N-terminal fragments of PTH and PTHrP, such as hPTH-(1-34) and hPTHrP-(1-34), are sufficiently similar with respect to amino acid sequence, location of functional domains, and higher order configuration to activate the same PTH/PTHrP receptor and the same two signal enzymes, adenylyl cyclase and phospholipase-Cβ. Therefore, it was expected that hPTHrP-(1-31)NH₂ would stimulate bone growth in ovariectomized rats as strongly as hPTH-(1-31)NH₂. Like hPTH-(1-31)NH₂, hPTHrP-(1-31)NH₂ stimulated adenyly cyclase in ROS 17/2 osteosarcoma cells as strongly as the standard hPTH-(1-34) and like hPTH-(1-31)NH₂, triggered a large drop in mean blood pressure when injected intravenously. Unlike hPTH-(1-31)NH₂, however, hPTHrP-(1-31)NH₂ could not stimulate trabecular growth in the distal femurs of young, sexually mature, ovariectomized rats.