the ultimate site of skeletal deposition of strontium

THE ULTIMATE SITE OF SKELETAL DEPOSITION OF STRONTIUM AND LEAD*

BY NORMAN S. MACDONALD, FLORITA EZMIRLIAN, PATRICIA SPAIN, AND CLARE McARTHUR

(From the School of Medicine, University of California at Los Angeles, Los Angeles, California)

(Received for publication, November 13, 1950)

The great avidity of the mammalian skeletal system for heavy metal ions has been recognized for several decades. The notorious tendencies of lead and radium to accumulate in bone are familiar examples. In recent years, interest in the elements which are products of nuclear fission, as well as i-n the Puns-uranium elements, has initiated many studies of the metabolic fate of such elements after entry into the body. It was soon noted that a large proportion of the metallic elements so studied are “bone seekers.”

Radioautographic studies on bone sections bearing radioactive metals have proved quite successful in demonstrating the sites of deposition of these materials on a microscopic scale. For instance, Srsg has been shown to be distributed throughout the femoral cortex as well as in the epiphyseal regions. Ygo, on the other hand, is stated to be concentrated primarily in organic matrix (1).

On the submicroscopic, that is the atomic scale, only meager direct evidence was available concerning the form in which metals accumulate in bone. It had been stated that studies in vitro on the uptake by powdered bone of SP from solutions indicated that surface adsorption alone could account for the observed uptake in viva (2). Ionic exchange had also been postulated as the major mechanism of cation deposition (3). In the hope of unearthing further direct evidence applicable to this problem, it was decided to apply the techniques of x-ray diffraction to bones heavily laden with foreign cations. Non-radioactive strontium and lead are the two elements to be reported upon at this time.

As the work progressed, it appeared likely that the inorganic material was a solid solution of the foreign element in crystals of the bone salt. The basic evidence for such a state of solid solution must come from precise determination of alt,erations in the dimensions of the crystallo- graphic unit cell of the matrix substance, the “solvent.” The entry of

* This paper is based on work performed under contract No. AT-04-l-gen-12 between the Atomic Energy Commission and the University of California at Los An- geles.

387

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388 SKELETAL DEPOSITION OF SR AND PB

foreign atoms into a lattice, either by substitution for ions already present or by the assumption of interstitial positions, will distort the parallelism of all the atomic planes to some degree. However, the closer together the members of a set of parallel planes are normally, the more obvious will be a distortion of a given magnitude. Thus, the smaller the interplanar spacings, the greater becomes the sensitivity of determinations of displacements of the diffraction interferences. For this reason, recourse was had to so called “back reflection” methods, which deal with diffraction patterns from crystal planes which are spaced more closely than those used for mere crystal identification.

The exact nature of the inorganic portion of normal bone is still a matter of contention. For discussion of the present status reference may be made to recent reviews (4, 5). It is certain, however, that the inorganic matter of bone possesses a crystalline structure which produces an x-ray diffraction pattern which differs only in minor degree from those of members of the apatite series of minerals. Furthermore, it is established that the apatite type lattice can accommodate moderate alterations in chemical composition without severe disruption. In fact, it seems likely that for bone salt, or any apatite for that matter, no single formula containing the atomic species in integer ratios can be written. The true situation is probably that of a crystal lattice which is common to a series of solid solutions.

Materials and Methods

Strontium-Laden Bone Specimens-Each member of a series of 15 weanling albino rats received an intraperitoneal injection of 500 mg. of Sr ++ per kilo of body weight every 48 hours, administered as an aqueous solution of SrClp containing 80 mg. of Sr++ per ml. Eleven mature rats, 8-12 months old, were treated similarly. Individuals were sacrificed at various intervals; the femurs and vertebrae were removed, scraped free of mar- row, and ashed at 600” for 15 hours. The residue was then ground to pass a 270 mesh sieve.

Lead-Laden Bone Specimens-Each of a group of twenty-five weanling rats received an intraperitoneal injection of 20 mg. of Pb++ per kilo of body weight every 48 hours, administered as an aqueous solution of lead acetate containing 5 mg. of Pb++ per ml. At death or sacrifice, the femurs and vertebrae were removed and prepared in the manner described above. In several cases a hard white deposit was noticed on the inner surface of the peritoneum near the area of injection. These pathological deposits were excised, ignited, and likewise ground to 270 mesh.

Spectrographic Determination of Ca and fir--The appropriate Sr bone samples as well as a large number of specimens from untreated control


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MACDONALD, EZMIRLIAN, SPAIN, AND MCARTHUR 389

animals were analyzed for Ca and Sr content by an emission spectrographic method. Details of the technique have been reported previously

(6). Polarographic Determination of Pb-The Pb content of the appropriate

specimens was determined by dissolving a weighed amount of the powdered material (10 to 60 mg.) in 0.2 ml. of concentrated HCl, diluting with 3 ml. of water, and adding 3 N KOH to pH 5.0. The volume was then made up to 15.00 ml. with 1 M aqueous KCl, which served as the supporting electrolyte. 0.2 ml. of 0.1 per cent gelatin was then added as a maximum suppressor. The polarogram was recorded on a Sargent model XXI polarograph between -0.3 and -0.7 volts, with a dropping mercury electrode versus a saturated calomel electrode. The temperature was maintained at 25” f 0.2”. A well defined cathodic wave for Pb++ + Pb was obtained at -0.44 volt. The concentration of Pb++ correspond- ing to a given wave height at this half wave potential was then obtained by comparison with a calibration curve prepared from a series of solutions containing known amounts of PbC12. Under these conditions, Pb++ at a concentration as low as 1 y per ml. was detected. The error at this level was f10 per cent. At concentrations of 10 to 100 y per ml., the error was around f2 per cent.

Density Determination by Flotation-The density of several of the powdered samples was determined by suspending 5 to 10 mg. in a solution of HgIl in saturated KI and adding water until no vertical displacement of the particles occurred upon centrifugation. The specific gravity of the clear fluid was then measured with a pycnometer.

x-Ray Difraction with Debye Powder Camera-To obtain the x-ray diffraction patterns of a specimen, 5 to 10 mg. were mixed with a small amount of collodion as a binder and rolled between two microscope slides until a rod about 0.5 mm. in diameter resulted. After drying for 4 hour, the rod was mounted in a 114.59 mm. diameter Debye type camera and exposed to Ni-filtered Cu radiation for 15 to 18 hours. The Kodak “no screen” film was developed according to standard procedures. Rela- tive intensities were determined with the aid of a photoelectric micro densitometer.

x-Ray Diffraction with Symmetrical Back-Reflection Focusing Camera- Lucite specimen holders of the proper curvature were made with the aid of a specially constructed mold. With these holders it was possible to obtain patterns in the back reflection region with 10 to 15 mg. of powder without the use of any binder. The diameter of the camera was 120.00 mm.

Assignment of Crystal Plane Indices to Di$raction Lines-The crystals which make up almost all of the inorganic material in bone belong to the


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hexagonal system. Furthermore, the apatite series of minerals produces diffraction patterns closely approximating that of bone salt. Bale (7) has determined the dimensions of the unit cell of bone salt and of hydroxy apatite to be a0 = 9.48 A and co = 6.88 A. However, in order to assign Miller indices to the great number of lines obtained, which had not previously been reported, it was thought advisable for the present work to prepare a list of all the possible interplanar spacings of a hexagonal crystal, space group C&, whose unit cell had the above dimensions. The basic equation for a crystal of the hexagonal system is

1 -= da

4(/L* + hk + AT*) + _”

3a* ea

where d = the interplanar spacing for a family of planes of Miller index h, k, and I, and a and c = lattice constants, i.e. unit cell dimensions. The numerical values of the interplanar spacings for all possible permutations of h, k, and 1, where h, k, and 1 can be any integer from 0 to 9, were obtained by the use of an International Business Machines punched card computer and sorter. This list greatly facilitated the tentative identification of the diffraction lines, particularly in the back reflection region. Unequivocal identification was then possible for twenty of the twenty-five back reflection lines, six of which were used in the determination of the lattice constants.

Precise Determination of Lattice Constants-It has been shown by several workers (8, 9) that the magnitude of the errors in the precise and accurate determination of crystal lattice parameters is a function of the angle of the diffracted beam used for such measurements. Systematic errors, such as in inaccurate alignment of the specimen, self-absorption of the specimen, and inaccurate knowledge of the camera radius, all tend to approach zero as the Bragg diffraction angle 8 approaches 90”. For the symmetrical focusing type back reflection camera, Cohen (10) has devised an analytical method of extrapolation to remove the systematic errors, and the purely random errors of measurement of diffraction ring diameters then become amenable to treatment by the method of least squares.

By such treatment of the diffraction data for lines in the back reflection area (0 > 45”) the unit cell dimensions for any given specimen were de- terminable with a precision of f0.01 per cent.

Results

Debye Powder Patterns-In the front reflection region (0 < 45”) it was possible to measure 53 distinct lines on samples of normal rat femur ash. Exactly the same pattern was obtained with samples of normal human femur ash. However, as other workers have likewise found (7, 11, 12),


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unequivocal indexing was possible for only thirty of these reflections. As the interplanar spacings decrease, the differences between the d values for possible planes become of the same order of magnitude as the imprecision of the measurements, thus making a valid choice impossible. The lines which could be positively identified agreed well with the listings of Bale (7) and Gruner et al. (11) both as to interplanar spacing and relative intensity. Our data on these lines will therefore be omitted.

All bone specimens containing Sr exhibited patterns in which all lines in the front reflection region conformed to the normal pattern. Shifts of position or relative intensity were undetectable. However, it was noticed that in specimens heavily laden with Sr no lines appeared in the back rejlection region, even though those in the front region (large interplanar spacings) were sharp and well defined. Thus, only one solid crystalline phase was present, even when the Sr content was as high as 8 per cent (in a mouse femur from a previous series of Sr absorption studies). It is pertinent to report that, when tertiary strontium phosphate was mixed with normal bone ash so that the Sr content was 7 per cent, the presence of the second solid phase was readily discerned by the appearance of two new lines superimposed on the hydroxyapatite pattern.

As for lead-bearing specimens of rat femur, again only one crystalline phase was evident from the patterns obtained with the Debye camera, although the Pb content was as high as 0.2 per cent on a weight basis. In a synthetic mixture of normal bone ash and added tertiary lead phosphate, it was possible to detect the presence of the lead crystals when the amount of Pb++ was 2 per cent or more.

Mention has been made of the abnormal “calculi” which appeared on the peritoneal surfaces of seven of the animals. One might presume this material to be an insoluble lead salt precipitated at t’he site of injection. Surprisingly, however, these samples contained 30 to 34 per cent calcium and 1.5 to 8.7 per cent lead. Diffraction patterns with the Debye camera were indistinguishable (in the front reflection region) from that of normal bone ash. Histological sections of these materials are being prepared for staining and a search for osteoblasts will be made. The Pb plays a definite role in this calculus formation, for it has not occurred in rats receiving intraperitoneal injections of saline or SrClz repeated regularly for even longer periods. Speculations on the physiological significance of this ectopic calcification will be reserved for a later report.

Symmetrical Back Resection Patterns-Table I presents the observed interplanar spacings responsible for the diffraction lines in a back reflection pattern from normal bone ash. After consulting the International Business Machines list mentioned above, the six most intense lines were tentatively assigned the indicated indices. Using these values and apply-


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ing Cohen’s method gave values for the lattice constants of a0 = 9.470 and co = 6.881. By substituting these lattice parameters in the basic equation relating interplanar distance to Miller indices, it was then possible to calculate the interplanar spacings for all the other lines. Since these values were compatible with the values observed experimentally, the tentative indexing was established as the correct one. However, unambiguous indexing was impossible for certain reflections indicated in Table I. The wave-length of Cu-K,, was taken as 1.5405 A, rather than

TABLEI

Identification of Back Reflection Lines from Normal Rat Femur Ash

d observed

A

0.7745* 0.7761 0.7773 0.7846 0.7856 0.7867

0.7886 0.7931* 0.7984 0.8014 0.8055* 0.8099

0.8168 0.8180*

-

--

-

d c&x&ted Miller index

A

0.7744 0.7749 0.7766 0.7840 0.7355 0.7867 0.7869 0.7386 0.7931 0.7980 0.8026 0.8052 0.8093 0.8100 0.8131 0.8176

456 480 465 661 570 292 257 t 1 176 048 067 291 094 382

1 275 374 157

7--

d obsenred

A

0.8205

0.8240* 0.8297+ 0.8324 0.8438 0.8467

0.8492 0.8529 0.8559

0.8628 0.8781

d calculated Miller index .-

A

0.8195 0.8204

0.8237 0.8296 0.8327 0.8452 0.8463 0.8469 0.8504 0.8526 0.8554 0.8560 0.8634 0.8785

076 356

I 038 446 554 380 166 118 093 1 470 175 018 373 256 066

- * Most intense lines. t The braces enclose ambiguous reflections.

the Siegbahn value of 1.5374 A. The lines due to the (~2 wave-length of the K doublet were resolved and identified, but are omitted from this tabulation for the sake of brevity. The standard deviation in the determination of d values was fO.OOO1 A. It may be mentioned that the lower order reflections for those planes in which the order was greater than 1 (e.g. -048) could be found among the lines appearing on the Debye camera photographs.

Table II presents the unit cell dimensions of the inorganic crystallites in normal bone ash from several sources. Of particular note is the con- stancy of the unit cell dimensions. The standard deviation for these and all following unit cell values was fO.OO1 A,


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Table III presents the data on Sr-bearing rat femur ash. As in the case of the Debye camera patterns, no anomalous lines appeared as a

TABLE II

Unit Cell Dimensions from Back Rejection Lines; Normal Bone Ash

Sample

Rat femur .............................. “ ‘I ............................... “ “ .............................. ‘I “ .............................. “ I‘ .............................. “ ‘I .............................. 6‘ l‘ ..............................

Average. .............................

Human femur ........................... “ rib .............................. I‘ “ .............................. ‘I “ .............................. “ radius ...........................

Average ...............................

Hydroxyapatite (Ward’s). ...............

-

-

-

-

-

Age

2 mos. 4 “ 9 “ 9 “

1 yr. 1 “ 1 “

5 mos. 9 yrs.

38 (‘ 42 “ 55 “

-

TABLE III

Unit Cell Dimensions from Back Reflection Lines &-Bearing Rat Femur Ash

Ca

per cen1

35.0 38.0 38.5 38.0 38.5 26.5 34.0 29.5 26.5

-~-

sr

per CL??21

0.23 0.25 0.28 0.38 0.45 1.5 1.7 2.0 2.4

a0 co

A A

9.471 6.881 9.470 6.881 9.472 6.878 9.468 6.882 9.471 6.879 Lines blurred

I‘ “ “ ‘I “ <‘

-

-

Ca sr

per cd fier cm1

34.0 2.4 30.0 2.6 33.5 2.6 28.5 2.9 34.0 3.0 37.0 3.0 33.0 3.6 31.0 4.7 29.5 4.8

a0

-

-

-

cd

A

9.469 9.469 9.468 9.477 9.470 9.471 9.471

A

6.883 6.882 6.882 6.872 6.880 6.881 6.881

9.471 6.880

9.473 9.476 9.474 9.473 9.472

6.882 0.884 6.881 6.883 6.882

9.474 6.882

9.467 6.879

a0 co

Lines blurred “ “ “ ‘I ‘I I‘ “ “ “ “ “ “ “ I‘ “ “

consequence of the presence of Sr in the material. It was impossible to determine lattice constants in those instances in which the Sr content was considerable, because of the broadness and low intensity of the lines. It


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must be emphasized, however, that the front reflection lines, obtained from these same samples with the Debye camera, were sharp and fitted the hydroxyapatite pattern.

Table IV presents the data of Pb-bearing ashed tissues of rats injected with lead acetate. By reason of the greater toxicity it was impossible to attain as high a level in the bones as was reached with Sr. Once again, the presence of considerable amounts of lead, particularly in the peritoneal samples, altered neither the number nor the sequence of the lines

TABLE IV

Unit Cell Dimensions from Back Reflection Lines; Pb-Bearing Ash from Rat

Pb a0 I co

Femur “ ._,,..__..,.._.......... 35.5 “ . . . . . . . . . . . . . . . . . 37.0 ‘I . . . . . . . . . . . . . . . 33.5 “ . . .._...__.,.__......... 36.0 “ . . . . . .._._...._........ 1‘ .._..__..___............ 32.0 ‘I . . . . . . . . . . . . . . . . “ .,..,,...,.............. 37.5 “ .._.__.................. 38.0 “ . .._....................

Peritoneum ‘I

35.5 34.0

A A

9.468 6.879

Lines blurred “ “ “ “

9.545 6.873 9.476 6.868 9.468 6.881 9.67 6.90 9.474 6.873

Lines blurred ‘I C‘

34.0 “ .,_.,........,.......... 29.5 “ 31.0 “ ,,.................. . 33.0 ‘I 32.5 “

per cent

0.07 0.10 0.13 0.14 0.15 0.16 0.17 0.17 0.18 0.19 0.23 0.90 1.53 1.68 1.75 1.89 4.59 8.70

9.488 6.863 9.481 6.862 9.485 6.862 9.501 6.911

Lines blurred

of the normal hydroxyapatite pattern, However, the positions of some

-

of the’ lines were shifted markedly, and all lines were broadened. Fig. 1 illustrates the changes in interplanar distances for nine of these

specimens. The base-lines represent the mean interplanar spacings obtained from the femur ash of nine normal rats. (Individual deviations from this mean were less than ~1~0.0003 A for normal samples.) As a result of these distortions of the normal spacings, the unit cell dimensions were also altered somewhat, as may be seen in Table IV. The fact that three of the line positions were shifted much more than their neighbors might indicate that there are preferred sites for the location of Pb++ ions in the lattice.

Density Computations-It became evident that some, if not all, of the


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MACDONALD, EZMIRLIAN, SPAIN, AND MCARTFfTJR 395

foreign ions were taking up positions within the lattice, probably as components of a solid solution. In the hope of ascertaining whether the solid solution was of the interstitial or of the substitutional type, density determinations were undertaken. Unfortunately, it was found that the variation in density of bone ash from one normal individual to another was greater than the difference between the theoretical densities of a substitutional solid solution and an interstitial solid solution at a given Sr content. The conclusion was reached that density studies held little

P

l-

n II 554 (0.8295 ii )

fl b-7 - n n i-l n 446 (0.8241 % )

+Pb IN SPECIMENS FIG. 1. Expansion of interplanar spacings of lead-bearing specimens. The ver-

tical unit at the left represents 0.0010 A. The normal interplanar dist.ances and Miller indices are given at the right.

promise of revealing the disposition of the foreign ions in the bone salt lattice.

DISCUSSION

One can conceive of four different sites in which cations deposited in living bone could ultimately take residence. First, the cations could be chemically bound to one or more of the organic components of the bone. Secondly, they could be deposited as discrete crystals of an insoluble compound in close association both with the organic material and with the inorganic crystallites, and yet maintain their identity. A third possibility would be the “physical” adsorption of the ions on the crystallite surfaces. Finally, the cations might assume positions actually within the


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crystalline structure of the inorganic salt, either by displacing other cations (ionic exchange) or by occupying lattice interstices.

Let us consider what effect each mode of deposition would have on the diffraction pattern of the bone after ignition.

1. Organic molecules containing bound cations would, upon ashing, leave behind an inorganic solid such as the metal oxide, carbonate, sulfate, or phosphate. If this material were crystalline, then its diffraction pattern would be superimposed on that of the apatite. If the material were amorphous or had a crystal size less than 1O-6 cm., it would escape de- tection, but in either event no distortion of the apatite pattern would result. The possibility of chemical reaction of such a solid phase with the bone salt to produce an “impure” apatite, which has been demonstrated with bones abnormally high in phosphate (13), may be ruled out. Ignition at 600” of intimate mixtures of fresh defatted normal bone with strontium phosphate and with lead phosphate produced no abnormalities in the apatite patterns.

2. It is quite unlikely that the Sr and Pb were deposited in the form of discrete crystals of some inorganic salt for the reasons discussed in (1).

3. It is very unlikely that ions adsorbed on the surfaces of the bone sait crystals could alter the dimensions of the unit cells of such crystals.

4. The final mode of deposition alone fits the experimental findings that the atomic planes of the normal bone salt crystals are distorted by the presence of Sr or Pb, and that only one solid phase exists, even when rather large amounts of these ions are present.

It is generally agreed that the inorganic crystallites in bone range from 1O-6 to 10m6 cm. in length (14). In an effort to elucidate the plausible ionic exchange mechanism, calculations were made of the percentage of the total number of Ca++ ions present at the surfaces of such a crystal. It was assumed that the bone salt was hydroxyapatite, and that the crystals were regular hexagonal prisms terminated by basal pinacoid faces. It was further assumed that the dimensions were 10 times those of the unit cell; i.e., each prism face was 95 X 69 A, and each pinacoid face was a hexagon 69 A on a side. This gives a crystal about 1O-6 cm. long. From geometrical considerations based on the structure of the apatite type lattice, determined by St. Naray-Szabo (15), it was calculated that surface Ca++ ions comprise about 6 per cent of the total number of Ca* ions present in a crystal of the order of lo+ cm. in size. However, mouse femur ash containing 8 per cent Sr had been obtained. On the basis of a 1: 1 replacement this corresponds to a substitution of 10 per cent of the total number of Ca++ ions by Sr++ ions. Admittedly, the assumptions are speculative. However, it does appear likely that some of the Sr and Pb is located in the interior of the crystals, though perhaps a large portion is fixed by exchange with Ca++ ions near the crystal surfaces.


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It must be remarked that the bone samples were from animals which had been chronically poisoned with Sr and Pb and that therefore these metals had ample time to reach their ultimate sites of deposition. Hence, the diffraction evidence presented here has little bearing on the early phases of skeletal uptake. It may well be that organic binding or surface adsorption or exchange constitutes the initial processes and that incor-

TABLE V

Some Natural and Synthetic Apatite-Like Substances -

-

-7 -7

Common name Theoretical formula QO co

_- .-

Pyromorphite Chloroapatite Fluoroapatit,e

“ Hydroxyapatite

“

Ca&WddOH)2 9.40 6.93 Sr&POn)6(OH)z 9.74 7.20 Pblo(POa)s(OH)n 9.88 7.32 Ba~(P04)s(OH)z 10.19 7.70 Pb&POJ&& 9.95 7.31 Calo(POd) 6Cl2 9.52 6.85 Calo(POd 82 9.36 6.85

C‘ 9.37 6.88 Cam(POds(OH)z 9.41 6.87

“ 9.47 6.88

Human and dog tooth enamel

Human tooth enamel

Rat femur ash

Human femur ash

9.41 9.47

9.471

9.474

6.87 6.88

6.880

6.882

-

f 5 :: -

S. “ <‘ ‘I

N. ‘C I‘ “ “ “

“ “

“

“ I - - -

1

ibliographic reference

No.

(1’3) (16) (16) (16) (17) (17) (17) (7)

(18) Present

work

(18) (7)

Present work “ I‘

rystal ionic adius

of valent ationt

A

3.99 1.13 3.93 1.35 3.93 3.99 cl.99 D.99 0.99 0.99

0.99 0.99

0.99

0.99 __.

= synthetic; N. = natural. ; the crystal ionic radii are those given by Pauling (19).

poration into the lattice of the bone salt proceeds at a much slower rate (6). It is also probable that such incorporation into any one crystal is not permanent, inasmuch as the components of living bone are constantly undergoing resorption and reformation.

Support for the thesis that Sr and Pb can enter the apatite lattice without serious disruption thereof is afforded by the existence of a series of apatite-like minerals, all of which are isomorphous. The compounds are capable of forming solid solutions, one with another. Table V lists some of these materials.

Undue emphasis should not be placed on similarity of ionic radius as a


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criterion of whether or not one ion can displace another and thus become part of a crystal structure. It is sometimes possible for a single foreign ion to displace more than one of the native ions and thus produce a “defect lattice.” However, such intrusions should be detectable by precision determinations of the unit cell dimensions. These techniques are currently being applied to the study of the skeletal deposition of several other “bone-seeking” elements.

SUMMARY

X-ray diffraction studies of the bone ash of rats receiving repeated injections of strontium chloride and of lead acetate indicate that both of these cations ultimately enter into the internal structure of the inorganic salt crystallites. Powder patterns made with the Debye camera showed no evidence of a second solid phase, even in bone samples containing as much as 8 per cent Sr or 5 per cent Pb. Determinations of the unit cell dimensions of such bones laden with Sr or with Pb were made with a precision of 3~0.01 per cent by the use of a symmetrical focusing back reflection camera. Cohen’s method was used for extrapolation of the data to a Bragg angle of 90”. These determinations clearly demonstrated distortions of the unit cell as a result of the presence of the foreign ions. It was impossible to ascertain by density determinations whether the foreign cations were present in the lattice interstices or had taken up lattice point positions by displacing t,he normal ionic occupants of those positions.

Large ectopic calcifications were noted on the peritoneal surfaces of the rats receiving intraperitoneal injections of lead acetate. The ash of this material showed the same crystalline structure as bone salt, except that the lattice was distorted by the presence of Pb.

Although the evidence sheds little light on the initial phases by which Sr and Pb ions are accumulated in bone, it is concluded that some, and perhaps most, of the cations ultimately become part of the crystalline structure of the bone salt. The length of. time during which such material remains fixed depends upon the rate of bone resorption and reformation.

The authors wish to express their gratitude to Dr. Ralph E. Nusbaum and Mr. G. V. Alexander for performing the spectrographic analyses for stront.ium and calcium. We wish also to thank Mr. Albert S. Cahn of the Institute for Numerical Analysis for preparing the list of possible interplanar spacings with the International Business Machines computer.

BIBLIOGRAPHY

1. Hamilton, J. G., in The use of isotopes in biology and medicine, Madison, 349 (194s).


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2. Hodge, H. C., Gavett, E., and Thomas, I., J. Biol. Ch,em., 163, 1 (1946). 3. Neuman, W. F., Neuman, M. W., Main, E. R., and Mulryan, B. J., J. Biol.

Chem., 179, 341 (1949). 4. Fankuchen, I., Ann. Rev. Biochem., 14,207 (1945). 5. Dallemagne, M. J., Ann. Rev. Physiol., 12, 101 (1950). 6. MacDonald, N. S., Nusbaum, R. E., Stearns, R., Ezmirlian, F., McArthur, C.,

and Spain, P., J. Biol. Chem., 188, 137 (1951). 7. Bale, W. F., Am. J. Roentgenol., 43, 735 (1940). 8. Bradley, A. J., and Jay, A. H., Proc. Phys. Sot., 44,463 (1932). 9. Jette, E. R., and Foote, F., J. Chem. Phys., 3, 605 (1935).

10. Cohen, M. U., 2. Krist., 94, 288 (1936). 11. Gruner, J. W., McConnell, D., and Armstrong, W. D., J. Biol. Chem., 121, 771

(1937). 12. Roseberry, H. H., Hastings, A. B., and Morse, J. K., J. Biol. Chem., 90, 395

(1931). 13. Hirschman, A., Sobel, A. E., Kramer, B., and Fankuchen, I., J. Biol. Chem.,

171, 285 (1947). 14. Bale, W. F., Hodge, H. C., and Warren, S. L., Am. J. RoentgenoE., 32,369 (1934). 15. St. Naray-Szabo, S., 2. K&t., 75, 387 (1930). 16. Klement, R., 2. unorg. Chem., 242, 215 (1931). 17. Hendricks, S. B., Jefferson, M. E., and Mosley, V. M., 2. Krist., 81, 352 (1932). 18. Thewlis, J., Glock, G. E., and Murray, M. M., TT. Faraday Sot., 35, 358 (1939). 19. Pauling, L., The nature of the chemical bond, Ithaca, 2nd edition, 346 (1940).


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Patricia Spain and Clare McArthurNorman S. MacDonald, Florita Ezmirlian,

LEADDEPOSITION OF STRONTIUM AND

THE ULTIMATE SITE OF SKELETAL

1951, 189:387-399.J. Biol. Chem.

http://www.jbc.org/content/189/1/387.citation

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the ultimate site of skeletal deposition of strontium

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