Effects of Dietary NaCl Supplementation on Bone Synthesis of Hydroxyproline, Urinary Hydroxyproline Excretion and Bone⁴⁵Ca Uptake in the Rat

Abstract

High sodium chloride intakes are regarded as a risk factor for osteoporosis because they increase the obligatory urinary calcium loss and stimulate parathyroid activity. Sodium chloride loads induce osteopenia in the rat. The effect could be due to a decrease in bone formation or a rise in bone resorption. Two experiments were undertaken to study the effects of dietary NaCl supplementation on 3H-hydroxyproline synthesis and 45Ca uptake in femoral bone. Salt-treated rats excreted 1.7 times more total urinary hydroxyproline (P less than 0.001) and 2.1 times more recently labelled 3H-hydroxyproline than controls (P less than 0.02) but they did not accumulate less 3H-hydroxyproline or less 45Ca in their bones than controls. These results indicate that salt-mediated osteopenia is due to an increase in bone resorption, rather than to a decrease in bone formation.

The effect of high salt and high protein intake on calcium metabolism, bone composition and bone resorption in the rat

“…Therefore, in spite of the hypercalciuria and increased rate of bone resorption in saltsupplemented rats, their bone mass, when adjusted for body weight, was unaffected. This is in agreement with the findings of other studies in rats that found that salt supplementation (80 g/kg diet) for 10 d-8 weeks had no effect on bone mass despite the presence of hypercalciuria and increased bone resorption, as measured by urinary hydroxyproline (Goulding & Gold, 1988;Chan et al 1993). Thus, it may be that, as suggested by Goulding & Gold (1988), the duration of the present study was too short to elicit significant osteopenia.…”

“…This is in agreement with the findings of other studies in rats that found that salt supplementation (80 g/kg diet) for 10 d-8 weeks had no effect on bone mass despite the presence of hypercalciuria and increased bone resorption, as measured by urinary hydroxyproline (Goulding & Gold, 1988;Chan et al 1993). Thus, it may be that, as suggested by Goulding & Gold (1988), the duration of the present study was too short to elicit significant osteopenia. There is, for example, considerable evidence that salt supplementation (80 g/kg diet) for longer periods (2-4 months) reduces bone mass and Ca content in young and adult rats consuming diets either deficient (Goulding & Campbell, 1982Goulding & Gold, 1986;Chan et al 1993) or adequate (Goulding & Campbell, 1984;Chan et al 1993;Chan & Swaminathan, 1994, 1998 in Ca, although some studies have failed to show this (Goulding, 1980).…”

The effect of calcium intake on bone composition and bone resorption in the young growing rat

“…A reduced femoral Ca level, but not Mg or P levels, arising from an increased rate of bone resorption has also been noted in a recent study in which young growing rats were fed a high-salt diet (Creedon & Cashman, 2000). It may be that, as suggested by Goulding & Gold (1988), the duration of the present study was too short to elicit significant osteopenia. Several studies have shown that bone Ca content (Thomas et al 1988, 1991Persson et al 1993Takeda et al 1993;Peterson et al 1995), bone strength (Thomas et al 1988(Thomas et al , 1991 and bone density (Persson et al 1993;Talbott et al 1998) in young growing rats were reduced by dietary Ca restriction (i.e.…”

Sodium-Calcium Inter-Relationships with Specific Reference to Osteoporosis

“…This has been demonstrated in studies examining the release of 45Ca from labelled skeletons (Goulding & Gold, 1986) and the uptake of [3H]hydroxyproline and 45Ca into bone (Goulding & Gold, 1988).…”

“…Goulding & Gold (1988) suggested that such increases in urinary hydroxyproline during salt supplementation were mediated by parathyroid hormone (PTH), since PTH is the major determinant of bone resorption rate. This is supported by the finding that parathyroidectomy abolishes the ability of salt to elevate urinary hydroxyproline (Goulding, 1980 6).…”