Humoral factor(s) produced by pressure overload enhance cardiac hypertrophy and natriuretic peptide expression

Cardiovascular changes in children with coarctation of the aorta treated by endovascular stenting

The aim of this study was to investigate the echocardiographic, biochemical short- and mid-term effects of the stenting procedure on left ventricular function, aortic stiffness, elasticity and systemic hypertension in children with coarctation of the aorta (CoA). Fifteen patients with native or recurrent CoA and 30 healthy controls who were sex and age matched were included in the study. The blood pressure values, echocardiographic measurements, elastic functions of ascending aorta and serum N-Terminal ProBNP (NT-ProBNP) levels were recorded prospectively before and at the first and sixth month after stenting. The mean arterial pressure recorded before stenting was 134.4±16.3 mm Hg; at the sixth month it was 115.5±9.5 mm Hg and in the control group it was 107.3±9.4 mm Hg. Although blood pressure levels were lower compared with the pre-stenting measurements (P<0.05), they were still significantly higher compared with the control group (P<0.05). Although a significant reduction was detected in the LVMIz at the end of the sixth month (50.4±14.3 g m(-2.7)) compared with the baseline (66.6±17.9 g m(-2.7); P<0.05), it was still higher compared with the control group (35.7±6.2 g m(-2.7); P<0.05). The baseline aortic elasticity (6.4±3.4 cm(2) dyn(-1) 10(-6)) was lower compared with the control group (10.0±1.7 cm(2) dyn(-1) 10(-6); P<0.05), and prestenting aortic stiffness was higher than that of the control group (5.6±1.6 dyn(-1) 10(-6); 2.5±0.45  dyn(-1) 10(-6); P<0.05). A statistically significant negative correlation was detected between the pressure gradient at the lesion site and aortic elasticity (r: -0.53, P: 0.04). Although resolution of the coarctation by endovascular stenting led to a reduction in the arteriopathy that had already begun before treatment, it was demonstrated that these children did not completely return to normal.

Increased natriuretic peptide receptor A and C gene expression in rats with pressure-overload cardiac hypertrophy

Both atrial (ANP) and brain (BNP) natriuretic peptide affect development of cardiac hypertrophy and fibrosis via binding to natriuretic peptide receptor (NPR)-A in the heart. A putative clearance receptor, NPR-C, is believed to regulate cardiac levels of ANP and BNP. The renin-angiotensin system also affects cardiac hypertrophy and fibrosis. In this study we examined the expression of genes for the NPRs in rats with pressure-overload cardiac hypertrophy. The ANG II type 1 receptor was blocked with losartan (10 mg·kg−1·day−1) to investigate a possible role of the renin-angiotensin system in regulation of natriuretic peptide and NPR gene expression. The ascending aorta was banded in 84 rats during Hypnorm/Dormicum-isoflurane anesthesia; after 4 wk the rats were randomized to treatment with losartan or placebo. The left ventricle of the heart was removed 1, 2, or 4 wk later. Aortic banding increased left ventricular expression of NPR-A and NPR-C mRNA by 110% ( P < 0.001) and 520% ( P < 0.01), respectively, after 8 wk; as expected, it also increased the expression of ANP and BNP mRNAs. Losartan induced a slight reduction of left ventricular weight but did not affect the expression of mRNAs for the natriuretic peptides or their receptors. Although increased gene expression does not necessarily convey a higher concentration of the protein, the data suggest that pressure overload is accompanied by upregulation of not only ANP and BNP but also their receptors NPR-A and NPR-C in the left ventricle.

The upregulation of ICAM-1 and P-selectin requires high blood pressure but not circulating renin–angiotensin system in vivo

OBJECTIVE

To investigate the separate contributions of blood pressure and the circulating renin-angiotensin system to the upregulation of vascular endothelial adhesion molecules in vivo.

METHODS

One or 4 weeks after constriction of the abdominal aortas of Wistar rats, the expressions of intercellular adhesion molecule-1 (ICAM-1), P-selectin, nuclear factor (NF) kappa B p65 subunit and monocytes were assessed at sites proximal and distal to the site of constriction, by western blot, immunohistochemistry, or both.

RESULTS

At 1 week, the mean arterial pressure was increased significantly at the cervical artery in the group with aortic constriction (160 +/- 4 mmHg, compared with 104 +/- 2 mmHg before constriction), but not at the femoral artery (111 +/- 10 mmHg, compared with 100 +/- 2 mmHg before constriction) (P < 0.05), and circulating angiotensin II was increased significantly only in the group with aortic constriction (124 +/- 28 pg/ml, compared with 14 +/- 2 pg/ml in the sham-operated group; P < 0.05). In the aorta-constricted group, the expressions of ICAM-1, P-selectin, and NF-kappa B p65 subunit were significantly upregulated (2-3.1-fold) at the aorta proximal to the constriction compared with those distal to it, which were the same as those in the sham-operated group. Immunolocalization of these molecules was observed to be on the endothelial cells. Adhesive monocytes on the endothelium were also increased significantly only proximal to the constriction in the aorta-constricted group. At 4 weeks the findings were the same, except that circulating angiotensin II was within the normal range in both the aorta-constricted and the sham-operated groups.

CONCLUSIONS

Our results indicate that the high blood pressure, but not the circulating renin-angiotensin system, upregulates the expression of ICAM-1 and P-selectin, suggesting that mechanical forces may be more important than humoral factors in the upregulation of adhesion molecules in hypertension.

Physiological and pathological cardiac hypertrophy induce different molecular phenotypes in the rat

Pressure overload, such as hypertension, to the heart causes pathological cardiac hypertrophy, whereas chronic exercise causes physiological cardiac hypertrophy, which is defined as athletic heart. There are differences in cardiac properties between these two types of hypertrophy. We investigated whether mRNA expression of various cardiovascular regulating factors differs in rat hearts that are physiologically and pathologically hypertrophied, because we hypothesized that these two types of cardiac hypertrophy induce different molecular phenotypes. We used the spontaneously hypertensive rat (SHR group; 19 wk old) as a model of pathological hypertrophy and swim-trained rats (trained group; 19 wk old, swim training for 15 wk) as a model of physiological hypertrophy. We also used sedentary Wistar-Kyoto rats as the control group (19 wk old). Left ventricular mass index for body weight was significantly higher in SHR and trained groups than in the control group. Expression of brain natriuretic peptide, angiotensin-converting enzyme, and endothelin-1 mRNA in the heart was significantly higher in the SHR group than in control and trained groups. Expression of adrenomedullin mRNA in the heart was significantly lower in the trained group than in control and SHR groups. Expression of beta(1)-adrenergic receptor mRNA in the heart was significantly higher in SHR and trained groups than in the control group. Expression of beta(1)-adrenergic receptor kinase mRNA, which inhibits beta(1)-adrenergic receptor activity, in the heart was markedly higher in the SHR group than in control and trained groups. We demonstrated for the first time that the manner of mRNA expression of various cardiovascular regulating factors in the heart differs between physiological and pathological cardiac hypertrophy.

A truncated cardiac troponin T molecule in transgenic mice suggests multiple cellular mechanisms for familial hypertrophic cardiomyopathy

Mutations in multiple cardiac sarcomeric proteins including myosin heavy chain (MyHC) and cardiac troponin T (cTnT) cause a dominant genetic heart disease, familial hypertrophic cardiomyopathy (FHC). Patients with mutations in these two genes have quite distinct clinical characteristics. Those with MyHC mutations demonstrate more significant and uniform cardiac hypertrophy and a variable frequency of sudden death. Patients with cTnT mutations generally exhibit mild or no hypertrophy, but a high frequency of sudden death at an early age. To understand the basis for these distinctions and to study the pathogenesis of the disease, we have created transgenic mice expressing a truncated mouse cTnT allele analogous to one found in FHC patients. Mice expressing truncated cTnT at low (< 5%) levels develop cardiomyopathy and their hearts are significantly smaller (18-27%) than wild type. These animals also exhibit significant diastolic dysfunction and milder systolic dysfunction. Animals that express higher levels of transgene protein die within 24 h of birth. Transgenic mouse hearts demonstrate myocellular disarray and have a reduced number of cardiac myocytes that are smaller in size. These studies suggest that multiple cellular mechanisms result in the human disease, which is generally characterized by mild hypertrophy, but, also, frequent sudden death.