Transfer of Sulphur to the Digestive Tract of Sheep

Abstract

The transfer of sulphate from plasma to digestive tract and from digestive tract to plasma in crossbred sheep was estimated by the use of isotope dilution techniques with Na235S04. The passage of 35S along the digestive tract was simultaneously measured by reference to two inert radioactive markers infused intraruminally.In the first experiment, three sheep given a roughage-based diet containing 174± 7 mg S/day received an intravenous infusion of Na2 3S S04 for 7 days before collections were made of plasma and of digesta from the rumen, abomasum and terminal ileum. Similar collections were made in the second experiment in which four sheep received intrahuninal infusions of Na23SS04. From estimates of infusion rate of 35S, specific radioactivity of 3SS in plasma and digesta and rate of flow of sulphur in the digestive tract the following calculations were made:The transfer of sulphate from the plasma to the rumen was calculated as 29 mg S/day. Of this only 12 mg S/day passed as organic sulphur in digesta from the stomach. As the net gain of sulphur in the stomach in this experiment was 153 mg/day, sulphate transferred from the plasma contributed only a small amount of sulphur derived from endogenous sources in the stomach.In contrast, the substantial passage of 3 5 S into the intestinal lumen during intravenous infusion of 35S04 suggested that 38 and 41 mg S/day of the 236 and 145 mg organic S/day flowing from the small and large intestine respectively was derived from plasma sulphate, corresponding to about 26 % of the dose.

Sulfur and Methionine Metabolism in Sheep. IV. Metabolism and Absorption in the Intestines

“…As with the small intestine, estimates of net absorption from the large intestine differ substantially from true absorption, as there may be considerable inputs of inorganic sulfate into the large intestine (Kennedy et al 1976).…”

“…Some estimates are available for daily sulfur inputs in the combined bile-pancreatic secretions (Bird 1972b), as plasma protein (Campbell et al 1961) and from plasma sulfate (Kennedy et al 1976). A substantial input may also occur from the turnover of mucosal cells.…”

“…Net changes in the reducible sulfur fraction during passage through the small intestine are small in comparison to changes in neutral sulfur fractions. These small net changes may be associated with considerable exchange of reducible sulfur between the tissues and gut in bile and pancreatic secretions (Bird 1972b), in the transport of plasma sulfate across the wall of the small intestine (Kennedy et al 1976), and in sulfate absorption from the intestines (Bird and Moir 1971).…”