Recent advances in calcium metabolism. I. Mechanisms of calcium homeostasis

Mineral metabolism in growing cats: changes in the values of blood parameters with age

The purpose of this study was to describe changes in calcium, phosphorus, magnesium, parathyroid hormone, calcitriol and calcidiol in cats from 3 to 15 months of age. Fourteen European shorthair healthy cats of both sexes (seven males, seven females) belonging to a research colony were studied from 3 to 15 months of age. Plasma concentrations of total calcium, ionised calcium, albumin, phosphorus, magnesium, intact parathyroid hormone (I-PTH), whole parathyroid hormone (W-PTH), calcidiol and calcitriol were measured at 3, 6, 9, 12 and 15 months of age. From 3 months of age to adulthood cats showed a decrease in calcium (both total and ionised), phosphorus and magnesium. No major changes in PTH were evident, although the ratio of W-PTH:I-PTH decreased significantly with age. A reciprocal change in vitamin D metabolites (decrease in calcitriol and increase in calcidiol) was identified during the growing process. Our results, showing changes in most parameters of mineral metabolism during growth, reinforce the need to use adequate age-related reference values for diagnostic purposes.

Bone mineral content in nephrotic children on long-term, alternate-day prednisone therapy

Bone mineral content (BMC) was measured by single-photon absorptiometry in 24 children with steroid-dependent, minimal-lesion nephrotic syndrome after 1 to 6.3 years of alternate-day prednisone therapy and in a sex- and age-matched control group. Bone mineral content was -0.002 +/- 1.2 standard deviation scores in patients and 0.3 +/- 1.4 in controls (t = 1.17; P = 0.25). No significant relation was found between BMC in patients and the amount of prednisone taken or the duration of therapy. Alternate-day prednisone therapy at doses usually needed to keep children with steroid-dependent nephrotic syndrome under control does not significantly affect BMC.

Effect of high levels of corticosteroids on the lipids of the long bones of the mature rabbit

Corticosteroid administration is associated with the development of nontraumatic osteonecrosis in man. However, the pathogenesis of steroid-induced osteonecrosis is unknown. Osteopenia, occurring as a result of corticosteroid treatment is thought to be one factor contributing to the compromise of vascular space. We have treated rabbits daily with hydrocortisone-acetate (15 mg per 4 kg rabbit for 4 and 9 weeks, respectively). These animals progressively developed osteoporosis. Cholesterol accumulated in both the unwashed cancellous bone and the marrow-free compact bones of the treated rabbits when contrasted with age-matched controls. Elevations in marrow lipid content were also observed in the treated animals. Although none of the treated rabbits developed osteonecrosis during the short time of the study, the findings of elevated cholesterol suggest that alterations in bone cell membranes may lead to cell dysfunction and osteopenia. This osteopenia may eventually cause osteonecrosis by occlusion of subchondral vessels. The elevated marrow lipids may also contribute to the development of osteonecrosis by increasing intramedullary pressure and causing venous stasis.

Late evolution of serum immunoreactive parathyroid hormones, calcitonin and plasma 25-hydroxy cholecalciferol concentrations in very low birthweight infants

The plasma concentrations of 25-hydroxycholecalciferol (25-OH-CC), immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) were measured at the age of 30 and 66 days in thirteen preterm neonates (birthweight: 970 to 1300 g). At the age of 30 days when all infants were fed only with breast milk (BM) serum iCT and iPTH levels were normal. During the second month 7 infants were fed with BM only (control group) and 6 infants were supplemented with formula (supplemented group). At the age of 66 days, mean +/- S.D. serum iPTH concentration was higher in the supplemented group than in the control group: 169 +/- 79 vs. 60 +/- 33 microliterEq/ml (p less than 0.01). Serum iCT levels remained undetectable (less than 150 pg/ml) in both groups. Plasma 25-OH-CC concentrations were normal and similar in both groups. Serum iPTH concentrations were positively correlated with phosphorus intake and negatively correlated with calcium intake from BM only. The results suggest that secondary hyperparathyroidism can be detected in very low birthweight infants supplemented with a formula, probably because of a phosphorus load or decreased intestinal absorption of calcium.

Pathophysiology of gastrointestinal hormones. Implications for paediatrics

Gastrointestinal hormones (GI hormones) have received growing interest in endocrinology, gastroenterology and neuroendocrinology. Because of new methodological techniques, they can be measured in plasma and therefore be related to different pathophysiological conditions. In childhood, our present knowledge is as yet limited to the physiological rôle of gastrin at different ages and in some diseases (gastrinoma; Verner-Morrison syndrome) caused by humoral dysfunction. The present review relates the clinical important GI hormones to chemically classified families. The diagnostic value of determining endogenous hormone concentration in plasma and the validity of function tests carried out by administration of exogenous hormones are pointed out. Particular emphasis is given to the trophic action of GI hormones in the development and function of the gastrointestinal tract during childhood. More speculatively, GI hormones are involved in the complex function of the central nervous system, thus making food intake a trophotropic action in a broader sense.

Calcification in porcine xenograft valves in children

Calcification developed in the degenerating collagen of the cusps of three porcine xenograft heart valves implanted in children for less than 4 years. The morphologic features and effects of this calcification are presented. Calcification of porcine xenografts seems to occur more frequently and at an earlier stage after insertion in children than in adults. Host factors, possibly related to calcium homeostasis, may promote calcification; hence, these valves may not be appropriate for use in children.

Rickets as a complication of intravenous hyperalimentation in infants

Fifteen newborn infants developed roentgenographic evidence of rickets while on long-term intravenous hyperalimentation. In each instance, the initial diagnosis of rickets was suggested on the chest roentgenogram, where characteristic cupped and frayed upper humeral metaphyses were noted; subsequent knee and wrist roentgenograms substantiated these findings. Factors which may have predisposed to the development of rickets include inadequate doses of vitamin D, prematurity and a rapid change in body weight during hyperalimentation therapy.

Increased growth after long-term oral 1alpha,25-vitamin D3 in childhood renal osteodystrophy

We evaluated oral 1,25-vitamin D3 for as long as 26 months in six prepubescent children with renal osteodystrophy previously treated with vitamin D2. Therapy was given at 14 to 41 ng per kilogram per day to correct hypocalcemia and reverse bone disease. Serum levels of 1,25-vitamin D3 were initially reduced at 15 +/- 5 pg per milliliter (mean +/- S.E.M.) and after treatment rose to 54 +/- 13. Serum calcium rose from 7.5 +/- 1.6 mg per deciliter (mean +/- S.D.) to 9.8 +/- 0.6 after one month (P less than 0.02). Alkaline phosphatase activity fell from 536 +/- 298 to 208 +/- 91 IU per liter after 12 months (P less than 0.05). Serum immunoreactive parathyroid levels fell from 900 +/- 562 microliter eq per milliliter 411 +/- 377. Healing of rickets and subperiosteal erosions was found. Remineralization of bone was demonstrated by the photon absorption technic. In four patients growth velocity, evaluated for 12 months before and after therapy, increased from 2.6 +/- 0.8 to 8.0 +/- 3.2 cm per year. Growth velocity per year increased from less than third percentile in each to the 10th to 97th percentile after therapy. Height increment ranged from 27 to 113 per cent of that expected for change in chronologic age and 40 to 114 per cent expected for change in bone age after therapy. This trial demonstrates that oral 1,25-vitamin D3 can reverse renal bone disease and increase growth in uremic children.

An improved method for the measurement of 1,25-(OH)2D3 in human plasma

Here we report a highly sensitive and convenient ligand binding assay for the determination of 1,25(OH)2D3 in small volumes of human plasma. This method involves: (1) extraction of vitamin D3 and its metabolites using methanol-methylene chloride with separation of phases by centrifugation; (2) gel chromatography and high pressure liquid chromatography for the quantitative isolation of 1,25-(OH)2D3; and (3) a sensitive ligand binding assay for 1,25-(OH)2D3 employing cytosol receptor from the intestinal mucosa of rachitic chicks. Using modified rachitogenic chick diets allows early (less than 4 wks) harvesting of active receptor for 1,25-(OH)2D3 in high yield. The method includes a rapid and effective procedure for stable and long-term storage of the active cytosol receptor. A convenient dextran-charcoal means is used for the separation of receptor bound from free 1,25-(OH)2D3 resulting in the achievement of a lower (less than 5%) background (i.e., nonspecific binding) than reported for other 1,25-(OH)2D3 assays. Analysis of this receptor shows it to be a saturable, single class of binding sites with a dissociation constant (Kd) of approximately 3.7 x 10-11. The final recovery of 1,25-(OH)2D3 following extraction and chromatography is 80 +/- 3% and triplicate determinations can be made on a 3 ml plasma sample. The ligand binding assay routinely detects less than or equal to 5pg of 1,25-(OH)2D3 per assay tube and the inter- and intraassay variation, based on repeated determinations of 1,25-(OH)2D3 in pooled normal human plasma, is less than 5%. Preliminary studies indicate that our methodology will permit measurement of plasma 1,25-(OH)2D3 levels in all normal subjects and in pathophysiologic states where 1,25-(OH)2D3 levels may be below or above normal values. 1,25-(OH)2D3 values (pg/ml +/- SEM) in human plasma obtained from both normals and patients with various untreated calcium homeostatic disorders were: normals = 33.5 +/- 1.8; end-stage chronic renal failure = 5.1 +/- 1.2; primary hypoparathyroidism = 18.3 +/- 2.8; primary hyperparathyroidism = 61.4 +/- 7.1; and hyperthyroidism with associated hypercalcemia = 42.1 +/- 8.4.

Rickets in low birth weight infants receiving total parenteral nutrition

Development of rickets in association with parenteral nutrition is described in four premature infants having gestational ages of 26-31 wk. In the first two infants there was a documented deficiency of vitamin D, but in the second two adequate supplementation was achieved. Vitamin D, whose primary action is to facilitate intestinal absorption of calcium, may also be a hormone of prime necessity in infant bone formation. Conversion of precursor cholecalciferol to the active form of hormone, 1,25-DHCC, requires intermediate hydroxylation by the liver. The premature infant liver may be deficient in its ability to carry out this step of metabolism, and in normal intrauterine existence the fetus may receive 1,25-DHCC, the active metabolite, from the mother. Calcium intake in these infants was far below that achieved by fetuses of comparable age in utero, even though in excess of that provided by usual premature infant oral formulas. Although calcium deficiency has not been incriminated as a cause of rickets in the past, it is possible that in very tiny premature infants rapid growth requirements lead to a relative calcium deficiency which may be manifested as uncalcified osteoid. Until the mechanism of the formation of rickets in small premature infants is clarified it is recommended that supplemental calcium and vitamin D be given to all premature infants receiving parenteral nutrition, and that periodic x-rays be obtained to detect the development of rickets.