The aging venous system: from varicosities to vascular cognitive impairment

Aging-induced pathological alterations of the circulatory system play a critical role in morbidity and mortality of older adults. While the importance of cellular and molecular mechanisms of arterial aging for increased cardiovascular risk in older adults is increasingly appreciated, aging processes of veins are much less studied and understood than those of arteries. In this review, age-related cellular and morphological alterations in the venous system are presented. Similarities and dissimilarities between arterial and venous aging are highlighted, and shared molecular mechanisms of arterial and venous aging are considered. The pathogenesis of venous diseases affecting older adults, including varicose veins, chronic venous insufficiency, and deep vein thrombosis, is discussed, and the potential contribution of venous pathologies to the onset of vascular cognitive impairment and neurodegenerative diseases is emphasized. It is our hope that a greater appreciation of the cellular and molecular processes of vascular aging will stimulate further investigation into strategies aimed at preventing or retarding age-related venous pathologies.

Network analysis of the left anterior descending coronary arteries in swim-trained rats by an in situ video microscopic technique

BACKGROUND

We aimed to identify sex differences in the network properties and to recognize the geometric alteration effects of long-term swim training in a rat model of exercise-induced left ventricular (LV) hypertrophy.

METHODS

Thirty-eight Wistar rats were divided into four groups: male sedentary, female sedentary, male exercised and female exercised. After training sessions, LV morphology and function were checked by echocardiography. The geometry of the left coronary artery system was analysed on pressure-perfused, microsurgically prepared resistance artery networks using in situ video microscopy. All segments over > 80 μm in diameter were studied using divided 50-μm-long cylindrical ring units of the networks. Oxidative-nitrative (O-N) stress markers, adenosine A2A and estrogen receptor (ER) were investigated by immunohistochemistry.

RESULTS

The LV mass index, ejection fraction and fractional shortening significantly increased in exercised animals. We found substantial sex differences in the coronary network in the control groups and in the swim-trained animals. Ring frequency spectra were significantly different between male and female animals in both the sedentary and trained groups. The thickness of the wall was higher in males as a result of training. There were elevations in the populations of 200- and 400-μm vessel units in males; the thinner ones developed farther and the thicker ones closer to the orifice. In females, a new population of 200- to 250-μm vessels appeared unusually close to the orifice.

CONCLUSIONS

Physical activity and LV hypertrophy were accompanied by a remodelling of coronary resistance artery network geometry that was different in both sexes.

Long-term exercise results in morphological and biomechanical changes in coronary resistance arterioles in male and female rats

Background

Biomechanical remodeling of coronary resistance arteries in physiological left ventricular hypertrophy has not yet been analyzed, and the possible sex differences are unknown.

Methods

Wistar rats were divided into four groups: male and female sedentary controls (MSe and FSe) and male and female animals undergoing a 12-week intensive swim training program (MEx and FEx). On the last day, the in vitro contractility, endothelium-dependent dilatation, and biomechanical properties of the intramural coronary resistance arteries were investigated by pressure microarteriography. Elastica and collagen remodeling were studied in histological sections.

Results

A similar outer radius and reduced inner radius resulted in an elevated wall to lumen ratio in the MEx and FEx animals compared to that in the sedentary controls. The wall elastic moduli increased in the MEx and FEx rats. Spontaneous and TxA₂ agonist-induced tone was increased in the FEx animals, whereas endothelium-dependent relaxation became more effective in MEx rats. Arteries of FEx rats had stronger contraction, while arteries of MEx animals had improved dilation.

Conclusions

According to our results, the coronary arterioles adapted to an elevated load during long-term exercise, and this adaptation depended on sex. It is important to emphasize that in addition to differences, we also found many similarities between the sexes in the adaptive response to exercise. The observed sport adaptation in the coronary resistance arteries of rats may contribute to a better understanding of the physiological and pathological function of these arteries in active and retired athletes of different sexes.

Effects of Vitamin D Deficiency on Proliferation and Autophagy of Ovarian and Liver Tissues in a Rat Model of Polycystic Ovary Syndrome

Aim: We aimed to examine the alterations of the insulin signaling pathway, autophagy, nitrative stress and the effect of vitamin D supplementation in the liver and ovaries of vitamin D deficient hyperandrogenic rats. Methods: Female Wistar rats received eight weeks of transdermal testosterone treatment and lived on a low vitamin D diet (D–T+). Vitamin D supplementation was achieved by oral administration of vitamin D3 (D+T+). Sham-treated (D+T–) and vitamin D deficient animals (D–T–) served as controls. (N = 10–12 per group). Results: D–T+ animals showed decreased LC3 II levels in the liver and increased p-Akt/Akt and p-eNOS/eNOS ratios with decreased insulin receptor staining in the ovaries. Vitamin D supplementation prevented the increase of Akt phosphorylation in the ovaries. Vitamin D deficiency itself also led to decreased LC3 II levels in the liver and decreased insulin receptor staining in the ovaries. D–T+ group showed no increase in nitrotyrosine staining; however, the ovaries of D–T– rats and the liver of D+T+ animals showed increased staining intensity. Conclusion: Vitamin D deficiency itself might lead to disrupted ovarian maturation and autophagy malfunction in the liver. Preventing Akt phosphorylation may contribute to the beneficial effect of vitamin D treatment on ovarian function in hyperandrogenism.

Insulin resistance in an animal model of polycystic ovary disease is aggravated by vitamin D deficiency: Vascular consequences

Hyperandrogenic state in females is accompanied with metabolic syndrome, insulin resistance and vascular pathologies. A total of 67%-85% of hyperandrogenic women suffer also from vitamin D deficiency. We aimed to check a potential interplay between hyperandrogenism and vitamin D deficiency in producing insulin resistance and effects on coronary resistance arteries. Adolescent female rats were divided into four groups, 11-12 animals in each. Transdermal testosterone-treated and vehicle-treated animals were kept either on vitamin D-deficient or on vitamin D-supplemented diet for 8 weeks. Plasma sexual steroid, insulin, leptin and vitamin D plasma levels were measured, and oral glucose tolerance test was performed. In coronary arterioles, insulin receptor and vitamin D receptor expressions were tested by immunohistochemistry, and insulin-induced relaxation was measured in vitro on isolated coronary resistance artery segments. Testosterone impaired glucose tolerance, and it diminished insulin relaxation but did not affect the expression of insulin and vitamin D receptors in vascular tissue. Vitamin D deficiency elevated postprandial insulin levels and homeostatic model assessment insulin resistance. It also diminished insulin-induced coronary arteriole relaxation, while it raised the expression of vitamin D and insulin receptors in the endothelial and medial layers. Our conclusion is that both hyperandrogenism and vitamin D deficiency reduce sensitivity of coronary vascular tissue to insulin, but they do it with different mechanisms.

A simple standard technique for labyrinthectomy in the rat: A methodical communication with a detailed description of the surgical process

Aims Labyrinthectomized rats are suitable models to test consequences of vestibular lesion and are widely used to study neural plasticity. We describe a combined microsurgical-chemical technique that can be routinely performed with minimum damage. Methods Caudal leaflet of the parotis is elevated. The tendinous fascia covering the bulla is opened frontally from the sternomastoid muscle's tendon while sparing facial nerve branches. A 4 mm diameter hole is drilled into the bulla's hind lower lateral wall to open the common (in rodents) mastoid-tympanic cavity. The cochlear crista (promontory) at the lower posterior part of its medial wall is identified as a bony prominence. A 1 mm diameter hole is drilled into its lower part. The perilymphatic/endolymphatic fluids with tissue debris of the Corti organ are suctioned. Ethanol is injected into the hole. Finally, 10 µL of sodium arsenite solution (50 µM/mL) is pumped into the labyrinth and left in place for 15 min. Simple closure in two layers (fascia and skin) is sufficient. Results and conclusion All rats had neurological symptoms specific for labyrinthectomy (muscle tone, body position, rotatory movements, nystagmus, central deafness). Otherwise, their behavior was unaffected, drinking and eating normally. After a few days, they learned to balance relying on visual and somatic stimuli (neuroplasticity).

Regional differences in statistical geometry of endothelial dense granules in human extremity veins

OBJECTIVES

Leg and arm human veins are exposed to different gravitational stresses. We investigated if there is difference in the amount and geometry of secretory vesicles in their endothelium.

METHODS

Superficial small vein segments were removed during vascular operations for electromicroscopic analysis. Vesicular area/total endothelial cross-sectional area was determined by computer-based morphometry. Long and short axes of granule cross sections were measured by image analyzing software.

RESULTS

Vesicular density in all samples was 2.26 ± 0.34%. There was no significant difference between the vesicular densities of upper extremity and leg. The shape of the vesicles was more frequently elongated in leg than in arm sections (p < 0.01).

CONCLUSIONS

The density of the vesicles does not depend on vascular region or orthostatic load. Ellipticity of these granules is significantly different in areas exposed to different gravitational stresses. This might contribute to the differences of thrombotic and hemodynamic properties of leg and upper body veins.

Heritability of Venous Biomechanics

Objective—

Altered venous biomechanics may contribute to the pathogenesis of venous diseases, and their heritability is less known.

Methods and Results—

Seventy-eight monozygotic twin pairs (aged 42.4±16.8 years) and 24 same-sex dizygotic twin pairs (aged 50.5±16.1 years) were examined. Anteroposterior and mediolateral diameters of the common femoral vein were measured by ultrasonography. Measurements were made both in supine and in standing body positions, with or without controlled forced expiration (Valsalva test). High correlation of diameter, capacity, and distensibility values was found between twin pairs. The univariate heritability (A), shared (C), and unshared (E) environmental effects model has shown 39.3% genetic component of the variance of low pressure, 37.9% of high-pressure venous capacity, and 36.4% of maximal capacity changes, even after elimination of sex, age, and body weight effects. Bivariate Cholesky analysis revealed substantial covariance of inherited body weight and venous capacity components (57.0%–81.4%).

Conclusion—

Femoral vein capacity and elasticity depend ≈30% to 40% on genetic factors, and this value in the standing body position can reach 50%. A relatively high genetic covariance was found between weight and femoral vein capacity and elasticity. Our work might yield some new insights into the inheritance of venous diseases that are associated with altered venous biomechanics and help elucidate the involved genes.

Determination of venous blood flow velocity using digital videomicroscopy (A short methodical communication)

BACKGROUND/AIM

There is a limited number of methods to measure blood flow velocity in small veins. A cheap and simple new videomicroscopic method developed in our laboratories is described in the paper.

METHODS

A stretch of the saphenous vein of the rat was exposed by careful micropreparation on the thigh of anesthetized animals. Bolus amount (approx. 5 μl) of saline was infused into a small side branch through a microcannula to dilute flowing blood. Videomicroscopic picture of the vein was then taken of the exposed upstream stretch of the vein. Serial pictures were digitized and analyzed using macro functions of the Image J software. Sensitive areas of serial pictures were selected and fitted. Consecutive pictures were subtracted from each other to better characterize their alteration in-between frames. Greyscale intensity values measured at different points of the inner diameter were averaged for each point of the vessel axis. Cross-correlations along the axis were then computed for consecutive frames with delays of 40, 80, 120 and 160 msec. Pixel offsets producing cross-correlation maxima were determined and used to compute mean flow velocity.

RESULTS

Combination of digital subtraction and cross-correlation computations yielded easily identifiable maximums. Mean flow velocities could be determined with limited uncertainty.

CONCLUSION

The described technique gives a cheap, simple and reproducible mean to determine mean blood flow velocities in small veins in anesthetized animals, where other current techniques (ultrasonography, laser-Doppler, fluorescently labelled red cell movement) are either expensive or can be applied with difficulty only.

Maintained geometry, elasticity and contractility of human saphenous vein segments stored in a complex tissue culture medium

OBJECTIVE

Improved maintenance of endothelial function and higher viability of saphenous vein grafts stored in a complex tissue culture medium (TCM) have been demonstrated. This article studies the biomechanical properties of saphenous vein segments.

DESIGN

Biomechanical properties of 72 saphenous vein segments remaining from coronary bypass grafting of 32 patients have been studied after different storage procedures.

MATERIALS

The materials studied included fresh segments, segments stored in a cooled conventional physiological salt solution (normal Krebs-Ringer (nKR)) for 1-2 weeks, segments stored in a cooled chemically defined TCM (X-Vivo) for 1,2,3 and 4 weeks and segments cryopreserved for a few weeks.

METHODS

Specimens were cannulated at both ends and pressure-diameter curves were recorded in the 0-85-mmHg range in nKR with 10 microM norepinephrine added to induce maximum smooth muscle contraction, as well as in Ca(2+)-free medium to induce full relaxation. Tensile strength was checked at 300 mmHg. Distensibility, elastic modulus and active strain were computed.

RESULTS

Segments stored in nKR dilated morphologically, their distensibility decreased and they lost their ability to contract (1.5+/-0.7% from 10.1+/-1.5% of control) in 1 week. The TCM-stored segments preserved their contractility until 1 week, and this parameter only slowly decreased afterwards (first week, 11.5+/-7.3%; fourth week, 3.9+/-0.6%). There was a slight decrease in wall thickness but the lumen diameter was not affected. The elastic parameters of these segments were practically identical to those of fresh segments. Cryopreserved segments narrowed morphologically, their wall thickened and contractility diminished.

CONCLUSIONS

Storage in TCM helps preserve the passive and active biomechanical properties of human saphenous vein segments. Such properties can be expected to improve graft tissue viability.

[New results in the research of the biomechanics of the venous system]

The upright posture of man had been a major evolutional challenge. The mechanisms responsible for orthostatic tolerance mostly affect the venous system. In this paper, we discuss new results regarding the biomechanics of the venous system highlighting a rather neglected field, the biomechanical properties of the vein wall. These properties change according to localization of veins, age, gender and body mass. The anti-gravitational adaptation of veins is a complex process involving all three layers of the venous wall. Local myogenic and humoral mechanisms as well as systemic hormonal and nervous influences control the adaptive processes in the veins. Long term adaptation involves structural and functional remodeling of the venous wall. Disorders of the veins mostly cause pathological remodeling. Hemodynamic factors (pressure and flow) together with inflammatory processes may lead to pathological alterations, changing the biomechanical properties of the vein wall, which further contribute to the reservation and progression of venous dysfunction. Appropriate testing of venous function can reveal biomechanical disorders even in clinically asymptomatic patients. Thus, biomechanical investigation of veins not only helps to understand the underlying pathomechanism but it also can contribute to early diagnosis and follow-up of venous disorders. When recognized in time, pathological remodeling can be prevented or treated. In this way, the incidence of venous disorder could be cut back reducing both human suffering and material loss.

Generalized alterations in the biomechanical properties of large veins in non-thrombotic thrombophilic young patients

AIM

In young, post-thrombotic patients, venous distensibility is decreased not only in the affected lower limb, but also in the contralateral limb and in the jugular vein when compared to age-matched control subjects. In the present study, we investigated venous wall mechanical properties in young, asymptomatic thrombophilic patients.

METHODS

Eleven young (24+/-0.4 years) control subjects and 9 age-matched patients (21.1+/-1.8 years) with proven thrombophilic molecular defects, but without any signs or history of previous deep vein thrombosis, were compared. Anterolateral and mediolateral diameters of the common femoral, axillary and internal jugular veins were measured by ultrasonography in situ. Pressure alterations were induced by altering body positions and by pressure-controlled Valsalva tests. Distensibility was calculated from diameter and pressure changes.

RESULTS

In thrombophilic patients, resting diameter of both the common femoral and of internal jugular veins at low transmural pressure was larger than those for the control subjects. Distensibility, however, was significantly less when high pressures were applied. Alterations in diameter of the axillary vein were minimal.

CONCLUSION

Our measurements suggest that there are generalized changes in venous mechanical properties in thrombophilic patients even before the appearance of thrombotic processes. These biomechanical alterations of the venous wall and/or surrounding connective tissue are similar to those found in connection with aging and in post-thrombotic patients. The pathological mechanisms behind these processes are unknown.

Nitric oxide modulates the interaction of pressure-induced wall mechanics and myogenic response of rat intramural coronary arterioles

Interactions between the biomechanical characteristics and pressure-induced active response of coronary microvessels are still not well known. We tested the hypothesis that pressure-dependent biomechanical characteristics of the coronary vascular wall are modulated by the active myogenic response and local vasodilators. We have utilized data obtained previously in isolated rat intramural coronary arterioles (approximately 100 microm in diameter), in which the diameter was investigated as a function of intraluminal pressure (Szekeres et al.: J. Cardiovasc. Pharmacol., 43, 242-249, 2004). To characterize the magnitude of myogenic response, diameter was expressed as percent of passive diameter as a function of pressure (normalized diameter; ND). In addition, circumferential wall stress (WS) and incremental distensibility (ID) were calculated. In control conditions, after an initial increase between 0-30 mm Hg, ND decreased substantially as pressure increased from 30 to 150 mm Hg. Correspondingly, WS gradually increased as a function of pressure (from 0.3 +/- 0.03 to 34.7 +/- 4.4 kPa) exhibiting a plateau phase between 40-80 mm Hg. In contrast, ID decreased and reached negative values (min: -104.9 +/- 21.9 10(-6) m2/N at 50 mm Hg). Inhibition of nitric oxide (NO) synthase by L-NNA decreased basal diameter (approximately 35% at 2 mm Hg), eliminated pressure-induced changes in ND, reduced the slope of pressure-WS curve, and decreased ID at lower pressures. Simultaneous administration of L-NNA and adenosine (which restored initial diameter, i.e. length of smooth muscle) restored--in part--the pressure-induced reduction in ND, reversed the pressure-induced behavior of WS to control, but not that of ID. These results not only confirm that in coronary arterioles wall stress is regulated by the myogenic response, but also suggest that there is interplay between the mechanical behavior of the wall and the myogenic response. Furthermore, the presence of NO seems to be necessary for maintaining a higher distensibility of intramural coronary arterioles allowing increases in diameter to lower pressures, which then activate the myogenic mechanism resulting in constrictions and full development of myogenic tone, as indicated by the presence of negative slope of pressure-diameter curve in the presence of NO.

Remodeling of the rat saphenous vein network in response to long-term gravitational load

Our main objective was to test whether chronic orthostatic body position induces network changes in the saphenous vein superficial tributary system of the rat. Fourteen male Sprague-Dawley rats were kept in tilted tube cages (45-degree head-up position) for two weeks to induce chronic gravitational load to their leg veins. Ten animals housed in normal cages and four animals kept in horizontally positioned tube cages served as controls. The whole superficial network of the left saphenous vein was microprepared surgically under anesthesia, superfused with saline and observed under a videomicroscope, while normal flow and pressure were maintained in the lumen. Branching angles, lengths of venous segments and their diameters were measured offline from digitized images using special image-analyzing software. Several branching angles at the popliteal confluence were significantly reduced by 12.5-15.8 %. The in vivo diameter of the main branch (936+/-34 vs. 805+/-44 microm) and of one of the popliteal tributaries (776+/-38 vs. 635+/-36 microm) increased (p<0.05), comparing vessels from tilted animals with those from normal controls. Maintaining the animals in horizontal tube cages did not induce the above alterations. The increased diameters and reduced branching angles of the saphenous vein network observed are adaptive responses of the venous network to a long-term gravitational load.

Pharmacologic inhomogeneity between the reactivity of intramural coronary arteries and arterioles

We hypothesized that because of their size, anatomic location, and hemodynamic function, coronary arteries and arterioles would respond differently to vasoactive substances. Intramural arteries (281.7 +/- 23.1 microm) and arterioles (77.3 +/- 6.6 microm) of the left anterior descending coronary of rats were isolated and cannulated. Spontaneous tone was lower in arteries than in arterioles (81.1 +/- 5.7 vs. 53.0 +/- 3.9% of passive diameter, p < 0.05 at 60 mm Hg intraluminal pressure). Arterial tone was adjusted by the thromboxane receptor agonist U46619 (5 x 10(-8) M ) to reach an active tone close to that of arterioles. Bradykinin elicited dilations in both types of vessels. Acetylcholine (10(-6) - 10(-5) M ) dilated arteries (by 42.6 +/- 11.5 microm) but constricted arterioles (by 16.4 +/- 9.3 microm). Sodium nitroprusside and adenosine elicited significantly greater dilations in arterioles than in arteries (by 7.9 and 11.9%, respectively, p < 0.05), whereas dilations to norepinephrine were similar. Inhibition of nitric oxide synthesis caused a significantly smaller constriction in arteries (10.2 +/- 3.31%) than in arterioles (31.6 +/- 6.9%) and completely blocked bradykinin-and acetylcholine-induced dilations, whereas it did not affect dilations to sodium nitroprusside, adenosine, and norepinephrine. Compared with arteries, arterioles have a greater spontaneous tone and enhanced nitric oxide modulation of basal tone and exhibit greater responsiveness to nitric oxide and adenosine. In addition, nitric oxide synthase is activated differently by pharmacologic stimuli in these segments. The qualitative and quantitative differences among vasoactive responses of coronary arteries and arterioles demonstrated in this study suggest segment-specific roles for endothelial and metabolic factors in regulation of coronary vascular resistance.

Acute, nongenomic vasodilatory action of estradiol is attenuated by chronic estradiol treatment

Deficiency of estradiol or chronic estrogen treatment may alter the responses to this hormone in many tissues. A possible interaction between the acute nongenomic and the chronic effects of estradiol on microvessels have not been investigated yet. In the present study we have investigated whether acute in vitro vasodilatory action of estradiol on a small artery is altered by chronic estradiol pretreatment. Female rats were surgically ovariectomized and subjected to either estradiol replacement therapy (estradiol propionate, 450 micrograms/kg/week) or vehicle administration for 5 weeks. Cylindrical segments of the saphenous artery were studied using videocomputerized microarteriography in vitro. Estradiol, in concentrations of 10(-6) to 10(-4) M relaxed norepinephrine precontracted vessel segments in a dose-dependent manner. Magnitude of relaxation observed in arteries of estradiol replaced animals was significantly smaller at all concentrations than that of nonreplaced ovariectomized rats; maximal relaxation in the control ovariectomized group was 64.5% +/- 3.6%, while it was 34.3% +/- 4.2% only in the ovariectomized and estradiol replaced group (P < 0.001). Comparison of acute relaxations in response to papaverine and nifedipine failed to prove a reduced activity of the general relaxation machinery in estradiol replaced animals. We conclude that chronic estradiol replacement can downregulate the acute nongenomic vasorelaxation effect of this hormone in small arteries of ovariectomized rats.

Sex hormone replacement therapy reverses decreased venous distensibility in pharmacologically ovariectomized rats

OBJECTIVE

To test the effect of female sex hormone depletion and replacement on the distensibility and geometry of the saphenous vein in female rats.

DESIGN

Twenty Sprague-Dawley rats were pharmacologically ovariectomized by triptorelin. Ten of these animals received combined hormone replacement with estradiol and medroxyprogesterone acetate. The rest were given vehicle. Ten animals kept parallel without pharmacological ovariectomy served as controls. After 3 months of treatment, a segment of the saphenous vein was dissected. Pressure-diameter curves were recorded in relaxed, contracted, and control states using a microangiograph.

RESULTS

Pharmacological ovariectomy lowered venous wall distensibility measured in contraction (at P=8 mm Hg: 4.41+/-1.21*10(-3) m2/N vs. control: 0.79+/-0.14*10(-3) m2/N; p < 0.05). Hormone replacement partially restored this value (1.8+/-0.49*10(-3) m2/N). No alterations in distensibility were found in the relaxed state. After adjusting for body weight, we found that pharmacological ovariectomy lowered venous inner radius significantly compared with control (p < 0.05), whereas hormone replacement increased it compared with pharmacological ovariectomy (p < 0.05) and more significantly compared with control (p < 0.01).

CONCLUSION

Sex hormone depletion induces significant alterations in venous distensibility, presumably by inducing initial remodeling of the venous wall. Hormone dependency of distensibility differed in relaxed and contracted states of the vein, so some alterations of contractile elements of the wall may be hypothesized. Lower distensibility of the venous wall found after pharmacological ovariectomy could be part of the mechanism of predisposition for postmenopausal hypertension. This can be reversed by female sex hormone replacement.

Effect of ovariectomy and hormone replacement therapy on small artery biomechanics in angiotensin-induced hypertension in rats

OBJECTIVES

To test the effects of chronic angiotensin II administration on blood pressure and small artery biomechanics in the female sex hormone-depleted state (proposed to increase cardiovascular vulnerability) and with hormone replacement.

DESIGN

Biomechanical properties of saphenous artery segments from ovariectomized (n = 10), ovariectomized + chronically angiotensin II infused-(n = 10), and ovariectomized + chronically angiotensin II-infused + sex hormone-replaced (n = 10) rats were studied.

METHODS

Surgical ovariectomy was performed. Osmotic minipumps were used for chronic angiotensin II infusion (100 ng/min per kg). For hormone replacement therapy, oestradiol-propionate, 450 microg/kg for 7 days + medroxyprogesterone-acetate, 15 mg/kg for 14 days were given, intramuscularly. After 4 weeks, cylindrical segments of the saphenous artery were prepared and subjected to in-vitro microarteriographic measurements. Pressure-diameter curves (0-200 mmHg) were recorded in Krebs-Ringer solution, with smooth muscle contracted (norepinephrine, 16 micromol/l) and with relaxed (papaverine, 28 micromol/l).

RESULTS

Chronic angiotensin II infusion significantly reduced the inner radius (at 100 mmHg: 298 +/- 17 microm versus 347 +/- 7 microm, P< 0.001), while wall-thickness did not change. Hormone replacement restored the morphological radius (333 +/- 7 microm). Angiotensin II infusion slightly increased the full contraction range of the segments (defined as the percentage difference between fully contracted and fully relaxed diameters), which was further significantly increased by hormone replacement (39 +/- 4%, 46 +/- 8%, 62 +/- 7% at 100 mmHg, in the three groups, respectively; P < 0.05). Despite unaltered stiffness in relaxed state, elastic moduli computed for the contracted segments decreased after hormone replacement.

CONCLUSIONS

These observations give further experimental support to the hypothesis that sex hormone replacement might be useful in preventing the development and/or stabilization of postmenopausal hypertension, as well as in treating existing disease.

Are there systemic changes in the arterial biomechanics of intracranial aneurysm patients?

Current theories on the development of intracranial aneurysm suggest that there is a general weakness of vascular connective tissue. Potential systemic alterations in arterial wall biomechanics were tested in the present study. A three-dimensional in vitro stress-strain analysis was made in the 0-200-0 mmHg pressure range on cylindrical segments excised from the anterior cerebral artery, the radial artery and from the arteria dorsalis pedis of aneurysm patients and of control cadavers. In the anterior cerebral artery from aneurysm patients (intracranial artery segments directly not affected by the aneurysm or by the subarachnoid bleeding), we found the wall thickness to be larger (0.1480+/-.019 versus 0.091+/-0.004 mm), the radius/wall thickness ratio smaller (9.7+/-1.4 versus 14.1+/-1.2), and the tangential wall stress lower [(0.122+/-0.019)x10(6) versus (0.181+/-0.016)x10(6) N/m2 at 100 mmHg] than in control subjects. Reduced radius was found in the extremity arteries studied. Elastic parameters, as incremental distensibility and elastic modulus, were remarkable similar. Our study demonstrates changes in the geometry of walls of arteries not directly affected by aneurysm formation, and it thus confirms systemic vascular pathology in this disease. At the same time, these data show that the molecular and morphological defects of arterial connective tissue formation generally thought to induce intracranial aneurysms will probably not affect the components responsible for the passive elastic properties of the vascular wall.

Effects of combined sex hormone replacement therapy on small artery biomechanics in pharmacologically ovariectomized rats

OBJECTIVES

The purpose of this study was to determine the effects of long-term combined sexual hormone replacement therapy on the biomechanical properties of the small artery wall in castrated female rats.

METHODS

30 non-pregnant mature female Sprague-Dawley rats were pharmacologically ovariectomized with 750 microg/kg triptorelin im. every 4th week. Ten of them received combined hormone replacement in form of 15 mg/kg medroxyprogesterone acetate (MPA) im. every 2 weeks and 450 microg/kg estradiol propionate im. once a week. Ten castrated animals received MPA only. Ten control, castrated animals were given the vehicles of these steroids. Ten other animals were kept parallelly, receiving the vehicles of all drugs (control animals). After 12 weeks of treatment cylindrical segments of the saphenous artery were isolated and cannulated at both ends and subjected to in vitro microarteriographic test. Pressure diameter curves, in the range of 0-200 mmHg, were recorded from segments in normal Krebs-Ringer (nKR) solution, in contraction with norepinephrine (1.6 x 10(-5) M), and then in relaxation with papaverine (2.8 x 10(-5) M). Biomechanical parameters were calculated based on the pressure diameter curves.

RESULTS

Combined hormone replacement therapy significantly increased the passive diameter of small arteries, as compared to those from ovariectomized animals without hormone replacement. MPA monotherapy did not alter the vessel diameter, the inner radii at 100 mmHg intraluminal pressure were, 300+/-9 microm in the control castrated, 340+/-7 microm in the estradiol + MPA replaced and 306+/-8 microm in the MPA treated groups (P < 0.05 between the control castrated and the combined treatment groups). The vascular reactivity to norepinephrine or papaverine was not changed significantly either by combined hormone replacement or by MPA monotherapy when compared with ovariectomized controls. No significant alterations were found in wall thickness and distensibility.

CONCLUSIONS

These results suggest that chronic medroxyprogesterone pretreatment does not influence the geometric, elastic and contractile properties of small arteries in castrated female rats. The combination of MPA + estradiol increased the morphological lumen: the morphological vasodilatation induced by estrogen, described earlier, was not affected by the addition of this progestin to the regimen.

The effect of ovariectomy and oestrogen replacement on small artery biomechanics in the rat

OBJECTIVE

To determine the effects of oestrogen deficiency and hormone replacement therapy on the biomechanical properties of a small artery.

SAMPLE

Thirty non-pregnant female Sprague-Dawley rats.

METHODS

Twenty animals were pharmacologically ovariectomised by triptorelin and received either oestradiol propionate or its vehicle. Ten other animals received only the vehicle for the same period of time (control group). After 12 weeks of treatment, cylindrical segments of the saphenous artery were isolated and cannulated at both ends. Pressure-diameter curves were recorded from segments in normal Krebs-Ringer, using norepinephrine, and then with papaverine. The vessel segment close to the examined one was histologically evaluated. Serum levels of oestradiol and cortisol were determined.

MAIN OUTCOME MEASURES

Biomechanical parameters based on the pressure-diameter curves.

RESULTS

Pharmacological ovariectomy decreased the passive diameter of the arteries and oestrogen replacement therapy prevented this. Decreased reactivity to norepinephrine was also restored by oestrogen treatment. Pressure induced myogenic tone was decreased significantly by oophorectomy and increased after oestradiol treatment. No significant changes were found in wall thickness, distensibility, elastic modulus or tangential stress. No significant histological alterations were seen in the vessel wall. Oestradiol levels were significantly decreased in the castrated animals compared with the other two groups.

CONCLUSIONS

These results suggest that oestrogen deficiency decreases and oestrogen replacement increases the passive diameter of small peripheral arteries, and that oestrogen enhances the reactivity of vascular smooth muscle. These responses may provide the background mechanisms for the increased incidence of arterial hypertension and hot flushes during the menopause and the ability of oestrogen substitution to prevent them.

Direct relaxing effect of estradiol-17beta and progesterone on rat saphenous artery

Although estrogen has been reported to relax large coronary arteries immediately, its direct acute effect on small vessel tone has not been fully defined. In this study, we investigated the effect of estradiol-17beta and progesterone on isolated rat saphenous artery segments-with an internal radius of 250 microm-by measuring the outer diameter of the vessels using in vitro angiometry. Estradiol and progesterone at concentrations of 1-100 and 8.6-86 microM induced a rapid, dose-dependent relaxation of the arterial segments precontracted with norepinephrine. Maximal changes of diameters were 85.8 +/- 10 and 90.9 +/- 8%. Clomiphene citrate, a cytoplasmic receptor antagonist, did not diminish this action of estradiol, with the exception of the highest concentrations of the hormone. Thus a nongenomic pathway for this effect can be suspected. Dexamethasone did not induce similar vasodilation. It is concluded that estradiol and progesterone have similar rapid vasorelaxing effects on small muscular arteries as found previously on coronary arteries.

Segmental differences in geometric, elastic and contractile characteristics of small intramural coronary arteries of the rat

The depedence of elastic and contractile properties on the caliber of small intramural coronary arteries was investigated in the rat in vitro. Different segments of the left anterior descending coronary artery branching system were prepared for microarteriography. The segments were cannulated at both ends, immersed in oxygenated normal Krebs Ringer (nKR) solution. Intraluminal pressure was changed at a rate of about 0.5 mm Hg/s between 0 and 150 mm Hg in repeated cycles. The outer diameter was continuously measured with microangiometry. Pressure-diameter curves were recorded after preconditioning pressure cycles in nKR, with PGF2alpha in the bath (7.5 x 10(-6) M), and in maximal relaxation with papaverine (2.8 x 10(-4) M). Biomechanical parameters were computed for vessels grouped according to their calibers (inner diameters: 50-150, 150-250, 250-350, >350 microm). Distensibility and contractility decreased with increasing caliber of the vessels, while the elastic modulus increased. Spontaneous tone was (at 100 mm Hg in mechanically preconditioned vessels) 18.8 +/- 4.5, 8.4 +/- 4.4, 9.7 +/- 3.7 and 8.3 +/- 3.8% in the four groups, respectively. PGF2alpha contraction was maximal around the 300- microm caliber. Our study is the first direct demonstration that intramural small coronary arteries exhibit characteristic variability in their elastic and contractile properties as a function of their caliber. Such differences may be important in segmentally specific control processes of the coronary microcirculation.

Sterically inhomogenous viscoelastic behavior of human saccular cerebral aneurysms

To clarify the mechanism leading to the development and rupture of intracranial aneurysms, tensile strength and viscoelastic parameters of 22 human saccular aneurysms were investigated. Meridional and circumferential strips from the thin and the thick part of the aneurysm sack and 18 control strips from the basilar artery of 8 patients with pathologies not affecting the cerebral arterial system were studied. The length of the strips was increased in 200- microm steps, while distending force was recorded. Tensile strength and viscoelastic parameters were computed. In both directions, tensile strength of thick strips was significantly lower than that of controls. In the meridional direction, tensile strength of thin strips was significantly larger than that of thick ones (14.5 +/- 4.1 x 10(6) vs. 7.5 +/- 2.0 x 10(6) dyn/cm2, p < 0.05). In the circumferential direction, thin strips tore at lower strain values than thick ones (29 +/- 4 vs. 55 +/- 16%, p < 0.05). Viscoelastic parameters changed in parallel. In circumferential direction, values of thick and thin strips were significantly lower than those of controls. In the meridional direction, values of thin strips were significantly higher than those of the thick ones. These observations show that characteristic mechanical deterioration and steric inhomogeneities accompany the loss of smooth muscle cells and the derangement of connective tissue elements in the wall of intracranial aneurysms, which may explain certain steps in their initiation, enlargement and rupture.

Nitric oxide-dependent opposite effects of somatostatin on arterial and venous caliber in situ

The vascular effects of somatostatin (ST) and its mechanism of action are not well understood. In the present study, we investigated the direct effects of ST on the vascular tone of rat saphenous artery and vein using videomicroangiometry in situ. ST was administered either in superfusion or in infusion. We found opposite effects in arteries and veins: ST (10(-12)-10(-7) M) dilated the artery (outer diameter increased from 533 +/- 28 to 600 +/- 29 microns, administered in superfusion) and contracted the vein (from 709 +/- 26 to 640 +/- 26 microns and from 775 +/- 30 to 708 +/- 60 microns in superfusion and infusion, respectively). These effects of ST were completely abolished after deendothelization (air bolus maintained for 6 min in vessel lumen) and after local infusion of NG-nitro-L-arginine (L-NNA; 10(-4) M), a nitric oxide (NO) synthesis inhibitor. An NO-dependent basal vasodilator tone in the rat saphenous vein responsible for 10.9 +/- 0.3% of the total vessel diameter was found. After ST administration the venous diameter reduction was similar to that measured after deendothelization or L-NNA. We conclude that ST in situ induces NO release from endothelial cells of rat saphenous artery causing vasodilation, whereas, in contrast, it inhibits the basal NO-dependent vasodilator tone of the saphenous vein inducing vasoconstriction.

In vivo dose-response characteristics of endothelin-1: studies on rat saphenous vein

Microangiometric studies were made in vivo on rat saphenous vein to obtain dose-response contraction curves with endothelin-1. During superfusion of the drug, threshold concentrations were found to be in the range of 4 x 10(-11) -4 x 10(-10) moles/lit, maximal concentrations were about 4 x 10(-8) moles/lit. These values are close to published in vitro threshold values. During intravascular administration of the drug contraction could be observed in response to a dose as small as 4.37 femtomoles/s. The data presented show that characteristic dose response curves resembling those found in vitro can be recorded in vivo with endothelin on appropriate vascular preparata. The rat in situ saphenous vein microangiometric technic can be used for delicate pharmacologic examination of venoactive substances in vivo.

Effect of two week lymphatic occlusion on the mechanical properties of dog femoral arteries

In order to study the long-term effect of impaired lymphatic drainage on the mechanical properties of the arterial wall, cylindrical femoral artery segments from 10 mongrel dogs after 2 weeks of hindlimb lymphatic occlusion were subjected to in vitro mechanical test and compared with the contralateral, sham-operated segments. Smooth muscle contraction was induced by norepinephrine (7.4 X 10(-6) M) and smooth muscle relaxation by papaverine (1.6 X 10(-4) M). As a result of 2 weeks of lymphatic occlusion, wall thickness increased from 243 +/- 18 to 343 +/- 35 microns (P less than 0.02), inner radius decreased from 1.69 +/- 0.11 to 1.42 +/- 0.12 mm (P less than 0.01) and elastic modulus decreased from 1.23 X 10(6) to 0.55 X 10(6) N/m2 (P less than 0.01), when determined at 100 mm Hg (13.3 kPa) intraluminal pressure and with relaxed smooth muscle. The contractile apparatus was able to produce active strain in the vessels with lymphostasis and at physiological pressures not significantly different from the controls (0.89 +/- 0.02 vs. 0.91 +/- 0.02), but at significantly lower levels of tangential stress. Active stress decreased significantly. This study shows that a reorganization of the vessel wall mechanical force-bearing elements occurs in lymphostasis, which, in some respects, resembles the mechanical alterations found in different forms of atherosclerosis.