Effects of Parathyroidectomy on the Development of Nephrocalcinosis and Calcium, Phosphorus and Magnesium Balance in Rats

Abstract

Rats of different strains raised on a semipurified casein\p=m-\sugar diet, develop a nephrocalcinosis in which deposits composed principally of calcium and phosphorus accumulate at the corticomedullary junction of the kidney. To determine whether the development of this nephrocalcinosis was in any way related to the activity of the parathyroid glands, female weanling 21-day-old rats were parathyroidectomized (PTX) or sham\x=req-\ operated and fed the semipurified diet for 3 weeks. Absorption, retention and excretion of Ca, P and Mg were studied during a 14-day balance period. The effects of injecting PTX rats with a small amount of parathyroid extract (15 U.S.P. units Lilly Para-thor-mone, every 12 h for 1 week) were examined.Compared with sham-operated animals PTX rats showed: lower serum Ca and higher P concentrations; a lower urinary excretion (% intake) of Ca, P and Mg; a higher retention (% intake) of P and Mg; a higher concentration of Mg in bone (% femur ash). Administration of parathyroid extract (PTE) tended to reverse changes induced by parathyroidectomy but PTE-treated animals remained slightly hypocalcaemic. Sham-operated and PTE-treated PTX rats developed nephrocalcinosis but untreated PTX rats did not do so.The results indicate that nephrocalcinosis did not develop in rats fed the semipurified diet in the absence of parathyroid hormone. It is postulated that although some activity of the parathyroid glands is needed for mineral deposition in the renal tubules, excessive activity is not necessarily a prerequisite to the development of this type of renal calcification.

Oestrogen‐progestogen Oral Contraceptives and Urinary Calcium Excretion

“…In our study, oestrogens in OCA may have inhibited bone resorption to a sufficient degree to lower serum calcium concentration, thus evoking a compensatory increase in FTH secretion. A rise in circulating PTH would, in effect, maintain a normal serum calcium concentration at a lower level of bone resorption andahigher level of tubular calcium reabsorption, since the response of bone to PTH is blunted by oestrogens while the response of the kidney is unaltered (Heaney, 1975).…”

“…Sodium and potassium were measured with an IL Model 143 flame photometer, with lithium as internal standard. Calcium and magnesium were determined by atomic absorption spectrophotometry (Goulding &, Malthus, 1971) and creatinine by a standard alkaline picrate procedure (Wootton, 1964). Data were processed on a Burroughs B6700 computer and statistical comparisons between mean values of different groups made by Student's t test.…”

“…However, such an osteotrophic effect could only be maintained if bone formation continued to exceed bone resorption (Rasmussen & Bordier, 1974). Although there is some evidence of sustained osteotrophic responses t o long-term administration both of oestrogens (Aitken et al, 1973) and OCA (Goldsmith & Johnston, 1975) increments of bone mineral induced by oestrogens may be transient rather than sustained (Riggs et aZ., 1972;Heaney, 1975). Therefore fm conclusions as to the effects of use of OCA upon the build-up, maintenance and loss of skeletal minerd must await further study of the effects of these agents upon bone metabolism.…”

Magnesium and Bone Disease

“…Animal studies have shown decreased [105] or in creased [107] bone magnesium content in parathyroidectomized magnesium-deficient rats, increased femoral magnesium content in parathyroidectomized rats and increased bone magnesium in uremic rats undergoing parathyroidectomy [108][109][110]. In vitro models focusing upon PTH have also been studied [111][112][113].…”