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A L Southren, K Altman, J Vittek, V Boniuk, G G Gordon; Steroid metabolism in ocular tissues of the rabbit.. Invest. Ophthalmol. Vis. Sci. 1976;15(3):222-228. doi: https://doi.org/.
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The metabolism of cortisol and other steroids was studied in normal untreated rabbit iris-ciliary body and cornea as part of an investigation into the mechanism of glucocorticoid-induced glaucoma. Cortisol is readily converted to the inactive metabolite cortisone by these eye tissues indicating the presence of an 11beta-oxidoreductase system. This reaction is reversible with cortisone being converted to cortisol in the presence of appropriate cofactor. However, due to the absence of a (or as yet undetectable) cortisol-A-ring-reductase system (rate-limiting reaction) the steroid is not irreversibly metabolized to biologically inactive compounds. The 11beta-oxidoreductase system readily converts other C21-11beta-hydroxysteroids, such as corticosterone, to its appropriate C21-11-ketosteroid (11-dehydrocorticosterone). Some C21-steroids lacking the 11-hydroxyl group (11-deoxycortisol, 11-deoxycorticosterone) remain virtually unmetabolized (exception to this was found with progesterone). Evidence of a C21-steroid A-ring reductase system was found only when cortisone and progesterone were used as substrates. However, testosterone a C19 steroid was converted to clearly identifiable A-ring reduced and 17beta-and 3alpha(beta)-oxidoreduced metabolites, thus indicating the presence of testosterone A-ring reductase, 17beta-and 3alpha(beta)-oxidoreductase systems in the eye tissues studied. The presence of a steroid 5alpha(beta)-reductase for some steroids but not for cortisol indicates a distinct substrate specificity for this enzyme system in the eye tissues.
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