The Stimulation of Vertebral and Tibial Bone Growth by the Parathyroid Hormone Fragments, hPTH-(1-31)NH₂, [Leu²⁷]cyclo(Glu²²-Lys²⁶)hPTH-(1-31)NH₂, and hPTH-(1-30)NH₂

Abstract.

The native human parathyroid hormone, hPTH-(1-84), and certain carboxyl truncated analogs such as hPTH-(1-34) and even smaller fragments such as hPTH-(1-31)NH₂, [Leu²⁷]cyclo(Glu²²-Lys²⁶)hPTH-(1-31)NH₂, and hPTH-(1-30)NH₂ stimulate femoral trabecular and cortical bone growth in ovariectomized (OVX) rats. Here we show that when injected once daily for 6 weeks starting 2 weeks after OVX in doses of 1 or 2 nmol/100 g of body weight, hPTH-(1-31)NH₂, [Leu²⁷]cyclo(Glu²²-Lys²⁶)hPTH-(1-31)NH₂, and hPTH-(1-34)NH₂ prevented the loss of trabecular volume in the L5 vertebrae induced by OVX. In fact, by the end of the sixth week of injections (i.e., the eighth week after OVX) the fragments had increased the volume and trabecular thickness significantly above the values in vehicle-injected sham-operated rats. hPTH-(1-30)NH₂ can stimulate vertebral bone growth as much as the larger fragments, but 10–25 times more of it was needed to do so. The same daily doses of hPTH-(1-31)NH₂, [Leu²⁷]cyclo(Glu²²-Lys²⁶)hPTH-(1-31)NH₂, and hPTH-(1-34)NH₂ also raised the trabecular volume and thickness in the L5 vertebrae of rats well above the values in vehicle-treated animals when the injections were started 9 weeks after OVX. This restoration of trabecular bone in the L5 vertebrae in estrogen-deprived animals was accompanied by a significant increase in the bone mineral density (BMD) of the L1–L4 vertebrae and tibias. However, there was no significant drop in the pelvic BMD in the estrogen-deprived animals and the effects of hPTH-(1-31)NH₂, [Leu²⁷]cyclo(Glu²²-(Lys) hPTH-(1-31)NH₂, and hPTH-(1-34)NH₂ on the pelvic BMD were equivocal.