Yamada M, Wilber J F
Section of Endocrinology and Metabolism, LSU Medical Center, New Orleans 70112.
Neuropeptides. 1990 Jan;15(1):49-53. doi: 10.1016/0143-4179(90)90160-z.
TRH mRNA has not been quantified concomitantly with TRH itself to examine graded effects of thyroid hormones (TH) upon TRH gene transcriptional regulation and post-transcriptional expression. To examine such TH effects, rats were rendered thyrotoxic with L-T3 (50 micrograms per 100g body weight) or hypothyroid by total thyroidectomy. After decapitation, frozen coronal brain sections were prepared in a matrix for hypothalamic micropunches. PreProTRH mRNA was quantified in punch pools by slot-blot hybridization and densitometry, using a 32P 1.2Kb rat riboprobe (gift of Drs. S. Lee and R. Goodman). T3 toxicosis resulted in parallel reductions in PreProTRH mRNA (-45%) and TRH concentrations determined by RIA (-43%), 1.1 versus 1.9 ng/mg protein, p less than 0.01. Conversely, elevations in PreProTRH mRNA were stimulated by hypothyroidism on Day 14 (+32%). However, TRH concentrations were reduced paradoxically from 2.2 +/- 0.05 ng/mg protein to 0.68 +/- 0.03, p less than 0.01. No changes, in contrast, were identified in whole hypothalamic extracts in either PreProTRH mRNA or TRH after T3 treatment. It is concluded that TH do exert inhibitory effects upon PreProTRH mRNA transcription, and in the specific hypothalamic nucleus concerned with thyroid regulation (PVN). The failure of TRH concentrations to rise concordantly with activated TRH gene transcription in hypothyroidism suggests that TH may exert inhibitory effects upon PreProTRH mRNA translation, in addition to inhibition of TRH gene transcription and TRH secretion.
促甲状腺激素释放激素（TRH）mRNA尚未与TRH本身同时进行定量分析，以研究甲状腺激素（TH）对TRH基因转录调控和转录后表达的分级效应。为了研究这种TH效应，用L-T3（每100克体重50微克）使大鼠产生甲状腺毒症，或通过全甲状腺切除术使大鼠甲状腺功能减退。断头后，在用于下丘脑微量打孔的基质中制备冷冻冠状脑切片。使用32P 1.2Kb大鼠核糖探针（由S. Lee博士和R. Goodman博士提供），通过狭缝印迹杂交和光密度测定法对打孔样本池中的前促甲状腺激素释放激素（PreProTRH）mRNA进行定量分析。T3中毒导致PreProTRH mRNA平行降低（-45%），通过放射免疫分析（RIA）测定的TRH浓度降低（-43%），分别为1.1与1.9纳克/毫克蛋白质，p<0.01。相反，甲状腺功能减退在第14天刺激PreProTRH mRNA升高（+32%）。然而，TRH浓度却自相矛盾地从2.2±0.05纳克/毫克蛋白质降至0.68±0.03，p<0.01。相比之下，T3处理后，全下丘脑提取物中的PreProTRH mRNA或TRH均未发现变化。结论是，TH确实对PreProTRH mRNA转录以及与甲状腺调节相关的特定下丘脑核（室旁核，PVN）发挥抑制作用。甲状腺功能减退时，TRH浓度未能与激活的TRH基因转录同步升高，这表明TH除了抑制TRH基因转录和TRH分泌外，还可能对PreProTRH mRNA翻译发挥抑制作用。
