Comparison of the effects of calcitonin gene-related peptide and amylin onosteoblasts

Calcitonin gene-related peptide (CGRP) and amylin are homologous 37-amino-a cid peptides which have been demonstrated to have anabolic effects on bane. It is not clear whether these effects are mediated by a common receptor, n or is it known which ligand is the more potent. These questions are address ed in the present study using cultures of fetal rat osteoblasts, CGRP incre ased cell number when present in a concentration greater than or equal to 1 0(-9) M, but 10(-8) M CGRP was required to stimulate thymidine and phenylal anine incorporation, Amylin was effective on these indices at 100-fold lowe r concentrations, and its maximal effects were about twice as great as thos e of CGRP, ED50's for the effects of amylin and CGRP on cell number were 10 (-12) M and 10(-10) M, respectively. There was no additivity between maxima l doses of the peptides on these indices. The effects of specific receptor blockers on the maximal stimulation of cell number by these peptides were a lso studied, The CGRP receptor-blocker, CGRP-(8-37), completely blocked the effect of CGRP at blocker concentrations greater than or equal to 10(-9) M . In contrast, the amylin receptor blocker, amylin-(8-37), completely block ed the effects of CGRP when the blocker was present in concentrations as lo w as 10(-11) M. The K-I of CGRP-(8-37) was 2 x 10(-10) M and that of amylin -(8-37) was 7 x 10(-12) M. In converse experiments studying the blockade of maximal doses of amylin, amylin-(8-37) 10(-10) M was effective (K-I 1 x 10 (-10) M), whereas a 100-fold greater concentration of CGRP-(8-37) was neces sary to achieve the same effect (K-I 6 x 10(-9) M). It is concluded that am ylin and CGRP probably act through a common receptor to stimulate osteoblas t growth, and that this receptor has a higher affinity for amylin than for CGRP.