Messenger RNA of steroid 21-hydroxylase (CYP21) is expressed in the human hippocampus

21-hydroxylase converts progesterone to 11-deoxycorticosterone and 17-hydro xyprogesterone to 11-deoxycortisol, the substrates which are required for t he production of the main adrenal steroids, corticosterone, aldosterone, an d cortisol. As 21-hydroxylase activity has been detected in rodent and feta l human brain, we studied whether and to what extent 21-hydroxylase mRNA is expressed in hippocampal tissue specimens from patients undergoing epileps y surgery (n = 42). 21-hydroxylase mRNA was detected in the hippocampus wit h an expression 10 000 times lower than in adrenal gland tissue. There was no significant difference in expression levels between women (9.5 +/- 2.7 a rbitrary units (aU); mean +/- SEM) and men (8.0 +/- 2.2 aU); however, mRNA concentrations in the hippocampus of children (n = 4, 1.8 +/- 0.5 aU) were considerably lower than in adults (n = 38, 8.6 +/- 1.7 aU). The expression of 21-hydroxylase mRNA in the hippocampus suggests that this human brain ar ea has the enzymatic capability to convert progesterone to 11-deoxycorticos terone and 17-hydroxyprogesterone to 11-deoxycortisol. (C) 2001 Elsevier Sc ience Ireland Ltd. All rights reserved.