Longitudinal changes in maternal serum 1,25-dihydroxyvitamin D and insulin like growth factor I levels in pregnant women who developed preeclampsia: comparison with normotensive pregnant women

This study was undertaken to determine the longitudinal changes of serum 1,25-dihydroxyvitamin D (1,25-(OH)(2)D) and insulin like growth factor I (IGF-I) levels at 20.7, 27.6, and 35.5 week periods of gestation in 40 pregnant women who remained normotensive (NT) and in 10 women who developed preeclampsia (PE). As compared with the first period, significant increases (P < 0.01) in maternal serum 1,25-(OH)(2)D and IGF-I were observed in the NT group. In the PE group, a similar increase in serum 1,25-(OH)(2)D was observed. In contrast, significant (P < 0.05) lower IGF-I levels were observed in the PE group at the moment of diagnosis. In addition a high incidence of subjects with low increase in IGF-I levels (相似文献   

24,25(OH)2D3 attenuates the calcemic effect of 1,25(OH)2D3 in rats with reduced renal mass

The present study was undertaken to evaluate the effect of 24,25(OH)2D3 on serum calcium concentration in rats with reduced renal mass. Adult 5/6 nephrectomized male rats were divided into four groups: (i) control rats, (ii) rats treated with 1,25(OH)2D3, (iii) rats treated with 24,25(OH)2D3, and (iv) rats treated with 1,25(OH)2D3 and 24,25(OH)2D3. After 4 days, serum calcium in the 1,25(OH)2D3-treated group was 7.13 +/- 0.32 meq/liter (P less than 0.001 vs control). With the combination of 1,25(OH)2D3 and 24,25(OH)2D3 serum calcium was higher than that in control, 6.25 +/- 0.5 meq/liter (P less than 0.001 vs control), but lower than that in rats receiving 1,25(OH)2D3 alone (P less than 0.05). No change in serum calcium was seen in animals treated with 24,25(OH)2D3 alone. On the eighth day serum calcium in the 1,25(OH)2D3-treated group, 6.52 +/- 0.25, was higher than in the 1,25(OH)2D3 + 24,25(OH)2D3 group, 5.87 +/- 0.17 meq/liter, P less than 0.05, P less than 0.001 vs control. In both 1,25(OH)2D3- and 1,25(OH)2D3 + 24,25(OH)2D3-treated rats, hypercalciuria of similar magnitude occurred on the fourth and eighth day of treatment. No change in urinary calcium was seen in the control and 24,25(OH)2D3-treated rats. Thus, in 5/6 nephrectomized rats combined administration of 1,25(OH)2D3 and 24,25(OH)2D3 attenuates the calcemic response to 1,25(OH)2D3 without changes in urinary calcium excretion. These observations suggest that the effect of 24,25(OH)2D3 on serum calcium is different in 5/6 nephrectomized rats as compared to normal rats, in which an augmentation of serum calcium was observed following administration of both vitamin D metabolites. The effect of 24,25(OH)2D3 on serum calcium in rats with reduced renal mass may result from a direct effect of 24,25(OH)2D3 on the bone.     

Diabetes and renal calcium binding protein in the rat

Renal calcium binding protein (CaBP), a vitamin D-dependent protein of 28,000 Mr, may be involved in calcium transport by cells of the renal tubule. The streptozotocin-diabetic rat is hypercalciuric and shows markedly decreased concentration of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] in serum and of CaBP in small intestine. To examine the relationship of renal CaBP in diabetes to 1,25-(OH)2D3 and urinary calcium excretion, renal CaBP, serum 1,25-(OH)2D3, and urinary calcium were measured in control, diabetic, and insulin-treated diabetic rats. Treatment of the diabetic rat with insulin decreased urinary calcium excretion and elevated 1,25-(OH)2D3 toward normal. Renal CaBP was found to be the same in controls and diabetics despite a tenfold difference in concentration of 1,25-(OH)2D3 in serum, and to be unaffected by insulin treatment, which elevated 1,25-(OH)2D3 by a factor of 7 above untreated diabetics. It is concluded that in the diabetic rat either (1) the threshold concentration of 1,25-(OH)2D3 for inducing synthesis of renal CaBP is set at a much lower level than that for intestinal CaBP, or (2) since both 1,25-(OH)2D3 and renal CaBP are produced in the kidney, 1,25-(OH)2D3 exerts a paracrine effect on renal CaBP production because of its high local concentration. The increased urinary calcium excretion in the untreated streptozotocin-diabetic rat is not secondary to an alteration in renal CaBP.     

Decreased mRNA expression of the PTH/PTHrP receptor and type II sodium-dependent phosphate transporter in the kidney of rats fed a high phosphorus diet accompanied with a decrease in serum calcium concentration

This study investigates the phosphorus (P) homeostasis in the process of an altered parathyroid hormone (PTH) action in the kidney of rats fed a high P diet. Four-week-old male Wistar strain rats were fed diets containing five different P levels (0.3, 0.6, 0.9, 1.2 and 1.5%) for 21 days. The serum PTH concentration and urinary excretion of P were elevated with increasing dietary P level. Compared to rats fed the 0.3% P diet, the serum calcium (Ca) concentration remained unchanged, while the serum 1,25(OH)(2)D(3) concentration and urinary excretion of cAMP were elevated with increasing dietary P level in rats fed the high P diets containing 0.6-0.9% P. On the other hand, a lower serum Ca concentration was observed in rats fed the high P diets containing 1.2% or greater P. The serum 1,25(OH)(2)D(3) concentration remained unchanged in rats fed the high P diets containing 1.2% or greater P, comparison with rats fed the 0.3% P diet. The urinary excretion of cAMP and PTH/PTH-related peptide (PTHrP) receptor and type II sodium-dependent phosphate transporter (NaPi-2) mRNA in the kidney were both decreased in rats fed the high P diets containing 1.2% or greater P. In conclusion, a high P diet with subsequent decrease in serum Ca concentration suppressed the PTH action in the kidney due to PTH/PTHrP receptor mRNA down-regulation. Furthermore, an increase in the urinary excretion of P might have been caused by decreased NaPi-2 mRNA expression without the effects of PTH and 1,25(OH)(2)D(3).     

An acromegalic patient with recurrent urolithiasis

A 52-year-old man with an acromegalic appearance of prolonged duration suffered abdominal colic attacks and hematuria during the middle of the course of the disease. The patient was diagnosed as having urolithiasis caused by increased urinary calcium. The calcium metabolic disorder was not considered to be due to hyperparathyroidism because serum calcium and PTH levels were within the normal range and no abnormality was observed in a parathyroidal scintigraph. The serum 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels (55.0 and 73.0 pg/ml) were higher than the normal range (27.2-53.8 pg/ml). A selective adenomectomy by the transsphenoidal route (Hardy's method) was performed, resulting in an improvement in the hypercalciuria and urolithiasis, and a decrease in the levels of serum 1,25-(OH)2D (23.0 and 23.0 pg/ml). These findings suggest that GH may promote the activation of vitamin D in the kidney in acromegaly, resulting in an acceleration of calcium absorption in the intestine through the action of activated vitamin D and the induction of increased urinary calcium excretion by the urinary excretion of excessive blood calcium.     

Altered Calcium and Vitamin D Homeostasis in First-Time Calcium Kidney Stone-Formers

Background

Elevated serum 1,25-dihydroxyvitamin D (1,25(OH)₂D) concentrations have been reported among cohorts of recurrent calcium (Ca) kidney stone-formers and implicated in the pathogenesis of hypercalciuria. Variations in Ca and vitamin D metabolism, and excretion of urinary solutes among first-time male and female Ca stone-formers in the community, however, have not been defined.

Methods

In a 4-year community-based study we measured serum Ca, phosphorus (P), 25-hydroxyvitamin D (25(OH)D), 1,25(OH)₂D, 24,25-dihydroxyvitamin D (24,25(OH)₂D), parathyroid hormone (PTH), and fibroblast growth factor-23 (FGF-23) concentrations in first-time Ca stone-formers and age- and gender frequency-matched controls.

Results

Serum Ca and 1,25(OH)₂D were increased in Ca stone-formers compared to controls (P = 0.01 and P = 0.001). Stone-formers had a lower serum 24,25(OH)₂D/25(OH)D ratio compared to controls (P = 0.008). Serum PTH and FGF-23 concentrations were similar in the groups. Urine Ca excretion was similar in the two groups (P = 0.82). In controls, positive associations between serum 25(OH)D and 24,25(OH)₂D, FGF-23 and fractional phosphate excretion, and negative associations between serum Ca and PTH, and FGF-23 and 1,25(OH)₂D were observed. In SF associations between FGF-23 and fractional phosphate excretion, and FGF-23 and 1,25(OH)₂D, were not observed. 1,25(OH)₂D concentrations associated more weakly with FGF-23 in SF compared with C (P <0.05).

Conclusions

Quantitative differences in serum Ca and 1,25(OH)₂D and reductions in 24-hydroxylation of vitamin D metabolites are present in first-time SF and might contribute to first-time stone risk.     

Evidence for calcium-dependent control of 1,25-dihydroxyvitamin D3 production by rat kidney proximal tubules

The role of calcium in the parathyroid hormone-mediated increase in 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) production was evaluated using isolated proximal tubules from rats fed a low calcium diet (0.002% Ca) for 14 days. Tubules were prepared by collagenase digestion and centrifugation through Percoll. Tubules from rats fed a low calcium diet produced 1,25-(OH)2D3 at rates 10 times that of tubules from rats fed normal calcium diet (1.2% Ca). In vitro 1,25-(OH)2D3 biosynthesis was highly dependent upon extracellular calcium with inhibition in the absence of medium calcium and maximal production at 0.25 mM medium calcium (0.9 +/- 0.25 versus 15.1 +/- 2.3 nmol/mg protein/5 min, p less than 0.03). Inhibition of 1,25-(OH)2D3 production was partly due to depressed ATP content (0 versus 1.2 mM calcium, 6.8 +/- 0.6 versus 12.7 +/- 0.6 nmol/mg protein, p less than 0.006). EGTA reduced 1,25-(OH)2D3 synthesis and total cell calcium and ATP production. Ruthenium red blocked the inhibitory effects of EGTA on 1,25-(OH)2D3 production. Barium (1.0 mM) inhibited 1,25-(OH)2D3 production (7.2 +/- 0.5 versus 3.4 +/- 0.3, p less than 0.001) without altering ATP production. The calcium ionophore A23187 increased 1,25-(OH)2D3 production in a calcium-dependent manner. It is concluded that parathyroid hormone-mediated increases in 1,25-(OH)2D3 production, as during low calcium diet, require extracellular calcium. Extracellular calcium maintains mitochondrial calcium at optimal concentrations for normal ATP production, a requirement for 25-hydroxyvitamin D3-1-hydroxylase (25-OH-D3-1-hydroxylase) activity. Inhibition of 25-OH-D3-1-hydroxylase activity by barium without an alteration of ATP suggests calcium may also control 1,25-(OH)2D3 production independent of its effects on oxidative phosphorylation, perhaps through a direct interaction with one or more components of the 25-OH-D3-1-hydroxylase.     

Effect of dietary calcium on serum BGP (osteocalcin).

The present study was designed to clarify the effects of dietary calcium (Ca) intake on serum BGP (osteocalcin) levels. Twelve women with a mean age of 21.2 years participated in the study. After one week of normal Ca intake (mean +/- SE, 535 +/- 2 mg/day), a low-Ca diet (163 +/- 1 mg/day) was given for one further week. Additional asparagine Ca (3 g as Ca/day) was also given to half of the subjects. Serum total and ionized Ca concentrations as well as BGP, PTH and 1,25(OH)2D3 were measured at the end of each period. Amounts of Ca and hydroxyproline excreted in urine were also determined. The plasma level of ionized Ca was significantly increased without any change in total Ca in either group. Low and high Ca intake decreased and increased urinary Ca excretion by 28% and 56%, respectively. Serum levels of BGP and 1,25(OH)2D3 were significantly augmented along with a transient increase in urinary hydroxyproline excretion after Ca deprivation. These results suggest that serum BGP is increased after one week of Ca restriction in healthy subjects.     

Different effects of physiologically and pharmacologically increased growth hormone levels on cholecalciferol metabolism at prepubertal age

The aim of the study was to investigate the influence of physiologically and pharmacologically increased plasma growth hormone (GH) levels on cholecalciferol metabolism at prepubertal age. Three groups of dogs raised on the same diet were studied from weaning till 21 weeks of age, i.e., small breed dogs (n = 7, control group); large breed dogs with 15-fold greater growth rates compared to the control group (n = 8, LB-group); and small breed dogs treated with pharmacological doses of growth hormone (n = 6, GH-group; 0.5IU GH per kg body per day) from 12 to 21 weeks of age. Excess of GH had the expected anabolic effect on growth rate and phosphate sparing. Increased plasma GH levels in the LB- and GH-groups versus the control group were accompanied by (1) greater plasma insulin-like growth factor I (IGF-I) levels, (2) greater plasma 1,25-dihydroxycholecalciferol (1,25(OH)(2)D(3)) levels, and (3) lower plasma 24,25(OH)(2)D(3) levels. In the LB-group, excess of GH favored plasma 1,25(OH)(2)D(3) levels by decreasing the clearance of 1,25(OH)(2)D(3), whereas in the GH-group by increasing the production of 1,25(OH)(2)D(3). The lowered plasma 24,25(OH)(2)D(3) levels in the LB- and GH-groups were likely attributed to a competitive inhibition of the production of 24,25(OH)(2)D(3) by GH and/or IGF-I.     

Regulation of renal vitamin D receptor is an important determinant of 1alpha,25-dihydroxyvitamin D(3) levels in vivo

The synthesis of 1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) is most strongly regulated by dietary calcium and the action of parathyroid hormone to increase 1alpha-hydroxylase (1alpha-OHase) and decrease 24-hydroxylase (24-OHase) in kidney proximal tubules. This study examines the hypothesis that 1,25-(OH)(2)D(3) synthesis, induced by dietary calcium restriction, is also the result of negative feedback regulation blockade. Rats fed a low calcium (0.02%, -Ca) diet and given daily oral doses of vitamin D (0, 0.5, 1.0, 2.0, 4.0, 8.0, and 16.0 microg) remained hypocalcemic despite increasing levels of serum calcium in relation to the vitamin D dose. Plasma levels of 1,25-(OH)(2)D(3) rose to high levels (1200 pg/ml) at the high vitamin D dose levels. As expected, thyroparathyroidectomy caused a rapid fall in serum 1,25-(OH)(2)D(3). In rats fed a 0.47% calcium diet (+Ca) supplemented with vitamin D (4 microg/day), exogenous 1,25-(OH)(2)D(3) suppressed renal 1alpha-OHase and stimulated the 24-OHase. In rats fed the -Ca diet, vitamin D was unable to suppress the renal 1alpha-OHase or stimulate the renal 24-OHase. In contrast, vitamin D was fully able to stimulate intestinal 24-OHase. Intestinal vitamin D receptor (VDR) was present under all circumstances, while kidney VDR was absent under hypocalcemic conditions and present under normocalcemic conditions. It appears that tissue-specific down-regulation of VDR by hypocalcemia blocks the 1,25-(OH)(2)D(3) suppression of the 1alpha-OHase and upregulation of the 24-OHase in the kidney, causing a marked accumulation of 1,25-(OH)(2)D(3) in the plasma.     

1,25(OH)2D3 increases calcium and phosphatidylinositol metabolism in differentiating cultured human keratinocytes

The effect of 1,25(OH)(2)D(3) on the intracellular calcium, (Ca(+2))i, in both cultured human keratinocytes and in cultured human dermal fibroblasts was investigated. When the intracellular calcium (Ca(+2))i in cultured human keratinocytes, grown in a serum-free medium containing 1.8 mM calcium, was measured by the fluorescent calcium-indicator, Furu-2, the (Ca(+2)i increased 154%, 202%, and 409% over the control value after incubation with 1,25(OH)(2)D(3) at 10(-10) m, 10(-8) m, and 10(-6) m, respectively. This response was immediate (15 seconds), specific (no effect with either 25(OH)D(3) at 10(-8) m or vitamin D(3) at 10(-8) m), and occurred with or without EGTA in the medium. In contrast, 1,25(OH)(2)D(3) did not increase the (Ca(2+))i in either cultured human keratinocytes that were grown in low calcium (0.05 mm), serum-free medium or in cultured human dermal fibroblasts that were grown in medium containing 0.05 mm calcium and 1% serum. The effect of 1,25(OH)(2)D(3) on the the turnover of phosphatidylinositol was investigated as a possible cause for the observed increase in (Ca(+2)i. Cultured human keratinocytes that were incubated with (3)H-inositol demonstrated a 50 % +/- 10% increase in the triphosphated, plasma membrane-bound metabolite of phosphatidylinositol, PIP(2), by 15 seconds, followed by a rapid decrease at 30 seconds, then a return toward basal levels by 1 minute. Lysophosphatidylinositol, which results from the sn-2 deacylation of phosphatidylinositol by phospholipase A(2), decreased 20% +/- 8% within 30 seconds, then increased to 200% +/- 10% of the control value by 5 minutes. The accumulation of IP(3) was increased 50% to 100% above the control value within 30 seconds and this increase was substained during the 5-minute incubation period. Stimulation of phosphatidylinositol turnover by 1,25(OH)(2)D(3) was not detected in either cultured human keratinocytes that were grown in serum-free, low calcium medium or in cultured human dermal fibroblasts that were grown in 1% serum.     

Hypercalcemia in glucocorticoid withdrawal

We found severe hypercalcemia in the course of hydrocortisone withdrawal in a patient who had undergone unilateral adrenalectomy to resect a cortisol-hypersecreting adenoma. Serum calcium gradually but progressively increased after unilateral adrenalectomy. Severe hypercalcemia developed on the 77th postoperative day (the 15th day after discontinuing hydrocortisone replacement). The serum concentration of calcium, PTH, 25(OH)D, and 1,25(OH)2D were 8.0 mEq/l, less than 100 pg/ml, 10.1 ng/ml and 29.6 pg/ml, respectively. This hypercalcemia was accompanied by marked urinary hydroxyproline excretion and less calcium excretion in the urine than the prevailing level of serum calcium. Serum concentrations of 25(OH)D, 1,25(OH)2D and PTH were not elevated during the severe hypercalcemia. We concluded that the hypercalcemia in this patient was due in part to enhanced bone resorption and increased renal tubular reabsorption of calcium as a result of glucocorticoid withdrawal, but not to the elevation of serum PTH or serum 25(OH)D and serum 1,25(OH)2D.     

Serum osteocalcin levels do not change during rapidly induced hypercalcemia in healthy subjects.

Since osteocalcin has been suggested to play a role in calcium homeostasis, we investigated its serum levels in 6 healthy subjects during a rapid calcium infusion. Serum levels of intact parathyroid hormone (PTH), 25-hydroxyvitamin D [25-(OH) D3] and 1,25-dihydroxyvitamin D [1,25-(OH)2 D3] were also determined. The calcium infusion increased plasma-ionized calcium levels from 1.25 +/- 0.04 to 1.54 +/- 0.07 mmol/l at 30 min (p less than 0.05). Concomitantly, serum levels of intact PTH declined from 2.1 +/- 0.9 to 0.2 +/- 0.3 mmol/l (p less than 0.05). In contrast, serum osteocalcin levels did not change. Further, during calcium infusion, serum levels of 1,25-(OH)2 D3 decreased from 81 +/- 17 to 75 +/- 15 pmol/l (p less than 0.05) whereas serum levels of 25-(OH) D3 did not change. The results therefore suggest that calcium per se does not influence osteocalcin secretion.     

Reduced Parathyroid Hormone-Stimulated 1,25-Dihydroxyvitamin D Production in Vitamin D Sufficient Postmenoposual Women with Low Bone Mass and Idiopathic Secondary Hyperparathyroidism

ObjectiveDistinguishing secondary hyperparathyroidism (sHPT) from eucalcemic primary hyperparathyroidism (EC-pHPT) is important. The objective of this study was to measure parathyroid hormone (PTH)-stimulated production of 1α,25-dihydroxyvitamin D (1,25[OH]₂D) in early postmenopausal patients with idiopathic sHPT, who also fit the criteria for EC-pHPT, compared to age-matched controls.MethodsIn this pilot case-control study, postmenopausal women aged 44 to 55 years with normal serum calcium (Ca), glomerular filtration rate (GFR) ≥65 mL/min, and 25-hydroxyvitamin D (25[OH]D) ≥75 nmol/L (30 ng/mL) were given an 8 hour infusion of PTH(1-34), 12 pmol/kg/h. Patients (n = 5) had elevated PTH, normal 1,25(OH)₂D, and no hypercalciuria. Controls (n = 5) had normal PTH. At baseline, 4, and 8 hours, serum Ca, creatinine (Cr), phosphorus (P), 1,25(OH)₂D, fibroblast growth factor (FGF23), and 24,25(OH)₂D as well as urine Ca, P, Cr, and cAMP/GFR were measured. The fractional excretion of calcium (FeCa) and tubular reabsorption of phosphorus (TMP)/GFR were calculated.ResultsPatients had lower 1,25(OH)₂D levels (± SD) than controls at 4 (39.8 ± 6.9 versus 58.8 ± 6.7; P = .002) and 8 hours (56.4 ± 9.2 versus 105 ± 2.3; P = .003) of PTH infusion, attenuated after adjusting for higher body mass index (BMI) in patients (P = .05, .04), respectively. The 24,25(OH)2D levels were lower in patients than controls (1.9 ± 0.6 versus 3.4 ± 0.6, respectively; P = .007). No differences were seen in serum Ca or P, urine cAMP/GFR, TRP/GFR, FeCa, or PTH suppression at 8 hours (patients 50%, controls 64%).ConclusionVitamin D sufficient patients who fit the criteria for EC-pHPT had reduced PTH-stimulated 1,25(OH)₂D compared to controls, partially attributable to their higher BMI. Other causes of reduced 1,25(OH)₂D production ruled out were excessive catabolism of vitamin D metabolites, elevated FGF23, and CYP27B1 mutation. Elevated BMI and idiopathic reduced PTH-stimulated 1,25(OH)₂D production should be considered in the differential of sHPT. (Endocr Pract. 2013;19:91-99)     

Effects of calcium and of the Vitamin D system on skeletal and calcium homeostasis: lessons from genetic models

Targeted deletion of genes encoding the 1,25-dihydroxyVitamin D [1,25(OH)(2)D]-synthesizing enzyme, 25 hydroxyVitamin D-1alpha-hydroxylase [1alpha(OH)ase or CYP27B1], and of the nuclear receptor for 1,25(OH)(2)D, the Vitamin D receptor (VDR), have provided useful mouse models of the inherited human diseases, Vitamin D-dependent rickets types I and II. We employed these models and double null mutants to examine the effects of calcium and of the 1,25(OH)(2)D/VDR system on skeletal and calcium homeostasis. Optimal dietary calcium absorption required both 1,25(OH)(2)D and the VDR. Skeletal mineralization was dependent on adequate ambient calcium but did not directly require the 1,25(OH)(2)D/VDR system. Parathyroid hormone (PTH) secretion was also modulated primarily by ambient serum calcium but the enlarged parathyroid glands which the mutants exhibited and the widened cartilaginous growth plates could only be normalized by the combination of calcium and 1,25(OH)(2)D, apparently independently of the VDR. Optimal osteoclastic bone resorption and osteoblastic bone formation both required an intact 1,25(OH)(2)D/VDR apparatus. The results indicate that calcium cannot entirely substitute for Vitamin D in skeletal and mineral homeostasis but that the two agents have discrete and overlapping functions.     

Klotho, a gene related to a syndrome resembling human premature aging, functions in a negative regulatory circuit of vitamin D endocrine system

The klotho gene encodes a novel type I membrane protein of beta-glycosidase family and is expressed principally in distal tubule cells of the kidney and choroid plexus in the brain. These mutants displayed abnormal calcium and phosphorus homeostasis together with increased serum 1,25-(OH)2D. In kl-/- mice at the age of 3 wk, elevated levels of serum calcium (10.9 +/- 0.31 mg/dl vs. 10.0 +/- 0.048 mg/dl in wild-type mice), phosphorus (14.7 +/- 1.1 mg/dl vs. 9.7 +/- 1.5 mg/dl in wild type) and most notably, 1,25-(OH)2D (403 +/- 99.7 mg/dl vs. 88.0 +/- 34.0 mg/dl in wild type) were observed.Reduction of serum 1,25-(OH)2D concentrations by dietary restriction resulted in alleviation of most of the phenotypes, suggesting that they are downstream events resulting from elevated 1,25-(OH)2D. We searched for the signals that lead to up-regulation of vitamin D activating enzymes. We examined the response of 1alpha-hydroxylase gene expression to calcium regulating hormones, such as PTH, calcitonin, and 1,25-(OH)2D3. These pathways were intact in klotho null mutant mice, suggesting the existence of alternate regulatory circuits. We also found that the administration of 1,25-(OH)2D3 induced the expression of klotho in the kidney. These observations suggest that klotho may participate in a negative regulatory circuit of the vitamin D endocrine system, through the regulation of 1alpha-hydroxylase gene expression.     

Peripheral effects of PTH are not altered after thyroid surgery in euthyroid patients

BACKGROUND: We have previously found decreased serum levels of both ionized calcium and 1,25(OH)2D and an increase in serum phosphate levels at 1 year after hemithyroidectomy. However, basal and stimulated parathyroid hormone (PTH) secretions were not altered. To investigate whether the observed biochemical changes after unilateral thyroid surgery may be due to a relative end-organ resistance to PTH, we studied the peripheral effects of infused hPTH-(1-34) in 6 patients preoperatively and 3 months after hemithyroidectomy. METHODS: Serum levels of TSH, FT4 and FT3 were measured pre- and postoperatively. hPTH-(1-34) was infused at 0.9 IU/kg/h during 6 h. Blood samples for analysis of ionized calcium, intact PTH, phosphate, 25(OH)D, 1,25(OH)2D and urinary samples for calcium, phosphate and nephrogenous(n)-cAMP analysis were taken at baseline, when the infusion was discontinued after 6 h and at 24 h. RESULTS: Three months after hemithyroidectomy, serum levels of FT3 were decreased and TSH levels increased. Pre- and postoperative hPTH-(1-34) infusions induced increased serum levels of ionized calcium, 1,25(OH)2D, increased urinary excretion of phosphate and elevated n-cAMP levels. The changes in the studied biochemical variables during the hPTH-(1-34) infusions did not differ between the two study occasions. CONCLUSION: By using a 6-hour hPTH-(1-34) infusion protocol, we have shown that the peripheral PTH effect is not altered by a slight reduction in thyroid hormone levels at 3 months after hemithyroidectomy.     

1,25-Dihydroxyvitamin D production after stimulation with synthetic human parathyroid hormone (1-34) in hypoparathyroid and renal tubular disorders

1,25-dihydroxyvitamin D production in response to two successive infusions of synthetic active 1-34 fragment of human PTH [hPTH-(1-34)] was evaluated in order to develop an understanding of the vitamin D metabolism and the rationale of vitamin D therapy in calcium disorders. Five normal controls, six hypoparathyroid patients, two patients with hypophosphatemic vitamin-D-resistant rickets, one patient with Lowe's synd. and one patient with primary Fanconi's synd. were investigated, and the following results were obtained. All normal controls showed a significant increase in serum 1,25(OH)2D[43 +/- 3.8 (m +/- SEM, n = 5, basal), 53 +/- 4.3 (three hours after the first PTH infusion), 65 +/- 7.7 (six hours) and 66 +/- 4.4 (nine hours) pg/ml]. All patients with PTH-deficient hypoparathyroidism showed a significant increase in serum 1,25(OH)2D, and serum 1,25(OH)2D values were within the normal range after hPTH-(1-34) stimulation. Serum 1,25(OH)2D remained low after hPTH-(1-34) infusions in a patient with pseudohypoparathyroidism type I who showed a significant increase in this value after infusion of dibutyryl cyclic AMP. On the other hand, a patient with normocalcemic pseudohypoparathyroidism type I had a high basal 1,25(OH)2D value, which increased further after hPTH-(1-34) infusions. An almost normal increase in serum 1,25(OH)2D was observed in two patients with hypophosphatemic vitamin-D-resistant rickets, one with Lowe's syndrome and the other with primary Franconi's syndrome. We conclude that these results ae important in obtaining an understanding of calcium and vitamin D metabolism in these disorders and that this PTH stimulation test is a useful method to use in evaluating renal responsiveness in 1,25(OH)2D production to PTH in various calcium disorders.     

Determination of vitamin D and its metabolites in plasma from normal and anephric man

A multiple assay capable of reliably determining vitamins D(2) and D(3) (ergocalciferol and cholecalciferol), 25(OH)D(2) (25-hydroxyvitamin D(2)) and 25(OH)D(3) (25-hydroxyvitamin D(3)), 24,25(OH)(2)D (24,25-dihydroxyvitamin D), 25,26(OH)(2)D (25,26-dihydroxyvitamin D) and 1,25(OH)(2)D (1,25-dihydroxyvitamin D) in a single 3-5ml sample of human plasma was developed. The procedure involves methanol/methylene chloride extraction of plasma lipids followed by separation of the metabolites and purification from interfering contaminants by batch elution chromatography on Sephadex LH-20 and Lipidex 5000 and by h.p.l.c. (high-pressure liquid chromatography). Vitamins D(2) and D(3) and 25(OH)D(2) and 25(OH)D(3) are quantified by h.p.l.c. by using u.v. detection, comparing their peak heights with those of standards. 24,25(OH)(2)D and 25,26(OH)(2)D are measured by competitive protein-binding assay with diluted plasma from vitamin D-deficient rats. 1,25(OH)(2)D is measured by competitive protein-binding assay with diluted cytosol from vitamin D-deficient chick intestine. Values in normal human plasma samples taken in February are: vitamin D 3.5+/-2.5ng/ml; 25(OH)D 31.6+/-9.3ng/ml; 24,25(OH)(2)D 3.5+/-1.4ng/ml; 25,26(OH)(2)D 0.7+/-0.5ng/ml; 1,25(OH)(2)D 31+/-9pg/ml (means+/-s.d.). Values in two normal human plasma samples taken in February after 1 week of high sun exposure are: vitamin D 27.1+/-7.9ng/ml; 25(OH)D 56.8+/-4.2ng/ml; 24,25(OH)(2)D 4.3+/-1.6ng/ml; 25,26(OH)(2)D 0.5+/-0.2ng/ml. Values in anephric-human plasma are: vitamin D 2.7+/-0.8ng/ml; 25(OH)D 36.4+/-16.5ng/ml; 24,25(OH)(2)D 1.9+/-1.3ng/ml; 25,26(OH)(2)D 0.6+/-0.3ng/ml; 1,25(OH)(2)D was undetectable.     

Calcium supplementation does not alter lipid oxidation or lipolysis in overweight/obese women

Based on cell culture and studies in mice, increased dietary calcium appears to stimulate lipolysis and could possibly reduce body adiposity through hormonal influences on adipocyte calcium uptake. In this study, we investigated the effects of 1,500 mg supplemental calcium daily for 3 months on hormones regulating calcium and energy metabolism and rates of lipid oxidation and lipolysis in overweight women. Fifteen overweight (BMI > 25 kg/m(2)) premenopausal women were supplemented with 1,500 mg of calcium, as CaCO(3), per day for 3 months while maintaining their usual diets and activity levels. Baseline and endpoint measurements were obtained after the subjects consumed a standardized 25% fat diet for 4 days. Lipid oxidation was measured by indirect calorimetry, lipolysis by infusion of deuterated glycerol, and body fat by dual-energy X-ray absorptiometry. Urinary calcium, circulating levels of hormones involved in energy and lipid metabolism (insulin, leptin, and adiponectin) or calcium metabolism (25(OH)D, 1,25(OH)(2)D), and parathyroid hormone (PTH)) were also measured. Urinary levels of calcium (P = 0.005) increased and 1,25(OH)(2)D declined (P = 0.03). However other parameters, including body weight, body fat, PTH, insulin, leptin, adiponectin, 25(OH)D, as well as rates of lipid oxidation and lipolysis were not altered by calcium supplementation. Calcium supplementation for 3 months increased urinary calcium excretion, decreased circulating levels of 1,25(OH)(2)-D, but had no effect on rates of lipid oxidation or lipolysis, in these overweight women.