Cardiac myocytes express both constitutive and cytokine-inducible nitric oxide synthases (NOS). NO and its congeners have been implicated in the regulation of cardiac contractile function. To determine whether NO could affect myocardial energetics, 31P NMR spectroscopy was used to evaluate high-energy phosphate metabolism in isolated rat hearts perfused with the NO donor S-nitrosoacetylcysteine (SNAC). All hearts were exposed to an initial high Ca2+ (3.5 mM) challenge followed by a recovery period, and then, either in the presence or absence of SNAC, to a second high Ca2+ challenge. This protocol allowed us to monitor simultaneously the effect of SNAC infusion on both contractile reserve (i.e., baseline versus high workload contractile function) and highenergy phosphate metabolism. The Recent evidence documents that endogenous nitric oxide (NO) production, exogenous NO donors, or agents that inhibit endogenous generation of nitrogen oxides can exert inotropic and lusitropic effects on cardiac myocytes, on isolated hearts, and on intact hearts in situ in several species including humans (1-6). Endogenous NO generated by the "high output" inflammatory cytokine-inducible NO synthase (iNOS or NOS2) in myocytes causes a reduction in contractile responsiveness to positively inotropic stimuli, including ,B-adrenergic agonists (7-15). Even in the absence of cytokine-induced NO production, endogenous release of NO by cardiac myocytes, and possibly by microvascular endothelial cells as well, has been shown to diminish the influx of Ca21 into myocytes through L-type voltage-sensitive ion channels and to blunt their responsiveness to f-adrenergic agonists (16)(17)(18)(19). Both cell types have been shown recently to express the endothelial constitutive isoform of NO synthase (ecNOS or NOS3) (16,17).Many of the actions of endogenous NO are known to be mediated by activation of soluble guanylate cyclase and an increase in intracellular cGMP (20-23). cGMP analogues have been shown to inhibit ICa-L and to produce a positive lusitropic effect in isolated mammalian cardiac myocytes (24). Also, intracellular dialysis with an agent such as methylene blue, which inhibits the activation of guanylyl cyclase by NO, blocks muscarinic cholinergic agonist attenuation of ICa-L in wholecell patch clamp experiments of ventricular myocytes exposed to a ,3-adrenergic agonist (17). However, it has recently been shown that activation of cGMP signaling pathways in skeletal muscle accounts for only a modest portion of the suppressive effect of increased endogenous NO production on the forcefrequency relationship of electrically stimulated muscle fibers (25,26). Potential non-cGMP-mediated actions of NO and related congeners include formation of peroxynitrite (OONO-), modification of enzymes and nuclear regulatory factors via binding to transition metals or sulfhydryl groups, and formation of nitrotyrosines influencing regulatory or catalytic sites (20,27,28). It has been proposed that either S-nitrosylation of Ca2+ regulatory proteins in...

Less than a quarter of the patients with juvenile-onset IDDM develop diabetic nephropathy during the first 20 years of diabetes. To study the determinants of this complication, we selected patients who had come with newly diagnosed IDDM to the Joslin Clinic between 1967 to 1972, and we examined them in 1986 to 1988, that is, 15 to 21 years after onset of diabetes. Using a case control design we compared three groups of cases, that is, advanced nephropathy (N = 43), only microalbuminuria (N = 41), and hypertension alone (N = 17), with a group of controls who remained normoalbuminuric and normotensive despite the long duration of IDDM (N = 61). In comparison with controls, patients with advanced nephropathy had more parents with hypertension (odds ratio 3.8), higher Vmax values of Na/Li countertransport in red blood cells (odds ratio 10.0 for the highest tertile), and higher mean arterial pressure during adolescence and early adulthood (odds ratio 3.1 for those above the median). They also had significantly poorer glycemic control during their first 12 years of diabetes. Patients with hypertension alone were similar to those with advanced nephropathy with regard to markers of predisposition to hypertension but differed from them with regard to glycemic control, having the best glycemic control of all the study groups. Patients who developed only microalbuminuria during 15 to 21 years of IDDM (some of whom will progress to overt proteinuria later) did not differ significantly from controls with regard to predisposition to hypertension. In conclusion, predisposition to hypertension is a major risk factor for the development of advanced diabetic nephropathy and essential hypertension during the first 20 years of IDDM.

Capacity for ATP resynthesis during recovery from ischemia or hypoxia is limited to the size of the adenine nucleotide pool. which is determined in part by the activity ofcytosolic 5'-nucleotidase (5'-NT): AMP -* adenosine plus inorganic phosphate (Pi). To define in vivo regulation of 5'-NT, we used the tools of 31P nuclear magnetic resonance (NMR) spectroscopy and chemical assay to measure the substrates (AMP), products (Pi, adenosine, and its catabolites), and inhibitors (Pi and H+) of 5'-NT in isolated perfused rat hearts exposed to hypoxia (where pH remains near 7) and no flow, global ischemia (where pH falls to 6.1). We estimated 5'-NT reaction velocity, assessed the relative contributions of Pi and H+ to enzyme inhibition, and defined the consequences of changes in 5'-NT activity on ATP resynthesis after hypoxia and ischemia. We conclude that (a) 5'-NT is activated during hypoxia and early ischemia but is inhibited during prolonged ischemia, (b) H' (pH < 6.2) is a potent inhibitor of 5'-NT, and (c) differences in AMP accumulation are sufficient to explain the differences in the capacity for net ATP resynthesis in ischemic and hypoxic tissue. These observations have implications for our understanding of heterogeneity of ischemic injury and myocardial protection during ischemia. (J. Clin. Invest. 1994. 93:40-49.)

These results indicated the tandem Y/Lu-DOTATATE therapy for patients with disseminated/inoperable NET as highly effective and safe, considering long-term side effects. In the majority of patients, clinical improvement was observed.

Glycated hemoglobin A1c (HbA1c) concentration in blood is an index of the glycemic control widely used in diabetology. The aim of the work was to validate two mathematical models of HbA1c formation (assuming irreversible or reversible glycation, respectively) and select a model, which was able to predict changes of HbA1c concentration in response to varying glycemia courses with higher accuracy. The experimental procedure applied consisted of an original combination of: in vivo continuous glucose concentration monitoring, long-term in vitro culturing of the human erythrocytes and mathematical modeling of HbA1c formation in vivo and in vitro with HbA1c values scaled according to the most specific analytical methods. Sixteen experiments were conducted in vitro using blood samples collected from healthy volunteer and stable type 1 diabetic patients whose glycemia was estimated beforehand based on long-term monitoring. The mean absolute difference of the measured and predicted HbA1c concentrations for the in vitro experiments were equal to 0.64 +/- 0.29% and 1.42 +/- 0.16% (p = 0.0007) for irreversible and for reversible model, respectively, meaning that the irreversible model was able to predict the glycation kinetics with a higher accuracy. This model was also more sensitive to a deviation of the erythrocytes life span.

The ability to resynthesize ATP during recovery from ischemia is limited to the size of endogenous pool of adenine nucleotides. Cytosolic AMP-specific 5′-nucleotidase (5′-NT) plays a key role in ATP degradation and hence the capacity for ATP resynthesis. We have suggested ( J. Clin. Invest. 93: 40–49, 1994) that intracellular acidosis [intracellular pH (pHi)] is a potent inhibitor of 5′-NT under in vivo conditions. To test this hypothesis further, we used the hyperthyroid rat heart because we could alter pHi during ischemia and determine the consequences of lower pHi on AMP accumulation (by chemical assay) and ATP resynthesis (by31P nuclear magnetic resonance spectroscopy) during reperfusion. Global no-flow ischemia caused pHi to decrease from 7.1 under well-oxygenated control perfusion to 6.7. We found that decreasing pHi further from pH 6.7 to 6.4 leads to increased accumulation (30%) of AMP during ischemia and to a 2.5-fold increase in ATP resynthesis during reperfusion. Analysis of all known substrates, products, activators, and inhibitors of the 5′-NT suggests that 5′-NT is activated primarily by Mg2+ and ADP and is inhibited by H+. Thus these observations provide evidence for a salutary effect of intracellular acidosis on preserving the AMP pool due to inhibition of 5′-NT and suggest a novel role of H+ in protecting ischemic tissue.

The objectives were as follows: (1) estimating mean value of the overall hemoglobin glycation rate constant (k); (2) analyzing inter-individual variability of k; (3) verifying ability of the hemoglobin A1c (HbA1c) formation model to predict changes of HbA1c during red blood cells cultivation in vitro and to reproduce the clinical data. The mean k estimated in a group of 10 non-diabetic subjects was equal to 1.257 ± 0.114 × 10(-9) L mmol(-1) s(-1). The mean k was not affected by a way of estimation of glycemia. The mean k differed less than 20% from values reported earlier and it was almost identical to the mean values calculated on basis of the selected published data. Analysis of variability of k suggests that inter-individual heterogeneity of HbA1c formation is limited or rare. The HbA1c mathematical model was able to predict changes of HbA1c in vitro resulting from different glucose levels and to reproduce a linear relationship of HbA1c and average glucose obtained in the A1C-Derived Average Glucose Study. This study demonstrates that the glycation model with the same k value might be used in majority of individuals as a tool supporting interpretation of HbA1c in different clinical situations.

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