Mineral Maturity Research Articles

The nature of bone carbonate.

Models of the bone salt and its synthetic analogues have been strenuously, and sometimes emotionally debated since the late nineteenth century. The main protagonist in the drama is the ubiquitous CO3=ion whose role has never been clearly understood. Initially regarded as an essential part of the calcium phosphate crystal complex, it came to be dubiously designated as a separate phase CaCO3, as an adsorbed ion, or even as a mere contaminant. More recent studies provide evidence that the original impression may be more nearly correct. Of particular interest in defining the role of CO3= in bone are the reactions involved in the formation of CO3-apatite under conditions approximating the physiological. These observations suggest that the synthesis of bone mineral involves hydrolysis of an initial acidic calcium phosphate precipitate to octacalcium phosphate, which is then converted to octacalcium phosphate carbonate (OCPC) by virtue of the replacement of PO4 identical to (HPO4=) by CO3=. OCPC satisfies many criteria for a satisfactory definition of the nature of the bone mineral. It can explain its solubility behavior and the intrinsic relationship between PO4 identical to (HPO4=) and CO3=, the normal variations in bone composition, the sequence of events in bone mineral maturation, and the loss of CO3= under normal and pathological conditions.

25-hydroxycholecalciferol-enhanced bone maturation in the parathyroprivic state.

In vitro evidence presently favors a direct osteolytic effect of biologically active vitamin D metabolites. Studies were designed to evaluate the effect of 25-hydroxycholecalciferol (25OHD3) on bone collagen and mineral maturation in vivo and its dependence on parathyroid hormone (PTH). After treatment of sham-operated control and parathyroidectomized (PTX) mature rats with either 25OHD3 or an oil vehicle for 2 wk, tibial bone mineral-collagen maturation was quantitated by bromoform-toluene density gradient fractionation techniques. Intestinal calcium absorption was measured by in vivo 45Ca transport procedures. In contrast to the control group, the response to 25OHD3 of PTX rats was dramatic. Bone mineral and matrix maturation were both accelerated by 25OHD3 treatment without concomitant reduction in total bone mineral or collagen content or changes in the intestinal calcium absorption. These observations support the premise that biologically active vitamin D metabolites stimulate bone tissue maturation, and that PTH is not required in this regard.

Abnormal bone mineral maturation in the chronic uremic state.

X-ray diffraction analysis of bone from chronically uremic but nonacidotic rats with normocalcemia and hyperphosphatemia revealed smaller apatite crystals and an increase in the X-ray amorphous mineral fraction when compared to age-matched, pair-fed control animals, indicating less advanced mineral maturation in the uremic animals. Studies in animals with varied degrees of chronic renal insufficiency revealed a progression of the bone crystal maturational defect with advancing uremia.

Effect of Experimental Chronic Renal Insufficiency on Bone Mineral and Collagen Maturation

The effect of chronic renal disease on bone matrix and mineral maturation was evaluated in rats with experimental renal insufficiency of 2-11 wk duration utilizing bromoform-toluene gradient fractionation of bone powder, pulse labeling experiments with (45)Ca and proline-(3)H differential extraction, and X-ray diffraction techniques.Maturation defects in both collagen and mineral ((45)Ca) metabolism were documented as early as 2 wk after the induction of uremia, when total bone calcium, inorganic phosphate, and hydroxyproline content were unchanged. The maturational defect progressed with advancing uremia despite insignificant changes in plasma pH and calcium, and normal bone carbonate levels. Although circulating levels of 25-hydroxycholecalciferol were significantly lower than normal in the uremic animals, pretreatment with either this vitamin D metabolite or vitamin D(3) itself failed to alter the observed changes in skeletal maturation.

Changes in the composition of bone during the metamorphosis of Rana temporaria.

Mineral matter in the bones ofRana temporaria changes in composition during metamorphosis. The change involves an increase in the Ca:P ratio of the mineral similar to that found in birds and mammals, indicating that the processes of bone mineral maturation may be similar in lower and higher vertebrates.