Glucocorticoids suppress growth in neonatal cardiomyocytes co-expressing AT(2) and AT(1) 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.


OBJECTIVE
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.
Porrello
Enzo R
ER
Department of Physiology, The University of Melbourne, Parkville,Vic. 3010, Australia.
Meeker
William F
WF
Thomas
Walter G
WG
Widdop
Robert E
RE
Delbridge
Lea M D
LM
D000818:Animals; D000831:Animals, Newborn; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D003345:Corticosterone / Q000008:administration & dosage / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D004336:Drug Antagonism; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology; D005938:Glucocorticoids / Q000008:administration & dosage / Q000494:pharmacology*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044140:Receptor, Angiotensin, Type 1 / Q000235:genetics* / Q000378:metabolism; D044139:Receptor, Angiotensin, Type 2 / Q000235:genetics* / Q000378:metabolism; D014161:Transduction, Genetic
D005938:Glucocorticoids; D044140:Receptor, Angiotensin, Type 1; D044139:Receptor, Angiotensin, Type 2; D010656:Phenylephrine; D003907:Dexamethasone; D003345:Corticosterone