11β-Hydroxysteroid dehydrogenase in the testis of Bufo arenarum: Changes in its seasonal activity

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.