Acid secretion in fetal rat stomach in vitro.

In vivo fetal rat stomach produces HCl 48 h before birth. This study examines the mechanisms of H+ secretion from days 19 to 21 before birth. Isolated fetal stomachs were mounted as flat sheets in Ussing chambers for measurement of the transepithelial H+ fluxes (JH+) and short-circuit current (Isc), as indexes of the active ionic fluxes, and for measurement of total ionic conductance (G) and unidirectional mannitol fluxes from serosa to mucosa (JMans leads to m), as indexes of passive permeability. The results indicate that JH+ was absent at day 19 but reached 0.75 +/- 0.1 and 0.75 +/- 0.09 mueq . h-1 . cm-2 at days 20 and 21, respectively. Concomitantly, Isc increased significantly (56%) between days 19 and 20 in the direction of anion secretion or cation absorption. Parallel reductions in G (45%) and in JMans leads to m (66%) were observed between days 19 and 20. In conclusion, the simultaneous appearance of active H+ secretion and decreased passive transepithelial permeability strongly suggests that both processes are involved in the mechanism of acidification of the fetal rat stomach before birth.