R. H. OPHAUG ANDL. SINGER Department of Biochemistry, University of Minnesota, Medical School, Alinneapolis, Minnesota 55455 ABSTRACT To investigate the effect of fluoride on the mobilization of skeletal magnesium and on kidney calcification during magnesium deple tion, male Holtzman rats were fed a magnesium-sufficient diet (400 ppm of magnesium) and drinking water containing either 0, 50 or 100 ppm of fluoride for a 20-day period prior to the initiation of magnesium deficiency. The high fluoride regimen resulted in a 100-fold increase in the fluoride content of the skeleton. On day 20 magnesium depletion was initiated by feeding the animals a diet containing 12 ppm of magnesium. Over a 4-week period of magnesium deprivation, a 26% decrease of the total magnesium in the numeri was observed. Fluoride exerted a significant effect in retard ing the mobilization of skeletal magnesium. Four weeks of magnesium deficiency was associated with a decreased rate of skeletal mineral accretion and with an increase in the kidney calcium content. The decreased rate of mineral accretion was accentuated by the administration of fluoride during the deficiency state. While fluoride exerted an initial protective effect on calcinosis of the kidneys, the overall effect of the administration of fluoride during magnesium deficiency was to promote calcification of the kidneys rather than to prevent it. J. Nutr. 106: Ill-Ill, 1976. INDEXING KEY WORDS deficiency • magnesium • bone • fluoride Although magnesium is present to some extent in all tissues, up to 70% of the total body magnesium is in the skeleton. Despite the fact that the skeleton is by far the major storehouse of magnesium in the body, very little is known about the role of this vast supply during periods of magnesium deprivation. Numerous investigators have shown that magnesium deprivation is invariably accompanied by a decrease in bone magnesium concentration (1-4). Smith and Field (5) and Hunt (6) have shown that the decrease in bone magnesium concentration during a period of magnesium deficiency is due primarily to dilution of the magnesium initially in bone as a result of continued bone growth in tVi» uKcpn/^f r>f matrnfxsiiim it is in tne aosence or magnesium. Thii, it is Only from

the

measurement

Of the

total

magnesium present at any one time in a complete bone that any meaningful conelusions can be drawn regarding the amount of magnesium in the skeleton that is available for mobilization during periods of deprivation. In cases where the total skeletal magnesium content has been measured, consistent results are lacking. Many investigators have shown a decrease in the total magnesium content of the skeleton during magnesium deprivation (3-5, 7) whereas others have not (8-10). A physiological interaction between magnesium and fluoride is suggested by several observations. First, the addition of Receivedfor publicationOctober22, 1975. 'This Investigation was supported by Public Health Servlce Research Grant NO. DE-OISSOfrom the National Institute oÃ-Dental Research. 771

Downloaded from https://academic.oup.com/jn/article-abstract/106/6/771/4768839 by East Carolina University Health Sciences Library user on 16 January 2019

Effect of Fluoride on the Mobilization of Skeletal Magnesium and Soft-Tissue Calcinosis During Acute Magnesium Deficiency in the Rat1

772

R. H. OPHAUG AND L. SINGER

METHODS

AND MATERIALS

One hundred sixty-five male albino rats of the Holtzman strain 2 were obtained at weaning (3 weeks of age) and fed, ad libitum, a magnesium-deficient diets sup plemented to a level of 400 ppm mag nesium as magnesium sulfate and pro vided drinking water containing 0, 50 or 100 ppm of fluoride as sodium fluoride. The fluoride content of the diet was 0.6 ppm. The food consumption of each group was measured daily. After 20 days, representative rats from each group were killed as base-line con trols, while others were continued on the same regimen to serve as controls for later killings. The remaining rats in each group were fed the magnesium-deficient diet (12 ppm magnesium) in such a manner that some continued to receive water con taining the same amount of fluoride as previously, while others were given deionized water. Representative rats from each group were killed on days 34 and 48 of the study ( 14 and 28 days after the dietary transfers were made). Starting on day 20,

the rats were "group pair-fed" in that the control rats were fed the average amount of food consumed by the magnesium-defi cient rats. Blood was obtained by heart puncture. The femora and humeri were removed from each rat, cleaned of all soft tissue and marrow, wrapped in gauze and defatted with a 1:1 mixture of absolute ethanol and anhydrous diethyl ether in a Soxhlet ap paratus for 48 hours. The fat-free humeri were dried at 110° overnight, weighed, ashed at 500°for 12 hours and reweighed. The non-lipid organic content of the humeri was calculated by subtracting the ash weight from the dry, fat-free weight. The ashed bone was ground to a fine powder in an agate mortar. The kidneys were dissected from the animal, dried at 103°for 12 hours, weighed and wet-ashed with nitric acid. The magnesium content of the bone and plasma and the calcium content of the kidneys were determined by atomic absorption techniques. The fluo ride content of the bones was assayed by the technique of Singer et al. (20). Groups were statisticallyt value compared calculating the "Student's (21)." by À probability value of less than 0.025 was chosen as indicating significance. RESULTS

AND DISCUSSION

The body weights of the rats at the time of killing are presented in table 1. There was no effect of fluoride intake on the body weight of the control rats until day 48. At this time, the control rats receiving 100 ppm of fluoride had a slightly lower mean body weight than the control rats receiving 0 ppm of fluoride. A toxic effect of fluoride administered during magnesium deficiency was indicated by the observa2 i i.ii i/ um i. Company, 421 Holtzman Road, Madison, Wisconsin. 8 The magnesium-deficient diet was obtained from General Biochemlcals, 925 Laboratory Park, Chagrin Palls, Ohio (Cat. No. 170490). Its composition Is: (in g/kg) Casein, vitamin-free, 300.0 ; dextrose, 499.7 ; corn oil. 150.0; NaHCO,. 12.6: KHCO.,, 16.1; CaCl* 5.7; CallPO,, 14.3; CuSO4-5H2O, 0.013; FeC«H,,O75H..O, 1.24; MnSO.-H^. 7H¡O. 0.024; vitamin "mix,0.174; 11.076. Nal, The 0.03; vitaminZnSO,mix provided the following : (in mg/kg) p-amlnobenzolc acid, 110.2; choline chloride, 1,000.0; chollne dlhydrogcn citrate, 3,715.1 ; calcium pantothenate, 86.1 ; niacin, 139.2; pyrodoxine-HCl, 26.1; riboflavin, 30.1; thiamin-HCl, 26.1; biotin. 0.4; ascorbic acid, 1.017; folie acid. 2.0 : i-lnositol, 110.2 ; menadione, 49.6 ; vitamin Bu, 29.8. In addition, retinyl palmitate, 57,341 IU ; ergocalciferol, 7,605 IU ; Di-a-tocopheryl acetate, 121 IU.

Downloaded from https://academic.oup.com/jn/article-abstract/106/6/771/4768839 by East Carolina University Health Sciences Library user on 16 January 2019

fluoride to diets low in fluoride resulted in an increase in the skeletal magnesium content in a number of species (11-15). More recently, fluoride exhibited a protec tive effect on the soft-tissue calcinosis of magnesium deficiency, particularly cal cinosis of the kidneys (14, 16-18). To date, only two studies (14, 19), both con ducted using guinea pigs, have attempted to correlate the intake of dietary fluoride with the changes in bone magnesium dur ing magnesium deficiency. In both of these studies, only the bone magnesium concen tration was measured therefore obscuring the interpretation of the results as the effect of dilution or of mobilization of magnesium. Additionally in these studies the feeding of fluoride began concurrently with the initiation of magnesium defi ciency. This paper describes the results of the effect of prior incorporation of fluoride into skeletal tissue on the mobilization of skeletal magnesium during acute mag nesium deficiency. In addition, data relat ing to the effect of fluoride and magnesium deprivation on the calcium content of the kidneys and upon the mineralization pro cess are presented.

EFFECT OF FLUORIDE ON MAGNESIUM DEFICIENCY

773

Body weight Group0

ppm Fluoride Control Deficient50 ppm Fluoride Control Deficient F*100 Deficient-Low

days0175±1.9

daysa225±1.9

days£/283

(41)1179±1.7

(17) (18)'229±3.1 215±4.4

±3.0 (8) (9)!278±3.6 234 ±8.3

(56)176±1.2

(16) 214±3.6 (18)' (17)'226±2.3 214±2.9

(8) 217±12.9 (9)1 (8)«-«273±2.6 237±3.5

(17) 203±2.5 (18)' 211 ±2.8

(9)' 206±3.4 (9)! 226±4.1 (9)''«in

ppm Fluoride Control Deficient (19)»'41 Deficient-Low F"20

(61)34

Mean ±SEM (No. of animals). 'Significantly lower than the control value the same group (P < 0.025). * Rats were given deionized water without fluoride beginning from 20 days. *Signin6Significantly lower cantly higher than the magnesium-deficient value in the same group (P < 0.025). than the 0 ppm fluoride control value (P < 0.025).48

tion that on day 48 of the study all groups of magnesium-deficient rats with a lowfluoride intake, regardless of fluoride treatment during the predeficiency period, had body weights which were significantly higher than that of magnesium-deficient rats receiving fluoride. The plasma magnesium levels are shown in table 2. In the control rats there was a

significant effect of fluoride in lowering the plasma magnesium level at the end of the predeficiency period (20 days) and at 34 days of the experiment. At day 48, the plasma magnesium levels of all control rats had decreased and the fluoride effect had disappeared. This may have been due to food restriction resulting from the pairfeeding procedure. All magnesium-defi-

TABLE 2 Effect of fluoride intake and magnesium deficiency on the plasma magnesium level Plasma magnesium Group0

ppm Fluoride Control Deficient50 ppm fluoride Control Deficient F3100 Deficient-Low ppm Fluoride Control Deficient Deficient^Low F320

daysmg/100

daysmg/100

daysmg/100

ml2.21

ml2.56±0.137

ml1.91

(7)12.06±0.093 ±0.069

(9) (9)s2.37±0.066 0.43 ±0.030

±0.098 (9) 0.38±0.041 (8)'1.81

(7)1.95±0.088

(9) 0.33±0.029 (8)» (9)J2.01 0.40±0.046

±0.095 (8) 0.28±0.018 (6)» 0.53±0.049 (9)''61.94±0.064

±0.079 (9)4-* 0.35 ±0.028 (9)» 0.31 ±0.029 (9)«48

(9) 0.46±0.069 (9)' 0.65±0.088 (10)'

(7)«34

1 Mean ±SEM (No. of animals). ' Significantly lower than the control value in the same groiip (P < 0.025). 3 Rats were given deionized water without fluoride beginning from 20 days. 4Signifi cantly lower than the 0 ppm fluoride control value (P < 0.025). 'Significantly lower than the 50 ppm fluoride control value (P < 0.025). 6Significantly higher than the 50 ppm fluoride, magnesium-deficient value (P < 0.025).

Downloaded from https://academic.oup.com/jn/article-abstract/106/6/771/4768839 by East Carolina University Health Sciences Library user on 16 January 2019

TABLE 1 Body weights of rats at time of killing

774

R. H. OPHAUG AND L. SINGER

fluoride34 ¡ruup0

Effect of fluoride on the mobilization of skeletal magnesium and soft-tissue calcinosis during acute magnesium deficiency in the rat.

To investigate the effect of fluoride on the mobilization of skeletal magnesium and on kidney calcification during magnesium depletion, male Holtzman ...
602KB Sizes 0 Downloads 0 Views