Steroids alter ion transport and absorptive capacity in proximal and distal colon
Sellin, J.H.; DeSoignie, R.C.
American Journal of Physiology 249(1 Pt 1): G113-G119
1985
ISSN/ISBN: 0002-9513 PMID: 3893155 Document Number: 259898
Steroids are potent absorbagogues, increasing Na and fluid absorption in a variety of epithelia. The in vitro effects of pharmacological doses of gluco- and mineralocorticoids on transport parameters of rabbit proximal and distal colon were studied. Treatment with methylprednisolone (MP, 40 mg im for 2 days) and deoxycortisone acetate (DOCA, 12.5 mg im for 3 days) resulted in a significant increase in short-circuit current (Isc) in distal colon, suggesting an increase in basal Na absorption. Amiloride (10-4 M) caused a significantly negative Isc in MP-treated tissue, demonstrating a steroid-induced, amiloride-insensitive electrogenic ion transport in distal colon. The effect of 2 absorbagogues, impermeant anions (SO4-Ringer) and amphotericin, were compared in control and steroid-treated distal colon. In controls, both absorbagogues increased Isc. Impermeant anions caused a rise in Isc in both MP and DOCA tissues, suggesting that the high rate of basal Na absorption had not caused a saturation of the Na pump. The steroid-treated colons did not consistently respond to amphotericin. Amiloride inhibited the entire Isc in MP-treated distal colon that had been exposed to amphotericin; this suggested that amphotericin had not exerted its characteristic effect on the apical membrane of steroid-treated colon. In proximal colon, steroids did not alter basal rates of transport; epinephrine-induced Na-Cl absorption was significantly greater in MP-treated vs. control (P < 0.005). Steroids increase the absorptive capacity of both proximal and distal colon for Na, while increasing basal Na absorption only in the distal colon. Steroids given subacutely over 48 h have a major effect in altering the Na pump, the principal determinant of absorptive capacity. Steroids modify the apical membrane of distal colon, preventing amphotericin-induced changes in Na transport and conductance.