The hypothesis that the diabetic rat is more susceptible to the adverse ren
al effects (i.e., urine concentrating defect) of inorganic fluoride was tes
ted by comparing fluid and sodium excretion rates in nondiabetic and diabet
ic rats before and after fluoride administration. Male Fischer 344 vats wer
e injected with either vehicle (0.1 M citrate buffer i.v.) or streptozotoci
n (55 mg/kg body weight). Renal excretions of fluid and sodium were determi
ned in conscious animals following administration (i.v.) of a saline volume
load containing or lacking inorganic fluoride (0.2 mg/ml). To examine the
effect of fluoride without the contribution of a saline load venal excretio
ns of fluid and sodium were determined following a gradual, graded elevatio
n in plasma fluoride concentration. The natriuretic and diuretic responses
to an isotonic saline load were similar between the groups prior to and aft
er fluoride administration. Graded elevations in the fluoride concentration
of plasma mediated a slight increase in fluid and sodium excretion in the
control rat while the treatment protocol led to a reduction in fluid excret
ion and an increase in the sodium excretion in the diabetic mt. As a result
, the ratio of sodium/fluid excretion following fluoride administration was
significantly higher in the diabetic compared to the control rat. These re
sults suggest a differential effect of inorganic fluoride on the renal excr
etion of sodium and fluid between the nondiabetic and diabetic rat. (C) 199
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