Studies on the absorption of zinc by rat intestine

Abstract

1. A technique is described for the measurement of the extent of65Zn absorption by different regions of the intestine in the intact rat. Using this technique it was shown that the duodenum contributed 60%, the ileum 30% and the jejunum 10% to the over-all absorption of65Zn. Negligible absorption of65Zn occurred from the caecum and colon.2. Using ligated loops of rat duodenumin situ,65Zn absorption was shown to be rapid, with 1% of a 5 μg dose being transferred to the carcase within 1 min of intraluminal dosing.3. When65Zn was injected into ligated loops in a dose range of 1–200 μg Zn/ml the rate of absorpion was linear with respect to time over the first 15 min. The rates of65Zn absorptionv.dose of65Zn exhibited saturation kinetics indicating absorpion by a ‘carrier’ or enzyme-mediated process.4. The binding of65Zn to loop tissue showed biphasic kinetics which suggested that at low intraluminal concentrations of Zn (1–50 μg Zn/ml) binding was to specific sites whereas, at higher concentrations (50–200 μg Zn/ml), non-specific binding occurred.5. A study of the fate of mucosally bound65Zn showed that over the first 30 min a proportion of the65Zn was rapidly transferred to the carcase and this was probably associated with the rapid phase of65Zn absorption described previously. From 30 min up to 6 h after the initial binding,65Zn was also transferred to the carcase albeit at a much slower rate indicating a slow phase of Zn absorption. A study of the kinetics of this slow phase indicated that the loss of bound65Zn to the body was a saturable process indicating an enzyme or ‘carrier’-mediated process. A comparison of the kinetics of the slow and rapid phases of65Zn absorption suggests that these processes are distinct.6. Histological examination of mucosal tissue of loops exposed to 200 μg Zn/ml revealed no discernable damage. Similarly, no effect was observed on either arginine or glucose uptake by isolated duodenal loopsin situ, although this concentration of Zn completely abolished fluid uptake. A study of the effect of different doses of Zn showed that 50 μg Zn/ml inhibited mucosal fluid uptake by more than 50% and 100 μg Zn/ml by more than 90%. It was concluded that these effects were due to a specific action on the fluid-transfer process and not due to a general poisoning of the mucosa.