Corticosteroids and ascorbic acid transport in adrenal cortex in vitro

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Abstract
The transport of [1-C14] ascorbic acid in guinea pigs adrenal cortex in vitro is a Na+ ion-dependent ouabain-sensitive process. Of the steroids examined, only corticosteroids with a ketol group at C-17 inhibit the transport of [1-C14] ascorbic acid in guinea pig adrenal cortex. A number of other steroids of adrenal, ovarian and testicular origin have no effect. The transport of serine, an energy-dependent and Na+ ion-dependent process, in guinea pig adrenal-cortex tissue is not inhibited by corticosteroids. The uptake of a number of other amino acids, glucose and succinic acid is not affected by corticosteroids. The pre-exposure of adrenal-cortex slices to cortisone, but not to testosterone, diminishes [1-C14] ascorbic acid uptake. [4-C14] Cortisone is bound by adrenal cortex by a temperature-dependent by energy-dependent process. Guinea pig-ovary slices, as well as rat-brain-cortex slices, transport [1-C14] ascorbic acid by an energy-dependent process. The uptake of [1-C14] ascorbic acid in a number of other tissues, including liver, pancreas and spleen, does not appear to be energy-dependent. The transport of [1-C14] ascorbic acid in rat-brain-cortex slices and guinea pig-ovary slices is inhibited by corticosteroids as well as by estradiol and testosterone. Steroids formed in situ in response to adreno-corticotrophic hormone inhibit the transport of [1-C14] ascorbic acid to a greater extent than do equivalent concentrations of commercially available individual steroids or mixtures of the latter. In adrenal-cortex slices preincubated with [1-C14]ascorbic acid an increased loss of the label is obtained under conditions that have been shown to inhibit transport of ascorbic acid. It is evident that adrenocorticotrophic hormone and corticosteroids cause an efflux of ascorbic acid from adrenal-cortex slices in vitro, this being due to inhibition of active transport into the tissue.