| Abstract: | The mechanism of impaired water excretion in adrenalectomized mammals is unclear. Previous workers have suggested that one cause might be increased water permeability of the distal nephron, allowing back diffusion of water from tubular fluid diluted by the ascending limb. Evidence to support this mechanism in previous studies has been confounded by simultaneous changes in steroid and antidiuretic hormone levels. We compared osmotic and diffusional water permeability of the surface late distal tubule in vivo in intact and adrenalectomized Brattleboro rats, which are free of antidiuretic hormone. The adrenalectomized rats were demonstrated to have impaired diluting capacity in clearance studies. Adrenalectomized rats had a sixfold increase in osmotic permeability and a 1.5-fold increase in diffusional permeability over intact controls. Adrenal steroids have a specific action on water permeability of the distal nephron, independent of antidiuretic hormone. |
