Factors contributing to pressure overload-induced immediate early gene expression in adult rat hearts in vivo

We determined the contributions of angiotensin II type 1 receptor (AT(1)) stimulation, adrenergic stimulation, and autonomic activation to pressure overload-induced c-fos expression in the adult rat heart in vivo. c-fos expression was increased in pressure-overloaded hearts created by aortic banding compared with sham-operated rats (458 +/- 100% vs. sham, P < 0.05). GR-138950, a selective AT(1) antagonist, did not blunt this expression (banding vs. banding + GR-138950: 458 +/- 100% vs. 500 +/- 125%, not significant). Atropine and hexamethonium partially decreased c-fos expression (banding vs. banding + atropine/hexamethonium: 700 +/- 67% vs. 400 +/- 67%, P < 0.05). Phentolamine had no significant effect on c-fos expression; however, propranolol inhibited the expression (banding vs. banding + propranolol: 492 +/- 108% vs. 154 +/- 15%, P < 0.05). The inhibition by propranolol was independent of the decreases in heart rate. Thus factors contributing to pressure overload-induced c-fos expression in adult rat hearts in vivo are different from those in neonatal myocytes in vitro undergoing stretch.

Identification of a new polymorphism in the 3'-untranslated region of the human serotonin receptor 2C (5-HT2C) gene

We identified a polymorphism (2831T > G) in the 3'-untranslated region of 5-HT2C receptor gene, approximately 100 kb from a previously reported coding sequence polymorphism, 796G > C (C23S). Allele frequencies were 0.90 (T) and 0.10 (G) and cosegregation analysis of the alleles at the two loci demonstrated frequencies of 0.82 (GT), 0.08 (CT), 0.10 (GG), and 0 (CC). The increased informativity gained by analysis of both polymorphisms will prove useful for future studies of this gene in X-linked neuropsychiatric disorders.

Effect of BAY y 5959 on myocardial function and metabolism in normal and failing hearts

BAY y 5959 is a dihydropyridine derivative with positive inotropic actions mediated by a direct increase in intracellular calcium. We characterized the direct myocardial actions of this new agent in hearts isolated from seven normal dogs and from five dogs with repeated coronary microembolization-induced heart failure. Inotropic actions of BAY y 5959 were accompanied by little effect on duration of contraction and by prolongation of the monophasic action potential (MAP); in contrast, isoproterenol decreased contraction and MAP durations. Whereas inotropic responsiveness to isoproterenol was blunted in embolized hearts, these actions of BAY y 5959 were relatively preserved in the heart failure state. Isoproterenol increased heart rate, whereas BAY y 5959 had little effect. Changes in coronary vascular resistance also decreased similarly for isoproterenol and BAY y 5959. Finally, for comparable inotropy, increases in myocardial oxygen consumption were similar for isoproterenol and for BAY y 5959. In summary, preserved inotropic responsiveness and lack of positive chronotropic actions are two clinically favorable features of this type of inotropic agents compared with a typical beta-adrenergic agonist.

Angiogenesis is enhanced in ischemic canine myocardium by transmyocardial laser revascularization

OBJECTIVES

This study sought to test whether transmyocardial laser revascularization (TMLR) stimulates angiogenesis in an animal model of chronic ischemia.

BACKGROUND

TMLR relieves angina and may also improve blood flow in patients who are not candidates for traditional therapies. The mechanisms of these benefits are not fully defined.

METHODS

Ischemia was created in 14 dogs by proximal left anterior descending coronary ameroid constrictors. TMLR was performed in the anterior wall (approximately 1 channel/cm2) of seven dogs; the remaining dogs served as the ischemic control group. Myocardial blood flow was measured (colored microspheres) at rest and during chemical stress (adenosine) in the acute setting and after 2 months.

RESULTS

TMLR did not influence blood flow in the acute setting. After 2 months, resting blood flow increased comparably in the anterior wall in both groups to approximately 80% of normal. However, the TMLR-treated dogs demonstrated an approximately 40% increase in blood flow capacity during stress in the ischemic territory compared with untreated dogs (left anterior descending coronary artery/left circumflex coronary artery flow 0.53+/-0.16 in the control group vs. 0.73+/-0.08 in TMLR animals, p < 0.05). Vascular proliferation, assessed by bromodeoxyuridine incorporation and proliferating cell nuclear antigen positivity in endothelial and smooth muscle cells was about four times greater in the TMLR group than in the control group (p < 0.001). The density of vessels with at least one smooth muscle cell layer was approximately 1.4 times greater in the myocardium surrounding the TMLR channel remnants than in control ischemic tissue (p < 0.001).

CONCLUSIONS

In this canine model of chronic ischemia, TMLR significantly enhances angiogenesis as evidenced by the increased number of vessels lined with smooth muscle cells, markedly increased vascular proliferation and increased blood flow capacity during stress.

Effect of ventricular stretch on contractile strength, calcium transient, and cAMP in intact canine hearts

Isovolumic contractions were imposed by intraventricular balloon in 39 isolated, blood-perfused canine hearts to investigate the effects of myocardial stretch on contractile force. After stabilization at 37 degrees C, left ventricular volume was increased so that end-diastolic pressure increased from 0 to 5 mmHg. After the immediate increase in developed pressure [DP; from 37 +/- 14 to 82 +/- 22 mmHg (means +/- SD)], there was a slow secondary rise in DP (97 +/- 27 mmHg) that peaked at 3 min. However, DP subsequently decreased over the next 7 min back to the initial value (84 +/- 25 mmHg). Light emission from microinjected aequorin (n = 10 hearts) showed that changes in intracellular calcium [3 min: 124 +/- 15% (P < 0.01); 10 min: 99 +/- 18% of baseline] paralleled DP changes. Increases in myocardial adenosine 3',5'-cyclic monophosphate (cAMP) content (n = 12) accompanied the secondary rise in DP. In contrast, the gradual elevation of DP after the stretch was not exerted during continuous beta-adrenergic stimulation by isoproterenol. Thus, in contrast to isolated muscle, stretch only transiently increases intracellular calcium and contractile strength in intact hearts. The findings of changes in cAMP and abolition of the phenomena by beta-stimulation suggest that a primary stretch-mediated influence on cAMP metabolism may underlie these phenomena.

Functional consequences of acute collagen degradation studied in crystalloid perfused rat hearts

OBJECTIVES

The impact of acute collagen disruption by the disulfide donor, 5,5'-dithio-2-nitrobenzoic acid (DTNB) on ventricular properties was tested in rat hearts.

METHODS

Collagen was degraded acutely in 13 isolated, isovolumically contracting rat hearts by perfusion with 1 mM DTNB added to Krebs-Henseleit solution for 1 hour followed by 2-hour perfusion with normal solution. Another 13 hearts were perfused with normal solution for 3 hours (Control).

RESULTS

Collagen content was 3.5 +/- 0.5% of ventricular dry weight in control group compared with 2.1 +/- 0.4% in DTNB group (decrease by 40%, p < 0.01). Scanning electron micrographs revealed loss of the delicate collagen network surrounding muscle fibers in DTNB treated hearts. Developed pressure at a fixed volume decreased to 86 +/- 17% of the baseline value after 3-hour perfusion in the control group, whereas in DTNB treated hearts developed pressure fell to 68 +/- 13% (p < 0.01). End-diastolic pressure was set at 5 mmHg at the beginning of the experiment and rose to 15 +/- 8 mmHg in control and 30 +/- 13 mmHg (p < 0.01) in the treated hearts. Concomitantly, wet-to-dry weight ratio increased from 5.63 +/- 0.26 in control to 6.07 +/- 0.11 (p < 0.05) in the DTNB treated hearts. A separate set of experiments on isolated myocytes excluded the possibility of a direct effect of DTNB on myocyte contractile function.

CONCLUSIONS

These data suggested that with 40% collagen disruption by DTNB there is a significant increase in tissue edema that results in a decrease in chamber capacitance; in addition, there is a significant decrease in systolic performance which reflects the combined effect of edema and loss of collagen.

Physiology, histology, and 2-week morphology of acute transmyocardial channels made with a CO2 laser

BACKGROUND

Transmyocardial revascularization with a CO2 laser appears to improve symptoms in patients with refractory angina. However, it remains controversial as to whether blood flow through the channels is the mechanism of benefit, especially in the acute setting.

METHODS AND RESULTS

Three protocols were used to test whether blood flows through transmyocardial CO2 laser revascularization channels. First, channels were made in excised, cross-perfused dog hearts (n = 5) using a CO2 laser (The Heart Laser; PLC Systems Inc, Milford, MA; 40 J/pulse) followed by ligation of the proximal left anterior descending coronary artery. Colored microspheres injected into the left ventricular chamber failed to detect any significant transmyocardial blood flow. In the second protocol (n = 4), laser channels were created in the left anterior descending artery territory, the left anterior descending artery was ligated, and the hearts were excised after 24 hours. Triphenyltetrazolium chloride staining revealed that no viable myocardium was detected around the laser channels in the ischemic myocardium. Finally, channels examined 2 weeks after creation in normal (n = 6) or ischemic (n = 4) myocardium did not maintain their original caliber but were invaded by granulation tissue, which included a large amount of smaller vascular spaces and vessels of various sizes.

CONCLUSIONS

Transmyocardial laser revascularization channels made with this CO2 laser did not provide acute myocardial perfusion or preserve myocardial viability in the face of acute ischemia. Channel morphology changes dramatically within the first 2 weeks. To the degree that these findings pertain to human myocardium, the results suggest that transmyocardial blood flow may not be the mechanism of benefit of this procedure, particularly in the acute setting.

Assessment of transmyocardial perfusion in alligator hearts

BACKGROUND

Techniques for achieving myocardial perfusion directly from the left ventricular chamber are currently under investigation. Although originally based on the anatomy of reptilian hearts, which are rich in transmural channels and reported to have a poorly developed coronary vasculature, the blood flow capacity of a transmyocardial blood supply has not been studied in these hearts. With the ultimate goal of providing insight into the potential for achieving transmyocardial perfusion in human hearts, we studied the relative contribution of transmyocardial and coronary perfusion in alligator hearts.

METHODS AND RESULTS

After explanation from six American alligators, the left ventricle was instrumented, and coronary arteries were perfused with oxygenated physiological solution. Using microspheres to estimate regional myocardial perfusion in the beating hearts, we show that although the epicardium was well perfused by the coronary arteries (0.20 +/- 0.08 versus 0.07 +/- 0.01 mL.min-1.g-1 owing to flow from the ventricular chamber), a significant proportion of endocardial perfusion was from the ventricular chamber (0.21 +/- 0.07 mL.min-1.g-1 from the left ventricle versus 0.13 +/- 0.04 mL.min-1.g-1 from coronary arteries).

CONCLUSIONS

A significant amount of direct transmyocardial perfusion is present in alligator hearts. The conditions that apparently permit this situation in reptilian hearts are reviewed, and their implications for aiding in the optimization of techniques for achieving transmyocardial flow in humans are discussed.

Blood flow capacity via direct acute myocardial revascularization

The concept of direct myocardial revascularization, achieving myocardial perfusion through means other than the normal coronary vasculature, has a long history with the most widely investigated technique being the Vineberg procedure; current interest centers around the encouraging preliminary clinical results obtained with transmyocardial laser revascularization. Despite significant previous research, the acute blood flow potential through the direct myocardial route remains unknown. Nontransmural laser channels were made in the distal LAD territory from the epicardial surface of 5 mongrel dogs to which an internal mammary artery was connected. A flow probe was placed on the distal most portion of the artery and an intercostal branch was cannulated for infusion of colored microspheres. Measurements were taken under baseline conditions and following LAD and epicardial collateral ligation. Under all conditions, blood flow pattern was of a to-and-fro nature. At baseline, there was an average 0.60 +/- 0.24 ml/min net flow into the myocardium which was all contained within 0.5 cm of the central channel with a final myocardial perfusion of 0.011 +/- 0.016 ml/min/g. Following induction of ischemia average flow increased to 1.41 +/- 0.51 ml/min which extended as far as 1 cm from the channel with a final myocardial perfusion of 0.22 +/- 0.19 ml/min/g. In conclusion, a limited amount of acute myocardial perfusion can be achieved by the present technique of direct myocardial revascularization and the amount of flow is highly dependent upon the amount of flow through the native circulation.

Does blood flow through holmium:YAG transmyocardial laser channels?

BACKGROUND

Early reports indicate that transmyocardial laser revascularization improves symptoms in patients with refractory angina. However, there is little experimental evidence of whether blood flow through channels is the mechanism of action.

METHODS

Endocardial channels were made in the distribution of the left anterior descending coronary artery in canine hearts (n = 5) using a holmium:yttrium-aluminum garnet laser. Hearts were excised acutely while perfused in a retrograde fashion from a second dog so that the aortic valve always remained closed. The proximal left anterior descending coronary artery was ligated. To measure direct transmyocardial blood flow, colored microspheres were injected into the left ventricular chamber.

RESULTS

The number of spheres per gram of tissue in the channel region was significantly higher than in the control region (low load, 302.5 +/- 169.0 versus 41.8 +/- 59.4; high load, 208.4 +/- 138.3 versus 5.8 +/- 11.7; both, p < 0.05). However, the estimated regional blood flow through the channels was extremely low (<0.01 mL/g/min. In the chronic setting (n = 4) (2-week survival), no flow as detected through the channels, and the endocardial entry points were closed.

CONCLUSIONS

Transmyocardial blood flow does not appear to occur through channels made with the holmium:yttrium-aluminum garnet laser. It remains to be determined whether this is the case with other types of lasers.

Changes in plasma endothelin-1 levels reflect clinical response to beta-blockade in chronic heart failure

Plasma levels of endothelin-1 are elevated in patients with chronic heart failure; however, it is unknown whether changes in plasma endothelin-1 levels accurately reflect clinical response to therapy in these patients. To determine this, we measured plasma endothelin-1 in addition to functional, hemodynamic, and other neurohormonal parameters as part of a double-blind, placebo-controlled study of the beta-blocker vasodilator carvedilol in patients with moderate to severe chronic heart failure. Patients were assigned (2:1 randomization) to receive carvedilol (25 mg twice daily, n = 10) or placebo (n = 5) for 14 weeks, with evaluations made before and after therapy. Compared to patients receiving placebo, patients receiving carvedilol improved significantly as assessed by the parameters described. These changes were paralleled by significant falls in endothelin-1 with carvedilol (-2.1 + 3.8 pg/ml) in comparison to placebo (2.2 + 3.9 pg/ml; p < 0.05 for between-group differences). Changes in endothelin-1 after treatment in both groups correlated significantly with changes in symptom severity, New York Heart Association class, 6-minute walk distance (r = 0.64 to 0.80; p < 0.05), hemodynamic parameters (ejection fraction, right atrial pressure, pulmonary artery diastolic pressure, pulmonary wedge pressure, right atrial pressure, and stroke volume index; r = 0.54 to 0.86; p < 0.05), and neurohormonal parameters (serum aldosterone and plasma norepinephrine (r = 0.74 to 0.76; p < 0.05). By stepwise regression analysis, change in endothelin-1 was an independent, noninvasive predictor of functional and hemodynamic responses to therapy in these patients. These findings suggest that endothelin-1 accurately reflects functional, hemodynamic, and neurohormonal responses to beta-blocker therapy in patients with congestive heart failure. Measurement of endothelin-1 may therefore be a useful, noninvasive approach to the evaluation of clinical response to drug therapy in these patients.

Effects of caffeine or EDTA post-treatment on EMS mutagenesis in soybean

Seeds of soybean cultivar LD4 were mutagenically treated with EMS (0.3, 0.5, 0.6, 0.9, 1.5 and 1.8%) for 3 h only or plus caffeine (50 mM) or EDTA (1 mM) post-treatment for 5 h. The experimental results indicated that: (1) of the different concentrations of EMS treatment, the M2 mutation frequency induced with 0.6% EMS was the highest (9.7%). When the EMS concentration was over 0.9%, the mutation frequency decreased rapidly. (2) Of the EMS treatments plus caffeine or EDTA post-treatment, the mutagenic effect of 0.6% EMS was the best for inducing morphological variations. Caffeine post-treatment decreased notably the mutation frequency of EMS treatment; when concentrations of EMS were very high (1.5% and 1.8%), mutation frequencies of EDTA post-treatment were still 5.0% and 4.88%, but no mutants were found in EMS treatment or plus caffeine post-treatment. (3) In the M2 mutation spectrum, 11 kinds of mutant types were observed in EMS treatment or plus caffeine or EDTA post-treatment. Relative frequencies of some mutant types (growth period, plant height, grain size, leaf shape and sterility, etc.) were similar among the three treatments, but EDTA post-treatment could change the relative frequencies of yield characteristics (number of pods and grains, grain weight/plant) induced by EMS treatment only.

Elastohydrodynamic Lubrication of Involute Gears

A criterion is suggested for the application of the steady state elastohydrodynamic theories to the analysis of involute gear contacts. The criterion is based on a comparison of two physical time scales characterizing the system. It is found that for heavily loaded gears the unsteadiness effect may be important. A mean-viscosity method using a composite pressure-viscosity model for the lubricant is introduced for contact zone temperature calculation. An example of involute gears is given for the computation of elastohydrodynamic contact variables based on quasi-steady state assumption. It is found that the surface temperature rise in the tooth tip contact is much higher than that in the pitch line contact.