Structural changes of small resistance arteries in spontaneously hypertensive rats after treatment with various doses of lacidipine

Downregulation of L-type Ca2+ channel in rat mesenteric arteries leads to loss of smooth muscle contractile phenotype and inward hypertrophic remodeling

L-type Ca2+ channels (LTCCs) are important for vascular smooth muscle cell (VSMC) contraction, as well as VSMC differentiation, as indicated by loss of LTCCs during VSMC dedifferentiation. However, it is not clear whether loss of LTCCs is a primary event underlying phenotypic modulation or whether loss of LTCCs has significance for vascular structure. We used small interference RNA (siRNA) transfection in vivo to investigate the role of LTCCs in VSMC phenotypic expression and structure of rat mesenteric arteries. siRNA reduced LTCC mRNA and protein expression in rat mesenteric arteries 3 days after siRNA transfection to 12.7 ± 0.7% and 47.3 ± 13%, respectively: this was associated with an increased resting intracellular Ca2+ concentration ([Ca2+]i). Despite the high [Ca2+]i, the contractility was reduced (tension development to norepinephrine was 3.5 ± 0.2 N/m and 0.8 ± 0.2 N/m for sham-transfected and downregulated arteries respectively; P < 0.05). Expression of contractile phenotype marker genes was reduced in arteries downregulated for LTCCs. Phenotypic changes were associated with a 45% increase in number of VSMCs and a consequent increase of media thickness and media area. Ten days after siRNA transfection arterial structure was again normalized. The contractile responses of LTCC-siRNA transfected arteries were elevated in comparison with matched controls 10 days after transfection. The study provides strong evidence for causal relationships between LTCC expression and VSMC contractile phenotype, as well as novel data addressing the complex relationship between VSMC contractility, phenotype, and vascular structure. These findings are relevant for understanding diseases, associated with phenotype changes of VSMC and vascular remodeling, such as atherosclerosis and hypertension.

Comparative study of the effects of lacidipine and enalapril on the left ventricular cardiomyocyte remodeling in spontaneously hypertensive rats

Antihypertensive medications are the most efficient drugs in achieving regression of myocardial hypertrophy in both clinical studies and animal models of hypertension. Nevertheless, there is a lack of clear and concise comparative study of their effects on the modulation of cardiomyocyte morphology and function. Here, we assessed the tissue-protective actions of 2 of these drugs, the calcium channel blocker lacidipine (3 mg/kg/day) and the angiotensin-converting enzyme-inhibitor enalapril (10 mg/kg/day) in vivo, after 8 weeks of treatment of 12-week-old spontaneously hypertensive rats, as well as in vitro, after short-term (4 min) application to isolated cardiomyocytes. Left ventricular hypertrophy (LVH) was compared at organ, tissue, and single-cell level. Our data showed that both drugs prevented the LVH of 20-week-old spontaneously hypertensive rats, but only lacidipine significantly decreased the cardiomyocyte size. Similarly, the single-cell contractility was significantly lowered in lacidipine-treated rats only. The effect of lacidipine was initiated shortly after exposure to the drug in a dose-dependent manner at 0.5 Hz, as well as at 2 Hz, with EC(50) of 10(-7) mol/L. These results can help in understanding the effects of these drugs on the prevention of LVH.

Prevention of increases in blood pressure and left ventricular mass and remodeling of resistance arteries in young New Zealand genetically hypertensive rats: the effects of chronic treatment with valsartan, enalapril and felodipine

The relative efficacy of three antihypertensive drugs in the prevention of further elevation of blood pressure (BP) and cardiovascular structural remodeling in 4-week-old genetically hypertensive (GH) rats was studied by means of two complementary methods, stereology and myography. Four to 10-week-old GH rats were treated with valsartan (10 mg/kg/day), enalapril (10 mg/kg/day) or felodipine (30 mg/kg/day). Untreated GH and normotensive control rats of Wistar origin served as controls. Tail-cuff systolic SBP was measured weekly and left ventricular (LV) mass determined at the end of the experiment. Mesenteric resistance arteries (MRA) were either fixed by perfusion, embedded in Technovit and sections stained for stereological analysis, or mounted on a wire myograph for structural and functional measurements. BP and LV mass were significantly reduced by all drugs; decreases in BP and LV mass were smaller after felodipine treatment. Valsartan and enalapril caused a decrease in BP to normotensive control values. Felodipine kept BP at the 4-week level and prevented further rise with age. Valsartan caused hypotrophic outward remodeling of MRA, enalapril eutrophic outward remodeling and felodipine hypotrophic remodeling. Myograph measurements showed remodeling of the same order. While all drugs lowered the media/lumen ratio in GH to normal, the outward remodeling after valsartan and enalapril indicates that valsartan and enalapril might be more effective in reversing the inward remodeling of resistance arteries found in essential hypertension.

New Insights into the Therapeutic Mechanism of Action of Calcium Channel Blockers in Salt-Dependent Hypertension: Their Interaction with Endothelin Gene Expression

It appears that the beneficial action of calcium channel blockers (CCBs) in hypertension may be related to short-term and long-term effects. This paper summarises pharmacological studies aiming to characterise those effects. The primary consequence of the short-term effects is the decrease of blood pressure related to a selective interaction of CCBs with calcium channels in hypertensive vessels. The long-term effects may additionally control the disease through prevention of end organ damage, accompanying the interaction of CCBs with the pathways, leading to the re-expression of embryonic genes and to the overactivation of type I collagen gene, which are amplified by a high-salt diet. ET-1 and tumour growth factor beta-1 could be among the main factors activating those pathways. The processes leading to overexpression of those factors and to tissue remodelling may be controlled by lacidipine, independent of the reduction of blood pressure.

Effects of hypotensive and non-hypotensive doses of manidipine on structure, responses to endothelin-1 and ICAM-1 production in mesenteric small resistance arteries of spontaneously hypertensive rats

OBJECTIVE

We have evaluated the effects of a new calcium channel blocker, manidipine, given at both high, hypotensive and low, non-hypotensive doses, on vascular morphology, response to endothelin-1 and ICAM-1 production in mesenteric small resistance arteries of spontaneously hypertensive rats (SHR).

METHODS

Ten SHR were treated with manidipine 3 mg/kg per day (high dose) and 10 with manidipine 0.3 mg/kg/per day (low dose). The drug was administered by gavage from the 4th to 12th weeks of age. Eighteen Wistar-Kyoto (WKY) rats and 18 SHR were kept untreated as controls. Rats were killed at 13 weeks. Mesenteric small arteries were dissected and mounted on a micromyograph for determination of indexes of vascular structure (media thickness, wall thickness, media/lumen ratio).

RESULTS

Systolic blood pressure was significantly reduced by the high dose of the drug, while no effect was observed with low-dose manidipine. A reduction in the media/lumen ratio was observed only in SHR treated with high-dose manidipine. The response to endothelin-1 in untreated SHR was significantly lower in comparison with WKY; a significant reduction was observed in SHR treated with high-dose manidipine. ICAM-1 vascular concentrations were higher in untreated SHR than in WKY controls. Both high- and low-dose manidipine reduced ICAM-1 concentrations toward normalization.

CONCLUSIONS

Manidipine at high, hypotensive, but not at low, non-hypotensive doses has been proven to reduce structural alterations in mesenteric small resistance arteries, and to normalize vascular responses to endothelin-1. In addition, manidipine, at both low and high doses, may reduce ICAM-1 vascular production, thus suggesting a possible anti-atherogenic effect.

Prevention of salt-dependent cardiac remodeling and enhanced gene expression in stroke-prone hypertensive rats by the long-acting calcium channel blocker lacidipine

OBJECTIVE

To analyze the effect of the long-acting calcium channel blocker lacidipine on cardiovascular remodeling induced by salt loading in a genetic model of hypertension.

DESIGN

We examined the influence of threshold doses of lacidipine, with little blood-pressure lowering effect, on cardiac weight and gene expression in stroke-prone spontaneously hypertensive rats (SHRSP).

METHODS

SHRSPs (8-week-old) were randomly allocated to four groups: control, salt-loaded SHRSP and salt-loaded SHRSP treated with lacidipine at 0.3 and 1 mg/kg per day. Systolic blood pressure was measured by the tail-cuff method. At the end of 6 weeks of treatment, ventricles were collected and weighed. Ventricular messenger RNA was extracted and subjected to Northern blot analysis.

RESULTS

Lacidipine (0.3 mg/kg per day) not only prevented the salt-dependent cardiac hypertrophy and the slight increase in systolic blood pressure induced by salt, but also prevented, largely or completely, salt-dependent increases in ventricular levels of several gene products: skeletal and cardiac alpha-actin, beta-myosin heavy chain (beta-MHC), type I collagen, long-lasting (L)-type calcium channel and preproendothelin-1. At a higher dose of 1 mg/kg per day, lacidipine further decreased systolic blood pressure below the level of control SHRSP, completely prevented salt-dependent overexpression of the beta-MHC gene and markedly attenuated salt-dependent overexpression of the transforming growth factor-beta1 gene.

CONCLUSIONS

Lacidipine prevents the cardiac remodeling and enhanced gene expression induced by salt loading in SHRSP at doses that only minimally affect the high systolic blood pressure.

Angiotensin converting enzyme inhibition and calcium antagonism attenuate streptozotocin-diabetes-associated mesenteric vascular hypertrophy independently of their hypotensive action

OBJECTIVES

To investigate the relative roles of angiotensin II, bradykinin, and calcium-dependent pathways in the genesis of mesenteric vascular hypertrophy in experimental diabetes.

DESIGN

Streptozotocin-induced diabetic Sprague-Dawley rats were randomly allocated to these treatments for 24 weeks: no treatment; ramipril at a hypotensive dose; ramipril plus the bradykinin type 2 receptor blocker icatibant; icatibant alone; ramipril at a low dose; the angiotensin II type 1 receptor antagonist, valsartan; the dihydropyridine calcium antagonist, lacidipine; and the nondihydropyridine calcium antagonist mibefradil.

METHODS

Systolic blood pressure was serially measured every 4 weeks by tail-cuff plethysmography. We assessed the vascular architecture in sections of mesenteric arteries obtained after in-vivo perfusion, which were stained with an antibody to alpha-smooth muscle actin.

RESULTS

Both blood pressure and the mesenteric arterial wall: lumen ratio were reduced by administration of ramipril, at the high dose, either alone or in combination with icatibant, and also by valsartan. Treatment either with the low dose of ramipril or with the calcium antagonists lacidipine and mibefradil was associated with a decrease in the wall : lumen ratio of the mesenteric arteries without influencing blood pressure.

CONCLUSIONS

These findings demonstrate that blockade both of angiotensin II-dependent and of calcium-dependent pathways attenuates mesenteric vascular hypertrophy in experimental diabetes. Furthermore, the antitrophic effects of these antihypertensive agents may be independent of their hypotensive effects.

Vascular structure in the forearm and calf after 6 months of angiotensin converting enzyme inhibition in elderly hypertensive subjects with left ventricular hypertrophy

OBJECTIVE

To investigate the effects of angiotensin converting enzyme inhibition on the structure of resistive arteries assessed from minimal vascular resistance in the forearm and the calf and on left ventricular mass index of elderly hypertensive subjects with left ventricular hypertrophy.

DESIGN AND METHODS

We evaluated 23 elderly patients [12 women and 11 men, aged 70 +/- 1 years (mean +/- SEM)] with essential hypertension assessed with ambulatory blood pressure monitoring and left ventricular hypertrophy before and at the end of 6 months' treatment with quinapril. Minimal vascular resistance was calculated as the ratio of mean arterial pressure to regional blood flow measured upon restoration of circulation after 13 min of ischaemia combined with exercise and taken as an index of resistive vessel structure (i.e. media:lumen ratio).

RESULTS

Daytime ambulatory blood pressure had decreased from 164 +/- 2/95 +/- 1 to 147 +/- 3/86 +/- 2 mmHg (P < 0.001) and left ventricular mass index decreased from 138 +/- 4 to 120 +/- 5 g/m2 (P < 0.001) at the end of treatment. Minimal vascular resistance in the forearm had decreased from 3.1 +/- 0.3 to 2.4 +/- 0.2 mmHg/ml per 100 ml per min (P < 0.01) whereas we observed no change in minimal vascular resistance in the calf after treatment (4.6 +/- 0.7 versus 4.2 +/- 0.4 mmHg/ml per 100 ml per min, NS). The decrease in minimal vascular resistance in the forearm was correlated significantly to the fall in 24 h ambulatory mean arterial pressure (r = 0.58, P < 0.01). Changes in left ventricular mass index were not correlated to those in ambulatory blood pressure or to those in minimal vascular resistance in the forearm.

CONCLUSIONS

A 6-month reduction in blood pressure under quinapril treatment was associated with decreases in left ventricular hypertrophy and in minimal vascular resistance in the forearm of elderly hypertensive patients. Absence of structural changes in leg vasculature could be related to the greater arterial pressure prevalent in the lower limbs while patients stood upright and, consequently, a proportionately smaller decrease in blood pressure, as well as greater structural changes and fibrous damage than those of the upper limbs.

Effects of enalapril and amlodipine on small-artery structure and composition, and on endothelial dysfunction in spontaneously hypertensive rats

OBJECTIVES

To determine whether an angiotensin converting enzyme inhibitor, enalapril, and a dihydropyridine calcium channel antagonist, amlodipine, regress the altered structure, media composition, and vascular relaxation of small arteries of spontaneously hypertensive rats.

METHODS

Spontaneously hypertensive rats aged 10 weeks were treated for 12 weeks with 10 mg/kg per day enalapril or 10-20 mg/kg per day amlodipine and compared with age-matched untreated spontaneously hypertensive rats. Small coronary, renal, mesenteric, and femoral arteries (lumen diameter 200-250 microm) were studied isometrically on a wire myograph, and mesenteric arteries isobarically as pressurized vessels. The composition of the vascular media of the latter was studied by electron microscopy.

RESULTS

Blood pressure, and cardiac and aortic hypertrophy were reduced in treated spontaneously hypertensive rats. Treatment significantly decreased media thickness and media: lumen ratio of coronary, renal, mesenteric, and femoral small arteries studied isometrically and of pressurized mesenteric small arteries. Media cross-sectional area was smaller for coronary arteries studied isometrically and mesenteric arteries studied isobarically. Electron microscopic analysis revealed an increase in collagen: elastin ratio in the media of spontaneously hypertensive rat vessels, and a decrease under treatment to levels found in Wistar-Kyoto rats, with no significant changes detected in smooth muscle cells. The amplitude of contractions induced by acetylcholine on wire-myograph-mounted mesenteric arteries from spontaneously hypertensive rats were decreased by treatment, and relaxation of pressurized arteries induced by acetylcholine was normalized.

CONCLUSION

Treatment of spontaneously hypertensive rats with enalapril or with amlodipine resulted in regression of cardiovascular hypertrophy and amelioration of endothelial dysfunction. Morphometric results obtained using an isometric myograph and a pressurized preparation to study rat small arteries were closely correlated. Regression of structural remodeling in small arteries was outward hypotrophic, with a reduction in the collagen: elastin ratio, and without net change in the absolute and relative volumes of smooth muscle and number of smooth muscle layers.