Human alpha-calcitonin gene-related peptide stimulates adenylate cyclase and guanylate cyclase and relaxes rat thoracic aorta by releasing nitric oxide

1. The signal transduction pathway for vasorelaxation induced by human a-calcitonin gene-related peptide (human a-CGRP) was studied in rat thoracic aortic rings preconstricted with noradrenaline (10^-7 M). 2. Vasorelaxation by human a-CGRP was inhibited by haemoglobin (10^-6 M) and methylene blue (10^-5 M) but was unaffected by ibuprofen (10^-5 M). 3. Acetylcholine caused a 16 fold increase in levels of guanosine 3':5'-cyclic monophosphate (cyclic GMP) with levels of adenosine 3':5'-cyclic monophosphate (cyclic AMP) being unaltered. Human a-CGRP caused a 12 fold increase in levels of cyclic GMP but, in contrast to acetylcholine, evoked a 2.5 fold rise in levels of cyclic AMP. The rises in cyclic nucleotides evoked by human a-CGRP and acetylcholine were dependent on the presence of an intact endothelium. 4. N^G-nitro-L-arginine (L-NOARG: 10^-5 M), which inhibits nitric oxide synthetase, inhibited the relaxant response to human alpha-CGRP and cyclic GMP accumulation without affecting the cyclic AMP accumulation. 5. The data presented in this paper suggests that human alpha-CGRP relaxes the rat thoracic aorta by releasing nitric oxide and stimulating guanylate cyclase. The stimulation of adenylate cyclase by human a-CGRP probably precedes the activation of nitric oxide synthase but could be unrelated to the relaxant response.