Human aortocoronary grafts and nitric oxide release: relationship to pulsatile pressure

Acute Effects of Combining Weight and Elastic Resistance Exercise on Vascular Function in Older Adults

Prior research has suggested that resistance exercise may result in a temporary decrease in vascular function, as measured by flow-mediated dilation (FMD), among untrained young individuals. However, the immediate impact of combined elastic and weight resistance training on older adults remains insufficiently explored. We assessed vascular function before, after, and 30 min after acute exercise under three resistance conditions to evaluate whether a combination of weight and elastic resistance exercises has an acute effect on vascular function in older adults. Fourteen older adults (65.6 ± 2.9 years) executed three sets of 12 repetitions at 65% of one repetition maximum (1 RM) of the bench press (BP) exercise. Testing was performed on three separate days as follows: (1) barbell alone (BA); (2) barbell plus elastic bands (10% of 65% 1 RM) (BE10); and (3) barbell plus elastic bands (20% of 65% 1 RM) (BE20). A two-way (time × condition) repeated measures analysis of variance was employed to assess the time and condition effects on flow-mediated dilation (FMD) and pulse wave velocity (PWV). At 0 min post-exercise, FMD was significantly higher during BE10 than during BA (p < 0.05); however, at 30 min post-exercise, no significant difference (p ≥ 0.05) was observed between the three conditions. In each condition, FMD results did not differ significantly at different times (p ≥ 0.05). For FMD, the main effect of the condition (F[2,26] = 3.86, p = 0.034) and that of the time and condition (F[4,52] = 3.66, p = 0.011) were significant. For PWV, only the difference between the BA and BE10 conditions was significant at 0 min (p < 0.05). PWV increased from baseline in the BA condition (p < 0.05) but not significantly in the BE10 and BE20 conditions (p ≥ 0.05). Therefore, BA, BE10, and BE20 demonstrated various changes in vascular function. Long-term training intervention studies are needed to validate these findings.

Low-to-Moderate-Intensity Resistance Exercise Is More Effective than High-Intensity at Improving Endothelial Function in Adults: A Systematic Review and Meta-Analysis

Aerobic exercise has been confirmed to improve endothelial function (EF). However, the effect of resistance exercise (RE) on EF remains controversial. We conducted this systematic review and meta-analysis on randomized controlled trials (RCTs) to determine the effect of RE and its intensities on EF. We searched Web of Science, PubMed/MEDLINE, Scopus, and Wiley Online Library, and included 15 articles (17 trials) for the synthesis. Overall, RE intervention significantly improved flow-mediated dilatation (FMD) in brachial artery (SMD = 0.76; 95% CI: 0.47, 1.05; p < 0.00001), which represents improved EF. Meta-regression showed that the RE intensity was correlated with changes in FMD (Coef. = −0.274, T = −2.18, p = 0.045). We found both intensities of RE improved FMD, but the effect size for the low- to moderate-intensity (30–70%1RM) was bigger (SMD = 1.02; 95% CI: 0.60, 1.43; p < 0.0001) than for the high-intensity (≥70%1RM; SMD = 0.48; 95% CI: 0.21, 0.74; p = 0.005). We further noticed that RE had a beneficial effect (SMD = 0.61; 95% CI: 0.13, 1.09; p = 0.01) on the brachial artery baseline diameter at rest (BAD_rest), and the age variable was correlated with the changes in BAD_rest after RE (Coef. = −0.032, T = −2.33, p = 0.038). Young individuals (<40 years) presented with a bigger effect size for BAD_rest (SMD = 1.23; 95% CI: 0.30, 2.15; p = 0.009), while middle-aged to elderly (≥40 years) were not responsive to RE (SMD = 0.07; 95% CI: −0.28, 0.42; p = 0.70). Based on our findings, we conclude that RE intervention can improve the EF, and low- to moderate-intensity is more effective than high-intensity.

Flow-Mediated Dilation in Healthy Young Individuals Is Impaired after a Single Resistance Exercise Session

The current pool of data investigating the effects of a single resistance exercise session on endothelial function is divergent and inconclusive. Therefore, the purpose of the present study was to evaluate the effect of a single resistance exercise session on flow-mediated dilation (FMD) in trained individuals. Eleven healthy, young, recreationally resistance-trained individuals participated in the study. After determining the resistance exercise workload, the participants performed three sets of 10–12 repetition of leg press and leg extension exercises. By using ultrasound equipment, brachial artery FMD was assessed before (PRE) and 30 min after (POST) the resistance exercise protocol or resting (control) to evaluate endothelial function. A significant reduction in FMD response (PRE: 5.73% ± 1.21% vs. POST: 4.03% ± 1.94%, p < 0.01) after resistance exercise was observed, accompanied by a large effect size (d = 1.05). No significant difference was observed in FMD in the control condition (PRE: 5.82% ± 1.19% vs. POST: 5.66% ± 1.24%, p = 0.704). Additionally, no significant difference in baseline brachial artery diameter between resistance exercise (PRE: 3.30 ± 0.32 vs. POST: 3.40 ± 0.34 mm, p = 0.494) and resting (PRE: 3.64 ± 0.41 vs. POST: 3.67 ± 0.62 mm, p = 0.825) was observed. Our findings showed that a single resistance exercise session induced a reduction in FMD in resistance-trained individuals.

Exercise-induced hypertension is associated with angiotensin II activity and total nitric oxide

Angiotensin II mediates exercise-induced hypertension (EIH), which adversely impacts future cardiovascular health. There is paucity of data on the association between EIH and angiotensin II in well-trained middle-aged marathoners. Therefore, we investigated the renin-angiotensin-aldosterone-system and total nitric oxide activity in middle-aged marathoners with EIH.Seventy middle-aged marathoners were divided into 3 groups: normal blood pressure ([NBPG] [n = 21]), EIH group ([EIHG] [n = 35]), and complex hypertension group ([CHG] [n = 14]). We defined NBPG as resting systolic BP/diastolic BP (SBP/DBP) of ≤140/90 mm Hg and maximal exercise SBP of ≤210 mm Hg, EIHG as resting SBP/DBP ≤140/90 mm Hg and maximal exercise SBP of ≥210 mm Hg, and CHG as resting SBP/DBP ≥140/90 mm Hg and maximal exercise SBP of ≥210 mm Hg. Renin-angiotensin-aldosterone-system and NO levels were measured before and 30 minutes after the graded exercise test.Renin level was elevated while angiotensin level was reduced after 30 minutes of graded exercise test. There was no change in angiotensin I and angiotensin converting enzyme levels. Comparing the groups, renin level was only elevated in the CHG during recovery, while aldosterone level was higher than the baseline level in the recovery phase in all groups. Angiotensin I level remained unchanged in all groups. Angiotensin II level reduced significantly in the NBPG group but remained at the baseline in the EIHG and CHG groups. NO level was unchanged in the NBPG group but reduced in the EIHG and CHG groups after exercise. At 3 minutes of recovery, SBP was the highest in the NBPG group, followed by the EIHG and CHG groups (P < .05).In conclusion, angiotensin II activity and reduced NO level are associated with EIH in middle-aged long-distance runners. Angiotensin II inhibitors may; therefore, be the more appropriate antihypertensive medication for runners with EIH.

Potential Immunoregulatory and Antiviral/SARS-CoV-2 Activities of Nitric Oxide

Nitric oxide (NO) represents a key signaling molecule in multiple regulatory pathways underlying vascular, metabolic, immune, and neurological function across animal phyla. Our brief critical discussion is focused on the multiple roles of the NO signaling pathways in the maintenance of basal physiological states of readiness in diverse cell types mediating innate immunological functions and in the facilitation of proinflammatory-mediated adaptive immunological responses associated with viral infections. Prior studies have reinforced the critical importance of constitutive NO signaling pathways in the homeostatic maintenance of the vascular endothelium, and state-dependent changes in innate immunological responses have been associated with a functional override of NO-mediated inhibitory tone. Accordingly, convergent lines of evidence suggest that dysregulation of NO signaling pathways, as well as canonical oxidative effects of inducible NO, may provide a permissive cellular environment for viral entry and replication. In immunologically compromised individuals, functional override and chronic rundown of inhibitory NO signaling systems promote aberrant expression of unregulated proinflammatory pathways resulting in widespread metabolic insufficiencies and structural damage to autonomous cellular and organ structures. We contend that restoration of normative NO tone via combined pharmaceutical, dietary, or complex behavioral interventions may partially reverse deleterious physiological conditions brought about by viral infection linked to unregulated adaptive immune responses.

Acute hypotension attenuates brachial flow-mediated dilation in young healthy men

PURPOSE

This study aimed to test our hypothesis that acute hypotension attenuates brachial flow-mediated dilation (FMD) as an index of endothelial function in healthy humans.

METHODS

Twelve healthy men (21.8 ± 1.6 years, body mass index; 22.2 ± 1.6 kg/m²) participated in this study. Brachial FMD was measured in three trials: standardized FMD protocol (control trial), abrupt decrease in blood pressure (BP) via thigh cuff inflation-deflation (hypotension trial) and decrease in shear rate (SR) via a shortened forearm occlusion time (SR reduction trial). Brachial diameter and blood velocity were measured using Duplex ultrasound.

RESULTS

Mean arterial pressure during reactive hyperaemia showed a marked decrease in the hypotension trial (- 23.7 ± 6.0 mmHg), but not in the control and SR reduction trials. SR area under the curve was attenuated in the SR reduction trial (P < 0.001), but not in the control and hypotension trials (P = 0.316). Consequently, FMD was attenuated in the hypotension and SR reduction trials compared with that in the control trial (P = 0.003 and P = 0.043, respectively), and was attenuated to a greater extent in the hypotension trial compared with the SR reduction trial (P = 0.006; control, 6.9 ± 3.5%; hypotension, 3.5 ± 1.7%; SR reduction, 5.0 ± 2.2%). After adjusting FMD using SR, FMD remained attenuated in the hypotension trial (P = 0.014), but not in the SR reduction trial.

CONCLUSION

Our findings indicate that arterial pressure as well as sympathetic nervous system activation could be an important determinant of FMD. Blunted FMD of peripheral arteries may be a rational response to restore BP and/or prevent further reduction of BP following acute hypotension in healthy humans.

Microvascular Vasodilator Plasticity After Acute Exercise

Endothelium-dependent vasodilation is reduced after acute exercise or after high intraluminal pressure in isolated arterioles from sedentary adults but not in arterioles from regular exercisers. The preserved vasodilation in arterioles from exercisers is hydrogen peroxide (H2O2) dependent, whereas resting dilation is nitric oxide (NO) dependent. We hypothesize chronic exercise elicits adaptations allowing for maintained vasodilation when NO bioavailability is reduced.

Hypertension during Weight Lifting Reduces Flow-Mediated Dilation in Nonathletes

PURPOSE

The purpose of this study was to determine whether increased intraluminal pressure is the damaging factor that reduces flow-mediated dilation (FMD) in young, healthy subjects after resistance exercise to maximal exertion.

HYPOTHESIS

Attenuating the rise in brachial artery pressure during weight lifting by placing a blood pressure cuff on the upper arm prevents postexercise impairment of brachial artery FMD in sedentary individuals.

METHODS

Nine sedentary individuals who exercise once a week or less and six exercise-trained individuals who exercise three times a week or more performed leg press exercise to maximal exertion on two separate occasions. During one visit, a blood pressure cuff, proximal to the site of brachial artery measurement, was inflated to 100 mm Hg to protect the distal vasculature from the rise in intraluminal pressure, which occurs during resistance exercise. Brachial artery FMD was determined using ultrasonography before and 30 min after weight lifting.

RESULTS

Without the protective cuff, brachial artery FMD in sedentary individuals was reduced after weight lifting (9.0% ± 1.2% prelift vs 6.6% ± 0.8% postlift; P = 0.005), whereas in exercise-trained individuals, FMD was unchanged (7.4% ± 0.7% prelift vs 8.0% ± 0.9% postlift; P = 0.543). With the protective cuff, FMD no longer decreased but rather increased in sedentary individuals (8.7% ± 1.2% prelift vs 10.5% ± 1.0% postlift, P = 0.025). An increase in FMD was also seen in exercise-trained subjects when the cuff was present (6.6% ± 0.7% prelift vs 10.9% ± 1.5% postlift, P < 0.001).

CONCLUSION

Protecting the brachial artery from exercise-induced hypertension enhances FMD in sedentary and exercise-trained individuals. These results indicate that increased intraluminal pressure in the artery contributes to the reduced FMD after heavy resistance exercise in sedentary individuals.

Effects of acute exercise on flow-mediated dilatation in healthy humans

Although the effects of exercise training on vascular function have been well studied, less is known about the effects of acute exercise bouts. This synthesis summarizes and integrates knowledge derived from papers relating acute impacts of exercise on artery function, specifically endothelial function assessed by flow-mediated dilatation (FMD). We propose that an immediate decrease in FMD ("nadir") occurs soon after exercise cessation and that this is followed by a (supra)normalization response. The magnitude of the nadir and (supra)normalization and duration of this biphasic pattern of response appears to be influenced by numerous factors, including the nature of the exercise stimulus (e.g., type, duration, intensity), the subject population (e.g., trained vs. untrained), and various methodological factors. The impact of these factors on the biphasic pattern are most likely mediated through stimuli that underpin altered FMD postexercise, including shear and oxidative stress, changes in arterial diameter, and antioxidant status. We propose that a combination of these stimuli act synergistically to balance the vasomotor responses postexercise. Finally, we discuss the potential (clinical) relevance of the biphasic response after acute exercise, as the immediate nadir may represent an essential response for subsequent training-induced adaptations but may also represent a transient period of increased cardiovascular risk leading to the "exercise paradox."

Effects of Plasma from Patients Affected by Mild Cognitive Impairment and Alzheimer's Disease on Cultured Endothelial Cells

There is accumulating evidence that Alzheimer's disease (AD) can have vascular contribution. In particular, endothelial dysfunction may impair nitric oxide (NO) production and cause cerebral hypoperfusion. Blood flow impairment can be provoked also by an increased production of reactive oxygen species (ROS). The present study was performed in order to investigate the effect of plasma from subjects affected by AD and mild cognitive impairment (MCI) on human aortic endothelial cells (HAECs) in vitro, since endothelial dysfunction has been suggested to be an early event in patients affected by AD. Plasma samples were obtained from 27 AD patients, 15 MCI subjects, and 19 age-and sex-matched healthy subjects. After a short incubation period the following parameters were evaluated: NO release, superoxide dismutase (SOD) and Na+/K+-ATPase activities, membrane fluidity, and thiobarbituric acid-reactive substance (TBARS) production. Exposure to MCI plasma provoked a decrease in NO release, more pronounced in the presence of AD plasma. Our data on SOD and Na+/K+-ATPase activities showed a similar trend, since the lowest values were recorded after incubation with AD plasma. Endothelial membrane fluidity was deeply affected by the exposure to MCI plasma, and even more following incubation with AD plasma. Finally, enhanced TBARS production after incubation with MCI and AD plasma was observed. In conclusion, our results showed that MCI and AD plasma affects endothelial cells, thus highlighting the need for early treatment aimed at protecting the endothelium.

Neocortical capillary flow pulsatility is not elevated in experimental communicating hydrocephalus

While communicating hydrocephalus (CH) is often characterized by increased pulsatile flow of cerebrospinal fluid (CSF) in the cerebral aqueduct, a clear-cut explanation for this phenomenon is lacking. Increased pulsatility of the entire cerebral vasculature including the cortical capillaries has been suggested as a causative mechanism. To test this theory, we used two-photon microscopy to measure flow pulsatility in neocortical capillaries 40 to 500 μm below the pial surface in adult rats with CH at 5 to 7 days (acute, n=8) and 3 to 5 weeks (chronic, n=5) after induction compared with intact controls (n=9). Averaging over all cortical depths, no increase in capillary pulsatility occurred in acute (pulsatility index (PI): 0.15±0.06) or chronic (0.14±0.05) CH animals compared with controls (0.18±0.07; P=0.07). More specifically, PI increased significantly with cortical depth in controls (r=0.35, P<0.001), but no such increase occurred in acute (r=0.06, P=0.3) or chronic (r=0.05, P=0.5) CH. Pulsatile CSF aqueductal flow, in contrast, was elevated 10- to 500-fold compared with controls. We conclude that even in the presence of markedly elevated pulsatile CSF flow in the aqueduct, there is no concurrent increase in microvascular pulsatile flow.

Nitric oxide and the CABG patient

The post surgery success of coronary artery bypass grafting (CABG) is counteracted by thrombosis and de-endothelialization, intimal hyperplasia and, over the long term, atherosclerosis. There are many reasons to assume that in CABG patients vascular bioavailability of NO generated by the endothelium plays an important role for graft function. This holds true for factors such as graft type, harvesting and storage, the type of surgery, non-pharmacologic prevention of risk factors, for example, regular physical activity (if feasible), and drug therapy. Although the precise role of graft endothelial NO bioavailability for graft patency and clinical endpoints is still uncertain, current data rather speak in favor of NO indicating that the potential of vasoprotective activities of NO in the CABG patient deserves further investigation.

Frequency dependent transmission characteristics between arterial blood pressure and intracranial pressure in rats

The pulsatile energy transmission between arterial blood pressure (BP) and intracranial pressure (ICP) is affected by cerebrospinal fluid (CSF) and brain tissue. Studies in dogs have shown that the transfer function (TF) between BP and ICP shows damping of pulsatile energy around heart rate frequency (1-3Hz) with notch filter characteristics, and the amount of damping is sensitive to cerebral compliance. This investigation aimed to assess whether this notch filter characteristic is an intrinsic property of the brain enclosed in a rigid skull and therefore applies across species with a large difference in body size. This was done by determining the TF between BP and ICP in rats with corresponding significantly smaller body size and higher heart rate (5-7 Hz) compared to dogs. Arterial BP and ICP waveforms were recorded in 8 anaesthetized (urethane) adult male Sprague-Dawley rats with solid state micro-sensor transducer catheters. The TF was computed as the ratio of ICP and arterial BP waveform amplitudes for the first 4 harmonics. Arterial BP and ICP signals were normalized for pulse amplitude such that attenuation or amplification is detected for any TF values significantly different to unity. Mean cardiac frequency was 5.72 Hz (range 4.6 - 7.11 Hz). Of the 4 harmonics only the heart rate frequency band showed a statistically significant attenuation of 17%, while the higher harmonics showed a progressive amplification. Findings show that the rat brain acts as a selective frequency pulsation absorber of energy centered at heart rate frequency. This similarity with larger animals indicates a possible allometric mechanism underlying this phenomenon, with notch filter characteristic frequency scaled to body size. This study suggests that the TF between arterial BP and ICP is an intrinsic property of the brain tissue and CSF enclosed in a rigid compartment and can be used to assess changes in cerebral compliance due to abnormal CSF pressure and flow as occur in hydrocephalus.

The pulsating brain: A review of experimental and clinical studies of intracranial pulsatility

The maintenance of adequate blood flow to the brain is critical for normal brain function; cerebral blood flow, its regulation and the effect of alteration in this flow with disease have been studied extensively and are very well understood. This flow is not steady, however; the systolic increase in blood pressure over the cardiac cycle causes regular variations in blood flow into and throughout the brain that are synchronous with the heart beat. Because the brain is contained within the fixed skull, these pulsations in flow and pressure are in turn transferred into brain tissue and all of the fluids contained therein including cerebrospinal fluid. While intracranial pulsatility has not been a primary focus of the clinical community, considerable data have accrued over the last sixty years and new applications are emerging to this day. Investigators have found it a useful marker in certain diseases, particularly in hydrocephalus and traumatic brain injury where large changes in intracranial pressure and in the biomechanical properties of the brain can lead to significant changes in pressure and flow pulsatility. In this work, we review the history of intracranial pulsatility beginning with its discovery and early characterization, consider the specific technologies such as transcranial Doppler and phase contrast MRI used to assess various aspects of brain pulsations, and examine the experimental and clinical studies which have used pulsatility to better understand brain function in health and with disease.

Association between exercise hemodynamics and changes in local vascular function following acute exercise

Skeletal muscle contractions are associated with physical stimuli that act upon muscle vasculature, including increased shear stress and blood pressure. It is unclear if acute dynamic exercise alters local vascular function. The purpose of this study was to examine the role of exercise hemodynamics on the effects of acute exercise on vascular function, as evaluated by brachial artery flow-mediated dilation (FMD). Healthy individuals (n = 14; age, 18–34 years) performed 30 min of handgrip exercise at fast and slow contractions. Blood pressure during exercise was measured using a Vasotrac system (Medwave Inc.), while shear rate during exercise and FMD at rest and after 30 min of recovery from exercise were measured in the brachial artery of the active arm using Doppler ultrasound. Estimated contractile work was correlated with blood pressure (r = 0.61, p < 0.01) and retrograde shear rate (r = –0.78, p < 0.01). As a result, blood pressure was higher (p < 0.05) and oscillatory shear index was lower (p < 0.05) during slow as compared with fast contractions. On average, FMD was unchanged following fast contractions (5.4 ± 3.4%dilation to 6.1 ± 3.8%dilation; p = 0.19), but significantly reduced following slow contractions (6.9 ± 4.2%dilation to 3.6 ± 2.5%dilation; p = 0.01). Within slow contractions, subgroup analysis revealed blood pressure to associate with the change in FMD; such that individuals with mean blood pressure >100 mm Hg (range, 102–139 mm Hg) during exercise had larger decreases in FMD than individuals with lower exercise blood pressure. These results indicate that impaired local vascular function following acute exercise with high contractile activity is associated with blood pressure stimuli in healthy individuals

Resonant and notch behavior in intracranial pressure dynamics

OBJECT

The intracranial pulse pressure is often increased when neuropathology is present, particularly in cases of increased intracranial pressure (ICP) such as occurs in hydrocephalus. This pulse pressure is assumed to originate from arterial blood pressure oscillations entering the cranium; the fact that there is a coupling between the arterial blood pressure and the ICP is undisputed. In this study, the nature of this coupling and how it changes under conditions of increased ICP are investigated.

METHODS

In 12 normal dogs, intracarotid and parenchymal pulse pressure were measured and their coupling was characterized using amplitude and phase transfer function analysis. Mean intracranial ICP was manipulated via infusions of isotonic saline into the spinal subarachnoid space, and changes in transfer function were monitored.

RESULTS

Under normal conditions, the ICP wave led the arterial wave, and there was a minimum in the pulse pressure amplitude near the frequency of the heart rate. Under conditions of decreased intracranial compliance, the ICP wave began to lag behind the arterial wave and increased significantly in amplitude. Most interestingly, in many animals the pulse pressure exhibited a minimum in amplitude at a mean pressure that coincided with the transition from a leading to lagging ICP wave.

CONCLUSIONS

This transfer function behavior is characteristic of a resonant notch system. This may represent a component of the intracranial Windkessel mechanism, which protects the microvasculature from arterial pulsatility. The impairment of this resonant notch system may play a role in the altered pulse pressure in conditions such as hydrocephalus and traumatic brain swelling. New models of intracranial dynamics are needed for understanding the frequency-sensitive behavior elucidated in these studies and could open a path for development of new therapies that are geared toward addressing the pulsation dysfunction in pathological conditions, such as hydrocephalus and traumatic brain injury, affecting ICP and flow dynamics.

Pharmacologic relaxation of vein grafts is beneficial compared with pressure distention caused by upregulation of endothelial nitric oxide synthase and nitric oxide production

OBJECTIVE

Pressure distention of veins during preparation for bypass surgery is believed to impair vascular integrity and reduce graft patency. We previously suggested a combination of pharmacologic vasodilatators as an alternative to distention. Vascular homeostasis is largely regulated by nitric oxide. We investigated the role of distention in comparison with pharmacologic vasorelaxation in the regulation of nitric oxide synthases, nitric oxide bioavailability, and vascular reactivity in vein grafts.

METHODS

In a porcine model the internal jugular vein from either side received pressure distention or the combination of vasodilators (alpha-adrenergic antagonist, phenoxybenzamine, 10 micromol/L; Rho-kinase inhibitor, HA-1077 [fasudil], 50 mumol/L; calcium blocker, nicardipine, 1 micromol/L) and then was grafted into the carotid artery. Regulation of nitric oxide synthase, as well as nitrate and nitrite levels, were examined in vein grafts after 2 weeks of implantation.

RESULTS

Distention of jugular veins resulted in reduction of vasoconstriction in response to depolarization and agonist stimulation. Arterial grafting doubled inducible nitric oxide synthase expression in both grafts but caused a pronounced upregulation of endothelial nitric oxide synthase protein (by 57.3% +/- 5%) only in drug-treated grafts, whereas in distended grafts the endothelial nitric oxide synthase level was decreased by 27.5% +/- 2.7%. The downregulated endothelial nitric oxide synthase level in the distended grafts was accompanied by a 45.2% +/- 3.1% reduction of phospho-endothelial nitric oxide synthase Ser1177 levels and by a significant reduction in nitric oxide synthase activity (12.1% +/- 1.2%) and nitrate production (48.9% +/- 5.6%) in comparison with that seen in drug-treated grafts.

CONCLUSIONS

Pharmacologic preparation of the vein grafts results in upregulation of endothelial nitric oxide synthase and increased nitric oxide production in the vein grafts after arterial implantation. This might provide greater clinical benefit than conventional pressure-distention methods.

Effect of moderate pressure distention on the human saphenous vein vasomotor function

BACKGROUND

Manual pressure distension, which is commonly applied to the human saphenous vein graft for coronary artery bypass, is believed to have detrimental consequences for the graft patency. The vasomotor function of the vein after distention during surgical preparation for grafting and after distention in laboratory conditions at pressure of 50 to 600 mm Hg was studied. The effect of a combination of vasodilative agents to prevent vasospasm was also tested.

METHODS

The contractile and dilatory responses of distended and undistended human saphenous veins and those after drug treatment were examined in organ baths under isometric conditions.

RESULTS

Distention at the pressure range 100 to 300 mm Hg resulted in an increased contractile response of the saphenous vein to both alpha-adrenergic activation with 50 micromol/L phenylephrine (153.73% +/- 15.69%) and depolarization with 80 mmol/L K(+) (141.03% +/- 15.13%) in comparison with the undistended vein and did not impair the relaxation. In contrast manual distention during surgical preparation abolished the contractile response and impaired the relaxation. The application of a combination of vasodilative drugs (alpha-adrenergic antagonist phenoxybenzamine, 10 micromol/L, Rho-kinase inhibitor HA-1077, 50 micromol/L, and calcium blocker nicardipine, 1 micromol/L) eliminated the contractile response of the vein to phenylephrine and 80 mmol/L K(+). This effect was sustained more than 20 hours after the washout of the drugs.

CONCLUSIONS

The distention of the human saphenous vein at moderate pressure combined with the application of the effective combination of vasodilative drugs before grafting into the arterial circulation could be a beneficial alternative to the current practice of uncontrolled pressure distension.

Evidence for a spontaneous nitric oxide release from the rat median eminence: influence on gonadotropin-releasing hormone release

The involvement of nitric oxide (NO) as a gaseous neurotransmitter in the hypothalamic control of pituitary LH secretion has been demonstrated. NO, as a diffusible signaling gas, has the ability to control and synchronize the activity of the neighboring cells. NO is secreted at the median eminence (ME), the common termination field for the antehypophysiotropic neurons, under the stimulation of other signaling substances. At the ME, NO stimulates GnRH release from neuroendocrine terminals. The present studies were undertaken to determine whether NO is secreted spontaneously from ME fragments ex vivo and whether its secretion is correlated to GnRH release. To accomplish this, female rats were killed at different time points of the day and/or of the estrous cycle. The spontaneous NO release was monitored in real time, with an amperometric probe, during 4 periods of 30 min, from individual ME fragments (for each time point, n = 4). GnRH levels were measured in parallel for each incubation-period by RIA. The results revealed that NO was released in a pulsatile manner from female ME fragments and, unambiguously, that the amplitude of NO secretion varied markedly across the estrous cycle. Indeed, though the NO pulse period (32 +/- 1 min, n = 36) and duration (21 +/- 2 min, n = 36) did not vary significantly across the estrous cycle, the amplitude of this secretion pulse was significantly higher on proestrus (Pro; 39 +/- 3 nM, n = 20), compared with diestrus (16 +/- 1 nM, n = 8) or estrus (23 +/- 3 nM, n = 8, P < 0.05). The GnRH levels in the incubation medium were positively correlated to NO secretion across the estrous cycle (r = 0.86, P < 0.003, n = 9), confirming that NO and GnRH release are coupled. Furthermore, 5 x 10(-7) M L-N(5)-(1-iminoethyl)ornithine (L-NIO), a NO synthase inhibitor, succeeded in inhibiting the strong NO-GnRH secretory coupling and GnRH release on PRO: Because at this concentration, L-NIO selectively inhibits endothelial NO synthase, the results further demonstrate that the major source of NO involved in GnRH release at the ME is endothelial in origin. Additionally, the induction of a massive NO/GnRH release in 15-day ovariectomized rat treated with estradiol benzoate strongly suggested that estradiol is participating in the stimulation of NO release activity between diestrus II and PRO: The present study is the first demonstrating that ME can spontaneously release NO and that NO's rhythm of secretion varies markedly across the estrous cycle. This pulsatile/cyclic ME NO release may constitute the synchronizing link to anatomically scattered GnRH neurons.

Evidence that Alzheimer's disease is a microvascular disorder: the role of constitutive nitric oxide

Evidence is fast accumulating which indicates that Alzheimer's disease is a vascular disorder with neurodegenerative consequences rather than a neurodegenerative disorder with vascular consequences. It is proposed that two factors need to be present for AD to develop: (1) advanced ageing, (2) presence of a condition that lowers cerebral perfusion, such as a vascular-risk factor. The first factor introduces a normal but potentially insidious process that lowers cerebral blood flow in inverse relation to increased ageing; the second factor adds a crucial burden which further lowers brain perfusion and places vulnerable neurons in a state of high energy compromise leading to a cascade of neuronal metabolic turmoil. Convergence of the two factors above will culminate in a critically attained threshold of cerebral hypoperfusion (CATCH). CATCH is a hemodynamic microcirculatory insufficiency that will destabilize neurons, synapses, neurotransmission and cognitive function, creating in its wake a neurodegenerative state characterized by the formation of senile plaques, neurofibrillary tangles, amyloid angiopathy and in some cases, Lewy bodies. Since any of a considerable number of vascular-related conditions must be present in the ageing individual for cognition to be disturbed, CATCH identifies an important aspect of the heterogeneic disease profile assumed to be present in the AD syndrome. It is proposed that CATCH initiates AD by distorting regional brain capillary structure involving endothelial cell shape changes and impairment of nitric oxide (NO) release which affect signaling between the immune, cardiovascular and nervous systems. Evidence is presented that in many tissues there is a basal level of NO being produced and that the actions of several signaling molecules may initiate increases in basal NO levels. Moreover, these temporary increases in basal NO levels exert inhibitory cellular actions, via cellular conformational changes. Findings indicate that (a) constitutive NO is responsible for a basal or 'tonal' level of NO; (b) this NO keeps particular types of cells in a state of inhibition and (c) activation of these cells occurs through disinhibition. Consequently, tissues not maintaining a basal NO level are more prone to excitatory, immune, vascular and neural influences. Under such circumstances, these tissues cannot be down-regulated to normal basal levels, thus prolonging their excitatory state. Thus, the clinical convergence of advanced ageing in the presence of a chronic, pre-morbid vascular risk factor, can, in time, contribute to an endotheliopathy involving basal NO deficit, to the degree where regional metabolic dysfunction leads to cognitive meltdown and to progressive neurodegeneration characteristic of Alzheimer's disease.

Basal nitric oxide limits immune, nervous and cardiovascular excitation: human endothelia express a mu opiate receptor

Nitric oxide (NO) is a major signaling molecule in the immune, cardiovascular and nervous systems. The synthesizing enzyme, nitric oxide synthase (NOS) occurs in three forms: endothelial (e), neuronal (n) and inducible (i) NOS. The first two are constitutively expressed. We surmise that in many tissues there is a basal level of NO and that the actions of several signaling molecules initiate increases in cNOS-derived NO to enhance momentary basal levels that exerts inhibitory cellular actions, via cellular conformational changes. It is our contention that much of the literature concerning the actions of NO really deal with i-NOS-derived NO. We make the case that cNOS is responsible for a basal or 'tonal' level of NO; that this NO keeps particular types of cells in a state of inhibition and that activation of these cells occurs through disinhibition. Furthermore, naturally occurring signaling molecules such as morphine, anandamide, interleukin-10 and 17-beta-estradiol appear to exert, in part, their beneficial physiological actions, i.e., immune and endothelial down regulation by the stimulation of cNOS. In regard to opiates, we demonstrate the presence of a human endothelial mu opiate receptor by RT-PCR and sequence determination, further substantiating the role of opiates in vascular coupling to NO release. Taken together, cNOS derived NO enhances basal NO actions, i.e., cellular activation state, and these actions are further enhanced by iNOS derived NO.