Hyperparathyroidism is augmented by ovariectomy in Nagase analbuminemic rats

The role of albumin in bone metabolism was studied in Nagase analbuminemic (NA) rats. Serum calcium (Ca), inorganic phosphate (Pi) and magnesium (Mg) concentrations did not differ between female NA and control Sprague-Dawley (SD) rats at the time of ovariectomy (ovx), although serum ionized Ca was s ignificantly lower in NA rats than in SD rats. Serum parathyroid hormone (P TH) and osteocalcin (OC) concentrations and urinary Ca excretion were signi ficantly greater in NA rats than in SD rats, suggesting hyperparathyroidism and the resultant enhanced bone turnover in NA rats. Paradoxically, ovx in creased serum PTH and OC in NA rats but not in SD rats. Ovx-induced exacerb ation of hyperparathyroidism was confirmed by significantly greater convers ion of 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D in ovx NA rats even a fter normalization to vitamin D-binding protein. Bone mineral density (BMD) in proximal tibia increased similarly in a time-dependent manner in sham-o perated NA and SD rats. However, ovx ablated the time-dependent increase of BMD in SD rats and significantly decreased BMD in NA rats by 2 wk after ov x, resulting in a significantly lower BMD in ovx NA rats than in ovx SD rat s. In summary, NA rats, which are analbuminemic with compensatory increases in lipid and protein synthesis, developed hyperparathyroidism, possibly du e to an increase in serum Pi and a reduction of ionized Ca, and ovx induced a greater BMD reduction in NA rats than in SD rats, probably by exacerbati ng hyperparathyroidism.