Rac-1-mediated O2- secretion requires Ca2+ influx in neutrophil-like HL-60 cells.

Neutrophil-like HL-60 cells reacted to N -formyl- l -Methionyl- l -Leucyl- l -P henylalanine (f MLP) with a rise in the intracellular calcium concentration ([Ca2]i), NADPH oxidase activation, and increased superoxide anion (O2-) production. [Ca2+]i mobilization and superoxide production were largely dependent on extracellular calcium (Ca2+]e) and a capacitative calcium entry. The monomeric G-protein, Rac-1, regulates NADPH oxidase activity. We tested the effect of removal of Ca2+]e on Rac-1 plasma membrane sequestration and activation of NADPH oxidase using immunodetection and a double labelling fluorescent method. Results showed that Rac-1 activation is mediated via a pertussis toxin (PTX)-sensitive heteromeric G-protein pathway, and that Rac-1 membrane sequestration was preceded by [Ca2+]i mobilization following entry of Ca2+ e. Therefore, we propose that O2- production is dependent on activation of PTX-sensitive G-proteins and sequestration of Rac-1 in the plasma membrane, following entry of Ca2+ e.

Intracellular concentrations of fura-2 and fura-2/am in vascular smooth muscle cells following perfusion loading of fura-2/am in arterial segments.

A new method for the determination of tissue concentrations of Fura-2 and Fura-2/AM was developed based upon acetonitrile extraction followed by RP-HPLC separation (using tetrahexylammonium as counter-ion), post-column alkaline hydrolysis of Fura-2/AM, and fluorimetric detection. The detection limit was 1.2 nM and 1 nM for Fura-2 and Fura-2/AM, respectively. When this technique was applied to perfusion-loaded segments of the rat tail artery, intracellular concentrations of Fura-2 determined by tissue disruption were 10 times those obtained by comparing the increase in fluorescence at the isoemissive point (following loading), with a calibration curve for Fura-2. Loading conditions of 90 min at [Fura-2/AM]e = 5 microM were optimal in terms of [Fura-2]i which attained a concentration not significantly different from [Fura-2/AM]e. Under such conditions, however, Fura-2/AM also accumulated in the arterial wall. Although incompletely de-esterified, Fura-2/AM metabolites produced by in vitro incubation of Fura-2/AM with pig liver esterases could be easily detected, fluorescent forms of Fura-2 with a different sensitivity for calcium were not detected in arterial extracts.

Effects of aging and antihypertensive treatment on aortic internal diameter in spontaneously hypertensive rats.

The effect of antihypertensive treatment on the development of large-artery remodeling in young animals has been widely studied, but reversal of established changes in older hypertensive animals has been largely ignored, although the latter represents a better paradigm for the human condition. We studied the effect of treatment with captopril plus hydrochlorothiazide, from 3 months onward, on geometry and wall stress of the thoracic aorta of adult (9 months, maturation) and old (15 months, senescence) spontaneously hypertensive rats; normotensive Wistar-Kyoto rats were used as controls. At 3 months of age, blood pressure, medial cross-sectional area, and internal diameter were higher in spontaneously hypertensive rats than in Wistar-Kyoto rats. In both strains, medial cross-sectional area and lumen diameter increased during maturation; there was little change with senescence. Changes in blood pressure were minor. Because medial hypertrophy failed to compensate for the wider lumen and higher intraluminal pressure in spontaneously hypertensive rats, medial stress was higher in these rats than in Wistar-Kyoto rats. Captopril plus hydrochlorothiazide rapidly lowered blood pressure and medial cross-sectional area. Despite a marked fall in blood pressure, the internal diameter of the thoracic aorta of treated animals was similar to that of untreated animals after 6 months of treatment and started to fall only after the animals had been treated for 1 year. Thus, under treatment with captopril plus hydrochlorothiazide, medial stress remained elevated, even after very-long-term treatment, because medial cross-sectional area was not adapted to internal diameter. We suggest that some changes in large-artery structure associated with hypertension and aging, such as the increase in diameter, take considerable time to regress after blood pressure is lowered, and this may explain why, despite treatment, wall stress remains elevated.

The consequences of aortic calcium overload following vitamin D3 plus nicotine treatment in young rats.

Treatment of young rats with vitamin D3 plus nicotine has been proposed as a model of cardiovascular calcium overload. This treatment produced a 20-35-fold increase in the calcium content of the aorta, a compliance vessel, and this increase was accompanied by a 1.6-fold elevation of pulse pressure. In aortic rings, the maximal inhibition by the endothelium-dependent vasodilator, carbachol, of vasoconstriction induced by noradrenaline decreased from 90% in controls to 61% in treated animals. There were significant correlations between aortic calcium content and pulse pressure and aortic calcium content and carbachol-induced relaxation. In conclusion, the vitamin D3 plus nicotine model may be useful for the study of the role of calcium overload in decreased arterial compliance coupled with endothelial injury.

Reduction of endothelial function with age in the mesenteric arterial bed of the normotensive rat.

1. Age-related changes in endothelial vasodilator function were studied in an in vitro preparation of the mesenteric arterial bed removed from male, normotensive, Wistar rats. 2. Animals were killed at 2, 12 or 22 months of age, the superior mesenteric artery was cannulated and the gut removed. The mesenteric arterial bed was perfused at a constant flow rate of 4 ml min-1 and perfusion pressure was taken as an index of arteriolar tone. 3. The muscarinic agonist, carbachol, antagonized noradrenaline-induced vasoconstriction in the presence, but not in the absence, of endothelium. This cholinoceptor agonist-induced release of endothelial-derived relaxing factor (EDRF) was impaired in 22 month old rats. 4. Noradrenaline-induced vasoconstriction increased following removal of endothelium suggesting that agonist-induced release of EDRF attenuates vasoconstrictor responses to noradrenaline measured in the presence of endothelium. 5. Removal of endothelium had less effect on noradrenaline-induced vasoconstriction in old rats suggesting once again that agonist-induced release of EDRF is impaired in old rats. 6. The noradrenaline dose-response curve established in the presence of endothelium was shifted to the left in 22 month old rats. 7. In conclusion, aging in the rat appears to lead to a reduction in endothelial vasodilator function in a resistance vessel.

Sympathetic neurotransmission in the tail artery of aging rats.

1. Age-related changes in noradrenergic neurotransmission in the tail arteries of three rat strains: outbred Wistar (WI/Ico), inbred Wistar (WAG/Rij) and inbred Fischer (F344) have been compared in the present study. 2. The arterial noradrenaline content varied from 5 to 10 ng mg-1 wet weight amongst young (3 to 6-month old) representatives of each strain, but did not change with age. As protein content increased in senescent rats (24-month old) by 30-40%, arterial tissue growth would not appear to receive a concomitant increase in sympathetic growth leading to relative, age-related, structural sympathectomy in all strains. 3. The vasoconstrictor response to transmural electrical stimulation was diminished in adult and senescent rats of all strains. 4. As far as could be judged from the increase in noradrenaline release following perfusion with the alpha-adrenoceptor antagonist, phentolamine (1 microM), the presynaptic alpha 2-adrenoceptor-mediated inhibition of noradrenaline release was intact in old representatives of all strains. 5. With blockade of the two main systems which control noradrenaline release in the rat tail artery, viz, neuronal reuptake with cocaine (4 microM) and presynaptic alpha 2-adrenoceptors with phentolamine (1 microM), stimulation-evoked release of noradrenaline was similar at all ages and in all strains. This suggests that in the rat tail artery the basic mechanism of neuronal release of noradrenaline is not functionally modified by aging. 6 We conclude that as sympathetic nerve terminals are apparently intact in all three strains of senescent rats used, the age-associated deficit of alpha-adrenergic control of vascular function is postsynaptic in nature.

Effects of chronic and acute aminoguanidine treatment on tail artery vasomotion in ageing rats.

1. This study was designed to evaluate the effects of aminoguanidine, a selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS), on the reactivity and intracellular calcium ([Ca(2+)](i)) mobilization induced by noradrenaline in the perfused tail artery from aged WAG/Rij rats. Global mean internal diameter was 350+/-15 microns and wall thickness 161+/-3 microns. The influence of the endothelium on these responses was also analysed. The intracellular dye fura-2 for [Ca(2+)](i) measurements was used. 2. Noradrenaline-induced vasoconstriction decreased progressively from 3 to 20 and 30 months. Removal of the endothelium attenuated vasoconstriction in 20 and 30 month-old rats (P<0.05) but not in young rats. 3. Chronic administration of aminoguanidine (50 mg kg(-1) day(-1), p.o.) to WAG/Rij rats from 20 to 30 months enhanced (P<0. 01) the [Ca(2+)](i)-sensitivity of noradrenaline-induced vasoconstriction. 4. Aminoguanidine (300 microM) in vitro significantly shifted the concentration-vasoconstriction curve to noradrenaline to the left (P<0.01) in denuded vessels from both 20 and 30 month-old rats. The acute inhibitory effect of aminoguanidine was also observed after chronic aminoguanidine treatment. Aminoguanidine failed to modify vasoconstriction in the presence of the endothelium. 5. Acute aminoguanidine (300 microM) treatment did not modify vasoconstriction induced by noradrenaline in young rats. 6. Quantification of iNOS mRNA expression in tail arteries from 3 and 20 month-old WAG/Rij rats showed that expression was enhanced (x2.1, P<0.01) with age. 7. These results suggest that an inflammatory process develops in the media of the rat tail artery with age and that the subsequent increase in non-endothelial iNOS activity attenuates noradrenaline-induced vasoconstriction.

Chronic treatment with the angiotensin I converting enzyme inhibitor, perindopril, protects in vitro carbachol-induced vasorelaxation in a rat model of vascular calcium overload.

1. Treatment of young rats with vitamin D3 plus nicotine produced 31 and 4 fold increases in the calcium content of the aorta and the mesenteric arterial bed, respectively. 2. Aortic rings and perfused mesenteric arterial beds from vitamin D3/nicotine-treated animals showed a diminished contractile response to noradrenaline in vitro. 3. In vascular preparations from vitamin D3/nicotine-treated animals, precontracted with noradrenaline, relaxation by the endothelium-dependent vasodilator, carbachol, was attenuated but responses to sodium nitroprusside were not modified. 4. Prolonged treatment with the angiotensin I converting enzyme inhibitor, perindopril, at a dose (1 mg kg-1) which did not significantly modify blood pressure, failed to prevent vascular calcium overload. 5. Perindopril treatment diminished noradrenaline-evoked vasoconstrictor responses of aortic rings in both groups, but restored responses in mesenteric arterial beds of vitamin D3/nicotine-treated rats. 6. Perindopril treatment also restored the maximal responses to carbachol of both aortic rings and mesenteric arterial beds of vitamin D3/nicotine-treated rats. 7. In conclusion, in the vitamin D3 plus nicotine model of calcium overload, reduced endothelial-mediated relaxation can be prevented by perindopril treatment.

Chronic antihypertensive treatment with captopril plus hydrochlorothiazide improves aortic distensibility in the spontaneously hypertensive rat.

1. Adult male spontaneously hypertensive rats (SHR) were given captopril plus hydrochlorothiazide mixed in the diet for 10 weeks. Calculated daily doses were 44 mg kg-1 per day for captopril, and 22 mg kg-1 per day for hydrochlorothiazide. Separate groups received captopril or hydrochlorothiazide alone, at similar doses, or no treatment. A final group of WKY normotensive rats received no drug. 2. Systolic arterial blood pressure, measured at regular intervals throughout the 10 weeks' period was lowered but not normalized, in groups receiving either captopril plus hydrochlorothiazide, or captopril alone, but not in the group receiving hydrochlorothiazide alone. 3. Following pentobarbitone anaesthesia, systolic arterial blood pressure, measured in the femoral artery, was found to be lower in all treated groups, but the greatest effect was observed in SHR previously treated with captopril plus hydrochlorothiazide. Aortic pulse wave velocity was also lower in treated SHR, and once again the greatest decrease was observed in the group previously treated with captopril plus hydrochlorothiazide. 4. Following pithing, systolic arterial blood pressures were similar in all SHR groups. Aortic pulse wave velocity was lower in pithed rats previously treated with captopril and hydrochlorothiazide. 5. In conclusion, antihypertensive treatment of SHR produces falls in blood pressure and pulse wave velocity, an indicator of aortic distensibility. Results in pithed rats suggest that treatment with the combination of captopril plus hydrochlorothiazide may increase aortic distensibility independently of blood pressure.

Haemodynamic effects of a new dihydropyridine calcium entry blocker, S-12968-(-), in a rat model of cardiovascular calcium overload.

1. The haemodynamic effects of S-12968-(-), a new dihydropyridine calcium entry blocker (enantiomer of S-11568), were compared with those of the stereoisomer, S-12967-(+), nifedipine, and sodium nitroprusside. 2. A first experiment was performed in conscious, young male rats chronically implanted with femoral artery and vein cannula and repeated in rats previously treated with vitamin D3 and nicotine. Such treatment produces marked vascular calcium overload, especially of the compliance arteries, with no overt sign of toxicity as far as can be judged from the plasma profile. 3. In conscious rats the hypotensive effects of S-12968-(-), nifedipine and sodium nitroprusside were of similar potency. The falls in blood pressure produced by nifedipine and sodium nitroprusside were accompanied by reflex tachycardia which was less marked in the vascular calcium overload model. S-12968-(-) did not induce reflex tachycardia. S-12967-(+) increased blood pressure in both models. 4. A second experiment was performed in open-chest pentobarbitone-anaesthetized rats with electromagnetic flowprobes on the ascending aorta. In controls the falls in blood pressure produced by low doses (0.1 and 0.3 mg kg-1, i.v.) of S-12968-(-) were accompanied by falls in total peripheral resistance. The higher dose (1 mg kg-1, i.v.) of S-12968-(-) produced no change in total peripheral resistance, and in rats pretreated with vitamin D3 and nicotine, cardiac output fell. 5. In conclusion, S-12968-(-) appears to have a dual action and to lower blood pressure at higher doses at least in part by a cardiac effect. This phenomenon is more pronounced in rats pretreated with vitamin D3 and nicotine.6. S-12967-(+) resembles a calcium channel activator in this model.

Pertussis toxin-sensitive G(i)-proteins and intracellular calcium sensitivity of vasoconstriction in the intact rat tail artery.

1. We studied the involvement of pertussis toxin (PTX)-sensitive G-proteins in the sensitivity of arterial constriction to intracellular calcium ([Ca(2+)](i)) mobilization. 2. Vasoconstriction was measured in vitro in perfused, de-endothelialized rat tail arteries loaded with the calcium-sensitive dye, fura-2 and treated or not with PTX (30 - 1000 ng ml(-1)). Arteries were stimulated with noradrenaline (NA, 0.1 - 100 microM) or KCl (15 - 120 mM). 3. KCl elicited a smaller vasoconstrictor response (E(max)=94+/-8 mmHg) than NA (E(max)=198+/-9 mmHg) although [Ca(2+)](i) mobilization was similar (E(max)=123+/-8 and 135+/-7 nM for KCl and NA, respectively). PTX (1000 ng ml(-1)) had no effect on [Ca(2+)](i) mobilization but lowered NA- (but not KCl-) induced vasoconstriction (E(max)=118+/-7 mmHg). 4. G(i/o)-proteins were revealed by immunoblotting with anti-G(i alpha) and anti-G(o alpha) antibodies in membranes prepared from de-endothelialized tail arteries. [alpha(32)P]-ADP-ribosylation of G-proteins by PTX (1000 ng ml(-1)) was demonstrated in the intact rat tail artery (pixels in the absence of PTX: 3150, presence: 25053). 5. In conclusion, we suggest that smooth muscle cells possess a PTX-sensitive G(i)-protein-mediated intracellular pathway which amplifies [Ca(2+)](i) sensitivity of contraction in the presence of agonists such as NA.

Lack of involvement of pertussis toxin-sensitive G-proteins in norepinephrine-induced vasoconstriction of rat aorta smooth muscle.

Several studies have shown that stimulation of pertussis toxin (PTX)-sensitive G-proteins amplified alpha-adrenoceptor (alpha-AR) agonist-induced vasoconstriction in small muscular and resistance arteries. The aim of this study was to assess the potential involvement of PTX-sensitive G-proteins in norepinephrine (NE)-induced constriction in a large diameter artery, the rat aorta. PTX (1 microg/mL, 2 hr; 3 microg/mL, 4 hr) did not modify concentration-response curves to NE in endothelium-denuded aortic rings. However, several lines of evidence suggested that aortic smooth muscle cells (SMC) had a PTX-sensitive G-protein pathway. [alpha-(32)P]ADP-ribosylation of G(i/o)-proteins by PTX (3 microg/mL, 4 hr) was demonstrated in situ in the intact aorta without endothelium. alpha(i/o) subunits were identified in vitro by both immunoblotting and ADP-ribosylation experiments in rat aorta SMC membranes. The measurement of G(i/o)-specific GTPase activity evidenced an effective coupling between NE receptors and G(i/o)-proteins, as NE induced an increase in basal G(i/o)-specific GTPase activity (20.7 +/- 2.8 vs 7.2 +/- 2.2 pmol P(i)/mg protein at 5 min; P < 0.05 vs basal). Co-immunoprecipitation revealed the in vitro coupling between alpha(1D)-ARs and G(i)-protein in rat aorta SMC membranes. In conclusion, we identified a PTX-sensitive G(i/o)-protein pathway in rat endothelium-denuded aorta. We showed an effective coupling between NE receptors and G(i)-proteins via alpha(1D)-ARs. Since PTX has no effect on NE-induced vasoconstriction, the PTX-sensitive G(i)-protein pathway does not play a predominant role in NE-induced responses in rat aorta SMC in contrast to small diameter muscular and resistance arteries.

Role of G(i)-proteins in norepinephrine-mediated vasoconstriction in rat tail artery smooth muscle.

We showed, in rat de-endothelialised tail artery, that pertussis toxin (PTX) (1 microg/mL, 2 hr) attenuated norepinephrine (NE)-induced vasoconstriction without modifying intracellular calcium concentration [Ca2+](i) mobilisation. We suggested the existence of two NE-induced intracellular pathways: a first, which would be insensitive to PTX and lead to [Ca2+](i) mobilisation, and a second sensitive to PTX and involved in the [Ca2+](i) sensitivity of NE-induced contraction. The aim of this study was to demonstrate the existence of the second intracellular pathway. PTX-sensitive G(i/o)-proteins in rat tail artery SMC membrane were identified by immunoblot and ADP-ribosylation. [(32)P]ADP-ribosylation of alpha(i/o)-subunits was demonstrated in situ by perfusing rat de-endothelialised tail artery segments with PTX (1 microg/mL, 2 hr), which suggested that G(i/o)-protein inactivation was involved in the reduction by PTX of the [Ca2+](i) sensitivity of NE-induced contraction. Coupling between G(i/o)-proteins and NE receptors was confirmed by the NE-induced increase in G(i/o)-specific GTPase activity (24.1 +/- 1.9 vs 8.8 +/- 0.4 pmol P(i)/mg protein at 5 min; P < 0.05 vs basal). [(3)H]Prazosin-binding data showed the presence of a heterogeneous alpha(1)-AR population in rat tail artery smooth muscle cells. We demonstrated the in vitro coupling between alpha(1A)-AR subtype and alpha(i)-subunits. In conclusion, we identified, in rat de-endothelialised tail artery, a PTX-sensitive G(i/o)-protein-modulated pathway that is coupled to NE receptors via alpha(1A)-AR. We suggest that NE stimulates two alpha(1)-AR-mediated intracellular pathways: a first, which is mediated by a G(q)-protein and leads to [Ca2+](i) mobilisation and contraction, and a second, which is mediated by a G(i)-protein and is involved in the amplification of the [Ca2+](i) sensitivity of NE-induced tension.

The role of endogenous norepinephrine release in potassium-evoked vasoconstriction of the rat tail artery.

Potassium-containing solutions are often used to study the sequence of events leading from excitation to vasoconstriction. In densely innervated vessels, such as the rat tail artery, potassium-induced vasoconstriction may be mediated via smooth muscle depolarization and release of endogeneous norepinephrine. The relative contribution of these two mechanisms--a 'direct' depolarization of the vascular smooth muscle cell membrane, and an 'indirect' sympathomimetic action--to the vasoconstrictor response was studied in the present paper. Perfusion/superfusion of the rat tail artery in vitro with potassium-containing solutions had different effects depending on the concentration used. A change in potassium concentration from 4.7 to 20 mM had no effect on either perfusion pressure or norepinephrine overflow. From 30 to 70 mM, potassium produced increasing amounts of norepinephrine overflow. Experiments with phentolamine and reserpine showed that this norepinephrine overflow contributed for up to half of the vasoconstrictor response observed. A second norepinephrine-independent mechanism was also involved but the latter appeared to be incapable of producing sustained contraction. At concentrations of potassium above 50-70 mM, the results of experiments with (+/-)-propranolol suggest that the norepinephrine released by potassium has a beta-adrenoceptor-mediated vasorelaxant effect.

Decrease in endothelium-dependent relaxation in the mesenteric arterial bed following vascular calcium overload produced by vitamin D3 and nicotine in rats.

Treatment of young rats with vitamin D3 plus nicotine, which has been proposed as a model of cardiovascular calcium overload, produced an increase in the calcium content of the mesenteric arterial bed and lowered in vitro vasoconstrictor responses to norepinephrine and serotonin. Attenuation of the vasoconstriction induced by norepinephrine by the endothelium-dependent vasodilators, carbachol and histamine, was diminished, but the effects of sodium nitroprusside and papaverine were unchanged. The vitamin D3 plus nicotine model may be useful for the study of the involvement of calcium overload in vascular endothelial dysfunction.

Age-related arterial calcification in rats.

In man, i) arteries calcify with age and ii) age-linked arterial calcification is amplified by vascular pathology such as hypertension or arteriosclerosis. Age-linked arterial calcification has a bad prognosis but drugs to prevent it are lacking. This is partially due to the lack of appropriate animal models. This paper looks at the extent to which arteries calcify with age in the rat and whether hypertension or arteriosclerosis amplifies such calcification. Total calcium levels were determined by acid digestion and flame spectrophotometry and intracellular calcium levels ([Ca2+]i) by the intracellular calcium-sensitive dye, fura-2. Arteries contained up to 5 times more calcium than other soft tissues. Arteries progressively calcified with age whereas other soft tissues did not. Accumulation of calcium with age was essentially extracellular. Hypertension had no effect on age-related arterial calcification. Calcification of the same order as in man was produced in a rat model of arteriosclerosis (vitamin D plus nicotine treatment). In conclusion, as in man, age-linked, organ-specific arterial calcification does occur in rats but its intensity is far less. Arterial calcification of a similar degree to that observed in man can be obtained in rats by hypervitaminosis D plus nicotine.

Cardiovascular aging: physiology, pathology, pharmacology and therapeutics. 23-24 July 1998, Faculty of Pharmacy, Nancy, France.

In developed countries, premature death and morbidity caused by cardiovascular diseases of the aged are an important issue. This is also an increasing problem in the developing world. This symposium discussed the structural and functional changes, which underlie the way in which the susceptibility of the cardiovascular system to disease increases with age, and how such changes are influenced by external factors.

[Effect of isosorbide dinitrate on vasomotricity-cytosolic calcium coupling during aging in the rat]. / Effet du dinitrate d'isosorbide sur le couplage vasoréactivité-calcium cytosolique lors du vieillissement chez le rat.

Simultaneous measurement of vasomotricity and variations of cytosolic calcium concentrations (mobilisation of intracellular calcium) on a preparation of a normotensive Wistar rat caudal artery allowed analysis of the vasomotricity-cytosolic calcium coupling with respect to age and after administration of isosorbide dinitrate. Vasomotricity was evaluated from changes in perfusion pressure (delta P) of arterial segments perfused at a steady flow state. These segments were exposed to a fluorescent probe, fura 2, the variations of the intensity of emission of which, at wave lengths of 340 and 380 nm, reflect variations in cytosolic calcium concentration (delta R%). The "efficacy" of the vasomotricity-cytosolic calcium coupling was estimated from the delta P/delta R% ratio. In the rat, ageing is accompanied by a reduction in vasomotricity and efficacy of the coupling during noradrenalin stress testing. However, these two parameters recorded during contractions induced by the calcium in a depolarising medium do not change with age. Isosorbide dinitrate reduces vasoconstriction and the delta P/delta R% ratio during noradrenalin stimulation in the young rat. The effect is less pronounced in older rats. Isosorbide dinitrate also reduced the vasomotricity and efficacy of coupling but to a lesser degree during vaso-constriction induced by the calcium in a depolarising medium, without changing the mobilisation of intracellular calcium irrespective of the age of the animals. In conclusion, ageing seems to affect the vasomotricity-cytosolic calcium coupling mainly during receptor stimulation (noradrenalin) rather than during depolarising stimulation (calcium in a depolarising medium). Isosorbide dinitrate acts mainly on the same depolarising stimulation, independent of age.

[Myoplasmic calcium-vasoconstriction coupling in the perfused caudal artery of adult spontaneously hypertensive rats. Effect of antihypertensive treatment]. / Couplage calcium myoplasmique-vasconstriction de l'artère caudale perfusée du rat spontanément hypertendu adulte. Effet du traitement antihypertenseur.

In order to investigate whether smooth muscle intracellular calcium levels ([Ca2+]i) are related to hypertension and drug-induced changes in blood pressure, we studied basal perfusion resistance and basal [Ca2+]i and increases in perfusion pressure and [Ca2+]i using the fluorescent dye, fura-2 (dual wavelength excitation) in perfused tail artery. These were removed from 6 month old SHR previously treated (CAP + HCZ) for 10 weeks with captopril plus hydrochlorothiazide (44 and 22 mg/kg/day po, respectively). Separate groups received captopril (CAP) or hydrochlorothiazie (HCZ) alone, at similar doses, or no treatment (SHR). A fifth group of WKY normotensive rats did not receive any drug. Following determination of systolic arterial pressure (SAP) in awake rats, tail artery segments were removed and perfused at a constant flow rate with physiological salt solution plus fura-2/AM. Basal resistance and [Ca2+]i were determined. Then a dose-response curve for calcium chloride in the presence of a depolarizing concentration of potassium chloride was constructed. SAP was lowered in groups CAP + HCZ or CAP, but not in the group HCZ. Basal [Ca2+]i were similar in treated and untreated SHR and in WKY. Basal resistance to flow was lower in groups CAP + HCZ or CAP, and in WKY, than in untreated SHR. In depolarized arterial segments, vasconstrictor responses to perfusion with calcium chloride were lower in groups CAP + HCZ or CAP, and in WKY. Increases in [Ca2+]i were diminished in WKY rats. SAP measured in awake SHR and WKY was significantly correlated to basal and stimulated intracellular calcium-vasoreactivity coupling measured in vitro.

[Cerebral blood flow. Changes in regulation with aging]. / Débit sanguin cérébral. Evolution de la régulation avec l'âge.

In subjects without cardiovascular or neuronal diseases ageing does not seem to be accompanied by a significant fall in global cerebral blood flow at rest. Yet non-negligible changes in cerebral blood flow rate can be demonstrated by haemodynamic or metabolic stimuli. Several intra- and extracranial vascular mechanisms may be involved in these changes. During ageing, a decrease of carotid artery compliance due to parietal calcium deposition might be an important factor in the disturbance of cerebral blood flow regulatory mechanisms.