Hyperphosphataemia in histamine injected laying hens

The effects of histamine on soluble calcium concentrations in gastrointestinal tract contents, acid secretion, urinary phosphorus excretion, plasma free-hydroxyproline and inorganic phosphorus levels were studied in laying hens during egg shell formation. Histamine induced hyperphosphataemia, hyperhydroxyprolinemia and decreased soluble gastrointestinal calcium at 3 hr after injection. Cimetidine inhibited all effects induced by histamine. This suggests that hyperphosphataemia arises from increased bone resorption provoked by decreased soluble intestinal calcium during egg shell formation.     

Effects of methyl mercury at different dose regimes on eggshell formation and some biochemical characteristics of the eggshell gland mucosa of the domestic fowl

Eggshell formation and egg production in domestic fowl were studied following the administration of methyl mercury (two dose regimes: 5 mg daily for 6 consecutive days and 1 mg daily for 50 consecutive days). A daily oral dose of 5 mg of methyl mercury for 6 consecutive days induced significant eggshell thinning and deformation and inhibited egg production. Uptake of ⁴⁵Ca and synthesis of prostaglandins by a homogenate of eggshell gland mucosa from methyl-mercury-treated birds were significantly reduced, as was the calcium content of blood plasma. A daily oral dose of 1 mg of methyl mercury administered for 50 consecutive days also induced eggshell deformation and thinning and reduced egg production. This dose did not, however, have significant effects on the following: ⁴⁵Ca uptake and prostaglandin synthesis by a homogenate of the eggshell gland mucosa; ⁴⁵Ca uptake by a homogenate of duodenal mucosa; the Ca content of the blood plasma, shell gland mucosa or shell gland lumen; the HCO₃⁻ content of the shell gland lumen or the specific gravity of tibia. Methyl mercury added in vitro to a homogenate of eggshell gland mucosa significantly stimulated the synthesis of prostaglandins PGF_2α and PGE₂. Addition of mercury chloride to the same type of preparation stimulated the synthesis of PGF_2α at the expense of thromboxane (T × B₂) synthesis. Administration of 5 mg methyl mercury for 6 consecutive days seemed to reduce the availability of calcium for eggshell formation. This effect could have been due to a direct inhibitory effect of methyl mercury on calcium uptake from the gastrointestinal tract and/or to mobilization of medullary bone. The administration of 1 mg methyl mercury for 50 consecutive days probably induced the reproductive effects by another mechanism. The effects of methyl mercury on avian eggshell formation are quite different from the effects p,p′-DDE exerts on that process.     

Transplacental 45Ca and 32P flux in the guinea pig: effect of maternal hypercalcaemia and hypocalcaemia

Transplacental 45Ca and 32P flux was measured across the in situ perfused guinea-pig placenta under conditions of acute maternal hypocalcaemia and hypercalcaemia. Maternal hypercalcaemia induced acutely by calcium gluconate infusion caused an increase in maternal-to-fetal 45Ca flux which was proportional to the increase in maternal plasma ionized calcium concentration. Acute maternal hypocalcaemia was induced by EGTA infusion and resulted in a decrease in maternal plasma ionized calcium concentration proportional to a corresponding decrease in transplacental 45Ca transfer. A bolus of calcium gluconate caused a transient decrease in 32P flux, whereas EGTA administration was without significant effect on transplacental 32P transfer. Calcium transport across the placenta is not saturated under conditions of maternal normocalcaemia and may be altered according to acute changes in maternal plasma calcium concentration. Thus, control of maternal-to-fetal calcium transfer does not appear to be at the placental level. This suggests that fetal calcium homeostasis may be regulated by the fetus itself.     

The Effects of Melatonin on the Physical Properties of Bones and Egg Shells in the Laying Hen

Laying hens often experience unbalanced calcium utilization which can cause deficiencies in bone and egg mineralization. Because melatonin has been shown to affect bone mineralization in other animals, we examined whether treating hens with melatonin would affect eggshell thickness and improve skeletal performance, thereby reducing skeletal and egg shell defects. Birds were given a diet containing either low (30 µg/kg), medium (300 µg/kg), or high (3 mg/kg) concentrations of melatonin, or control feed through approximately one laying cycle. We examined the weight, length, and strength of egg, femur, tibia, and keel. Hens treated with a high concentration of melatonin showed significant strengthening in their femur and tibia, as measured by maximum force sustained and breaking force, compared to controls. Egg weights from hens treated with melatonin were significantly greater than those from hens that were not treated with melatonin. Conversely, egg shell mass of hens treated with melatonin was significantly lower than those of hens not treated with melatonin. Our data suggest that melatonin may affect the allocation of calcium to bone at the expense of egg shell mineralization.     

Acute versus chronic effects of whey proteins on calcium absorption in growing rats

The acute and chronic effects of whey proteins on calcium metabolism and bone were evaluated. In acute studies, 8-week-old male rats were gavaged with 50 mg whey protein concentrate (WPC) and 25 mg calcium. 45Ca was administered intravenously or orally. Kinetic studies were performed, and femurs were harvested. Four of seven WPCs significantly increased femur uptake of 45Ca compared with controls. One WPC at 50 mg enhanced calcium absorption over a range of calcium intakes from 35.1 +/- 9.4% to 42.4 +/- 14.0% (P < 0.01). Three of the most effective WPCs were tested further in a chronic feeding study. One hundred 3-week-old rats were randomly divided into four adequate dietary calcium (ADC; 0.4% Ca) groups (control of 20% casein and three WPC groups with 1% substitution of casein with each of three WPCs) and two low calcium (LC; 0.2% Ca) groups (control of 20% casein and one WPC group with 1% substitution of casein with one WPC). After 8 weeks, there was no effect of WPCs on femur uptake of 45Ca among ADC groups and there was no effect of WPCs on calcium retention, femur breaking force, femur bone mineral density, or total femur calcium at either dietary calcium intake. However, whole body bone mineral content (BMC) was significantly higher (P < 0.05) in the three whey protein concentrate ADC groups compared with the ADC control group. Total BMC at the proximal tibia in whey protein ADC groups was increased, as shown by peripheral quantitative computed tomography. Our results indicate that the acute calcium absorption-enhancing effect of whey proteins did not persist through long-term feeding in rats. However, the initial enhancement of calcium absorption by whey protein was sufficient to increase BMC.     

Effects of dietary NaCl supplementation on bone synthesis of hydroxyproline, urinary hydroxyproline excretion and bone 45Ca uptake in the rat

High sodium chloride intakes are regarded as a risk factor for osteoporosis because they increase the obligatory urinary calcium loss and stimulate parathyroid activity. Sodium chloride loads induce osteopenia in the rat. The effect could be due to a decrease in bone formation or a rise in bone resorption. Two experiments were undertaken to study the effects of dietary NaCl supplementation on 3H-hydroxyproline synthesis and 45Ca uptake in femoral bone. Salt-treated rats excreted 1.7 times more total urinary hydroxyproline (P less than 0.001) and 2.1 times more recently labelled 3H-hydroxyproline than controls (P less than 0.02) but they did not accumulate less 3H-hydroxyproline or less 45Ca in their bones than controls. These results indicate that salt-mediated osteopenia is due to an increase in bone resorption, rather than to a decrease in bone formation.     

Bone and shell contribution to lactic acid buffering of submerged turtles Chrysemys picta bellii at 3 degrees C

To evaluate shell and bone buffering of lactic acid during acidosis at 3 degrees C, turtles were submerged in anoxic or aerated water and tested at intervals for blood acid-base status and plasma ions and for bone and shell percent water, percent ash, and concentrations of lactate, Ca(2+), Mg(2+), P(i), Na(+), and K(+). After 125 days, plasma lactate concentration rose from 1.6 +/- 0.2 mM (mean +/- SE) to 155.2 +/- 10.8 mM in the anoxic group but only to 25.2 +/- 6.4 mM in the aerated group. The acid-base state of the normoxic animals was stable after 25 days of submergence. Plasma calcium concentration (?Ca(2+)) rose during anoxia from 3.2 +/- 0.2 to 46.0 +/- 0.6 mM and ?Mg(2+) from 2.7 +/- 0.2 to 12.2 +/- 0.6 mM. Both shell and bone accumulated lactate to concentrations of 135.6 +/- 35.2 and 163.6 +/- 5.1 mmol/kg wet wt, respectively, after 125 days anoxia. Shell and bone ?Na(+) both fell during anoxia but the fate of this Na(+) is uncertain because plasma ?Na(+) also fell. No other shell ions changed significantly in concentration, although the concentrations of both bone calcium and bone potassium changed significantly. Control shell water (27.8 +/- 0.6%) was less than bone water (33.6 +/- 1.1%), but neither changed during submergence. Shell ash (44.7 +/- 0.8%) remained unchanged, but bone ash (41.0 +/- 1.0%) fell significantly. We conclude that bone, as well as shell, accumulate lactate when plasma lactate is elevated, and that both export sodium carbonate, as well as calcium and magnesium carbonates, to supplement ECF buffering.     

Effect of dietary phosphate on intestinal calcium and phosphate absorption

Intestinal Ca and P absorption was investigated on rachitic chicks raised on diets with a 1% Ca and 0.3% or 1% P contents. 45Ca and 32P absorption was determined by the technique of the isolated gut sac in vivo. In addition, 32P transport was also measured by the everted gut sac procedure in vitro. Treatment with vit. D3 during 7 days increased the 45Ca absorption in animals fed diets containing 0.3% or 1% P. 32P absorption showed an increase after 2 days of treatment and a decrease afterwards. The reduction of 32P absorption was larger in animals fed diet with 1% P. Study of 32P transport with the everted gut sac technique showed an increase after vit. D3 and a loss of intracellular P, regardless the duration of treatment.     

Changes in Calcium Reserves in Breeding Lesser Snow Geese (Chen caerulescens caerulescens)

Calcium and fat reserves of the femur medullary bone were examined in sexually mature lesser snow geese (Chen caerulescens caerulescens) collected during the 1974–1975 season. In females, femur calcium and fat levels increased by 80 and 30%, respectively, during the spring migration, much of the increase taking place while the birds staged in southwestern Manitoba and North Dakota prior to their departure for the breeding area. In males. femur calcium levels showed no seasonal change but femur fat increased in a manner similar to that found in the females, although the increase was not as great (17%). In the females, femur fat content fell by 40% during egg-laying whereas in males a decrease in femur lipid was not evident until incubation was well underway. Femur calcium levels in females declined during egg production and early incubation, showing a 56% decrease over spring migratory levels, indicating that dietary calcium intake was limited during the nesting period. However, the low femur calcium levels in birds collected during the spring were not significantly different from those of wintering birds, suggesting that no calcium deficiencies were apparent. Plasma calcium levels in males remained relatively constant throughout the year, although there was some elevation in May. Plasma calcium levels in the females increased almost threefold during egg laying and returned to pre-laying levels during incubation. Medullary bone was evident only in reproducing females and appeared during spring migration, concomitant with increased femur weight, fat and calcium content. Medullary bone degradation commenced during the first week of incubation and no medullary bone was in evidence by molt. Calcium reserves of medullary bone accounted for only 17.2% of the calcium required for eggshell production, suggesting that. at least during the laying period, the female must depend on some exogenous source, perhaps from grit or brackish water.     

Application and comparison of two models to study effects of calcium sources in sheep

The aim of this research was to assess and compare two compartmental models by studying effects of different Ca sources on Ca and P metabolism of sheep. Brazilian male sheep (20) were fed a basal diet supplemented with different sources of Ca, being: limestone (L), alfalfa hay (AH), shell meal (OSM) and citrus pulp (CTP). After 21 days, each sheep was given, as a single dose via the right jugular vein, 7.4 MBq of radio-calcium (⁴⁵Ca) and 7.4 MBq of radio-phosphorus (³²P). Calcium and P metabolism were evaluated by comparing the Vitti–Dias (VD) and Fernández–Lopes (FL) models [Dias, R.S., Kebreab, E., Vitti, D.M.S.S., Roque, A.P., Bueno, I.C.S., France, J., 2006. A revised model for studying phosphorus and calcium kinetics in growing sheep. J. Anim. Sci. 84, 2787–2794; Lopes, J.B., Vitti, D.M.S.S., Abdalla, A.L., Haddad, M.L., Figueredo, A.V., Moraes, R.C.B., 2001. Modelo do fluxo biológico do fósforo de fontes de fosfato em suínos, usando o ³²P como marcador. Rev. Bras. Zoot. 30, 165–173], by contrasting flows between gut and plasma, plasma and bone, and plasma and tissue. There were no differences in Ca and P intakes for the treatments. Ca flows from tissue and bone to plasma and vice versa were similar among treatments, though net bone and net tissue Ca retentions were higher for treatments L and OSM and lower, as well as negative, for AH and CTP (P<0.05). Net bone Ca results were consistent between the VD and FL models, although net tissue Ca retention was slightly higher for the VD. The presence of pectin in CTP and oxalate in AH could have affected Ca balance on these treatments. Total Ca absorption was higher (P<0.05) for L with both models. The chemical form of Ca in the different sources affected its metabolism, but did not affect P metabolism. Both models had higher P resorption than P absorption in bone, suggesting that the sheep were mobilizing P. It could be inferred that impaired digestion induced P mobilization from bone to supply P for metabolic needs. Both the VD and FL models had the same pattern for the P flows, and for net bone and tissue P retentions. Both models can be used to assess Ca and P kinetics in ruminants, and both suggest that our sheep tended to be deficient in Ca and P as well as that the inorganic sources of Ca were better utilized.     

口服补钙对甘肃鼢鼠钙磷代谢的影响

利用原子吸收分光光度计、可见光分光光度计、全自动生化分析仪测定了2007年4～5月捕获的甘肃鼢鼠(Myospalax cansus)补钙组(n=7)和对照组(n=7)股骨钙、磷含量,血浆钙、磷浓度,分析口服补钙对甘肃鼢鼠钙、磷代谢的影响,初步探讨甘肃鼢鼠钙、磷吸收机制。结果表明,甘肃鼢鼠补钙后股骨钙、磷含量明显增加(P0.05),血浆钙、磷浓度无明显变化(P0.05),股骨钙、磷含量与钙、磷摄入总量显著正相关(P0.01),呈不饱和趋势,股骨钙、磷含量与血浆钙、磷浓度呈不显著负相关(P0.05)。说明甘肃鼢鼠骨骼对钙、磷有较高储留能力,推测甘肃鼢鼠对钙、磷的吸收可能是非依赖VD3的被动吸收途径。     

Immunohistochemical localization of a calcium pump and calbindin-D28k in the oviduct of the laying hen.

The localization of a plasma membrane calcium pump in the oviduct of the laying hen was investigated by immunohistochemical techniques, utilizing a monoclonal antibody (5F10) produced against the human erythrocyte calcium pump. This antibody was shown to react with an epitope of the pump in oviductal tissue, and prominent staining was observed on the microvilli of the tubular gland cells of the hen shell gland (uterus) and the isthmus. The Ca2+ pump was not detectable in the infundibulum or the magnum. Calbindin-D28k, also localized by immunohistochemical means, was observed to be present in the tubular gland cells of the shell gland and the distal isthmus (adjacent to shell gland) but not in either the proximal isthmus (adjacent to the magnum), the magnum or the infundibulum. The localization of the Ca2+ pump in the oviduct corresponds to known sites of mineral deposition during egg shell formation. The distribution of calbindin-D28k differed, co-localizing with the Ca2+ pump in the shell gland and distal isthmus but not in the proximal isthmus. This might reflect a greater rate of active Ca2+ secretion in the distal isthmus and shell gland as compared to the proximal isthmus.     

Lactic acid buffering by bone and shell in anoxic softshell and painted turtles

We tested two hypotheses: first, that the inferior anoxia tolerance of the softshell turtle, Apalone spinifera, compared to the western painted turtle, Chrysemys picta bellii, is related to its less mineralized shell, and second, that turtle bone, like its shell, stores lactate during prolonged anoxia. Lactate concentrations of blood, hindlimb bone, and shell were measured on normoxic Apalone and Chrysemys and after anoxic submergence at 10 degrees C for 2 and 9 d, respectively. Blood and shell concentrations of Ca(2+), Mg(2+), Na(+), K(+), and inorganic phosphate (P(i); for shell only) were also measured. Because a preliminary study indicated lactate distribution in Chrysemys throughout its skeleton during anoxia at 20 degrees C, we used hindlimb bones as representative skeletal samples. Apalone shell, though a similar percentage of body mass as Chrysemys shell, had higher water content (76.9% vs. 27.9%) and only 20%-25% as much Ca(2+), Mg(2+), CO(2), and P(i). When incubated at constant pH of 6.0 or 6.5, Apalone shell powder released only 25% as much buffer per gram wet weight as Chrysemys shell. In addition, plasma [Ca(2+)] and [Mg(2+)] increased less in Apalone during anoxia at an equivalent plasma lactate concentration. Lactate concentrations increased in the shell and skeletal bone in both species. Despite less mineralization, Apalone shell took up lactate comparably to Chrysemys. In conclusion, a weaker compensatory response to lactic acidosis in Apalone correlates with lower shell mineralization and buffer release and may partially account for the poorer anoxia tolerance of this species.     

Relationship between phosphatidylinositol synthesis and recovery of 5-hydroxytryptamine-responsive Ca2+ flux in blowfly salivary glands.

Each salivary gland contains about 135 pmol of phosphatidylinositol. In glands prelabelled by incubation for 1 h with [32P]Pi or [3H]inositol there was a subsequent breakdown of 80% of the labelled phosphatidylinositol over a 2 h incubation period with 10 micrometer-5-hydroxytryptamine. However, there was no detectable decrease either in total phosphatidylinositol based on phosphorus analysis by chemical estimation or in the radioactivity of [32P]phosphatidylinositol in salivary glands of flies raised from the larval stage on diets containing[32P]Pi and whose phospholipids were uniformly labelled. These results suggest that the pool of phosphatidylinositol involved with Ca2+ gating is a small fraction of the total phosphatidylinositol content. Furthermore it is this small compartment that is preferentially radioactively labelled during short-term incubations with radioactively labelled precursors. In salivary glands incubated for 2 h with 10 micrometer-5-hydroxytryptamine there was a marked decrease in the flux of 45Ca2+ across the gland. After removal of the hormone, incubation of salivary glands for 1 h in the presence of 2mM-inositol, but not choline or ethanolamine, resulted in a recovery of hormone-responsive 45Ca2+ flux. Quantitative studies revealed that less than 9 pmol of phosphatidylinositol must be formed to fully restoret he 5-hydroxytryptamine-responsive 45Ca2+ flux.     

Cestrum diurnum leaf as a source of 1,25(OH)2 Vitamin D3 improves egg shell thickness

A continuing concern of the poultry industry is the high incidence (12%) of egg losses in the laying house due to poor egg shell quality. Calcium (Ca) homeostasis is a key factor in egg shell formation. The economy of Ca utilisation is under the control of Vitamin D(3), particularly its active metabolite 1,25-dihydroxy cholecalciferol [1,25(OH)(2)D(3)]. Supplementation of 1,25(OH)(2)D(3) has been shown to increase specific gravity, shell thickness and shell weight of the egg. However, commercially available synthetic 1,25(OH)(2)D(3) is very expensive. Earlier studies from our Institute [Phytochemistry 37 (1994) 677] have identified a cheap, natural and rich source of 1,25(OH)(2)D(3) in the leaves of Cestrum diurnum (CD), a member of the Solanaceae family. In this study, CD leaves were explored as a source of 1,25(OH)(2)D(3) in the feed of layer birds to improve the egg shell thickness. Fifteen-week-old white leghorn layers were divided into four treatments of 60 birds each and as follows: (I) normal diet with Vitamin D(3), (II) normal diet with Vitamin D(3) + CD, (III) normal diet without Vitamin D(3) and, (IV) normal diet without Vitamin D(3) + CD powder. CD leaf powder was incorporated in to the feed at 0.3% level. The experimental feeding was continued up to 72 weeks of age of the birds. Weekly food intake and daily egg production were noted throughout the experimental period and the specific gravity of the eggs, feed consumed to lay one egg and egg shell thickness were determined. Incorporation of CD leaves in the feed had the maximal effect on all the parameters studied. The feed consumed to lay one egg was 20 g less than the control group. The specific gravity of the egg was higher by 0.005, than the control egg, indicating a 5% decrease in the breakage of eggs in CD fed chicks. Also there was a significant increase (P < 0.001) in egg shell thickness. The data suggest that incorporation of CD leaf powder in the feed of poultry layers increased the egg shell thickness, which in turn could decrease the economic loss due to breakage of eggs.     

Histamine-induced hyperphosphatemia and hypocalcemia in the laying hen

The effects of histamine on plasma inorganic phosphorus (Pi) and total calcium values were studied in laying hens during egg formation and in non-laying hens. Histamine induced hyperphosphatemia and slight hypocalcemia during eggshell calcification, whereas the most pronounced hypocalcemia was observed during the early stages of egg formation. The histamine-induced hyperphosphatemia was completely inhibited by cimetidine but only partly by promethazine. However, the histamine-induced hypocalcemia was totally inhibited by cimetidine and promethazine.     

Preloading of micromolar intracellular Ca2+ during capacitation of Sicyonia ingentis sperm, and the role of the pHi decrease during the acrosome reaction.

In studying the mechanism controlling the sperm acrosome reaction (AR) in the marine shrimp Sicyonia ingentis, intracellular Ca2+ and pH were measured using the fluorescent indicators Fura-2 and Fluo-3 for Ca2+, and SNARF-1 for pH. Capacitated sperm possessed an apparent resting Ca2+ concentration of 1-2 microM which remained constant upon induction of the AR with egg water. Uncapacitated sperm had extremely low Ca2+ levels and did not respond to egg water. These results suggest that, while in other species the Ca2+ is elevated to micromolar levels during initiation of the AR, S. ingentis sperm are preloaded with Ca2+ during capacitation and the trigger for the AR is downstream of the Ca2+ increase. The notion that Ca2+ influx is not involved at the actual time of the AR in capacitated S. ingentis sperm is supported by the inability of Ca2+ ionophore A23187 to induce the AR and the ineffectiveness of Ca2+ channel antagonists to block egg water-induced AR. Measurements of capacitated sperm pH showed a significant decrease during the first 10-15 min of the AR, which did not correlate temporally to either acrosomal exocytosis (at 5 min post-induction) or filament formation (after 45 min). Inhibition of egg protease activity required for induction of filament formation did not inhibit the pH drop, indicating that intracellular acidification is not the final trigger for filament formation, although it may be required prior to action of the protease.     

In vitro anti-resorptive activity and prevention of ovariectomy-induced osteoporosis in female Sprague-Dawley rats by ormeloxifene, a selective estrogen receptor modulator

Antiosteoporotic activity of ormeloxifene, a multifunctional SERM, using inhibition in parathyroid hormone (PTH) induced resorption of 45Ca from prelabeled chick and rat fetal limb bones in chase cultures and modulation of certain biochemical markers of bone turnover and bone mineral density (BMD) in ovariectomized adult female rats, was investigated. Ormeloxifene concentration-dependently inhibited PTH-induced resorption of 45Ca from chick fetal femora with treated/control (T/C) ratio of 0.71, 0.32 and 0.20 at 50, 100 and 200 microM concentration, in comparison to 0.49, 0.53 and 0.95 in case of CDRI-85/287 (a pure antiestrogen), tamoxifen and ethynylestradiol (100 microM), respectively. Using rat fetal limb bones, ormeloxifene (100 microM) exhibited T/C ratio of 0.67, in comparison to 1.43 with PTH alone. Heat-killed bones exhibited negligible resorption (2.9%; T/C: 0.098) in response to PTH. In adult female rats, ormeloxifene (1.25 and 12.5 mg/kg per day) inhibited ovariectomy-induced increase in serum total and bone-specific alkaline phosphatase and osteocalcin and urine calcium/creatinine ratio to almost intact control level. Ovariectomy was accompanied by marked decrease in bone mineral density of isolated femur and tibia, being maximum in femur neck (28.3%; P < 0.01) and midshaft (23.7%; P < 0.01), but only marginal (6.7%; P > 0.05) in region proximal to tibio-fibular separation point. Decrease in BMD based on T-/Z-score, too, was >2.5 S.D. than mean value of normal young adult/age-matched females. This was prevented by ormeloxifene and the effect, though apparently more in females supplemented with higher dose of ormeloxifene, was not always significantly different and clear dose-response was not evident until BMD data was evaluated on T-/Z-score basis. The analysis also demonstrated much higher threshold level of tibia than femur and more so for their mid-shafts. Increase in BMD of isolated bones was also observed in ormeloxifene-treated intact females, without significantly altering biochemical markers of bone turnover or uterine weight. Findings suggest potential of ormeloxifene in management of post-menopausal osteoporosis and beneficial effect on BMD in women taking this SERM for contraception or any hormone-related clinical disorder.     

Rapid activation of the medullary bone osteoclast cell surface by parathyroid hormone

Quantitative transmission electron microscope methods were used to determine the response of functionally inactive avian medullary bone osteoclasts to parathyroid hormone (PTH). Egg-lying Japanese quail were used during a period of the egg cycle when medullary bone was not being resorbed for egg shell calcification and when medullary bone osteoclasts were functionally inactive. Ruffled borders adjacent to bone surfaces were rarely, if ever, found on these cells. 20 min after the administration of PTH, over 70% of the osteoclast profiles had ruffled borders adjacent to bone surfaces. These ruffled borders were bounded by filamentous-rich "clear zones" and resembled ruffled borders found on functionally active cells. There was also a marked increase in plasma calcium levels after PTH administration. This study demonstrates that PTH stimulates the de novo generation of ruffled borders on osteoclasts in vivo and suggests that osteoclasts may be involved in the acute regulation of calcium metabolism by exogenous PTH.     

Osteoclast cell-surface changes during the egg-laying cycle in Japanese quail

The medullary bone serves as a source of labile calcium mobilized during calcification of the egg shell in birds. Quantitative histological methods demonstrate that the numbers of medullary bone osteoclasts and nuclei per osteoclast remain unchanged during the egg cycle in the Japanese quail (Coturnix). Therefore, cyclic changes in bone resorption cannot be explained by modulations of osteoclasts from and into other bone cells, a mechanism previously suggested for certain species of birds. Rather, dramatic changes in osteoclast cell-surface features occur during the egg cycle, which might account for cyclic variations in resorptive activity. During egg shell calcification, osteoclasts with ruffled borders are closely apposed to bone surfaces; the cytoplasm is rich in vacuoles that contain mineral crystals and seem to derive from the ruffled border. At the completion of egg shell calcification, the ruffled borders and vacuoles move away from the bone surface, although the osteoclast remains attached to the bone along the filamentous or "clear" zone. Associated with the disappearance of the ruffled borders is the appearance of extensive interdigitated cell processes along the peripheral surface of the osteoclast away from the bone. These unusual structures, which may serve as a reservoir of membrane, largely disappear when ruffled borders and associated structures reappear. Therefore, in these hens, the osteoclasts modulate their cell surface rather than their population during the egg cycle.