Role of parathyroid hormone in phosphate transport across rat duodenum

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Abstract
The effect of parathyroid extract (PTE) on phosphate transport was studied by perfusing everted duodenal loops of rats in vitro. It was found that PTE had no effect on the membrane potential or on the pH of the medium. However, PTE increased the influx (transfer from mucosa to serosa) 70%, the uptake by the tissue from the mucosal side 30%, and the lactate transfer into the serosal fluid 30%. Outflux of phosphate (transfer from serosa to mucosa) was as great as the influx but unaffected by PTE. Phosphate uptake from the serosal side was a third of the mucosal uptake and also unaffected by PTE. Metabolic inhibitors, iodoacetate, arsenite, and DNP strongly inhibited phosphate influx and tissue uptake. Lactate formation and transfer were also inhibited by iodoacetate and arsenite but not by DNP. In addition the three inhibitors suppressed completely the PTE effects. It is suggested that phosphate movements across the intestine follow different pathways whose dependence upon metabolism, hormonal action, or electrochemical gradient might be different and independent.

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