Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9113174 | General and Comparative Endocrinology | 2005 | 8 Pages |
Abstract
In rat Leydig cells, glucocorticoids (GC) inhibit testosterone (T) synthesis via glucocorticoid receptor (GR). However, GC access to GR is regulated by the local expression of 11β-hydroxysteroid dehydrogenase (11β-HSD). Two isoforms were identified in mammals: type 1, a NADP+-preferring enzyme with Km in the μM range for GC and type 2, NAD+-dependent, with Km in the nM range for GC. In amphibians, a seasonal rhythm in baseline GC levels was described. However, a shift in the amount of deactivating 11β-HSD activity could alter GC effects. The purpose of this work is to describe seasonal changes in testicular activity of 11β-HSD in Bufo arenarum as well as the annual and seasonal patterns of plasma corticosterone (B) and T. The activity of 11β-HSD was assayed in homogenate and subcellular fractions in pre-reproductive (Pre-R), reproductive (R) and post-reproductive (Post-R) periods, using [3H]B. Plasma B and T were determined by RIA. Testicular 11β-HSD is a microsomal NAD+-dependent enzyme with a Km in the nM order, its activity being strongly reduced by glycyrrhetinic acid. These results indicate that toad testes express an 11β-HSD similar to mammalian type 2. Although 11β-HSD activity is higher in the Post-R than in the R and Pre-R seasons (Vmax: Pre-R: 0.26 ± 0.10, R: 0.14 ± 0.01, Post-R: 1.37 ± 0.45, pmol/min mg protein), Km value remains constant throughout the year. A seasonal rhythm in baseline GC concentrations inversely correlated with plasma T was also described. T concentration is lower in the R season than in the other periods (Pre-R: 90 ± 6; R: 12 ± 1; Post-R: 56 ± 3, nM) while total B concentration is higher in the breeding than in the other seasons (Pre-R: 62 ± 10; R: 145 ± 18; Post-R: 96 ± 10, nM). Furthermore, free B (Pre-R: 51 ± 8; R: 94 ± 12; Post-R: 70 ± 7, nM) was always below Km values. In conclusion, this work shows that the activity of 11β-HSD in toad testes could modulate GC action by transforming active hormones in the corresponding inactive steroid.
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Authors
Daniela Denari, Nora R. Ceballos,