Some Characteristics of Corticosterone Uptake by the Dorsal Hippocampus and the Adenohypophysis in the Rat

Abstract

In addition to confirming the reports by McEwen and co-workers of a selective uptake of corticosterone by the dorsal hippocampus in adrenalectomized rats, our findings have brought to light an inverse relationship between corticosterone retention by the hippocampus and its binding by plasma transcortin, 4 days after adrenalectomy, which raises the possibility of a competition between extracellular and intracellular binding sites for corticosterone.A subsequent study of the uptake characteristics of the 30 000 × g pellet and supernatant of the dorsal hippocampus, the cerebral cortex, and the adenohypophysis, under conditions of dynamic equilibrium between corticosterone and its binding sites achieved by perfusing at a constant rate graded concentrations of the steroid, has yielded evidence for the selective uptake of corticosterone by both the particulate (chiefly nuclei and mitochondria) and the soluble (cytosol) fractions of the dorsal hippocampus and of the adenohypophysis, the hippocampus showing a greater uptake capacity than the hypophysis. The observed saturation of the sites of the dorsal hippocampus and of the adenohypophysis at physiological concentrations of plasma corticosterone is consistent with the involvement of these two structures in the feedback control of adrenocorticotropin secretion by circulating corticosteroids.