Uptake and binding of [3H]aldosterone by the anterior pituitary and brain regions in adrenalectomized rats

The uptake of [3H]-aldosterone by the brain and anterior pituitary (AP) was studied after i.v. injection of the isotope into adrenalectomized rats. The AP showed the higher uptake ratio (i.e., radioactivity in tissue/radioactivity in blood), while the brain regions examined (hippocampus, hypothalamus, amygdala, cerebellum and cortex) contained lower levels of radioactivity, although they concentrated the hormone from blood. Neither [3H]-corticosterone nor [3H]-18-hydroxydeoxycorticosterone accumulated in the AP as much as [3H]-aldosterone, while [3H]-corticosterone's uptake was greatest in the hippocampus. Competition experiments demonstrated that [3H]-aldosterone uptake in the AP was inhibited by pretreatment of animals with excess aldosterone, corticosterone and dexamethasone, whereas aldosterone and corticosterone but not dexamethasone competed in the brain regions. Binding sites were demonstrated in vitro in cytosol fractions from AP and several brain regions. Scatchard plot analysis demonstrated high affinity, low capacity binding sites in cytosol from AP and hippocampus. These results suggest the AP and brain areas may be considered as targets for aldosterone, although the functions of the mineralocorticoid in these tissues are a matter of speculation.