Caveolae in ventricular myocytes are required for stretch-dependent conduction slowing

Mechanical stretch of cardiac muscle modulates action potential propagation velocity, causing potentially arrhythmogenic conduction slowing. The mechanisms by which stretch alters cardiac conduction remain unknown, but previous studies suggest that stretch can affect the conformation of caveolae in myocytes and other cell types. We tested the hypothesis that slowing of action potential conduction due to cardiac myocyte stretch is dependent on caveolae. Cardiac action potential propagation velocities, measured by optical mapping in isolated mouse hearts and in micropatterned mouse cardiomyocyte cultures, decreased reversibly with volume loading or stretch, respectively (by 19±5% and 26±4%). Stretch-dependent conduction slowing was not altered by stretch-activated channel blockade with gadolinium or by GsMTx-4 peptide, but was inhibited when caveolae were disrupted via genetic deletion of caveolin-3 (Cav3 KO) or membrane cholesterol depletion by methyl-β-cyclodextrin. In wild-type mouse hearts, stretch coincided with recruitment of caveolae to the sarcolemma, as observed by electron microscopy. In myocytes from wild-type but not Cav3 KO mice, stretch significantly increased cell membrane capacitance (by 98±64%), electrical time constant (by 285±149%), and lipid recruitment to the bilayer (by 84±39%). Recruitment of caveolae to the sarcolemma during physiologic cardiomyocyte stretch slows ventricular action potential propagation by increasing cell membrane capacitance.

Evaluation of the humoral immune response in BALB/c mice immunized with a naked DNA vaccine anti-methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is the major pathogen involved in nosocomial infections, leading to high rates of morbidity and mortality in hospitals worldwide. The methicillin resistance occurs due to the presence of an additional penicillin-binding protein, PBP2a, which has low affinity for beta-lactam antibiotics. In the past few years, vancomycin has been the only antibiotic option for treatment of infections caused by multiresistant MRSA; however, reports of vancomycin-resistant strains have generated great concerns regarding the treatment to overcome these infections. In the present study, we report preliminary results regarding the humoral immune response generated in BALB/c mice by two different doses of naked DNA vaccine containing an internal region, comprising the serine-protease domain, of the PBP2a of MRSA. The immunization procedure consisted of four immunizations given intramuscularly within 15-day intervals. Blood was collect weekly and anti-PBP2a-specific antibodies were screened by ELISA. BALB/c mice immunized with DNA vaccine anti-PBP2a have shown higher antibody titers mainly after the fourth immunization, and intriguingly, no correlation between the humoral immune response and DNA dose was observed. Our results suggest that the DNA vaccine anti-PBP2a induced an immune response by production of specific antibodies anti-MRSA in a non-dose-dependent manner, and it could represent a new and valuable approach to produce specific antibodies for passive immunization to overcome MRSA infections.

Compartmentation of G-protein-coupled receptors and their signalling components in lipid rafts and caveolae

G-protein-coupled receptors (GPCRs) and post-GPCR signalling components are expressed at low overall abundance in plasma membranes, yet they evoke rapid, high-fidelity responses. Considerable evidence suggests that GPCR signalling components are organized together in membrane microdomains, in particular lipid rafts, enriched in cholesterol and sphingolipids, and caveolae, a subset of lipid rafts that also possess the protein caveolin, whose scaffolding domain may serve as an anchor for signalling components. Caveolae were originally identified based on their morphological appearance but their role in compartmentation of GPCR signalling has been primarily studied by biochemical techniques, such as subcellular fractionation and immunoprecipitation. Our recent studies obtained using both microscopic and biochemical methods with adult cardiac myocytes show expression of caveolin not only in surface sarcolemmal domains but also at, or close to, internal regions located at transverse tubules/sarcoplasmic reticulum. Other results show co-localization in lipid rafts/caveolae of AC (adenylyl cyclase), in particular AC6, certain GPCRs, G-proteins and eNOS (endothelial nitric oxide synthase; NOS3), which generates NO, a modulator of AC6. Existence of multiple caveolin-rich microdomains and their expression of multiple modulators of signalling strengthen the evidence that caveolins and lipid rafts/caveolae organize and regulate GPCR signal transduction in eukaryotic cells.

Occupational genotoxicity risk evaluation through the comet assay and the micronucleus test

The micronucleus (MN) test and the alkaline single cell gel or comet assay were applied to exfoliated cells of the buccal mucous in order to evaluate the genotoxic risk associated with occupational exposure of 10 storage battery renovation workers, and 10 car painters, with age matched controls, in Pelotas, RS, in southern Brazil. In the MN test, 2000 exfoliated buccal cells were analyzed for each individual, while 100 cells were examined in the comet assay. In the comet test, both comet tail length and a damage index were calculated. Highly significant effects of occupational exposure were found with both the MN test and the comet assay (P<0.001). The comet assay was found to be rapid, of simple visualization, and it is a sensitive technique for measuring and analyzing DNA damage in human cells.

Absence of germline infection in male mice following intraventricular injection of adenovirus

The possibility of inadvertent exposure of gonadal tissue to gene therapy vectors has raised safety concerns about germline infection. We show here that the receptor for coxsackie B viruses and adenoviruses 2 and 5 (CXADR) is expressed in mouse germ cells, suggesting the possibility that these viruses could infect germ cells. To directly assess the risk of germline infection in vivo, we injected an adenovirus carrying the germ-cell-specific protamine promoter fused to the bacterial lacZ reporter gene into the left ventricular cavity of mice and then monitored expression of the reporter gene in germ cells. To differentiate between infection of stem cells and differentiating spermatogenic cells, we analyzed expression of the reporter cassette at different times after viral delivery. Under all conditions tested, mice did not express the Escherichia coli beta-galactosidase protein in developing spermatids or in mature epididymal spermatozoa. Primary germ cells cultured in vitro were also refractory to adenoviral infection. Our data suggest that the chance of vertical germline transmission and insertional mutagenesis is highly unlikely following intracoronary adenoviral delivery.

Promoting safe motherhood in the community: the case for strategies that include men

Although a decade has now passed since the launching of the Safe Motherhood Initiative, maternal mortality continues to be the health indicator showing the greatest disparity between developed and developing countries. Recently revised WHO and UNICEF figures indicate that an estimated 90% of the 585,000 worldwide maternal deaths that occur each year take place in sub-Saharan Africa and Asia. In terms of the lifetime risk of maternal death, this disparity remains striking: 1 in 12 women in parts of sub-Saharan Africa, compared with 1 in 4,000 women in Northern Europe. In addition, for every woman who dies, an estimated 16-17 will suffer from pregnancy-related complications. Research suggests that, in addition to biomedical interventions and the strengthening of health care services, improving awareness of obstetric complications among members of a pregnant woman's immediate and wider social network is an important step in improving her chances of survival when such complications occur. Many of the interventions implemented so far have focused exclusively on improving women's knowledge and practices as they relate to maternal health issues. Nevertheless, it is now increasingly being recognised that the actions required to achieve improvements in reproductive health outcomes in general, and maternal health in particular, should involve communities in the process and encourage men's active participation. Despite this, very few studies on risk perceptions or interventions to raise community awareness of obstetric risk factors, their complications and their consequences have targeted men. The present article argues for the development and testing of risk awareness interventions, which, in addition to women, target men in their familial and social roles within communities and as workers within health care services as a means of improving maternal health outcomes.

Intracoronary delivery of adenovirus encoding adenylyl cyclase VI increases left ventricular function and cAMP-generating capacity

BACKGROUND

We tested the hypothesis that intracoronary injection of a recombinant adenovirus encoding adenylyl cyclase type VI (AC(VI)) would increase cardiac function in pigs.

METHODS AND RESULTS

Left ventricular (LV) dP/dt and cardiac output in response to isoproterenol and NKH477 stimulation were assessed in normal pigs before and 12 days after intracoronary delivery of histamine followed by intracoronary delivery of an adenovirus encoding lacZ (control) or AC(VI) (1.4x10(12) vp). Animals that had received AC(VI) gene transfer showed increases in peak LV dP/dt (average increase of 1267+/-807 mm Hg/s; P=0.0002) and cardiac output (average increase of 39+/-20 mL. kg(-1). min(-1); P<0.0001); control animals showed no changes. Increased LV dP/dt was evident 6 days after gene transfer and persisted for at least 57 days. Basal heart rate, blood pressure, and LV dP/dt were unchanged, despite changes in cardiac responsiveness to catecholamine stimulation. Twenty-three hour ECG recordings showed no change in mean heart rate or ectopic beats and no arrhythmias. LV homogenates from animals receiving AC(VI) gene transfer showed increased AC(VI) protein content (P=0.0007) and stimulated cAMP production (P=0.0006), confirming transgene expression and function; basal LV AC activity was unchanged. Increased cAMP-generating capacity persisted for at least 18 weeks (P<0.0002).

CONCLUSIONS

Intracoronary injection of a recombinant adenovirus encoding AC provides enduring increases in cardiac function.

Cardiac-directed adenylyl cyclase expression improves heart function in murine cardiomyopathy

BACKGROUND

We tested the hypothesis that increased cardiac myocyte adenylyl cyclase (AC) content increases cardiac function and response to catecholamines in cardiomyopathy.

METHODS AND RESULTS

Transgenic mice with cardiac-directed expression of AC type VI (ACVI) were crossbred with mice with cardiomyopathy induced by cardiac-directed Gq expression. Gq mice had dilated left ventricles, reduced heart function, decreased cardiac responsiveness to catecholamine stimulation, and impaired beta-adrenergic receptor (betaAR)-dependent and AC-dependent cAMP production. Gq/AC mice showed improved basal cardiac function in vivo (P=0.01) and ex vivo (P<0.0005). When stimulated through the betaAR, cardiac responsiveness was increased (P=0.02), and cardiac myocytes showed increased cAMP production in response to isoproterenol (P=0.03) and forskolin (P<0.0001).

CONCLUSIONS

Increasing myocardial ACVI content in cardiomyopathy restores cAMP-generating capacity and improves cardiac function and responsiveness to betaAR stimulation.

Adenylylcyclase increases responsiveness to catecholamine stimulation in transgenic mice

BACKGROUND

The cellular content of cAMP generated by activation of adenylylcyclase (AC) through the beta-adrenergic receptor (betaAR) is a key determinant of a cell's response to catecholamine stimulation. We tested the hypothesis that increased AC content, independently of betaAR number, increases responsiveness to catecholamine stimulation in vivo.

METHODS AND RESULTS

Transgenic mice with cardiac-directed expression of ACVI showed increased transgene AC expression but no change in myocardial betaAR number or G-protein content. When stimulated through the betaAR, cardiac function was increased, and cardiac myocytes showed increased cAMP production. In contrast, basal cAMP and cardiac function were normal, and long-term transgene expression was not associated with abnormal histological findings or deleterious changes in cardiac function.

CONCLUSIONS

The amount of AC sets a limit on cardiac beta-adrenergic signaling in vivo, and increased AC, independent of betaAR number and G-protein content, provides a means to regulate cardiac responsiveness to betaAR stimulation. Overexpressing an effector (AC) does not alter transmembrane signaling except when receptors are activated, in contrast to receptor/G-protein overexpression, which yields continuous activation and has detrimental consequences. Our findings establish the importance of AC content in modulating beta-adrenergic signaling in the heart, suggesting a new target for safely increasing cardiac responsiveness to betaAR stimulation.

Determination of monensin in high-moisture cattle rations by liquid chromatography with postcolumn derivatization

An existing liquid chromatographic method using postcolumn derivatization has been used extensively to quantitate monensin in animal feeds. Because of the relatively high moisture content of many cattle feed rations, some modifications were made to this method. Several sample-processing steps were evaluated to determine optimum sample-processing procedure. The sample weight/sample diluent ratio was modified, and method linearity was validated for the lower monensin concentrations anticipated in high-moisture cattle rations. The accuracy and precision of data generated at these lower concentrations were also determined. Because of the high moisture content of these rations, data analysis for this method required correction of feed potency for loss on drying. With these modifications, monensin can be accurately determined in high-moisture cattle rations.

Heparin accelerates coronary collateral development in a porcine model of coronary artery occlusion

BACKGROUND

Coronary collaterals develop in response to an ischemic stimulus. However, collateral growth is not sufficient to result in the complete recovery of coronary reserves. Using a porcine model of gradual coronary artery occlusion, we investigated the effect of continuous heparin infusion on coronary collateral development.

METHODS AND RESULTS

We placed ameroid constrictors on the left circumflex coronary artery of 16 minipigs; the ameroid constrictors completely occluded the left circumflex coronary artery at 10 +/- 1 days. Half of the animals also were instrumented with subcutaneously placed osmotic pumps and catheters that delivered heparin (300 units/h) into the external jugular vein. At 2, 3, and 4 weeks, we assessed blood flow at rest and during vasodilation using radioactive microspheres. Our results indicate that the animals receiving heparin restored resting myocardial blood flow to normal levels at or before 2 weeks; in contrast, we did not see normal resting myocardial blood flow levels in the untreated-ameroid animals until 3 weeks. Under vasodilated conditions, untreated-ameroid animals experienced a severe loss of coronary reserves at 2 weeks. Although this improved with time, these animals still were significantly underperfused at 4 weeks. In contrast, in the heparin-treated animals, coronary reserves returned to near-normal levels between 3 and 4 weeks. In addition, infarct size was significantly smaller in the heparin-treated animals.

CONCLUSIONS

These experiments suggest that the administration of heparin in the early phases of gradual coronary occlusion accelerates the rate of return of normal blood flow under resting conditions, substantially increases the recovery of coronary reserve, and reduces the risk of infarction.

Intracoronary C5a induces myocardial ischemia by mechanisms independent of the neutrophil: leukocyte filters desensitize the myocardium to C5a

Activation of the complement cascade with the generation of anaphylatoxins accompanies the inflammatory response elicited by acute myocardial ischemia and reperfusion. Although complement is activated in the interstitium during acute myocardial ischemia, we have studied mechanisms whereby complement might exacerbate ischemia by using a model employing intracoronary injection of C5a in nonischemic hearts. Intracoronary injection of complement component C5a induces transient myocardial ischemia, mediated through the production of the coronary vasoconstrictors thromboxane A2 and peptidoleukotrienes (LTC4, LTD4), and causes sequestration of polymorphonuclear leukocytes (PMN) in the coronary vascular bed. To further investigate the role of the PMN in the C5a-induced vasoconstriction, the left anterior descending coronary artery (LAD) in pigs was perfused at constant pressure and measurements of coronary blood flow, myocardial contractile function (sonomicrometry), arterial/coronary venous blood PMN count, and thromboxane B2 (TxB2) levels were performed. The myocardial response to intracoronary C5a (500 ng) was determined before, during, and after perfusion with blood depleted of PMNs using leukocyte filters (Sepacell R-500, Pall PL-100). In additional animals, the myocardial response to the PMN chemotactic agent, LTB4, and the effects of intracoronary C5a during constant flow perfusion were measured. Control intracoronary injection of C5a decreased flow (41% of baseline) and contractile function (39% of baseline), PMNs were trapped (5.1 x 10(3) cells/microliters), and TxB2 concentration increased in coronary venous blood. The response to C5a during coronary perfusion with arterial blood depleted of PMNs with Sepacell or Pall filters (less than 0.1 x 10(3) cells/microliters) was greatly blunted, with flow and contractile function falling by less than 14 and 8%, respectively, from baseline, and release of TxB2 was greatly attenuated. However, the myocardial ischemia and TxB2 release remained depressed in response to C5a after removal of the filters and perfusion with either arterial blood containing normal levels of PMNs or stored arterial blood never exposed to filters. In contrast, the repeat C5a challenge resulted in equivalent myocardial extraction of PMNs, thus indicating a dissociation of PMN sequestration from the acute ischemic response and release of TxB2. In separate experiments, the intracoronary injection of LTB4 also resulted in a pronounced myocardial extraction of PMNs (8.6 x 10(3) cells/microliters) greater than during C5a, but did not depress coronary flow or function. Perfusion at constant flow greatly diminished the ischemic response to C5a, indicating that vasoconstriction and resultant ischemia is the main cause of the contractile dysfunction. These data indicate that leukocyte filters inhibit the myocardial ischemia and release of TxB2 induced by C5a via mechanisms not related to PMN depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of long-term exercise on regional myocardial function and coronary collateral development after gradual coronary artery occlusion in pigs

The effect of myocardial ischemia, induced by long-term exercise, on regional myocardial function and coronary collateral development was examined in pigs after gradual occlusion of the left circumflex coronary artery (LCx) with an ameroid occluder. Thirty days after surgery, regional myocardial function and blood flow were assessed during exercise in 22 pigs separated into exercise (n = 12) and sedentary groups (n = 10). The exercise group trained on a treadmill for 25 +/- 1 days, 30-50 min/day, at heart rates of 210-220 beats/min. After 5 weeks, another exercise test was performed. In the exercise group, after training, we observed an improvement in systolic wall thickening, expressed as a percentage of rest, in the collateral-dependent LCx region from 64 +/- 8% to 87 +/- 6% (p less than 0.01) at moderate exercise levels (220 beats/min) and from 45 +/- 7% to 73 +/- 7% (p less than 0.01) at severe exercise levels (265 beats/min). Transmural myocardial blood flow in the LCx region expressed as a ratio of flow in the nonoccluded region of the left ventricle also increased significantly (p less than 0.01) during severe exercise after 5 weeks. The sedentary group showed an improvement in systolic wall thickening in the LCx region during moderate exercise compared with the initial exercise test (p less than 0.05) but no significant change in systolic wall thickening or myocardial blood flow ratios during severe exercise after 5 weeks. We conclude that long-term exercise after gradual LCx coronary artery occlusion in pigs improves myocardial function and coronary collateral reserve in collateral-dependent myocardium during exercise.

Thromboxane A2 and peptidoleukotrienes contribute to the myocardial ischemia and contractile dysfunction in response to intracoronary infusion of complement C5a in pigs

Intracoronary infusions of activated complement C5a result in myocardial ischemia, contractile dysfunction, and leukocyte accumulation. The hypothesis was tested that the generation of the coronary vasoconstrictors, thromboxane A2 and the 5-lipoxygenase leukotrienes (LTC4 and LTD4), contributes to the C5a-induced decrease in coronary blood flow and contractile function. The left anterior descending coronary artery in anesthetized swine was cannulated and servo pump-perfused with arterial blood at constant pressure and measured flow. Regional subendocardial contractile function was assessed with sonomicrometry. The interventricular vein was cannulated for sampling of coronary venous blood for leukocyte count. The responses in left anterior descending coronary artery blood flow and percent segment shortening to intracoronary infusions of LTC4 (1 microgram), LTD4 (1 microgram), thromboxane agonist U46619 (7.5 micrograms), and C5a (500 ng) were assessed before and after 1) LTD4/LTE4 receptor blockade with leukotriene receptor blocker LY171883 (10 mg/kg i.v.) (n = 5), 2) thromboxane A2/prostaglandin H2 receptor blockade with thromboxane receptor blocker BM13505 (2 mg/kg i.v.) (n = 5), and 3) combined thromboxane and leukotriene receptor blockade (n = 5). In the absence of receptor blockade, intracoronary C5a decreased coronary flow (50-60%) and regional segment function (60-70%) compared with the preinfusion levels. This was accompanied by a fall in coronary venous blood leukocyte levels by 5-6 x 10(6) cells/ml in the absence of alterations in arterial blood leukocyte count. Intracoronary injections of LTD4, LTC4, or U46619 also resulted in prompt decreases in coronary blood flow (50-60%) and segment function (70-80%) from preinfusion levels. Leukotriene receptor blockade with LY171883 abolished these responses to LTD4 and LTC4. Administration of LY171883 also attenuated (p less than 0.05) the myocardial response to C5a; coronary flow and segment function decreased by approximately 28% from preinfusion levels. Thromboxane receptor blockade with BM13505 eliminated the response in coronary flow and segment function to intracoronary U46619. Similar to LY171883, administration of BM13505 blunted (p less than 0.05) the C5a-induced decreases in coronary flow and contractile function, which fell by approximately 20-25% from the preinfusion level. After the combined LTD4/LTE4 receptor and thromboxane A2/prostaglandin H2 receptor blockade, intracoronary C5a resulted in little change in both coronary blood flow and segment shortening. In contrast to the flow and function effects, the C5a-induced myocardial leukocyte extraction was not decreased by leukotriene and/or thromboxane receptor blockade.(ABSTRACT TRUNCATED AT 400 WORDS)

Thromboxane is produced in response to intracoronary infusions of complement C5a in pigs. Cyclooxygenase blockade does not reduce the myocardial ischemia and leukocyte accumulation

Activated polymorphonuclear leukocytes (PMNs) contribute to myocardial injury during ischemia and reperfusion. There is evidence that activation of the complement pathway may be one of the mechanisms of PMN activation during ischemia. Intracoronary infusion of complement C5a during normal perfusion pressure is associated with decreased coronary flow, contractile dysfunction, and PMN accumulation. The mechanisms responsible for these changes have not been identified. Thromboxane A2 (TXA2) is a potential mediator of this myocardial ischemic response. Activated PMNs produce TXA2, a known coronary vasoconstrictor, and TXA2 was shown to be a mediator of the pulmonary hypertensive response to activated complement. The goal of the present study was to determine if an enhanced TXA2 production is associated with the myocardial response to C5a and whether cyclooxygenase blockade would reduce the myocardial ischemia. In open-chest pigs, intracoronary C5a (500 ng) caused reversible reductions in blood flow (50.0% of control), regional contractile function (25.8% of control), leukocyte trapping (1.0 x 10(6) cells/g myocardium or a peak artery-coronary venous difference of 5.3 x 10(3) cells/microliters blood), and increased coronary venous TXB2 (the TXA2 breakdown product) from 1.6 pmol/ml to a peak of 6.9 pmol/ml. Cyclooxygenase blockade with aspirin or indomethacin, which prevented TXB2 production, did not alter the response in flow, function, or PMN trapping. Ibuprofen, a known direct inhibitor of PMNs in addition to its cyclooxygenase blockade effect, reduced the response slightly. The pig coronary vascular bed was responsive to the TXA2 agonist U46619, which reduced flow and function without PMN trapping. Mechanical reductions in coronary flow to levels equivalent to those during the C5a infusions did not increase coronary venous TXB2 nor cause PMN trapping but did cause equivalent contractile dysfunction. Incubation of whole blood with C5a at concentrations equivalent to those achieved in vivo did not cause TXB2 production. We conclude that 1) TXA2 is produced in response to intracoronary C5a and 2) cyclooxygenase blockade does not prevent the C5a-induced myocardial ischemia, contractile dysfunction, and PMN trapping. The TXA2 production likely involves a vascular site or a blood cell-vascular interaction. This model system indicates the potential for persistently activated PMNs to cause continued ischemia during myocardial reperfusion.

Coronary collateral reserve during exercise induced ischemia in swine

We determined coronary collateral vasodilator reserve during exercise-induced ischemia in 17 mini-swine. We induced coronary collateral development in the left circumflex bed by placing an ameroid occluder on that artery. Four weeks later we studied the animals at rest and during exercise (EX) eliciting heart rates (HR) of 240 and 265 beats/min. We measured myocardial blood flow with microspheres and myocardial function by wall thickness sonomicrometry gauges. At matched exercise HRs we treated the animals with nifedipine (10 micrograms/kg IV) (EXN 10), nifedipine (100 micrograms/kg IV), (EXN 100), and adenosine infusion (1.2 mg/min/kg) EXAD. EXN 10 did not significantly alter hemodynamics compared to EX but EXN 100 and EXAD both decreased blood pressure significantly (p less than 0.05). Ischemic endocardial/nonischemic endocardial flow ratios and collateral resistance served as indices of vasodilator reserve. In the ischemic zone exercise reduced vasodilator reserve to 24 +/- 3% in the endocardium and 64 +/- 7% in the epicardium. Neither EXN 10 nor EXAD improved exercise-induced ischemia measured either as flow or function. However EXN 100 improved function during exercise-induced ischemia without improving coronary collateral flow. We conclude there is no additional coronary flow reserve during exercise-induced ischemia in the collateral dependent bed of the pig a few days after occlusion that can be recruited. Large doses of nifedipine improve function by direct action on the myocardium or by reducing afterload. The lack of development and deep myocardial distribution of the coronary collateral vessels in the pig may be an important factor of why these nifedipine responses differ from those reported in species which have primarily large epicardial coronary collaterals.

C5a decreases regional coronary blood flow and myocardial function in pigs: implications for a granulocyte mechanism

Granulocytes cause some of the pathophysiological effects associated with the capillary no-reflow phenomenon during ischemia and in ischemia-reperfusion injury. However, no study has examined the consequences of in vivo granulocyte activation during normal perfusion pressures. In this study, we examined the effects of intracoronary administration of the complement component C5a, which is known to be a potent granulocyte activating factor. Nine open-chest, anesthetized pigs were instrumented to monitor regional coronary blood flow and segment shortening, left ventricular dP/dt, heart rate, and pulmonary artery and aortic blood pressures and to sample arterial and regional coronary venous blood for oxygen content and complete blood counts. Intracoronary infusion of human or porcine C5a in doses ranging from 10 to 500 ng produced a significant reduction in regional coronary blood flow and myocardial function. Although perfusion pressure and heart rate remained constant, venous oxygen content fell, indicating an imbalance between myocardial oxygen supply and demand. In addition, the arteriovenous difference of white blood cells was increased significantly after anaphylatoxin infusion, indicating intravascular trapping in the myocardium. Granulocytes accounted entirely for the differences in leukocyte counts because no significant changes in platelet, lymphocyte, or hematocrit levels were observed. Injection of vehicle alone did not alter any of the monitored variables.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered minimal coronary resistance to antegrade reflow after chronic coronary artery occlusion in swine

We examined coronary pressure-flow relations after chronic coronary artery occlusion induced by placement of an ameroid occluder on the left circumflex coronary artery in swine. An acute open-chest procedure was performed in nine pigs 27 +/- 2 days (mean +/- SEM) after surgical placement of the ameroid occluder, and in eight nonoperated control pigs. Coronary vascular resistances were measured during maximal coronary vasodilation with adenosine. Minimal coronary resistance was assessed before and after cannulation and extracorporeal perfusion of the left circumflex coronary artery distal to the site of the ameroid occluder in pigs from the ameroid group and in a similar site in control pigs. Minimal coronary resistance to antegrade reflow in the left circumflex region was decreased significantly in ameroid pigs compared with control pigs (0.06 +/- 0.01 vs. 0.26 +/- 0.03 mm Hg.min.100 g/ml, p less than 0.001, respectively). Decreased minimal coronary vascular resistance was present transmurally in the left circumflex region of ameroid pigs. Altered vascular resistance occurred only in myocardium distal to the ameroid occluder since the nonoccluded left anterior descending region in ameroid pigs had minimal coronary resistance similar to that of the same region from control pigs (0.23 +/- 0.03 vs. 0.19 +/- 0.02 mm Hg.min.100 g/ml). Thus altered minimal coronary vascular resistance occurs and probably reflects vascular proliferation and/or vascular alterations which result in an increased total cross-sectional area of the vasculature in the myocardium distal to the occlusion.

Effects of left circumflex Ameroid constrictor placement on adrenergic innervation of myocardium

We evaluated the adrenergic innervation of the swine and canine myocardium after placement of an Ameroid constrictor around the left circumflex coronary artery (LCX). Fluorescent histochemistry was used to identify adrenergic nerve terminals in the myocardium and coronary vasculature. Ameroid occlusion of the proximal LCX in 10 pigs for 3 wk resulted in 6 +/- 1% infarction as well as myocardial ischemia in the left circumflex region of pigs studied during exercise. However, placement of the Ameroid constrictor did not significantly alter the surface density of the nerve terminals in the LCX region of myocardium when compared with innervation of control hearts. Histological examination of the coronary arterial adrenergic innervation in Ameroid-occluded pigs revealed that coronary vessels in the circumflex region of the heart were innervated. Similarly, in seven LCX Ameroid-occluded dogs, no significant decrease in adrenergic innervation of the LCX region of myocardium was observed when compared with control dogs. In contrast LCX Ameroid-occluded pigs demonstrated significant (P less than 0.01) denervation of the left anterior descending (LAD) region of myocardium when compared with control animals. The close proximity of adrenergic nerve bundles in the proximal LAD region indicates that denervation of the myocardium supplied by the LAD may result from the dissection and/or fibrosis associated with placement of the Ameroid constrictor on the proximal LCX. Our results suggest that placement of an Ameroid constrictor on the proximal LCX does not significantly alter the adrenergic innervation of the LCX-perfused myocardium or its associated coronary vasculature. However, denervation of LAD-perfused myocardium and its vasculature may result.

Development of coronary collateral circulation in left circumflex Ameroid-occluded swine myocardium

Coronary collateral development was examined in 34 pigs after gradual occlusion of the left circumflex coronary artery (LCX) with an Ameroid constrictor. Collateral development was assessed by measurements of myocardial blood flow and regional myocardial function at rest and during exercise over a 16-wk period after placement of the constrictor. Coronary collateral development was adequate to prevent severe infarction and restore blood flow to the collateral-dependent LCX region within 3-7 wk. Infarction averaged 5.0 +/- 1.3% of the LCX region. Blood flows at rest were 1.05 +/- 0.14 and 1.13 +/- 0.15 ml.min-1.g-1 in the subendocardium of the collateral and control regions, respectively, 7 wk postoperatively. Concurrently, collateral vessel development supported normal myocardial function at rest as determined by systolic wall thickening in the LCX region. However, collateral development was limited, since blood flows during moderate and severe exercise were reduced in the LCX region compared with control and left anterior descending and right coronary regions. Blood flow ratios (collateral/control flow) during severe exercise 3 wk postoperatively were 0.23 +/- 0.03 and 0.57 +/- 0.05 in the subendocardium and subepicardium and were constant throughout the 16-wk period throughout the study. Myocardial function of the collateral region also was reduced during exercise and a 30-min recovery period. We suggest that this limited coronary collateral circulation, which develops in response to gradual coronary occlusion in swine, serves as a model for the human collateral circulation for the study of protocols to alter growth and development of coronary collateral vessels.

Contractile responses to sympathetic activation after coronary instrumentation

The consequences of acute coronary dissection and chronic coronary instrumentation on contractile responses to sympathetic activation were examined in dogs. Stimulation of the left ventrolateral cervical cardiac nerve in seven anesthetized dogs after acute dissection of the left circumflex coronary artery (CX) did not change the increase in systolic shortening velocity. After acute dissection of the left anterior descending coronary artery (LAD), nerve stimulation increased shortening velocity of the posterior wall in all dogs but enhanced that of the anterior wall in only five dogs. In six conscious dogs with chronic instrumentation of the CX, reflex sympathetic activation induced by occlusion of the inferior vena cava comparably increased thickening velocities of both the anterior wall and posterior walls both at 1 and 3 wk after instrumentation. In six other dogs with chronic instrumentation of the LAD, responses to caval occlusion were nonuniform and correlated to the morphological degree of sympathetic denervation. Therefore, acute dissection and chronic instrumentation of the LAD may produce sympathetic denervation but do not cause functionally significant sympathetic denervation of the CX region.

The pig as a model for myocardial ischemia and exercise

The pig has been well characterized as an appropriate model for the study of coronary physiology, the coronary collateral circulation and exercise physiology. We compared both Yucatan miniature swine and young farm pigs in experiments involving myocardial ischemia, infarction and exercise. The Yucatan pig was vigorous, docile and proved to be an appropriate model of coronary physiology and exercise in man. The exercise capacity of the Yucatan pig was greater than that of the similar weight Hampshire pig, apparently because of the higher hematocrit and larger heart size. Both breeds were able to increase their maximal oxygen consumption (VO2 max) by approximately 25% after 10 weeks of training. Experiments measuring maximal coronary capacity suggest that the vascular capacity was similar to that of man, but less than that of the dog. Acute occlusion of the coronary artery in pigs infarcted most of the tissue of the vascular bed at risk. The collateral circulation of the pig is less than one fourth that of the dog and is similar to that of man. Slow occlusion of the left circumflex coronary artery produces an ischemic vascular bed which is collaterally dependent with only 5% infarction. Collateral flow is sufficient to meet resting conditions, but during exercise, severe ischemia is unmasked. This ischemia is present for up to 16 weeks following occlusion. The observation of limited infarction in conjunction with limited collateral vessel development suggests that this is a good model for investigating the growth and development of coronary collateral circulation in man.

Modulation of receptor mediated leukotriene release in the perfused heart

The chemotactic peptide n-formyl-methionyl-leucyl-phenylalanine (FMLP) induces peptide leukotriene release at concentrations of 20-25 pmol/ml 3 min after the start of FMLP infusion. FMLP-induced leukotriene release in rabbit hearts is not blocked by the leukotriene receptor antagonist FPL-55712 at concentrations that totally antagonize the hemodynamic effects of exogenously infused peptide leukotrienes. Moreover, propyl gallate, a lipoxygenase inhibitor, does not block FMLP-induced leukotriene release. However, the chemotactic peptide antagonist (Boc-Phe-Leu-Phe-Leu-Phe-OH) totally antagonized FMLP-induced leukotriene release suggesting that the release is via a different mechanism, possibly a receptor mediated event.

Outpatient surgery in pediatric urology

Indications for ambulatory pediatric urological surgery have been broadened to include most inguinal and scrotal surgery, many endoscopic procedures and distal hypospadias repairs with or without chordee or urethroplasty. We have reviewed a 1-year experience with the 440 outpatient urological procedures performed at Children's Hospital of Michigan in 1984, and found a low (3.4 per cent) incidence of postoperative hospitalization and only a single complication. We conclude that outpatient surgery in well selected patients and procedures is safe, timely and economical.

Effects of peptide leukotrienes on cardiac dynamics in rat, cat, and guinea pig hearts

The purpose of the present investigation was to examine potential inotropic effects of leukotrienes C4 (LTC4) and D4 (LTD4) in relation to their potent coronary constricting effects. The experiments were carried out in isolated Langendorff perfused hearts and isolated electrically driven isometrically contracting papillary muscle preparations. Tissues from cat, rat, and guinea pig were used in the study. Both LTC4 and LTD4 at 50 ng/ml had no effect on papillary muscles isolated from the rat, guinea pig, or cat. These papillary muscles responded to known negative inotropic agents including pentobarbital sodium and methanol. In isolated hearts perfused under constant flow, both LTC4 and LTD4 at 50 ng/ml increased coronary perfusion pressure and decreased contractile force of the heart in all three species. In hearts perfused under constant pressure perfusion, both LTC4 and LTD4 decreased coronary flow with concomitant decreases in contractile force. The leukotriene antagonist, FPL 55712, blocked both the coronary constrictor and the cardiodepressant effects of both leukotrienes. Pentobarbital (100 micrograms/ml) significantly decreased cardiac contractile force without inducing coronary vasoconstriction. These findings demonstrate that LTC4 and LTD4 do not possess direct negative inotropic activity in cardiac muscles of these three species. However, LTC4 and LTD4 are potent coronary constrictors that can secondarily decrease myocardial contractile force via their coronary constrictor action.

Modulation of leukotriene synthesis and actions by synthetic derivatives of arachidonic acid

Seven analogs of arachidonic acid were tested for their coronary vasoactivity and their ability to inhibit LTC4 and LTD4 synthesis by lung tissue and to antagonize LTD4 induced coronary constriction. None of the seven arachidonic acid analogs significantly altered peptide leukotriene production by minced cat lung. Two of the analogs (i.e., 7, 13-diethanoarachidonic acid and 7, 10, 13-triethanoarachidonic acid) exerted modest but significant coronary vasodilation in isolated cat coronary arteries, and significantly antagonized the coronary vasoconstrictor response to LTD4. These analogs may be of interest in modulating leukotriene actions.

Specificity of anti-leukotriene actions of nicardipine

The calcium channel blocker, nicardipine (100 ng/ml) markedly antagonized the coronary vasoconstrictor effect of the peptide leukotrienes LTC4 and LTD4 on the isolated perfused cat coronary artery. However, nicardipine even at 300 ng/ml failed to antagonize the leukotriene induced contraction of either tracheal or pulmonary parenchymal strips from guinea pigs. However, at higher concentrations (i.e., 10 micrograms/ml), nicardipine inhibited the production of peptide leukotrienes from minced cat lung incubated in the presence of A23187. Thus, nicardipine exerts some selectivity in its anti-leukotriene actions.

Leukotriene production in isolated tissues of diabetic rats

We examined the ability of heart, aorta and lung obtained from alloxan diabetic rats as well as control rats to produce peptide leukotrienes (LT). The isolated perfused heart preparation as well as incubated minced tissue preparations were studied. Upon infusion of the Ca++ ionophore A23187, hearts from diabetic rats produced significantly less peptide LT when compared to control hearts. Lung tissue from diabetic animals incubated with A23187 also produced less immunoreactive peptide leukotrienes (iLT) when compared to the control group. In both preparations, incubation with the lipoxygenase inhibitor propyl gallate significantly inhibited the production of iLT in both the diabetic and control group. The observed differences in production of leukotrienes may alter vascular reactivity and thus play a role in the cardiovascular complications observed in diabetes.

Coronary vascular responsiveness to non-eicosanoid vasoconstrictors in the perfused diabetic rat heart

We tested arginine vasopressin, and a dihydropyridine calcium agonist, BAY K-8644 in isolated perfused hearts from control and diabetic rats. Arginine vasopressin (1-100 ng/ml) and BAY K-8644 (100-500 ng/ml) significantly increased coronary perfusion pressure during constant flow perfusion indicative of coronary vasoconstriction. However, no significant potentiation was observed between diabetic rats and their weight matched controls for either vasoconstrictor.

Potentiation of leukotriene formation in pulmonary and vascular tissue

Leukotriene (LT) release from vascular and pulmonary tissue was assessed by a radioimmunoassay for peptide leukotrienes (i.e., LTC4, LTD4 and LTE4). The calcium ionophore A-23187 at 1-3 micrograms/ml and platelet activating factor (PAF) at 10 micrograms/ml produced marked formation of peptide leukotrienes in minced cat pulmonary tissue. This was also confirmed by bioassay of the incubates in isolated perfused cat coronary arteries. Rat pulmonary tissue was comparable to cat with regard to LT production, but guinea-pig lung produced about 30-50% less on a weight basis. In addition, aortic and coronary artery vessel walls produced significant amounts of LTs. The time course for maximal leukotriene production occurred at 45-60 min of incubation at 37 degrees C in both the radioimmunoassay and the bioassay. Cat coronary artery constricted markedly to LTC4 or LTD4 (30-40 mm Hg) and to the lung or blood vessel incubate. This constriction was virtually totally blocked by the leukotriene antagonist FPL-55712, but not by the thromboxane receptor antagonist, pinane thromboxane A2, the alpha-adrenergic receptor antagonist, phenoxybenzamine, or the angiotensin receptor antagonist, saralasin. Thus, pulmonary and vascular tissue produce leukotrienes that appear to exert coronary constrictor effects on specific leukotriene receptors. These results indicate that the ischemia of shock and anaphylaxis may be accentuated by the release of peptide leukotrienes.

Altered coronary vascular responsiveness to leukotrienes in alloxan-diabetic rats

Altered responsiveness to and metabolism of various eicosanoids in diabetic animals and patients has been reported by several investigators. The purpose of this investigation was to examine the coronary vascular responsiveness of alloxan-diabetic rats to the leukotrienes. Hearts from 12- to 16-week-old alloxan-diabetic rats and weight-matched controls were perfused at constant flow by the Langendorff method. Coronary vasoactivity to leukotrienes B4, C4, D4 and E4 was assessed by measuring the change in coronary perfusion pressure upon infusion of these eicosanoids. Hearts from diabetic rats showed increased responsiveness to leukotrienes C4 (4-40 nM) and D4 (10-100 nM). Both control and diabetic rat hearts were only slightly responsive to leukotriene E4, and no difference between the two groups existed in the reactivity to this leukotriene. Neither group was responsive to the chemotactic leukotriene, B4. Perfusion of the hearts with the cyclooxygenase inhibitor, ibuprofen, failed to alter the coronary vascular responses to the leukotrienes. The coronary constrictor effects of the leukotrienes are the primary effect of these agents on the rat heart, since heart rate does not change significantly, and changes in contractile force are secondary to the coronary vascular constriction. These alterations in responsiveness to leukotrienes may play a role in the cardiovascular complications associated with diabetes.

Effects of lipoxygenase inhibitors in arachidonate-induced sudden death

Both BW 755c, a cyclo-oxygenase and lipoxygenase inhibitor, and nordihydroguaiaretic acid (NDGA), a selective lipoxygenase inhibitor, were tested for their protection against arachidonate-induced sudden death in rabbits. 100% survival was seen with BW 755c (1 mg kg-1), while NDGA showed 0 and 17% survival (2 mg kg-1 and 4 mg kg-1). BW 755c prevented 12-fold increase in plasma thromboxane B2 concentrations and the formation of pulmonary artery thrombi normally seen with arachidonate-induced sudden death, while NDGA showed no such protective effect. Radioimmunoassay of rabbit plasma for leukotrienes (LTC4, LTD4 and LTE4) indicated that they do not accumulate in blood in the model and BW 755c had no effect, suggesting that the deleterious effects seen are caused by cyclo-oxygenase pathway metabolites such as thromboxane A2, but not by lipoxygenase pathway products such as leukotrienes.

Hyperreactivity of coronary vasculature in platelet-perfused hearts from diabetic rats

Coronary vascular responsiveness to platelet-produced eicosanoids was examined in isolated perfused hearts of alloxan-diabetic rats. Coronary perfusion pressure was increased in isolated hearts of control and diabetic rats on perfusion with platelets and arachidonic acid (AA). However, the increase in perfusion pressure was approximately twofold higher in hearts of diabetic rats when compared with those isolated from control rats. This was associated with increased thromboxane B2 (TxB2) and prostaglandin F2 alpha (PGF2 alpha) production that was comparable in platelet-perfused hearts of control and diabetic animals. Ibuprofen, a cyclooxygenase inhibitor, blocked the increase in perfusion pressure and TxB2 and PGF2 alpha production by greater than 90% in both control and diabetic hearts perfused with platelets and AA. Dazoxiben, a thromboxane synthetase inhibitor, blocked the increase in perfusion pressure by 50%, totally inhibited TxB2 production, but increased PGF2 alpha production by 60% in both groups of platelet-perfused hearts. Increased levels of PGF2 alpha and possibly other constrictor eicosanoids (e.g., leukotriene D4) may account for the partial constriction observed in platelet-perfused hearts with dazoxiben. Results of the present study suggest that vascular reactivity to vasoconstrictor eicosanoids is increased in hearts of diabetic animals.

Studies on the mechanism of leukotriene induced coronary artery constriction

Leukotriene (LT) C4, D4, and E4 at concentrations of 10 to 100 ng/ml were found to be potent coronary artery constrictors in the perfused cat coronary artery and perfused rat heart. In contrast, LTB4, was essentially inactive. The coronary constrictor effect of leukotrienes was not related to thromboxane release, but rather appeared to be due to a calcium mediated activation of specific leukotriene receptors.

Vascular responsiveness and eicosanoid production in diabetic rats

Vascular responsiveness to vasoactive eicosanoids as well as vascular prostacyclin and thromboxane production was investigated in 7-10 weeks alloxan-diabetic rats. Aortic rings from diabetic rats exhibited increased responsiveness to carbocyclic thromboxane A2, a thromboxane analogue, when compared to control rat aortae. Isolated perfused hearts of diabetic rats showed increased vascular responsiveness to 9,11-methanoepoxy PGH2 (U-46619), an endoperoxide analogue. Diabetes resulted in a reduction in prostacyclin generation by isolated incubated aortae which was overcome by the addition of arachidonic acid but not by homogenization of incubated aortic tissue. In contrast, prostacyclin, but not thromboxane, generation was elevated in isolated perfused hearts of diabetic animals in response to moderate doses of arachidonic acid, but at high doses of arachidonate, more thromboxane was formed by perfused hearts of diabetic rats. These results suggest that different vessels can either increase or decrease their prostaglandin production in response to diabetes. The alterations in prostanoid production may be due to differential changes in prostacyclin and thromboxane synthesis in vessels which, in turn, may be related to the changes in vascular responsiveness.

Antagonism of platelet aggregation by 13-azaprostanoic acid in acute myocardial ischemia and sudden death

The effects of 13-azaprostanoic acid (13-APA) were studied during acute myocardial ischemia in cats and in rabbit sudden death induced by sodium arachidonate (Na-Ar). To more clearly define the mechanism of action of 13-APA, we also examined its effects on isolated cat and rabbit coronary arteries, in vitro aggregation of cat and rabbit platelet-rich plasma (PRP) and circulating rabbit platelet count measured in vivo. 13-APA provided minimal protection during myocardial ischemia in cats, partially reversing ischemia-induced ST segment elevations by 3-5 hours after coronary artery occlusion. However, 13-APA was ineffective in inhibiting the rise in plasma creatine kinase (CK) activity or the loss of CK from ischemic myocardial tissue. 13-APA (1.0 - 100 microM) did not inhibit contraction of cat coronary arteries produced by a stable thromboxane A2 analog. However, 13-APA (100 microM) inhibited aggregation of cat PRP induced by AA (1.0 microM). 13-APA also provided significant protection against sudden death induced by Na-Ar in rabbits. While this agent was ineffective in reducing vasoconstriction of rabbit coronary arteries or inhibiting platelet aggregation in response to 500 microM AA, aggregation of rabbit PRP by 250 microM AA was completely inhibited. AA injection produced a significant decrease in circulating platelet count in vehicle-treated rabbits. However, 13-APA reduced the decrease in circulating platelet count in rabbits which survived AA injection during the 13-APA infusion. These results indicate that antagonism of thromboxane A2 receptors in platelets may be an important feature in protecting against sudden death. The difference in sensitivities of vascular and platelet thromboxane receptors as well as the accessability of 13-APA to these receptors may explain the lack of protection of 13-APA in myocardial ischemia.

Protective actions of ibuprofen in arachidonate-induced sudden death

Sodium arachidonate given intravenously at a dose of 2 mg/kg is uniformly lethal in rabbits. Rabbits die within 2-5 min following a dramatic decrease in mean arterial blood pressure (MABP), and in circulating platelets, and a large increase in plasma thromboxane B2 (TxB2) concentration. The nonsteroidal anti-inflammatory agent, ibuprofen, given 15 min prior to challenge with sodium arachidonate, significantly protects against the abrupt decrease in MABP and in circulating platelets and prevents the increase in circulating TxB2 concentrations. These rabbits all survive the lethal effects of arachidonic acid when given ibuprofen at doses of 0.75, 6.25 or 12.5 mg/kg intravenously 15 min prior to arachidonate challenge. At 0.375 mg/kg, only 20% of the animals survive. Concomitant with survival is a significant attenuation of the decrease in MABP (84 +/- 8 mm Hg without ibuprofen vs. 1 +/- 1 to 33 +/- 12 mm Hg with 12.5-0.75 mg/kg ibuprofen). Similarly, these rabbits show a greatly reduced loss of circulating platelets, and virtually no increases in the formation of TxB2. Ibuprofen protects against arachidonate-induced sudden death in a dose-related manner. The mechanism of the protection appears to involve prevention of adherence or aggregation of platelets and the subsequent formation of thromboxane A2. The net result is prevention of pulmonary thrombosis, the major pathological event in triggering sudden death.

Anti-thromboxane A2 actions of pinane thromboxane A2 derivatives

Six pinane-thromboxane A2 analogs have been synthesized and tested for their ability to antagonize carbocyclic thromboxane A2 (CTA2) induced coronary vasoconstriction and prostaglandin endoperoxide analog induced platelet aggregation. Two of the derivatives, 5C-15S BPTA2 and 5T-15S BPTA2 and 5T-15S BPTA2 (1 microM) showed 76 +/- 3 and 72 +/- 9 percent inhibition of CTA2 (15 nM) induced vasoconstriction of cat coronary arteries respectively, while the other compounds showed between 15 and 50 percent inhibition at 1.0 and 2.0 microM. 5C-15S BPTA2 also antagonized prostaglandin-endoperoxide analog induced human platelet aggregation, although the other compounds showed little or no antagonism of aggregation in this system.