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Estrogen deficiency is associated with bone loss, and estrogen replacement is an effective treatment of this osteoporotic process. This study examines the early (5-120 s) effects of 17 beta-estradiol on the intracellular calcium and phospholipid metabolism in confluent female rat osteoblasts. The cytosolic free Ca2+ concentration ([Ca2+]i) was determined using fura-2/AM as Ca2+ probe. Cells were labeled with myo-[2-3H]inositol or [14C]arachidonic acid for inositol or lipid determination. Inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG) production were determined by either mass measurement or anion-exchange chromatography or by thin-layer chromatography, respectively. 17 beta-Estradiol (1 pM to 1 nM) increased [Ca2+]i in a biphasic manner within 10 s via Ca2+ influx from the extracellular milieu, as shown by the effects of the calcium chelator EGTA and the Ca2+ channel blockers nifedipine and verapamil, and via Ca2+ mobilization from the endoplasmic reticulum (ER), as shown by the effects of thapsigargin. 17 beta-Estradiol (1 pM to 1 nM) induced a biphasic and concomitant increase in IP3 and DAG formation. Estradiol immobilized on bovine serum albumin (BSA) [E-(O-carboxymethyl)oxime BSA] and its derivative (O-carboxymethyl)oxime rapidly increased ([Ca2+]i, IP3, and DAG and were full agonists, although they were less potent than the free estradiol. They had the same action time course and acted via Ca2+ influx and Ca2+ mobilization from ER. Tamoxifen, a potent inhibitor of genomic steroid responses, did not block the rapid increase in Ca2+, IP3, and DAG induced by estradiol. Finally, inhibitor of phospholipase C (neomycin) and pertussis toxin abolished the effects of 17 beta-estradiol on IP3 and DAG formation. These results suggest that female rat osteoblasts bear non-genomic unconventional cell surface receptors for estradiol, belonging to the class of the membrane receptors coupled to a phospholipase C via a pertussis toxin-sensitive G protein.

The calcaemic response of thyroidectomized parathyroid transplanted rats to a single dose of biosynthetic 1,25-dihydroxycholecalciferol (50 ng) injected into a jugular vein, was evaluated. The animals were fed a vitamin D-free, low calcium diet. Compared to sham-operated and to thyroidintact parathyroid transplanted rats thyroidectomized animals had a significantly reduced calcaemic response to 1,25-dihydroxycholecalciferol, Daily supplementation with d,l-thyroxine (100 μg/rat) during the experimental period restored a normal response. The increase in serum calcium concentration after 1,25-dihydroxycholecalciferol injection was similar in thyroidectomized bilaterally nephrectomized animals, and in thyroidectomized kidney-intact rats. The results suggest that in thyroxine depleted rats, the sensitivity of bone to the calcaemic effect of 1,25-dihydroxycholecalciferol is decreased.

Bone ultrastructure and x-ray microanalysis of aluminum-intoxicated hemodialyzed patients. In hemodialyzed patients aluminum (Al) intoxication may induce osteomalacic lesions which are mainly observed when plasma immunoreactive parathyroid hormone (iPTH) concentrations are low, and osteitis fibrosa absent. In this study, the bone tissue of eight hemodialyzed patients with elevated plasma and bone Al concentrations was examined by histomorphometry, electron microscopy, and x-ray microanalysis. Five patients (group 1) had osteomalacia and minimal osteitis fibrosa, three patients (group 2) had severe osteitis fibrosa. In group 1, Al was concentrated at the mineralizing front, in hexagonal structures measuring 200 to 1,000 Å which also contained phosphorus, but not calcium. Hydroxyapatite needles had a normal aspect. Osteoblasts appeared inactive. In group 2, Al was also present at the mineralizing layer of osteoid, but, in these cases, in small clusters next to abnormal calcium deposits. Osteoblasts appeared very active. Their mitochondria contained calcium and phosphorus granules, or amorphous material, measuring 1,500 to 2,000 Å, emitting x-rays characteristic for Al and phosphorus. These results suggest that secondary hyperparathyroidism, by stimulating the cellular activity, may increase the uptake and release of Al by the osteoblasts. The presence of Al within the mitochondria of these cells may be one of the factors inducing the mineralization defect.Ultrastructure et microanalyse x du tissu osseux de malades hémodialysés intoxiqués par l'aluminium. Chez des malades hémodialysés l'intoxication par l'aluminium (Al) peut induire des lésions ostéomalaciques qui s'observent principalement quand la concentration plasmatique de l'hormone parathyroïdienne immunoréactive (iPTH) est peu augmentée, et en l'absence d'ostéite fibreuse. Dans cette étude le tissu osseux de huit malades hémodialysés dont la concentration plasmatique et osseuse de l'Al était élevée, a été examiné par l'histomorphométrie, la microscopie électronique et la microanalyse x. Cinq malades (groupe 1) avaient une ostéomalacie et des lésions minimes d'ostéite fibreuse, trois malades (groupe 2) avaient une ostéite fibreuse sévère. Dans le groupe 1, l'Al était concentré entre ostéoïde et tissu minéralisé, dans des structures hexagonales mesurant 200 à 1000 Å, qui contenaient également du phosphore, mais pas de calcium. Les aiguilles d'hydroxyapatite avaient un aspect normal. Les ostéoblastes paraissaient peu actifs. Dans le groupe 2, l'Al était aussi présent entre ostéoïde et tissu minéralisé, mais, dans ce cas, sous forme de petits amas, près de dépôts anormaux de calcium. Les ostéoblastes semblaient très actifs. Leurs mitochondries contenaient des granules de calcium et de phosphore ou bien du matériel amorphe, mesurant 1500 à 2000 Å, dont l'émission x était caractéristique de l'Al et du phosphore. Ces résultats suggèrent que l'hyperparathyroïdie secondaire, en stimulant l'activité cellulaire, favorise la captation et le dépôt de l'Al par les ostéoblastes. La présence d'Al dans les mitochondries de ces cellules pourrait être un des facteurs à l'origine du trouble de la minéralisation.

The circulating concentrations of calcium, phosphorus, and vitamin D metabolites were measured in 25 infants (fifteen to 30 days of age) with congenital hypothyroidism before treatment or during the first 6 months of thyroxine therapy. Five of the children before treatment and four during the early 3 months of treatment had mild hypercalcemia (10.8 to 12.4 mg/dl). Hypercalcemia before treatment did not appear to be related to the vitamin D status of the infant nor to an alteration in vitamin D metabolism, but to the presence of a residual thyroid secretion. In contrast, hypercalcemia during thyroxine therapy was related to vitamin D supplementation, even though the serum calcium concentration could not be correlated with the circulating concentration of any of the vitamin D metabolites assayed and obvious changes in vitamin D metabolism could not be demonstrated.

The metabolism of 25-hydroxycholecalciferol (25-(OH)Da) was investigated in vitamin D normal rats, 4 weeks after hypophysectomy. Compared to sham-operated controls, these animals were hypophosphatemic and their parathyroid glands were significantly smaller than normal. Eighteen hours after ip injection of a single dose of tritiated 25-(OH)D3 (50 pmol), chromatography of serum extracts on Sephadex LH-20 and high pressure liquid chromatography showed that the percentage of radioactivity corresponding to 24,25-dihydroxycholecalciferol [24,25-(OH)2D3] was significantly higher in hypophysectomized rats (11.7 ± 0.95% vs. 6.9 ± 0.78%). No radioactivity was detected in the area corresponding to 1,25-dihydroxycholecalciferol. In hypophysectomized rats injected 2 weeks with radioactive 25-(OH)D3 the amount of 24,25(OH)2D3) was still higher than in sham-operated controls. Parathyroidectomy 48 h before the injection of [2H]25(OH)D3 abolished the difference between the two groups. The percentage of 24,25-(OH2D3t in th...

Serum calcidiol, calcitriol, and 24,25-dihydroxyvitamin D concentrations were measured in 20 children with vitamin D-deficiency rickets. Vitamin D metabolite concentrations were measured in 17 of 20 patients before treatment and in 14 of 20 patients after vitamin D administration. Conclusions are as follows. (1) Before treatment, serum calcidiol seems to be the best criterion of D deficiency, as it was low (less than 8 ng/ml) in 15 of 17 studied children, whereas calcitriol and 24,25-dihydroxyvitamin D concentrations ranged from undetectable to high values (350 pg/ml and 5.9 ng/ml, respectively). (2) Low calcidiol concentrations may occur despite recent vitamin D intake: low serum values were found in children given vitamin D2 up to two months after the onset of therapy (50 micrograms/day). (3) Elevated calcitriol serum concentrations were observed in all children after initiation of vitamin D therapy; these high concentrations persisted for four weeks or more, even after normalization of serum calcium, phosphorus, and parathyroid hormone values. (4) Healing of biochemical abnormalities can occur even in children with low circulating concentrations of calcidiol and 24,25-dihydroxyvitamin D.

Deflazacort was substituted for Prednisone (based on the equivalence 1 mg Prednisone equals 1.2 mg Deflazacort), during maintenance glucocorticoid therapy in 9 children, 5 with renal diseases and 4 with connective tissue or immunoproliferative disorders. Six patients received 0.26-0.35 mg/kg body weight (B.W.)/day and 3 0.48-1.2 mg/kg B.W. on alternate days, for 10-16 months. Except for a child with chronic juvenile arthritis, who was also unresponsive to Prednisone, the therapeutic effects of Deflazacort were excellent. Steroid side effects present in 8 patients decreased or disappeared. Plasma Ca, P, Mg, creatinine, alkaline phosphatase, iPTH(1-34), urinary excretion of Ca, cAMP, and TRP remained normal. Plasma iPTH(1-84) remained normal in 5 children; in the other 4 patients it increased from normal to slightly elevated values. On Deflazacort, plasma calcidiol concentrations were within the normal range in 6/8 patients prescribed daily doses of vitamin D2 (1,600-2,400 IU) or calcidiol (20 micrograms). Plasma 1,25(OH)2D levels monitored in 5 children were also normal. The osteoporosis, evaluated on the tibial cortico-diaphyseal ratio and the trabecular aspect of bone radiograms, present in 5 patients, persisted in 1 and improved in the others. On Deflazacort, statural growth proceeded normally in all subjects, with a modest acceleration of growth velocity in 3 children. These results seem encouraging for extending clinical trials with Deflazacort to the active phase of pediatric diseases requiring glucocorticoid.

The effect of high doses of 25-hydroxycholecalciferol on plasma calcium concentration was studied in rats receiving a low-calcium normal vitamin D diet. In bilaterally nephrectomized animals, as in sham-operated controls, 62.5 nmol of 25-hyroxycholecalciferol did not produce a rise of plasma calcium concentration. In contrast, the administration of 125 or 625 nmol, doses 1,000-5,000 times the minimal active dose in D-deficient rats, was followed in both groups of animals by a significant increase of plasma calcium concentration. Removal of either parathyroids alone or parathyroid and thyroid glands did not suppress this effect. These data suggest that when large doses are used in vivo, the renal conversion of 25-hydroxycholecalciferol to more polar metabolites is not an obligatory step for its calcium-mobilizing action. The present study does not elucidate, however, the exact mechanism(s) of this effect.

The effects of 25-hydroxycholecalciferol were studied in 4 children with deficiency rickets and 22 children with D-resistant rickets, including patients with hereditary hypophosphatemic D-resistant rickets, “pseudo-deficiency” rickets, and rickets secondary to cystinosis or to tyrosinosis. Three protocols were used. (a) 8 days after a single oral dose of 16,000 IU of 25-hydroxycholecalciferol, normalization of all biological parameters was observed in all cases of deficiency rickets. A complete lack of response was observed in the different types of resistant rickets. (b) Under prolonged administration of 2,640 IU/day for 2 months, clinical-biological symptoms and X-ray lesions disappeared, and a catch-up growth pattern was observed in deficiency rickets; no relapse of rickets occurred up to 5 months after therapy was stopped. The same dose had no significant effect in 10 patients with hereditary hypophosphatemic D-resistant rickets. A bone biopsy performed in one case showed the persistence of characteristic lesions. (c) With increasing doses of 25-hydroxycholecalciferol varying from 6,000 to 30,000 IU/day and a follow-up of 6 months up to 2 yr duration, clinical-biological-radiologic recovery and catch-up growht was obtained in all cases of “pseudo-deficiency” rickets. In hypophosphatemic hereditary D-resistant rickets, 5 out of 13 patients' serum concentration of phosphorus reached at least 30 mg/liter, but a catch-up growth pattern was not observed. These results indicate that (a) 25-hydroxycholecalciferol is highly active in deficiency rickets; (b) a defect in the conversion of vitamin D3 to its active 25-hydroxy metabolite is probably not the metabolic defect in any of the different types of vitamin D-resistant rickets studied.

Effects of 25-hydroxycholecalciferol on bone lesions of children with terminal renal failure. Quantitative histology was performed on serial iliac crest biopsies obtained from 14 children with terminal renal failure. A long-term study on the comparative effects of vitamin D 2 and 25-hydroxycholecalciferol [25-(OH)D 3 ], in five patients with severe lesions of osteomalacia and/or osteitis fibrosa, demonstrated the efficiency of 25 to 200µg/day of 25-(OH)D 3 and the lack of therapeutic action of 345 to 685 µg/day of vitamin D 2 . In nine subjects with normal roentgenograms or minimal skeletal alterations, the first biopsy taken at the beginning of intermittent hemodialysis showed evidence of defective mineralization and/or lesions of resorption. Four of these children were treated with 25-(OH)D 3 (25 to 50µg/day) and calcium supplementation orally (0.5 to 1.5 g/day); five children received calcium orally (0.5 to 0.75 g/day) alone. Aggravation of bone lesions during intermittent hemodialysis was observed in patients treated with calcium supplements alone. In subjects who were given 25-(OH)D 3 , mineralization improved and marrow fibrosis disappeared. However, as the two groups of patients were different in composition and in the manner in which they were treated, it is difficult to state whether the beneficial effects observed were solely attributable to 25-(OH)D 3 administration. 25-(OH)D 3 therapy induced severe intoxication in two patients. A rise in plasma calcium concentration to 11.0 to 11.5 mg/100 ml was observed in two other patients. It is concluded that: a) pharmacologic doses of 25-(OH)D 3 are highly effective in healing bone lesions of children with terminal renal failure; b) such treatment requires strict clinical surveillance as 25-(OH) D 3 intoxication may occur even in anephric patients. Effets du 25-hydroxycholecalciferol sur les lesions osseuses dans l'insuffisance renale terminale de l'enfant. Le tissu osseux de quatorze enfants en insuffisance renale terminale a ete etudie par des techniques d'histologie quantitative sur des biopsies iteratives de la crete iliaque. Chez cinq malades ayant des lesions severes d'osteomalacie et/ou d'osteite fibreuse la comparaison des effets therapeutiques a long terme de la vitamine D 2 (345 a 685 mg/jour) et du 25-(OH)D 3 (25 a 200µg/jour) a mis en evidence la grande efficacite du 25-(OH)D 3 et le manque d'action de la vitamine D. Chez neuf enfants devant etre traites par hemodialyse chronique et dont les radiographies du squelette etaient normales ou a peine alterees, les biopsies ont montre un defaut de mineralisation et/ou des lesions de resorption. Parmi ces sujets quatre malades ont recu un traitement associant 25-(OH)D 3 (25 a 50 µg/jour) et une supplementation orale de calcium (o,5 a 1,5 g/jour), les cinq autres seulement du calcium (o,5 a o,75 g/jour). Chez les malades recevant seulement une supplementation orale de calcium les lesions osseuses se sont aggravees sous hemodialyse chronique; par contre chez les malades recevant du 25-(OH)D 3 la mineralisation s'est amelioree et la fibrose medullaire a disparu. Cependant, la composition des deux groupes de malades et leur traitement n'ayant pas ete identiques, il est diffcile d'affirmer que les ameliorations observees ne sont dues qu'au 25-(OH)D 3 . Chez deux malades, le 25-(OH)D 3 a entraine une intoxication severe. Chez deux autres la calcemie s'est elevee a 11,0 -11,5 mg/100 ml. En conclusion, ces resultats montrent: a) l'activite therapeutique du 25-(OH)D 3 sur les lesions osseuses d'enfants en insuffisance renale terminale; b) la possibilite d'intoxication par le 25-(OH)D 3 meme de sujets anephriques d'ou la necessite d'une surveillance clinique et biologique constante de tout malade traite par ce derive de la vitamine D.

We investigated the in vitro metabolism of [26,27-3H]-25-(OH)D3 in different eel tissues. After incubation with [3H]-25-(OH)D3, tissues were extracted with methanol-chloroform and chromatographed on Sephadex LH 20 columns. Two derivatives less polar than 25-(OH)D3 were detected, the first one being sensitive to KOH treatment. Three peaks more polar than 25-(OH)D3 were also found: peak I migrated close to the 24,25-(OH)2D3 area and was quantitatively the most important, but the presence of 24,25-(OH)2D3 could not be demonstrated; peak II migrated in the 1,25-(OH)2D3 region; and peak III had an elution position twice that of peak II. After 6-h incubation of tissues isolated from control eels, peak I was found in all tissues including intestine and gills. It was highest in pituitary gland and brain and lowest in ovaries and muscle. It was not significantly modified 20 days after ablation of the corpuscules of Stannius. In contrast, in vivo daily calcium chloride injection was followed 24 hr later by a significant increase in the [3H]-25-(OH)D3 conversion into peak I in gills, intestine, and the spinal cord and by an inhibition of this conversion in pituitary gland, skin, and muscle. The inhibition was found in all tissues after five daily calcium injections. Calcium injection had no effect on the in vitro metabolite synthesis by the corpuscules of Stannius. These results suggest that vitamin D is not metabolized in the same way in eel as in mammals and that this metabolism could in part be calcium dependent.

Parathyroid gland transplanted rats and hypophysectomized rats were raised from weaning on a diet without vitamin D and low in calcium (0.02%) for 4 weeks. At the end of this period the animals of both experimental groups, when compared to their respective controls (i.e., sham-operated animals for parathyroid-transplanted ones, and hypophysectomized plus bovine growth hormone-supplemented ones for hypophysectomized rats) were characterized by (a) moderate or absent secondary hyperparathyroidism; (b) near normal bone calcium content; and (c) a maintained responsiveness to the calcemic effect of parathyroid extract (PTE). The PTE action is a bone effect that does not require the presence of the kidneys and is not related to changes in serum calcium and/or phosphorus concentrations. These results indicate that when severe hyperparathyroidism is prevented, the sensitivity of bone to the calcemic action of PTE can be maintained in D-deficient calcium-deprived rats. They also suggest that in these animals the main factor leading to resistance to PTH is the state of severe chronic hyperparathyroidism.

The possible suppressive effects of 24,25-dihydroxycholecalciferol on secondary hyperparathyroidism and increased bone resorption were investigated in adult rats raised on a diet normal in calcium, phosphorus, and vitamin D, and subjected to acute bilateral nephrectomy. The animals had received subcutaneous radiocalcium 4 wk before the experiment. 5 h after nephrectomy an increase in serum total calcium, (45)Ca-specific activity, citrate, phosphorus, and magnesium concentrations were observed. Serum immunoreactive parathyroid hormone increased, while serum calcitonin decreased. The osteoclast count in the tibial metaphyses was augmented. The biochemical and histological changes observed were partly parathyroid hormone and calcitonin independent, as they also occurred in parathyroidectomized hypocalcemic rats. Pretreatment with 650 pmol of 24,25-dihydroxycholecalciferol 16 h before nephrectomy prevented bone calcium mobilization and diminished the rise in serum total calcium and citrate both in parathyroid-intact and in parathyroidectomized animals. In parathyroid-intact rats, serum immunoreactive parathyroid hormone and calcitonin remained normal in spite of the fall in serum-ionized calcium, and the number of osteoclasts did not increase. In parathyroidectomized rats, 24,25-dihydroxycholecalciferol did not prevent the postnephrectomy rise in the osteoclast count. This latter observation suggests that this metabolite exerts its effect on bone either by acting on cells other than osteoclasts, i.e., the osteocytes, or by inhibiting cell activity. At equimolar dosage 1,25-dihydroxycholecalciferol had a potent stimulatory effect on bone resorption. This effect of 1,25-dihydroxycholecalciferol was partly blocked by the simultaneous administration of 24,25-dihydroxycholecalciferol. The potential clinical significance of these observations remains to be determined.

Gallium nitrate (GaN) reduces cancer-related hypercalcemia and inhibits bone resorption in vitro. This study investigated the effects of chronic GaN administration on bone, kidney, and parathyroid gland activity of growing rats. Experimental animals received GaN (1.75 mg elemental gallium i.p. QOD X 8, Ga+), and controls received the solvent (Ga-). In the bone of Ga+ rats the number of osteoclasts was increased (Ga+: 70.4 +/- 2.31 osteoclasts/mm2; Ga-: 46.5 +/- 1.61 osteoclasts/mm2, P less than 0.001), and apposition rate and osteoid width were unchanged. Ga was concentrated in bone (2.4 mumol/g cortical bone) and detected by electron microprobe on the surface of a few trabeculae. Alkaline (Alp) and acid (Acp) phosphatase activities were higher in Ga+ than in Ga- calvaria (Ga+: Alp 223 +/- 23.4 U/mg prot, Ga-: Alp 145 +/- 13.3 U/mg prot, P less than 0.02; Ga+: Acp 69.5 +/- 4.7 U/mg prot, Ga-: 57.5 +/- 2.8 U/mg prot, P less than 0.05). Serum iPTH was increased (Ga+: 112.9 +/- 17.6 pg/ml, Ga-: 41.4 +/- 7.4 pg/ml, P less than 0.01), serum calcium was reduced (Ga+: 2.4 +/- 0.02 mmol/l, Ga-: 2.6 +/- 0.03 mmol/l, P less than 0.001); calciuria remained comparable to controls. Relative to the hypocalcemia this suggests renal loss of Ca. The calcemic response to hPTH 1-34 (i.v. 50 micrograms/kg) was decreased 2 hours after injection of the hormone (delta Ca: TPTX Ga+: 0.11 +/- 0.04 mmol/l, Ga-: 0.33 +/- 0.03 mmol/l P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Weanling rats raised for 21 days on a vitamin D deprived, low Ca diet (0.02%), and given chronic cortisone administration (5 mg/kg/d), maintain responsiveness to the hypercalcemic effect of endogenous and exogenous parathyroid extract (PTE). The PTE action is a bone effect that does not require the presence of the kidneys, and is not related to a higher concentration of calcium or cortisone. Maintained sensitivity of D− Ca− Cort+ rats to PTE does not appear to be the consequence of a lesser degree of D-deficiency: the whole body vitamin D pool and its chloroform-soluble fraction in these animals are not different from those of their D− Ca− PTE− unresponsive controls. Repeated PTE injections for 4 days exhaust the sensitivity to the hypercalcemic action of PTE of D− Ca− Cort+ rats. The present data seem to indicate that cortisone-treated D− Ca− rats, responsive to the bone action of PTE, are characterized by a near normal bone calcium content and Ca/P ratio, and a significant increase in the number of osteoclasts.

Mice, 1 week old, prelabelled with 45Ca, were either thyroparathyroidectomised or sham-operated; 1 day later half of the mice of each group were injected with 1,25-dihydroxycholecalciferol (5 ng/g), and 20 h later all the mice were killed. Bone resorption in explants was then measured by an in vivo/in vitro technique previously published; compared with untreated mice it was found that 1,25-dihydroxycholecalciferol had increased resorption irrespective of whether the mice had been thyroparathyroidectomised or not. These data suggest that 1,25-dihydroxycholecalciferol is able to increase bone resorption independently of parathyroid hormone.

Microelectrodes were used to investigate the possible involvement of cAMP and Ca2+ ions in the parathyroid hormone's, bPTH(1-34), effect on the membrane potential of rat osteoblasts in primary culture. Parathyroid hormone (10(-7) M) depolarized cell membrane by 25.0 +/- 6.1 mV (mean +/- standard deviation, SD; n = 17). Blocking Ca2+ influx with the Ca channel blocker cobalt revealed two phases in the hormone effect: a rapid and slight membrane hyperpolarization followed by sustained depolarization. In addition, cobalt significantly (p less than 0.01) decreased the magnitude of the PTH depolarizing action. The addition of dibutyryl-cAMP (10(-3) M) to the perfusion solution also resulted in a biphasic effect. At a lower concentration (10(-4) M), dibutyryl-cAMP produced only membrane hyperpolarization, suggesting a cAMP dose dependence of the opposite membrane potential changes. Forskolin (10(-5) M) and the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) (10(-4) M) mimicked the depolarizing effect of PTH. IBMX at a low concentration (5 x 10(-6) M) potentiated the depolarizing effect of PTH. Increases in [Ca2+]i using Ca2+ ionophore A23187 and intracellular injection of CaCl2 or inositol trisphosphate decreased the PTH depolarizing action, whereas intracellular injection of EGTA enhanced this effect. These results indicate that PTH evokes a biphasic change in rat osteoblast membrane potential that seems to be mediated by an increase in cAMP and modulated by intracellular calcium.

We report the beneficial effects of calcium infusions in a child with hereditary resistance to 1,25(OH)2D and alopecia. This patient after transient responsiveness to vitamin D derivatives became unresponsive to all therapy despite serum 1,25(OH)2D concentrations maintained at levels approximately 100-fold normal. A 7-mo trial with calcium infusions led to correction of biochemical abnormalities and healing of rickets. Bone biopsies (n = 3) showed a normal mineralization and the disappearance of the osteomalacia. Cultures of bone-derived cells demonstrated a lack of activation of 25-hydroxyvitamin D 24-hydroxylase and osteocalcin synthesis by 1,25(OH)2D3 (10(-9) and 10(-6) M). These results demonstrate that even in the absence of a normal 1,25(OH)2D3 receptor-effector system in bone cells, normal mineralization can be achieved in humans if adequate serum calcium and phosphorus concentrations are maintained; and calcium infusions may be an efficient alternative for the management of patients with this condition who are unresponsive to large doses of vitamin D derivatives.

We measured plasma concentrations of 1,25-dihydroxyvitamin D (1,25-(OH)2D) in the course of a 6-to-37-month survey of four children with hypercalcemia and an elfin facies (Williams syndrome). Levels of 1,25-(OH)2D were elevated (160 to 470 pg per milliliter) during the hypercalcemic phase of the disease, when the children were five to nine months old, and they decreased thereafter. Plasma 1,25 (OH)2D levels were higher than those found in three children (16 to 60 months old) with the elfin facies syndrome and no hypercalcemia (42 to 71 pg per milliliter) and eight children (1 to 36 months old) with hypercalcemia and no dysmorphy (12 to 140 pg per milliliter), including two children with vitamin D intoxication. Hypercalcemia in the three children with elfin facies was controlled by a low-calcium diet. Serum calcium levels fell to the normal range, and plasma 1,25-(OH)2D levels were normal for age (18 to 105 pg per milliliter) at 14 to 47 months of age, even after appropriate therapy had been discontinued. These observations suggest that hypercalcemia may be the consequence of abnormal synthesis or degradation of 1,25-(OH)2D in children with the elfin facies syndrome.