Hippocampal and renal type I receptors are differentially regulated

Previously, we have shown that renal mineralocorticoid receptors and hippocampal "corticosterone-perferring" sites have identical intrinsic steroid specificity in vitro. Others have shown that the aldosterone binding species in kidney and hippocampus have identical trypsin fragmentation patterns on isoelectric focusing. To further explore possible areas of identity, we determined levels of type I receptors in hippocampus, renal outer medulla cortex, and renal inner medulla papilla from 22 min to 16 days after adrenalectomy. Available type I sites in kidney fractions increased postadrenalectomy to plateau levels in 22 (inner medulla papilla) or 90 min (outer medulla cortex). In contrast, available hippocampal receptors attained maximal levels 24-48 h postadrenalectomy. Animals, 24-h adrenalectomized, showed no differences in steroid uptake or washout between kidney and hippocampus, determined by in vitro tracer binding 22 or 90 min after intravenous aldosterone or corticosterone. We interpret the marked difference in receptor levels between kidney and hippocampus postadrenalectomy as evidence for tissue-specific differences in the control of receptor levels by endogenous steroids.