Steroid hormones: modulators of Na⁺ absorption and Cl^- secretion in cultured tracheal epithelia

Cultures of tracheal epithelial cells from adult nonpregnant female rabbits maintained a different balance of Na⁺ absorption and Cl^- secretion from cells of pregnant animals and fetal cultures. Cells of nonpregnant rabbits had a large Na⁺ absorptive current (11 μA/cm² or 53% of baseline short circuit current) and a small Cl^- secretory current (2.4 μA/cm² or 11%). In contrast, fetal cells had greater Cl^- secretion (15.1 μA/cm² or 61%) and much less Na⁺ absorption (1.6 μA/cm² or <10%). Cells of pregnant animals had amounts of Cl^- secretion (11.4 μA/cm² or 41%) and Na⁺ absorption (6.7 μA/cm² or 22%) that were in between that of fetal and adult nonpregnant animals. In addition to these striking differences in baseline ion transport among the three groups, epinephrine was found to stimulate Cl^- secretion in cells from pregnant rabbits, both Na⁺ absorption and Cl^- secretion in cells from nonpregnant animals, and neither in fetal cells. Steroid hormones of pregnancy, progesterone and estradiol, when added to cells cultured from nonpregnant rabbits, altered the magnitudes of the individual transport pathways to mimic cells cultured from pregnant animals. In addition to changing baseline transport, these steroids modified the epinephrine-stimulated currents to resemble those in the fetus and in pregnancy. We conclude that steroid hormones regulate the balance of Na⁺ absorption and Cl^-secretion in tracheal epithelia in utero and in adulthood.