Influence of gastric acidity on fluoride absorption in rats.

The rate of F absorption from the stomach is pH-dependent, with greater absorption at low pH. Since the rate of absorption is also strongly influenced by the rapidity of gastric emptying, we have compared the relative importance of gastric acidity and gastric emptying in overall F absorption. Male rats (350 g, n = 85) were pre-treated with cimetidine (to inhibit gastric acid secretion) or pentagastrin (to stimulate gastric acid secretion) or were untreated controls, and given 50 micrograms F by stomach intubation. The pH of the F-containing solution was varied in the cimetidine-pre-treated group (pH 1.5, 5.5, 8.5), and was 5.5 for the control and pentagastrin-pre-treated groups. Gastric emptying was measured by addition of 14C polyethylene glycol to the F solution as an unabsorbed marker of fluid movement. F absorption was measured after 10, 20, and 40 min. The rate of gastric emptying was unaffected by pre-treatment or pH of the intubating solution. Initially, F absorption was greatest at low pH. After 40 min, absorption was comparable in all groups, averaging approximately 70% of the initial dose. The extent of absorption from the stomach was inversely related to pH, but increased absorption from the small intestine compensated for the low gastric absorption at high pH.

Fluoride redeposition and retention during bone turnover in lactating rats.

The ability of the adult skeleton to retain fluoride (F) during times of Ca stress was assessed in lactating rats. Rats incorporated F into their skeletons throughout growth by consumption of water containing 50 ppm F from weaning to 11 weeks of age. The rats were then changed to a low-F intake and mated. At delivery, nine dams were killed as a baseline group, and 20 dams were fed a low-F diet plus distilled water during lactation. Half of the rats were subjected to the additional stress of a low-Ca intake to stimulate bone resorption. F loss was determined during lactation. Bone turnover was measured by the loss of previously incorporated tritiated tetracycline (3H-TC), and changes in bone Ca and F contents were compared with changes in 3H-TC content. The extent of bone resorption ranged from 16.5% in the humerus of the adequate-Ca group to 77.1% in the vertebrae of Ca-deficient dams. Loss of bone F was greatest in animals with greatest loss of 3H-TC. Once F was resorbed from bone, only a relatively small portion was redeposited (0-31.4%). The low extent of F redeposition appears to be related to a low Ca deposition in lactating rats.

Topical fluoride in orthodontic bonding.

Neutral and acidified sodium fluoride solutions were topically applied to enamel etched in a manner typical for orthodontic bonding procedures. Enamel fluoride levels were greater with the acidified solutions.

Acid diffusion analysis of different forms of fluoride in human dental plaque.

Fluoride concentration was determined by: (a) extraction with diphenylsilanediol after combustion of the plaque in an oxygen bomb; (b) acid diffusion from 0.5 M HClO4 for 16 h at room temperature; (c) acid diffusion from 4.6 M HClO4 for 16 h at room temperature; and (d) acid diffusion from 18 M H2SO4 for 16 h at 60 degrees C. The total fluoride was determined by all the diffusion procedures, and there was no evidence of a large proportion of the plaque fluoride being released only after treatment with strong acid (18 M H2SO4). When approx. 10 mg of plaque was extracted three times with 0.1 ml 0.5 M HClO4, 81 per cent of the fluoride was released by one 5 min extraction. After three extractions no further fluoride was detected when the residue was diffused from 4.6 M HClO4 for 16 h at room temperature. When larger plaque samples (21-66 mg) were extracted four times with 1 ml 0.5 M HClO4, 85 per cent of the fluoride was in the first extract, and none was detected in the fourth. Treatment of the residue with 18 M H2SO4 for 16 h at 60 degrees C released a further, small amount which may constitute up to 3 per cent of the total plaque fluoride. Thus the amount of tightly-bound plaque fluoride, released only by treatment with strong acid, is much smaller than previously believed.

An investigation of calcium intake, 1-alpha(OH)D3, and etidronate on bone.

The synthetic metabolite of vitamin D3 [1 alpha(OH)D3] caused a significant plasma calcium elevation in rats only when dietary calcium was low. Animals given the low calcium diet (0.005%) had lower plasma parathyroid hormone (PTH) levels when the diet contained 1 alpha(OH)D3 and significantly higher levels than animals on a high calcium (0.95%) diet, with or without the vitamin. The nutritional stress of a low calcium diet without 1 alpha(OH)D3 resulted in a prolonged severe hypocalcemia and elevated serum PTH levels. A higher ash, phosphate, and calcium content was found in the bones of animals fed the high calcium diet, with no vitamin D3 that were given etidronate (EHDP). When animals received the same calcium diet with 1 alpha(OH)D3 supplementation, EHDP administration increased the percentage of bone ash but had no effect on ash weight. 1 alpha(OH)D3 or EHDP did not affect ash weight, dry fat free weight, and percentage of ash of bone of animals receiving a low calcium diet. The percentage of calcium and phosphorus in bone ash was similar among all groups, although the amounts per humerus were characteristically related to the calcium intake. There was approximately 20-25% less bone mineral and calcium and phosphorus in the humeri of low calcium intake animals than in animals provided an adequate dietary calcium.

Dietary fluoride intake of 15-19-year-old male adults residing in the United States.

The average daily dietary fluoride intakes of 15-to-19-year-old males were estimated from the analysis of 24 FDA "market basket" food collections made from 1975 to 1982. The data indicate that 15-to-19-year-old males residing in fluoridated (greater than 0.7 ppm) cities had an average daily dietary fluoride intake of 1.85 mg/day when the diet provided an estimated caloric intake of 11.72 megajoules (2800 calories). In non-fluoridated cities, with less than 0.3 ppm in the drinking water, the average dietary fluoride intake was 0.86 mg/day. The beverages and drinking water contributed an average of 75 +/- 2% of the daily dietary fluoride intake.

Dietary fluoride intake of 6-month and 2-year-old children in four dietary regions of the United States.

Based upon the analysis of 44 market basket food collections, the average daily dietary fluoride intakes of 6-mo-old and 2-yr-old children residing in cities with water fluoride levels of 0.05 to 1.04 ppm were determined. In cities with greater than 0.7 ppm fluoride in the drinking water, a 6-mo-old child (infant) and a 2-yr-old child (toddler) had mean dietary fluoride intakes of 0.418 mg/day (0.052 mg/kg body weight) and 0.621 mg/day (0.050 mg/kg body weight) respectively. The data indicate that the average dietary fluoride intake of infants and toddlers did not exceed 0.08 mg/kg, and in all but three cases was within or below the optimum range of 0.05-0.07 mg/kg. The ingestion of fluoride-containing dentifrice or milk formula diluted with fluoridated water may result in intake levels exceeding that associated with the development of dental fluorosis (0.1 mg F/kg body wt).

Promotion of bone dissolution by excessive fluoride in acidic buffer solution.

In order to quantitatively examine fluoride uptake by bone and the effect on its chemical and physical properties, rat bone was incubated in acidic buffer solutions (pH 5) with fluoride concentrations of 0-1000 ppm F. After 1 wk incubation, there was a substantial increase in the crystallinity of the bone mineral with increasing fluoride concentration in the solution. The calcium concentration in the solutions used for incubation decreased dramatically, with increased levels of fluoride in the solution, approaching a plateau. The phosphate concentration initially decreased, with increasing levels of fluoride in proportion to the decrease of calcium concentration, and then increased when the fluoride concentration of the solution was above 200-300 ppm. These phenomena, when considered with X-ray diffraction data, reflected the formation of CaF2. The increase of the phosphate concentration in the solution suggests that the presence of excessive fluoride in the acidic buffer solution may promote the dissolution of soluble bone apatites, in spite of the dissolution-preventive activity of fluoride.

The effect of vitamin A deficiency and fluoride on glycosaminoglycan metabolism in bone.

The effects of fluoride intake and vitamin A deficiency on glycosaminoglycan metabolism in vivo were investigated. Weanling female rats were fed either a vitamin A deficient diet ad libitum, a vitamin A supplemented diet pair-fed to the deficient animals, or the vitamin A supplemented diet ad libitum. Additionally, each vitamin A dietary group was divided into three subgroups with the animals receiving water containing 0, 10 or 50 ppm fluoride. The results showed that the groups receiving 10 and 50 ppm fluoride at all dietary levels of vitamin A had significantly higher in vivo 35SO4 incorporation in both the epiphyseal and diaphyseal regions of the bone than the animals receiving 0 ppm fluoride. The vitamin A deficient animals incorporated significantly less 35SO4 into glycosaminoglycans in the epiphyseal and diaphyseal regions of the bone compared to the pair-fed, vitamin A sufficient animals for all three fluoride receiving groups. There was no interaction between fluoride intake and dietary vitamin A levels on 35SO4 incorporation into glycosaminoglycans. Fluoride either increased sulfation or turnover of glycosaminoglycans.

Effect of lactation and/or calcium deficiency on cyclic-AMP production and bone enzyme activities in rats: lack of effect of long-term fluoride administration.

The effect of 50 ppm F as sodium fluoride in the drinking water for 15 weeks on bone, plasma, and urinary cAMP levels, and on bone alkaline and acid phosphatase activities have been investigated in rats stressed with calcium deficiency and/or lactation, as well as in normal rats. Lactation and calcium deficiency (0.1% calcium in diet) was found to cause an increase in urinary cAMP excretion but did not cause any significant alteration in plasma and bone cAMP levels. Bone alkaline and acid phosphatase activities were lower in lactating rats furnished the 1.0% calcium diet when compared to the nonlactating controls. Fluoride had no effect on all parameters studied.

Effect of lactation and calcium deficiency, and of fluoride intake, on bone turnover in rats: isotopic measurements of bone resorption and formation.

The rates of bone formation and resorption were investigated, using isotopic measurements, in calcium-deficient lactating rats and compared to those of calcium-sufficient non-lactating animals. Bone formation was measured by 3H-proline uptake and 3H-hydroxyproline formation, and resorption was measured by the loss of previously incorporated 3H-tetracycline, in whole humerus. The effect of 50 ppm fluoride in the drinking water on both parameters was also examined. The stress of lactation and calcium deficiency significantly increased the rates of bone resorption and formation, but the increase in resorption was greater than in formation which resulted in a net decrease in bone mineral and matrix. Fluoride had no effect on various parameters measured.

Estimated fluoride intake of average two-year-old children in four dietary regions of the United States.

Analysis of toddler "Market Basket" food collections indicates that an average two-year-old child living in cities with water supplies containing 0.37 to 1.04 ppm of fluoride has a daily fluoride intake of 0.315 to 0.610 mg/day (0.025 to 0.049 mg/kg body weight) from food, water, and beverages.

Estimated fluoride intake of 6-month-old infants in four dietary regions of the United States.

Eleven composite food groups comprising the infant "market basket" food collections for 1977 or 1978 from each of four dietary regions of the United States were analyzed for their fluoride content. Based upon the determined fluoride content of each composite and Food and Drug Administration estimates of food consumption the daily fluoride intake of an average 6-month-old infant residing in each of the dietary regions was calculated. The daily fluoride intake varied from 0.207 mg/day in Grand Rapids, Mich. (north central dietary region) to 0.541 mg/day in Orlando, Fla. (south dietary region). Flouride intakes of 0.272 and 0.354 mg/day were calculated for Philadelphia, Pa. (northeast dietary region) and Los Angeles, Calif. (west dietary region), respectively. The fluoride content of the water supplies ranged from 0.37 ppm (Los Angeles) to 1.04 ppm (Grand Rapids). Drinking water, dairy products and substitutes (other than milk), and grain and cereal products contributed 44 to 80% of the daily fluoride intake. In three of the four dietary regions the daily fluoride intake was less than the optimum level of 0.05 mg/kg body weight.

Fluoride intakes of young male adults in the United States.

The total daily fluoride intake for young male adults living in four geographical areas of the United States has been estimated by the analysis of "market basket collections" obtained in 1975 and 1977. The fluoride intake in 1975 vaired from 0.912 mg/day in an unfluoridated city (Kansas City, Mo.) to 1.720 mg/day in a fluoridated city (Atlanta, Ga.). The 1977 collection from San Francisco, Calif. contained more fluoride (1.636 mg/day) than the 1975 collection (1.213 mg/day). The level of intake found in this study is less than that reported by San Filippo and Battistone (Clin. Chem. Acta 31: 453, 1971) who analyzed similar collections from Baltimore, Md. in 1967 to 1968 (2.09 to 2.34 mg/day). This study, as well as the earlier one, indicates that relatively low levels of fluoride are being consumed in the United States by the young adult male 16 to 19 years of age.

Metabolic aspects of bone resorption in calcium-deficient lactating rats.

Lactating female rats were fed diets containing 1.0, 0.1, or 0.04% Ca for 21 days. Fat-free dry weight, ash weight, calcium and phosphorus content of the humerus, plasma calcium levels, and bone acid and alkaline phosphatase activities were compared to those of nonlactating rats fed the same diets. Bone, plasma, and urinary cAMP levels were also studied. Dietary calcium deficiency and/or lactation caused significant loss of bone mass from experimental animals. Urinary cAMP levels reflecting increased parathyroid activity were elevated by the stresses of lactation and calcium deficiency over those of control animals. Plasma and bone levels of cAMP were not different. Bone alkaline and acid phosphatase activities were affected only by the most extreme stress. The results demonstrated that the calcium-deficient lactating rat is an excellent model for bone resorption studies.

Lack of effect of fluoride on urinary cAMP excretion in rats.

The urinary excretion of cyclic 3'5'-adenosine monophosphate (cAMP) was measured in rats provided a low fluoride diet (less than 0.5 ppm) and drinking water containing either 0 or 25 ppm of fluoride. The pMole cAMP/microgram creatinine ratio decreased with age but was not influenced by fluoride intake.