Calcitonin gene-related peptide (8-37) does not antagonize calcitonin gene-related peptide in rat spinal cord.

We have examined the effects of intrathecal (i.t.) human calcitonin gene-related peptide (hCGRP) and its C-terminal fragment hCGRP(8-37), a proposed CGRP antagonist, on the flexor reflex in decerebrate, spinalized, unanesthetized rats. I.t. hCGRP at 26 pmol caused a moderate facilitation of the reflex which was not antagonized by hCGRP(8-37) at doses ranging from 26 pmol to 5.2 nmol. Furthermore, hCGRP(8-37) by itself facilitated the reflex, with no signs of inhibition. It is concluded that the spinal CGRP receptor mediating the spinal facilitatory effect of hCGRP is not antagonized by hCGRP(8-37). Thus, it is unlikely that hCGRP(8-37) can be useful as a spinal analgesic.