Vitamin D and bone

Mechanical, Biochemical, and Structural Effects of Vitamin D Deficiency on the Chick Heart

The effects of vitamin D depriva tion on the chick heart were investi gated from three aspects: cardiac contractility (±dP/dT), intracellular high-energy phosphorus compounds, and structural differences. Four- week-old vitamin D-deficient chicks were divided into four groups: Group A served as the normal group and re ceived subcutaneous injections of cholecalciferol; Groups B and C were vitamin D-deficient hearts but per fused differently; Group D received daily subcutaneous injections of 5 μg of 1,25(OH) 2D3. When the isolated spontaneously beating hearts (modi fied Langendorff preparation) were perfused with Krebs-Henseleit (KH) solution containing a calcium concen tration of 2.5mM, the myocardial contractility of the vitamin D-defi cient hearts was significantly in creased when compared with group A. After the isolated heart had beaten for one hour, the myocardial contractility in the vitamin D-defi cient hearts was found to decline to significantly lower values. Presacri fice administration of 1,25(OH) 2D3 improved cardiac performance. Vita min D deficiency resulted in an en hanced rate of decline of the intracellular high-energy phosphorus compounds. No differences were found in the microscopic study. These observations suggest that vitamin D has a role in cardiac function.

Understanding vitamin D metabolism in pregnancy: From physiology to pathophysiology and clinical outcomes

This critical time frame of intrauterine life development is considered of major importance on the metabolic imprinting of overall health of the offspring, in later life. This requires a delicate immune balance that nurtures the allogeneic fetus, while maintaining reactivity against pathogens. Dysregulation of these tightly controlled biophenomena at a systemic and placental level, have been considered as a potential mechanism mediating pathogenesis of preeclampsia and spontaneous birth. In this context, vitamin D has been considered as a significant regulator of both innate and adaptive immunity by regulating cell proliferation, differentiation and apoptosis. Vitamin D metabolism during pregnancy manifests striking differences as compared to the non-pregnant state. Calcitriol is increasing >2-3 fold in the first weeks of pregnancy whereas maternal 25-hydroxyvitamin D crosses the placental barrier and represents the main pool of vitamin D in the fetus. Moreover, during pregnancy, vitamin D receptor and regulatory metabolic enzymes are expressed in the placenta and decidua, indicating a potential critical point in the immunomodulation at the maternal-fetal interface. Considering these effects, maternal hypovitaminosis D during pregnancy has been associated with pregnancy related disorders. This review focuses on the mechanistic basis of these adaptive changes, as a background for the development of pregnancy related disorders, with a discourse on the pathophysiology relating hypovitaminosis D and clinical outcomes.

Tooth movement

This article reviews the evolution of concepts regarding the biological foundation of force-induced tooth movement. Nineteenth century hypotheses proposed two mechanisms: application of pressure and tension to the periodontal ligament (PDL), and bending of the alveolar bone. Histologic investigations in the early and middle years of the 20th century revealed that both phenomena actually occur concomitantly, and that cells, as well as extracellular components of the PDL and alveolar bone, participate in the response to applied mechanical forces, which ultimately results in remodeling activities. Experiments with isolated cells in culture demonstrated that shape distortion might lead to cellular activation, either by opening plasma membrane ion channels, or by crystallizing cytoskeletal filaments. Mechanical distortion of collagenous matrices, mineralized or non-mineralized, may, on the other hand, evoke the development of bioelectric phenomena (stress-generated potentials and streaming potentials) that are capable of stimulating cells by altering the electric charge on their membrane or their fluid envelope. In intact animals, mechanical perturbations on the order of about 1 min/d are apparently sufficient to cause profound osteogenic responses, perhaps due to matrix proteoglycan-related "strain memory". Enzymatically isolated human PDL cells respond biochemically to mechanical and chemical signals. The latter include endocrines, autocrines, and paracrines. Histochemical and immunohistochemical studies showed that during the early places of tooth movement, PDL fluids are shifted, and cells and matrix are distorted. Vasoactive neurotransmitters are released from periodontal nerve terminals, causing leukocytes to migrate out of adjacent capillaries. Cytokines and growth factors are secreted by these cells, stimulating PDL cells and alveolar bone lining cells to remodel their related matrices. This remodeling activity facilitates movement of teeth into areas in which bone had been resorbed. This emerging information suggests that in the living mammal, many cell types are involved in the biological response to applied mechanical stress to teeth, and thereby to bone. Essentially, cells of the nervous, immune, and endocrine systems become involved in the activation and response of PDL and alveolar bone cells to applied stresses. This fact implies that research in the area of the biological response to force application to teeth should be sufficiently broad to include explorations of possible associations between physical, cellular, and molecular phenomena. The goals of this investigative field should continue to expound on fundamental principles, particularly on extrapolating new findings to the clinical environment, where millions of patients are subjected annually to applications of mechanical forces to their teeth for long periods of time in an effort to improve their position in the oral cavity.(ABSTRACT TRUNCATED AT 400 WORDS)

Serum vitamin D metabolite concentrations in primary hyperparathyroidism

Forty-nine patients with primary hyperparathyroidism were examined preoperatively and three months after parathyroid operation for their serum vitamin D metabolites and routine laboratory samples related to calcium metabolism. The preoperative serum 24,25-dihydroxyvitamin D level, mean (SE) was 1.86 (0.22) nmol/l and the postoperative level 5.35 (0.63) nmol/l, the difference being highly significant (P less than 0.001). Serum 1,25-dihydroxyvitamin D levels fell significantly (P less than 0.001) from a preoperative level of 175.5 (17.9) pmol/l to 102.8 (10.1) pmol/l postoperatively. The preoperative 25-hydroxyvitamin D level did not change significantly after surgery. The preoperative serum 24,25-dihydroxyvitamin D level was very low, especially in patients with bone disease while serum parathormone was significantly higher than in patients without bone disease.

Prevention of glucocorticoid-induced osteopenia: effect of oral 25-hydroxyvitamin D and calcium

Twenty-four patients (9 M and 15 F, age range 51-82) with polymyalgia rheumatica receiving 6-methylprednisolone for a period of 9 months (16 mg/daily/two weeks, 14 mg/daily/two weeks, 12 mg/daily/1 month, 10 mg/daily/1 month, 8 mg/daily/1 month, 6 mg/daily/1 month and 4 mg/daily for the last four months) were randomly assigned to receive either 250HD3 (35 mcg/day for 25 days/month) (Group A) or placebo (Group B) in a double-blind study. All patients also received 500 mg elemental calcium daily. Before and at 3, 6 and 9 months ESR, tenderness on palpation and subjective pain were evaluated. At the same times, mineral metabolism parameters (serum calcium, phosphorus, alkaline phosphatase, 24-h urinary calcium, phosphate and 24-h hydroxyproline excretion) and radial bone mineral content (BMC) were evaluated. Activity indexes (ESR and clinical parameters) improved in both groups. Furthermore, serum alkaline phosphatase and 24-h hydroxyproline excretion decreased significantly only in Group A, and BMC decreased significantly in Group B but rose slightly in Group A. No side effects were observed in any of the patients.

Overall tolerance and safety of quinapril in clinical trials

A comprehensive analysis of the reporting of adverse events, withdrawals due to adverse events, and serious adverse events has been conducted on 2,010 patients treated with quinapril hydrochloride. An analysis of all events (from both double-blind and open label studies combined) showed no increase in the incidence of events reported in congestive heart failure (CHF) patients compared to hypertensive patients. When the data for all studies were combined, an age analysis showed no increase in the total reporting of adverse events in the 379 elderly patients studied. The incidence of events was lower in those patients who did not take concomitant diuretic therapy. A comparison of the double-blind phases showed quinapril to have a lower incidence of adverse events than captopril, enalapril, or chlorthalidone. An analysis of the onset of events, or withdrawals, did not show an increase with time on quinapril therapy, and no dose-relationship. A review of serious adverse events did not reveal an unexpected occurrence or a high incidence of serious events considered to be related to quinapril therapy. The proportion of patients who experienced "first-dose" hypotension, or symptomatic hypotension was similar to captopril or enalapril. Quinapril, a nonsulfhydryl ACE inhibitor, has been extensively studied and is equally well tolerated in the young and elderly for the treatment of hypertension and CHF.

An organ culture system designed to study interaction of fetal rat calvaria with human head and neck squamous cell carcinoma

The development of permanent cell lines of human head and neck squamous cell carcinoma in culture has enabled these cell lines to be used to investigate the interaction of the tumor cells with bone. After the squamous carcinoma lines on fetal rat skulls were implanted the explants with their added tumor were maintained in long-term tissue culture by use of the procedures developed for growing these tumor cells. Results confirm direct interaction with the bone by the malignant cells. Specific surface and cytoplasmic markers have been demonstrated by use of monoclonal antibodies against the tumor cells. Furthermore, tumor angiogenesis without the addition of any endogenous endothelial components has been verified. Investigations into the degree of bone infiltration and susceptibility of these interacting tumor cells to various factors, radiation therapy, and chemotherapeutic agents have been carried out. The establishment of a model system for bony invasion by squamous cell carcinoma of the head and neck permits the investigation of the mechanism of tumor invasion and the study of various potential treatment modalities.

Bone "mass" and the "mechanostat": a proposal

The observed fit of bone mass to a healthy animal's typical mechanical usage indicates some mechanism or mechanisms monitor that usage and control the three longitudinal growth, bone modeling, and BMU-based remodeling activities that directly determine bone mass. That mechanism could be named a mechanostat. Accumulated evidence suggests it includes the bone itself, plus mechanisms that transform its mechanical usage into appropriate signals, plus other mechanisms that detect those signals and then direct the above three biologic activities. In vivo studies have shown that bone strains in or above the 1500-3000 microstrain range cause bone modelling to increase cortical bone mass, while strains below the 100-300 microstrain range release BMU-based remodeling which then removes existing cortical-endosteal and trabecular bone. That arrangement provides a dual system in which bone modeling would adapt bone mass to gross overloading, while BMU-based remodeling would adapt bone mass to gross underloading, and the above strain ranges would be the approximate "setpoints" of those responses. The anatomical distribution of those mechanical usage effects are well known. If circulating agents or disease changed the effective setpoints of those responses their bone mass effects should copy the anatomical distribution of the mechanical usage effects. That seems to be the case for many agents and diseases, and several examples are discussed, including postmenopausal osteoporosis, fluoride effects, bone loss in orbit, and osteogenesis imperfecta. The mechanostat proposal is a seminal idea which fits diverse evidence but it requires critique and experimental study.

Side-chain hydroxylation of vitamin D3 and its physiological implications

Evidence is accumulating that, in vivo and in vitro, both 25-OH-D3 and 1,25-(OH)2D3 undergo side-chain modification leading to side-chain cleaved metabolites lacking the 24, 25, 26, and 27 carbons. The enzymes involved are D-dependent and are located in the kidney, bone, intestine, and perhaps other sites. We speculate that the extra-renal side-chain pathway may be primarily for target organ destruction of 1,25-(OH)2D3, whereas the renal pathway may be primarily for destruction of 25-OH-D3 formed in large amounts in hypervitaminosis D.

The metabolism and functions of vitamin D

Vitamin D functions by stimulating intestinal calcium and phosphorus absorption, by stimulating bone calcium mobilization, and by increasing renal reabsorption of calcium in the distal tubule. These functions on bone and possibly kidney, but not intestine, require the parathyroid hormone. As a result of these functions, serum calcium and phosphorus concentrations are elevated to supersaturating levels required for the mineralization of bone to prevent rickets, osteomalacia, and hypocalcemic tetany. Recent experiments demonstrate that maintaining serum calcium and phosphorus levels in vitamin D-deficient rats in the normal range results in normal bone growth and mineralization. However, increased calcification results because bone resorption by osteoclasts is a vitamin D-dependent process. Thus, bone resorption, modeling and remodeling must be considered vitamin D-dependent processes. Vitamin D must be metabolized to 25-hydroxyvitamin D3 by the liver and subsequently by the kidney to 1,25-dihydroxyvitamin D3 before function. 1,25-Dihydroxyvitamin D3 is metabolized to a C-23 carboxylic acid (calcitroic acid) but the pathway is unknown. Although 25-hydroxyvitamin D3 is metabolized to 24R,25-dihydroxyvitamin D3, 25,26-dihydroxyvitamin D3 and 25-hydroxyvitamin D3-26,23-lactone, these pathways play no role in the function of vitamin D as shown by appropriate fluoro analogs of 25-hydroxyvitamin D3. 1,25-Dihydroxyvitamin D3 binds to a specific receptor in the intestinal nuclei to elicit a stimulation of calcium transport. 1,25-Dihydroxyvitamin D3 plus the receptor causes transcription of specific genes that code for calcium and phosphorus transport proteins. Only one protein, the calcium binding protein, has been identified as being vitamin D dependent. Two others have been described, but no clear description of the molecular mechanism of action of 1,25-dihydroxyvitamin D3 is yet available.

Vitamin D and skeletal tissues

It is now accepted that vitamin D is an integral part of a complex endocrine system, one with far-reaching implications in mineral metabolism. Reviews of the sources, functions and metabolism of vitamin D, as currently understood, are presented as a prelude to discussions of the role of vitamin D in calcium and phosphorous homeostatis and possible specific roles for vitamin D in mineralized tissues. Data describing a possible regulatory function for vitamin D in bone and bone protein metabolism are presented. Some of the controversy which presently exists regarding the biochemical mechanism of the action of this vitamin is discussed. Finally, the possible relationship of vitamin D and disorders of skeletal tissues is described.

Effects of 1,25-dihydroxycholecalciferol on fracture healing. Calcium, phosphate, and zinc in callus and serum

The incorporation of calcium, phosphate, and zinc into the callus of closed tibial fractures was studied in adult rats fed a standard diet. Low doses (60 ng/kg per day) of 1,25(OH)2D3 5 days a week greatly increased early callus mineralization. This was not related to an increased serum calcium-phosphate molar product but rather to a decreased ratio. The incorporation of zinc into callus seemed to be correlated to the mineralization process but not to the 1,25(OH)2D3 administration as such. The question of a direct, indirect, or a complex role of 1,25(OH)2D3 in bone formation and mineralization is discussed.

Effects of vitamin D metabolites on healing of low phosphate, vitamin D-deficient induced rickets in rats

A model of low-phosphate, vitamin D-deficient rachitic rats was used to compare the effects of 1 alpha(OH)D3, 1,25(OH)2D3, and 24,25(OH)2D3 on cartilage and bone. The rats were maintained for 3 weeks on a high-calcium, low-phosphate, vitamin D-deficient diet, during which period they developed severe rickets. The rachitic rats were injected for 2 or 3 consecutive days with a physiologic dose of either metabolite. Other littermates were given a single dose of 50,000 IU of cholecalciferol in combination with a normal diet. Samples of cartilage fluid (Cfl) and of blood were removed prior to sacrifice for biochemical studies of some parameters of calcification. These parameters were correlated with the results of light and electron microscopic studies of the growth plate cartilage and bone. Treatment with 1 alpha (OH)D3 or with 1,25(OH)2D3, in spite of increasing Ca and P levels in the Cfl, induced only partial healing of the rickets. In contrast, 24,25(OH)2D3 or vitamin D with a normal diet resulted in complete morphologic and biochemical healing of the rickets. Transmission electron microscopic (TEM) studies have shown partial mineralization of the wide hypertrophic zone of the growth plate following treatment with 1 alpha(OH)D3 or with 1,25(OH)2D3. Mineralization was more complete with 24,25(OH)2D3 treatment. The results of this study emphasize the importance of 24,25(OH)2D3 for normal endochondral bone formation and mineralization.

Extrarenal metabolism of 25-hydroxycholecalciferol in the rat: regulation by 1,25-dihydroxycholecalciferol

To determine the role of the kidney in regulation of 25-hydroxycholecalciferol (25OHD3, metabolism, the effects of 1,25-dihydroxycholecalciferol [1,25(OH)2D3] on 3H-25OHD3 were compared in intact and nephrectomized vitamin D-deficient rats. Sixteen hours after the intravenous administration of 3H-25OHD3, extracts of serum and pooled small intestinal mucosa were fractionated by Sephadex LH-20 column chromatography followed by high performance liquid chromatography. In intact rats, 1,25(OH)2D3 (50 ng/day i.p. for 7 days) increased mean serum 3H-24,25-dihydroxycholecalciferol [3H-24,25(OH)2D3] from 2 +/- 2-210 +/- 80 fmol/ml (mean +/- 1 SD), increased mean serum 3H-25,26-dihydroxycholecalciferol [3H-25,26(OH)2D3] from 2 +/- 2-12 +/- 6 fmol/ml and lowered mean serum 3H-1,25(OH)2D3 from 210 +/- 40-4 +/- 4 fmol/ml. Similarly, in nephrectomized animals, 1,25(OH)2D3 increased mean serum 3H-24,25-(OH)2D3 from 6 +/- 11-115 +/- 30 fmol/ml and increased mean serum 3H-25,26(OH)2D3 from 3 +/- 3-26 +/- 10 fmol/ml. Nephrectomy increased serum 3H-25(OH)D3 in untreated (from 1450 +/- 225-2675 +/- 225 fmol/ml serum) and 1,25(OH)2D3 treated rats (from 1600 +/- 175-3075 +/- 100 fmol/ml). 3H-1,25(OH)2D3 averaged 74 +/- 16% of total radioactivity in intestinal mucosa of untreated intact rats and was not detected in either the serum or intestinal mucosa of nephrectomized animals. The results suggest that in intact animals, extrarenal synthesis can account for substantial 24,25(OH)2D3 production and for most 25,26(OH)2D3 production.(ABSTRACT TRUNCATED AT 250 WORDS)

A chick bone model for evaluating radial bone growth. 1. Effects of vitamin D3 deficiency

Vitamin D3 is essential for calcification and normal bone development in chicks. In its absence, calcification is reduced but the volume (and mass) of bone increases. In vitamin D3-deficient chicks, this study shows the major defect to be in bone resorption rather than formation. Bone formation measured serially by the apposition of periosteal matrix was normal, whereas bone resorption measured by dissolution at the endosteal surface was dramatically reduced. Bone cells, therefore, would appear to retain their capacity to synthesize a collagenous matrix in the absence of vitamin D3 but lose their capacity to resorb bone. Calcification and its putative dependence on bone resorption (and vitamin D) remain to be elucidated. The vitamin D3-deficient chick provides a convenient and easily quantifiable model in which the morphological and biochemical effects of vitamin D3 can be further studied.

24-hydroxylation of 25-hydroxyvitamin D3: is it required for embryonic development in chicks?

As shown previously, laying hens given 1,25-dihydroxyvitamin D3 as their sole source of vitamin D produce fertile eggs having normal shells, but only 35 to 55 percent of the embryos are normal. Giving these hens additional 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, or 24,24-difluoro-25-hydroxyvitamin D3 at 1.25 nanomoles per day resulted in 90 to 100 percent normal embryos, and hence, hatchability. Since 24,24-difluoro-25-hydroxyvitamin D3 cannot be 24-hydroxylated, 24-hydroxylation is not required for this function of 25-hydroxyvitamin D3.

Altered vitamin D metabolism and bone remodelling in patients with medullary thyroid carcinoma and hypercalcitoninemia

Fourteen patients with medullary carcinoma of the thyroid (MCT) and hypercalcitoninemia were studied. Serum concentrations of calcium, phosphorus and iPTH (C-terminal) were normal. Serum 1,25-dihydroxyvitamin D (1,25-(OH)2D) levels were increased (p less than 0.001) in spite of reduced serum 25-hydroxyvitamin D (25-OHD) levels (p less than 0.02) indicating an enhanced activity of the renal 1 alpha-hydroxylase. Serum 24,25-dihydroxyvitamin D levels were normal and correlated positively with serum 25-OHD. Histomorphometric analyses of iliac crest bone biopsies after in vivo tetracycline double-labelling were performed in patients and controls. The patients showed a normal trabecular bone volume. The mean size of the cortical osteocytic lacunae was increased (p less than 0.001). Significant increases were found in fractional formation surfaces (p less than 0.05), fractional labelled surfaces (p less than 0.01) and fractional resorption surfaces (p less than 0.005) in trabecular bone. The appositional rate of newly mineralized bone was reduced (p less than 0.025). The mean osteoid seam width was normal due to an unchanged mineralization lag time and a normal osteoid appositional rate. The bone formation rate at tissue level was high normal. The altered vitamin D metabolism may be caused by a direct effect of hypercalcitoninemia on the renal l alpha-hydroxylase or may represent an adaptive change in calcium-phosphorus homeostasis. The dynamic bone changes are similar to those found in primary hyperparathyroidism and may be caused by an enhanced sensitivity to circulating PTH induced by the increased 1,25-(OH)2D.

The biochemical basis of renal osteodystrophy and post-menopausal osteoporosis: a view from the vitamin D system

The vitamin D endocrine system is now known to play an essential role in the regulation of plasma calcium and phosphorus concentrations and in overall organismal calcium economy. These two basic functions of the vitamin D endocrine system have provided important new insight into several disease states. The two disease states discussed here are the genesis of renal osteodystrophy and of post-menopausal osteoporosis. It seems likely that defects of alternations in the vitamin D system play important roles in the development of these disease states. Successful treatment undoubtedly will involve the vitamin D system and most likely the active form of vitamin D, 1,25- (OH)2D3.

Subcellular mechanisms involving vitamin D

During the past 15 years a vitamin D endocrine system has been demonstrated in which vitamin D produced normally in the skin is activated first by conversion in the liver and subsequently in the kidney to a hormonal form, 1,25-(OH)2D3. The production of the hormonal form of vitamin D3, is regulated, and much has been learned regarding the molecular mechanism of the hydroxylations of vitamin D and regarding the physiologic regulators of the 25-OH-D-1-hydroxylase. Much remains to be learned regarding the mechanism whereby the 1-hydroxylase is modulated. 1,25-(OH)2D3 appears to function in the target organs of bone, intestine, kidney, and elsewhere by a nucleus-mediated process. Receptors for 1,25-(OH)2D3 have been clearly demonstrated and characterized in crude form. How the receptor and ligand interact with the nucleus is not clear, nor are the gene products that result from this interaction known. One product, a calcium binding protein, is known but its role in calcium transport is in debate. Although much has been learned in the last decade and a half, much remains to be learned regarding the molecular mechanisms whereby vitamin D brings about its remarkable changes in mineral metabolism.

1,25(OH)2D3 is not the only D metabolite involved in the pathogenesis of osteomalacia

Three patients are described in whom there was no simple correlation between plasma 1,25(OH)2D3 concentration and the occurrence of osteomalacia. One patient had severe osteomalacia with high plasma 1,25(OH)2D3 and normal mineral ion product; the second had a normal mineral ion product and no evidence of osteomalacia even though plasma 1,25(OH)2D3 was undetectable; and the third had osteomalacia, low plasma 1,25(OH)2D3 and a reduced mineral ion product. In considering these data in the light of presently available information, it is concluded that osteomalacia can occur as a consequence of a lack of a vitamin D metabolite other than 1,25(OH)2D3, or a consequence of a reduced mineral ion product, but not as a consequence of 1,25(OH)2D3 lack if the mineral ion product is normally maintained and other D metabolites are present. However, a deficiency of 1,25(OH)2D3 normally leads to a reduction in the mineral ion product hence 1,25(OH)2D3 deficiency may play a role in the development of certain forms of osteomalacia.

Early diagnosis of juvenile renal osteodystrophy

Renal osteodystrophy has assumed growing importance as a major and frequently disabling complication of chronic renal failure in children since the advent of successful hemodialysis and renal transplantation programs. The frequency and severity of renal osteodystrophy appears greatest in younger children with congenital diseases of the kidney and urinary tract, who experience long intervals of chronic renal failure prior to reaching end-stage. Twenty-nine children with varying degrees of chronic renal failure were studied to learn: (1) how early renal osteodystrophy can be diagnosed; and (2) how the various clinical, biochemical, and hormonal abnormalities correlate with abnormal bone histomorphometry as determined from percutaneous transilial bone biopsies. Results showed: (1) marked-to-moderate reductions in GFR (mean = 35 ml/minute/1.73 m2; range 11 to 65 ml/minute/1.73 m2); (2) elevations of serum PTH concentrations in all patients with a GFR < 45 ml/minute/1.73 m2; (3) abnormal bone histomorphometry in all patients with elevated PTH concentrations; (4) "early" renal osteodystrophy (elevated PTH concentrations and abnormal bone histomorphometry but normal serum chemistry values and radiographs) in one quarter of the patients; (5) poor correlations of serum chemistry values and radiographs with bone histomorphometry; and (6) a wide range of histologic abnormalities including predominant osteomalacia (n = 7), predominant hyperparathyroidism (n = 6), or a mixed picture (n = 11).

Paradoxical effect of 1,25 dihydroxycholecalciferol on osteoblastic and osteoclastic activity in the skeleton of the eel Anguilla anguilla L

Female mature eels (300 to 500 g) received one intraperitoneal injection of 1.25(OH)2D3 (10 microgram). Their vertebral bone was compared, 8 h and 24 h after the injection, with vertebral bone of control mature female eels receiving solvent alone (ethanol). Sexual maturation in female eels induces a bone decalcification with hypercalcaemia and hyperphosphataemia. The control eels showed marked osteoclastic resorption and osteocytic osteolysis and the degree of mineralization of the intercellular substance decreased. Injection of 1.25 (OH)2D3 into these female mature eels provoked as early as 8 h: 1) an increase in hypercalcaemia and hyperphosphataemia; 2) a major conversion of lining cells to osteoblasts and a stimulation of osteoblastic activity with new bone formation; 3) diminished osteoclastic resorption without changing osteocytic osteolysis or bone matrix mineralization.

Tetracycline labeling of bone in vivo

We have analyzed various aspects of tetracycline labeling technique for the measurement of bone apposition rate in vivo. Our efforts were restricted to those aspects that are frequently questioned when data obtained using this technique are interpreted as representing the rate of bone apposition. Rat bone was labeled in vivo by sequential injections of oxytetracycline at a dose range of 3 to 24 mg/kg body weight and at intervals ranging from 24 to 72 h. The bone apposition rate was calculated by measuring the distance from the first dose of label to the subsequent ones. As these distances are by far too small to be determined accurately by any available micrometer eyepiece, we have used a scanning microscope photometer which allows measurements on slow-forming sites that otherwise would have been considered nongrowing sites. Using these techniques, we have demonstrated that oxytetracycline has no effect on the bone apposition rate when used in the concentrations indicated. In addition, we found that at labeling intervals of 96 h or more, periods of osteoblastic inactivity are likely to be included in measurements at individual sites. The instantaneous apposition rate is thus underestimated at these long time intervals.

Acute effects of Solanum malacoxylon on bone formation rates in growing rats

The plant Solanum malacoxylon is responsible for a syndrome of hypercalcemia, soft tissue mineralization, and progressive wasting in South American cattle known as enteque seco or espichamento. There is evidence that a glycoside of 1,25-dihydroxycholecalciferol is the active principle in the plant. The basis for the hyperostosis seen in the disease is unclear. To study the acute effects on bone formation rates, 8-week-old rats were given an aqueous extract equivalent to 250 or 1000 mg of Solanum daily per os for 7 days. Bones were labeled by injection of fluochrome 2 days before the start of treatment and 2 days prior to sacrifice. Morphometric evaluation of undecalcified sections of caudal vertebrae revealed an increased amount of trabecular bone in both Solanum treated groups with no difference due to dose level. This was associated with an increase in the bone apposition rate on trabecular surfaces. No differences were found in the amount of osteoid seam width. Periosteal apposition rate and endochondral bone formation were also measured and no significant differences found. The findings indicate that acute stimulation of cell level bone formation on trabecular surfaces may play a role in the hyperostosis seen in the naturally occurring condition.

The response of bone apposition rate to some nonphysiologic conditions

The response of bone apposition to some nonphysiologic conditions was investigated. In rabbits, the normal osteogenic rhythm was totally abolished shortly following treatment of hydrocortisone at a dose of 2 mg/kg body weight daily. A new rhythm developed after the treatment was continued for 20 1/2--34 days. The rate of bone apposition was significantly depressed compared to normal data reported previously. In rats receiving one U.S.P. unit of parathyroid extract daily for 14 days, the rate of bone apposition was significantly higher than that in control rats. In both sepcies, the response to an exogenous hormone was identified for all skeletal locations. It was concluded that new bone apposition was a function of activated osteoblasts, and that this function responded only to general body control mechanisms.