Phosphate absorption at different intestinal sites in the developing lamb

Net phosphate absorption was studied at different sites of the intestine in milk-fed lambs of different age (1 week, 3-4 weeks, 10-13 weeks) and also in lambs fed a solid diet (age: 10-13 weeks). Disappearance of phosphate from ligated intestinal segments filled or perfused with an electrolyte solution containing 1.2 mmol/l phosphate was employed as measure for phosphate absorption. In all groups of animals the mid-jejunum absorbed phosphate with the greatest velocity. In the 1-week-old lambs the proximal colon descendens was almost as efficient, though phosphate absorption at this site was minimal in the other groups of animals. With the exception of the distal jejunum, phosphate absorption appeared to decrease with age. Between animals of the same age fed either a liquid milk diet or a solid diet phosphate absorption did not differ significantly. Phosphate absorption from the mid-jejunum was inhibited by galactose and glucose in the 1-week-old lambs. The significance of these findings in relation to control of phosphate absorption in the developing lamb is discussed.