Complete and Rapid Conversion of Hydrazine Monohydrate to Hydrogen over Supported Ni-Pt Nanoparticles on Mesoporous Ceria for Chemical Hydrogen Storage

The development of active, selective, and robust catalysts is a key issue in promoting the practical application of hydrazine monohydrate (N2 H4 ⋅H2 O) as a viable hydrogen carrier. Herein, the synthesis of a supported Ni-Pt bimetallic nanocatalyst on mesoporous ceria by a one-pot evaporation-induced self-assembly method is reported. The catalyst exhibits exceptionally high catalytic activity, 100 % selectivity, and satisfactory stability in promoting H2 generation from an alkaline solution of N2 H4 ⋅H2 O at moderate temperatures. For example, the Ni60 Pt40 /CeO2 catalyst enabled complete decomposition of N2 H4 ⋅H2 O to generate H2 at a rate of 293 h(-1) at 30 °C in the presence of 2 M NaOH, which compares favorably with the reported N2 H4 ⋅H2 O decomposition catalysts. Phase/structural analysis by XRD, TEM, and Auger electron spectroscopy was conducted to gain insight into the excellent catalytic performance of the Ni-Pt/CeO2 catalyst.

Effect of isoflurane on the beta-adrenergic and endothelium-dependent relaxation of pig cerebral microvessels after cardiopulmonary bypass

We examined the direct vasomotor effect of isoflurane as well as its effect on endothelium-dependent and beta-adrenergic vasodilation of cerebral microcirculation following either normothermic cardiopulmonary bypass (CPB) or profoundly hypothermic CPB with circulatory arrest. Pigs were placed on CPB; the systemic temperature was either maintained at 37 degrees C or lowered to 15 degrees C with 60 minutes of circulatory arrest. After 2 hours of CPB, the animals were separated from CPB; 15 minutes later the brain was quickly harvested in cold Krebs solution. Control animals were not instrumented and their brains were similarly harvested. Arteries of approximately 100 microm were dissected and changes in diameter monitored by in vitro videomicroscopy. Following preconstriction with the thromboxane analogue U46619 1 micromol/L, percent relaxation to the endothelium-dependent dilator adenosine diphosphate (ADP) 10(-9) to 10(-4) mol/L, the endothelium-independent dilator sodium nitroprusside (SNP) 10(-9) to 10(-4) mol/L, or the beta-adrenergic agonist isoproterenol 10(-12) to 10(-4) mol/L was measured either in the presence or absence of isoflurane 2%. Additionally, with or without preconstriction with U46619 1 micromol/L, vessel diameter changes were monitored with increasing concentrations of isoflurane 0-3%. Dose-response curves were compared by two-way analysis of variance. Vasodilation to ADP or isoproterenol, but not SNP, was attenuated after normothermic CPB (N-CPB) or profoundly hypothermic CPB (PH-CPB). Although isoflurane attenuated vasodilation of control vessels to ADP or isoproterenol, isoflurane did not further attenuate vasodilation to ADP or isoproterenol after N-CPB or PH-CPB. The direct vasomotor effect of isoflurane depended on the preexisting tone of the vessels, constricting vessels without preconstriction and dilating them after preconstriction. These findings may have implications on the incidence of neuropsychological dysfunction after CPB and use of isoflurane.

[Effects of androgen on microstructure and mechanics nature of bone in orchiechtomied male rats]

OBJECTIVE

To investigate the effect of androgen on microstructure and mechanics nature of bone in orchiechtomied (ORX) male rats and reveal its mechanism by using the Micro CT analysis, bone biomechanics test, bone histomorphometric parameter test, and total body bone mineral density (BMD) measured by dual-energy X-ray absorptiomery (DXA).

METHODS

Thirty 12-month-old male Wister rats were randomly divided into three groups including ORX, sham-operated (Sham) and androgen (AD) group, ten rats in every group. Total body BMD was measured by DXA. Femurs and vertebrae were then harvested at the 12 th week after ORX for micro-computed tomography (Micro CT), histology and biomechanical were tested.

RESULTS

The administration of testosterone may reverse the decreasing BMD of total body and may prevent the decreasing weight. The biomechanical values of Maximum load, Enery, Maximum stress, Elastic Modulus of AD group significantly enhanced compared with ORX group (P < 0.05). The results of histomorphometric parameters showed that cancellous bone volume, osteoblast-osteoid interface, linear extent of bone formation, mineralizing surfaces, mineral apposition rate increased in the therapy group.

CONCLUSION

Androgen can accelerate cancellous bone formation and bone turnover, improve bone microstructure and enhance bone intensity and BMD.

Enhancing relevance feedback in image retrieval using unlabeled data

Relevance feedback is an effective scheme bridging the gap between high-level semantics and low-level features in content-based image retrieval (CBIR). In contrast to previous methods which rely on labeled images provided by the user, this article attempts to enhance the performance of relevance feedback by exploiting unlabeled images existing in the database. Concretely, this article integrates the merits of semisupervised learning and active learning into the relevance feedback process. In detail, in each round of relevance feedback two simple learners are trained from the labeled data, that is, images from user query and user feedback. Each learner then labels some unlabeled images in the database for the other learner. After retraining with the additional labeled data, the learners reclassify the images in the database and then their classifications are merged. Images judged to be positive with high confidence are returned as the retrieval result, while those judged with low confidence are put into the pool which is used in the next round of relevance feedback. Experiments show that using semisupervised learning and active learning simultaneously in CBIR is beneficial, and the proposed method achieves better performance than some existing methods.

Microvascular endothelial dysfunction and its mechanism in a rat model of subarachnoid hemorrhage

After subarachnoid hemorrhage (SAH), large cerebral arteries are prone to vasospasm. Using a rat model of SAH, we examined whether cortical microvessels demonstrate vasomotor changes that may make them prone to spasm and whether endothelial dysfunction may account for any observed changes. Two days after percutaneous catheterization into the cisterna magna, 0.3 mL of autologous blood was injected into the subarachnoid space. The brain tissue was harvested 20 min later, and microvessels were dissected from the parietal cortex. Vasomotor responses to the thromboxane analog U46619, the protein kinase C agonist phorbol acetate, endothelin-1, adenosine diphosphate, nitroprusside, and isoproterenol were examined in vitroin cerebral arterioles from the control, sham-operated, and SAH animals. Endothelial nitric oxide synthase (NOS3) messenger RNA and protein concentration was measured by northern and western blotting, respectively. Arterioles from the SAH animals demonstrated attenuated dilation to the endothelium-dependent dilator adenosine diphosphate and accentuated constriction to endothelin-1, while responses to the other agents tested were unchanged. NOS3 protein concentration was decreased, but NOS3 messenger RNA was increased after SAH. After SAH, cortical arterioles demonstrate endothelial dysfunction, which may be the basis for microvascular spasm. This is in part related to decreased NOS3, which occurs despite an increase in its transcription.

IMPLICATIONS

Acute microvascular endothelial dysfunction may occur after subarachnoid hemorrhage and contribute to microvascular spasm.

Dilation by isoflurane of preconstricted, very small arterioles from human right atrium is mediated in part by K(+)-ATP channel opening

The adenosine triphosphate (ATP)-sensitive potassium channels (K(+)-ATP channels) are activated by decreases in intracellular ATP and help to match blood flow to tissue needs. Such metabolism-flow coupling occurs predominantly in the smallest arterioles measuring 50 microm or less in diameter. Previous studies demonstrated that isoflurane may activate the K(+)-ATP channels in larger arteries. We examined whether isoflurane also activates the channels in the smallest arterioles of approximately 50 microm. Microvessels of approximately 50 microm were dissected from right atrial appendages from patients undergoing coronary artery bypass surgery and were monitored in vitro for diameter changes by videomicroscopy. With or without preconstriction with the thromboxane analog U46619 1 microM, vessels were exposed to isoflurane 0%-3% either in the presence or absence of the K(+)-ATP channel blocker glibenclamide 1 microM. Without preconstriction, isoflurane neither dilated nor constricted the vessels significantly. After preconstriction, isoflurane had a concentration-dependent dilation of the small arterioles (39 +/- 13% [mean +/- SD] dilation at 3% isoflurane) (P < 0.001), and this effect was significantly attenuated by glibenclamide (18 +/- 5% dilation at 3% isoflurane) (P < 0.01). In comparison, nitroprusside 10(-4) M produced 79 +/- 6% dilation, and adenosine diphosphate 10(-4) M produced 29 +/- 7% dilation. We conclude that isoflurane-mediated dilation of the smallest resistance arterioles may be in part based on activation of the K(+)-ATP channels when the arterioles are relatively constricted.

IMPLICATIONS

Vasodilation of very small coronary arterioles by isoflurane depends on preexisting tone and may in part be mediated by the K(+)-ATP channels.

Epithelium-dependent bronchodilatory activity is preserved in pig bronchioles after normothermic cardiopulmonary bypass

Analogous to vascular endothelium, bronchial epithelium modulates bronchomotor activity by releasing epithelium-derived relaxing factors. Cardiopulmonary bypass (CPB) is associated with endothelial dysfunction. We examined whether CPB may be associated with bronchiolar epithelial dysfunction in pigs. Pigs were exposed to normothermic CPB for 1.5 h and then separated from CPB. Lung tissues were biopsied before and 30 min after CPB. For time control, lung tissues were biopsied at baseline and after 2 hr of anesthesia. Bronchioles measuring about 100 microm were dissected, and the epithelium was either left intact or denuded. Each bronchiolar segment was preconstricted with 10 microM 5-hydroxytryptamine and relaxation responses to nitroprusside 10(-9)-10(-4) M, isoproterenol 10(-9)-10(-4) M, or the inhaled anesthetics halothane or isoflurane 0-2.5 minimum alveolar anesthetic concentration were examined in vitro by videomicroscopy. Bronchiolar segments demonstrated concentration-dependent relaxation responses to each of the dilators examined. Epithelial denudation reduced bronchodilation to isoproterenol, isoflurane, and halothane, but not to nitroprusside. Bronchodilation was not significantly affected by CPB. We conclude that, unlike vascular endothelial function, porcine bronchiolar epithelium-modulated bronchomotor activity is not significantly affected by normothermic CPB.

IMPLICATIONS

Normothermic cardiopulmonary bypass does not result in epithelial dysfunction in pigs. Epithelium-dependent and epithelium-independent bronchodilators may be equally effective before and after cardiopulmonary bypass.

Attenuation of endothelium-dependent dilation of pig pulmonary arterioles after cardiopulmonary bypass is prevented by monoclonal antibody to complement C5a

We examined whether pulmonary endothelial dysfunction associated with cardiopulmonary bypass (CPB) may be mediated by complement C5a in pigs. Pigs were placed on normothermic CPB for 1 h with or without a previous administration of 1.6 mg/kg anti-C5a monoclonal antibody (MAb), then reperfused for 2 h. Pulmonary tissue myeloperoxidase activity was measured. Expression of nitric oxide synthase (NOS) was measured by reverse transcriptase polymerase chain reaction and Western blotting. Pulmonary arterioles approximately 100 microm in diameter were preconstricted with the thromboxane analog U46619 1 microM, and relaxation responses to adenosine diphosphate 10(-9)-10(-4) M, substance P 10(-12)-10(-6) M, and sodium nitroprusside 10(-9)-10(-4) M were examined in vitro by videomicroscopy. Relaxation to the endothelium-dependent dilators adenosine diphosphate and substance P was attenuated after CPB; this attenuation was prevented by the previous administration of MAb. Relaxation to sodium nitroprusside was not affected by CPB. Neutrophil sequestration, as measured by MPO activity, increased after CPB, either with or without MAb. Transcription of NOS was unchanged by CPB, but translation of constitutive NOS was decreased after CPB, and this decrease was prevented by a previous administration of MAb. We conclude that pig pulmonary endothelial dysfunction associated with CPB may be mediated by C5a. The mechanism may involve changes in NOS translation.

IMPLICATIONS

In pigs, pulmonary endothelial dysfunction may occur after cardiopulmonary bypass due to product(s) of complement activation.

Effect of sevoflurane and desflurane on the myogenic constriction and flow-induced dilation in rat coronary arterioles

BACKGROUND

Determinants of myocardial blood flow distribution include metabolic, myogenic, endothelial, and neurohumoral control mechanisms. The authors studied the effect of sevoflurane and desflurane on the myogenic and endothelial mechanisms.

METHODS

Wistar rat subepicardial microvessels, approximately 100 microm in diameter, were monitored for diameter changes in vitro using a video detection system. Myogenic vasomotion was studied by varying the intraluminal pressure from 10 mmHg to 120 mmHg. Flow-induced, endothelium-dependent dilation was evaluated in U46619-preconstricted vessels by varying the pressure gradient across the isolated vessel from 10 mmHg to 80 mmHg, while maintaining the midpoint luminal pressure constant at 40 mmHg to avoid myogenic effects. Myogenic and flow-induced vasomotion both were studied in the presence of sevoflurane, 1 or 2 minimum alveolar concentration (MAC) (MAC is a unit of inhalational anesthetic potency), desflurane, 1 or 2 MAC, or no anesthetic (control).

RESULTS

Myogenic constriction was shown above intraluminal pressures of 70 mmHg. Myogenic constriction was unchanged by sevoflurane, 1 MAC (P = 0.24), but was mildly enhanced by sevoflurane, 2 MAC (P < 0.05), or desflurane, 1 (P < 0.05) or 2 MAC (P < 0.01). Flow-induced dilation was shown over the pressure gradient range of 10-80 mmHg. Flow-induced dilation was not altered significantly by sevoflurane, 1 or 2 MAC (P > 0.3 each), but was significantly attenuated by desflurane, 1 or 2 MAC (P < 0.001 each).

CONCLUSIONS

Sevoflurane maintains myogenic and endothelial determinants of myocardial blood flow distribution. Conversely, desflurane attenuates endothelium-dependent flow-induced dilation while mildly enhancing myogenic constriction.

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.

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.

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.

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.

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.

Intrinsic tone as potential vascular reserve in conductance and resistance vessels

BACKGROUND

The purpose of this study was to define the degree of intrinsic tone in conductance and resistance vessels, to define the calcium dependency of intrinsic tone in these vascular preparations, and to investigate the efficacy of vasodilatory agents on the level of intrinsic tone in these vascular preparations.

METHODS AND RESULTS

All vessels were deendothelialized. Isometric force was recorded from strips of ferret aorta, ferret pulmonary artery, and human coronary artery. Vessel diameter was recorded from the ferret epicardial coronary artery and from ferret coronary microvessel in a pressurized no-flow state. Intrinsic tone was defined as the active increase in force or decrease in diameter with warming from 6 degrees C to 37 degrees C. Changes in force or diameter with various pharmacological agents were expressed as a percentage of intrinsic tone. Our results indicate that intrinsic tone accounts for approximately 35% to 40% of total tone in all vascular preparations studied and is not dependent on extracellular calcium. Agents that increased cAMP levels (eg, forskolin, milrinone) and agents that decreased protein kinase C activity (eg, staurosporine) were partially effective in decreasing intrinsic tone. Nitroprusside, adenosine, hydralazine, and nifedipine had no significant effect.

CONCLUSIONS

Our results indicate that intrinsic tone represents a significant component of vascular tone that has not been previously recognized and remains largely unexploited by current pharmacological therapies.

Direct vasomotor effects of isoflurane in subepicardial resistance vessels from collateral-dependent and normal coronary circulation of pigs

BACKGROUND

The purpose of the current investigation was to determine and compare the direct effect of isoflurane on normal resistance coronary arteries and similarly sized coronary arteries in collateral-dependent (CD) circulation. A differential vasomotor effect of isoflurane might contribute to flow redistribution, either adverse or favorable, between normal and CD regions.

METHODS

The authors used a swine model of chronic coronary occlusion. Six weeks after ameroid occluder placement around the left circumflex artery, the heart was removed. Myocardial blood flow, measured in vivo before the removal, was lower during rapid atrial pacing in the CD region than in the normally perfused region. These in vivo studies established the existence and location of CD circulation. Subepicardial microvessels, measuring approximately 100 microns, were dissected from both the CD region and the normal region. Either with or without preconstriction of the vessels with the thromboxane analogue U46619 1 microM, direct vasomotor effect of isoflurane was examined in vitro by video microscopy. In addition, vasomotor responses to endothelin-1, the endothelium-dependent dilator adenosine 5' diphosphate, and the endothelium-independent dilator sodium nitroprusside were compared between CD and normal resistance vessels.

RESULTS

Isoflurane caused greater concentration-dependent constriction of the normal vessels than of the CD vessels (P < 0.05); this constrictive effect was masked by preconstriction of the vessels. Vasodilation of ADP was less in CD vessels than in normal vessels (P < 0.001), but vasodilation to sodium nitroprusside was not significantly different (P = 0.45). Vasoconstriction to endothelin-1 was greater in CD vessels than in normal vessels (P < 0.01).

CONCLUSIONS

The vasoconstrictive effect of isoflurane normally observed in coronary resistance vessels is impaired in resistance vessels that supply a CD area. The basis of this may be related to endothelial dysfunction.

Protein kinase C-induced contraction is inhibited by halothane but enhanced by isoflurane in rat coronary arteries

Protein kinase C (PKC), important in signal transduction, may help generate and maintain vascular smooth muscle tone. We sought to examine the effect of the volatile anesthetics isoflurane and halothane on PKC agonist-induced vasoconstriction and PKC inhibitor-induced vasorelaxation. Subepicardial resistance arteries were dissected from rat hearts. Changes in vessel diameters were monitored in response to the membrane-bound PKC agonist 12-deoxyphorbol-13-isobutyric-20-acetate (PBE) 10(-8)-10(-7) M or the cytosolic PKC agonist oleic acid 10(-7)-10(-5.5) M either in the presence of isoflurane 1.15%, isoflurane 2.3%, halothane 0.77%, halothane 1.54%, or no volatile anesthetics (control). In addition, after preconstriction with the thromboxane analog U46619 1 microM, relaxation responses to the PKC inhibitor staurosporine 10(-8)-10(-7) M were examined in the presence or absence of the anesthetics as above. PBE-induced constriction was attenuated by either concentration of halothane (P < 0.05) but was unaltered by isoflurane (P > 0.5). Oleic acid-induced constriction was abolished by halothane (P < 0.001) but enhanced by isoflurane (P < 0.01). Staurosporine-induced relaxation of U46619-preconstricted vessels was attenuated by isoflurane (P < 0.05) but unaltered by halothane (P > 0.3). We conclude that isoflurane may enhance cytosolic PKC-mediated vasoconstriction, whereas halothane may attenuate both cytosolic and membrane-bound PKC-mediated vasoconstriction.

Steady-state myogenic response of rat coronary microvessels is preserved by isoflurane but not by halothane

The myogenic response of vascular smooth muscle produces vasomotion in response to changes in vessel transmural pressure. While this is an important determinant of coronary blood distribution, the effect of volatile anesthetics on the response has not been previously investigated. In this study, we examined the effect of isoflurane and halothane on this myogenic response. Coronary resistance arteries were isolated from Wistar rats. As the intraluminal pressure was increased from 10 to 120 mm Hg in the presence of either isoflurane (1%, 2%, and 3%), halothane (1% and 2%), or no volatile agent (control), the vessel intraluminal diameter was monitored using a video detection system. Passive changes in vessel diameter were measured after exposure to papaverine 100 microM. Additionally, the myogenic responses of endothelium-intact and endothelium-denuded vessels were compared. Endothelium-intact control vessels demonstrated myogenic constriction above 80 mm Hg of intraluminal pressure. This response was not affected by endothelial denudation. The response was preserved by isoflurane 1%, 2% or 3% but abolished by halothane 1% or 2%. We conclude that, in rat coronary resistance arteries, myogenic constriction can be demonstrated above 80 mm Hg of intraluminal pressure and is endothelium independent. This response is preserved by isoflurane but abolished by halothane. These findings may have implications for the effect of the anesthetics on coronary blood flow distribution.

Propofol-associated dilation of rat distal coronary arteries is mediated by multiple substances, including endothelium-derived nitric oxide

Previous in vitro studies on the effect of propofol on coronary arteries have shown variable results, ranging from constriction to no effect to dilation. Although most of these studies reported that the observed effect is endothelium-independent, propofol also releases nitric oxide from cultured porcine endothelial cells. The present study examines the direct effect of propofol in rat distal coronary arteries in vitro, especially in regard to endothelial dependence and involvement of the adenosine triphosphate (ATP)-sensitive potassium channels (KATP channels). Forty-three subepicardial arteries (size 91.1 +/- 15.8 microns) from Wistar rats were studied in vitro in a no-flow, pressurized (40 mm Hg) state, using an optical density video detection system. After preconstriction with the thromboxane analog U46619 1 microM, relaxation responses to increasing concentrations of propofol (10(-6)-10(-4) M) were measured after 1) endothelial denudation, 2) pretreatment with the nitric oxide synthase inhibitor NG-nitro-L-arginine (L-NNA), 3) pretreatment with the cyclooxygenase inhibitor indomethacin, 4) pretreatment with the KATP channel blocker glibenclamide, or 5) no intervention (control). Propofol produced a significant concentration-dependent vasodilation of the U46619-preconstricted coronary arteries. This effect was significantly attenuated by endothelial denudation, pretreatment with L-NNA, or indomethacin, but was not affected by glibenclamide. We conclude that propofol has a direct vasodilatory effect on distal coronary arteries in rats. This effect is primarily endothelium-dependent and is mediated by multiple substances, including nitric oxide (NO) and a vasodilatory prostanoid. The effect is not mediated by opening of the K(ATP) channels.

Vasomotor responses of rat coronary arteries to isoflurane and halothane depend on preexposure tone and vessel size

BACKGROUND

The authors previously reported that in rabbits, isoflurane exhibited a heterogeneous vasomotor effect, constricting small resistance coronary arteries and dilating larger conductance arteries. The novelty of isoflurane-induced constriction of small coronary arteries raised the question of whether the finding depended on the unique experimental setup or species used. The purpose of this study was to address these questions. Therefore, a second species was studied, namely rats, as well as a second volatile anesthetic, halothane. In addition, the dependence of the vasomotor effect on the preexisting tone of the vessels was examined.

METHODS

Thirty-six large coronary arteries (262 +/- 23 microns) and 42 small coronary arteries (99 +/- 15 microns) from 31 Wistar rats were isolated. Each vessel was placed in a microvessel chamber and was (1) submaximally preconstricted with the thromboxane analog U46619; (2) submaximally predilated with sodium nitroprusside; or (3) neither preconstricted nor predilated. The vessel was then subjected to increasing concentrations of either isoflurane or halothane, 0-3%. Changes in inner diameter were monitored and recorded with optical density video detection system.

RESULTS

Isoflurane constricted predilated or untreated small coronary arteries, but had no effect on preconstricted small arteries. Isoflurane dilated large coronary arteries, with the preconstricted vessels dilating the most. In contrast, halothane dilated both the small and large coronary arteries to a similar extent. Preconstricted vessels dilated more to halothane than vessels with no added tone.

CONCLUSIONS

Whereas isoflurane has a heterogeneous vasomotor effect in rat coronary arteries, constricting the small vessels and dilating the large ones, halothane dilates both the small and large arteries. The vasoconstriction effect was most evident in vessels with no added tone, whereas the vasodilatory effect was most significant in preconstricted vessels.

Isoflurane attenuates cAMP-mediated vasodilation in rat microvessels

BACKGROUND

Endothelium-dependent vasodilation mediated by cGMP is known to be attenuated by the inhalational anesthetic isoflurane. The present study examines the effect of isoflurane on beta-adrenergic and cAMP-mediated vasodilation.

METHODS AND RESULTS

Fifty-three subepicardial coronary arteries (diameter, 103 +/- 13 microns) from Wistar rats were studied in vitro in a pressurized (40 mm Hg), no-flow state with use of optical density video detection system. After preconstriction of vessels with the thromboxane A2 analogue U46619 10(-6) mol/L, concentration response curves to the nonselective beta-adrenergic agonist isoproterenol, the Gs protein activator sodium fluoride, the adenylate cyclase activator forskolin, the cAMP analogue 8-Br-cAMP, or the phosphodiesterase inhibitor RO20-1724 were obtained either in the presence of absence (control) of 2% isoflurane. Relaxations to all the agents tested were significantly reduced in the presence of isoflurane compared with controls.

CONCLUSIONS

Isoflurane attenuates cAMP-mediated vasodilation. The impairment appears to be distal to adenylate cyclase and is not due to enhancement of cAMP phosphodiesterase.

Beta-adrenergic modulation of the collateral-dependent coronary microcirculation

The effect of chronic, collateral-dependent perfusion on beta-adrenergic coronary microvascular responses was examined. Ameroid constrictors were placed on the proximal left circumflex (LCx) coronary artery in 16 pigs. In 8 pigs, heparinized saline containing vascular endothelial growth factor (VEGF) was administered into the perivascular space of the proximal LCx artery using an implanted osmotic pump. After 5-7 weeks, coronary arterial microvessels (70-150 microns) were studied in a pressurized (40 mm Hg) no-flow state with video-microscopy. beta-Adrenoceptor-mediated relaxations of isolated microvessels from the collateral-dependent LCx region to isoproterenol (P < 0.01) were markedly reduced, as were those to the adenylate cyclase activator forskolin (P < 0.01), compared to the respective response of vessels from the normally perfused left anterior descending artery region. Responses to the Gs-protein activator NaF showed a similar trend, but the differences were not significant. Chronic treatment with VEGF normalized responses to isoproterenol, NaF, and forskolin in the collateral-dependent LCx region. Blood flow in the LCx region increased in both control (P < 0.01) and VEGF-treated (P < 0.05) groups during rapid atrial pacing. The absolute increase in LCx blood flow was greater in the VEGF group than in the control group at rest (P < 0.05), but not during rapid pacing. Thus, beta-adrenergic microvascular relaxation is impaired in the collateral-dependent coronary microcirculation. The periadventitial delivery of VEGF improves myocardial perfusion to the collateral-dependent area and preserves beta-adrenergic-mediated relaxation of microvessels in the collateral-dependent myocardium.

Myogenic and agonist induced responses of coronary venules after cold hyperkalaemic cardioplegia

OBJECTIVE

The aim was to examine agonist induced and myogenic venular responses after crystalloid cardioplegia in conditions simulating cardiopulmonary bypass.

METHODS

Hearts of pigs were arrested with cold hyperkalaemic ([K+] = 25 mM) crystalloid cardioplegic solution for 1 h under conditions of cardiopulmonary bypass. In another group, hearts were arrested and then reperfused with warm blood for 1 h while being separated from cardiopulmonary bypass. In a third group, animals were supported on cardiopulmonary bypass for 75 min without diversion of coronary blood flow. Hearts from non-instrumented animals served as controls. Coronary venules (91-197 microns in internal diameter) were studied in vitro in a pressurised no flow state using video microscopy. Agonist induced responses were assessed in vessels precontracted with the thromboxane A2 analogue U46619.

RESULTS

Endothelium dependent relaxations to adenosine diphosphate (ADP, P = 0.11 v control), or serotonin (P = 0.67), and endothelium independent relaxations to the beta adrenergic cyclic AMP mediated agonist isoprenaline (P = 0.20), adenosine (P = 0.98), or the KATP channel opener pinacidil (P = 0.40) were not significantly altered after cold cardioplegia alone. After cardioplegia followed by 1 h of warm blood reperfusion, venular responses to ADP (P = 0.003 v control), isoprenaline (P = 0.013), adenosine (P = < 0.001), and pinacidil (P = 0.005) were reduced compared to the respective control responses, while the response to serotonin (P = 0.97) remained unchanged. Endothelium independent cyclic GMP mediated relaxation to sodium nitroprusside was similar in all groups (P > 0.90). Myogenic reactivity was assessed after incremental increases in the intraluminal pressure from 2-40 mm Hg. As intraluminal pressure was increased, the diameter of control venules increased and reached a plateau. Following cardioplegia, the pressure-diameter relationship of venules was shifted upward (P = 0.04 v control) suggesting impaired myogenic tone. After reperfusion, myogenic tone partially recovered. Extracorporeal circulation without diversion of coronary perfusion did not significantly affect venular responses.

CONCLUSIONS

Ischaemic cardioplegia using a cold hyperkalaemic solution under conditions of cardiopulmonary bypass does not significantly alter agonist induced venular responses, whereas myogenic contraction is slightly reduced. After 1 h of reperfusion, agonist induced relaxations of coronary venules are significantly impaired, whereas myogenic contraction recovers. These findings may have implications for the control of myocardial perfusion and diastolic properties of the heart after ischaemic cardioplegia under conditions of extracorporeal circulation.

Oxygen-derived free radicals mediate isoflurane-induced vasoconstriction of rabbit coronary resistance arteries

Isoflurane induces endothelium-dependent constriction of rabbit coronary resistance arteries in vitro. This effect is inhibited by the cyclooxygenase inhibitor indomethacin. To determine whether thromboxane or oxygen-derived free radicals, a byproduct in the cyclooxygenase pathway, mediate this effect, subepicardial coronary arterioles (103 +/- 21 mu) from New Zealand White rabbits were studied in vitro in a pressurized (40 mm Hg), no-flow state using videomicroscopy. The vessels were subjected to increasing concentrations of isoflurane, 0%-3%, in the presence of Dazmegrel (a specific inhibitor of thromboxane synthesis; Pfizer Ltd., Sandwich, UK) or SOD-Mn (manganese superoxide dismutase, a scavenger of superoxide radicals) or mannitol (hydroxyl radical scavenger) 20 or 100 mM or in their absence (control). The control vessels showed a concentration-dependent constriction to isoflurane (P < 0.0001), with reduction in internal diameter of 11.4% +/- 3.5% at isoflurane 3%. This response was unaffected by Dazmegrel (P = 0.78), but was abolished by SOD-Mn (P < 0.01) or mannitol (P < 0.01). We conclude that isoflurane causes concentration-dependent constriction of rabbit coronary resistance arteries and that this effect is mediated by oxygen-derived free radicals.

Cocaine and the porcine coronary microcirculation: effects of chronic cocaine exposure and hypercholesterolemia

OBJECTIVE

To examine the acute effect of cocaine on the coronary microcirculation and whether chronic cocaine administration with or without a concomitant high-cholesterol diet affects beta-adrenoceptor and endothelial functions in the coronary microcirculation.

DESIGN

Prospective experimental study.

SETTING

Laboratory and animal research facility.

PARTICIPANTS

Yorkshire pigs.

INTERVENTIONS

Pigs were fed a high (2%)-cholesterol diet or a regular diet for 3 months. Animals in both groups received cocaine chronically (7 mg/kg/day, IM). Control animals were fed a regular diet.

MEASUREMENTS AND MAIN RESULTS

Responses of the porcine coronary arterioles (90 to 190 microns in diameter) were examined in vitro in a pressurized (40 mmHg) no-flow state using a video-imaging apparatus. Acute application of cocaine caused a significant contraction with a mean maximal diameter decrease of 14% +/- 5%, which was markedly reduced by muscarinic blockade but not significantly affected by alpha 1-adrenergic blockade. Lidocaine or procainamide had no vasoconstrictor effect. Chronic exposure of animals to cocaine diminished contractile responses to cocaine and reduced relaxation responses to the nonselective beta-adrenergic receptor agonist isoproterenol. Phenylephrine caused a minimal (< 4%) contraction of vessels in all groups. Chronic cocaine administration with concomitant high-cholesterol feeding attenuated endothelium-dependent relaxations to serotonin, whereas endothelium-dependent relaxations to bradykinin were unaffected. Endothelium-independent relaxations to sodium nitroprusside were similar in all groups.

CONCLUSIONS

These results suggest that cocaine can exert a direct vasoconstrictor effect on the porcine coronary microcirculation via a muscarinic mechanism. Chronic exposure to cocaine significantly decreases beta-adrenoceptor-mediated relaxation and blunts endothelium-dependent relaxation to a small degree.

Pulmonary microvascular responses to protamine and histamine. Effects of cardiopulmonary bypass

Total cardiopulmonary bypass with associated reduced pulmonary blood flow causes significant alterations of endothelium-dependent pulmonary microvascular responses after resumption of normal perfusion. To determine if this change in pulmonary vascular reactivity may influence the responses of pulmonary arterioles to protamine and histamine, we examined isolated pulmonary microvessels after cardiopulmonary bypass. Sheep were heparinized, cannulated, and placed on either total bypass without ventilation or partial bypass (70% of baseline pulmonary arterial flow) with continued ventilation. After 90 minutes, sheep were separated from cardiopulmonary bypass and the lungs were perfused normally for 60 minutes. Vessels from noninstrumented sheep were used as controls. Peripheral pulmonary arterioles (90 to 190 microns) were cannulated, pressurized (20 mm Hg) in a no-flow state, and examined with video microscopy. After precontraction of vessels with the thromboxane A2 analog U46619 by 18% to 25% of the baseline diameter, vasoactive agents were applied. Protamine sulfate, histamine, heparin, and the protamine-heparin complex caused significant dose-dependent relaxations of control pulmonary microvessels. These relaxation responses were substantially reduced or converted to contractile responses in endothelium-denuded vessels, which suggests that these relaxations are mediated through endothelium-dependent mechanisms. After partial bypass, responses to protamine and histamine were slightly reduced compared with the respective responses of control vessels, whereas the relaxation to protamine-heparin complex was not significantly altered. After total bypass, relaxation responses to protamine and protamine-heparin complex were markedly reduced, whereas histamine induced contraction of pulmonary microvessels. Endothelium-independent relaxation to sodium nitroprusside was not affected by partial cardiopulmonary bypass and was slightly reduced after total bypass. A reduced direct vascular relaxation response to protamine and increased contractile response to histamine (or other humoral substances released during the systemic administration of protamine sulfate) may contribute to the elevation of pulmonary vascular resistance during infusion of protamine after cardiopulmonary bypass.

Heterogeneous vasomotor responses of rabbit coronary microvessels to isoflurane

BACKGROUND

Previous in vitro studies on the mechanism of isoflurane-elicited vasodilation have examined conductance arteries and reported conflicting data on whether the vasomotor response is mediated through the release of endothelium-derived nitric oxide. The current study was undertaken to define the effect of isoflurane on both resistance and conductance coronary arteries in rabbits and to elucidate the mechanism of the effect.

METHODS

Rabbit coronary arteries of varying sizes were dissected and each placed in a microvessel chamber. The arteries were studied in a pressurized (40 mmHg), no-flow state and were exposed to increasing concentrations of isoflurane, 0-3%, by an in-line bubble-through vaporizer. The vessel lumen diameter was monitored using an optical density video detection system. Selected experiments were performed on microvessels after preincubation with indomethacin, NG-monomethyl-L-arginine, or methylene blue or after endothelial denudation.

RESULTS

Isoflurane caused a dose-dependent constriction of small rabbit coronary arteries (internal diameter of 139 +/- 34 mu, mean +/- SD), whereas it caused dilation of large coronary arteries (371 +/- 54 mu). The vasoconstriction of the small coronary arteries by isoflurane was abolished by endothelial denudation or after preincubation with indomethacin. The vasodilation of the large vessels by isoflurane was inhibited by endothelial denudation or after preincubation with NG-mono-methyl-L-arginine, methylene blue, or indomethacin.

CONCLUSIONS

Our data suggest that vessel size is a determinant of the vasomotor response to isoflurane. Exposure to isoflurane produces vasodilation of conductance coronary arteries, whereas it is associated with vasoconstriction of resistance coronary microvessels. The latter appears to be endothelium-dependent and mediated by cyclooxygenase product(s), whereas the former, also endothelium-dependent, is mediated by both product(s) of cyclooxygenase and endothelium-derived nitric oxide.

Coronary microvascular responses after exposure to iodinated contrast media

RATIONALE AND OBJECTIVES

Iodinated contrast media can cause a number of well-described acute hemodynamic and vascular effects including vascular spasm, hypotension, and arrhythmias. Coronary microvessels were studied in vitro after high-dose exposure to an ionic, high-osmolar contrast agent diatrizoate meglumine in vivo. The aim of this study was to examine the endothelium-dependent and endothelium-independent vasodilator responses of the microvessels after previous contrast media administration in a clinically relevant setting.

METHODS

Left coronary angiography was performed on six pigs using a cumulative dose of 60 mL (5 mL/injection) of diatrizoate meglumine. After 1 hour of reperfusion, epicardial coronary microvessels were studied in vitro in a pressurized, no-flow state with video microscopy. The vasodilators bradykinin, calcium ionophore A23187, and sodium nitroprusside were sequentially applied extraluminally after preconstriction. Serotonin and the thromboxane A2 analog U46619 were studied without preconstriction.

RESULTS

Microvessels exposed to diatrizoate meglumine had normal relaxation responses to the endothelium-dependent vasodilators bradykinin and calcium ionophore A23187 when compared to control vessels. The vasoconstrictor responses to U46619 and serotonin were not significantly altered compared to control vessels. Responses to the endothelium-independent vasodilator sodium nitroprusside were not reduced or were slightly enhanced after exposure to contrast media.

CONCLUSION

Coronary resistance vessels responses to the endothelium-dependent vasodilators bradykinin and calcium ionophore A23187 are not diminished after previous exposure to diatrizoate meglumine. The vasoconstrictor responses to U46619 and serotonin were similarly unaffected by previous exposure to contrast media. This suggests that, when used in clinically relevant amounts, diatrizoate meglumine does not cause functional endothelium or vascular smooth muscle impairment.

Adenosine and AICA-riboside fail to enhance microvascular endothelial preservation

Crystalloid cardioplegia may cause coronary microvascular endothelial dysfunction during cardiopulmonary bypass. The perioperative administration of either adenosine or AICA-riboside (acadesine, 5-aminoimidazole-4-carboxamide-1-ribofuranoside) has been associated with improved myocardial functional preservation and improved coronary blood flow after ischemic arrest. To examine if this enhanced recovery of myocardial function and perfusion may be related to improved endothelial preservation, pigs were placed on cardiopulmonary bypass and the hearts were arrested with plain cold, hyperkalemic (K+ = 25 mmol/L) crystalloid cardioplegia, or cardioplegic solution containing either 0.1 mmol/L adenosine or 50 mumol/L AICA-riboside, which causes the release of endogenous adenosine. AICA-riboside (375 mg) also was infused over 30 minutes before cardioplegia in the later group. After 1 hour of ischemic cardioplegia, hearts were reperfused for 1 hour while the pigs were weaned from cardiopulmonary bypass. Coronary arterioles (90 to 190 microns in diameter) from both subepicardial and subendocardial regions of the left ventricle were studied in vitro in a pressurized, no-flow state with videomicroscopy. After contraction of vessels by 25% to 40% of the baseline diameter, drugs were applied extraluminally. Relaxation of control arterioles to serotonin was slightly greater in vessels from the subendocardial region compared with vessels from the subepicardial region, and subendocardial arterioles were more affected by cardioplegia than were subepicardial vessels. In contrast, relaxations of control microvessels to bradykinin and the calcium ionophore A23187 were similar in the two transmural myocardial regions. Responses to bradykinin and A23187 were significantly and similarly reduced after ischemic arrest with plain crystalloid cardioplegia.(ABSTRACT TRUNCATED AT 250 WORDS)

Epicardial and endocardial coronary microvascular responses: effects of ischemia-reperfusion

To examine whether endocardial microvascular function is preferentially impaired by ischemia and reperfusion, we studied endothelium-dependent responses of epicardial and endocardial coronary microvessels (130-220 microns) from control pigs and from pigs subjected to 1-h regional myocardial ischemia (circumflex occlusion) followed by 1-h reperfusion (n = 8) in vitro using videomicroscopy. In control animals (n = 8), no significant transmural differences were apparent in microvascular responses to the endothelium-dependent agents bradykinin or the calcium ionophore A23187, to the endothelium-independent agent sodium nitroprusside (SNP), or to adenosine. Serotonin caused a slight but statistically insignificant greater relaxation of endocardial than of epicardial microvessels. After ischemia-reperfusion, relaxations to all endothelium-dependent agents (serotonin, bradykinin, A23187) and to adenosine were significantly reduced (p < 0.05 for all agents) as compared with the respective control responses. There were no significant differences between epicardial and endocardial responses in the ischemia-reperfusion group for any of the vasoactive agents. Endothelium-independent responses to SNP were not affected by ischemia-reperfusion, indicating no alteration in the ability of vascular smooth muscle to relax through guanylate cyclase-mediated mechanisms. Control epicardial microvascular responses were examined after endothelial denudation and after pretreatment with NG-monomethyl-L-arginine (L-NMMA), indomethacin, or glibenclamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms causing coronary microvascular dysfunction following crystalloid cardioplegia and reperfusion

OBJECTIVE

The aim was to examine the mechanisms of coronary microvascular dysfunction during cardiopulmonary bypass and ischaemic arrest using a crystalloid cardioplegic solution.

METHODS

Porcine hearts were arrested with cold hyperkalaemic (K+ = 25 mmol.litre-1) cardioplegic solution for 1 h during cardiopulmonary bypass and then reperfused for 1 h. Selected hearts were arrested but not reperfused. Coronary vessels of non-instrumented pigs were used as controls. In vitro vascular responses of subepicardial and subendocardial arterioles were examined in a pressurised (40 mm Hg) no flow state with video microscopy.

RESULTS

Following 1 h of ischaemic cardioplegia, endothelium dependent relaxations of epicardial arterioles to the receptor mediated agent ADP and the non-receptor-mediated agent calcium ionophore A23187 were moderately reduced, and the contractile responses to KCl or the thromboxane A2 analogue U46619 were reduced compared to responses of vessels from control animals. After 1 h of reperfusion, U46619 caused contraction greater than control values, while contraction to KCl and endothelium dependent relaxations to ADP or A23187 were further reduced. Responses of endocardial microvessels to serotonin were slightly more affected by cardioplegia and reperfusion than were epicardial vessels, while the effect on responses of epicardial and endocardial vessels to bradykinin or A23187 were similar. Endothelium independent relaxation to sodium nitroprusside was not altered in any of the experimental groups. The addition of manganese superoxide dismutase to the cardioplegic solution markedly preserved endothelium dependent responses to ADP and A23187 and contractile response to U46619, compared to the responses of vessels from the plain crystalloid cardioplegia group, but had no effect on relaxation to sodium nitroprusside or on contraction to KCl. Five hours of normokalaemic hypothermia (5-10 degrees C) in Krebs buffer had minimal effect on vasodilator responses. Electron microscopy revealed preserved endothelial and smooth muscle cell structure, and focal mononuclear leucocyte-endothelium adherence following cardioplegic arrest and reperfusion.

CONCLUSIONS

Ischaemic cardioplegia-reperfusion induced endothelium dependent and direct smooth muscle microvascular dysfunction is at least partially mediated by prolonged exposure of vessels to hyperkalaemia and to the generation of oxygen derived free radicals. Leucocytes probably mediate injury during reperfusion, while hypothermia has minimal effect on recovery of vasomotor function.

Altered pulmonary microvascular reactivity after total cardiopulmonary bypass

Pulmonary vascular resistance is frequently elevated after cardiac operations in which cardiopulmonary bypass is used. In our study of the possible contribution of altered pulmonary microvascular reactivity to this condition, sheep were heparinized, cannulated via the aorta and right atrium, and placed on total cardiopulmonary bypass. After 90 minutes of total cardiopulmonary bypass and pulmonary arterial occlusion, the sheep were removed from cardiopulmonary bypass, and their lungs were perfused normally for 60 minutes. Noninstrumented animals were used as controls. To evaluate the effect of 90 minutes of extracorporeal circulation without reduced pulmonary perfusion, we studied additional sheep after they underwent right heart bypass with a pump-oxygenator. Pulmonary microarterial vessels (130 to 230 microns in diameter) from each group were examined in vitro in a pressurized (20 mm Hg), no-flow state with video microscopic imaging and electronic dimension analysis. After preconstriction of vessels with the thromboxane A2 analog U46619 by 30% to 40% of the baseline diameter, vasoactive drugs were applied extraluminally. Serotonin caused control microvessels to dilate. In the presence of the nitric oxide synthetase inhibitor NG-methyl-L-arginine, this was converted to a significant contractile response. Acetylcholine alone had minimal effect on control vessels. However, in the presence of the cyclooxygenase inhibitor indomethacin, acetylcholine caused a significant relaxation response. After total cardiopulmonary bypass and pulmonary reperfusion, pulmonary microvessels contracted significantly when exposed to acetylcholine and serotonin, compared with respective control responses. Both these contractile responses were inhibited in the presence of indomethacin. Endothelium-independent responses to sodium nitroprusside and U46619 and dilation responses to adenosine were not altered after cardiopulmonary bypass. Extracorporeal circulation with continued pulmonary arterial perfusion (right heart bypass group) had no effect on microvascular responses. In conclusion, total cardiopulmonary bypass with associated reduced pulmonary perfusion causes significant alterations of endothelium-dependent pulmonary microvascular responses because of the increased release of a constrictor prostanoid substance and possibly because of reduced release of endothelium-derived relaxing factor.

Responses of porcine epicardial venules to neurohumoral substances

OBJECTIVE

The coronary microvenous system may be determinant of ventricular distensibility and of resistance to coronary flow under conditions of arteriolar dilatation. Because responses of venules have not been well defined, in vitro responses of porcine venules and arterioles to neurohumoral substances were examined.

METHODS

Porcine subepicardial venules (125-250 microns in diameter) and arterioles (100-200 microns in diameter) were studied in a pressurised no flow state with video microscopical imaging and electronic dimension analysis. After precontraction of vessels with the thromboxane A2 analogue U46619, agents were applied extraluminally.

RESULTS

Responses of precontracted venules to sodium nitroprusside, adenosine, and adenosine 5' diphosphate (ADP) were comparable with those of similarly sized arterioles. By contrast, precontracted venules responded minimally to noradrenaline, whereas arterioles were dilated potently by this agent. Precontracted arterioles were dilated minimally by serotonin and were contracted slightly by acetylcholine, whereas venules dilated in response to either serotonin or acetylcholine. Serotonin and acetylcholine both produced greater contraction in non-precontracted arterioles than in non-precontracted venules. Responses of venules to most substances were minimally affected by changes in oxygen tension except when this was very low. Relaxation of venules by ADP, serotonin, and acetylcholine were all inhibited to varying degrees by indomethacin, methylene blue, and NG-methyl-L-arginine (L-NMMA). Both methylene blue and L-NMMA produced minimal but significant contraction of non-precontracted venules, indicating a small amount of basal release of endothelium derived relaxing factor.

CONCLUSION

Responses of coronary venules to acetylcholine, serotonin, and noradrenaline are opposite or of a significantly different magnitude when compared with the respective arteriolar responses. Relaxation of venules to ADP, serotonin, and acetylcholine is likely mediated at least in part by the release of endothelium derived relaxing factor and prostaglandins.

Blood and albumin cardioplegia preserve endothelium-dependent microvascular responses

Alterations of vascular reactivity may be a cause of reduced myocardial perfusion after cardioplegic arrest. The effects of blood and albumin cardioplegia on endothelium-dependent coronary microvascular function and ultrastructure were examined after cardiopulmonary bypass, ischemic arrest, and reperfusion. During cardiopulmonary bypass, porcine hearts were arrested with either blood, albumin-crystalloid, or crystalloid cardioplegia for 1 hour, followed with reperfusion for 1 hour. Noninstrumented pigs were used as controls. Coronary microarterial vessels (90 to 190 microns in diameter) were studied in a pressurized, no-flow state with video microscopic imaging and electronic dimension analysis. Ischemic arrest with crystalloid cardioplegia markedly reduced endothelium-dependent relaxations to the adenine nucleotide adenosine diphosphate and the calcium ionophore A23187. Enhanced contractile responses were observed to the platelet-derived vasoactive substance serotonin and to the thromboxane A2 analogue U46619. Indomethacin corrected the enhanced contractile responses to serotonin, indicating the enhanced release of a constrictor prostanoid substance. Indomethacin had no effect on the impaired relaxations to adenosine diphosphate or A23187. Endothelium-dependent relaxations to adenosine diphosphate, serotonin, and A23187 were significantly preserved with either blood or albumin-crystalloid cardioplegia, whereas contractile responses to U46619 were normal. Endothelium-independent relaxation to nitroprusside was similar in all groups, indicating normal smooth muscle responsiveness. Electron microscopy revealed minimal alterations of vascular morphology of vessels in both crystalloid and blood cardioplegia groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Bombesin increases fetal lung growth and maturation in utero and in organ culture

Pulmonary neuroendocrine cells (PNECs) in fetuses synthesize gastrin-releasing peptide (GRP, or mammalian bombesin) at high levels, but the role of this hormone in lung development has been obscure. The present study demonstrates that bombesin administered for 2 to 4 d toward the end of gestation in utero led to increased DNA (days 17 and 18) and saturated phosphatidylcholine (SPC) synthesis (day 18) in a dose-dependent fashion in fetal lung. These kinetics coincide with the timing of endogenous GRP gene activation in untreated fetal mouse lung, where GRP mRNA is detectable on day 16 and peaks at day 18. Electron microscopy on in vivo bombesin-treated fetal lung showed an increase in the number of cells containing lamellar bodies on both days 17 and 18, consistent with increased growth and/or maturation of type II cells. In mouse fetal lung organ cultures, the addition of bombesin led to accelerated uptake of [3H]thymidine into DNA, [3H]leucine into protein, and [3H]choline into SPC, indicating that increased growth and maturation may be direct effects. Extending these observations to another species, bombesin was found to induce growth and maturation of human fetal lung in organ culture. A monoclonal antibody to bombesin (2A11) prevented bombesin-induced increases in choline and thymidine incorporation in lung organ cultures and also blocked baseline automaturation of control lung organ cultures in serum-free medium. These data suggest that bombesin, and thus PNECs, play a role in normal lung development.