Barrier Offered by Gastric Mucosa of Healthy Persons to Absorption of Sodium

¹ From the Section of Medicine, the Section of Physiology and the Section of Biophysics and Biophysical Research, Mayo Clinic and Mayo Foundation, Rochester, Minnesota

This study was undertaken to determine the rates of passage of isotopically labeled water (D₂O) and sodium (Na²² or Na²⁴) from the contents of the stomach into the blood stream of a group of healthy adult human beings. The solution of the isotopes was swallowed by the subjects while lying in a modified head-down position. Samples of arterial blood were withdrawn at frequent intervals during the course of absorption. The concentration of D₂O in the samples of blood was determined by a mass spectrometer and that of radiosodium by a well-type scintillation counter. The actual rate of absorption of the two isotopes was calculated by integration of their rate of appearance in the arterial blood during their absorption with their previously established rate of disappearance from the arterial blood following their rapid intravenous injection.

In nine of the 11 tests, the isotopes resided in the stomach for 2–32 minutes after their ingestion and during this entire time no radiosodium could be detected in the blood, although the D₂O in which the sodium was dissolved passed from the gastric contents into the blood stream at the rate regularly observed during its absorption from the stomach. Later, the radiosodium sometimes appeared slowly in the arterial blood, while the D₂O continued to be absorbed at its gastric rate. This slow absorption of radiosodium may have been via the antral gastric mucosa. Finally, when the isotopes passed into the small intestine they were always quickly absorbed. It is concluded that the acid-secreting portion of the gastric mucosa of healthy adult human beings offers a barrier to the absorption of sodium.