Cardiac growth during high and low dose perindopril treatment in spontaneously hypertensive rats

Angiotensin II type 2 receptor gene transfer elicits cardioprotective effects in an angiotensin II infusion rat model of hypertension

The role of the angiotensin II type 2 receptor (AT2R) in cardiovascular physiology remains elusive. We have developed an in vivo lentiviral vector-mediated gene transfer system to study the physiological functions of the AT2R. Our objectives in this study were to determine whether the AT2R influences cardiac hypertrophy and myocardial and perivascular fibrosis in a nongenetic rat model of hypertension. Lentiviral vector containing the AT2R or saline was injected intracardially in 5-day-old Sprague-Dawley rats. This resulted in a persistent overexpression of the AT2R in cardiac tissues. At 15 wk of age, animals were infused with either 200 ng·kg−1·min−1 of angiotensin II or saline by implantation of a 4-wk osmotic minipump. This resulted in an increase in blood pressure (BP) that reached maximal by 2 wk of treatment and was associated with a 123% increase in left ventricular wall thickness (LVWT) and a 129% increase in heart weight to body weight ratios (HW/BW). In addition, the increase in cardiac hypertrophy was associated with a 300% and 158% increase in myocardial and perivascular fibrosis, respectively. Cardiac transduction of the AT2R resulted in an 85% attenuation of LVWT, 91% attenuation of HW/BW, and a 43% decrease in myocardial fibrosis induced by angiotensin infusion. These improvements in cardiac pathology were observed in the absence of attenuation of high BP. Thus our observations indicate that long-term expression of the AT2R in the heart attenuates cardiac hypertrophy and fibrosis in a nongenetic rat model of hypertension.

Prevention of Cardiac Hypertrophy by Angiotensin II Type-2 Receptor Gene Transfer

The role of the angiotensin II type-2 receptor (AT2R) in cardiac hypertrophy remains elusive despite its demonstrated involvement in cardiovascular development. We have previously shown that a lentiviral vector gene delivery system is able to transduce cardiac tissue with high efficiency in vivo. Using such an approach, our objectives in the present study were 2-fold: (1) to overexpress the AT2R in cardiac tissue after completion of natural embryonic development of the heart and (2) to determine the effects of this overexpression on cardiac hypertrophy and basal blood pressure (BP). A lentiviral vector encoding the AT2R (lenti-AT2R) was administered (1.5x10(8) transducing units) into the left ventricular space of 5-day-old spontaneously hypertensive rats (SHRs). AT2R transgene expression increased in these animals and persisted for 30 weeks. In contrast, the expression of the angiotensin II type-1 receptor remained unchanged following lenti-AT2R treatment. At 21 weeks following gene transduction, the lenti-AT2R-treated SHRs exhibited decreased left ventricular wall thickness compared with control animals. In contrast, basal BP did not differ between the two SHR groups. Finally, heart weight to body weight ratios indicated a significant decrease in lenti-AT2R-treated SHRs compared with SHR controls. Our data indicate that AT2R overexpression attenuates cardiac hypertrophy in the SHR. This beneficial outcome was observed despite the existence of elevated BP.

Kinin B2 receptor is not involved in enalapril-induced apoptosis and regression of hypertrophy in spontaneously hypertensive rat aorta: possible role of B1 receptor

1. Treatment with enalapril induces smooth muscle cell apoptosis and regression of aortic hypertrophy in spontaneously hypertensive rats (SHRs), whereas combined blockade of angiotensin II AT(1) and AT(2) receptors does not. We postulated that vascular apoptosis with enalapril involves enhanced half-life of bradykinin (BK) and kinin B(2) receptor stimulation. 2. SHR, 11-weeks old, were treated for 4 weeks with enalapril (30 mg kg(-1) day(-1)), Hoe 140 (500 microg kg(-1) day(-1); B(2) receptor antagonist), alone or in combination. Controls received vehicle. 3. The half-life of hypotensive responses to intra-arterial bolus injections of BK were significantly increased in SHR anesthetized after 4 weeks of enalapril, an effect prevented by Hoe 140. The magnitude of BK-induced hypotension was significantly attenuated in all rats treated with Hoe 140. 4. As compared to placebo, enalapril treatment significantly reduced blood pressure (-34+/-2%), aortic hypertrophy (-20+/-3%), hyperplasia (-37+/-5%) and DNA synthesis (-61+/-8%), while it increased aortic DNA fragmentation by two-fold. Hoe 140 given alone or in combination with enalapril affected none of these parameters. 5. As a possible alternative mechanism, aortae isolated during the second week of enalapril treatment showed a transient upregulation of contractile responses to des-Arg(9)BK (EC(50)<1 nM), which were significantly reduced by [Leu(8)]des-Arg(9)BK (10 microM). Moreover, in vitro receptor autoradiography revealed an increase in expression of B(1) and B(2) receptor binding sites by 8-11 days of enalapril treatment. 6. Aortic apoptosis induction and hypertrophy regression with enalapril do not involve kinin B(2) receptors in SHR. Kinins acting via B(1) receptors remains a candidate mechanism.

Local cardiac renin-angiotensin system: hypertension and cardiac failure

In addition to the effect on arterial pressure, angiotensin II, the effector peptide of the renin-angiotensin system (RAS), exerts mitogenic and growth promoting effects on cardiac myocytes and non-myocytic elements; and both of these effects significantly contribute to the development and progression of hypertensive heart disease (HHD). The traditional concept of the RAS as a systemic, endocrine system has been expanded and the identification of its components in many organs and tissue has been amassed. This paper reviews evidence that supports the concept that the cardiac RAS participate importantly in the development and risk of HHD.

Effect of angiotensin-converting enzyme inhibition on myocardial vascularization in the adolescent and adult spontaneously hypertensive rat

OBJECTIVE

To determine whether angiotensin-converting enzyme (ACE) inhibition treatment enhances myocardial vascularization in adolescent and adult spontaneously hypertensive rats (SHRs).

METHODS

Male SHRs were treated from 7 to 14 or from 16 to 24 weeks of age with the ACE inhibitor, perindopril, in either a low dose (0.1 mg/kg per day) or a high dose (1 mg/kg per day). Some rats were concomitantly treated with a bradykinin antagonist. At termination of treatment, the left ventricular wall was extensively sampled and the surface area density and length density of myocardial blood vessels stereologically determined.

RESULTS

High-dose perindopril treatment prevented the development of hypertension and left ventricular hypertrophy in adolescent SHRs and markedly reduced blood pressure and left ventricular size in adult SHRs. SHRs treated with the low dose of perindopril remained hypertensive, although there were significant reductions in blood pressure and left ventricular growth. High-dose perindopril treatment in adolescent SHRs led to a significant increase in the surface area density of blood vessels in the left ventricle after 4 weeks of treatment and an increase in both the surface area density and length density of blood vessels after 7 weeks of treatment Co-administration with the bradykinin antagonist did not reverse these effects. In contrast, ACE inhibitor treatment had no effect on myocardial vascularization in adult rats with established hypertension.

CONCLUSION

ACE inhibitor treatment enhances vascularization in the adolescent heart through reductions in myocardial mass, but not capillary growth. ACE inhibition in the adult heart with established hypertension reduces left ventricular hypertrophy, but does not enhance myocardial capillarization.

Pharmacology and cardiovascular implications of the kinin-kallikrein system

Kinins are peptide hormones that can exert a significant influence on the regulation of blood pressure and vascular tone due to their vasodilatatory, natriuretic and growth modulating activity. Their cardiovascular involvement in physiological and pathophysiological situations has been studied intensively since inhibitors for angiotensin I-converting enzyme and selective receptor antagonists have become available for pharmacologically potentiating or inhibiting kinin-mediated reactions. Molecular biological analysis and the establishment of genetically modified animal models have also allowed newer information to be acquired on this subject. In this review, the components and cardiovascularly relevant mechanisms of the kinin-kallikrein system shall be described. Organ-specific effects concerning the kidneys, the vascular system, the heart and nervous tissue shall also be illustrated. On this issue, the physiological functions and pathophysiological implications of the kinin-kallikrein system should be clearly distinguished from the many, mostly endothelium-mediated protective effects which occur during ACE inhibition due to the potentiation of kinin effects. Finally, a view shall also be cast upon newly discovered targets of action, which could be exploited for therapeutically altering the kinin-kallikrein system.

Cardioprotective effects of an angiotensin-converting-enzyme inhibitor, imidapril, and Ca2+ channel antagonist, amlodipine, in spontaneously hypertensive rats at established stage of hypertension

The present study was performed to compare cardioprotective effects of an angiotensin-converting-enzyme inhibitor, imidapril, and of a Ca2+ channel antagonist, amlodipine, against the cardiac hypertrophy in male spontaneously hypertensive rats (SHRs) at the established stage of hypertension. Fifteen-week-old SHRs were given imidapril (2 and 5 mg/kg/day) or amlodipine (10 mg/kg/day) by gavage for 8 weeks. Three hours after the 1st treatment, imidapril moderately reduced blood pressure without changing heart rate, while amlodipine caused a marked reduction in blood pressure accompanied by transient tachycardia. At the end of the treatments, ventricular weight in the imidapril-treated groups was markedly lower, but that in the amlodipine-treated group was only slightly lower than that in the vehicle-treated group. Myocardial collagen content in the imidapril-treated group tended to be decreased, and significant reduction was observed in the low-dose group. In another experiment, the isolated heart of the imidapril-treated animals demonstrated better cardiac compliance than that in the vehicle-treated animals. In contrast, amlodipine failed to improve cardiac function. The present results suggest that imidapril possesses advantageous effects to prevent cardiac hypertrophy and deteriorated cardiac function in SHRs of established stage of hypertension as compared with amlodipine.

Cardiac hypertrophy in diabetic spontaneously hypertensive rats: role of angiotensin II?

1. In the present study the role of angiotensin II (AngII) in the development of cardiac hypertrophy in diabetes combined with hypertension was investigated. 2. Diabetes was induced in 8-week-old male spontaneously hypertensive rats (SHR) by intravenous injection of streptozotocin (45 mg/kg bodyweight). Diabetic SHR were treated with the angiotensin-converting enzyme (ACE) inhibitor ramipril at a dose of 0.4 mg/kg per day. 3. Twelve weeks following the onset of diabetes, hearts were arrested in diastole and were perfusion-fixed. The right ventricle and left ventricle plus septum were weighted and the volume of the ventricular walls was determined using the Cavalieri principle. 4. Induction of diabetes in SHR led to a significant reduction in bodyweight compared with non-diabetic control SHR and this was not affected by ramipril treatment. The development of hypertension was not as great in diabetic SHR compared with controls, such that at 12 weeks following the onset of diabetes systolic blood pressure (SBP) averaged 191 +/- 3 and 230 +/- 4 mmHg in diabetic SHR and controls, respectively. Ramipril treatment significantly lowered SBP in diabetic SHR. 5. The left ventricle plus septum volume:bodyweight ratio (LV vol:BW) was significantly higher in diabetic SHR compared with controls (3.83 +/- 0.19 and 3.26 +/- 0.16 mm3/g, respectively). Ramipril treatment did not affect growth of the left ventricle in diabetic SHR with the LV vol:BW ratio averaging 3.95 +/- 0.14 mm3/g. Similar trends on growth were observed in the right ventricle. 6. In conclusion, the development of cardiac hypertrophy in diabetic SHR appears to occur by mechanisms independent of AngII and the elevation of blood pressure.