Hormonal and pharmacologic regulation of sodium absorption in rabbit cecum in vitro.

The rabbit cecum is a moderately tight epithelium with amiloride-resistant but phenamil-sensitive electrogenic Na absorption. We performed flux and electrical studies under short-circuit conditions in vitro to further characterize the mechanisms of ion transport in cecum in normal and animals pretreated with methylprednisolone (MP) and deoxycorticosterone acetate (DOCA). MP treatment increased Na absorption and decreased tissue conductance. In contrast, DOCA increased Isc but did not significantly alter Na or Cl fluxes. Amiloride analogs with primary specificity for Na channel and Na/H exchanger both inhibited Isc and Na absorption. Ethacrynic acid, but not bumetanide, inhibited Isc. Nystatin and amphotericin B increased Isc. We conclude that: (1) Steroids have a differential effect on cecal ion transport; methylprednisolone increases Na absorption, but DOCA does not. (2) The response to amiloride analogs is different from other electrogenic transport systems, suggesting a distinct mechanism of Na transport in cecum. (3) The effect of ethacrynic acid was unexpected, suggesting an inhibitory response on an alternate transport system. (4) The effects of polyene antibiotics are similar to those found in other tight epithelia. Electrogenic Na absorption in rabbit cecum represents a distinct transport system, significantly different from Na absorptive mechanisms in other segments of the gut.