Dexamethasone increases RAMP1 and CRLR mRNA expressions in human vascular smooth muscle cells

A recent report has shown that in vitro the RAMP2/CRLR complex is a functional adrenomedullin receptor in human endothelial and vascular smooth muscle cells. However, in vivo, it is well known that CGRP receptors are expressed in human coronary arteries and that a beneficial effect is observed in patients after CGRP infusion of patients with congestive cardiac failure. This contrast may be explained by the in vivo impregnation of major hormones, so we have tested if glucocorticoids were able in vitro to enhance the expression of the RAMP1/CRLR expression leading to functional CGRP receptors. The expression of RAMP1, RAMP2, CRLR, and adrenomedullin was evaluated by semiquantitative reverse-transcriptase polymerase chain reaction (RT-PCR) using (33)P in human coronary arteries vascular smooth muscle cells (VSMC) cultured in the presence of dexamethasone. Under basal conditions, the CRLR mRNA was expressed, but RAMP2 mRNA was clearly more abundant than RAMP1 mRNA. Increases in CRLR and RAMP1 mRNA expressions occurred 4 h after treatment of VSMC with 10(-7) M dexamethasone and no change was found for RAMP2 mRNA. Adrenomedullin mRNA increased later, i.e., 8 and 16 h after dexamethasone treatment. The RAMP1 mRNA expression was elevated with doses of dexamethasone ranging from 10(-10) to 10(-7) M, thus a 5-fold increase in the ratio between RAMP1 and RAMP2 was observed with the lowest dose of dexamethasone and a 2-fold rise at 10(-7) M. CRLR mRNA levels were half-reduced with the two lowest doses of dexamethasone (10(-10) and 10(-9) M), but increased from 10(-8) to 10(-7) M. Thus, we suggest that, in vivo, glucocorticoids are involved in the expression of CGRP receptors by human coronary VSMC.