Biphasic development of pentagastrin sensitivity in rat stomach.

Rat stomach sensitivity to pentagastrin was examined in fetal (days 19--21) and newborn (5--day-old) preparations in vivo and in vitro. Gastric acidification in vivo was expressed as the gastric content pH and in vitro as the net transepithelial H+ fluxes determined in an Ussing chamber. In both preparations, fetal stomach first responded to pentagastrin on day 20. Dose-dependent H+ secretion was demonstrated in vitro for pentagastrin concentrations of 10(-8) to 10(-6) M, with half-maximal stimulations at 1.9 x 10(-7) and 4 x 10(-7) M on days 20 and 21, respectively. In contrast, isolated fundic mucosa of 5-day-old rat pups exhibited very low H+ secretion rates, and pentagastrin did not significantly stimulate acid output. Fetal serum immunoreactive gastrin was detected as early as day 16 in fairly constant concentrations (about 77.5 pg eq synthetic human gastrin/ml). These results indicate that, although immunoreactive gastrin is present in serum as early as day 165, pentagastrin does nt stimulate acid secretion until day 20 when fetal stomach exhibits active H+ secretion and decreased passive permeability. Pentagastrin sensitivity disappears during the 1st days of extrauterine life. These findings strongly suggest that the development of pentagastrin sensitivity in rat stomach is biphasic.