Aging induces muscle-specific impairment of endothelium-dependent dilation in skeletal muscle feed arteries.

We tested the hypothesis that aging decreases endothelium-dependent vasodilation in feed arteries perfusing rat skeletal muscle. In addition, we tested the hypothesis that attenuated vasodilator responses are associated with decreased endothelial nitric oxide synthase (eNOS) and superoxide dismutase-1 (SOD-1) expression. Soleus feed arteries (SFA) and gastrocnemius feed arteries (GFA) were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats. Feed arteries from the right hindlimb were cannulated with two glass micropipettes for examination of endothelium-dependent [acetylcholine (ACh)] and endothelium-independent [adenosine (Ado) or sodium nitroprusside (SNP)] vasodilator function. Feed arteries from the left hindlimb were frozen and used to assess eNOS and SOD-1 protein and mRNA expression. In SFA, endothelium-dependent dilation to ACh was reduced in old rats (0.9 +/- 0.04 vs. 0.8 +/- 0.03), whereas dilator responses to Ado and SNP were similar in SFA of young and old rats. In GFA, vasodilator responses to ACh, Ado, and SNP were not altered by age. eNOS and SOD-1 protein expression declined with age in SFA (-71 and -54%, respectively) but not in GFA. eNOS and SOD-1 mRNA expression were not altered by age in SFA or GFA. Collectively, these data indicate aging induces muscle-specific impairment of endothelium-dependent vascular function in SFA.     

Selected Contribution: Aging impairs nitric oxide and prostacyclin mediation of endothelium-dependent dilation in soleus feed arteries.

We tested the hypothesis that endothelium-dependent dilation in soleus muscle feed arteries (SFA) is impaired by aging due to attenuated nitric oxide (NO)-mediated vasodilation. SFA were isolated from young (4 mo) and old (24 mo) male Fischer 344 rats and cannulated with two glass micropipettes for examination of endothelium-dependent [flow or acetylcholine (ACh)] and endothelium-independent [sodium nitroprusside (SNP)] vasodilator function. Flow- and ACh-induced dilation was significantly attenuated by age, whereas dilation to SNP was not compromised. To determine the mechanism(s) by which aging affected dilator responses to flow and ACh, dilation was assessed in the presence of Nomega-nitro-L-arginine (L-NNA; to inhibit NO synthase), indomethacin (Indo; to inhibit cyclooxygenase), and L-NNA + Indo. In the presence of L-NNA, Indo, or L-NNA + Indo, flow-induced dilation was inhibited in young SFA, resulting in a response to flow that was no longer greater than old SFA. In the presence of L-NNA or Indo, ACh-induced dilation was not significantly inhibited in young or old SFA; however, double blockade with L-NNA + Indo inhibited ACh-induced dilation in young SFA such that the response to ACh was no longer greater than old SFA. Collectively, these data indicate that aging impairs vasodilator responses in SFA by attenuating NO- and prostacyclin-mediated, endothelium-dependent, dilation.     

Hindlimb unweighting decreases ecNOS gene expression and endothelium-dependent dilation in rat soleus feed arteries.

We tested the hypothesis that hindlimb unweighting (HLU) and the associated reduction in soleus muscle blood flow causes decreased expression of endothelial cell nitric oxide synthase (ecNOS) mRNA and protein and attenuated endothelium-dependent vasodilator responses in rat soleus feed arteries (SFA). Male Sprague-Dawley rats were exposed to HLU (n = 12) or cage control (Con; n = 12) conditions for 14 days. At the end of this period, SFA were isolated, removed, and cannulated with two glass micropipettes for examination of vasodilator responses or frozen for analysis of ecNOS mRNA and protein expression. RT-PCR of RNA from single SFA was used to measure ecNOS mRNA, and immunoblots on single SFAs were used to measure ecNOS protein content. Results revealed that both ecNOS mRNA and ecNOS protein expression were lower in SFA from HLU rats. Dilation to increased intraluminal flow was attenuated in SFA from HLU rats (Con: 88 +/- 8% vs. HLU: 53 +/- 8%) as was maximal vasodilation to acetylcholine (10(-9)-10(-4) M; Con: 88 +/- 5% vs. HLU: 73 +/- 5%). Sensitivity to the endothelium-independent vasodilator sodium nitroprusside (10(-10)-10(-4) M) was enhanced by HLU (EC(50): Con: 4.46 x 10(-7) M vs. HLU: 5.00 x 10(-8) M). Collectively, these data indicate that the chronic reduction in soleus blood flow associated with the reduced physical activity during HLU results in reduced expression of ecNOS mRNA and protein in SFA and attenuated endothelium-dependent vasodilation.     

Attenuation of endothelium-dependent relaxation in mesenteric artery during noise-induced hypertension

The present study was designed to determine whether there is a causal relationship between noise-induced hypertension and changes of endothelial function. Rats were exposed to noise stress (100 dB, 1 kHz, 4 h/day, 6 days/week) for 1–4 weeks. The systolic blood pressure was significantly increased after rats were exposed to noise stress for 3 weeks. The relaxant responses of isolated mesenteric arterial rings to endothelium-dependent vasodilators (A23187 and acetylcholine) in noise-treated rats were significantly less than those in control rats. This difference in response to acetylcholine still existed in the presence of methylene blue or N-nitro-L-arginine. On the other hand, the responses to the endothelium-independent vasodilator nitroglycerin were not affected in rats exposed to noise stress. The attenuation to endothelium-dependent vasodilators during noise stress may result in increasing peripheral vascular resistance and thus elevate blood pressure. This indicates that noise-induced hypertension may be partly due to the alterations of endothelial activity.     

Chronic exercise training does not alter pulmonary vasorelaxation in normal pigs.

Exercise training increases acetylcholine-induced pulmonary vasorelaxation in pigs with coronary occlusion. The present study tested the hypothesis that chronic exercise training enhances endothelium-mediated vasorelaxation in pulmonary arteries from normal pigs. Yucatan miniswine exercised for 16 wk on a treadmill (Ex); control pigs (Sed) remained in pens. Pulmonary artery rings (2- to 3-mm OD) were studied using standard isometric techniques. Contractile responses to 80 mM KCl and norepinephrine (NE) were determined. Vessels were constricted with levels of NE that resulted in half-maximal contraction to examine endothelium-dependent relaxation to ACh and endothelium-independent relaxation to sodium nitroprusside in the presence and absence of nitric oxide synthase inhibition, cyclooxygenase inhibition, and endothelial denudation. Arteries from Ex pigs developed increased contraction to 80 mM KCl, but the response to NE did not differ between groups. Endothelium-dependent and endothelium-independent responses did not differ between Sed and Ex in the presence or absence of pharmacological inhibitors or denudation. We conclude that chronic exercise training does not alter endothelium-dependent or endothelium-independent vasorelaxation responses of pulmonary arteries from normal pigs.     

Regulation of the endogenous NO pathway by prolonged inhaled NO in rats

Nitric oxide(NO) modulates the endogenous NO-cGMP pathway. We determined whetherprolonged inhaled NO downregulates the NO-cGMP pathway, which mayexplain clinically observed rebound pulmonary hypertension. Rats wereplaced in a normoxic (N; 21%O₂) or hypoxic (H; 10%O₂) environment with and withoutinhaled NO (20 parts/million) for 1 or 3 wk. Subsequently, nitric oxidesynthase (NOS) and soluble guanylate cyclase (GC) activity andendothelial NOS (eNOS) protein levels were measured. Perfusate cGMPlevels and endothelium-dependent and -independent vasodilation weredetermined in isolated lungs. eNOS protein levels and NOS activity werenot altered by inhaled NO in N or H rats. GC activity was decreased by60 ± 10 and 55 ± 11% in N and H rats, respectively, after 1 wkof inhaled NO but was not affected after 3 wk. Inhaled NO had no effecton perfusate cGMP in N lungs. Inhaled NO attenuated the increase incGMP levels caused by 3 wk of H by 57 ± 11%, but there was norebound in cGMP after 24 h of recovery. Endothelium-dependentvasodilation was not altered, and endothelium-independent vasodilationwas not altered (N) or slightly increased (H, 10 ± 3%) byprolonged inhaled NO. In conclusion, inhaled NO did not alter theendogenous NO-cGMP pathway as determined by eNOS protein levels, NOSactivity, or endothelium-dependent vasodilation under N and Hconditions. GC activity was decreased after 1 wk; however, GC activitywas not altered by 3 wk of inhaled NO and endothelium-independentvasodilation was not decreased.

     

Chronic exercise training improves ACh-induced vasorelaxation in pulmonary arteries of pigs.

We hypothesized that exercise training would lead to enhanced endothelium-dependent vasodilation in porcine pulmonary arteries. Pulmonary artery rings (2- to 3-mm OD) were obtained from female Yucatan miniature swine with surgically induced coronary artery occlusion (ameroid occluder). Exercise training was performed for 16 wk, and vasomotor responses were studied by using standard isometric techniques. Contractile responses to 80 mM KCl, isosmotic KCl (10-100 mM), and norepinephrine (10(-8) to 10(-4) M) did not differ between sedentary (Sed) and exercise-trained (Ex) pigs. Relaxation was assessed to endothelium-dependent and endothelium-independent vasodilators after norepinephrine contraction. Pulmonary arteries of Ex pigs exhibited greater maximal relaxation to ACh (61.9 +/- 3.5%) than did those of Sed pigs (52.3 +/- 3.9%; P < 0.05). Endothelium-independent relaxation to sodium nitroprusside did not differ. Inhibition of nitric oxide synthase significantly decreased acetylcholine-induced relaxation, with greater inhibition in arteries from Ex pigs (P < 0.05). Inhibition of cyclooxygenase enhanced relaxation to acetylcholine in arteries from Sed pigs. We conclude that exercise training enhances endothelium-dependent (ACh-mediated) vasorelaxation in pulmonary arteries by mechanisms of increased reliance on nitric oxide and reduced production of a prostanoid constrictor.     

Time- and order-dependent changes in functional and NO-mediated dilation during exercise training

Lash, Julia M., and H. Glenn Bohlen. Time- andorder-dependent changes in functional and NO-mediated dilation during exercise training. J. Appl. Physiol.82(2): 460-468, 1997.Arterial vessel responses to sodiumnitroprusside (SNP) and acetylcholine (ACh) were measured in thespinotrapezius muscle of sedentary (Sed) and treadmill-trained (Tr)rats to determine whether these endothelium-dependent (ACh) and-independent (SNP) mechanisms contribute to thetraining-induced increase in functional vasodilation previouslyobserved. Control and maximal vessel diameters were similar between Sedand Tr. After 8 wk of training, functional dilation (2-, 4-, and 8-Hzcontractions) was enhanced in all orders of vessels studied[terminal feed artery (FA), largest arterioles (1A), andintermediate-sized arterioles (2A)], but responses to SNP wereincreased only in FA. Responses to ACh were not significantly increasedin any vessel order. After 16 wk of training, functional dilation hadregressed in Tr such that only the FA response to 4 Hz wassignificantly elevated relative to Sed. However, the FA and 1Aresponses to SNP were significantly greater in Tr than in Sed, as werethe 1A and 2A responses to ACh. These results show a dissociation offunctional dilation and SNP- or ACh-mediated responses, as well asage-dependent interactions, a time-dependent progression, and vesselorder specificity in the adaptations to training.

     

Acetylcholine induces vasoconstriction in the microcirculation of cardiomyopathic hamsters: reversal by L-arginine.

The goal of this study was to determine whether endothelium-dependent responses of the microcirculation are altered during cardiomyopathy. We examined in vivo responses of cheek pouch arterioles to an endothelium-dependent agonist (acetylcholine) and an endothelium-independent agonist (nitroglycerin) in normal and in cardiomyopathic hamsters. In normal hamsters, acetylcholine produced dose-related dilatation of arterioles. In contrast, acetylcholine produced constriction of arterioles in cardiomyopathic hamsters. Nitroglycerin produced similar dose-related dilatation in normal and cardiomyopathic hamsters. We also examined whether impaired responses to acetylcholine in cardiomyopathic hamsters were related to an alteration in the L-arginine/nitric oxide pathway. We found that L-arginine (100 microM) restored endothelium-dependent vasodilatation to acetylcholine in cardiomyopathic hamsters. Thus, cardiomyopathy impairs endothelium-dependent responses of the microcirculation which is reversed by L-arginine.     

NAD(P)H oxidase-derived reactive oxygen species contribute to age-related impairments of endothelium-dependent dilation in rat soleus feed arteries

We tested the hypothesis that age-related endothelial dysfunction in rat soleus muscle feed arteries (SFA) is mediated in part by NAD(P)H oxidase-derived reactive oxygen species (ROS). SFA from young (4 mo) and old (24 mo) Fischer 344 rats were isolated and cannulated for examination of vasodilator responses to flow and acetylcholine (ACh) in the absence or presence of a superoxide anion (O(2)(-)) scavenger (Tempol; 100 μM) or an NAD(P)H oxidase inhibitor (apocynin; 100 μM). In the absence of inhibitors, flow- and ACh-induced dilations were attenuated in SFA from old rats compared with young rats. Tempol and apocynin improved flow- and ACh-induced dilation in SFA from old rats. In SFA from young rats, Tempol and apocynin had no effect on flow-induced dilation, and apocynin attenuated ACh-induced dilation. To determine the role of hydrogen peroxide (H(2)O(2)), dilator responses were assessed in the absence and presence of catalase (100 U/ml) or PEG-catalase (200 U/ml). Neither H(2)O(2) scavenger altered flow-induced dilation, whereas both H(2)O(2) scavengers blunted ACh-induced dilation in SFA from young rats. In old SFA, catalase improved flow-induced dilation whereas PEG-catalase improved ACh-induced dilation. Compared with young SFA, in response to exogenous H(2)O(2) and NADPH, old rats exhibited blunted dilation and constriction, respectively. Immunoblot analysis revealed that the NAD(P)H oxidase subunit gp91phox protein content was greater in old SFA compared with young. These results suggest that NAD(P)H oxidase-derived reactive oxygen species contribute to impaired endothelium-dependent dilation in old SFA.     

Short-term exercise training increases ACh-induced relaxation and eNOS protein in porcine pulmonary arteries.

We tested the hypothesis that short-term exercise (STEx) training and the associated increase in pulmonary blood flow during bouts of exercise cause enhanced endothelium-dependent vasorelaxation in porcine pulmonary arteries and increased expression of endothelial cell nitric oxide synthase (eNOS) and superoxide dismutase-1 (SOD-1) protein. Mature, female Yucatan miniature swine exercised 1 h twice daily on a motorized treadmill for 1 wk (STEx group, n = 7); control pigs (Sed, n = 6) were kept in pens. Pulmonary arteries were isolated from the left caudal lung lobe, and vasomotor responses were determined in vitro. Arterial tissue from the distal portion of this pulmonary artery was processed for immunoblot analysis. Maximal endothelium-dependent (ACh-stimulated) relaxation was greater in STEx (71 +/- 5%) than in Sed (44 +/- 6%) arteries (P < 0.05), and endothelium-independent (sodium nitroprusside-mediated) responses did not differ. Sensitivity to ACh was not altered by STEx training. Immunoblot analysis indicated a 3.9-fold increase in eNOS protein in pulmonary artery tissue from STEx pigs (P < 0.05) with no change in SOD-1 or glyceraldehyde-3-phosphate dehydrogenase protein levels. We conclude that STEx training enhances ACh-stimulated vasorelaxation in pulmonary arterial tissue and that this adaptation is associated with increased expression of eNOS protein.     

Effects of 17ß-estradiol on endothelium-dependent relaxation induced by acetylcholine in female rat aorta

Estrogens have been postulated to play an important role in modulation of vascular responses to endogenous reactive substances. The effects of chronic in vivo treatment with 17ß-estradiol on relaxant responses to acetylcholine were investigated in the rat aorta isolated from prepubertal female rats. The selectivity of effects of 17ß-estradiol on acetylcholine-induced relaxation was evaluated using histamine, another endothelium-dependent relaxant in the rat aorta. 17ß-Estradiol significantly enhanced endothelium-dependent relaxation induced by acetylcholine, but did not alter the vascular responses to acetylcholine in endothelium-denuded aortic rings isolated from prepubertal female rats. In contrast, 17ß-estradiol did not change endothelium-dependent relaxation induced by histamine in endothelium-intact aortic rings. The results of the present study demostrate that 17ß-estradiol selectively enhanced acetylcholine-induced endothelium-dependent relaxation in the rat aorta.     

Supercritical fluid-aerosolized vitamin E pretreatment decreases leak in isolated oxidant-perfused rat lungs

Hybertson, Brooks M., Roger P. Kitlowski, Eric K. Jepson,and John E. Repine. Supercritical fluid-aerosolized vitamin Epretreatment decreases leak in isolated oxidant-perfused rat lungs.J. Appl. Physiol. 84(1): 263-268, 1998.We hypothesized that direct pulmonary administration ofsupercritical fluid-aerosolized (SFA) vitamin E would decrease acuteoxidative lung injury. We previously reported that rapid expansion ofsupercritical CO₂ formedrespirable particles of vitamin E and that administering SFA vitamin Eto rats increased lung vitamin E levels and decreased neutrophil-mediated lung leak. In the present investigation, we foundthat pretreatment with SFA vitamin E protected isolated rat lungsagainst the oxidant-induced lung leak caused by perfusion with xanthineoxidase (XO) and purine, an enzyme system that generates superoxideanion () and hydrogenperoxide. SFA vitamin E droplets were 0.7-3 µm in diameter, andinhalation of the airborne droplets for 30 min deposited ~55 µg ofvitamin E in rat lungs. Isolated rat lungs perfused with XO (0.02 U/ml) and purine (10 mM) gained more weight (1.75 ± 0.12 g,n = 8), retained more Ficoll(11.5 ± 1.2 mg/left lung,n = 7), and accumulated more Ficoll intheir lung lavages (700 ± 146 µg/ml,n = 8) than control lungs [0.25 ± 0.06 g (n = 10), 6.2 ± 1.2 mg/left lung (n = 9), and 141 ± 31 µg/ml (n = 8), respectively,P < 0.05]. In contrast,isolated lungs from rats that were pretreated with SFA vitamin E haddecreased (P < 0.05) weight gains(0.32 ± 0.06 g, n = 7), Ficollretentions (3.3 ± 1.1 mg/left lung,n = 7), and lung lavage Ficollconcentrations (91 ± 26 µg/ml,n = 6) after perfusion with XO andpurine compared with isolated lungs from control rats perfused with XOand purine. This protective effect was not observed in rat lungs givensham treatments (CO₂ alone orvitamin E acetate aerosolized with supercriticalCO₂). Our results suggest thatdirect pulmonary supplementation of vitamin E decreases susceptibilityto vascular leakage caused by XO-derived oxidants.

     

Effects of aging and exercise training on spinotrapezius muscle microvascular PO2 dynamics and vasomotor control

With advancing age, there is a reduction in exercise tolerance, resulting, in part, from a perturbed ability to match O(2) delivery to uptake within skeletal muscle. In the spinotrapezius muscle (which is not recruited during incline treadmill running) of aged rats, we tested the hypotheses that exercise training will 1) improve the matching of O(2) delivery to O(2) uptake, evidenced through improved microvascular Po(2) (Pm(O(2))), at rest and throughout the contractions transient; and 2) enhance endothelium-dependent vasodilation in first-order arterioles. Young (Y, ～6 mo) and aged (O, >24 mo) Fischer 344 rats were assigned to control sedentary (YSED; n = 16, and OSED; n = 15) or exercise-trained (YET; n = 14, and OET; n = 13) groups. Spinotrapezius blood flow (via radiolabeled microspheres) was measured at rest and during exercise. Phosphorescence quenching was used to quantify Pm(O(2)) in vivo at rest and across the rest-to-twitch contraction (1 Hz, 5 min) transition in the spinotrapezius muscle. In a follow-up study, vasomotor responses to endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) stimuli were investigated in vitro. Blood flow to the spinotrapezius did not increase above resting values during exercise in either young or aged groups. Exercise training increased the precontraction baseline Pm(O(2)) (OET 37.5 ± 3.9 vs. OSED 24.7 ± 3.6 Torr, P < 0.05); the end-contracting Pm(O(2)) and the time-delay before Pm(O(2)) fell in the aged group but did not affect these values in the young. Exercise training improved maximal vasodilation in aged rats to acetylcholine (OET 62 ± 16 vs. OSED 27 ± 16%) and to sodium nitroprusside in both young and aged rats. Endurance training of aged rats enhances the Pm(O(2)) in a nonrecruited skeletal muscle and is associated with improved vascular smooth muscle function. These data support the notion that improvements in vascular function with exercise training are not isolated to the recruited muscle.     

Functional assessment of cryopreserved human femoral arteries for pharmaceutical research

An established method for cryopreservation that might preserve the vascular and endothelial responses of human femoral arteries (HFAs) to be transplanted as allografts was studied. HFAs were harvested from multiorgan donors and stored at 4 degrees C in saline solution before cryostorage. Thirty HFA rings were isolated and randomly assigned to one control group of unfrozen HFAs (eight rings) and one group of cryopreserved HFAs (22 rings).Cryopreservation was performed in RPMI solution containing dimethylsulfoxide (DMSO) and the rate of cooling was -1 degrees C/min until -40 degrees C and faster rates until -150 degrees C was reached. The contractile and relaxant responses of unfrozen and frozen/thawed arteries were assessed in organ bath by measurement of isometric force generated by the HFAs.After thawing, the maximal contractile responses to the contracting agonist tested (noradrenaline) were in the range of 43% of the responses in unfrozen HFAs. The endothelium-independent responses to sodium nitroprusside were not altered whereas the endothelium-dependent relaxant responses to acetylcholine were weakly altered.The cryopreservation method used provided a limited preservation of contractility of HFAs, a good preservation of the endothelium-independent relaxant responses, and a good preservation of endothelium-dependent relaxation. It is possible that further refinements of the cryopreservation protocol, such as a slower rate of cooling and a more controlled stepwise addition of DMSO, might allow better post-thaw functional recovery.     

Contractile responsiveness of coronary arteries from exercise-trained rats

Parker, Janet L., Mildred L. Mattox, and M. Harold Laughlin.Contractile responsiveness of coronary arteries from exercise trained rats. J. Appl. Physiol. 83(2):434-443, 1997.The purpose of this study was to determine whetherexercise training alters vasomotor reactivity of rat coronary arteries.In vitro isometric microvessel techniques were used to evaluatevasomotor properties of proximal left anterior artery rings (1 ring peranimal) from exercise-trained rats (ET;n = 10) subjected to a 12-wk treadmill training protocol (32 m/min, 15% incline, 1 h/day, 5 days/wk) andcontrol rats (C; n = 6) restricted tocage activity. No differences in passive length-tension characteristicsor internal diameter (158 ± 9 and 166 ± 9 µm) were observedbetween vessesls of C and ET rats. Concentration-response curves toK⁺ (5-100 mM), prostaglandinF₂(10⁸-10⁴M), and norepinephrine(10⁸-10⁴)were unaltered (P > 0.05) incoronary rings from ET rats compared with C rats; however, lower valuesof the concentration producing 50% of the maximal contractile responsein rings from ET rats (P = 0.05)suggest that contractile sensitivity to norepinephrine wasenhanced. Vasorelaxation responses to sodium nitroprusside (10⁹-10⁴M) and adenosine(10⁹-10⁴M) were not different (P > 0.05)between vessels of C and ET rats. However, relaxation responses to theendothelium-dependent vasodilator acetylcholine (ACh;10¹⁰-10⁴M) were significantly blunted (P < 0.001) in coronary rings from ET animals; maximal ACh relaxationaveraged 90 ± 5 and 46 ± 12%, respectively, in vessels of Cand ET groups. In additional experiments, two coronary rings (proximaland distal) were isolated from each C(n = 7) and ET(n = 7) animal. Proximal coronaryartery rings from ET animals demonstrated decreased relaxationresponses to ACh; however, ACh-mediated relaxation of distal coronaryrings was not different between C and ET groups.N^G-monomethyl-L-arginine(inhibitor of nitric oxide synthase) blocked ACh relaxation of allrings. L-Arginine (substrate fornitric oxide synthase) did not improve the blunted ACh relaxation in proximal coronary artery rings from ET rats. These studies suggest thatexercise-training selectively decreases endothelium-dependent (ACh) butnot endothelium-independent (sodium nitroprusside) relaxation responsesof rat proximal coronary arteries; endothelium-dependent relaxation ofdistal coronary arteries is unaltered by training.

     

Short-term exercise training improves vascular function in hypercholesterolemic rabbit femoral artery

Chronic exercise in healthy or hypercholesteremic animals for at least two months improves their vascular functions. This study is to examine whether short-term exercise training protocols can correct early-stage vascular dysfunction induced by high-cholesterol diet feeding. Male New Zealand White rabbits were fed for 2, 4 or 6 weeks with rabbit chow with or without the addition of 2% (w/w) cholesterol. They were further divided into control and exercise groups. Animals in exercise groups ran on a leveled treadmill for the same time periods as diet intervention. At the end of experiments, femoral arteries were dissected, loaded with fura 2-AM, and mounted in a tissue flow chamber. Phenylephrine-precontracted vessel specimens were exposed to acetylcholine. The endothelial intracellular calcium elevation and vasorelaxation were determined simultaneously under an epifluorescence microscope with ratio imaging capability. En face oil red O staining was used to evaluate fatty streak formation. Our results showed that 1) high-cholesterol diet feeding for > or = 4 weeks caused lipid deposition, reduced the acetylcholine-evoked endothelial calcium signaling, and impaired both endothelium-dependent and endothelium-independent vascular responses in a time-dependent manner; 2) vasorelaxation at given levels of endothelial intracellular calcium elevation decreased in hypercholesterolemia; 3) concomitant exercise program had reverse effects. We conclude that high-cholesterol diet intervention for as short as 4 weeks induces vascular structural changes, impairs endothelial intracellular calcium signaling and vasodilatation in rabbit femoral arteries. Short-term exercise training in parallel completely eliminates these adverse effects so long as the diet intervention is no more than 6 weeks.     

Effects of training and a single session of exercise on lipids and apolipoproteins in hypercholesterolemic men

Crouse, Stephen F., Barbara C. O'Brien, Peter W. Grandjean,Robert C. Lowe, J. James Rohack, and John S. Green. Effects oftraining and a single session of exercise on lipids and apolipoproteins in hypercholesterolemic men. J. Appl.Physiol. 83(6): 2019-2028, 1997.To differentiatebetween transient (acute) and training (chronic) effects of exercise attwo different intensities on blood lipids and apolipoproteins (apo), 26 hypercholesterolemic men (cholesterol = 258 mg/dl, age = 47 yr, weight = 81.9 kg) trained three times per week for 24 wk, 350 kcal/session athigh (80% maximal O₂ uptake,n = 12) or moderate (50% maximalO₂ uptake, n = 14) intensity. Serum lipid andapolipoprotein (apo) concentrations (plasma volume adjusted) weremeasured before and immediately, 24, and 48 h after exercise on fourdifferent occasions corresponding to 0, 8, 16, and 24 wk of training.Data were analyzed using three-way repeated-measures multivariateanalysis of variance followed by analysis of variance and Duncan'sprocedures ( = 0.05). A transient 6% rise inlow-density-lipoprotein cholesterol measured before training at the24-h time point was no longer evident after training. Triglyceridesfell and total cholesterol, high-density-lipoprotein cholesterol(HDL-C), HDL₃-C, apo A-I, and apoB rose 24-48 h after exercise regardless of training or intensity.Total cholesterol, HDL₃-C, apoA-I, and apo B were lower andHDL₂-C was higher after trainingthan before training. Thus exercise training and a single session ofexercise exert distinct and interactive effects on lipids andapolipoproteins. These results support the practice of training atleast every other day to obtain optimal exercise benefits.

     

Functional assessment of human femoral arteries after cryopreservation

An established method for the cryopreservation of human femoral arteries for subsequent transplantation as allografts has been studied with particular attention to preservation of smooth muscle and endothelium. Human femoral arteries (HFAs) were harvested from multi-organ donors. Two groups were established; a control group of unfrozen HFAs and a group of cryopreserved HFAs. Cryopreservation was performed using RPMI solution containing dimethyl sulfoxide and the rate of cooling was 1 degrees C/min to -40 degrees C and faster thereafter until -150 degrees C was reached. The contraction and relaxation responses of unfrozen and frozen/thawed arteries were assessed by measurement of the isometric force generated by the HFAs in an organ bath. After thawing (warming was at 15 degrees C/min) the maximal contractile response to noradrenaline was 43% of the response of unfrozen HFAs. The endothelium-independent response to sodium nitroprusside was not altered, whereas the endothelium-dependent relaxation response to acetylcholine was slightly altered. The cryopreservation method used provided limited preservation of the contractility of human femoral arteries, and good preservation of both endothelium-independent and endothelium-dependent relaxation responses.     

The endothelium-dependent and the endothelium-independent vasodilators in the isolated, perfused guinea pig heart.

The endothelium-dependent (acetylcholine, bradykinin, substance P) and the endothelium-independent (gliceryl trinirate, 3-morpholinsydnominine, sodium nitroprusside) vasodilators were studied in the Langendorff-perfused heart of the guinea pig. The involvement of prostanoids and EDRF in the endothelium-dependent responses were assessed by using indomethacin, an inhibitor of cyclooxygenase, and NG-nitro-L-Arginine, an inhibitor of NO synthase. The endothelium-independent agents were used as reference compounds. Both indomethacin and NG-nitro-L-Arginine elevated significantly baseline coronary perfusion pressure, indicating that prostanoids (most likely PGI2 and PGE2) and EDRF modulate the resting tone of the guinea pig coronary circulation. NG-nitro-L-Arginine, but not indomethacin, considerably reduced receptor-stimulated responses. It is concluded that acetylcholine, bradykinin or substance P-induced vasodilation is mediated by EDRF. In contrast, prostanoids do not contribute to endothelium-dependent responses. In addition, short-term tachyphylaxis to bolus injection of gliceryl trinitrate but not of sodium nitroprusside was demonstrated, suggesting that this preparation may be of value for studying nitrate tolerance.