RESUMO
We have recently reported the isolation of three new members of the calcitonin (CT) gene-related peptide family of peptides, the CT receptor (CT-R)-stimulating peptides (CRSPs). We now report the sequencing and characterization of ovine/caprine CRSP-1 and caprine CRSP-2. Mature ovine and caprine CRSP-1 are identical and have strong structural homology to CRSP-1s identified to date from other species. As with other CRSP-1s, ovine/caprine CRSP-1 binds to and activates the CT-R but not the CT-like receptor (CL-R) in combination with the receptor activity-modifying proteins (RAMPs). By contrast, caprine CRSP-2 does not activate any of these receptor-RAMP complexes. Intravenous infusions of ovine CRSP-1 to normal conscious sheep induced dose-dependent reduction in plasma total Ca levels (P=0.02) and corrected Ca levels (P=0.017) associated with increases in plasma cAMP (P=0.002). CRSP-1 reduced both plasma amino-terminal pro-C-type natriuretic peptide levels (P=0.006) and plasma renin activity (P=0.028). There were no significant effects observed on hemodynamic or renal indices measured. In conclusion, we have sequenced ovine/caprine CRSP-1 and caprine CRSP-2 precursors. This newly identified CRSP-1 has been shown to share the structural and biological features of CRSP-1s known to date. In vivo studies confirm that ovine CRSP-1 reduces plasma Ca levels in sheep, presumably via a cAMP-mediated mechanism. By contrast, caprine CRSP-2 did not stimulate any combination of CT-R, CL-R, and RAMPs. Accession numbers of cDNA determined in this study are caprine CRSP-1, AB364646; caprine CRSP-2, AB364647; and ovine CRSP-1, AB364648.