Ageing ovariectomized vitamin D deficient rats as a model for postmenopausal osteoporosis with concurrent vitamin D deficiency: the effect of PTH: abstract

Osteoporosis is a multifactorial chronic disease which causes much suffering and which socioeconomic impact is considerable. ln the elderly, vitamin D shortage occurs rather frequently. ln this animal model, this condition is induced in order to mimic the human situation as far as possible. The plasma 1,25(OH)2D level increases by a bone anabolic intermittent PTH treatment. This has been shown in ovariectomized (OVX) rats. lt is not clear what part of the etfect is caused by this vitamin D metabolite. The aim of lhis study was to elucidate an eventual effect of vitamin D in combination with estrogen depletion. Normocalcaemic Vitamin D normal (+D) and deplete (-D) female BN/BiRij rats were ovariectomized (OVX) or SHAM-ovariectomized (SHAM) at an age ol 11 months. Atter one week, PBS or hPTHI-34 was given daily al 160 ¡rgikgBW s.c. for two weeks. Plasma 25(OH)D levels of all -D rats were below lnmol/I. OVX increased the plasma 1,25(OH)2D level significantly in +D but not in -D rats. The PTH treatment increased the plasma 1,25(OH)2D level in the +D rats more than ¡n .-D rats. lt had similar eflects in SHAM and OVX rats. PTH decreased the plasma calcium level significantly in all groups, whereas it increased the plasma phosphate level significantly only in +D rats. ln -D OVX rats, however, PTH decreased the plasma phosphate level significantly. The trabecular bone volume (Bvffq of the tibial metaphysis of +D and -D animals was similar. PTH caused in -D rats lwice more osteoid surface (OS/BS) than in +D rats. The alkaline phosphatase positive surface (APS/BS) was increased significantly but equally by PTH in +D and -D rats. Vitamin D depletion caused a significant increase in TRAP positive surfaces. PTH treatment did not change this difference between +D and -D ral bones. lt is concluded that an eventual mediating role of 1,25(OH)2D, during intermittent PTH treatment is to be found in mineralization of bone matrix and through an effect on osteoclasls.