Hyperplasia of rat arteries smooth muscle cells associated with development and reversal of renal hypertension

Hypersensitivity to acute ANG II in female growth-restricted offspring is exacerbated by ovariectomy

Female growth-restricted offspring are normotensive in adulthood. However, ovariectomy induces a marked increase in mean arterial pressure (MAP) that is abolished by renin angiotensin system (RAS) blockade, suggesting RAS involvement in the etiology of hypertension induced by ovariectomy in adult female growth-restricted offspring. Blockade of the RAS also abolishes hypertension in adult male growth-restricted offspring. Moreover, sensitivity to acute ANG II is enhanced in male growth-restricted offspring. Thus, we hypothesized that an enhanced sensitivity to acute ANG II may contribute to hypertension induced by ovariectomy in female growth-restricted offspring. Female offspring were subjected to ovariectomy (OVX) or sham ovariectomy (intact) at 10 wk of age. Cardio-renal hemodynamic parameters were determined before and after an acute infusion of ANG II (100 ng·kg(-1)·min(-1) for 30 min) at 16 wk of age in female offspring pretreated with enalapril (40 mg·kg(-1)·day(-1) for 7 days). Acute ANG II induced a significant increase in MAP in intact growth-restricted offspring (155 ± 2 mmHg, P < 0.05) relative to intact control (145 ± 4 mmHg). Ovariectomy augmented the pressor response to ANG II in growth-restricted offspring (163 ± 2 mmHg, P < 0.05), with no effect in control (142 ± 2 mmHg). Acute pressor responses to phenylephrine did not differ in growth-restricted offspring relative to control, intact, or ovariectomized. Furthermore, renal hemodynamic responses to acute ANG II were significantly enhanced only in ovariectomized female growth-restricted offspring. Thus, these data suggest that enhanced responsiveness to acute ANG II is programmed by intrauterine growth restriction and that sensitivity to acute ANG II is modulated by ovarian hormones in female growth-restricted offspring.

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.

Regulation of vascular smooth muscle growth by alpha 1-adrenoreceptor subtypes in vitro and in situ

Rat aorta smooth muscle cells which express all three alpha 1-adrenoreceptors (alpha 1A, alpha 1B and alpha 1D) were used to determine the effect of stimulation of alpha 1-adrenergic receptor subtypes on cell growth. "Combined" alpha 1-adrenoreceptor subtype stimulation with norepinephrine alone caused a concentration-dependent, prazosin-sensitive increase in protein content and synthesis: 48 h of stimulation at 1 microM increased cell protein to 216 +/- 40% of time-matched controls (p = 0.008) and RNA to 140 +/- 13% (p = 0.03); protein synthesis increased to 167 +/- 13% (p < 0.01) after 24 h. Stimulation with norepinephrine plus the selective alpha 1A/alpha 1D antagonist 5-methylurapidil produced greater increases in alpha-actin mRNA (270 +/- 40% at 8 h; p = 0.007), total cell protein (220 +/- 45% at 24 h; p = 0.004), and RNA (135 +/- 8% at 24 h; p = 0.01). These effects were prevented by pretreatment with the selective alpha 1B antagonist chloroethylclonidine. Comparable results were obtained for intact aortae. Stimulation with norepinephrine plus 5-methylurapidil increased (p < 0.05) tissue protein, RNA, dry weight, and alpha-actin mRNA; and as in culture cells, combined stimulation with norepinephrine alone attenuated these responses. By comparison, adventitia (fibroblasts) was unaffected. Removal of endothelial cells had no effect. alpha 1B mRNA decreased by 42 +/- 12% (p = 0.01) in cultured cells during combined alpha 1-adrenoreceptor stimulation and by 23 +/- 8% (p = 0.03) for intact aorta. alpha 1D and beta-actin mRNA were unchanged in cultured cells, aorta media, and adventitia. These findings suggest that prolonged stimulation of chloroethylclonidine-sensitive, possibly alpha 1B-adrenoceptors induces hypertrophy of arterial smooth muscle cells and that stimulation of 5-methylurapidil-sensitive, non-alpha 1B-adrenoreceptors attenuates this growth response.

Effects of hypertension and hyperlipidemia on the myocardium and coronary vasculature of the WHHL rabbit

This study was undertaken to study the effects of hyperlipidemia and hypertension on the coronary circulation and on the myocardium of Watanabe heritable hyperlipidemic (WHHL) rabbits. Surgery to induce hypertension by the one-kidney, one-clip technique was performed on the WHHL rabbits at 3 months of age. At 3 and 6 months after surgery, the right and left coronary arteries and the left ventricle and posterior papillary muscle from normotensive and hypertensive animals were assessed. Atherosclerotic involvement was found at the coronary origin in 94% of the arteries evaluated. Lesions were usually confined to the proximal 1-2 mm of the coronary artery. The prevalence of coronary atherosclerosis in the WHHL rabbit was found to be higher than previously reported in rabbits of the same age. Hypertension-induced muscular and vascular changes such as left ventricular hypertrophy, medial thickening of the arteries, and hyaline arteriolosclerosis were found in most of the hypertensive animals. These changes were rarely seen in the normotensive rabbits. Characteristics of ischemia and cell injury such as eosinophilic fibers, fiber vacuolization, and contraction band necrosis were found more often in hypertensive than in normotensive WHHL rabbits. Confluent areas of severe necrosis indicative of myocardial infarction were not found; myocardial damage was diffuse and involved individual cells and small microscopic areas. This model may be valuable in further studies of coronary artery disease and myocardial injury that result from the combination of hypercholesterolemia and hypertension.

Drug-induced modification of vascular structure: effects of antihypertensive drugs

It has long been realized that hypertension causes alterations in the peripheral vasculature, with the arterial wall becoming thicker and the lumen relatively smaller. This is particularly true in small resistance arteries, but larger vessels are also affected. The precise mechanisms remain to be determined, although it is highly likely that growth-promoting autacoids are involved as well as mechanical forces. Numerous studies of hypertension in animal models and a few in hypertensive humans have tried to establish the reversibility of these changes after successful lowering of blood pressure. Too few data are available to form firm conclusions, but thiazides and hydralazine-like vasodilators appear to have only a minimal effect on the vasculature. On the other hand, angiotensin-converting enzyme inhibitors are clearly effective, and alpha-blockers may be active. However, it is difficult to derive even tentative conclusions from the available information on calcium antagonists and beta-blockers. These results are discussed in the context of future therapeutic and investigative approaches.

Remodeling of the rat right and left ventricles in experimental hypertension

Pathological left ventricular hypertrophy in renovascular hypertension is associated with the accumulation of fibrillar collagen within the extracellular space and around intramyocardial coronary arteries. Even though the angiotensin converting enzyme inhibitor captopril was previously found to attenuate this interstitial and perivascular fibrosis, the relative importance of arterial and ventricular systolic pressures versus circulating angiotensin II (AII) and aldosterone (AL) in promoting hypertrophy and collagen accumulation in renovascular hypertension is uncertain. By drawing on the in-parallel arrangement of the right and left ventricles, with respect to their coronary circulation, and the in-series mechanical alignment of the ventricles, with a pressure-overloaded left and a normotensive right ventricle, this study sought to address this uncertainty. Three models of experimental hypertension, each having a different circulating AII and AL profile, were examined and compared with their controls: renovascular hypertension, where both AII and AL are increased; infrarenal aorta banding, where AII and AL are normal; and a chronic infusion of AL, where AII is suppressed or normal and AL is increased. In renovascular hypertension, as well as with AL, we found a significant rise in the interstitial collagen volume fraction and perivascular collagen area of the pressure-overloaded, hypertrophied left ventricle as well as the normotensive, nonhypertrophied right ventricle. This remodeling was not seen in either ventricle with infrarenal aorta banding despite comparable systemic hypertension and left ventricular hypertrophy. Thus, in experimental arterial hypertension in the rat, myocyte and nonmyocyte compartments of the myocardium are under separate controls: myocyte hypertrophy is most closely related to ventricular loading while circulating AII and AL, acting alone or in concert with other humoral factors, regulate the accumulation of collagen within the right and left ventricles.

Effect of static stretching on elastin production by porcine aortic smooth muscle cells

An in vitro model was developed to assay the effects of static stretching on soluble elastin (tropoelastin, TE) synthesis by porcine aorta smooth muscle cells (SMC). Culture dishes containing SMC adherent to the deformable bottoms were placed over hard convex templates. Stress was applied by placing a weight on the dish covers. Measurement of TE was accomplished by a specific ELISA assay. With this model we demonstrated reproducible stimulation of TE synthesis by stretched SMC. Significant results (161.4% of control; p = less than 0.003 by Student's t-test) were obtained by stretching passage 2 SMC for 3 days with a medium change after the first 18-24 hours, use of 5% newborn calf serum in cultures during stretching, and 50-g weight. DNA content in stretched cultures did not increase over control values. Thus, stretching alone did not cause hyperplasia or hyperploidy in these SMC and, in the absence of other vascular cell elements, was sufficient to increase production of this extracellular matrix protein. Transduction of mechanical force into elastin gene expression by SMC may contribute to the development of thickened arterial tunica media characteristic of hypertensive vessels.

STZ-induced diabetes in SHR and renovascular hypertensive rats: dissociation between changes in arterial pressure and vascular collagen synthesis

Streptozotocin (STZ)-induced diabetes depresses the rate of vascular collagen synthesis in the spontaneously hypertensive rat (SHR), but it also reduces arterial pressure (SAP) in this strain. We investigated this phenomenon further by comparing the SHR with the renovascular hypertensive (RVH) rat, because diabetes does not affect SAP in the latter model of hypertension. Renovascular hypertension was induced by clipping the left renal artery of Wistar-Kyoto (WKY) rats; sham-operated WKY were included as normotensive controls. Collagen synthesis of arterial tissue in vitro was quantified as prolyl hydroxylase activity and the rate of radioactive proline incorporation into collagen. Arterial collagen synthesis of nondiabetic SHR and RVH animals was elevated compared to that of the nonhypertensive WKY controls. STZ-induced diabetes (8 weeks) reduced SAP of SHR, but had no effect on SAP of either RVH or normotensive WKY rats. However, diabetes significantly depressed vascular collagen synthesis of both SHR and RVH rats, and, less consistently, of the WKY. The results strongly suggest that STZ-induced diabetes in SHR impairs arterial collagen synthesis independent of associated changes in arterial pressure.

Influence of antihypertensive treatment with budralazine on autoregulation of cerebral blood flow in spontaneously hypertensive rats

We studied the effect of chronic antihypertensive treatment with budralazine on the lower blood pressure limit of cerebral blood flow autoregulation using spontaneously hypertensive rats. Cerebral blood flow in the parietal cortex and caudate nucleus was measured to determine the lower limit using the hydrogen clearance method. The lower limit in both cerebral regions was significantly higher in 10 untreated spontaneously hypertensive rats than in 10 Wistar-Kyoto rats. The upward-shifted lower limit was restored to close to normal in the caudate nucleus and was partially restored in the parietal cortex of nine rats by 9 weeks of treatment with the high dose (50-68 mg/kg/day) of budralazine, which kept blood pressure constant at approximately normotension during the treatment period; the lower limit was slightly restored in both cerebral regions of seven rats by 4 weeks of treatment with the high dose. However, 9 weeks of treatment with the low dose (19-27 mg/kg/day) of budralazine, which produced moderate continuous hypotension in nine rats, did not apparently influence the lower limit. Our results suggest that long-term antihypertensive therapy with budralazine reduces the upward-shifted lower blood pressure limit of cerebral blood flow autoregulation toward normal and that the restoration induced by budralazine depends on the degree of blood pressure reduction as well as on the duration of the therapeutic period.

Effects of chronic hypertension and its reversal on arteries and arterioles

The reversibility of functional and structural microvascular alterations in chronic renal hypertension has not been established. Twelve weeks after surgery to induce hypertension, in vivo arteriolar and venular dimensions were measured in the cremaster muscle of rats with one-kidney, one-clip hypertension (1K1C), rats in which the clip was removed after 8 weeks (1KNT), and controls. Systolic blood pressure was significantly elevated after 3 days in 1K1C rats and reached a plateau by 6 weeks. In 1KNT rats, systolic blood pressures were similar to 1K1C rats but were normalized 1 day after unclipping. A marked medial-intimal hypertrophy was found by histological techniques in the thoracic and abdominal aortae (45% and 69%, respectively) but not in cremaster feeding arteries of 1K1C rats. These arterial changes were reversed after unclipping. In 1K1C rats, medial-intimal area decreased in first- through fourth-order (1A, 2A, 3A, and 4A) arterioles along with a decline in relaxed diameter (41%, 30%, 20%, and 21%, respectively), which was only partially restored after unclipping. Heart weight was increased by 67% in 1K1C rats, but it did not differ between 1KNT and controls. Therefore, the reversal of chronic renal hypertension can normalize gross structural alterations in the heart and large vessels, but more time may be required to normalize completely the arteriolar changes. These data indicate that long-term structural adaptations in renal hypertension are different in arterioles and arteries, and they may be related to chronic changes in blood flow and/or pressure.

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.

Effects of hypertension and its reversal on canine arterial wall properties

Segments of carotid, femoral, saphenous, and left circumflex coronary arteries were obtained from control, renal hypertensive, and nephrectomized hypertensive dogs for in vitro study of mechanical properties. Hypertension was produced in two-kidney dogs by unilateral renal artery constriction. After 3 months, the compromised kidney was removed in half of the dogs. Mean arterial pressure was significantly elevated in the hypertensive dogs after 3 months (127 +/- 2 vs 94 +/- 1 mm Hg for controls) and partially returned toward normal 3 months after nephrectomy (105 +/- 2 mm Hg). Pressure-diameter relations were determined under conditions of maximum active and passive smooth muscle activation. Contiguous segments were used for the determination of water and connective tissue content. Hypertension was associated with increased passive arterial wall stiffness at most sites, with a partial return toward normal after nephrectomy. Maximum responses to smooth muscle activation (active stress and constriction response) were augmented in arteries from hypertensive dogs and partially returned toward normal in the nephrectomized hypertensive group. The elastin content of these arteries was unchanged, while collagen content was nonuniformly decreased in renal hypertensive dogs. Small decreases were found in the radius-wall thickness ratio of some arteries. No significant mechanical changes occurred in the saphenous artery. The largest hypertension-related changes were found in the coronary arteries, which also exhibited the smallest recovery toward normal properties after nephrectomy. Considerable regional variability of changes in arterial wall in renal hypertensive and nephrectomized hypertensive dogs was found. Incomplete resolution of the hypertension and arterial wall changes by nephrectomy was found in this animal model.

The arterial smooth muscle cell in systemic hypertension

Both the pathogenesis and vascular complications of hypertension appear to involve change in vascular smooth muscle cell (SMC) structure and function. Recent data on vascular SMC biology are reviewed. Specific questions that should be addressed by future research on SMC polyploidy in hypertension; SMC differentiation, growth and function; SMC hypertrophy and hyperplasia in hypertension; and hypertension, vascular aging and atherogenesis are posed.

Inhibition of nuclear polyploidy by propranolol in aortic smooth muscle cells of hypertensive rats

The ability of propranolol to inhibit the development of polyploidy in aortic vascular smooth muscle cells associated with hypertension was studied in deoxycorticosterone (DOC)-salt treated rats. Six-week treatment with DOC-salt resulted in significant increases in systolic blood pressure, heart weight, and aortic weight in treated animals compared to increases in uninephrectomized controls. Additionally, the percentage of tetraploid nuclei in aortic smooth muscle cells increased to 17.0 +/- 0.2% in DOC-salt treated rats versus 7.8 +/- 0.3% in normotensive controls. Administration of propranolol (500 mg/L in drinking water) did not inhibit the development of hypertension for up to 4 weeks or the associated increase in cardiac or aortic weight in DOC-salt-treated rats, but did prevent the increase in polyploidy of aortic smooth muscle cell nuclei (8.9 +/- 0.9% in propranolol-treated rats compared to 7.8 +/- 0.3% in normotensive controls). These results indicate that propranolol inhibits the development of hypertension-induced polyploidy in aortic smooth muscle cells of DOC-salt-treated rats and that factors other than blood pressure may be important in this change.

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)

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

The rate of DNA synthesis was determined in rats with developing and established two-kidney, one clip renal hypertension. Rate of DNA synthesis was measured as [3H]thymidine incorporation into DNA per hour. After stenosis of the renal artery, blood pressure increased over a 2-week period. Five days after clipping, there was an increase in the rate of aortic DNA synthesis before an increase in blood pressure was detected, whereas there was no DNA effect in sham-operated animals. This difference in [3H]thymidine incorporation into aortic DNA could not be accounted for by alterations in thymidine pool sizes. The increase in DNA synthesis was still present 3 weeks after renal artery stenosis, although by that time blood pressure had plateaued. The role of DNA synthesis in the development of renal hypertension was investigated by determining whether inhibition of DNA synthesis with cytosine arabinoside could prevent the increase in blood pressure. Treatment of clipped rats with cytosine arabinoside for 5 days delayed the increase in blood pressure for more than 4 days, as compared with the effect of saline treatment in clipped rats. Although the possibility remains that some effect of cytosine arabinoside other than its effect on DNA synthesis could have influenced blood pressure, there were no differences in body weight, food intake, water intake, or urine output between cytosine arabinoside-treated and saline-treated rats with renal artery clips, and cytosine arabinoside treatment had no effect on blood pressure or body weight in normal rats. These results suggest that an increase in DNA synthesis may be an obligatory step in the genesis of renal hypertension.

Replication of smooth muscle cells in vascular disease

Smooth muscle proliferation has been recognized as central to the pathology of both major forms of vascular disease: atherosclerosis and hypertension. Recent advances in our knowledge of mechanisms of control of proliferation suggest that events occurring in adult animals may recapitulate portions of the developmental biology of the smooth muscle cell. This review attempts to consider the current state of knowledge of the mechanisms controlling smooth muscle proliferation in these two diseases, to put that knowledge into the context of what is known about smooth muscle biology, and to offer two hypotheses on the possible roles of smooth muscle developmental biology in manifestations of atherosclerosis and hypertension in adult humans.

Relationship between the early arterial reaction to hypertension and the development of intimal proliferation

Malignant renal hypertension was induced in male Wistar rats. In the early phase of the disease, ie. the 1st week, a transient and generalized activation of arterial cellular functions was observed, while later, on day 21 widespread intimal proliferations developed in the arteries. This early activation included an increase in transmural permeability, DNA-, protein, collagen, elastin and ground substance synthesis, a rise in mural PGI2 content and an increase in number of Weibel-Palade bodies. An activation of platelets and monocytes could also be detected during the 1st week. In a group of rats the development of malignant hypertension was interrupted following the early activation of arteries and the incidence of intimal proliferations was compared with that of rats with maintained hypertension. No intimal proliferation was observed on day 21 in the rats with interrupted hypertension. It is concluded that the early activation of the artery does not furnish enough stimulus for triggering intimal proliferations and intimal plaques are not direct sequelae of the early arterial reaction. Furthermore the entrance of plasma materials during transmural permeability increase can not induce smooth muscle proliferation if the hypertension is interrupted.

Differential effects of antihypertensive drug therapy on vascular smooth muscle cell hypertrophy, hyperploidy, and hyperplasia in the spontaneously hypertensive rat

The present report extends our previous studies of smooth muscle cell hypertrophy, hyperploidy, and hyperplasia in the 5-month-old spontaneously hypertensive and Wistar-Kyoto rats to include analyses of 3- and 7-month-old rats and explores the effects of antihypertensive drug treatment on the accelerated growth of vascular smooth muscle in aortas of spontaneously hypertensive vs. Wistar-Kyoto rats. Drug-treated rats were administered a combination of reserpine, hydralazine, and chlorathiazide in their drinking water, either between 3 and 5 months or between 5 and 7 months of age. Drug treatment decreased the blood pressure of spontaneously hypertensive rats to values at or below those of Wistar-Kyoto rats for both age-treatment groups. Smooth muscle growth was evaluated by morphometric analyses of aortic smooth muscle content, flow cytometric and microdensitometric measurements of the frequency of polyploid smooth muscle cells, biochemical estimates of aortic medial smooth muscle cell number, and microdensitometric measurements of individual smooth muscle cell protein content. The following results were obtained. Aortic medial smooth muscle content was not significantly increased in 3-month spontaneously hypertensive compared to Wistar-Kyoto rats, indicating that aortic smooth muscle hypertrophy occurred post-3 months, as well as after blood pressure was elevated. In 5-month-old spontaneously hypertensive and Wistar-Kyoto rats, medial smooth muscle hypertrophy could be accounted for by cellular hypertrophy without hyperplasia; in contrast, medial hypertrophy in 7-month-old spontaneously hypertensive rats involved both cellular hypertrophy and hyperplasia. Antihypertensive treatment prevented the accelerated growth of vascular smooth muscle that occurred in spontaneously hypertensive rats via cellular hypertrophy and hyperploidy, but it did not prevent an increase in smooth muscle cell number in spontaneously hypertensive rats between 5 and 7 months of age. Furthermore, it had no effect on the parallel increases in aortic medial smooth muscle cell number that occurred in both spontaneously hypertensive and Wistar-Kyoto rats between 3 and 5 months of age. Whereas drug treatment prevented accelerated development of smooth muscle cell polyploidism in spontaneously hypertensive rats, in no case (spontaneously hypertensive or Wistar-Kyoto rats) did it reverse changes in ploidy that existed at the time of initiation of drug treatment, although it did cause cellular atrophy in smooth muscle cells of each ploidy class.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of alterations in cell phenotype and hypokalemia on sodium-potassium pump activity in rabbit vascular smooth muscle

We investigated in cell culture, how alterations in phenotype accompanying proliferation of rabbit aortic smooth muscle and chronic hypokalemia could affect the Na,K pump. Total rubidium-86 uptake as well as ouabain and frusemide-sensitive uptake into cells was measured in physiological salts solution (PSS), PSS containing 5% foetal calf serum and PSS containing foetal calf serum plus 15 microM monensin. In physiological salts solution 90% of the rubidium-86 uptake into contractile or synthetic state cells was frusemide-sensitive and less than 8% ouabain-sensitive. Total and frusemide-sensitive rubidium-86 uptakes, measured in PSS or PSS containing foetal calf serum were similar in cells cultured and maintained in the contractile phenotype, cells in the synthetic phenotype and those which had recently reverted from the synthetic to contractile phenotype. When cells were sodium loaded in the presence of monensin and foetal calf serum, ouabain-sensitive rubidium-86 uptake was 50% higher in cells which were maintained in culture in the contractile phenotype. Frusemide-sensitive rubidium-86 uptake was similar in each cell phenotype. To examine how cell culture in hypokalemic media would affect the Na,K pump, we determined ouabain-sensitive rubidium-86 uptake in the presence of monensin plus foetal calf serum in cells incubated for 24 hours in low and normal potassium containing culture media. Ouabain-sensitive uptake was 20% higher in cells cultured in a 0.76 mM potassium medium than in those cultured in 5.4 mM potassium medium. Frusemide-sensitive rubidium-86 uptake was unaffected. These results demonstrate that 'maximal' Na,K pump activity in sodium-loaded cells is reduced when cells change from the contractile to synthetic phenotype. This reduction appears only very slowly reversible when cells revert from the synthetic to contractile phenotype. Prolonged hypokalemia increases 'maximal' activity of the Na,K pump.

Recent advances in molecular pathology. The effects of hypertension on the arterial wall

Hypertension is a major risk factor for clinically significant atherosclerotic vascular disease in Western Society, although the link between these conditions remains very poorly understood. Recent studies which are reviewed here have demonstrated that major arterial intimal and medial abnormalities occur as a result of hypertension. These include functional changes in endothelial permeability as well as alterations in the endothelial cells themselves with an increase in their turnover and number and distinct changes in morphology. However, endothelial cell loss leading to denudation of the arterial intimal surface appears to be relatively uncommon. Intimal and medial thickening are consistent features of hypertension and result from increases in both cellular and extracellular components. The cells accumulating in the subendothelial space appear to be of both blood-borne and medial origins, although their complete characterization has not been performed as yet. The adherence of blood cells to the endothelial surface appears to be promoted by the presence of hypertension along with their increased entry into the intima through endothelial cell junctions. Medial thickening with hypertension is attributable primarily to increased smooth muscle cell mass, although enhanced deposition of collagen and elastin plays a contributory role. Recent data would indicate that smooth muscle cell hypertrophy rather than hyperplasia is primarily responsible for the greater smooth muscle mass with hypertension. Although elevated DNA content of hypertensive arteries has been demonstrated, such changes may be secondary to a marked increase in cells showing nuclear polyploidy. Prolonged normalization of blood pressure in hypertensive animals can produce considerable regression of arterial changes toward the control state. The changes appear more marked with respect to the cellular rather than the extracellular abnormalities induced by hypertension. In man, little is known about the effects of antihypertensive therapy on the vasculature itself, although clinical complications related to both hemorrhagic or thrombotic strokes are clearly reduced by blood pressure reduction. On the other hand, the influence of treatment on the atherosclerotic process or on the course of coronary artery disease and its complications is not currently understood. The accelerating effect of hypertension on atherosclerosis generally requires a critical level of circulating lipoproteins. Enhanced atherosclerosis is not observed in hypertensive animals without hyperlipoproteinemia or in human subjects with low lipoprotein concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Hemodynamic modification of aortic atherosclerosis. Effects of propranolol vs hydralazine in hypertensive hyperlipidemic rabbits

According to hemodynamic theories of atherogenesis, atherosclerotic plaques are a reaction to endothelial damage caused by arterial flow disturbances such as turbulence. Earlier studies showed that hydralazine increased, whereas propranolol decreased, the product of heart rate X blood velocity, a predictor of arterial flow disturbances, and that hydralazine aggravated, whereas propranolol decreased turbulence in the region of carotid artery stenosis. This study was done to test the hypothesis that drugs which reduce arterial flow disturbances may be more effective in preventing atherosclerosis, than antihypertensive drugs which worsen arterial flow disturbances. Eighty-three New Zealand white rabbits were made hypertensive by a one-kidney Goldblatt procedure, and were fed a 1% cholesterol diet. Untreated hypertensive (P less than 0.01) and hydralazine-treated hypertensive rabbits (P less than 0.05) had significantly more atherosclerosis than did the normotensive controls; propranolol-treated rabbits did not differ significantly from the normotensive controls. Analysis of covariance showed that propranolol-treated rabbits had significantly less atherosclerosis than hydralazine-treated rabbits with blood pressure (P less than 0.04) or heart rate (P less than 0.006) as the covariates.

Cellular proliferation in atherosclerosis and hypertension

We have tried to compare the proliferative responses seen in two vascular diseases: atherosclerosis and hypertension. Both diseases involve endothelial injury and proliferation, but our knowledge of this phenomenon is just beginning to emerge. In atherosclerosis the best evidence is that denudation does not occur in the normal young animal. Man, however, ages over a much longer time than our usual animal models, and the study of denudation during the chronic progression of atherosclerotic lesions remains to be done. We need to consider the possibility that repetitive, small lesions may occur at sites of endothelial turnover. We also need to know more about the possible role of nondenuding injuries, including death of endothelial cells in situ and the apparent increased stickiness of endothelial cells and monocytes during the early stages of hypercholesterolemia. The role of endothelial injury in hypertension also needs more study. We know that extensive denudation and thrombosis occur in small vessels subjected to high blood pressure. It is highly probable that release of PDGF occurs at these sites, possibly accounting for the characteristic hyperplasia seen in malignant hypertension. Whether this process is related to the more subtle changes in vessel wall mass seen in chronic hypertension remains unknown. Finally, there are remarkable differences in the proliferative behavior of the smooth muscle cells themselves in these two diseases. Hypertensive vascular disease is, in large part, a disease of the media. Atherosclerosis is characterized by intimal hyperplasia. Injury results in migration of smooth muscle cells from the media and cell division in the intima. It is possible to identify chemotactic factors using putative atherosclerosis risk factors or normal components of serum. This has already been done for one component of lesion formation, PDGF, and there is a report of a monocyte chemotactic factor released by smooth muscle cells. Factors released by other components of lesions may be of considerable interest. In contrast, changes in hypertension occur within a more orderly preservation of vessel wall structure. The wall thickens, but this occurs by increased synthesis of cell mass in the media. The cells themselves do not even divide, but they undergo a form of amitotic replication of their DNA.(ABSTRACT TRUNCATED AT 400 WORDS)

Vascular smooth muscle cell hypertrophy and hyperploidy in the Goldblatt hypertensive rat

Our major objective in this study was to examine the hypothesis that the aortic smooth muscle cell hypertrophy and hyperploidy observed in previous studies of spontaneously hypertensive rats is not peculiar to that model, but also occurs in Sprague-Dawley rats made hypertensive by a Goldblatt procedure (two-kidney, one-clip model). Flow microfluorometric and microdensitometric analysis of smooth muscle cell DNA content showed a significant increase in the frequency of tetraploid smooth muscle cells from 5.6 +/- 0.9% in controls to 14.6 +/- 1.94% in hypertensives 1 month after Goldblatt surgery. Neither differences in ploidy nor elevation in blood pressure were apparent 2 weeks after surgery. The frequency of polyploid smooth muscle cells increased with age, duration of hypertension, and level of blood pressure. Analysis of the interrelationship between smooth muscle cell ploidy and hypertrophy in 5-month post-surgery Goldblatts by cytospectrophotometric measurements of the protein and DNA content of individual smooth muscle cells showed that tetraploid and octaploid cells from Goldblatt rats had 64% and 129% greater protein mass, respectively, than diploid cells. In addition, the mean protein mass of smooth muscle cells from Goldblatts was approximately 100% greater than that of normotensive controls, with each of the ploidy classes in Goldblatts having a higher frequency and mass than the corresponding cells in controls. Estimates of cell number per centimeter aortic length, based on measurements of average DNA/cell and total aortic medial DNA, showed no difference between hypertensives and controls. Furthermore, the rate of accumulation of polyploid cells could account for the increased frequency of cells undergoing DNA synthesis as measured by [3H]thymidine autoradiography. Thus, smooth muscle cell hypertrophy, not hyperplasia, was responsible for the increased mass of smooth muscle in aortas of Goldblatt hypertensive rats compared with normotensive controls, and this smooth muscle cell hypertrophy was accompanied by an increase in DNA ploidy.

Vascular structural changes in the artery wall of unilateral nephrectomized rats

Wet and dry weight, concentration and total amount of nucleic acids and proteins, and incorporation of tritiated thymidine were measured in the arteries of rats after 7 and 15 days of unilateral nephrectomy, sham operation and in control animals. Arteries of uninephrectomized rats showed increased wet and dry weight, increased DNA and protein content after 7 and 15 days and a higher rate of tritiated thymidine uptake after the first week. These results suggest an early proliferative process in the arteries of unilateral nephrectomized rats.

Alterations in vascular smooth muscle mass in the spontaneously hypertensive rat. Role of cellular hypertrophy, hyperploidy, and hyperplasia

In a previous brief report we demonstrated that differences in aortic smooth muscle mass between spontaneously hypertensive and Wistar-Kyoto rats were due to smooth muscle cell hypertrophy, without hyperplasia. Smooth muscle cell hypertrophy, however, was accompanied by an increase in the frequency of polyploid cells. This study reports (1) the relationship between changes in smooth muscle cell mass and DNA ploidy, (2) the proportion of the increase in mass of smooth muscle in spontaneously hypertensive rats that can be accounted for by polyploid cells, and (3) the time-course of changes in ploidy during the development of hypertension. Flow microfluorimetric and Feulgen-DNA microspectrophotometric measurements demonstrated that the frequency of polyploid smooth muscle cells was 2-3 times greater in spontaneously hypertensive rats than in Wistar-Kyoto rats at 3 months of age and older. The frequency of polyploid cells increased with age and level of blood pressure. No differences in the frequency of polyploid cells were apparent between prehypertensive 1-month spontaneously hypertensive and Wistar-Kyoto rats. By cytospectrophotometric analysis, spontaneously hypertensive rat diploid, tetraploid, and octaploid smooth muscle cells had 36%, 136%, and 377%, respectively, the protein content of Wistar-Kyoto rat diploid cells. The increase in mean cellular protein (53% by cystospectrophotometry) in spontaneously hypertensive rats could account for the total increase (56%) in aortic smooth muscle mass, measured by morphometry. Thus, smooth muscle cell hypertrophy alone can account for the increased mass of smooth muscle in spontaneously hypertensive rat aortas, while the majority of change in smooth muscle mass is due to the increased frequency and mass of polyploid cells.