Christine Capdeville-Atkinson

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−1and 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.

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.

Impact of chronic treatment with red wine polyphenols (RWP) on cerebral arterioles in the spontaneous hypertensive rat.

Several reports suggest that consumption of red wine is associated with a lower risk of stroke. We investigated the chronic effect of red wine polyphenols (RWP) on the functional and structural characteristics of cerebral arterioles in chronic hypertension, which is an important risk factor of stroke. Spontaneous hypertensive rats (SHR) were treated with RWP extract (100 mg/kg/day in drinking water) for 10 weeks. We measured the effect of agonist- and hypotension-induced changes in internal diameter of cerebral arterioles using an open cranial window technique. Wall mechanical parameters were determined in deactivated cerebral arterioles. The activity of antioxidant enzymes in plasma was determined. Adenosine diphosphate-induced vasodilatation was decreased by 48% in SHR and normalized in SHR treated with RWP. RWP had no effect on hypotension-induced dilatation. RWP decreased the wall thickness/external diameter ratio by 13% and significantly shifted the stress-strain relationship of the arteriole wall to the left. There was a decrease in glutathione-S-transferase and glutathione peroxidase after treatment of RWP in SHR. In summary, chronic oral administration of RWP to SHR improved endothelium-dependent dilatation, normalized wall stress and diameter, and altered the systemic antioxidant state. These effects of RWP could be useful in the prevention of stroke in hypertensive patients.

Nitric oxide lowers the calcium sensitivity of tension in the rat tail artery

1 Controversy exists as to whether a fall in the intracellular Ca2+ concentration ([Ca2+]i) is a requisite element of the vasodilatory response to nitric oxide (NO). 2 We studied the effect of NO on the coupling between [Ca2+]i and vasoconstriction in arterial segments loaded with the [Ca2+]i‐sensitive, intracellular dye fura‐2. As data interpretation is equivocal when fura‐2 is loaded into both endothelial and smooth muscle cells, we compared results from in vitro experiments on segments of the rat tail artery in which fura‐2 and noradrenaline were applied on the luminal or adventitial side, and endothelium was removed ‘physically’ (rubbing or air) or ‘functionally’ (Nω‐nitro‐l‐arginine methyl ester). The use of air perfusion to remove endothelium is of considerable benefit since it allows paired observations in a single tissue. 3 Fura‐2 loaded into endothelial cells but endothelial ‘contamination’ of the smooth muscle cell [Ca2+]i signal was minimal. 4 Endogenous NO decreased vasoconstrictor responses to noradrenaline but had no effect on [Ca2+]i. 5 Nitroglycerine decreased vasoconstrictor responses in a concentration‐dependent fashion but had no effect on [Ca2+]i. 6 In conclusion, NO causes vasodilatation via a mechanism which is downstream of [Ca2+]i mobilization.

Red wine polyphenols improve endothelium-dependent dilation in rat cerebral arterioles.

Moderate consumption of red wine is associated with a lower incidence of cardiovascular disease. Red wine polyphenols (RWP) have been proposed to be beneficial, but there is lack of evidence concerning the cerebrovascular effects of RWP. We studied the effect of local administration of a RWP extract (10−2 mg/mL) on the diameter of rat cerebral arterioles using an open cranial window technique in vivo. We measured cerebral arteriolar diameter and systemic blood pressure. Cerebral arterioles reacted concentration-dependently to adenosine diphosphate [ADP, dilatation EC50 5.3 × 10−5 M (95% confidence interval: 3.1 to 9.0 × 10−5 M)], NG-nitro-L-arginine methyl ester [L-NAME, constriction EC50 5.8 × 10−9 M (95% CI: 2.5 × 10−9 to 1.4 × 10−8 M)]. and sodium nitroprusside [SNP, dilatation EC50 1.0 × 10−6 M (95% CI: 9.2 × 10−7 to 1.1 × 10−6 M)]. RWP enhanced vasodilation induced by ADP (10−4 M) from 17 ± 2% to 29 ± 4% and reversed L-NAME-induced vasoconstriction but did not affect SNP-induced vasodilation. Systemic hypotension induced by hemorrhage caused myogenic arteriolar dilation. RWP further dilated cerebral arterioles (from −1 ± 2% to 8 ± 3%) with 1 mL of blood withdrawn. In summary, RWP improved endothelium-dependent and pressure-induced vasodilation in rat cerebral arterioles. This could be beneficial in improving cerebral blood flow under ischemic condition.

Sensitivity of norepinephrine-evoked vasoconstriction to pertussis toxin in the old rat

In male Wistar rats, the in vitro vasoconstrictor response of the perfused tail artery elicited by norepinephrine or serotonin decreased with age (24 mo old vs. 3 mo old), whereas the fluorescent signal (fura 2) produced by intracellular calcium ([Formula: see text]) mobilization increased. Both vasoconstriction and the increase in intracellular calcium concentration elicited by a high-K+, depolarizing solution were unaffected by aging. Pertussis toxin, a G protein inhibitor, had no effect on vasoconstriction induced by high K+ but diminished vasoconstrictor responses to norepinephrine in 3- and 12-mo-old animals but not in 24-mo-old animals. Pertussis toxin had no effect on[Formula: see text] mobilization. The sensitivity of receptor activation to pertussis toxin in tail arteries from 24-mo-old animals was restored by pretreatment with the α-adrenoceptor antagonist nicergoline. Nicergoline had no effect on vasoconstriction induced by high K+. Plasma norepinephrine concentration rose with age; nicergoline had no effect on this rise. We suggest that aging leads to a decrease in the intracellular G protein-modulated amplification of vasoconstriction produced by receptor activation and that this could be linked to the hyperadrenergic state. Ca2+sensitivity can be restored by chronic treatment with an α-adrenoceptor antagonist.

Effect of Lovastatin on Cerebral Circulation in Spontaneously Hypertensive Rats

Statins, which are often given to hypertensive patients, reduce the incidence of stroke. However, their effects on the cerebral circulation have been scarcely studied, although lovastatin has been reported to reduce hypertension-induced renal arteriolar hypertrophy. We examined the structure and mechanics of cerebral arterioles and the lower limit of cerebral blood flow (CBF) autoregulation in spontaneously hypertensive rats (SHR) that were untreated (n=9) or treated for 1 month with lovastatin (n=12; 20 mg x kg(-1) x d(-1)) and in untreated Wistar-Kyoto rats (WKY; n=8). We studied the lower limit of CBF autoregulation by repeated measurement of CBF (arbitrary units; laser Doppler) and internal arteriolar diameter (microm; cranial window) at baseline and during stepwise hypotension. Stress-strain relationships were calculated from repeated measurement of internal arteriolar diameter during stepwise hypotension and cross-sectional area (CSA) of the vessel wall in maximally dilated cerebral arterioles (EDTA, 67 mmol/L). Lovastatin slightly reduced mean arterial pressure (treated, 153+/-3 versus untreated, 171+/-5 mm Hg, P<0.05; WKY, 106+/-3 mm Hg) and normalized CSA (treated, 826+/-52 versus untreated, 1099+/-16 microm(2), P<0. 05; WKY, 774+/-28 microm(2)). Stress-strain curves show that lovastatin also attenuated the increase in passive distensibility. Lovastatin had no effect on the external diameter of cerebral arterioles or the lower limit of CBF autoregulation. Our results show that although lovastatin has substantial effects on arteriolar mechanics and wall CSA, it has little effect on internal diameter. This phenomenon may explain its lack of effect on CBF autoregulation.

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

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 ([Ca2+]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 [Ca2+]i measurements was used. 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. 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 [Ca2+]i‐sensitivity of noradrenaline‐induced vasoconstriction. Aminoguanidine (300 μM) 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. Acute aminoguanidine (300 μM) treatment did not modify vasoconstriction induced by noradrenaline in young rats. Quantification of iNOS mRNA expression in tail arteries from 3 and 20 month‐old WAG/Rij rats showed that expression was enhanced (×2.1, P<0.01) with age. 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.