groups (92+/-2% control). Surprisingly, relaxation induced by 8-bromo-cAMP was markedly reduced after normothermic CPB, and this change was directly related to temperature during CPB. The intraluminal exposure of vessels to zymosan-induced complement activated serum had no effect on relaxation to ISO, while 2 hours of exposure of vessels to ISO caused a dose-dependent reduction in subsequent relaxation to ISO, but not to forskolin.

CONCLUSIONS

Moderately hypothermic CPB or PHCA desensitizes alpha-adrenoceptors more than normothermic CPB. This is likely due in part to the exposure of vessels to endogenous catecholamines during CPB. Thus, whereas baseline cerebral blood flow is similar after normothermic and hypothermic CPB, beta-adrenergic responses are markedly abnormal.

Comparative effects of continuous warm blood and intermittent cold blood cardioplegia on coronary reactivity

BACKGROUND

Cardioplegia is known to affect coronary vascular reactivity. We examined the effects of intermittent cold and continuous warm blood cardioplegia on beta-adrenoceptor-mediated, adenosine triphosphate-sensitive K+ (K+ATP)-channel-mediated, and endothelium-dependent relaxation and on the myogenic tone of coronary arterioles.

METHODS

Pigs were placed on cardiopulmonary bypass. Hearts were arrested for 1 hour with a cold blood cardioplegic solution administered intermittently (n = 12; iCB-CP) or with a warm blood cardioplegic solution delivered continuously (n = 12; cWB-CP). Selected hearts (n = 6 in each group) were then reperfused for 1 hour. In vitro relaxation responses of precontracted microvessels (50 to 160 microns) were studied in a pressurized no-flow state.

RESULTS

Relaxation in response to isoproterenol (beta-adrenergic agonist) was similar after iCB-CP and cWB-CP, whereas forskolin (adenylate cyclase activator)-induced relaxation was impaired more after iCB-CP than after cWB-CP. After reperfusion the respective responses were similar. Both iCB-CP and cWB-CP preserved receptor-mediated, endothelium-dependent relaxation in response to adenosine, 5'-diphosphate; non-receptor-mediated endothelium-dependent relaxation in response to A23187; endothelium-independent cyclic guanosine monophosphate-mediated relaxation in response to sodium nitroprusside, and K+ATP-channel-mediated relaxation. Relaxations in response to 8-bromo-cyclic guanosine monophosphate (a cyclic guanosine monophosphate-dependent protein kinase activator) and to 8-bromo-cyclic adenosine monophosphate (a cyclic adenosine monophosphate-dependent protein kinase activator) were impaired after iCB-CP alone and after reperfusion, whereas the respective responses were not affected after cWB-CP. Myogenic tone was decreased similarly after iCB-CP and cWB-CP but was not further altered after reperfusion. Cardiac function was similar after iCB-CP and cWB-CP.

CONCLUSIONS

These results suggest that cWB-CP is similar to iCB-CP in its ability to preserve endothelium-dependent relaxation and K+ATP-channel function. The superior preservation of beta-adrenergic-cyclic adenosine monophosphate-mediated coronary responses after cWB-CP is brief and associated with minimal improvement of myocardial function and myogenic tone.

The direct vasomotor effect of thyroid hormones on rat skeletal muscle resistance arteries

The present study examines the hypothesis that the hormones have direct vasodilatory effects and attempts to determine whether the effects are endothelium-dependent. Rat skeletal muscle resistance arteries of approximately 100 microns were dissected, and vessel diameter changes were monitored using a videodetection system. After equilibration at 37 degrees C, each vessel was preconstricted with the thromboxane analog U46619 1 microM, and the percentage of dilation was measured after exposure to increasing concentrations of triiodothyronine (T3) or levothyroxine (T4) (10(-10) to 10(-7) M). Dilation in response to T3 was also measured after endothelial denudation and pretreatment with the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine (L-NNA) 10 microM, the cyclooxygenase inhibitor indomethacin 10 microM, the adenosine triphosphate-sensitive K+ channel blocker glibenclamide 1 microM, or the beta-adrenergic antagonist propranolol 1 microM. Both T3 and T4 demonstrated concentration-dependent dilation of the U46619-preconstricted vessels (P < 0.001 each), with T3 having a greater effect than T4 (P < 0.05) (36% +/- 9% [mean +/- SD] dilation at 10(-7) M T3 vs 24% +/- 6% dilation at 10(-7) M T4). In comparison, isoproterenol 10(-7) M produced 56% +/- 6% dilation. T3-mediated vasodilation was attenuated but not abolished by endothelial denudation (18% +/- 3% dilation at 10(-7) M T3) (P < 0.01), L-NNA (15% +/- 7% dilation at 10(-7) M T3) (P < 0.01), indomethacin (20% +/- 9% dilation at 10(-7) M T3) (P < 0.05), and glibenclamide (22% +/- 7% dilation at 10(-7) M T3) (P < 0.01), but it was not affected by propranolol (37% +/- 20% dilation at 10(-7) M T3) (P = 0.99). We conclude that thyroid hormones possess direct vasodilatory effects with both endothelium-independent and endothelium-dependent components.

IMPLICATIONS

Thyroid hormones may have modest direct vasodilatory effects. This may partially account for the cardiovascular actions of the hormones in hyperthyroidism or when administered pharmacologically in cardiac surgery.

Hemodynamic effects of intracoronary VEGF delivery: evidence of tachyphylaxis and NO dependence of response

Vascular endothelial growth factor (VEGF) has been utilized to improve blood flow in the setting of myocardial or peripheral vascular ischemia. In this investigation we studied the hemodynamic effects of intracoronary VEGF administration. Hemodynamic parameters and Doppler flow wire recordings from the left anterior descending coronary artery were measured after intracoronary infusion of VEGF (1, 10, and 100 micrograms) in 28 intubated pigs. Additional studies were performed using an in vitro isolated microvessel preparation. VEGF produced a highly significant dose-dependent increase in coronary blood flow (maximal 3.51 +/- 0.85-fold) in the absence of significant changes in epicardial artery diameter, a decline in mean arterial pressure (maximal 43%), and a decrease in left ventricular end-diastolic pressure (maximal 52%), all of which could be inhibited by pretreatment with NG-nitro-L-arginine. The increase in coronary flow seen with 10 or 100 micrograms VEGF was significantly greater than the maximal vasodilation achieved with serotonin or nitroglycerin and was equivalent to a maximal adenosine response. In summary, VEGF stimulates nitric oxide (NO)-dependent dilation of coronary microvessels, and repeat administrations of VEGF resulted in rapid development of tachyphylaxis to VEGF as well as serotonin, but not to nitroglycerin or adenosine, which appeared to be secondary to impaired NO production.

Cardiopulmonary bypass alters vasomotor regulation of the skeletal muscle microcirculation

BACKGROUND

Cardiopulmonary bypass (CPB) is associated with alterations in the regulation of organ perfusion and vascular permeability. The purpose of this study was to examine the effects of hypothermic CPB on the regulation of the skeletal muscle microcirculation and the modulating influence of the priming solution.

METHODS

Sheep were placed on hypothermic CPB with a prime of either Pentastarch hydroxylethyl starch (HS) solution (n = 7), a solution in which HS is conjugated with deferoxamine (n = 7), or Ringer's lactate solution (n = 7). Sheep were placed on hypothermic CPB (27 degrees C) for 90 minutes while the heart was protected with cold blood cardioplegia. Sheep were then separated from CPB and perfused for an additional 3 hours off CPB. Hemodynamics and total water content were measured.

RESULTS

In vitro relaxation responses of gracilis muscle arterioles (70 to 180 microns) to the endothelium-dependent agent acetylcholine, the endothelium-independent cyclic GMP-mediated vasodilator sodium nitroprusside, the beta-adrenergic agonist isoproterenol, and the adenylate cyclase activator forskolin were studied. No statistically significant hemodynamic differences were observed between groups. However, weight gain was significantly less when the priming solution was HS or HS-deferoxamine compared to when Ringer's lactate was used. Skeletal muscle arteriolar relaxations to the endothelium-dependent vasodilator acetylcholine and the beta-adrenergic agonist isoproterenol were impaired after CPB in the HS and Ringer's lactate groups. Acetylcholine response was preserved in the HS-deferoxamine group, whereas the response to isoproterenol remained impaired. The responses to sodium nitroprusside and forskolin were similar in all groups.

CONCLUSIONS

Skeletal muscle microvascular endothelium-dependent relaxation and beta-adrenergic relaxation are reduced after CPB using either a crystalloid or HS prime. Skeletal muscle microvascular endothelial dysfunction may be attributable to oxygen-derived free radical-mediated injury, whereas altered beta-adrenergic regulation is attributable to mechanisms other than the generation of oxygen-derived free radicals during CPB.

Predictors of CABG within one year of successful PTCA: a retrospective, case-control study

BACKGROUND

We previously have established characteristics predictive of the need for coronary artery bypass grafting (CABG) over many years after successful percutaneous transluminal coronary angioplasty (PTCA). In this study, we examined the factors associated with the need for CABG within 1 year of successful PTCA, and the recent impact of newer, catheter-based technologies.

METHODS

From January 1982 through December 1995, 234 patients underwent CABG within 1 year of a successful "index" PTCA at our hospital. Emergency operations within 12 hours of index PTCA were excluded. These cases were matched with 234 controls who underwent a successful index PTCA but did not require a subsequent CABG during the next year. Cases were matched by the date of their index PTCA, and 1-year follow-up was complete for all patients.

RESULTS

Before index PTCA there were no differences between the groups in terms of age, sex, diabetes, prior myocardial infarction, ejection fraction, duration of anginal symptoms, hypertension, hyperlipidemia, family history, or obesity (all nonsignificant). At index PTCA the cases had a greater mean number of lesions measuring 70% or greater compared with the controls (2.8 versus 1.8, respectively; p < 0.0001). The cases were more likely to have critical (70% or greater) proximal left anterior descending artery, proximal first obtuse marginal artery, and right posterior descending artery stenoses. The use of stents or atherectomy devices was not significantly more common among the controls (21% of controls versus 17.1% of cases; p = 0.35). Complete revascularization was achieved in significantly fewer of the cases than the controls (91 versus 156, respectively; p < 0.0001). The cases underwent CABG at a mean of 3 months (86% within 6 months) after PTCA. Among those who had a diagnostic catheterization, 52% of the patients had both restenosis of a dilated lesion and progression of other disease. Only 5 of 75 patients who had restenosis of a dilated lesion had a stent or an atherectomy device used at index PTCA. Of note, 13% (30 of 234) required an emergency operation, with an overall operative mortality rate of 3% (7 of 234).

CONCLUSIONS

Although the likelihood of local restenosis is decreased by newer interventional techniques, the need for CABG within 1 year after successful PTCA is not diminished. The number of critical lesions and their location are the best predictors of the need for early CABG. If early post-PTCA CABG is to be avoided, patients who cannot be completely revascularized by PTCA should be revascularized by CABG.

Basic fibroblast growth factor in a porcine model of chronic myocardial ischemia: a comparison of angiographic, echocardiographic and coronary flow parameters

Recently, a number of growth factors including basic fibroblast growth factor (bFGF) have been shown to promote angiogenesis in vivo. In this study, we evaluated dose-dependent effect of bFGF administration in the setting of chronic myocardial ischemia. A total of 18 Yorkshire pigs subjected to ameroid occluder placement on the left circumflex artery were randomized to treatment with 10 (n = 6) or 100 microg (n = 5) of bFGF incorporated into heparin-alginate microspheres or inactive control pellets (n = 7). Eight weeks later, all animals underwent angiographic evaluation of collateral development as well as studies of coronary flow and global and regional left ventricular function. Both bFGF groups had significantly higher angiographic collateral index, TIMI flow scores and coronary flow in the ameroid-compromised territory compared with controls. Left ventricular function studies demonstrated improved global and regional function in both fibroblast growth factor groups with significantly better preservation of regional wall motion in high dose (100 microg) bFGF animals. We conclude that local perivascular delivery of bFGF results in significant improvement in myocardial function in the setting of chronic myocardial ischemia.

Isoflurane- and halothane-mediated dilation of distal bronchi in the rat depends on the epithelium

BACKGROUND

Respiratory epithelium releases substance(s) that can modulate bronchoconstriction in response to constrictive agonists and enhance bronchodilation in response to certain bronchodilators. The hypothesis that the bronchodilatory effect of isoflurane and halothane depends on the epithelium was tested in rat distal bronchial segments.

METHODS

Wistar rat bronchial segments of the fourth order (diameter approximately 100 microns) were dissected. After preconstriction with 5-hydroxytryptamine, each bronchial segment was exposed to increasing concentrations of 0% to 3% isoflurane or 0% to 3% halothane under four conditions: after epithelial rubbing, after pretreatment with the nitric oxide synthase inhibitor NG-nitro-L-arginine, after pretreatment with the cyclooxygenase inhibitor indomethacin, or with no preintervention (control). Changes in bronchial diameter were monitored using an in vitro video detection system.

RESULTS

Both isoflurane and halothane produced concentration-dependent bronchodilation (P < 0.001 for either anesthetic; 40% +/- 11% [mean +/- SD] dilation for 3% isoflurane and 57% +/- 10% dilation for 3% halothane). For both anesthetics, bronchodilation was significantly but incompletely attenuated by epithelial rubbing (12% +/- 7% dilation for 3% isoflurane [P < 0.01] and 31% +/- 10% dilation for 3% halothane [P < 0.01]), by pretreatment with indomethacin (20% +/- 8% dilation for 3% isoflurane [P < 0.02] and 21% +/- 9% dilation for 3% halothane [P < 0.001]), or by L-NNA (9% +/- 7% dilation for 3% isoflurane [P < 0.005] and 39% +/- 12% dilation for 3% halothane [P < 0.05]). Epithelial rubbing did not impair nitroprusside-associated bronchodilation.

CONCLUSIONS

Isoflurane- and halothane-mediated bronchodilation depends at least partially on the epithelium and may involve both a prostanoid and nitric oxide in distal rat bronchi.

Effects of magnesium cardioplegia on regulation of the porcine coronary circulation

We compared the effect of hypermagnesium and hyperkalemic crystalloid cardioplegia on beta-adrenoceptor-mediated and endothelium-dependent relaxation and myogenic responses of coronary arterioles. Pigs were placed on cardiopulmonary bypass. Hearts were arrested with cold hypermagnesium (25 mM Mg2+, hyper-Mg, n = 12) or hyperkalemic (25 mM K+, hyper-K, n = 12) crystalloid cardioplegia for 1 hr. Hearts of selected pigs (n = 6 in each group) were then reperfused for 1 hr. In vitro relaxation responses of acetylcholine-pre-contracted arterioles were studied in a pressurized no-flow state with video-microscopy. Relaxation of pre-contracted coronary microvessels (70-150 microns) to isoproterenol (beta-adrenergic agonist) and forskolin (adenylate cyclase activator) was preserved after cardioplegia using a hyper-Mg solution. In contrast, responses were impaired to isoproterenol [P < 0.01 (two-factor ANOVA) vs. controls, n = 6] and forskolin (P < 0.01) after hyper-K cardioplegia. After 1 hr of reperfusion, relaxation responses to isoproterenol and forskolin were partially recovered. Hyper-Mg cardioplegia and post-cardioplegic reperfusion did not affect receptor-mediated endothelium-dependent relaxation to ADP, non-receptor-mediated endothelium-dependent relaxation to A23187, and endothelium-independent relaxation to nitroprusside. However, responses to ADP (P < 0.01) and A23187 (P < 0.05) were selectively impaired after hyper-K cardioplegia. Myogenic contraction was impaired after either hyper-Mg or hyper-K cardioplegia. Left ventricular systolic pressure, coronary blood flow, and +dP/dt were similar after hyper-Mg or hyper-K cardioplegia. These results suggest that hyper-Mg cardioplegia is superior to hyper-K cardioplegia in terms of preserving beta-adrenoceptor-mediated and endothelium-dependent regulation of the coronary microcirculation, yet it has minimal if any additional beneficial effect on preserving myogenic responses or myocardial contractile function.

Chronic septicemia alters alpha-adrenergic mechanisms in the coronary circulation

The purpose of the present study was to determine the effect of chronic sepsis on alpha-adrenergic responsiveness in the coronary microcirculation. Male Sprague-Dawley rats (n = 6) were made septic by intraperitoneal implantation of a gelatin capsule containing 35 mg sterile rat feces and 1 x 10(8) viable colony-forming units of Escherichia coli (strain Sm 018). Control rats (n = 6) were implanted with capsules containing only sterile feces. Forty-eight hours after surgery, subepicardial coronary arterioles (80-170 mm) were isolated. In vitro arteriolar responses were studied in a pressurized, no-flow state with video-microscopy. Chronic sepsis decreased the contractile responses to the alpha 1-adrenoceptor agonist phenylephrine and the protein kinase C (PKC) activator 12-deoxyphorbol 13-isobutyrate 20-acetate. Relaxation responses to the alpha 2-adrenoceptor agonist clonidine, the endothelium-dependent vasodilator adenosine 5'-diphosphate, and the PKC inhibitor staurosporine were reduced, but the relaxation to the endothelium-independent cyclic GMP-mediated vasodilator sodium nitroprusside was preserved. Relaxation to clonidine was inhibited by endothelial denudation or after blockade of nitric oxide synthase. Chronic sepsis may reduce alpha 2-adrenoceptor-mediated relaxation of coronary microvessels by causing endothelial dysfunction. The alpha 1-adrenergic mechanism is downregulated, possibly due to alterations in the receptor and/or downstream signal transduction via PKC.

Decreased myogenic reactivity in skeletal muscle arterioles after hypothermic cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is associated with a generalized defect in the intrinsic control of vascular smooth muscle. To determine if myogenic reactivity of skeletal muscle arterioles was altered by CPB, sheep (n = 7) were placed on hypothermic CPB (27 degrees C) for 90 min and hearts were arrested by cold blood cardioplegia ([K+] = 25 mM) for 60 min. Arterioles (70-180 microns) were isolated from the gracilis muscle before (control) and 15 min after CPB. In vitro arteriolar responses were studied with video-microscopy. Myogenic reactivity was examined to stepwise increases in intraluminal pressure from 10 to 100 mm Hg. Mean arterial pressure was decreased from 80 +/- 15 prior to CPB to 55 +/- 4 mm Hg (P < 0.01) 15 min after CPB. Myogenic contraction was observed in control vessels and was markedly attenuated by the protein kinase C inhibitor staurosporine (P < 0.01). CPB decreased myogenic contraction and shifted the pressure-diameter relation upward, suggesting a decrease in the intrinsic tone (both P < 0.05 vs control). CPB reduced contractile responses to the alpha 1-adrenoceptor agonist phenylephrine from -43 +/- 7% to -23 +/- 5% (P < 0.01) and the protein kinase C activator 12-deoxyphorbol 13-isobutyrate 20-acetate (phorbol ester) from -64 +/- 6% to -38 +/- 16% (P < 0.01). CPB-associated decrease in myogenic reactivity of skeletal muscle arterioles is likely due to alterations in protein kinase C and/or downstream signal transduction. This may account in part for reduction in systemic vascular resistance and hypotension associated with CPB.

Isoflurane and halothane attenuate endothelium-dependent vasodilation in rat coronary microvessels

Volatile anesthetics attenuate endothelium-dependent vasodilation but the mechanism of attenuation remains controversial. The present study examines the mechanism of isoflurane- and halothane-mediated attenuation of endothelium-dependent vasodilation in Wistar rat coronary microvessels of about 100 microns internal diameter. The vessels were studied in vitro in a pressurized (40 mm Hg), no-flow state using video microscopy. After preconstriction of the vessels with the thromboxane analog U46619 1 microM, concentration response curves to acetylcholine (ACh), the calcium ionophore A23187, sodium nitroprusside (SNP), or the stable cyclic guanosine monophosphate (cGMP) analog 8-bromo-cGMP (Br-cGMP) were obtained in the presence of 0% (control), 1% or 2% isoflurane, or 1% or 2% halothane. Isoflurane 1% and 2% significantly attenuated vasodilation to ACh and A23187. Isoflurane 2%, but not 1%, attenuated vasodilation to SNP. Vasodilation to Br-cGMP was not affected by isoflurane. Halothane attenuated vasodilation to ACh, but had no effect on vasodilation to A23187, SNP, or Br-cGMP. We conclude that isoflurane attenuates endothelium-dependent vasodilation by impairing at least two distinct steps in the nitric oxide (NO)-cGMP pathway, the first being between endothelial increase of calcium and smooth muscle guanylate cyclase and the second being inhibition of soluble guanylate cyclase activity. These two steps appear to have different sensitivities to the effect of isoflurane. Halothane has an effect at the endothelial receptor level, but not any distal steps in the NO-cGMP pathway.