Nitric oxide synthase activity in the abdominal aorta of rats is decreased after 4 weeks of simulated microgravity.

1. The aim of the present study was to investigate the effects of simulated microgravity on the arterial dilatory responsiveness and L-arginine (L-Arg)-nitric oxide (NO)-cGMP pathway in the abdominal aorta of rats. 2. Twenty healthy male Sprague-Dawley were randomly divided into control and simulated microgravity groups. Rats in the simulated microgravity group were subjected to hindlimb unweighting (HU). After 4 weeks, arterial dilatory responsiveness was examined in vitro in isolated abdominal aortic rings. Western blotting was used to measure endothelial (e) and inducible (i) NO synthase (NOS) protein content. Total concentrations of nitrate and nitrite (NO(x)), the stable metabolites of NO, were determined by the chemiluminescence method. Nitric oxide synthase activity in the abdominal aorta was determined through the conversion of [(3)H]-L-Arg to [(3)H]-L-citrulline. 3. The data showed that the dilatory responses of the arterial rings to L-Arg and acetylcholine decreased in rats exposed to simulated microgravity, but the dilatory responses to sodium nitroprusside and 8-bromo-cGMP were similar in both simulated microgravity and control rats. The expression of eNOS and iNOS did not differ significantly between the two groups. The NO(x) concentration in the abdominal aorta of HU rats was significantly less than that in control rats. Nitric oxide synthase activity in the aorta decreased after 4 weeks of HU. 4. The data indicate that endothelium-dependent vasorelaxation in the abdominal aorta decreased due to 4 weeks of simulated microgravity in rats and that this impaired dilatory responsiveness may result from decreased NOS activity.

Hindlimb unweighting induces changes in the RhoA-Rho-kinase pathway of the rat abdominal aorta.

Hindlimb unweighting (HLU) in rats mimics the fluid shift experienced by astronauts and may serve as a model for ground-based orthostatic hypotension. It has been shown that the abdominal aorta of HLU rats exhibits a deficit in contractile response to adrenergic agonists. The hypothesis of the present study was that decreased activity in the RhoA/Rho-kinase pathway could contribute to that deficit. Wistar rats were subjected to 20 days of HLU treatment. Abdominal aorta rings from HLU and control rats were suspended in baths for measurement of contraction. Concentration response curves were obtained to the alpha adrenergic agonist, phenylephrine and the thromboxane-mimetic, U46619. HLU treatment caused decreased contraction in response to both. The Rho-kinase inhibitor, Y27632, caused a reduction in the phenylephrine-induced contraction in control, but not HLU aorta. Other rings were frozen after stimulation 1 microM U46619 or phenylephrine. Western analysis revealed a decreased expression of RhoA, but increased expression of both Rho kinase and MYPT1, the regulatory subunit of myosin light chain (MLC) phosphatase. MYPT1 and MLC phosphorylation was decreased by HLU in phenylephrine stimulated aorta. Decreased activity in the RhoA/Rho-kinase pathway may be involved in the decreased contraction seen in the HLU abdominal aorta.

Effect of exercise training on aortic tone in chronic renal insufficiency.

BACKGROUND: Chronic renal insufficiency (CRI) is associated with a high incidence of hypertension (HTN), endothelial dysfunction, atherosclerosis and cardiovascular disease. Sedentary life style increases, whereas regular exercise reduces the risk of cardiovascular disease. This study was designed to test the effect of regular exercise on vasodilatory and vasoconstrictive responses of the thoracic aorta in rats with renal mass reduction. METHODS: One week after 5/6 nephrectomy (CRI) or sham operation (control), rats were housed in either regular cages or cages equipped with running wheels for 4 weeks. Thereafter, thoracic aorta was harvested and contractile response to potassium and phenylephrine (PhE), and relaxation response to acetylcholine (ACh) and sodium nitroprusside (SNP) were determined. RESULTS: Compared with the control animals, sedentary CRI animals exhibited significant azotemia, proteinuria, HTN, oxidative stress, and increased sensitivity to potassium and PhE, and reduced sensitivity to ACh and SNP. Exercise training for 4 weeks reduced oxidative stress, reversed CRI-induced heightened sensitivity of the aorta to PhE and potassium, and restored its sensitivity to ACh (but not SNP) without affecting arterial pressure or renal function. CONCLUSIONS: CRI results in heightened sensitivity to potassium- and alpha-1 adrenergic-mediated contractility and depressed sensitivity to endothelium-dependent relaxation in the aorta. Regular exercise improves these abnormalities without affecting arterial pressure or renal function. These observations suggest that exercise training can improve vascular function in animals, and perhaps humans, with chronic kidney disease.

Endothelial role in the thoracic aorta response to hindlimb unloading in rats.

BACKGROUND: Hindlimb unloading (HLU) is used to simulate microgravity in rats and has been shown to decrease contractile response in the abdominal aorta. The thoracic aorta has not been studied as thoroughly. METHODS: Wistar and Sprague-Dawley rats were subjected to HLU for 20 d and the thoracic aortas were isolated and sectioned into 3-mm rings for the measurement of isometric force development. Concentration response curves (CRCs) to phenylephrine (PHE) were obtained in endothelium-intact and -denuded rings from both strains of rats. Acetylcholine, methylfurmethide (MFM), and sodium nitroprusside (SNP) CRCs were obtained in the Wistar rats. RESULTS: HLU had no effect on the contractions of endothelium-intact Wistar aortas to PHE, but decreased the maximal PHE-induced contraction (2.82 +/- 0.16 g Control vs. 2.18 +/- 0.11 g HLU) in intact Sprague-Dawley aortas. After endothelium removal, HLU increased the contractions of Wistar, but not Sprague-Dawley, aortas to PHE (1.91 +/- 0.12 g Control vs. 2.95 +/- 0.13 g HLU). HLU had no effect on the relaxation to acetylcholine, but increased the sensitivity to the relaxing effects of MFM (LOG EC50 -6.96 +/- 0.12 Control vs.-7.31 +/- 0.17 HLU) and SNP (LOG EC50 -7.90 +/- 0.15 Control vs.-8.35 +/- 0.10 HLU) in the Wistar rats. SUMMARY: It is concluded that HLU increased smooth muscle contracting and endothelium-dependent relaxing capacities equally in the Wistar aortas, and had no effect on smooth muscle, but increased endothelium-dependent relaxation, in the Sprague-Dawley aortas.

Simulated microgravity effects on the rat carotid and femoral arteries: role of contractile protein expression and mechanical properties of the vessel wall.

The goal of this study was to determine the effects of microgravity on myofilament protein expression and both passive and active length-force relationships in carotid and femoral arteries. Microgravity was simulated by 20-day hindlimb unweighting (HU) in Wistar male rats, and carotid and femoral artery segments were isolated from both HU and control (CTL) rats for Western blot and length-force analysis. Western blots revealed that HU significantly decreased myosin light chain-20 (MLC-20) protein levels in both carotid and femoral arteries and decreased myosin heavy chain (MHC) in femoral artery. alpha-Actin levels were not altered by HU treatment in either artery. Length-force analysis demonstrated that HU did not change either passive or active length-force relationships in the femoral artery. HU-treated arterial rings developed significantly less force to 100 mM K(+) than CTL, but optimal lengths were identical. In the carotid artery, length-active force curves were identical for both CTL and HU; however the length-passive force curve for HU-treated rings exhibited a steeper slope than CTL, suggesting decreased compliance of the artery wall. In conclusion, our data suggest that the HU-induced decreases in both MLC-20 and MHC in femoral artery are responsible for the decreased contraction to 100 mM K(+) in HU-treated femoral artery rings. In the carotid artery, the HU-induced decrease in vessel wall compliance may counter any decrease in contractility caused by the decreased MLC-20 levels.

Extended ex vivo myocardial preservation in the beating state using a novel polyethylene glycolated bovine hemoglobin perfusate based solution.

Cardiac preservation for transplantation is generally limited by ischemic hypothermic storage of 4-6 hours. Earlier studies in the authors' laboratory have demonstrated that hypothermic perfusion preservation using a novel oxygen carrying hemoglobin solution may extend preservation times to 8 hours and decrease ischemic injury. The purpose of this study was to compare extended cardiac function after 12 and 24 hours of continuous hypothermic perfusion with a polyethylene glycolated bovine hemoglobin perfusate (PEG-Hb) solution to the clinical standard of hypothermic ischemic preservation. The hearts of 54 anesthetized and intubated New Zealand White rabbits were harvested after cold cardioplegic arrest. Group I (n = 12) hearts were perfused with a PEG-Hb solution at 20 degrees C and 30 mm Hg for 24 hours. Group II (n = 10) hearts were preserved similarly with PEG-Hb for 12 hours. Group III (n = 12) hearts were preserved for 8 hours with PEG-Hb; Group IV (n = 10) were preserved by cold ischemic storage for 4 hours at 4 degrees C; and Group V (n = 10) were tested after fresh extirpation. Left ventricular (LV) function was measured in the nonworking state at 15 minute, 1 hour, and 2 hour intervals after transfer to a standard crystalloid Langendorff circuit. Developed LV pressure at 0.5 ml LV volume was superior in Group II at early time points, yet it was similar in all preserved groups at 2 hours. +dP/dt(max) at 0.5 ml LV volume was consistent at all time points and greater in PEG-Hb preserved groups compared with Group V. -dP/dt(max) at 0.5 ml LV volume was significantly greater in Groups II and III compared with Group V initially (p < 0.05), but all were similar at the end of testing. Continuous perfusion preservation of rabbit hearts for time increments up to 24 hours with this novel PEG-Hb solution at 30 mm Hg and 20 degrees C yields LV function that is similar to 4 hours of ischemic hypothermic storage. Extended cardiac perfusion preservation with this PEG-Hb solution deserves further investigation in large animal transplant models.

Effects of simulated microgravity on arterial nitric oxide synthase and nitrate and nitrite content.

The aim of the present work was to investigate the alterations in nitric oxide synthase (NOS) expression and nitrate and nitrite (NOx) content of different arteries from simulated microgravity rats. Male Wistar rats were randomly assigned to either a control group or simulated microgravity group. For simulating microgravity, animals were subjected to hindlimb unweighting (HU) for 20 days. Different arterial tissues were removed for determination of NOS expression and NOx. Western blotting was used to measure endothelial NOS (eNOS) and inducible NOS (iNOS) protein content. Total concentrations of NOx, stable metabolites of nitric oxide, were determined by the chemiluminescence method. Compared with controls, isolated vessels from simulated microgravity rats showed a significant increase in both eNOS and iNOS expression in carotid arteries and thoracic aorta and a significant decrease in eNOS and iNOS expression of mesenteric arteries. The eNOS and iNOS content of cerebral arteries, as well as that of femoral arteries, showed no differences between the two groups. Concerning NOx, vessels from HU rats showed an increase in cerebral arteries, a decrease in mesenteric arteries, and no change in carotid artery, femoral artery and thoracic aorta. These data indicated that there were differential alterations in NOS expression and NOx of different arteries after hindlimb unweighting. We suggest that these changes might represent both localized adaptations to differential body fluid redistribution and other factors independent of hemodynamic shifts during simulated microgravity.

Vascular neuroeffector mechanisms: the next 30 years.

The 10th International Symposium on Vascular Neuroeffector Mechanisms was held on 12-15 July 2002 in Lake Tahoe, California, USA.