The aim was to determine whether increased oxidative stress during the adaptation to chronic intermittent hypoxia (CIH) plays a role in the induction of improved cardiac ischemic tolerance. Adult male Wistar rats were exposed to CIH in a hypobaric chamber (7,000 m, 8 h/day, 5 days/wk, 24-30 exposures). Half of the animals received antioxidant N-acetylcysteine (NAC; 100 mg/kg) daily before the exposure; the remaining rats received saline. Control rats were kept under normoxia and treated in a corresponding manner. One day after the last exposure (and/or NAC injection), anesthetized animals were subject to 20 min of coronary artery occlusion and 3 h of reperfusion for determination of infarct size. In parallel subgroups, biochemical analyses of the left ventricular myocardium were performed. Adaptation to CIH reduced infarct size from 56.7 +/- 4.5% of the area at risk in the normoxic controls to 27.7 +/- 4.9%. NAC treatment decreased the infarct size in the controls to 42.0 +/- 3.4%, but it abolished the protection provided by CIH (to 41.1 +/- 4.9%). CIH decreased the reduced-to-oxidized glutathione ratio and increased the relative amount of PKC isoform-delta in the particulate fraction; NAC prevented these effects. The expression of PKC-epsilon was decreased by CIH and not affected by NAC. Activities of superoxide dismutase, catalase, and glutathione peroxidase were affected by neither CIH nor NAC treatment. It is concluded that oxidative stress associated with CIH plays a role in the development of increased cardiac ischemic tolerance. The infarct size-limiting mechanism of CIH seems to involve the PKC-delta-dependent pathway but apparently not the increased capacity of major antioxidant enzymes.

No abstract

Posthypoxic fluctuations in the levels of two excitatory amino acids, glutamate and aspartate, may be related to changes in mechanism(s) which are responsible for their reuptake. As gamma-glutamyl transpeptidase (GGT) plays a role in mediating the uptake of glutamate and aspartate into various compartments of the brain, we studied changes in the activity of this enzyme in main regions of the brain in young and adult rats. We found a posthypoxic increase in bound GGT activity in some brain regions of 18-day-old animals after acute exposure, but no changes were observed after prolonged altitude hypoxia, with the exception of a decrease in cortical GGT activity. In contrast, acute hypoxia decreased GGT activity in the cortical capillaries to 59%, but prolonged hypoxic exposure was ineffective. However, the activity of soluble GGT in the cerebrospinal fluid of both groups of rats was several-times elevated in comparison with controls. At the same time, bound GGT activity was increased in the liver after acute or prolonged altitude hypoxia. The soluble GGT activity in plasma was only increased after prolonged exposure. Ninety days after prolonged hypoxic exposure the bound GGT activity was reduced in all brain regions to about 60-70% of controls (significantly higher in females than in males) as long-term developmental sequel from early postnatal hypoxia.

Matrix metalloproteinases (MMPs) is a family of proteolytic enzymes involved in remodeling of extracellular matrix. Although proteolytic enzymes are produced by many cell types, mast cells seem to be more important than other types in remodeling of pulmonary arteries during hypoxia. Therefore, we tested in vitro production of MMPs and serine proteases in four cell types (mast cells, fibroblasts, vascular smooth muscle cells and endothelial cells) cultivated for 48 h under normoxic or hypoxic (3 % O2) conditions. MMP-13 was visualized by immunohistochemistry, MMP-2 and MMP-9 were detected by zymography in cell lysates. Enzymatic activities (MMPs, tryptase and chymase) were estimated in the cultivation media. Hypoxia had a minimal effect on total MMP activity in the cultivation media of all types of cells, but immunofluorescence revealed higher intensity of MMP-13 in the cells exposed to hypoxia except of fibroblasts. Tryptase activity was three times higher and chymase activity twice higher in mast cells cultivated in hypoxia than in those cultured in normoxia. Among all cell types studied here, mast cells are the most abundant source of proteolytic enzymes under normoxic and hypoxic conditions. Moreover, in these cells hypoxia increases the production of both specific serine proteases tryptase and chymase, which can act as MMPs activators.

The activity of gamma‐glutamyl transferase (GGT) was measured in amniotic fluid collected between the 16th and 30th weeks of gestation from 81 pregnancies with fetuses affected by chromosomal aberrations, nine with different types of inborn errors of metabolism, two with hemophilia A and one with fragile X syndrome. The GGT activity was compared with that from 1000 normal pregnancies and deliveries resulting in healthy newborns. Contamination of amniotic fluid by blood did not affect the GGT activity. Pathologically decreased activity was found in 25 of 56 amniotic samples from pregnancies with fetal autosomal chromosomal aberrations (44.6%). It was decreased in 15 of 35 pregnancies with fetal trisomy 21 (43%), in 11 of 19 pregnancies with fetal trisomy 18 (58%), in one of three pregnancies with fetal trisomy 13 and in two pregnancies with fetal trisomy 8 and triploidy, respectively. In only three of 16 pregnancies with fetal sex chromosomal aberrations was the GGT activity low. Increased GGT activity was found in three of six pregnancies with unbalanced structurally rearranged karyotypes of the fetuses. Normal GGT activity was observed in all nine amniotic fluid samples from pregnancies with fetuses affected with different forms of inborn errors of metabolism diseases, in the two pregnancies with hemophilia A and in the pregnancy with a male fetus with fragile X syndrome. These and earlier findings indicate that the GGT activity in amniotic fluid is mostly decreased in pregnancies with severe fetal developmental abnormalities, such as autosomal chromosomal aberrations, which could possibly be secondary to an alteration of the microvillar transport system of GGT to the amniotic fluid. GGT testing could thus be a valuable screening method for routine use in prenatal diagnosis of second‐trimester pregnancy.