Kinetics of proliferation of rat aortic smooth muscle cells in Goldblatt one-kidney, one-clip hypertension

Evidence for in vivo carotid and femoral wall thickening in human hypertension. Groupe de Prévention Cardio-vasculaire en Médecine du Travail

Little is known of the in vivo structural changes of large arteries in uncomplicated hypertension. Therefore, we measured the intima-media thickness and lumen diameter of common carotid and femoral arteries by a computerized ultrasonographic technique in 25 normotensive and 25 never treated hypertensive men of similar age (from 25 to 72 years). The intraobserver variability of carotid and femoral wall thicknesses was 4.3% and 5.6%, respectively. Moreover, an in vitro study of 13 human arterial segments removed at autopsy demonstrated a strong correlation (r = .989, P < .001) between computerized ultrasonic and histological intima-media thickness measurements. Compared with control subjects, hypertensive patients had similar arterial diameters but higher carotid and femoral intima-media thicknesses (P < .001) as well as higher ratios of carotid and femoral intima-media thickness to lumen (P < .001, P < .01). The carotid thickness was correlated with age in control subjects (r = .48, P < .05) but not in hypertensive patients. The femoral thickness was correlated with age both in control subjects (r = .55, P < .01) and in hypertensive patients (r = .46, P < .05). Thus, carotid and femoral arterial walls of hypertensive patients were thickened. This thickening was not due to age, although aging also thickened both vessels in control subjects and the femoral artery only in hypertensive patients. Such a wall thickening associated with a normal diameter provides direct evidence of vascular growth and represents a new target to monitor noninvasively in vivo for large artery changes in human hypertension.

Hypertension, plasma lipids and antihypertensive drugs

Treatment of hypertension is quite effective in preventing cerebrovascular disease. Morbidity and mortality from coronary heart disease, the major complications of high blood pressure are not, however, generally affected when mild to moderate hypertension is treated with antihypertensive drugs. This is probably owing to the multifactorial nature of atherosclerosis, the main cause of coronary heart disease. For example, dyslipidemias and other risk factors are very common among hypertensive patients. Prevention of coronary heart disease among hypertensive subjects is possible only by intervening in the many contributory risks. Non-pharmacological hypolipidemic treatments such as adequate nutrition and exercise are positive steps in the treatment of all hypertensive patients. The role of various antihypertensive agents should also be carefully considered. The associations between hypertension, several metabolic abnormalities, development of organ complications and various antihypertensive drugs should be explored in detail.

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.

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.

Angiotensin II-induced contraction of mesangial cells in acute renal artery stenosis in dogs

1. Renal artery stenosis was induced in anaesthetized dogs, and the kidney rapidly fixed after 30 min. 2. Electron microscopy revealed marked folding of the paramesangial basement membrane in stenotic kidneys (n = 7). The extent of this folding was significantly less in dogs treated with captopril (n = 6). 3. It is suggested that this folding reflects angiotensin II-induced contraction of the mesangial cells, which may help maintain glomerular filtration rate following stenosis.

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.

Arterial metabolism as studied in vitro by NMR: preliminary results in normotensive and hypertensive aortas

Arterial tissue has been analysed by 31P-, 13C-, 23Na- and 1H-NMR spectroscopy. Rabbit thoracic aortas were mounted on a system with perfusate circulation and studied in basal conditions. Phosphorus spectra remained stable for hours and showed low levels of phosphocreatine (PCr) compared to skeletal, cardiac or even to nonvascular smooth muscle. Significant levels of sugar-phosphates (SP), phosphodiesters (PDE) were detected, as well as occasionnally a peak in the diphosphodiester region. Experiments with phosphate-free perfusate demonstrated a very low level of intracellular inorganic phosphate. As expected from previous data, free ADP levels in tonic arterial tissue were found much higher than in any other muscle. Addition of norepinephrine into the perfusate induced transient decrease in ATP and PCr levels, associated with an increased production of phosphorylated intermediates. At the early stage of renovascular hypertension, aortic energetic pattern was characterized by an increased ADP/ATP ratio. Natural abundant 13C spectra were recorded from dog aortic fragments and showed mainly resonances attributed to fatty components. After addition of a shift-reagent, dysprosium tripolyphosphate, 23Na-NMR allowed separation of intra- and extracellular Na of perfused rabbits aortas. Proton NMR of lyophilized aortic fragments revealed several peaks originating from biologically relevant molecules, lactate, creatine, taurine... These preliminary data demonstrate the feasability of multinuclear NMR spectroscopy of vascular tissue and are suggestive of the potential of the method when it will be combined with monitoring of functional parameters.

Changes in blood pressure, heart rate and blood constituents during heat exposure in men with elevated blood pressure

Although the vascular volume response of hypertensive men during exercise has been rather well characterized, the effect of resting heat exposure in this patient population has not been examined. This was done in the present report in seven men with high blood pressure (BP) (i.e., diastolic pressure greater than 12 kPa (90 mmHg) upon initial interview) and 5 normotensive control subjects. 50 min after each subject had consumed an amount of water equal to 1% of his body weight, he reclined on a cot. 10 min later the subject was carried into an environmental chamber equilibrated at Tdb = 45 degrees C, Twb = 28 degrees C. Free-flowing venous blood samples were obtained from a cubital vein, and BP and heart rate were measured, before the heat exposure and at 15 min intervals during the experiment. Within 30 min systolic, diastolic and mean BP of the high BP subjects had decreased to normal levels; no BP changes were detected in normotensive subjects. Accompanying this depressor response was an exaggerated elevation in plasma glucose concentration. No alterations were found with haematocrit, plasma osmolality or electrolytes, or total protein and albumin. The data suggest that heat exposure may have been more stressful for the subjects with high BP than for their controls. This finding implies that phasic depressor responses may be as important as phasic pressor episodes in the aetiology of established essential hypertension.

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.