Dual effects of dichloroacetate on cardiac ischaemic preconditioning in the rat isolated perfused heart.

1. Ischaemic cardiac preconditioning represents an important cardioprotective mechanism which limits myocardial ischaemic damage. The aim of this investigation was to assess the impact of dichloroacetate (DCA), a pyruvate dehydrogenase complex activator, on preconditioning. 2. Rat isolated hearts were perfused by use of the Langendorff technique, and were subjected to either preconditioning (3 x 4 or 3 x 6 min ischaemia) or continuous perfusion, followed by 30 min global ischaemia and 60 min reperfusion. DCA (3 mM) was either given throughout the protocol (pretreatment), during reperfusion only (post-treatment), or not at all. Throughout reperfusion mechanical performance was assessed as the rate-pressure product (RPP: left ventricular developed pressure x heart rate). 3. In non-preconditioned control hearts, mechanical performance was substantially (P < 0.001) depressed on reperfusion (the RPP after 60 min of reperfusion (RPP(t=60)) was 4,246+/-974 mmHg beats min(-1) compared to baseline value of 21,297+/-1,728 mmHg beats min(-1)). Preconditioning with either 3 x 4 min or 3 x 6 min cycles caused significant protection, as shown by enhanced recovery (RPP(t=60) = 7,818+/-1,138, P < 0.05, and 11,123+/-587 mmHg beats min(-1), P < 0.001, respectively). 4. Addition of DCA (3 mM) to hearts under baseline conditions significantly (P < 0.001) enhanced systolic function with an increased left ventricular developed pressure of 108+/-5 mmHg compared to 88.3+/-3.0 mmHg in the controls. 5. Pretreatment with 3 mM DCA had no effect on recovery of mechanical performance in the non-preconditioned hearts (RPP(t=60) = 3,640+/-1,235 mmHg beats min(-1)) while the beneficial effects of preconditioning were reduced in the preconditioned hearts (3 x 4 min: RPP(t=60) = 2,919+/-1,060 mmHg beats min(-1); 3 x 6 min: RPP(t=60) = 8,032+/-1,367 mmHg beats min(-1)). Therefore, DCA had increased the threshold for preconditioning. 6. By contrast, post-treatment of hearts with 3 mM DCA substantially improved recovery on reperfusion in all groups (RPP(t=60) = 5,827+/-1,328 (non-preconditioned), 14,022+/-3,743 (3 x 4 min; P < 0.01) and 23,219+/-1,374 (3 x 6 min; P < 0.001) mmHg beats min(-1)). 7. The results of the present investigation clearly show that pretreatment with DCA enhances baseline cardiac mechanical performance but increases the threshold for cardiac preconditioning. However, post-treatment with DCA substantially augments the beneficial effects of preconditioning.

The beta/alpha peak height ratio of ATP. A measure of free [Mg2+] using 31P NMR.

From 31P NMR measurements made in vitro at 38 degrees C, I = 0.25, pH 5. 75-8.5, and calculated free [Mg2+] from 0 to 5 mM, we show that, within the physiological range of cytosolic free [Mg2+] from 0.25 to 1.5 mM, the chemical shift difference between the alpha- and beta-ATP resonances, deltaalphabeta, changes by only 0.6 ppm. Consequently, we developed new formalisms from known acid and Mg2+ dissociation constants by which the observed chemical shift of Pi, deltaPi, and the peak height ratio of the beta- and alpha-ATP resonances, hbeta/alpha, could be related to free [Mg2+] by simultaneous solution of: [equation: see text] We found that hbeta/alpha changed 2.5-fold as free [Mg2+] varied from 0.25 to 1.5 mM, providing a more sensitive and accurate measure of free cytosolic [Mg2+]. In working rat heart perfused with glucose, free [Mg2+] was 1.0 +/- 0.1 from hbeta/alpha and 1.2 +/- 0.03 from measured [citrate]/[isocitrate] but 0.51 +/- 0.1 from deltaalphabeta. Addition of ketone bodies to the perfusate decreased free [Mg2+] estimated from hbeta/alpha to 0.61 +/- 0.02 and 0.74 +/- 0.11 by [citrate]/[isocitrate] but the estimate from deltaalphabeta was unchanged at 0.46 +/- 0.04 mM. Such differences in estimated free [Mg2+] alter the apparent Keq of the creatine kinase reaction and hence the estimated cytosolic free [SigmaADP].

Insulin, ketone bodies, and mitochondrial energy transduction.

Addition of insulin or a physiological ratio of ketone bodies to buffer with 10 mM glucose increased efficiency (hydraulic work/energy from O2 consumed) of working rat heart by 25%, and the two in combination increased efficiency by 36%. These additions increased the content of acetyl CoA by 9- to 18-fold, increased the contents of metabolites of the first third of the tricarboxylic acid (TCA) cycle 2- to 5-fold, and decreased succinate, oxaloacetate, and aspartate 2- to 3-fold. Succinyl CoA, fumarate, and malate were essentially unchanged. The changes in content of TCA metabolites resulted from a reduction of the free mitochondrial NAD couple by 2- to 10-fold and oxidation of the mitochondrial coenzyme Q couple by 2- to 4-fold. Cytosolic pH, measured using 31P-NMR spectra, was invariant at about 7.0. The total intracellular bicarbonate indicated an increase in mitochondrial pH from 7.1 with glucose to 7.2, 7.5 and 7.4 with insulin, ketones, and the combination, respectively. The decrease in Eh7 of the mitochondrial NAD couple, Eh7NAD+/NADH, from -280 to -300 mV and the increase in Eh7 of the coenzyme Q couple, Eh7Q/QH2, from -4 to +12 mV was equivalent to an increase from -53 kJ to -60 kJ/2 mol e in the reaction catalyzed by the mitochondrial NADH dehydrogenase multienzyme complex (EC 1.6.5.3). The increase in the redox energy of the mitochondrial cofactor couples paralleled the increase in the free energy of cytosolic ATP hydrolysis, delta GATP. The potential of the mitochondrial relative to the cytosolic phases, Emito/cyto, calculated from delta GATP and delta pH on the assumption of a 4 H+ transfer for each ATP synthesized, was -143 mV during perfusion with glucose or glucose plus insulin, and decreased to -120 mV on addition of ketones. Viewed in this light, the moderate ketosis characteristic of prolonged fasting or type II diabetes appears to be an elegant compensation for the defects in mitochondrial energy transduction associated with acute insulin deficiency or mitochondrial senescence.

Ionescu-Shiley valve failure. I: Experience with 125 standard-profile explants.

A group of standard-profile Ionescu-Shiley valve implants, 357 aortic and 190 mitral, was reviewed for cases of failure requiring surgical explantation. To date, 90 (25.2%) of the aortic and 35 (18.4%) of the mitral valves have failed, and are the subject of this analysis. Observations of these explants confirm previous suggestions about the clinical and pathologic patterns of the Ionescu-Shiley valve's failure, but are extended in this study to allow more confident statistical analyses. Cusp tear with insufficiency remains the most important reason for explantation, precipitating removal to date of 19.1% of the aortic and 10.0% of the mitral valves implanted. This difference, aortic versus mitral, is significant (p less than 0.006) and the reverse of observations made in other studies of pericardial valves. In this review there is no significant difference in the proportion of aortic and mitral valves that failed with calcification (2.2% and 3.1%, respectively). Aortic Ionescu-Shiley valves failing with tears had a mean of 3.1 tears per valve, whereas mitral valves had 1.2. Aortic valves also showed considerably more pretear wear than did mitral valves. Although the large number of these Ionescu-Shiley valve failures has been a profound clinical disappointment, it has provided an opportunity to observe and detail the pathology of their failure.

Ionescu-Shiley valve failure. II: Experience with 25 low-profile explants.

A group of patients who had low-profile Ionescu-Shiley valves implanted, 237 aortic and 130 mitral, was reviewed for cases of bioprosthetic failure requiring explantation. Fourteen such aortic and 11 mitral valves were recovered at operation. The most common reason for explantation was valvular insufficiency due to cusp tears, accounting for 50.0% of aortic and 82.0% of mitral explants. Morphologic examination of the valves suggested a common mode of failure with tears, and this is illustrated. The clinical and pathologic patterns of this valve's failure are compared with those of the standard-profile Ionescu-Shiley valve, and many similarities exist. A tendency for a larger proportion of mitral valve failures with tears is, however, in contrast to observations of the standard-profile valve, in which aortic failures are more common. Additionally, low-profile valves, in either the aortic or mitral positions, fail after a shorter time in situ than their standard-profile counterparts, at a mean of 45.1 months versus 78.0 in the aortic position (p less than 0.01) and at 52.2 months versus 73.8 in the mitral position (p less than 0.05). These differences in the performance of the Ionescu-Shiley valve models may have implications for the design of future bioprostheses.

The University of Ottawa Heart Institute Cardiac Transplant Program: the first 100 transplants. A pathologic study of the explanted hearts.

Since 1984, 122 orthotopic heart transplants have been performed at the University of Ottawa Heart Institute. Of the 114 adult patients, 100 (87.8%) were males and 14 (12.2%) females, with mean ages of 45.8 and 47.9 yr, respectively. The hearts of these adults were pathologically diagnosed as chronic ischemic heart disease (CIHD) in 55 (48.2%), acute ischemic heart disease (AIHD) in 17 (14.9%), dilated cardiomyopathy (DC) in 30 (26.3%), valvular heart disease in five (4.4%), congenital heart disease in three (2.6%), myocarditis in three (2.6%), and other in one (0.9%) of the cases. The adult hearts (94) among the first 100 transplants were studied morphologically, to look for differences among the three major groups with clinical "end-stage" heart failure. The mean heart weights were 435, 356, and 463 gm in the CIHD, AIHD, and DC groups, respectively, with AIHD less than CIHD or DC (p less than 0.01). The ventricular wall thicknesses were similar in CIHD and DC, but the left ventricular (LV) wall thicknesses in AIHD were more than in CIHD or DC (p less than 0.01). The ventricular diameters were greater in DC than in CIHD or AIHD (p less than 0.01) and greater in CIHD than in AIHD (p less than 0.01). The mean LV cavity volumes were 158, 94, and 200 ml in CIHD, AIHD, and DC, respectively, with DC greater than in CIHD or AIHD (p less than 0.01) and CIHD greater than in AIHD (p less than 0.01). The relative differences in AIHD compared to CIHD and DC are referrable to the shorter duration of disease in the acute ischemic group.2+ off