Günnur Koçer

Effect of exercise training on resistance arteries in rats with chronic NOS inhibition

Regular exercise has blood pressure-lowering effects, as shown in different types of experimental hypertension models in rats, including the nitric oxide synthase (NOS) inhibition model. We aimed to investigate possible mechanisms implicated in the exercise effect by evaluating the vasoreactivity of resistance arteries. Exercise effects on agonist-induced vasodilatory responses and flow-mediated dilation were evaluated in vessel segments of the rat chronic NOS inhibition model. Normotensive and hypertensive rats were subjected to swimming exercise (1 h/day, 5 days/wk, 6 wk), while rats in other sedentary and hypertensive groups did not. Hypertension was induced by oral administration of the nonselective NOS inhibitor l-NAME (25 mg/kg day) for 6 wk. Systolic blood pressure, as measured by the tail-cuff method, was significantly decreased by the training protocol in exercising hypertensive rats. The vasoreactivity of resistance arteries was evaluated by both wire and pressure myography studies. An impaired nitric oxide-mediated relaxation pathway in untrained hypertensive rats led to decreased relaxation responses in vessels with intact endothelium. Exercise training significantly improved the responses to acetylcholine and flow-mediated dilation in exercise-trained hypertensive rats in parallel with a decrease in blood pressure. On the other hand contraction (norepinephrine and KCl) and relaxation (sodium nitroprusside) responses of vascular smooth muscle were not different between the groups. Vascular endothelial NOS protein expression was found to be increased in both exercising groups. In conclusion, these results revealed evidence of an increased role of the nitric oxide-dependent relaxation pathway in exercising hypertensive rats.

Biphasic Pattern of Exercise-Induced Proteinuria in Sedentary and Trained Men

Background/Aims: Exercise-induced proteinuria is a common consequence of physical activity, although its mechanism is not clear. Oxidant stress has been proposed as one of different factors involved in postexercise proteinuria in rats. In this study we investigated whether reactive oxygen radicals generated during exercise play a role in exercise-induced proteinuria in sedentary and trained men. Methods: The validity of oxidant stress following stepwise maximal exercise on proteinuria was investigated in sedentary and trained subjects before and after antioxidant vitamin treatment (A, C, and E) for 2 months. While protein carbonyl content in serum and thiobarbituric acid reactive substances (TBARS) in erythrocytes and urine were used as oxidant stress markers, total protein, albumin, β2-microglobulin in urine were assayed for proteinuria in five consecutive specimens after exercise. Urines were collected before exercise, then 30 min, 2, 8 and 24 h postexercise. Results: Increased urinary protein levels and mixed type proteinuria were determined after 30 min of exercise in sedentary and trained subjects. Proteinuria was normalized at 2 and 8 h specimens. However, glomerular type proteinuria was identified at 24 h specimen in both groups. Oxidant stress markers were significantly elevated in sedentary and trained subjects. Antioxidant treatment prevented the increase in oxidant stress markers, urinary protein levels and the occurrence of glomerular type proteinuria after exhaustive exercise at 24 h in both groups. Conclusions: These findings suggest that the exercise-induced oxidant stress may contribute to exercise-induced proteinuria in sedentary and trained men.

Potential sources of oxidative stress that induce postexercise proteinuria in rats.

Exercise-induced proteinuria is a common consequence of physical activity and is caused predominantly by alterations in renal hemodynamics. Although it has been shown that exercise-induced oxidative stress can also contribute to the occurrence of postexercise proteinuria, the sources of reactive oxygen species that promote it are unknown. We investigated the enzymes nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and xanthine oxidase (XO) as possible sources of oxidative stress in postexercise proteinuria. First, we evaluated the effect of blocking the NADPH oxidase enzyme on postexercise proteinuria. We found a significant increase in urinary protein level, kidney thiobarbituric acid-reactive substances (TBARS), and protein carbonyl content after exhaustive exercise, and NADPH oxidase activity was induced by exercise. Rats that were treated with an NADPH oxidase inhibitor for 4 days before exhaustive exercise showed no increase in kidney TBARS or protein carbonyl derivative level and no proteinuria or NADPH oxidase activation. In the next set of experiments, we investigated the effect of XO blockage on postexercise proteinuria. Oxypurinol, an XO inhibitor was administered to rats for 3 days before exercise. Although XO inhibition significantly decreased kidney TBARS levels and protein carbonyl content in exercised rats, the inhibition did not prevent exercise-induced proteinuria. However, plasma and kidney XO activity was not induced by exercise, but rather it was suppressed under oxypurinol treatment. These results suggest that increased NADPH oxidase activity induced by exhaustive exercise is an important source of elevated oxidative, stress during exercise, which contributes to the occurrence of postexercise proteinuria.

Effect of magnesium on vascular reactivity in NOS inhibition-induced hypertension.

This study investigated the effect of magnesium on the vascular reactivity of conduit and resistance arteries in a nitric oxide synthase inhibition-induced hypertension model. The aorta and third-order branches of the mesenteric artery were dissected from normotensive control and hypertensive rats, and their constriction and dilation responses in physiological saline solution containing normal (1.2 mM) or high (4.8 mM) magnesium concentrations were examined. The responses of the vessels were evaluated using potassium chloride (KCl) and phenylephrine (Phe), acetylcholine (ACh) and sodium nitroprusside. The Phe-induced constriction response of the aortic rings increased, whereas the ACh-induced dilation response decreased, in the hypertensive group compared to controls, in the presence of a normal magnesium concentration. High magnesium did not alter these responses in either group. Both the KCl- and Phe-induced constriction responses of the mesenteric arteries increased, and the ACh-induced dilation response decreased in the hypertensive group compared to controls, in the presence of a normal magnesium concentration. High magnesium significantly decreased the KCl and Phe-induced constriction and increased the ACh-induced dilation response of the mesenteric arteries in the hypertensive group, while it did not alter these responses in controls. This study suggests that high magnesium improves vascular reactivity of resistance-, but not conduit-type arteries in the nitric oxide synthase inhibition-induced hypertension model.

The Effect of Exercise Training on the Responsiveness of Renal Resistance Arteries in Rats

Abstract Blood flow to several tissues changes during an acute bout of exercise. The kidney is one of the organs that are most affected by exercise-induced blood redistribution. The aim of the present study was to investigate possible exercise-induced vascular reactivity changes in renal resistance arteries in rats. Renal resistance arteries were isolated from rats that underwent 8 weeks of swimming and sedentary control rats, and the arteries were evaluated using wire myography. Similar dilation responses to acetylcholine, bradykinin, adenosine, isoproterenol, and sodium nitroprusside were observed in both groups. The vasoconstrictive agents vasopressin, endothelin-1, potassium chloride, and thromboxane A2 also induced similar responses in both groups; however, the trained group had an increased constrictive response to norepinephrine compared to the control rats. The results of our study show that renal resistance arteries of trained rats behave differently than conduit-type renal arteries and exhibit an increased contractile response to sympathetic agonists. This finding provides supporting evidence that renal blood flow markedly decreases during exercise in trained individuals.

Hypertension alters phosphorylation of VASP in brain endothelial cells

Hypertension impairs cerebral vascular function. Vasodilator-stimulated phosphoprotein (VASP) mediates active reorganization of the cytoskeleton via membrane ruffling, aggregation and tethering of actin filaments. VASP regulation of endothelial barrier function has been demonstrated by studies using VASP−/− animals under conditions associated with tissue hypoxia. We hypothesize that hypertension regulates VASP expression and/or phosphorylation in endothelial cells, thereby contributing to dysfunction in the cerebral vasculature. Because exercise has direct and indirect salutary effects on vascular systems that have been damaged by hypertension, we also investigated the effect of exercise on maintenance of VASP expression and/or phosphorylation. We used immunohistochemistry, Western blotting and immunocytochemistry to examine the effect of hypertension on VASP expression and phosphorylation in brain endothelial cells in normotensive [Wistar–Kyoto (WKY)] and spontaneously hypertensive (SH) rats under normal and exercise conditions. In addition, we analyzed VASP regulation in normoxia- and hypoxia-induced endothelial cells. Brain endothelial cells exhibited significantly lower VASP immunoreactivity and phosphorylation at the Ser157 residue in SHR versus WKY rats. Exercise reversed hypertension-induced alterations in VASP phosphorylation. Western blotting and immunocytochemistry indicated reduction in VASP phosphorylation in hypoxic versus normoxic endothelial cells. These results suggest that diminished VASP expression and/or Ser157 phosphorylation mediates endothelial changes associated with hypertension and exercise may normalize these changes, at least in part, by restoring VASP phosphorylation.

The Renin–Angiotensin System, Not the Kinin–Kallikrein System, Affects Post-Exercise Proteinuria

Background/Aims: Temporary proteinuria post-exercise is common and is caused predominantly by renal haemodynamic alterations. One reason is up-regulation of angiotensin II (Ang II) due to the reducing effect of angiotensin-converting enzyme (ACE) inhibitors. However, another, ignored, reason could be the kininase effect of ACE inhibition. This study investigated how ACE inhibition reduces post-exercise proteinuria: by either Ang II up-regulation inhibition or bradykinin elevation due to kininase activity inhibition. Methods: Our study included 10 volunteers, who completed 3 high-intensity exercise protocols involving cycling at 1-week intervals. The first protocol was a control arm, the second evaluated the effect of ACE inhibition and the third examined the effect of angiotensin type 1 receptor blockade. Upon application, both agents reduced systolic and diastolic blood pressure; however, there were no statistically significant differences. In addition, total protein, microalbumin and β2-microglobulin excretion levels in urine specimens were analysed before, 30 min after and 120 min after the exercise protocols. Results: Total protein levels in urine samples were elevated in all 3 protocols after 30 min of high-intensity exercise, compared to baseline levels. However, both ACE inhibition and angiotensin type 1 receptor blockade suppressed total protein in the 30th min. In each protocol, total protein levels returned to the baseline after 120 min. Urinary microalbumin and β2-microglobulin levels during the control protocol were significantly higher 30 min post-exercise; however, only angiotensin type 1 receptor blockade suppressed microalbumin levels. Conclusion: The results indicated Ang II up-regulation, not bradykinin elevation, plays a role in post-exercise proteinuria.