Hypertension and the arterial system: clinical and therapeutic aspects

There is very clear evidence that active changes in the arterial wall contribute substantially to the pathophysiology, prognosis and treatment of hypertension. Reduced aortic compliance independently affects the blood pressure through an increase in systolic pressure and a decrease in diastolic pressure at any given mean arterial pressure. With the subsequent increase in pulse pressure, arterial abnormalities may specifically influence cardiac morbidity and mortality, in particular by triggering coronary ischemic accidents. The pathophysiological and epidemiological results of these mechanisms clearly indicate that a severe decrease in diastolic blood pressure might precede some hypertensive coronary ischemic accidents.

[Current physiopathological concerns in arterial hypertension]

The changes of the cardiovascular system observed in hypertension are, on the one hand, functional (neurohumoral), and on the other hand, structural (cardiac and vascular hypertrophy). They affect the whole of the cardiovascular system (heart, arteries, arterioles, veins). Clinical studies using non-invasive methods suggest a close interaction between the heart and large arteries, independent of the degree of peripheral arteriolar constriction. Our understanding of the value of the mean arterial pressure which may damage target organs has been improved by automatic ambulatory blood pressure recordings over the 24 hour period. Finally, recent technological developments based on sophisticated computer systems have contributed to our appreciation of parameters of arterial distensibility, so giving a better understanding of arterial physiopathology in hypertension and helping orientate the choice of therapeutic strategy.

Influence of diuretics on brachial artery diameter and distensibility in hypertensive patients

Blood pressure, brachial artery diameter and pulse wave velocity were determined before and after diuretic treatment in 2 groups of hypertensive patients treated either by indapamide (2.5 mg per d) or by canreonate (50 mg per d). Brachial artery diameter, measured from pulsed Doppler flowmetry, and pulse wave velocity, evaluated from mechanography, did not alter significantly despite a significant blood pressure reduction. The study indicates that, in hypertensive patients of middle age, diuretics did not change brachial artery diameter and distensibility, whether the drug caused an increase or a decrease in plasma potassium levels.

Intra-articular and subcutaneous prilocaine with adrenaline for pain relief in day case arthroscopy of the knee joint

A randomised, double-blind study was conducted to assess the influence of intra-articular and subcutaneous prilocaine with adrenaline on postoperative pain in day case arthroscopy of the knee. The time to first dose of oral analgesia postoperatively was significantly prolonged in those patients receiving prilocaine but no significant difference in analgesic effect was demonstrated at 4, 8, and 12 h after operation between the two groups.

Growth and growth hormone therapy in hypochondroplasia

The growth of 84 patients with hypochondroplasia (56 male, 28 female) was studied. A wide spectrum of severity was found from quite severe short limbed dwarfism to short apparently normal prepubertal children who manifested disproportion only at puberty when growth failed. The onset of puberty was at the normal time but the pubertal growth spurt appeared not to materialize and it is this lack which resulted in severely compromised adult heights of 145-165 cm in boys and 133-151 cm in girls. Twenty (12 M, 8 F) hypochondroplastic children aged between 4.3 and 12.8 years were recruited to a study of the effects of biosynthetic growth hormone. All had normal growth hormone responses (greater than 15 mU/l) to a pharmacological test of growth hormone secretion. Biosynthetic growth hormone in doses between 12-32 mu/m2/week produced a significant acceleration in height velocity standard deviation score (SDS) for chronological age (CA) from a pretreatment mean of -1.66 (SD 1.36) to +1.62 (SD 1.52) (p less than 0.001). Significant increases were also observed in the height SDS for bone age (BA), sitting height (SH) SDS and subischial leg length (SILL) SDS. A longer period will be required to assess the effect of treatment on adult height prognosis.

Intrachromosomal recombination mediated by papovavirus large T antigens

To investigate the mechanism by which the large T antigen (T-Ag) of polyomavirus and simian virus 40 can promote recombination in mammalian cells, we analyzed homologous recombination events occurring between two defective copies of the polyomavirus middle T (pmt) oncogene lying in close proximity on the same chromosome in a rat cell line. Reconstitution of a functional pmt gene by spontaneous recombination occurred at a rate of about 2 x 10(-7) per cell generation. Introduction of the polyomavirus large T (plt) oncogene into the cell line by DNA transfection promoted recombination very efficiently, with rates in the range of 10(-1) to 10(-2) per cell generation. Recombination was independent of any amplification of viral sequences and could even be promoted by the large T-Ag from simian virus 40, which cannot activate polyomavirus DNA replication. To explain the role of large T-Ag, we propose a novel mechanism of nonconservative recombination involving slipped-strand mispairing between the two viral repeats followed by gap repair synthesis.

Autonomic Nervous System and Brachial Artery Diameter in Normotensive and Hypertensive Patients

Studies using pulsed-Doppler velocimetry reveal that in the absence of changes in blood pressure and heart rate, the human brachial artery dilates on raising the legs from the supine position. The dilatation cannot be explained exclusively by the increase in blood flow and probably involves a reflex from stimulation of cardiopulmonary receptors.

Flow-dependent vasodilation of brachial artery in essential hypertension

Brachial artery hemodynamics including brachial artery diameter (D) and local blood flow velocity (V) was studied in 15 normotensive subjects (NT) and 19 age-matched hypertensive patients (HT) at rest using a bidimensional pulsed Doppler system during a 2-min period of distal circulatory occlusion and during reactive hyperemia. Kinetics of changes in V and D were determined during successive and reproducible maneuvers. V and D decreased significantly during distal circulatory occlusion in both groups. During reactive hyperemia, V reached similar maximum values in both groups, and D increased significantly in NT and HT. Changes in D during reactive hyperemia were positively and significantly correlated with changes in V recorded at the same level. No significant difference was found between the two groups. These results demonstrate noninvasively that there are velocity-dependent variations in the diameter of a large artery in humans and suggest that velocity-dependent vasodilation of the brachial artery is not impaired in essential hypertension.

[Methods for studying vasodilator agents in arterial hypertension]

The concept of vasodilatation has evolved with regards to the treatment of hypertension. Large multicentre trials have shown that decreasing mean arterial pressure alone does not reduce coronary morbidity and mortality related to hypertension. The authors suggest that the haemodynamic abnormalities related to hypertensive disease were not totally reversed by the antihypertensive agents used in these trials. Regression of structural arterial changes, regression of LVH without altering systolic function, reduction of the variability of blood pressure and maintenance of regional blood flow should all be objectives of any antihypertensive vasodilator therapy. Methods of studying vasodilators are described and the effects of the main classes of antihypertensive drugs on these parameters are analysed.

Brachial artery diameter changes associated with cardiopulmonary baroreflex activation in humans

Stimulation of receptors in the cardiopulmonary compartment produces a vasodilatation of forearm resistive vessels. A possible participation of large conduit arteries in such adjustments, studied in situ, has not been clearly documented in humans. We used a dual-crystal pulsed Doppler system to determine whether leg elevation in recumbent subjects is associated with changes in brachial artery diameter (BAD) and blood velocity (BV) in humans. BA diameter, velocity, and flow, together with arterial pressure and heart rate, were measured in 20 normal subjects in supine position and after passive leg raising. BAD increased immediately after leg elevation from 4.03 +/- 0.11 to 4.56 +/- 0.13 mm (P less than 0.001) parallel with an increase in BV from 6.05 +/- 1.18 to 7.1 +/- 1.36 cm/s (P less than 0.02). A positive correlation between BAD enlargement and BV increase was observed during the initial peak response (P less than 0.01). Subsequent measures indicated that BAD remained enlarged throughout the whole period of leg raising, whereas BV returned to the base-line values. Brachial artery volumic flow augmented during the initial phase of leg raising from 46 +/- 8 to 74 +/- 15.5 ml/min (P less than 0.01) and remained elevated throughout the whole period of leg elevation. This study shows that arteries participate in hemodynamic adjustments induced by positional changes associated with cardiopulmonary baroreflex activation.

[Influence of the autonomic nervous system on the diameter and compliance of the brachial artery in normotensive subjects and hypertensive patients]

Studies based on non-invasive methods, using a pulsed Doppler flowmeter technique, show that, in hypertensive patients, the brachial artery reacts actively to posture changes and to a norepinephrin perfusion: in the latter situation, there is an abnormal constriction, and its vasodilation is more marked when the lower extremities are raised in a patient in decubitus. These modifications occur in the absence of any significant variation of the blood pressure and the heart rate, and the high output resulting from the vasodilation is not sufficient to explain these changes. According to the authors, the brachial artery reacts actively to alterations of the autonomous nervous system. Variation observed following elevation of the lower extremities would probably result from the stimulation of the mechanical receptors of a low pressure system.

Effects of twenty-four hours of bed rest with head-down tilt on cardiopulmonary baroreflex control: preliminary study

The cardiopulmonary baroreflex response was studied before and after 24 h bed rest with head-down tilt (-5 degrees) in six normal male subjects, through lower body negative pressure (-5, -10, -15 mmHg) and passive leg raising. The reflex response was assessed (using plethysmography) by changes in forearm vascular resistance. During the lower body negative pressure and leg raising, forearm vasoconstriction and vasodilation were similar before and after head-down tilt. The study shows that orthostatic intolerance following head-down tilt is not explained by an abnormality in the response of low pressure baroreceptors.

Endothelin has potent direct inotropic and chronotropic effects in cultured heart cells

To determine whether endothelin, a highly potent vasoconstrictor peptide, may affect cardiac myocyte contractility directly, we studied the effects of synthetic porcine endothelin-1 in cultured chick embryo ventricular cells. Endothelin-1 had a potent chronotropic effect (EC50 0.17 nmol/l) in spontaneously beating cells. The increase in the beating rate was accompanied by a frequency-dependent decrease in the amplitude of contraction. In electrically driven cells (1 Hz), endothelin-1 increased the amplitude of contraction dose-dependently, with an EC50 of 0.3 nmol/l, smaller than that of the calcium channel blocker BAY K 8644 (EC50 3.3 nmol/l), and with an efficacy close to that of BAY K 8644 and isoproterenol. Nicardipine (100 nmol/l) shifted to the right, by two orders of magnitude, the dose-response curve of endothelin-1 for inotropism. These results indicate that endothelin-1 is one of the most potent inotropic agents in cultured cardiac myocytes, and suggest that this effect involves, at least in part, a calcium ion influx through voltage-sensitive calcium channels.

Large and small forearm arteries of essential hypertensives are less reactive to angiotensin II than to noradrenaline

In order to investigate the reactivity to angiotensin II (Ang II) in large and small arteries in situ, brachial artery diameter, blood flow velocity, local volumic blood flow and local vascular resistance (mean arterial pressure divided by local blood flow) were determined non-invasively, using a pulsed Doppler system. Increasing doses of Ang II (0.5, 1.0 and 2.0 ng/kg per min) were given intravenously and double-blind to nine normotensive subjects (group I) and 10 hypertensive patients (group III); placebo (glucose) was given to nine hypertensives (group II). Angiotensin II did not change the brachial artery diameter, blood flow velocity, local blood flow or local resistance. Mean arterial pressure was increased slightly but significantly (P less than 0.05) by Ang II at 2 ng/kg per min in groups I and III. In contrast, we had shown previously, following the same procedure, that subthreshold doses (for the increase in mean arterial pressure) of noradrenaline reduced branchial artery diameter, velocity and local blood flow and increased local resistance in hypertensives. These results indicate that in hypertensives the vascular reactivity of the brachial circulation (1) is lower than that of other territories in response to Ang II and (2) is lower in response to Ang II than in response to noradrenaline.

Central cardiovascular effects of dihydropyridines in spontaneously hypertensive rats

Intracerebroventricular (i.c.v.) injections of dihydropyridine derivatives calcium channel agonist (BAY K8644) and antagonist (nifedipine, nicardipine, PN 200-110) induced opposite long-lasting changes in blood pressure (BP) in pentobarbital anesthetized spontaneously hypertensive rats (SMR). I.c.v. nifedipine (NIF), nicardipine (NIC), and PN 200-110 decreased mean blood pressure dose-dependently and stereoselectively, (+) NIC and (+) PN being 8 and 3 times more potent than their (-) isomers, respectively. The decrease in BP was due to a withdrawal of the sympathetic tone, since NIF- and NIC-induced falls in BP were suppressed after either hexamethonium (HXM), 6 OHDA or bilateral adrenalectomy. I.c.v. BAY K8644 increased BP dose-dependently. The i.c.v. BAY K8644-induced hypertensive effect was inhibited: a), by NIF and (+) PN but not by (-) PN, therefore probably occurring at central DHP sites; b), by HXM and reserpine, thus probably mediated by an increase in sympathetic tone; c) by i.c.v. methylatropine (MA) while i.v. MA and i.c.v. HXM had no inhibitory effect, thus probably involving central muscarinic sites. In SHR, NIC did not after the K(+)-evoked ACh release but suppressed the BAY K8644-induced increase in ACh release. In anesthetized normotensive control rats (WKY), neither i.c.v. NIF, NIC or BAY increased BP and HR while, in conscious SHR it decreased BP without any change in HR. These data increased BP and HR while, in conscious SHR it decreased BP without any change in HR. These data suggest that central DHP sites may be involved in the cholinergic transmission and may participate in genetic hypertension via sympathetic tone.

Cardiopulmonary baroreflex control of brachial artery diameter in sustained essential hypertension

An exaggerated reflex response of forearm resistance vessels following stimulation of cardiac mechanoreceptors has been observed in human hypertension. In the present study we analyze the possibility that such an increased response also involves the large brachial artery. For that purpose, the influence of leg elevation in subjects in a supine position on brachial artery diameter and blood flow velocity was studied in 12 healthy, normal males and 17 males of the same age with sustained essential hypertension. Brachial artery diameter and blood flow velocity were measured using a two-dimensional pulsed Doppler velocimeter, with subjects in a supine horizontal position, after passive elevation of the legs and again in a supine horizontal position. Blood pressure and heart rate remained unchanged throughout the study. Elevation of the legs induced an immediate increase in brachial artery diameter (P less than 0.001) and blood flow velocity (P less than 0.001) in both normal subjects and hypertensive patients. The maximal increase in these two parameters was similar in the two groups. In normal subjects, the increases were short-lived, with values returning to baseline levels even when leg elevation was maintained. In hypertensive patients, the increases persisted throughout the period of leg elevation, and brachial artery diameter remained significantly increased in comparison with normal subjects (P less than 0.01). This study provides evidence that loading cardiac mechanoreceptors causes a large dilation of the conduit arteries which is long-lasting in essential hypertensives and short-lived in normal subjects.

Nicardipine decreases blood pressure and heart rate at nucleus tractus solitarii of spontaneously hypertensive rats

The effects of the dihydropyridine (DHP) calcium channel antagonist, nicardipine, on central cardiovascular regulation were investigated by injecting it into the cisterna magna or directly into the nucleus tractus solitarii (NTS), in anesthetized normotensive or spontaneously hypertensive (SHR) rats. Intracisternal injections of nicardipine (1-10 micrograms/kg) dose-dependently decreased blood pressure in SHR; there was no significant change in cardiovascular parameters in normotensive rats. In SHR, nicardipine (100 ng) microinjected bilaterally into the NTS produced hypotension and bradycardia. The same doses of nicardipine intravenously injected did not change either parameter. Previous administration of the beta-adrenoceptor blocking drug, tertatolol (50 micrograms/kg i.v.), prevented the nicardipine-induced bradycardia and hypotension after injection into the NTS. These data suggest that part of the central cardiovascular effects of nicardipine result from an interaction with DHP sites within the NTS leading to a withdrawal of the sympathetic tone.

[Therapeutic response to canrenone of patients with essential hypertension as a function of sodium transport anomalies and ouabain sensitivity of erythrocytes]

The presence of Na+ transport abnormalities (decreased affinity of the Na+/K+ pump or the Na+, K+ cotransport for internal Na+, increased Na+:Li+ countertransport, increased Na+ leak), Na+ content, Na+/K+ pump activity and sensitivity to ouabain were investigated in erythrocytes from 13 patients with essential hypertension. According to the presence or absence of Na+ transport abnormalities, the patients were divided into two groups: TrNa(+) (n = 9) and TrNa(-) (n = 4) respectively. Compared with TrNa(-) patients, TrNa(+) patients were characterized by: (i) a higher arterial pressure (131.4 +/- 11.8 vs 110.0 +/- 13.2 mmHg, p less than 0.05), (ii) an increased erythrocyte Na+ content (8.9 +/- 1.0 vs 6.3 +/- 0.8 mmol/l.cells, p less than 0.01) associated with (iii) a decreased rate constant of Na+/K+ pump activity (235 +/- 26 vs 309 +/- 45 h-1, p less than 0.05) and (iv) a higher sensitivity to ouabain (0.76 +/- 0.23 vs 1.12 +/- 0.26 microM, p less than 0.05). Oral administration of canrenone 50 mg per day during 7 weeks decreased mean arterial pressure by 10-30 mmHg in 6 out of the 9 TrNa(+) patients. Conversely, it decreased mean arterial pressure in only one out of the 4 TrNa(-) patients. The hypotensive effect of canrenone in TrNa(+) patients was not associated with normalization of their Na+/K+ pump activity. Canrenone did not modify the sensitivity to ouabain of either the TrNa(+) or the TrNa(-) patients. Before treatment, acute injection of ouabain provoked an inhibition of the erythrocyte Na+/K+ pump, without any change in Na+ content.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction between isoproterenol and dihydropyridines in heart cells

The negative inotropic potencies (IC50) of the calcium channel blockers nicardipine (12 +/- 2 nM) and nifedipine (9 +/- 2 nM) measured in cultured chick embryo ventricular cells were not significantly different. Exposure of the cells to isoproterenol potentiated the negative inotropic effect of low concentrations of nicardipine (10(-9)-10(-8) M) and decreased the effect of higher concentrations (10(-7) M). In contrast, isoproterenol shifted the entire dose-response curve for nifedipine to the right. These results provide evidence that activation of beta-adrenoceptors modulates the negative inotropic effect of nifedipine and nicardipine differently.

[Anomalies in the hemodynamic response to short lasting emotional stress in essential hypertensive subjects]

Systemic hemodynamics, brachial artery diameter (D) and blood flow velocity (v) were determined non-invasively in 26 normotensive subjects (NT) and 34 age- and sex-matched essential hypertensive patients (HT) using pulsed Doppler systems (4 and 8 MHz), at rest and during 2 min periods of mental arithmetic (MA) inducing reproducible changes in blood pressure. During MA in HT, v increased (from 5.3 +/- 1.1 to 8.4 +/- 1.6 cm/sec) to a greater extent (p less than 0.01) than in NT (from 4.9 +/- 0.7 to 6.3 +/- 1.4 cm/sec). Hand exclusion did not change the increase in v in HT and in NT. During MA, D did not change in both groups. Systolic and diastolic arterial pressure increased to a greater extent (p less than 0.01) in HT than in NT, while HR and pulse pressure increased to the same extent in both groups. Since cardiac output and D did not change during MA, instantaneous variations of v likely reflected modulation of arteriolar tone. These results suggest an enhanced vasodilatory response of muscle resistance vessels in HT as compared to NT. The lack of change in D suggest an increase in vascular tone of large arteries likely contributing to the rise in pulse pressure during MA in both groups.

[Central modulation of the baroreflex response to phenylephrine in rats. Lack of interaction between calcium channel modulators and the renin-angiotensin system]

We have previously shown that a calcium channel activator (BAY K 8644) can decrease the baroreflex control of heart rate in SHR when intracerebroventricularly (i.c.v.) administered. In pentobarbital anesthetized SHR, the inhibitory effect of BAY (3 micrograms/kg i.c.v.) on baroreflex sensitivity (BRS; ramp method: phenylephrine 2 micrograms i.v.; BAY: 0.14 +/- 0.05 vs control: 0.39 +/- 0.08 msec/mmHg; p less than 0.01) was fully suppressed after pretreatment with the muscarinic antagonist atropine methylnitrate (80 micrograms/kg i.c.v.) suggesting the involvement of cholinergic pathways in the inhibitory effect. Since A II was reported to centrally increase arterial pressure through an enhanced release of acetylcholine and to depress BRS, we tested whether the effect of BAY on BRS could involve central A II systems. The A II antagonist [Sar 1Ile8] A II (30 micrograms/kg/min i.c.v.) suppressed the inhibitory effect of A II on BRS (control: 0.32 +/- 0.09; A II: 0.10 +/- 0.02; Sar1 Ile8 + A II: 0.39 +/- 0.08 msec/mmHg) but not the inhibitory effect of BAY (3 mu g/kg i.c.v.) on BRS. These results suggest that the central inhibition of BRS by BAY unlikely involves central A II systems.

Effects of dihydropyridine drugs on reversal by imipramine of helpless behavior in rats

The present study was undertaken in order to determine the effects of the dihydropyridine calcium channel blocker, nimodipine and the dihydropyridine calcium channel activator BAY k 8644, in the learned helplessness test in the rat. Nimodipine dose dependently (0.5-2 mg/kg per day) reversed the behavioral deficit induced by inescapable shocks. The reversal of helpless behavior by imipramine (32 mg/kg per day) was antagonized by BAY k 8644 (0.5 and 1 mg/kg per day), and the effects of imipramine 8 and 16 mg/kg per day) were potentiated by a subeffective dose (0.5 mg/kg per day) of nimodipine. These results suggest that central dihydropyridine binding sites may be specifically involved in the modulation of the imipramine reversal of helpless behavior and favor a physiological role for dihydropyridine binding sites in the brain.

Pulsatile diameter and elastic modulus of the aortic arch in essential hypertension: a noninvasive study

A noninvasive evaluation of the aortic arch diameter was performed in 16 subjects with sustained essential hypertension and in 15 normal subjects of similar age, gender and body surface area. In all subjects, measurements were obtained of brachial mean arterial pressure and pulse pressure, cardiac mass (judged on echocardiography) and carotid-femoral pulse wave velocity together with ultrasound determinations of aortic arch diastolic and systolic diameter (suprasternal window). For each subject, pulsatile change in aortic diameter, strain and aortic arch elastic modulus were calculated. Compared with normal subjects, the hypertensive subjects showed an increase in aortic arch diameter (diastolic diameter 29.6 +/- 1.0 versus 25.4 +/- 1.0 mm, p less than 0.01), in elastic modulus (1.071 +/- 0.131 versus 0.526 +/- 0.045 10(5) N.m-2, p less than 0.001) and pulse wave velocity (11.8 +/- 0.5 versus 8.9 +/- 0.3 m/s, p less than 0.001). In the study group, a positive correlation was observed between diastolic aortic arch diameter and mean arterial pressure (r = 0.54, p less than 0.01) and between elastic modulus and cardiac mass (r = 0.60, p less than 0.01). Elastic modulus and age were positively correlated (r = 0.73, p less than 0.01) in hypertensive but not in normal subjects (r = 0.08, NS). This study is the first to demonstrate noninvasively that both the aortic arch diameter and the elastic modulus are increased in patients with sustained uncomplicated essential hypertension. These findings suggest that the increase in elastic modulus could influence the development of cardiac hypertrophy, and that both age and blood pressure act independently as factors that alter the arterial wall of subjects with sustained essential hypertension.

Influence of the autonomic nervous system on brachial artery diameter and compliance in normotensive and hypertensive patients

Based on non-invasive studies using pulsed Doppler velocimetry, it appears that the brachial artery in hypertensive humans responds actively to positional changes and norepinephrine infusion, exhibiting an abnormal constriction following norepinephrine administration and an enhanced vasodilating response when raising the legs from supine position. Such modifications occur in the absence of significant change in blood pressure and heart rate and could not be explained exclusively on the basis of high flow dilatation. It is suggested that the hypertensive brachial artery responds actively to modifications of the autonomic nervous system. Changes observed following legs raising probably involved stimulation of mecanoreceptors in the low pressure system.

Indirect, noninvasive evaluation of pressure wave transmission in essential hypertension

Blood pressure, carotid-femoral and brachioradial pulse wave velocities were measured in 123 male subjects: 32 normal subjects and 91 age-matched patients with sustained essential hypertension. The ratio between brachioradial (BR) and carotid-femoral (CF) pulse wave velocities was used as a marker of pressure wave amplitude changes from the aorta to the brachial artery. The ratio was similar in normotensive and hypertensive subjects and decreased with age to the same extent in both populations. In older subjects, the decrease in the ratio indicated that the amplitude of pulse pressure was quite similar in the aorta and the brachial artery whether the subjects were normotensives or hypertensives. The study provided evidence that adaptive changes occur in the arterial (aortic) wall in hypertension, for the effects of age on pressure wave transmission are similar in normal subjects and hypertensive patients. Such findings may be of prime importance in understanding the brachial blood pressure readings of patients with hypertension.

Atrial natriuretic peptide decreases contractility of cultured chick ventricular cells

To determine whether atrial natriuretic peptide (ANP) has an inotropic effect, the contractility of spontaneously beating cultured chick embryo ventricular cells was studied in response to rat-ANP (1-23) superfused at concentrations ranging from 10(-10) M to 2.5 x 10(-7) M. r-ANP reversibly decreased contractility with a threshold concentration of 10(-8) M; at the highest concentration, r-ANP decreased contractility to a moderate extent (-30 +/- 4%) r-ANP increased dose-dependently intracellular cGMP levels. Stimulation of contractility with [Ca2+], the calcium-channel agonist BAY K 8644 or isoproterenol attenuated to various degrees the inhibitory effect of r-ANP. By contrast, the inhibitory effect of r-ANP on contractility was unchanged or even enhanced after stimulation of contractility by angiotensin II. There was no difference in r-ANP-induced increase in cGMP whether cells were pre-incubated with angiotensin II or not. These results indicate that r-ANP was able to decrease contractility of cultured cardiac myocytes and suggest a preferential antagonism of the inotropic effect of angiotensin II.

Endogenous opiate system and dihydropyridine-induced central regulation of sympathetic tone in rats

Intracerebroventricular injections of nicardipine (10 micrograms/kg) to SHR induced hypotension which was suppressed by pretreatment with 6-OHDA. This hypotension was also inhibited by a previous injection of naloxone (100 micrograms/kg i.c.v.) whereas the hypotension induced by intravenously injected nicardipine (10 micrograms/kg) was not changed. It is suggested that the release of endogenous opioids is involved in the sympatho-inhibitory effect of centrally administered dihydropyridine calcium channel antagonists.

Non-invasive ultrasonic study of maximal aortic blood acceleration in patients with borderline and sustained essential hypertension

Using a pulsed Doppler method to evaluate the aortic velocity curve transcutaneously, the maximal aortic blood acceleration was evaluated in normal subjects and in age-matched patients with borderline and sustained essential hypertension. Maximal aortic blood acceleration was significantly elevated in patients with borderline hypertension and remained within the normal range in patients with sustained hypertension. Since maximal aortic blood acceleration is relatively insensitive to preload and afterload, these findings might give indirect information on the contractile state of the myocardium in patients with hypertension.

Flow-dependent vasodilation of the brachial artery in essential hypertension: preliminary report

Brachial artery haemodynamics including brachial artery diameter and local blood flow velocity were studied in 10 normotensive subjects and 10 age-matched hypertensive patients. A bidimensional pulsed Doppler system was used at rest, during a 2-min period of distal circulatory occlusion and during reactive hyperaemia. The kinetics of changes in blood flow velocity and brachial artery diameter were determined during successive and reproducible manoeuvres. The two parameters decreased significantly during distal artery occlusion in both groups. During reactive hyperaemia, blood velocity reached similar maximal values in both groups and brachial artery diameter increased significantly in both normotensives and hypertensives. Changes in the brachial artery diameter during reactive hyperaemia were positively and significantly correlated to changes in blood flow velocity recorded at the same level. No significant difference was found between normotensives and hypertensives. This study has provided a demonstration of velocity-dependent variations in the diameter of a large artery in humans; the results suggest that velocity-dependent vasodilation of the brachial artery is not impaired in essential hypertension.

Atrial natriuretic peptide decreases contractility of cultured heart cell: preliminary report

We tested the hypothesis that atrial natriuretic peptide (ANP) has a direct negative inotropic effect on the cultured chick embryo ventricular cell, an experimental system devoid of endogenous neurotransmitters. At 10(-8) and 2.5 x 10(-7) mol/l ANP [rat ANP-(1-23)] significantly and reversibly decreased contractility in spontaneously beating cells. The positive inotropic effect of angiotensin II (2.5 X 10(-7) mol/l) on spontaneously beating cells was fully antagonized by ANP (2.5 X 10(-7) mol/l) and the amplitude of contraction decreased below control levels. In contrast (1) the increase in contractility in response to extracellular calcium was significantly less altered by ANP and (2) the time-course of the positive inotropic effect of the calcium-channel agonist Bay-K-8644 (5 x 10(9) mol/l) or of the beta-adrenergic agonist isoproterenol (10(-6) mol/l) was unchanged by ANP. These results indicate that ANP-(1-23) has a direct negative inotropic effect on cultured chick heart cells and may affect intracellular messengers involved in the cardiac effects of angiotensin II.

The common carotid circulation in patients with essential hypertension

We review carotid artery hemodynamics in hypertensive men, with particular reference to common carotid artery diameter and blood flow, and emphasize the changes in artery diameter and compliance implied by antihypertensive therapy.

Reversion of cardiac hypertrophy and reduced arterial compliance after converting enzyme inhibition in essential hypertension

Blood pressure, forearm arterial hemodynamics (with a pulsed Doppler flowmeter), and echocardiographic parameters were studied in 16 patients with sustained essential hypertension before and 3 months after administration of the converting enzyme inhibitor perindopril. In a single-blind study versus placebo, it was shown that perindopril significantly reduced blood pressure (p less than 0.01), whereas there was an increase in brachial blood flow (p less than 0.01) because of a simultaneous increase in blood flow velocity (p less than 0.01) and arterial diameter (p less than 0.01). During a 5-minute period of wrist occlusion, blood flow velocity was reduced to a greater extent with perindopril than with placebo (p less than 0.001), whereas corresponding reductions in arterial diameter were equivalent, indicating that the increase in diameter after perindopril could not be explained simply on the basis of flow-dependent dilatation. During active treatment, brachial artery compliance increased (p less than 0.01) and pulse wave velocity decreased (p less than 0.01), whereas there was no change in the tangential tension of the arterial wall, defined as the product of mean arterial pressure and arterial diameter. Four weeks after treatment was stopped, blood pressure and forearm arterial hemodynamics returned toward baseline values. Cardiac mass was significantly decreased after perindopril (p less than 0.01) and remained decreased 4 weeks after cessation of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Relative negative inotropic potencies of nine calcium channel blockers in cultured heart cells

The direct inhibitory effects on contractility and beating rate of the calcium channel blockers diltiazem, verapamil and dihydropyridine derivatives nicardipine, nifedipine, nitrendipine, PY 108-068, (+/- ) PN 200-110 and its 2 stereoisomers, were compared in cultured chick embryo ventricular cells. In spontaneously beating cells, the negative inotropic and chronotropic potencies of nicardipine, nifedipine, nitrendipine and PY 108-068 were not significantly different. The inhibitory effects of verapamil, nifedipine and nicardipine were studied in cells electrically driven at a frequency close to their spontaneous beating rate: verapamil, nifedipine and nicardipine had similar negative chronotropic potencies; when the rate of stimulation was increased 1.5 and 2-fold, a frequency-dependent inhibitory effect on contraction was shown for verapamil, but not for nifedipine and nicardipine. Therefore, in our model, where the effects of beating rate on the amplitude of contraction were taken into account, no significant difference in the direct negative inotropic potenties of nifedipine and nicardipine was shown.

Central modulation of baroreceptor reflex response to phenylephrine by dihydropyridines in rats

The effects of two dihydropyridine derivatives, the calcium channel agonist BAY k 8644 or the antagonist PN 200-110, on the central nervous components of the baroreceptor reflex control of heart rate during activation of baroreceptors by phenylephrine (2 micrograms i.v.) were studied in pentobarbital-anesthetized normotensive (Wistar) rats and spontaneously hypertensive rats (SHR). To rule out an effect on peripheral vessels or on the sinoauricular node (or on both), BAY k 8644 and PN 200-110 were administered intracerebroventricularly (i.c.v.) at doses that did not change blood pressure. Baroreceptor reflex sensitivity was calculated as the slope of the relationship between systolic arterial pressure and heart period. Baroreceptor reflex sensitivity increased with time following the onset of anesthesia. In SHR, injection of BAY k 8644 (3 micrograms/kg i.c.v.) suppressed the time-dependent increase in baroreceptor reflex sensitivity. The inhibitory effect of BAY k 8644 (3 micrograms/kg i.c.v.) on the time-dependent increase in baroreceptor reflex sensitivity was suppressed by pretreatment with PN 200-110 (0.6 microgram/kg i.c.v.) but not with the solvent, indicating that the central effect of BAY k 8644 occurred at the level of specific dihydropyridine binding sites. In addition, the inhibitory effect of BAY k 8644 (3 micrograms/kg i.c.v.) on the time-dependent increase in baroreceptor reflex sensitivity was suppressed by pretreatment with the muscarinic antagonist atropine methylnitrate (80 micrograms/kg i.c.v.) but not with the solvent. In normotensive rats, the time-dependent increase in baroreceptor reflex sensitivity was not significantly altered by BAY k 8644 (3 micrograms/kg i.c.v.).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased response of brachial artery diameter to norepinephrine in hypertensive patients

The hyperresponsiveness of small arteries to norepinephrine is well documented in essential hypertensive patients. Our objective was to investigate in situ the reactivity to norepinephrine of the diameter of large arteries, which are involved in the arterial disease of hypertension as well as small arteries. Brachial artery diameter, blood flow velocity, local volumic blood flow, and local vascular resistances were determined noninvasively with a pulsed Doppler system in 19 patients with essential hypertension and 9 normotensive subjects, before and after the administration of placebo (glucose) or increasing doses of norepinephrine (10, 20, and 40 ng.kg-1.min-1 iv) given in a single-blind fashion. In hypertensive patients, norepinephrine (40 ng.kg-1.min-1) induced 1) a significant decrease in brachial artery diameter, local blood velocity, volumic flow, and conductance and 2) a small increase in mean arterial pressure. These hemodynamic changes did not occur in the placebo group and were significantly greater in hypertensive patients than in normotensive subjects, although plasma norepinephrine increased to the same extent in both groups. We conclude that in hypertensive patients the increase in vascular reactivity to norepinephrine involves not only the resistive vessels but also the large arteries thus decreasing their conducting and buffering function.

Renal and systemic hemodynamics in borderline hypertension

Cardiac output (CO), renal blood flow (RBF), and glomerular filtration rate were measured in 29 young patients with borderline hypertension, in comparison with 26 normotensive controls of the same age and sex. In patients with borderline hypertension, both CO and RBF were significantly increased, whereas the RBF/CO ratio remained within the normal range. No significant changes in glomerular filtration rate and renal filtration fraction were observed. The study clearly demonstrated that renal ischemia was absent in young patients with borderline hypertension.

[Flow-dependent vasodilation of the brachial artery in the normotensive and essential hypertensive patient]

Brachial artery hemodynamics including brachial artery diameter (D), local blood flow velocity (V) and local volumic blood flow, was studied in 10 normotensive subjects (NT) and 10 age-matched hypertensive patients (HT) (50 +/- 4 vs 43 +/- 4 years; m +/- SEM; NS), using a bidimensional pulsed doppler system at rest (control period), during a 2 (or 4) mn-period of distal circulatory occlusion (DO) and during the following reactive hyperemia (RH). Kinetics of change in blood flow velocity and diameter were determined during successive and reproducible manoeuvres. V and D decreased significantly during DO. During RH (1) V reached similar maximum values in both groups (after 2 mn DO: NT: from 2.4 +/- 1.1 to 19.0 +/- 6.9 cm/s; HT: from 2.9 +/- 0.8 to 17.2 +/- 7.6 cm/s) and (2) D increased significantly in both groups (after 2 mn DO: NT: from 0.395 +/- 0.016 to 0.450 +/- 0.025 cm; p less than 0.001; HT: from 0.408 +/- 0.018 to 0.467 +/- 0.018 cm; p less than 0.001), reaching levels significantly higher than during the control period. The brachial artery vasodilation observed in both groups (NT: +12 +/- 3 p. 100; HT: +15 +/- 3 p. 100 of initial diameter) was significantly greater (p less than 0.001), than the reproducibility of the diameter measurement (3 +/- 1 p. 100). Mean arterial pressure and heart rate dit not change during the whole investigation. Increasing the duration of DO from 2 to 4 mn further enhanced the reactive blood flow velocity but did not change the magnitude of the reactive brachial artery vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

[Central control of the baroreflex response to phenylephrine by dihydropyridines in the anesthetized rat]

We have previously shown that a calcium channel activator (BAY K 8644) and a calcium channel inhibitor (CCI) (nifedipine), both dihydropyridine derivatives (DHP), can modulate in opposite fashion calcium dependent mechanisms involved in the central control of blood pressure and heart rate in SHR but not in Wistar rats. These results suggested that central DHP receptor sites might modulate baroreflex function. Therefore, we studied in pentobarbital anaesthetized SHR, the effects of BAY K 8644 and PN (200-110) (CCI) on central integration of baroreflex function (ramp method: phenylephrine 2 microgram i.v.). In order to rule out peripheral vascular effects, BAY and PN were administered intracerebroventricularly (i.c.v.) at doses which did not change BP. Baroreflex sensitivity (BRS) increased with time following the onset of anesthesia. In SHR, i.c.v. injection of BAY (3 microgram/kg) but not PN (0.6 micrograms/kg) suppressed the time dependent increase in BRS. The inhibitory effect of BAY on the time-dependent increase in BRS was suppressed by a pretreatment with PN (0.6 micrograms/kg i.c.v.) and by a pretreatment with the muscarinic antagonist atropine methylnitrate (80 micrograms/kg i.c.v.). BAY i.c.v. dit not change BRS in Wistar rats. These results indicate that DHP may centrally modulate BRS in SHR and suggest a central sympatho-excitatory effect for BAY mediated by an enhanced release of acetylcholine.

[Atrial natriuretic factor diminishes the contractility of the cardiac cell in culture]

The hypotensive effect of ANP has been associated with lowered cardiac output. Although only minor or no negative inotropic effect was found in vitro, a direct myocardial depressant effect of ANP remains a possible mechanism in vitro, in addition to the reduction in cardiac preload. Therefore we tested the hypothesis of a direct negative inotropic effect of ANP on the cultured chick embryo ventricular cell, an experimental system which contains no neural elements and no endogenous neurotransmitters. ANP (rat-ANP 1-23) 10(-8) M significantly and reversibly decreased contractility in spontaneously beating cells. A further decrease (-30 +/- 4 p. 100 of initial amplitude of contraction) was observed at 2.5 x 10(-7) M: -17 +/- 4 p. 100 of initial amplitude). The positive inotropic effect of angiotensin II (2.5 x 10(-7) M) on spontaneously beating cells was fully antagonized by ANP (2.5 x 10(-7) M) and amplitude of contraction decreased under control levels. By contrast (1) the increase in contractility in response to extra-cellular calcium (increased from 1.5 to 2.1 mM) was significantly less altered by ANP and (2) the time-course of the positive inotropic effect of the calcium-channel agonist BAY K 8644 (5 x 10(-9) M) or the beta-adrenergic agonist isoproterenol (10(-6) M) was unchanged by ANP. These results indicate a direct negative inotropic effect of ANP (1-23) on cultured chick heart cells and suggest an effect on intracellular messengers involved in the cardiac effects of angiotensin II.(ABSTRACT TRUNCATED AT 250 WORDS)

[Pulse wave velocity and ambulatory blood pressure in essential arterial hypertension]

Cardiovascular morbidity and mortality of hypertensive patients is mainly related to lesions of large arteries. Arterial distensibility estimated by carotid-femoral pulse wave velocity (PWV) was evaluated in 22 patients with sustained essential hypertension, together with three different methods of blood pressure (BP) measurement: mercury sphygmomanometer, semi-automatic BP recording using the Dinamap apparatus and 24 H ambulatory BP monitoring using the Spacelabs Monitor (5200). Table shows that, while PWV was not correlated with BP measured by mercury sphygmomanometer, it was strongly and positively correlated with BP measured by the other procedures. The best correlation coefficient was noted for the systolic BP measured in the Day Time (7 h-22 h) by the ambulatory method. This study shows that BP Monitoring correlates more strongly than clinic or casual BP with indices of target organ damage. (Table: see text).

[Pulse pressure and echocardiographic parameters in essential arterial hypertension]

We measured systolic, diastolic, mean (MAP) and pulsed (PP) arterial pressures (Dinamap 845 XT), carotid femoral pulse wave velocity (PWV) and cardiac parameters (echocardiography) to evaluate myocardiac mass and indexed cardiac mass to body surface area (IM) in 47 subjects (11 normotensives and 36 with sustained essential hypertension). Hypertensives were allocated between two groups with same age, weight and height, same mean arterial pressure (119.8 +/- 9.1 mmHg, 119.7 +/- 11.9 mmHg, NS) and PWV (11.90 +/- 2.20 m/s, 12.51 +/- 1.83 m/s, NS): group I (22 subjects) with pulsed pressure less than 60 mmHg, group II (14 subjects) with pulsed pressure greater than or equal to 60 mmHg. (Table: see text). Newman-Keuls between group I and group II: p less than 0.01 for cardiac mass and IM, p less than 0.001 for PP. Cardiac mass (p less than 0.01) and indexed mass to body surface area (p less than 0.01) were greater in group II (with pp greater than or equal to 60 mmHg) than in group I.

CONCLUSION

arterial hypertension is linked with left ventricular hypertrophy which is increased when pulsed pressure is enhanced. This fact could give evidence of importance of pulsatory work in cardiac consequence of hypertension.

[Effects of beta-blockers on hemodynamics of the forearm after tobacco stimulation]

In mild hypertension, a betablocker treatment could reduce cardiovascular events. But in smoking men the benefit disappears and this interaction is unexplained. In 6 healthy non smoking men, we studied the effects of acute oral administration of propranolol (80 mg) pindolol (15 mg) and placebo after cigarette smoking (CS) (two cigarettes within 10 minutes). In a double blind cross over randomized study, arterial pressure and heart rate (HR) were recorded within 20 minutes after CS. Brachial artery diameter (D), Local vascular Resistance (RL), Local arterial Compliance (CL) and pulse wave velocity (VOP) were determined non invasively (using a pulsed doppler system) before and 20 mn after CS. Under placebo, mean arterial pressure (PAM), HR and RL increased significantly after CS (+9.2 +/- 3 mmHg, +4.5 +/- 3 b/mn and +36 +/- 14 per cent, respectively). These modifications were not different after propranolol, pindolol or placebo (ANOVA). Arterial distensibility (CL) was decreased after CS and this alteration was not prevented by beta-blockers. Brachial artery diameter was not modified after CS. Our results demonstrate that acute treatment with non selective beta-blockers with or without sympathomimetic intrinsic activity does not prevent haemodynamic modifications induced by cigarette smoking.

Central and peripheral cardiovascular effects of the enantiomers of the calcium antagonist PN 200-110

The negative inotropic effects and the central and peripheral hypotensive effects of (+) and (-) PN 200-110 were investigated in cultured chick heart cells and in spontaneously hypertensive rats, respectively. There was a large difference in negative inotropic potency between the two enantiomers in cultured chick embryo ventricular cells: the (+) enantiomer was 140 fold more potent (IC50 = 1.1 +/- 0.2 nM) than the (-) enantiomer (IC50 = 160 +/- 20 nM). (+) PN 200-110 was 10 fold more potent than (-) PN 200-110 in lowering blood pressure after intravenous injection and only three fold more potent after intra-cerebroventricular injection (i.c.v.) into pentobarbital-anaesthetized spontaneously hypertensive rats. I.c.v. administered (+) PN 200-110 (1 microgram/kg) partially antagonized the hypertensive response to i.c.v. administered BAY K 8644 (30 micrograms/kg), a calcium channel agonist, while the same dose of the (-) enantiomer did not change the i.c.v. BAY-induced increase in blood pressure. These results suggest that the dihydropyridine calcium channel antagonist, PN 200-110, may act centrally and stereoselectively at the level of the dihydropyridine receptor sites involved in the control of blood pressure in spontaneously hypertensive rats.

Converting enzyme inhibition and the common carotid circulation in older patients with sustained essential hypertension

Arterial diameter, blood flow and vascular resistance of the common carotid artery were studied using a pulsed Doppler system in patients with uncomplicated sustained essential hypertension and compared with age-matched normal subjects. In hypertensive patients below the age of 45 years, arterial diameter and blood flow remained within the normal range, while vascular resistance was increased. In hypertensive patients over 45 years of age, arterial diameter was also normal, but blood flow was reduced and vascular resistance markedly increased. Thus, both small and large arteries were altered in the common carotid circulation of patients with sustained essential hypertension. Acute oral administration of converting enzyme inhibitor produced dilatation of both small (vascular resistance) and large (arterial diameter) arteries in the carotid circulation. In addition, in older patients, blood flow significantly increased and vascular resistance markedly decreased both in acute and long-term situations. Thus converting enzyme inhibition was able to reverse the abnormalities of the common carotid circulation of older subjects with sustained essential hypertension.

Hemodynamics of the carotid artery after vasodilation in essential hypertension

We performed simultaneous noninvasive measurements of common carotid artery and brachial artery hemodynamics in nine normal subjects and 10 subjects with sustained essential hypertension. In hypertensive subjects, brachial artery blood flow and forearm vascular resistance were in the normal range while carotid artery blood flow and carotid artery resistance were decreased and increased, respectively. The most important findings were the changes in the internal caliber of large arteries. Although the brachial and carotid artery diameters of hypertensive subjects were measured for the same level of mean arterial pressure, brachial artery diameter was significantly increased and carotid artery diameter was strictly normal as compared with values found in normal subjects. To assess whether carotid artery circulation could influence the baroreceptor reflex response to arteriolar vasodilation, carotid artery and brachial artery hemodynamics were measured in immediate succession in normotensive and hypertensive subjects before and after oral administration of cadralazine, a dihydralazine derivative. After cadralazine treatment, carotid artery tangential tension decreased in hypertensive subjects, and the changes were significantly correlated to the increase in heart rate. A similar correlation was found in normal subjects, but it was reset toward higher heart rates. These results indicate that the carotid artery does not behave like the brachial artery in response to a chronic increase in blood pressure. This behavior indicates intrinsic alterations of the arterial wall and might be involved in the resetting of the carotid baroreceptor reflex. Carotid artery circulation could play a role in hypertension by modulating the carotid baroreceptor mechanisms involved in the response to drug-induced arteriolar vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)