Calcium and phosphorus balance studies were carried out in subtotally nephrectomized rats (NX), with or without parathyroidectomy (NX-PTX; NX sham-PTX) in order to determine the ability of the remnant kidney to regulate excretion of these elements in the absence of parathyroid hormone. The rats were fed three different phosphorus diets, and calcium intake was also varied. We found that the NX-PTX rats adapted to the three different phosphorus diets in a manner indistinguishable from the NX sham-PTX rats. The per cent of ingested phosphorus excreted in the urine increased as dietary phosphorus increased. When supplementary calcium was added to the diet urinary phosphorus excretion fell and fecal phosphorus increased, in an identical fashion in the NX-PTX and NX sham-PTX animals. Urinary calcium excretion decreased as dietary phosphorus increased, and UCaV increased when supplementary calcium was provided in the diet. Total body calcium and phosphorus balance (intake-(urine+feces)) varied with intake, but was not significantly different between the NX-PTX and NX sham-PTX rats. These experiments demonstrate that subtotally nephrectomized rat have a parathyroid-independent mechanism(s) for regulating both urinary and fecal calcium and phosphorus excretion. The mechanism is not revealed by the present study, but may relate to changes in serum calcium and/or phosphorus which occur following parathyroidectomy.
Animal ; Calcium/metabolism* ; Homeostasis* ; Kidney/physiology ; Male ; Nephrectomy* ; Parathyroid Glands/surgery* ; Parathyroid Hormones/physiology ; Phosphorus/metabolism* ; Rats ; Rats, Inbred Strains

OBJECTIVETo investigate the correlation of serum sex hormones and parathyroid hormone (PTH) with the biochemical markers of bone turnover in aged men.

METHODSWe collected the laboratory data of 465 men aged 60- 93 (73. 1 +/- 8. 3) years old, who came for routine physical examinations in our hospital. We obtained the levels of serum follicle- stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), testosterone (T), sex hormone binding globulin (SHBG), PTH, 25-hydroxy-vitamin D3 (25(OH) D3), and bone turnover markers C-terminal telopeptide of type I collagen (CTX), osteocalcin (OC) and amino-terminal propeptide of type I procollagen (PINP). We also determined free testosterone (FT) , bioactive testosterone (BT) , testosterone secretion index (TSI) and FT index (FTI), and analyzed the correlation of each index with the biochemical markers of bone turnover.

RESULTSThe concentrations of serum FSH, LH, and SHBG increased, while the levels of FT, BT, TSI, FTI, PTH, CTX, OC and PINP decreased with age, especially in those over 80 years old (P <0.05). PTH was positively correlated with CTX, OC and PINP (r =0. 227, 0. 269 and 0. 162, P <0. 01), even after the adjustment for age, while SHBG negatively correlated with OC (r = -0. 100, P <0.05). The bone turnover markers increased with the elevation of the PTH quartiles, with significant differences between the first and the fourth quartile (P <0. 01). Multiple stepwise regression analysis showed that age was correlated inversely with CTX, OC and PINP ( beta = -0. 126, -0. 141 and -0. 122, P <0.05) , PTH positively with the three markers (beta = 0. 196, 0.279 and 0.189; P <0. 001), and SHBG negatively with OC ( beta = -0. 100, P <0.05) .

CONCLUSIONAging is the fundamental cause of reduced bone turnover in aged men. The levels serum PTH and SHBG are significantly associated with the biochemical markers of bone turnover.

Aged ; Aged, 80 and over ; Aging ; Bone Density ; Bone Remodeling ; physiology ; Bone and Bones ; metabolism ; Estradiol ; blood ; Follicle Stimulating Hormone ; blood ; Gonadal Steroid Hormones ; blood ; Humans ; Male ; Middle Aged ; Parathyroid Hormone ; blood ; Testosterone ; blood