Pressure overload induces cardiac growth in the rat, which implies the hypertrophy of cardiac muscle cells and proliferation of nonmuscle cells. The cardiac cell loss observed in parallel has generally been attributed to necrosis. Using an in situ assay, we demonstrated a phase of apoptosis or programmed cell death during the first 7 d after pressure overload with a peak at day 4 while cardiac growth continued for over 30 d. The increase in apoptosis was confirmed by quantification of 180-1500-bp DNA oligonucleosomes with agarose gel electrophoresis and in situ labeling via 3 Ј -terminal deoxynucleotidyl transferase assay. While some apoptosis was observed in the basal state in nonmuscle cells, pressure overload induced apoptosis mainly in cardiomyocytes. These data suggest that cardiac hypertrophy is initiated by a wave of apoptosis of cardiomyocytes. Thus, apoptosis may be involved in the pathogenesis of heart remodeling. ( J. Clin. Invest. 1996. 97:2891-2897.) Key words: apoptosis • heart • hypertrophy • aortic stenosis • pressure overload

We previously reported that apoptosis is increased m smooth muscle cells cultured from the aorta of spontaneously hypertensive rats versus normotenslve controls. As an mtttal m viva exploration, we now exammed smooth muscle cell apoptosis regulation during the regression of vascular hypertrophy m the thoracic aorta media of spontaneously hypertensive rats receiving the antihypertensive drug enalapnl (30 mg kg-' d-'), losartan (30 mg kg-' d-'), mfedipme (35 mg kg-' d-l), hydralazme (40 mg kg-' d-'), propranolol(50 mg kg-' d-'), or hydrochlorothiazide (75 mg kg-' d-') for 1 to 4 weeks starting at 10 to 11 weeks of age Three criteria were used to evaluate smooth muscle cell apoptosis (1) ohgonucleosomal fragmentation of the extracted aortm DNA, (2) reduction in aortic DNA content, and (3) depletion of smooth muscle cells m the arterial media Arterial DNA synthesis was evaluated by [3H]thymidme mcorporation m viva After 4 weeks of treatment, systohc blood pressure was reduced stgmficantly by >42% wtth losartan, enalapnl, and hydralazme, and by 23% with mfedipme, versus control values of 22025 mm Hg. However, these agents affected vascular growth and apoptosis differently Losartan, enalapnl, and mfedipme stimulated smooth muscle cell apoptosrs threefold to fivefold before there was a significant reduction m DNA synthesis (>25%), vascular mass (>19%), or vascular DNA content (>38%), and these treatments markedly reduced (by 38% to 50%) medial cell number as measured at 4 weeks by the three-dimensional disector method Losartan and mfedipme stimulated smooth muscle cell apoptosis before reducing blood pressure In contrast, hydralazme did not affect vascular mass, apoptosis, or DNA synthesis, although blood pressure was lowered Propranolol or hydrochlorothiazlde failed to affect hypertension or vascular growth Thus, smooth muscle cell apoptosls represents a novel therapeutic target for the control of hypertensive vessel remodeling m response to therapeutic agents (Hypertension. 1997;29[part 2]:340-349.) Key Words l apoptosts l smooth muscle cell . angtotensm II l calcmm channel antagonist S tudies m humans and in experimental models of hypertension have clearly demonstrated the importance of vascular structure m the regulation of blood pressure i-6 Increased vascular mass is an important feature of hypertensive vessels. At the level of small muscular arteries, vascular hypertrophy accompanied by smooth muscle cell (SMC) hypertrophy or hyperplasia acts as an amplifier for elevated vascular resistance and blood pressure.7%8 At the level of the aorta and its main branches, increased mass and ngidtty of the arterial wall contribute to systolic hypertension and represent an mdependent risk factor for left ventricular hypertrophy.9 The remodeling of vascular structure, mcludmg the regression of vascular hypertrophy, is now considered a key therapeutic target in the effort to reduce mortahty and morbidity associated with high blood pressure lo-13Increased vascular mass associated with the replication and accumulatio...

Abstract-Angiotensin type 2 (AT 2 ) receptors for angiotensin II suppress cell growth and induce apoptosis in vitro, but their role is poorly defined in vivo. We reported that transient induction of smooth muscle cell (SMC) apoptosis precedes DNA synthesis inhibition and aortic hypertrophy regression in spontaneously hypertensive rats treated with the AT 1 antagonist losartan or the converting-enzyme inhibitor enalapril. Although both drugs are equipotent in reducing SMC number, apoptosis occurs significantly earlier with losartan than enalapril. To examine the role of AT 2 receptors in this model, spontaneously hypertensive rats were given valsartan, an AT 1 antagonist, or enalapril, in combination or not with the AT 2 antagonist PD123319 for 1 or 2 weeks. Control rats received vehicle. Systolic blood pressure was reduced similarly by valsartan and enalapril but it was not significantly affected by PD123319. Angiotensin II plasma levels were increased (6-fold) with valsartan and reduced (80%) with enalapril but unaffected by PD123319. Valsartan significantly increased internucleosomal DNA fragmentation indicative of apoptosis at 1 week only (2.7-fold) and significantly reduced aortic mass (18%), SMC number (33%), and DNA synthesis (24%, measured by 3 H-thymidine incorporation) at 2 weeks. These valsartan-induced changes were prevented by PD123319. In contrast, enalapril-induced DNA fragmentation (2-fold increase at 2 weeks) was not affected by PD123319. PD123319 given alone did not affect growth or apoptosis. AT 1 and AT 2 receptor mRNAs were detected in the aorta by reverse transcription-polymerase chain reaction. Together, these results provide the first evidence that AT 2 receptors mediate vascular mass regression by stimulating SMC apoptosis in vivo, an effect seen during AT 1 receptor blockade but not during convertingenzyme inhibition.

Abstract-We previously reported that increased apoptosis participates in the regression of aortic hypertrophy in spontaneously hypertensive rats. To further document the potential role of apoptosis in cardiovascular therapy, we examined apoptosis during regression of hypertrophy in the heart of spontaneously hypertensive rats receiving the antihypertensive drug enalapril (30 mg ⅐ kg) for 1 to 4 weeks, starting at 10 to 11 weeks of age. Systolic blood pressure and heart rate were measured by the tail-cuff method. Markers of apoptosis included oligonucleosomal DNA fragmentation in extracted cardiac DNA or in situ in ventricular cross sections labeled with terminal deoxynucleotidyl transferase. Cardiac DNA synthesis was evaluated by [ 3 H]-thymidine incorporation in vivo. All drugs reduced cardiac workload, defined as the product of blood pressure and heart rate, by Ͼ20% at 4 weeks. However, only nifedipine, enalapril, losartan, and propranolol reduced cardiac mass (Ͼ19%) within 4 weeks. Regression of cardiac hypertrophy was accompanied by a 50% to 300% increase in DNA fragmentation and a Ͼ20% reduction in DNA synthesis, resulting in a Ͼ20% reduction in cardiac DNA content after 4 weeks. Apoptosis induction occurred early and was transient within 4 weeks of nifedipine, enalapril, or losartan administration. With all regression-inducing drugs, the increase in DNA fragmentation occurred mainly in the subepicardium. Thus, transient induction of apoptosis in the subepicardium appears to be a characteristic feature of the early response to drug-induced regression of cardiac hypertrophy in spontaneously hypertensive rats. (Hypertension. 1999;34:229-235.)Key Words: ␤-adrenergic antagonist Ⅲ calcium channel blocker Ⅲ AT 1 antagonist Ⅲ ACE inhibitor A lthough cardiac hypertrophy is an independent risk factor for cardiovascular morbidity and mortality, the mechanisms regulating cardiac mass remain poorly defined. Different classes of antihypertensive drugs are not equally effective at reducing left ventricular mass, suggesting a blood pressure-independent regulation. 1 Cardiac hypertrophy involves both cellular hyperplasia (mainly in nonmyocytes) and hypertrophy (mainly in myocytes). 2 A potential mechanism contributing to the suppression of cardiac hypertrophy is the gene-regulated process of physiological cell self-destruction called apoptosis. 3 Cardiac apoptosis has been documented during normal neonatal maturation, 4,5 aging, 6 hypertension, 7-10 ischemia, and failure. 11 The spontaneously hypertensive rat (SHR) is a model of genetically determined cardiac hypertrophy with increased cardiac mass and DNA content at birth, 12 further suggesting blood pressure-independent regulation. In this model, cardiac alterations evolve from concentric hypertrophy to dilated cardiomyopathy and heart failure. 13 Results from our group suggest that neonatal cardiac hypertrophy in SHRs might be due in part to an imbalance between cell growth and apoptosis favoring DNA accumulation. 5 As the heart of untreated adult SHRs adapts to hyperte...