Cross Talk Between Angiotensin AT sub 1 and alpha sub 1-Adrenergic Receptors: Angiotensin II Downregulates alpha sub 1a-Adrenergic Receptor Subtype mRNA and Density in Neonatal Rat Cardiac Myocytes

Signaling mediated by the angiotensin (Ang) II and alpha1-adrenergic receptor (alpha1-AR) pathways is important for cardiovascular homeostasis. However, it is unknown whether Ang II has any direct effect on alpha1-AR expression and signaling in cardiac myocytes. In the present study, we determined alpha1-AR subtype mRNA levels by RNase protection; receptor density by competition binding with 5-methylurapidil; and alpha1-AR-mediated c-fos expression by Northern blot analysis. We found that Ang II had no effect on alpha1b- and alpha1d-AR mRNA levels but decreased the alpha1a-AR mRNA level in a time- and dose-dependent manner. The maximal effect occurred at 6 hours with 100 nmol/L Ang II (40.0 +/- 8.2% reduction, n=4, P