The stimulation of vertebral and tibial bone growth by the parathyroid hormone fragments, hPTH-(1-31)NH2, [Leu(27)]cyclo(Glu(22)-Lys(26))hPTH-(1-31)NH2, and hPTH-(1-30)NH2

The native human parathyroid hormone, hPTH-(1-84), and certain carboxyl tru ncated analogs such as hPTH-(1-34) and even smaller fragments such as hPTH- (1-31)NH2, [Leu(27)]cyclo(Glu(22)-Lys(26))hPTH-(1-31)NH2, and hPTH-(1-30)NH 2 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, [Leu(27)]cyclo(Glu(22)-Lys(26))hPTH-(1-31)NH2, and hPTH-(1-34)NH2 prev ented 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 aft er OVX) the fragments had increased the volume and trabecular thickness sig nificantly above the values in vehicle-injected sham-operated rats, hPTH-(1 -30)NH2 can stimulate vertebral bone growth as much as the lar ger fragment s, but 10-25 times more of it was needed to do so. The same daily doses of hPTH-(1-31)NH2, [Leu(27)]cyclo(Glu(22)-Lys(26))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 injectio ns were started 9 weeks after OVX. This restoration of trabecular bone in t he L5 vertebrae in estrogen-deprived animals was accompanied by a significa nt increase in the bone mineral density (BMD) of the L1-L4 vertebrae and ti bias. However, there was no significant drop in the pelvic BMD in the estro gen-deprived animals and the effects of hPTH-(1-31)NH2, [Leu(27)]cyclo(Glu( 22)-(Lys) hPTH-(1-31)NH2, and hPTH-(1-34)NH2 on the pelvic BMD were equivoc al.