We previously described the protection by calcitonin gene-related peptide (CGRP) against hypoxic pulmonary hypertension (HPH). We here examine the roles of its putative receptor RDC-1 and receptor activity modifying protein (RAMP) 1 in mediating this protection by selectively inhibiting their synthesis. RAMP1 is an accessory protein for another putative CGRP receptor calcitonin receptor-like receptor (CRLR). Antisense oligodeoxyribonucleotides (ASODNs, 5 mg/kg/day, also 10 mg/kg/day for RDC-1) targeting RAMP1 and RDC-1 mRNAs were chronically infused to the pulmonary circulation of male Sprague-Dawley rats during 7 days of normoxia or hypobaric hypoxia (380 mmHg), and -CGRP ASODN was used as a technical control. CGRP, RAMP1 and RDC-1 ASODNs significantly elevated pulmonary artery pressure (P_PA) in chronic hypoxic rats compared to hypoxic mismatched ASODN (MMODN) and saline vehicle controls. CGRP and RAMP1 ASODNs raised P_PA in normoxic rats briefly exposed to 10% O₂ above MMODN and saline controls. Moreover, normoxic rats treated with CGRP ASODN had higher basal pulmonary vascular tone compared with controls. These data confirm the protective role of CGRP in the pulmonary circulation, and suggest that endogenous RAMP1 and RDC-1 are essential in regulation of P_PA in hypoxia. This is the first in vivo evidence supporting RDC-1 and RAMP1 as functional CGRP receptor and receptor component.