A two cell type theory for aldosterone biosynthesis: the roles of 11 beta-hydroxylase and aldosterone synthase, and a high capacity tightly binding steroid carrier for 18-hydroxydeoxycorticosterone in rat adrenals.
Several lines of experimentation suggest that a tissue-sequestered pool of 18-hydroxydeoxycorticosterone (18-OH-DOC) in the rat adrenal may be mobilized as an aldosterone precursor. We show here that this steroid is maintained in a non-extractable form in the membranes of collagenase-dispersed fasciculata/reticularis cells. Because of this stability, the complex can be identified by immunocytochemistry and also, in IEF gels of solubilized inner adrenocortical zone membrane preparations, by immunoblotting. However, the complexed steroid cannot be extracted from the gels into organic solvent unless first treated with trypsin. Preincubation of viable whole glandular tissue with trypsin significantly enhanced aldosterone output and eliminated the trypsin-releasable 18-OH-DOC pool in IEF gels of solubilized inner zone membranes. Both prior sodium depletion and acute trypsin stimulation of whole glands enhanced extractable 18-OH-DOC in glomerulosa tissue membranes. Other experiments using in situ hybridization show that mRNA coding for 11 beta-hydroxylase (which generates 18-OH-DOC) is confined to the inner adrenocortical zones, whereas aldosterone synthase (which does not) is transcribed exclusively in the glomerulosa. The data suggest that a pool of 18-OH-DOC in inner zone membranes can be mobilized for utilization as an aldosterone precursor in the glomerulosa. The results also indicate the existence of an entirely novel tightly binding steroid carrier from which steroid cannot be extracted by organic solvent unless first subjected to proteolytic degradation.
Vinson
G P
GP
Department of Biochemistry, Queen Mary and Westfield College, London, UK.
Teja
R
R
Ho
M M
MM
Puddefoot
J R
JR
D015070:18-Hydroxydesoxycorticosterone / Q000378:metabolism; D000302:Adrenal Cortex / Q000378:metabolism*; D000450:Aldosterone / Q000096:biosynthesis*; D000818:Animals; D019405:Cytochrome P-450 CYP11B2; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D005260:Female; D015151:Immunoblotting; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D051381:Rats; D017208:Rats, Wistar; D013252:Steroid 11-beta-Hydroxylase / Q000378:metabolism*
D015070:18-Hydroxydesoxycorticosterone; D000450:Aldosterone; D003577:Cytochrome P-450 Enzyme System; D019405:Cytochrome P-450 CYP11B2; D013252:Steroid 11-beta-Hydroxylase