Differential antagonism of amylin's metabolic and vascular actions with amylin receptor antagonists

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Abstract
High affinity amylin binding sites are present in the rat nucleus accumbens. These sites bind [125I]amylin with an affinity of 27 pM and have high affinity for salmon calcitonin (sCT) and moderately high affinity for calcitonin gene related peptide (CGRP). N-terminally truncated peptides were tested for their ability to compete for [125I]amylin binding to these sites and to antagonize the metabolic and vascular actions of amylin. CGRP(8–37), sCT(8–32), and ac-[Asn30,Tyr32]sCT(8–32) (AC187) inhibited [125I]amylin binding to rat nucleus accumbens. Order of potency at inhibiting amylin binding (AC187 > sCT(8–32) > CGRP(8–37)) differed from the order of potency at inhibiting [125I]CGRP binding to SK-N-MC neuroblastoma cells (CGRP(8–37) > AC187 > sCT(8–32)). AC187 was the most potent antagonist of amylin's effects on isolated rat soleus muscle glycogen metabolism, and it was more effective than either sCT(8–32) or CGRP(8–37) at reducing amylin-stimulated hyperlactemia in rats. In contrast, CGRP(8–37) was the most potent peptide at antagonizing amylin-induced hypotension in rats. Amylin's hypotensive actions appear to be mediated by a weak action at CGRP receptors, while its metabolic actions are mediated by receptors with a distinct antagonist profile. AC187 is a potent antagonist of amylin binding sites in nucleus accumbens and of amylin's metabolic actions.Key words: amylin, calcitonin gene related peptide, diabetes, skeletal muscle, peptide receptors.