title: Biochemical characterization and seasonal changes in the concentration of testosterone-metabolizing enzymes in the European great tit (Parus major) brain.
abstract: Homogenates of diencephala obtained from brains of European great tits (Parus major) were incubated in the presence of tritiated testosterone (T) as precursor, and four metabolites produced from this steroid were formally identified and quantified. Conversion into 5 beta-dihydrotestosterone (5 beta-DHT) constituted the major metabolic pathway of T. Smaller amounts of 5 alpha-dihydrotestosterone (5 alpha-DHT), 5 beta-androstane-3 alpha, 17 beta-diol (5 beta-DIOL), and estradiol (E2) were also produced. The metabolism of T was time-dependent, and it varied as a function of the initial precursor concentration. The kinetics of 5 beta- and 5 alpha-reductases, as well as aromatase, followed the Michaelis-Menten model. It was found that 5 beta-reductase has a low apparent affinity for T, but is present in large concentrations. In contrast, the apparent affinity for T and the concentration of aromatase were approximately 3.9 times higher and 130 times smaller, respectively, than those of 5 beta-reductase. Intermediate values were found for 5 alpha-reductase. The validated assay was used to measure seasonal changes in the in vitro metabolism of T in the anterior (AH) and posterior (PH) hypothalamus and the cerebellum (CER) of free-living juvenile and adult male great tits. The production of 5 beta-DHT was low during the winter period in the PH of adult males, whereas the 5 beta-DIOL production was low in both parts of the hypothalamus at this time of the year. During autumn the production of these metabolites showed a transitory decrease in both parts of the hypothalamus of the juveniles. The production of 5 beta-reduced metabolites by the CER was high at all times of the year. In juveniles, the CER production of 5 beta-DHT did not change seasonally, whereas 5 beta-DIOL production peaked during summer. In the CER of adults, maximum production of both metabolites occurred during summer. Generally, less T was converted into 5 beta-reduced metabolites by the PH than by either the AH or the CER. E2 production was observed only in the AH and PH. With one exception (summer; AH), E2 production was high in both parts of the hypothalamus of adults throughout the year. In both AH and PH of juveniles, E2 production was low during summer. In these birds, it increased between summer and autumn in both parts of the hypothalamus, and also between autumn and winter in the PH. The production of 5 alpha-DHT did not change as a function of the season, the age of the birds, or the brain region.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Zoology, University of Gothenburg, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Silverin
authors.forename: P
authors.initials: P
authors.lastname: Deviche
mesh_terms: D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase / Q000032:analysis*; D000222:Adaptation, Physiological; D000367:Age Factors; D015113:Androstane-3,17-diol / Q000032:analysis; D000818:Animals; D000835:Animals, Wild / Q000378:metabolism*; D001141:Aromatase / Q000032:analysis; D001717:Birds / Q000378:metabolism*; D001921:Brain / Q000201:enzymology / Q000502:physiology*; D013196:Dihydrotestosterone / Q000032:analysis / Q000378:metabolism; D004958:Estradiol / Q000032:analysis; D008297:Male; D010088:Oxidoreductases / Q000032:analysis*; D012621:Seasons; D013739:Testosterone / Q000378:metabolism
chemical_list: D013196:Dihydrotestosterone; D015113:Androstane-3,17-diol; D013739:Testosterone; D004958:Estradiol; D010088:Oxidoreductases; D001141:Aromatase; D013741:3-Oxo-5-alpha-Steroid 4-Dehydrogenase; C021936:3-oxo-5 beta-steroid delta 4-dehydrogenase