Denari Daniela, Ceballos Nora R
Laboratorio de Endocrinología Comparada and PRHOM-CONICET, Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
Gen Comp Endocrinol. 2005 Sep 1;143(2):113-20. doi: 10.1016/j.ygcen.2005.03.006. Epub 2005 Apr 7.
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 11beta-hydroxysteroid dehydrogenase (11beta-HSD). Two isoforms were identified in mammals: type 1, a NADP+-preferring enzyme with K(m) in the muM range for GC and type 2, NAD+-dependent, with K(m) 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 11beta-HSD activity could alter GC effects. The purpose of this work is to describe seasonal changes in testicular activity of 11beta-HSD in Bufo arenarum as well as the annual and seasonal patterns of plasma corticosterone (B) and T. The activity of 11beta-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 11beta-HSD is a microsomal NAD+-dependent enzyme with a K(m) in the nM order, its activity being strongly reduced by glycyrrhetinic acid. These results indicate that toad testes express an 11beta-HSD similar to mammalian type 2. Although 11beta-HSD activity is higher in the Post-R than in the R and Pre-R seasons (V(max): Pre-R: 0.26+/-0.10, R: 0.14+/-0.01, Post-R: 1.37+/-0.45, pmol/minmg protein), K(m) 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 K(m) values. In conclusion, this work shows that the activity of 11beta-HSD in toad testes could modulate GC action by transforming active hormones in the corresponding inactive steroid.
在大鼠睾丸间质细胞中，糖皮质激素（GC）通过糖皮质激素受体（GR）抑制睾酮（T）的合成。然而，GC与GR的结合受11β-羟基类固醇脱氢酶（11β-HSD）局部表达的调控。在哺乳动物中已鉴定出两种同工型：1型，一种对NADP + 有偏好的酶，对GC的K(m)值在微摩尔范围内；2型，依赖NAD + ，对GC的K(m)值在纳摩尔范围内。在两栖动物中，已描述了基线GC水平的季节性节律。然而，失活的11β-HSD活性量的变化可能会改变GC的作用。本研究的目的是描述阿根廷蟾蜍睾丸中11β-HSD的季节性变化以及血浆皮质酮（B）和T的年度和季节性模式。使用[3H]B在生殖前期（Pre-R）、生殖期（R）和生殖后期（Post-R）的匀浆和亚细胞组分中测定11β-HSD的活性。通过放射免疫分析法测定血浆B和T。睾丸11β-HSD是一种微粒体NAD + 依赖性酶，K(m)值在纳摩尔级别，其活性被甘草次酸强烈降低。这些结果表明蟾蜍睾丸表达一种与哺乳动物2型相似的11β-HSD。尽管11β-HSD活性在生殖后期高于生殖期和生殖前期（V(max)：生殖前期：0.26±0.10，生殖期：0.14±0.01，生殖后期：1.37±0.45，pmol/minmg蛋白），但K(m)值全年保持恒定。还描述了基线GC浓度的季节性节律与血浆T呈负相关。T浓度在生殖期低于其他时期（生殖前期：90±6；生殖期：12±1；生殖后期：56±3，nM），而总B浓度在繁殖期高于其他季节（生殖前期：62±10；生殖期：145±18；生殖后期：96±10，nM）。此外，游离B（生殖前期：51±8；生殖期：94±12；生殖后期：70±7，nM）始终低于K(m)值。总之，本研究表明蟾蜍睾丸中11β-HSD的活性可通过将活性激素转化为相应的无活性类固醇来调节GC的作用。
