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Journal of Lipid Research, Vol. 43, 861-871, June 2002
Copyright © 2002 by Lipid Research, Inc.

Hormonal regulation of adrenal microvillar channel formation

Salman Azhar, Ann Nomoto and Eve Reaven¹

Geriatric Research, Education and Clinical Center, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94304

¹ To whom correspondence should be addressed. e-mail: eve.reaven{at}med.va.gov

This study examined the in vivo relationship between expression of the HDL receptor scavenger receptor class B (SR-BI) and corresponding structural changes in the rat adrenocortical cell microvillar compartment. Using hormonal stimulation and withdrawal protocols, we were able to manipulate adrenal SR-BI levels and carry out qualitative and quantitative measurements correlating SR-BI expression with microvillar mass and microvillar channel formation. Young male rats were used as controls or treated with adrenocorticotropin hormone (ACTH) (24 h), 17-ethinyl estradiol (17-E2) (5 days), or dexamethasone (DEX) (24 h). Quantitative Western blot analysis and immunocytochemistry indicated that ACTH and 17-E2 treatment greatly increased SR-BI expression in the adrenal (especially in the microvillar compartment of adrenocortical cells), whereas DEX treatment led to a decrease of SR-BI by all measurements. At the same time, striking ultrastructural changes occurred in the adrenocortical cell microvillar compartment: e.g., microvillar area and microvillar channel formation and complexity dramatically increased (compared with control values) after ACTH or 17-E2 treatment, whereas the same values declined after DEX treatment.

These measurements illustrate the exceptional flexibility and responsiveness of the microvillar compartment to hormonal stimuli, and suggest that regulation of SR-BI expression and structural configuration of the surface of steroidogenic cells goes hand in hand.

Abbreviations: ACTH, adrenocorticotropin hormone; CRF, corticotropin-releasing factor; DEX, dexamethasone; SR-BI, scavenger receptor class B type I; 17-E2, 17-ethinyl estradiol

Supplementary key words SR-BI • HDL • steroid hormone • ACTH • corticosterone • cholesterol • 17-ethinyl estradiol • steroidogenesis

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