Glucocorticoids Suppress Growth in Neonatal Cardiomyocytes Co-Expressing AT₂ and AT₁ Angiotensin Receptors

BACKGROUND: Perinatal glucocorticoid treatment is associated with hypertrophic cardiomyopathy, but the cellular mechanism is controversial. An underlying interaction between glucocorticoids and the renin-angiotensin system may be important, but whether glucocorticoids modulate angiotensin II (AngII)-dependent cardiomyocyte growth responses in the neonate has not been investigated. OBJECTIVES: The major aim of this investigation was to determine whether glucocorticoids modulate the neonatal cardiomyocyte growth response to AngII. In particular we sought evidence to determine whether angiotensin II type 2 (AT(2)) receptor co-expression with angiotensin II type 1 (AT(1)) receptor is of specific importance in this modulatory function. METHODS: In this study, we used AT(1) and AT(2) receptor-expressing adenoviruses (Ad-AT(1) and Ad-AT(2)) in a well-defined in vitro neonatal cardiomyocyte culture model to assess whether glucocorticoids affect cardiomyocyte growth responses (i.e. total protein content). RESULTS: Following addition of AngII (0.1 micromol/l) to neonatal cardiomyocytes infected with Ad-AT(1) alone, a significant growth response was measured (133.2 +/- 4.8%). Expression of Ad-AT(2) alone induced a approximately 20% increase in total cellular protein content, which was unaffected by addition of AngII. Neither corticosterone (1 micromol/l) nor dexamethasone (1 micromol/l) had any significant effect on the AT(1)- or AT(2)-mediated growth responses. In contrast, the growth response to AngII was augmented following co-expression of AT(2) and AT(1) receptors (149.2 +/- 4.2%), which was reduced by approximately 20% in the presence of either corticosterone or dexamethasone (p < 0.05). CONCLUSIONS: The present study provides novel evidence that glucocorticoids suppress neonatal cardiomyocyte growth responsiveness when AT(2 )and AT(1) receptor subtypes are co-expressed.