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Biomedical subjects

J Nopakun

Publications and source records attributed to J Nopakun.

8 recordsLinked to original sources
PubMed1989

Fluoride absorption from the gastrointestinal tract of rats.

The contribution of the stomach and the small intestine to absorption of fluoride from the gastrointestinal tract was examined in rats. Fasted adult male rats weighing approximately 350 g were given 50 micrograms of fluoride in 1 ml of water by stomach intubation, with 14C-labeled polyethylene glycol as a marker of water movement through the gastrointestinal tract. Rats were killed at intervals up to 120 min, and the stomach, duodenum, jejunum, ileum, distal ileum and cecum were rapidly clamped and removed for fluoride analysis and 14C counting. Approximately 90% of the fluoride dose was absorbed in 120 min. Peak plasma fluoride concentration occurred 10 min after intubation and began to decline after 40 min as the rate of fluoride absorption slowed. Absorption from the stomach was derived from rates of gastric emptying and remaining fluoride. Even at 10 min after intubation, when the bulk of the fluoride remained in the stomach, only approximately 25% of fluoride absorption had occurred from the stomach and 75% from the small intestine. After 120 min, 19.8% of total fluoride absorption had occurred from the stomach. Although the stomach is unquestionably a significant site for fluoride absorption, its contribution is much smaller than that of the small intestine.

Animals↗
PubMed1988

Retention of skeletal fluoride during bone turnover in rats.

Deposition of fluoride (F) in the skeleton is a major factor in the metabolic regulation of F. The progressive increase in bone F levels with age suggests that F is rather firmly sequestered once it is deposited in bone. We have examined the extent to which F is resorbed and redeposited during bone turnover in growing rats. The skeleton was first preloaded with F by intake of water containing a high level of F (50 mg F/L) and simultaneously labeled with [3H]tetracycline (3H-TC) to provide a measure of subsequent bone turnover. Rats were then changed to a very low F intake, and bone F loss was compared with 3H-TC loss in animals undergoing normal bone turnover or turnover accelerated by a low calcium (Ca) intake. Approximately 60% of F mobilized during bone resorption was redeposited in the skeleton (humerus and vertebrae). The redeposition of F showed a positive correlation with mineral deposition. Thus the retention of F in the skeleton of growing rats results predominantly from redeposition of resorbed F rather than passive retention associated with low bone turnover.

Age Factors↗
PubMed1988

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.

Animals↗