PTHrP(107-111) inhibits in vivo resorption that was stimulated by PTHrP(1-34) when applied intermittently to neonatal mice.

Stimulated resorption by PTH(1-34) and PTHrP(1-34) was studied in a neonatal mouse model by injecting a relatively high dose (0.2 microgram/g BW) of the peptides for 6 or 16 consecutive daily injections. 3H-Tetracycline was applied once, before the beginning of the injection period. Only PTHrP(1-34) increased resorption as revealed by decreased radioactivity remaining in the tibia when compared with vehicle-treated mice. This activity was related to increased numbers of mature osteoclasts in the metaphysis of the young bones. PTHrP(107-111) completely aborted the stimulated resorption when applied simultaneously with PTHrP(1-34).