Low density lipoprotein receptor activity in the guinea pig adrenal cortex. I. Zonal characterization and response to adrenocorticotropin

The binding of [125I]iodo-low density lipoprotein ([125I]iodo-LDL) to isolated membranes was determined for the outer (glomerulosa/fasciculata) and inner (reticularis) zones of the guinea pig adrenal cortex. Binding of [125I]iodo-LDL to membranes from both zones was found to be highly specific and dependent on the presence of divalent cations, such as calcium. Saturation analysis revealed that the maximum high affinity binding capacity was similar for both zones under control conditions (approximately 400 ng/mg protein). When ACTH was administered, however, the maximum high affinity binding capacity increased in the outer zone by at least 3-fold, while there was no significant change for the inner zone. It was also noted that dexamethasone administration decreased [125I]iodo-LDL high affinity binding activity to less than half the control level in the outer zone without altering the binding activity in the inner zone. The cholesterol content in the outer zone was 2-3 times greater than that in the inner zone. When ACTH was administered, the concentration of cholesterol decreased significantly in both zones. Thus, ACTH appeared to influence cholesterol metabolism in the outer and inner adrenocortical zones, but was able to modulate LDL receptor activity only in the outer zone