AbstractThe presence of cytochrome P‐45011βin rat brain was studied by immunohistochemistry using polyclonal rabbit antibodies raised against purified bovine adrenocortical P‐45011β, which is involvedin the steroid 11β‐hydroxylation and glucocorticoid formation. The results showed that cytochrome P‐45011βimmunoreactivity is selectively localized to the tracts of myelinated fibers throughout the brain. The specificity of immunohistochemical stainings with P‐45011βantibodies was established by control tests including nonimmune rabbit immunoglobulin Gs and P‐45011βantibodies absorbed with purified antigen.Western immunoblots of homogenates from different brain areas with P‐45011βantibodies, together with biochemical enzymatic assays for cytochrome P‐45011β}monooxygenase activity in these homogenates, confirmed the selective localization of this enzyme observed with immunohistochemistry. Cytochrome P‐45011βand 11β‐hydroxylase activity were detected in a homogenate from the cortical white matter (brain area rich in myelinated fibers) as in that from the rat adrenal, but were not detectable in a homogenate from the cerebral cortex (brain area poor in myelinated fibers). Furthermore, quantitation of the P‐45011βbands on the immunoblots by the areal density revealed that the cortical white matter contains approximately 1.4 pmol of cytochrome P‐45011β/mg of tissue protein, the value of which was about one sixth ofthe corresponding value estimated in the rat adrenal. This relatively highcontent of cytochrome P‐45011βwas also reflected in a relatively high level of 11β‐hydroxylase activity measured in a homogenate ofthis brain area by biochemical enzymatic assays using 4‐14C‐11‐deoxycorticosterone.Thus, from the present data it can be concluded that rat brain containscytochrome P‐45011βin myelinated tracts, in which the 11β‐hydroxylation mechanism (corticosterone synthesis) occurs as in adrenal cortex. This enzyme was detected in the same brain structures in which cytochrome P‐450scc(an enzyme involved in cholesterol side‐chain cleavage and preg‐nenolone synthesis) has been previously shown to be present, which suggests an important role of myelinated tract
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