R. H. Ophaug

The Sex-Related Difference in Perfluorooctanoate Excretion in the Rat

Abstract The urinary excretion of perfluorooctanoic acid (PFO) by male and female rats was investigated. Female rats excreted 76 ± 2.7 (SEM)% of a 2-mg dose of nonionic fluorine (as PFO) in the urine in 24-hr whereas male rats excreted only 9.2 ± 3.5% of the dose. The PFO clearance, inulin clearance, net excretion rate of PFO, and the glomerular filtration rate of PFO were measured. The effect of probenecid, an inhibitor of the organic acid transport system, on these measurements was also determined. In female rats the PFO clearance was severalfold greater than the inulin clearance and the clearance of PFO was markedly reduced by probenecid. Conversely, in male rats the PFO clearance was only a fraction of the inulin clearance and was virtually unaffected by probenecid. The data indicate that female rats are able to rapidly eliminate PFO in the urine by an active secretory mechanism which is inhibited by probenecid. In male rats this secretory mechanism is either absent or relatively inactive. This difference in PFO excretion by the male and female may explain the sex-related difference in PFO toxicity in which male rats are more susceptible to high doses than females.

Metabolic Handling of Perfluorooctanoic Acid in Rats

Summary The metabolic fate of perfluorooctanoic acid administered by stomach intubation to female rats was investigated. The nonionic fluorine level in the serum was increased 200-fold after administration of the dose but returned to baseline levels by 52.5 hr. Although perfluorooctanoic acid is rapidly absorbed and bound to nonultrafilterable components in the serum, the entire dose of nonionic fluorine was recovered in the urine and feces after 96 hr. Neither the ionic fluoride level in the serum nor the rate of ionic fluoride excretion in the urine was significantly altered by the administration of perfluorooctanoic acid. Although perfluorooctanoic acid has not been identified in the urine, the available data suggest that it has been excreted intact or in possibly conjugated form.

Lack of cytogenetic effects in mice or mutations in Salmonella receiving sodium fluoride

We have examined the possible effect of fluoride intake on chromosome damage. There was no evidence of increased frequency of chromosomal aberration in bone marrow or testis cells of mice with either 50 ppm fluoride intake over several generations or 100 ppm intake for 6 weeks compared to animals drinking distilled water. Fluoride was not found to be mutagenic in a widely used bacterial mutagenesis assay over a range of 0.1 to as high as 2000 microgram fluoride per plate.

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

SummaryLactating 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 activites 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.

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 μg 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.

Effects of acute fluoride intoxication on rats.

Summary Young male rats (~200 g) were employed to study the distribution of parenterally administered inert and radiolabeled fluoride. Animals receiving 25 mg of fluoride/kg body weight did not live longer than one hr and the plasma fluoride level reached a concentration of 48 ± 2.1 ppm. Other animals receiving 15 or 20 mg of fluoride/kg had plasma fluoride levels greater than 30 ppm 10 min after the dose but returned to preexperimental levels (~0.10 ppm) by 24 hr. Total and ionic calcium levels in plasma were severely depressed in all animals following the fluoride administrations. The calcium levels at 30 and 60 min did not seem compatible with life although animals receiving 20 mg or less of fluoride/kg survived 24 hr. Radiofluoride concentrations in plasma, muscle, tendon, bone and gastrointestinal tract indicated the relative distribution and retention of the dose as well as the fluoride concentration at 10, 30, and 60 min after the dose was given. Muscle fluoride levels at all dose levels were 5-9 ppm after 10 min. These levels rapidly decreased in animals receiving 15 mg/kg but remained relatively constant for the other animals.

Influence of Variations in Fluoride Intake on the Ionic and Bound Fractions of Plasma and Muscle Fluoride

Summary The changes occurring in the ionic, bound, and total fluoride contents of plasma and muscle from rats shifted from low fluoride intake to high fluoride intake and back to low fluoride intake were examined. Approximately 10 days were required for the reequilibration of the ionic and total fluoride levels of plasma and muscle following changes in the dietary fluoride intake. Data have been obtained that show the systematic changes produced in the bound fraction of plasma and muscle fluoride by variations in dietary fluoride intake.

The effect of fluoride intake on the total lipid, cholesterol and vitamin E levels in a sera and liver of guinea pigs on high fat diet

Abstract Guinea pigs were raised on a diet containing 18 percent fat and were provided 25 or 0 ppm fluoride in the drinking water. Animals were sacrificed at the end of 0, 3, 6, 9 and 13 weeks on the dietary regimen and blood serum was analyzed for fluoride, total lipid, cholesterol and alpha tocopherol. The serum total lipid levels, cholesterol and alpha tocopherol levels were increased in the high fluoride group between 9 and 13 weeks. An increase in total lipid and alpha tocopherol levels was also observed in the livers of these animals. The increase in liver content of alpha tocopherol was proportional to the increase in total lipid content whereas the corresponding increase in serum alpha tocopherol content was significant even when the increase in total lipid was taken into account. The data suggest a specific effect of fluoride on the serum alpha tocopherol levels of the high fluoride animals.

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.

Magnesium in Bone Mineral: An In Vitro Study

The solubility of magnesium in bone mineral from control and magnesium-deficient rats receiving varying fluoride intakes was assessed. Evidence for the existence of a fluoride-related pool of skeletal magnesium possessing a diminished solubility was obtained.