title: Assessment of mineralocorticoid activity in the rabbit colon.
abstract: Analyses of [3H]corticosteroid binding sites in distal colon indicated high-affinity binding sites or receptors for both [3H]aldosterone (Type I, Kd = 6.5 X 10(-9) M) and [3H]dexamethasone (Type II, Kd = 5.5 X 10(-8) M). The relative affinity of dexamethasone (D) was 1/20 that of aldosterone (A) for Type I sites and the affinity of A for Type II sites was 1/50 that of D at 37 degrees C. Citrate synthase (CS) activity was assayed and found to be reduced in enterocytes harvested from adrenalectomized (ADX) vs. normal colon segments (0.24 vs. 0.44 U/mg protein, P less than 0.025). Aldosterone (10 micrograms/kg body wt) increased CS at 2 h to a level intermediate between normal and ADX animals and thus not significantly different from either group, but was significantly increased over ADX + D values. Transmural potential difference was increased by 10(-8) M A but not by 10(-8) M D. Since both steroids enhanced short-circuit current at this concentration, the dichotomy of the glucocorticoid vs. mineralocorticoid results can be best explained by the pronounced effect of D on resistance (R) across the tissue (R at 4 h + D was 50% that of paired controls). These findings would suggest that the rabbit distal colon is a target segment for both mineralocorticoids and glucocorticoids. Furthermore, as in the kidney, the two steroids may play coordinated but, perhaps in some way, unique roles in the regulation of transport.
mesh_terms: D000315:Adrenalectomy; D000450:Aldosterone / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002950:Citrate (si)-Synthase / Q000378:metabolism; D003106:Colon / Q000378:metabolism*; D003907:Dexamethasone / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology; D005260:Female; D011817:Rabbits; D018161:Receptors, Mineralocorticoid; D011987:Receptors, Steroid / Q000378:metabolism*
chemical_list: D018161:Receptors, Mineralocorticoid; D011987:Receptors, Steroid; D000450:Aldosterone; D003907:Dexamethasone; D002950:Citrate (si)-Synthase