I. Rats were deprived of food for periods of from 0 to 40 h and then given lo3Pb, *03Hg, ""e, e4Ccu, 65Zn or 45Ca by stomach tube. The abiorption and retention of these metals in tissues was measured 1 h and 2 d after dosing.2. After 1624 h of food deprivation between two and ten times more metal was retained than after &I2 h. 3. The effects of length of fast on metal uptake by the intestinal mucosa were greatest in the duodenum.4. Lactate production by duodenal mucosa was halved after 12 h of food deprivation but galactose absorption was little changed after a 40 h ?ast.Most studies of the effects of fasting on intestinal absorption of organic and inorganic substances have involved total starvation for periods of approximately 3 d (for example, Steiner & Gray, 1969; Netwry et al. 1970;Beck & Dinda, 1973; Lichtenberger et al. 1976). Such starvation periods produce considerable changes in the size and morphology of the intestinal mucosa. Fasting for 24 h or less also produces smaller but measurable effects on the weight and total DN,4 of the mucosa and on the absorption of sugars, fats and some drugs (Mead et al. 1951 ; McManus & Isselbacher, 1970; Orr & Benet, 1975). An increase of heavy metal absorption due to short fasts has been reported by many workers (for example, Taylor et al. Ekenved & Arvidsson, 1976; Gruden & Buben, 1979) and food restriction over a period of weeks increased the retention of lead (Quarterman et al. 1976), but the process has not been examined in detail. We were particularly interested in the shorter periods of fasting for several reasons. These periods occur in normal circumscances, in animals or humans eating one or two meals daily and even overnight. Subjects exposed to toxic or essential metals may modify their retention of these metals according to their meal-eating pattern. Such considerations may be particularly important in experiments in which subjects are prepared (usually by overnight fasting) for observations on metal retention.
MATERIALS A N D METHODSMetal absorption experiments. Male Hooded Lister (Rowett strain) rats weighing approximately 100 g were used in all the experiments except one. The food was a semi-purified diet based on that of Williams & Mills (1970) but containing casein instead of albumin. For 1 week before the experiments the rats were allowed free access to food for two 1 h periods daily, and then deprived of food for periods of from 0 to 40 h. Five or six rats were used for each fasting period. After the period of fasting they were given approximately 5 pCi (135 kBq) of radioactive metal ion in saline (9 g sodium chloride/l) by tube into the stomach. Exactly 1 h after this dose a sample of blood was taken from the tail and the rats were restored to their nonnal meal-feeding regimen. This involved immediate feeding except in the instance of those ra.ts which were dosed directly after a meal. At 2 d after dosing (1 d when s4Cu was used) the rats were killed and samples of blood, liver, kidney and in some instances bone and intestinal mucosa were removed...
