Cardiovascular role of urotensin II: effect of chronic infusion in the rat.

Urotensin II (UII) is a potent vaso-active peptide thought to have multiple roles in the regulation of cardiovascular physiology and pathophysiology. The actions of UII are complex and difficult to interpret given its systemic hemodynamic effects and variable action on different vascular beds and isolated vessels. Direct effects of UII on the myocardium, include myocyte hypertrophy, extracellular matrix deposition and contractility. These observations, together with elevated plasma levels found in disease, are common traits reported in other pathophysiologically implicated neurohormonal systems. In this review, we include original data obtained from chronic infusion of UII in rats. We report a reduction in first derivative of left ventricular pressure (+dP/dt), as well as an increase in the ratio of left ventricular collagen I:III, that may contribute to the reduced myocardial contractility observed in these animals.

p38 mitogen-activated protein kinase inhibition improves cardiac function and attenuates left ventricular remodeling following myocardial infarction in the rat.

OBJECTIVES: The aim of this study was to examine the effect of the p38 mitogen-activated protein kinase (MAPK) inhibitor, RWJ-67657 (RWJ), on left ventricular (LV) dysfunction and remodeling post-myocardial infarction (MI) in rats. BACKGROUND: p38 MAPK signaling has been implicated in the progression of chronic heart failure. METHODS: From day 7 post-MI (coronary artery ligation), rats received either RWJ (50 mg/day, by gavage, n = 8, MI+RWJ) or vehicle (by gavage, n = 8, MI+V) for 21 days. Echocardiography was performed on day 6, before the commencement of treatment, and on day 27. In vivo hemodynamic measurements were made on day 28. Sham-operated rats served as controls. RESULTS: The LV end-diastolic pressure and lung/body weight ratio were reduced, whereas the maximum rate of rise of LV pressure was increased towards sham levels in MI+RWJ compared with MI+V. Baseline echocardiographic studies demonstrated uniform LV remodeling and dysfunction in MI rats. Fractional shortening (FS) further deteriorated in MI+V, whereas FS was preserved in MI+RWJ. Progressive LV dilation and infarct expansion observed in MI+V were inhibited in MI+RWJ. MI+RWJ also demonstrated increased myocyte hypertrophy in the peri-infarct and non-infarct zones, and reduced myocardial collagen and alpha-smooth muscle actin (SMA) immunoreactivity compared with MI+V. The antifibrotic effects of RWJ in vivo may reflect direct effects on cardiac fibroblasts, because RWJ attenuated transforming growth factor beta-1-stimulated collagen synthesis and alpha-SMA expression in isolated cardiac fibroblasts. RWJ also protected cultured myocytes from hydrogen peroxide-induced apoptosis. CONCLUSIONS: RWJ-67657 treatment post-MI had beneficial effects on LV remodeling and dysfunction, supporting a key role for p38 MAPK in pathologic cell signaling in these processes and its inhibition as a novel therapy.

Direct actions of urotensin II on the heart: implications for cardiac fibrosis and hypertrophy.

Urotensin II (UII) is a somatostatin-like peptide recently identified as a potent vasoconstrictor. In this study, we examined whether UII promotes cardiac remodeling through nonhemodynamic effects on the myocardium. In a rat model of heart failure after myocardial infarction (MI), increased UII peptide and UII receptor protein expression was observed in both infarct and noninfarct regions of the left ventricle compared with sham. Moreover, post-MI remodeling was associated with a significant 75% increase in UII receptor gene expression in the heart (P<0.05 versus sham controls), with this increase noted in both regions of the left ventricle. In vitro, UII (10-7 mol/L) stimulation of neonatal cardiac fibroblasts increased the level of mRNA transcripts for procollagens alpha1(I), alpha1(III), and fibronectin by 139+/-15% (P<0.01), 59+/-5% (P<0.05), and 141+/-14% (P<0.01), respectively, with a concomitant 23+/-2% increase in collagen peptide synthesis as determined by 3H-proline incorporation (P<0.01). UII had no effect on cellular hypertrophy, as determined by changes in total protein content in isolated neonatal cardiomyocytes. However, expression of recombinant rat UII receptor in neonatal cardiomyocytes resulted in significant UII-dependent activation of hypertrophic signaling as demonstrated by increased total protein content (unstimulated, 122.4+/-4.0 microg/well; rat UII, 147.6+/-7.0 microg/well; P<0.01) and activation of the hypertrophic phenotype through Galpha(q)- and Ras-dependent pathways. These results indicate that, in addition to potent hemodynamic effects, UII may be implicated in myocardial fibrogenesis through increased collagen synthesis by cardiac fibroblasts and may also be an important determinant of pathological cardiac hypertrophy in conditions characterized by UII receptor upregulation.

Altered signaling and regulatory mechanisms of apoptosis in focal and segmental glomerulosclerosis.

The purpose of this study was to investigate signaling and regulatory mechanisms of apoptosis in a model of focal and segmental glomerulosclerosis. Sprague-Dawley rats received two doses of puromycin aminonucleoside (PAN) (day 0 and week 3) and a uninephrectomy (PAN model). Apoptosis was detected with the use of the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling technique. Bax, Bcl-2, Fas, and Fas ligand expression was analyzed by competitive reverse transcription-PCR. Bax, Bcl-2, and Fas mRNA were localized by in situ hybridization. Renal function was transiently impaired after the first PAN dose. After the second PAN dose, further progressive renal impairment, tubular atrophy, interstitial fibrosis, and glomerulosclerosis were evident. Eighteen percent of PAN samples demonstrated up to 4 apoptotic cells/50 glomeruli, compared with 7% of sham controls (not significant). No consistent significant change in glomerular Bax, Bcl-2, Fas, and Fas ligand mRNA was evident by reverse transcription-PCR, although focal increases in glomerular Bcl-2 mRNA were demonstrated by in situ hybridization. In the tubulointerstitium, apoptosis was increased from weeks 1 to 12 (P < 0.01 PAN versus sham), correlated to renal function and tubulointerstitial injury (P < 0.01). Total renal Bax, Fas, and Fas ligand mRNA were upregulated in the PAN model, peaking at week 17 (P < 0.01 versus sham), whereas Bcl-2 mRNA was not significantly different in PAN versus sham controls. In situ hybridization in the PAN model demonstrated prominent Bax mRNA in dilated tubules and infiltrating leukocytes. Fas mRNA signal was localized to tubular epithelial cells and leukocytes. The results suggest that altered apoptotic signaling and regulatory mechanisms contribute to the tubulointerstitial injury in this model.