In vivo intestinal bicarbonate transport in infant rats.

Transport of bicarbonate (HCO3-) was studied in segments of the jejunum and ileum in two-, three-, and eight-wk-old rats using and in vivo, one-pass perfusion technique. From isotonic solutions the net absorption of HCO3-(/B5mol/hr/g dry wt) in the jejunal segments was about twice as gret (P-0.01) in the two- and three- as in the eight-wk-old rats. In ileal segments, HCO3-transport was quite variable; in the two- and three-wk-old rats, there was net absorption, whereas in the eight-wk-old rats, there was net secretion. In both segments, net absorption was unaffected by addition of glucose (5 mmoles/liter), or acetazolamide (10 mmoles/liter) to the perfusion solution. Perfusion of a hypertonic old rats induced metabolic acidosis, which was associated with net secretion of relatively large amounts of bicarbonate into the lumen of both segments. Perfusion of the hypertonic solution in the eight-wk-old rats did not change blood acid-base status. In these rats, net absorption of bicarbonate in the jejunum was decreased, and net secretion in the ileum was enhanced in comparison to values noted during perfusion of the isotonic solution.