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Abstract
Adrenomedullin and calcitonin gene-related peptide (CGRP) inhibited the pressor response
to transmural electrical stimulation in perfused isolated canine mesenteric arteries.
The response was abolished by treatment with either prazosin or tetrodotoxin. Adrenomedullin-(22-52),
an adrenomedullin receptor antagonist, reduced the inhibitory effect of adrenomedullin
(10(-10) to 10(-8) mol/l), but did not alter the action of CGRP. CGRP-(8-37), a CGRP(1)
receptor antagonist, did not affect the inhibition induced by adrenomedullin, but
reversed the CGRP-induced inhibition. In helical strips of the arteries, adrenomedullin
(up to 10(-8) mol/l) did not influence the contraction induced by noradrenaline, whereas
CGRP attenuated the response. Adrenomedullin decreased the release of noradrenaline
from adrenergic nerves elicited by transmural electrical stimulation, but CGRP had
no effect. Adrenomedullin-(22-52) reversed the decrease in noradrenaline release induced
by adrenomedullin. The adrenomedullin-induced relaxation of vascular strips precontracted
with prostaglandin F(2alpha) was suppressed by CGRP-(8-37) but was unaffected by adrenomedullin-(22-52).
These findings suggest that adrenomedullin impairs noradrenaline release from adrenergic
nerves by acting on adrenomedullin receptors located in the nerve terminals, whereas
arterial relaxation caused by adrenomedullin and CGRP is due to activation of CGRP(1)
receptors in vascular smooth muscle.