Increased aortic DNA synthesis precedes renal hypertension in rats. An obligatory step?

Acute elevations in salt intake and reduced renal mass hypertension compromise arteriolar dilation in rat cremaster muscle

Alterations in arteriolar reactivity to dilator agonists were assessed in the skeletal muscle microcirculation of normotensive male Sprague-Dawley rats fed either high- (4% NaCl; HS) or low- (0. 4% NaCl; LS) salt diets and in reduced renal mass hypertensive rats (RRM-HT) on a high-salt diet for 3 days. An in situ cremaster muscle preparation was superfused with physiological salt solution, transilluminated, and viewed via television microscopy. A videomicrometer was used to measure changes in diameter of distal arterioles in response to increasing concentrations of acetylcholine (ACH), iloprost (ILO), cholera toxin (CT), forskolin (FOR), and sodium nitroprusside (SNP). Arteriolar dilation in response to ACH, ILO, and CT was significantly reduced in both HS and RRM-HT rats, while responses to FOR and SNP were decreased in RRM-HT rats only. The maximum dilation of the arterioles (determined during superfusion of the muscle with Ca2+-free solution containing 10(-4) M adenosine) was similar in the normotensive control animals on LS and HS diets, but was reduced in the RRM-HT rats, suggesting that early anatomic remodeling of the vessel wall may be occurring with RRM-HT. We conclude that arteriolar reactivity to endothelium-dependent and -independent vasodilator agonists is impaired as early as 3 days after the development of RRM hypertension or commencement of a high-salt diet in normotensive rats. Structural remodeling of the arteriolar wall, although becoming evident in the hypertensive rats, takes longer to develop than the impaired vasodilator reactivity.

Effects of captopril, losartan, and nifedipine on cell hypertrophy of cultured vascular smooth muscle from hypertensive Ren-2 transgenic rats

1. We hypothesized that tissular renin-angotensin system (RAS) induces vascular hypertrophy in hypertensive Ren-2 transgenic rats (TGR; strain name TGR(mRen2)L27). This assumption was tested in cell cultures of vascular smooth muscle (VSMC) from both hypertensive TGR and control normotensive Sprague-Dawley (SD) rats. Planar cell surface area, protein synthesis, and protein content per cell were studied, the role for locally produced angiotensin II (AII) was evaluated and the possible pharmacological interference by different drugs was analysed. 2. By use of radioimmunoassay techniques, AII could be determined in TGR cultures (10.25 +/- 0.12 pg per 10(7) cells) while it could not be detected in SD ones. 3. Under serum-free conditions, VSMC from hypertensive TGR were hypertrophic when compared to SD VSMC, as they presented a higher protein content per cell (335 +/-18 and 288 +/- 7 pg per cell respectively; P<0.05) and increased mean planar cell surface area, as determined by image analysis (4,074 +/- 238 and 4,764 +/- 204 microm2, respectively; P < 0.05). 4. When exogenously added to cultured SD and TGR VSMC, AII (100 pM to 1 microM) promoted protein synthesis and protein content in a concentration-dependent manner without affecting DNA synthesis. Maximal effects were observed at 100 nM. At this concentration, AII effectively increased planar cell surface area in both SD and TGR cultures by approximately 20%. 5. Treatment of TGR cultures, in the absence of exogenous AII, with the angiotensin-converting enzyme inhibitor captopril or the angiotensin AT1 receptors antagonist losartan (100 nM to 10 microM) reduced planar cell surface area in a concentration-dependent manner. In addition, both captopril and losartan (10 microM), decreased protein synthesis by approximately 15%. 6. Treatment of SD VSMC, in the absence of exogenous AII, with both captopril and losartan had no effect either on planar cell surface area or protein synthesis. 7. Treatment with the Ca2+ antagonist nifedipine (100 nM to 10 microM) reduced cell size in both SD and TGR cultures. Maximal cell reduction reached by nifedipine averaged 906 +/- 58 and 1,292 +/- 57 microm2, in SD and TGR, respectively (P<0.05). In addition, nifedipine, nitrendipine and nisoldipine (all at 10 microM) decreased protein synthesis in both cell types by 15-25%. 8. We concluded that cultured VSMC from TGR are hypertrophic in comparison with those from SD. This cell hypertrophy can be the consequence of the expression of the transgene Ren-2 that activates a tissular RAS and locally produces AII, which acts in a paracrine, autocrine, or intracrine manner. Cell hypertrophy in TGR cultures could be selectively reduced by RAS blockade, while nifedipine decreased cell size and protein synthesis in both hypertrophic and non hypertrophic cells.

Heterogeneity of adenovirus-mediated gene transfer in cultured thoracic aorta and renal artery of rats

Replication-deficient recombinant adenovirus vectors have been used to transfer foreign genes effectively to a wide variety of cell types in vivo and in vitro. We have now used adenovirus containing either the Escherichia coli beta-galactosidase (beta-gal) gene (AdHCMVsp1LacZ) or the firefly luciferase gene (Ad5-luc3) to test the hypothesis that efficiencies of adenovirus-mediated gene delivery into organ cultures of smooth muscle differ according to the anatomic origin of the muscle. Thoracic aorta and renal artery were isolated from 9-week-old male Sprague-Dawley rats and exposed to adenovirus after 16 hours of incubation with serum-free medium (Dulbecco's modified Eagle's medium). With the use of histochemical methods, beta-gal staining was noted in both endothelial and adventitial cells but not in the muscular media of thoracic aorta and renal artery exposed to AdHCMVsp1LacZ. The efficiency of the transfection, assessed either by counting of beta-gal-stained cells in intact vessels or by measurement of beta-gal activity in tissue extracts, was higher in renal artery than thoracic aorta (P < .05). Consistent with this result, luciferase activity in renal artery exposed to Ad5-luc3 (15.9 +/- 2.1 x 10(6) relative light units per milligram protein) was higher than that in thoracic aorta (8.3 +/- 2.0 x 10(6), P < .05). To determine whether increased efficiency of adenovirus-mediated gene transfer into renal artery is a function of the replication status of vessels, we assessed [3H]thymidine incorporation. [3H]Thymidine uptake by thoracic aorta was only 63% of that in renal artery (P < .05), indicating that more proliferating cells are present in renal artery. We conclude that the efficiency of adenovirus-mediated gene transfer into cultured renal artery is enhanced compared with that into thoracic aorta and propose that the increase in efficiency is related to the higher proliferative activity of renal artery.

Differential effects of pressure and flow on DNA and protein synthesis and on fibronectin expression by arteries in a novel organ culture system

Structural adaptation of the blood vessel wall occurs in response to mechanical factors related to blood pressure and flow. To elucidate the relative roles of pressure, flow, and medium composition, we have developed a novel organ culture system in which rabbit thoracic aorta, held at in vivo length, can be perfused and pressurized at independently varied flow and pressure for several days. Histology and histomorphometry, as well as scanning electron microscopy, revealed a well-preserved wall structure. In arteries perfused and pressurized at 80 mm Hg, endothelial injury led to a 2-fold increase in [3H]thymidine incorporation in the media, which peaked at 3 to 5 days and returned to baseline level at 6 to 8 days. In intact endothelialized vessels cultured for 3 days under no-flow conditions, pressure per se had no effect on DNA synthesis. In contrast, in the presence of serum, total protein synthesis, as assessed by [35S]methionine incorporation into the media, was enhanced 6-fold at 150 mm Hg compared with vessels pressurized at 0 or 80 mm Hg. In intact vessels perfused at a constant flow of 40 mL/min for 3 days, DNA synthesis was unchanged regardless of the pressure level when vessels were cultured in the presence of serum but increased 8-fold at both 80 and 150 mm Hg in the absence of serum. Unlike DNA synthesis, total protein synthesis was enhanced 12-fold by flow regardless of the presence or absence of serum. Expression of fibronectin was markedly enhanced at high transmural pressure, and serum potentiated its expression in the arterial wall. This novel organ culture system of perfused and pressurized vessels allowed identification of differential effects of pressure, flow, and serum on DNA and total protein synthesis, including cellular fibronectin expression.

The role of growth factors in vascular cell development and differentiation

The control of vascular growth and differentiation is a complex system of activity and interaction between positive and negative modulators of these processes. A number of important stimulators and inhibitors of both smooth muscle cells and endothelial cells have now been purified and biochemically characterized. Imbalances in the activity of these factors can result in serious pathologies. In this chapter, we briefly discuss the biology of blood vessel development and growth, review the current literature which describes these stimulators and inhibitors, and discuss current therapeutic strategies designed around these growth modulators.

New perspectives in hypertension research. Potentials of vascular biology

The vessel wall was once considered to be a passive conduit responding to the circulating endocrine system. However, the emergence of molecular and vascular biology in hypertension research has redefined our understanding of the role of the vasculature as a vital organ in the pathogenesis of hypertension. It is now recognized that the vasculature can regulate its own tone by a variety of previously unknown autocrine and/or paracrine vasoactive systems. Recent evidence indicates that the process of vascular remodeling in hypertension appears to be mediated by locally generated factors within the vessel wall. This review examines the implications of this new paradigm in hypertension, focusing on five topics that have developed through the emergence of molecular vascular biology: the discovery and characterization of novel biologically active molecules synthesized by the vessel wall, the molecular mechanisms and consequences of vascular remodeling, the developmental biology of the blood vessel and the relation to pathobiology, the use of in vivo gene transfer to test hypotheses in vivo, and novel treatment strategies based on gene therapy of the vessel wall.

Culture of rat mesenteric arteriolar smooth muscle cells: effects of platelet-derived growth factor, angiotensin, and nitric oxide on growth

We cultured smooth muscle cells as explants from rat mesenteric arterioles (40-200 microns in diameter) obtained by injecting a suspension of iron oxide intraarterially and magnetically separating the arterioles after collagenase digestion of adventitial tissue. In third-passaged cells we ascertained smooth muscle purity of > 98% by characteristic morphology, contraction responses, and specific immunofluorescence staining. Treatment of growth-arrested (in 0.4% fetal calf serum) cells with platelet-derived growth factor (0.3-7.5 nM) or angiotensin II (0.001-1000 nM) induced 3H-thymidine incorporation and cell proliferation in a dose-dependent manner (P < 0.01). S-nitroso-N acetylpenicillamine (0.05-0.5 mM), a nitric oxide-generating compound, inhibited 10% fetal calf serum-induced 3H-thymidine incorporation (P < 0.05) and cell proliferation (P < 0.01). The antimitogenic effect of S-nitroso-N-acetylpenicillamine was significantly reduced by hemoglobin and potentiated by superoxide dismutase (P < 0.01). In addition to a new technique for culturing mesenteric arteriolar smooth muscle cells, these findings provide evidence that platelet-derived growth factor, angiotensin II, and nitric oxide may be involved in their growth control.

Pharmacology of smooth muscle cell replication

The suggestion that smooth muscle cell proliferation contributes to hypertension, atherosclerosis, and restenosis after angioplasty has led to a growing interest in the use of drugs to inhibit this process. This review summarizes pharmacological studies of smooth muscle cell proliferation in vitro and in vivo and identifies specific mediators of proliferation that are implicated by drugs binding with high affinity to enzymes or receptors.

Culture of renal arteriolar smooth muscle cells. Mitogenic responses to angiotensin II

We cultured smooth muscle cells from rat renal preglomerular arterioles by injecting a suspension of iron oxide into the left ventricle, separating the arterioles magnetically, and growing cells from explants. In passaged cultures we ascertained vascular smooth muscle purity of > 98% by morphology; contraction to norepinephrine and angiotensin; positive immunofluorescence staining through the sixth passage with monoclonal antibodies to smooth muscle-specific alpha- and gamma-isoactins, myosin, and desmin; and the absence of von Willebrand factor. Angiotensin II (10(-12)-10(-5) M) induced dose-dependent DNA synthesis and proliferation of subcultured (three times) arteriolar smooth muscle cells from a growth-arrested state (p < 0.01). Angiotensin II (10(-5) M) also induced the cells to express c-fos mRNA. We find no previous report of culture of smooth muscle cells from renal preglomerular arterioles. Our findings also provide evidence that angiotensin II is mitogenic to arteriolar muscle cells and thus may be involved in their hyperplasia accompanying hypertension.

Immunolocalization of native antioxidant scavenger enzymes in early hypertensive and atherosclerotic arteries. Role of oxygen free radicals

To elucidate the role of oxygen free radicals and lipid peroxidation in the pathogenesis of early hypertension and atherosclerosis, we studied the native distribution of three primary arterial antioxidant enzymes (AEs). Specific immunohistochemical localization of superoxide dismutase (Cu-Zn SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) was examined in the arterial wall of New Zealand White rabbits: six sham-operated normotensive/normolipidemics (NT/NL), seven coarctation-induced hypertensive/normolipidemics (HT/NL), eight normotensive diet-induced hyperlipidemics (NT/HL), and six hypertensive/hyperlipidemics (HT/HL). All three AEs were confined primarily to the endothelium in NT/NL rabbit aortas. However, in HT and HL rabbits a greater proportion of the arterial wall, including the endothelium, inner media, and middle media, displayed immunolocalization of three AEs. Multiple linear-regression analysis revealed that more than 70% of the total variability in the depth of immunolocalization of arterial AEs could be explained by changes in blood pressure and/or total cholesterol. Also, levels of plasma and arterial cholesterol oxides were significantly different (p less than 0.05) in HT and HL rabbits compared with controls, with twofold increases in NT/HLs, threefold increases in HT/NLs, and fourfold increases in HT/HLs. We conclude that intense free-radical activity in the arterial wall of HT and HL animals is one possibility and that this occurs despite the presence of abundant AEs.

Rapid accumulation of elastin and collagen in the aortas of sheep in the immediate perinatal period

While characterizing developmental changes in aortic wall composition in sheep, we observed very rapid accumulation of elastin and collagen in the immediate perinatal period. Thoracic aortic elastin content increased by 41%, and collagen content increased by 49% in approximately 1 week, between 140 days gestation and 3 days postpartum (term = 145 days). Even larger changes were observed in the abdominal aorta. Elastin content increased by 66%, and collagen increased by 57%. The pronounced increase in wall tissue accumulation near birth preceded a marked postnatal increase in arterial pressure. We propose that this elastin and collagen accumulation is a preadaptive response in preparation for the later increase in pressure. The prenatal and postnatal events that initiate this synthesis and accumulation are not known. We also found that, in the 3 weeks after this initial rapid increase, accumulation of elastin and collagen was markedly reduced in the abdominal, but not the thoracic, aorta. This latter finding may be linked to the dramatic decrease in flow through this vessel that results from the loss of the placental circulation. Finally, we observed that relatively high smooth muscle cell replication rates in the abdominal aorta postpartum resulted in no net DNA accumulation. This finding indicates that cell turnover plays an important role in postnatal arterial growth and development.

Angiotensin II causes vascular hypertrophy in part by a non-pressor mechanism

Angiotensin II, when given in low doses, raises blood pressure slowly. When tested in vitro on vascular smooth muscle cells, it has mitogenic and trophic effects; it is not known if it has these effects in vivo. Our purpose was to determine whether vascular hypertrophy develops during slow pressor infusion of angiotensin II and, if so, whether it is pressure induced. Three experiments were done in rats infused subcutaneously with angiotensin II (200 ng/kg/min) by minipump for 10-12 days. Experiment 1: Angiotensin II gradually raised systolic blood pressure (measured in the tail) from 143 +/- 2 to 208 +/- 8 mm Hg (mean +/- SEM), significantly suppressing plasma renin and increasing threefold (NS) plasma angiotensin II. There was no loss of peptide in the pump infusate when tested at the end of the experiment. Experiment 2: In the perfused mesenteric circulation, vasoconstrictor responses to norepinephrine, vasopressin, and KCl were enhanced in rats given a slow pressor infusion of angiotensin II, but sensitivity of responses was not altered. This combination of changes suggests that vascular hypertrophy develops during slow pressor infusion of angiotensin II. Experiment 3: Vessel myography was done after angiotensin II infusion with and without a pressor response. Angiotensin II raised systolic blood pressure, increased heart weight, and produced myographic changes of vascular hypertrophy in the mesenteric circulation, increasing media width, media cross-sectional area, and media/lumen ratio. Hydralazine given with angiotensin II prevented the rise of pressure and the cardiac effect but not the vascular changes. Two-way analysis of variance showed that angiotensin II significantly increased media width, media cross-sectional area, and media/lumen ratio, all independent of hydralazine. Thus, although hydralazine inhibits the pressor and cardiac effects of angiotensin II, suggesting a pressor mechanism for the cardiac change, it does not inhibit structural vascular change, which suggests that at least part of the effect has a non-pressor mechanism.

Aortic ornithine decarboxylase activity in deoxycorticosterone/salt hypertensive rats

Previous studies from our own and other laboratories have shown that hypertension induces changes in the growth of arterial smooth muscle cells (SMC). The purpose of this study was to examine the role of ornithine decarboxylase (OrnDCase) in this process. OrnDCase, the rate limiting enzyme in polyamine biosynthesis, increases in activity early in the cell cycle, and has been used as a marker of cell growth or proliferation. Deoxycorticosterone (DOC)/salt hypertension was induced in male Wistar rats. At 1-3 day intervals of DOC/salt treatment, the aortas were removed and OrnDCase activity and DNA content were determined. The results indicated that OrnDCase activity increased as early as day 2 of DOC/salt administration, reached a peak at day 10, and fell to a baseline by day 16. DNA content increased after day 10 to levels approximately 25% greater than in controls. Significant increases in blood pressure were not observed until after day 8. The findings indicate that OrnDCase activity is stimulated by DOC/salt even before the rise in blood pressure and that factors other than blood pressure per se may be important in stimulating aortic smooth muscle cell growth in the development of hypertension.

Effects of antihypertensive drugs on glomerular morphology

We quantitated the glomerular size and the degree of sclerosis simultaneously in individual glomeruli with the use of three-dimensional histological analysis on serial sections obtained from remnant kidneys with highly heterogeneous glomerular lesions after subtotal nephrectomy (sNPX). Four to six weeks after sNPX (Group I, N = 7), 90% of glomeruli had mild sclerosis (sclerosis index, SI; less than 1.5 on a 0 to 4 scale) with a strong positive correlation between the maximum planar area of glomerulus (PAmax) versus SI. Twelve weeks after sNPX (Group II, N = 6) more than 50% of glomeruli had advanced sclerosis (average SI:1.88), and a significant positive correlation was again found between PAmax and SI in glomeruli with mild to modest sclerosis (SI less than 1.5), whereas these two variables were correlated inversely in glomeruli with advanced sclerosis. Administration of enalapril (50 mg/liter drinking water) or hydralazine (200 mg/liter) + hydrochlorothiazide (50 mg/liter) for 12 weeks (Group III, N = 12) markedly attenuated the sclerosis to comparable degrees (average SI: 0.15 vs. 0.22). The former antihypertensive therapy decreased glomerular capillary hydraulic pressure (PGC) to normal range, whereas the latter triple drug therapy was largely without effect on PGC. Of note, the positive correlation between SI and PAmax remained unaffected by these anti-hypertensive drugs. SI of the glomeruli from both treated groups was expressed as a first-order function of PAmax. The correlation coefficient is identical to that found in non-treated Group II remnant glomeruli, so that the degree of sclerosis is mathematically uniquely correlated with the glomerular size, regardless of drug treatment. Thus, within a given remnant kidney, the magnitude of glomerular hypertrophy has a direct correlation with the degree of sclerosis, while the altered glomerular hemodynamic pattern has little modulatory role in determining the magnitude of this hypertrophy. Enalapril and triple drug therapy, at equi-depressor doses in regard to systemic blood pressure, had identical potency in sparing glomerular structure. The primary determinant for this antisclerotic potency appears to be related to the drugs' potency to inhibit glomerular growth rather than an effect on the abnormal hemodynamics which develop in the glomerulus.

Noradrenaline induces the polyploidization of smooth muscle cells: the synergism of second messengers

The effect of noradrenaline (NA) on DNA replication of cultured smooth muscle cells (SMC) isolated from rat aorta was examined. It was found that 10 microM NA significantly increased (approximately by twofold) the frequency of tetraploid cells. Cultivation of 4C cells isolated by flow cytometric cell sorting revealed that they were true polyploid cells. This receptor-mediated effect of NA was blocked only by simultaneous action of alpha- and beta-adrenoreceptor antagonists. SMC polyploidization was also stimulated by simultaneous application of direct activators of "second messenger" systems forskolin and phorbolmyristate-acetate. Thus, NA may be one of mediators of the "hypertensive" response of vessel wall SMC, which probably occurs due to synergism of two second messenger systems.

Aortic hypertrophy and "waterlogging" in the development of coarctation hypertension

To study the mechanisms and roles of vascular structural changes during the development of hypertension, we coarcted or sham-coarcted the abdominal aorta of rats. At intervals of 3 to 56 days later, we obtained standardized segments of thoracic and abdominal aortas for measurement of dry weight, water content, and amino acid content. Carotid arterial pressure was elevated by day 5 in coarcted rats and remained elevated. Femoral and tail arterial pressures remained normal. Cardiac ventricular weight and dry weight of the thoracic aorta, normalized for body weight, rose rapidly over 3-10 days in coarcted rats, remaining constant at 50-60% above levels in sham-coarcted rats thereafter. In contrast, water content of thoracic aorta in coarcted rats peaked at 123% of control values on day 7 (p less than 0.001), falling rapidly thereafter to levels about half of peak. Increments in dry weight and water content of the normotensive abdominal aortic segments were of far lesser magnitude and occurred 1 to 2 weeks later, probably reflecting the effects of initial hypotension of the hindquarters. Percent hydroxyproline of intima-media segments of the thoracic aorta remained normal during the 8-week period, indicating that increases in aortic dry weight did not represent disproportional fibrosis and thus are attributable to muscular hypertrophy. These results provide support for the hypothesis that arterial wall "waterlogging" is primarily an early manifestation of the hypertensive process. The greatest magnitude of waterlogging coincides with the rapid early increase in aortic dry weight, representing hypertrophy, which suggests common mechanisms, such as activation of Na+-H+ antiport.

Cell biology of vascular hypertrophy in systemic hypertension

Recent data demonstrate that in addition to its conduit function, the blood vessel is an active synthetic and secretory organ containing several autocrine and paracrine systems that are involved with the local regulation of its own function (i.e., structure and growth). The endothelium secretes vasorelaxant and vasoconstrictive substances, growth factors and inflammatory mediators that exert paracrine influences on vascular myocyte function. The vascular myocyte also expresses autocrine substances that influence its own function. The autocrine systems include angiotensin, prostaglandins, platelet-derived growth factor, insulin-like growth factor and heparin. These local factors exert modulatory influences on myocyte contractility and growth. These autocrine and paracrine systems serve as an adaptive mechanism by which the vasculature autoregulates its structural and functional state. We speculate that an alteration in this delicate balance of these local factors, due to genetic or acquired abnormalities, can result in increased vascular tone and vessel hypertrophy and thereby contribute to the pathogenesis of hypertension.

The oxygen environment of the arterial media in early rabbit hypertension

Hypertensive stimuli in experimental animals appear to cause early arterial wall hypermetabolism before hypertension is established and before histomorphic changes are marked. Hypermetabolism and the large diffusion distances for oxygen characteristic of large arteries imply that mural hypoxia could occur early in the disease but this has not been studied. Therefore, we measured aortic wall tissue oxygen distributions in male New Zealand White rabbits 2 weeks (1) after production of upper body hypertension by coarctation of the abdominal aorta, (2) after sham operation, and (3) in normal controls. As compared to normal and sham operated animals, blood pressure in the coarctation animals was significantly elevated from control levels, and the oxygen partial pressures were significantly reduced throughout the media. However, the hypoxic mural oxygen tensions in this relatively thin wall were not low enough to terminate classical respiration. At the time of measurement, moderate microscopic pathology was already present, including increased connective tissue production. The accompanying histomorphic changes are compatible with reports of extrarespiratory oxygen sensitivity of connective tissue metabolism.

Morphometric evidence for non-pressure-related arterial wall thickening in hypertension

To investigate the relation of pressure and vascular wall thickening in hypertension, we coarcted the abdominal aorta upstream to the renal arteries in 14 rats. Sham-coarcted (n = 16) and two-kidney, one-clip (Goldblatt) hypertensive rats (n = 13) served as controls. Tail, femoral, and carotid arterial pressures rose (p less than 0.01) in the two-kidney, one-clip hypertensives; only carotid pressure rose (p less than 0.01) in the coarcted rats, tail and femoral pressures remaining normal (p greater than 0.25). Thus, the hindquarters of the coarcted rats remained normotensive. Four to six weeks after surgery we perfusion-fixed vascular tissues of the hindquarters, including kidneys, with formalin at in vivo levels of pressure. Glycol methacrylate-embedded tissues were sectioned at 1 micron thickness and vessels quantitatively evaluated. The outer medial and lumen perimeters of abdominal aorta, femoral artery, and renal arterioles were measured; from these measurements, vessel outer and lumen diameters, medial thickness, medial area, and medial thickness-to-lumen radius ratios were calculated. Compared with sham-coarcted rats, abdominal aorta, femoral arteries, and renal arterioles less than 61 microns outer diameter in rats with coarctation and Goldblatt hypertension had significantly increased (up to +100%) medial area, medial thickness, and medial thickness-to-lumen radius ratios. In general, magnitudes of abnormalities were similar in Goldblatt and coarcted rats. Renal arterioles greater than 60 microns outside diameter in Goldblatt hypertensive, but not coarcted, rats also were thickened. These results indicate that vascular wall thickening occurs in conduit arteries and smaller renal arterioles in the normotensive hindquarters of coarcted rats, providing morphometric evidence for non-pressure-related mechanisms involved in vascular growth in this form of hypertension.

Changes in vascular endothelium and its function in systemic arterial hypertension

The various functions of arterial endothelium may be altered during pulmonary and arterial hypertension. Changes in the endothelium (or function) associated with hypertension are described. In both acute and chronic hypertension, permeability of the endothelium is enhanced. During the acute phase of hypertension, hyperplasia (cell replication) of the endothelium occurs while cell hypertrophy (enlarged cell size) and an increase in homocellular tight junctions are associated with sustained elevations of blood pressure. Endothelium may contribute to the increase in smooth muscle mass or cell number reported with various models of hypertension. Increased endothelial uptake or metabolism of norepinephrine and serotonin occurs during hypertension. The biotransformation of adenine nucleotides and various peptides by the endothelium is not altered by hypertension. Synthesis of prostacyclin is enhanced in the spontaneously hypertensive and Goldblatt hypertensive rat. Metabolism of prostaglandin E2, prostaglandin F2 alpha and prostacyclin by prostaglandin 15-hydroxydehydrogenase is impaired in the genetic models. Responses to endothelium-dependent vasodilators are impaired in acute and chronic models of hypertension. Production of relaxing factor by the endothelium is not inhibited, but rather the vascular smooth muscle fails to respond. Acute, severe hypertension potentiates the response to serotonin, presumably by attenuating the release or response to relaxing factor(s). In the aorta of the spontaneously hypertensive rat, the endothelium releases a constricting factor in response to acetylcholine. Pulmonary arterial endothelium (and other vessels) releases a vasoconstrictor that is blocked by inhibitors of cyclooxygenase. It is not clear whether this pressor factor is thromboxane A2. Cultured endothelial cells release a polypeptide that contracts arteries; however, any relation to hypertension is not known.

Antihypertensive drugs inhibit hypertension-associated aortic DNA synthesis in the rat

The effect of antihypertensive drug treatment on aortic DNA synthesis was examined in rats with two-kidney, one clip renal hypertension and in spontaneously hypertensive rats (SHR). In two-kidney, one clip hypertensive rats, hypertension developed over a 2-week period. Four days after clipping the renal artery, during the onset of hypertension, there was an increase in aortic DNA synthesis. Aortic DNA synthesis was also increased 3 weeks later, when hypertension had been established. Captopril, hydralazine, and verapamil were each able to prevent the increase in aortic DNA synthesis and the rise in blood pressure when given throughout the first 5 days of the developing phase of hypertension, or when given to rats with established hypertension. Drug treatment of sham-operated rats had no significant effect on DNA synthesis, although blood pressure was decreased. There were no differences in blood pressure or aortic DNA synthesis in 4-week-old SHR, as compared with age-matched Wistar-Kyoto (WKY) controls or normal Wistar rats. At 17 weeks of age, when hypertension was established, aortic DNA synthesis was significantly enhanced in the SHR. Captopril or hydralazine treatment was able to reduce blood pressure and DNA synthesis to levels seen in the WKY. At 21 weeks of age, DNA synthesis in the SHR had declined to the same levels as in the WKY. Captopril, hydralazine, and verapamil may have a common ability to reduce intracellular calcium and therefore inhibit DNA synthesis. In support of this, ouabain treatment, which increases intracellular calcium by inhibiting the Na+-K+ pump, produced a significant increase in the rate of DNA synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)