Harvey R. Weiss

Bioenergetic remodeling of heart mitochondria by thyroid hormone

Changes in thyroid status are associated with profound alterations in biochemical and physiological functioning of cardiac muscle impacting metabolic rate, contractility and structural hypertrophy. Using an in vivo model of chronic treatment with thyroid hormone (T4, 0.3 mg/kg/day), we evaluated how mitochondria are regulated in response to T4, and assessed the relationship of T4-induced mitochondrial biogenesis and bioenergetics to overall cardiac hypertrophy. The role of thyroid hormone in cardiac bioenergetic remodeling was addressed in rats treated with T4 for 5, 10 and 15 days. Over that time, myocardial oxygen consumption substantially increased as did cardiac hypertrophy. Myocardial levels of mitochondrial enzyme activities, mitochondrial DNA (mtDNA), specific proteins and transcript were assessed. Activity levels of respiratory complexes I-V and citrate synthase significantly increased with 15 but not with 5 or 10-day T4 treatment. Myocardial levels of mtDNA, mitochondrial proteins (e.g. cytochrome c, cytochrome b, ATPase subunits, MnSOD) and the global transcription factor PPARα were significantly elevated with 15-day T4. Transcript analysis revealed increased expression of transcription factors and cofactors involved in mitochondrial biogenesis including PPARα, mtTFA, ErbAα and PGC-1α. Our findings indicate parallel increases in myocardial mitochondrial bioenergetic capacity, oxygen consumption and markers of mitochondrial biogenesis with 15-day T4; these changes were not present with 10-day T4 even with significant cardiac hypertrophy. The marked, parallel increases in PPARα levels suggest its potential involvement in mediating myocardial-specific remodeling of mitochondria in response to T4. (Mol Cell Biochem xxx: 97–106, 2004)

Blood O2 saturation determination in frozen tissue

Abstract We have developed a method for microspectrophotometric determination of oxygen saturation in small arteries and veins of a quick-frozen tissue. Optical densities of 10- to 30-μm sections of frozen dog blood were determined with a Zeiss microspectrophotometer, and oxygen saturation was determined by a three-wavelength (560, 523, 506 nm) method. Blood sections were covered with silicone oil to prevent O 2 diffusion. Calibration lines were constructed by comparing absorbance ratios computed by the three-wavelength method against blood O 2 saturation determined by the Van Slyke method. The method was tested in arteries and veins of frozen dog gracilis muscle against Van Slyke. The mean saturation determined from three different vessels had an accuracy of ±2.6%.

Effect of hypoxia on small vessel blood content of rabbit brain.

Abstract The small vessel blood content (SVBC) of several brain areas was determined in anesthetized rabbits exposed to various forms of hypoxia using [ 59 Fe-]siderophilin labeling of plasma. Under control conditions SVBC was significantly higher in cortical gray matter (1.00 ml/100 grams) than in cortical white matter (0.60), pons (0.61), or medulla (0.75). Inhalation of 10%O 2 , 8%O 2 plus 5%CO 2 , 1%CO in 40%O 2 , or asphyxia resulted in increasing levels of average brain SVBC, in that order, from a control value of 0.77 to 2.04 during asphyxia. Estimation of regional capillary density from these data suggests that although total capillary number (i.e., during asphyxia) is similar in forebrain and hindbrain, a greater portion of total capillaries are perfused during moderate hypoxia in the forebrain than in the hindbrain.

Diffusion distances, total capillary length and mitochondrial volume in pressure-overload myocardial hypertrophy

We examined the relationships between blood pressure, coronary blood flow, cardiac output, myofiber growth, capillarity, mitochondrial content, and capillary and mitochondrial distributions in a pressure-overload model of myocardial hypertrophy. The Goldblatt one kidney-one clip (1K1C) procedure was performed on seven adult rabbits. After 1 month, mean blood pressure increased 50% and mean heart mass increased 30%. Coronary blood flow and cardiac output at rest were similar in control and 1K1C hearts; cardiac output fell 40% when 1K1C hearts were paced to 35% above basal heart rate. Capillary density in the left ventricular free wall (LV) decreased with increasing fiber size by as much as 30%. However, capillary-to-fiber ratio and total capillary length in the LV increased with heart size by up to 30% and 80%, respectively. This indicated that there was some proliferation of capillaries taking place, but not enough in comparison to fiber growth to prevent the lengthening of distances between capillaries. Mitochondrial volume density decreased by as much as 30% with increasing heart size, but total mitochondrial volume increased up to 80%. This indicated that there was some proliferation of mitochondria, but not enough to prevent dilution of mitochondria by the growing myofibrillar elements. Analysis of the distribution of mitochondria suggested that the new mitochondrial material was added to the center of myofibers, thereby further lengthening oxygen diffusion distances. There was a constant ratio of 10.4 +/- 0.3 km of capillaries per ml of mitochondria in 1K1C and control hearts, demonstrating that the structures for oxygen supply and consumption were remaining in fixed proportion to each other. There was no evidence that the decreased performance of paced 1K1C hearts was attributable to an oxygen diffusion limitation to mitochondria.

Effects of VEGF and nitric oxide synthase inhibition on blood–brain barrier disruption in the ischemic and non-ischemic cerebral cortex

Abstract Objectives: This study was performed to compare the effects of exogenous vascular endothelial growth factor (VEGF) and nitric oxide synthase (NOS) inhibition on blood–brain barrier (BBB) disruption in the ischemic cortex (IC) and non-ischemic contralateral cortex (CC) during the early stage of focal cerebral ischemia in rats. Methods: A middle cerebral artery (MCA) was occluded after a craniotomy in each rat under isoflurane anesthesia. Two more craniotomies were performed over the contralateral non-ischemic hemisphere to expose cerebral cortex. For the control rats, the normal saline patches were applied to all three craniotomy holes (control group). To inhibit NOS, NG-nitro-L-arginine-methyl ester (L-NAME) (10 mg/kg) was administered i.v. 20 minutes after MCA occlusion (L-NAME group). In another group, VEGF (10−10 M) was topically applied 30 minutes after MCA occlusion on the IC as well as one of the holes of the contralateral cortex (VEGF group). To investigate the effects of the combination of VEGF and L-NAME, both L-NAME and VEGF were administered as described above (L-NAME+ VEGF group). The transfer coefficient (Ki) of 14C-α-aminoisobutyric acid and the volume of 3H-dextran (70000 Da) distribution were determined to measure the degree of BBB disruption at 1 hour after MCA occlusion. Results: In the control group, Ki of the IC was significantly higher than the contralateral cortex (CC) (p<0.005). VEGF application increased the Ki of the IC further when compared with the control group (+51%, p<0.05%). L-NAME administration produced no significant decrease in the Ki of the IC when compared with the control group. With L-NAME+ VEGF administration, the Ki of the IC became significantly lower than that of the VEGF alone (−38%, p<0.005). Thus, L-NAME produced a much greater decrease in the Ki of the IC in the VEGF treated than the control animals (p<0.05). In the non-IC, VEGF, L-NAME, or their combination did not affect BBB disruption. The volume of dextran distribution followed a similar pattern to Ki. Discussion: Our data suggest that even in the early stage of focal cerebral ischemia, the degree of BBB disruption in response to the exogenous VEGF is much greater in the ischemic than in the non-IC and that the mechanism of the increase of BBB disruption by VEGF in the IC involves the NOS pathway.

Control of myocardial oxygenation—Effect of atrial pacing

Myocardial oxygenation is controlled by alterations in both oxygen supply and oxygen demand of the heart. The factors determining oxygen supply and demand in controlled and stressful conditions are discussed on a regional basis. Evidence is presented to show that the subendocardial (ENDO) region of the left ventricle has a lesser oxygen supply versus its demand compared to the subepicardial (EPI) region. The effects of stress are shown to worsen the disparity in myocardial oxygenation of the ENDO in relation to the EPI. Data is presented on the stress of atrial pacing. Experiments were conducted on 31 anesthetized open chest dogs. Electrodes were placed in the ENDO and EPI to measure tissue PO2 and blood flow by hydrogen clearance. The hearts were paced by left atrial stimulation at 150, 175, 200, and 225 beats/min. Tissue PO2 fell in a stepwise manner at every pacing rate. ENDO PO2 fell to a greater extent than EPI PO2 at every pacing rate. Pacing increased regional blood flow in the EPI more at every pacing rate. It can be concluded that the increases in flow observed did not totally compensate for the increased demand for oxygen in the heart brought on by the stress of pacing. This effect is considerably greater in the ENDO. These results are discussed in terms of several clinical findings.

Effects of carbon monoxide or low oxygen gas mixture inhalation on regional oxygenation, blood flow, and small vessel blood content of the rabbit heart.

AbstractThe effects of lowering arterial O2 content, approximately 30%, by inspiration of low O2 or CO gas mixtures on regional myocardial relative tissuen

Effect of naltrexone on regional brain oxygen consumption in the cat

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