Calcitonin gene-related peptide and its novel receptors in hypoxic pulmonary hypertension

The primary goal of this research was to examine the vasodilatory action of calcitonin gene-related peptide (CGRP) in the pulmonary circulation in hopes to enhance the efficacy of this endogenous lung peptide during pulmonary hypertensive states.; The first aim was to investigate the protective efficacy in rats of selected N-terminal CGRP fragments in hypoxic pulmonary hypertension (HPH). This strategy has the potential of avoiding the competitive inhibitory effects of C-terminal CGRP metabolites. When chronically infused via the right jugular vein during 14 days of hypobaric hypoxia, CGRP_{1–8, 1–13} and _1–14 significantly diminished the hypoxia-induced elevation of pulmonary artery pressure (PPA), pulmonary arterial medial thickness, and right ventricular hypertrophy, suggesting that these CGRP sequences can mitigate chronic HPH in rats.; The second aim was to examine pulmonary existence of the novel putative CGRP receptors RDC-1 and calcitonin receptor-like receptor (CRLR), and also receptor activity modifying proteins (RAMPs) 1, 2, and 3. RAMP1 and RAMP2 are required for CRLR's function as CGRP and adrenomedullin receptors, respectively, whereas the function of RAMP3 is unclear. Changes in their specific mRNA levels upon airway hypoxia were also determined. This was accomplished by using qualitative, semiquantitative, and real-time RT-PCR. Our results show upregulation of RDC-1 and RAMPs 1 and 3 in hypoxic rat lung, whereas there was no change in CRLR and RAMP2 mRNAs.; The third aim was to investigate the roles of RDC-1 and RAMP1 in mediating pulmonary vasodilation by selectively inhibiting their synthesis using in vivo antisense oligonucleotide (AS) -mediated gene knock-down. CGRP AS was used as a technical control. CGRP, RAMP1 and RDC-1 AS significantly exacerbated HPH in 1-week hypobaric hypoxic rats compared to hypoxic mismatched-AS (MM) and saline vehicle controls. CGRP- and RAMP1 AS also raised PPA in normoxic rats acutely exposed to 10% O₂ to levels above MM and saline controls, and normoxic CGRP AS-treated rats had higher basal vascular tone. These data confirm the protective role of CGRP in the pulmonary circulation, and suggest that endogenous RAMP1 and RDC-1 are essential in modulating P_PA during hypoxia.