Determinação do período de remoção do flúor incorporado ao esqueleto de ratos após exposição aguda

Abstract

Determination of the lag period required from removal of fluoride incorporated in the bone of rats after acute exposure Bone is the major site for fluoride (F) accumulation in the body. Part of the ingested F can transit between bone surface crystals and plasma, through a steady-state mechanism, which can also occur during bone remodeling. This could maintain constant plasma F levels for some time after the F intake is reduced. The aim of this study was to evaluate the lag time required to remove F accumulated in bone of rats after acute exposure. Three experimental groups, containing ten 70-day-old Wistar rats each, received, by gastrogavage, a single dose of 50 mgF/Kg body weight (as NaF), while 3 control groups received deionized water. The animals were euthanized 30, 90 or 180 days after F administration. The animals were anesthetized, blood and femurs were collected and analyzed for F. F on the femur surface was removed through an acid biopsy and F in whole bone was analyzed after ashing. Ash and plasma F were analyzed with the electrode following HMDS-facilitated diffusion. Data were analyzed by Kruskal-Wallis and Dunn’s tests (p<0.05). Plasma F levels in control group were constant along time and similar to the levels found for the experimental group euthanized after 30 days. For the experimental groups euthanized after 90 and 180 days, a significant reduction in plasma F levels in respect to control was found. F in bone surface for the experimental group was significantly higher than for the control group only 30 days after F administration. For the other experimental times, despite F concentration was higher in the experimental group when compared to control, this difference was not significant. For both groups an increase in bone surface F levels along time was seen. For whole bone, the experimental group had similar F concentrations for all times of euthanasia and these levels were similar to those found for control group 30 days after F administration. Control group, 30 and 90 days after F administration had values significantly lower when compared to the other situations. Data suggest that F incorporated into bone surface of rats after acute exposure does not seem to be irreversibly bound and is lost along time. It seems to be completely lost between 90 and 180 days after F administration. On the other hand, F levels incorporated in whole bone 30 days after acute exposure to F do not seem to be lost along time. The lack of increase in whole bone F levels in the experimental group along time suggests that there is a limit for F uptake in whole bone, probably related to the number sites available to bind F irreversibly.