Fjeldheim Ase-Karine, Høvring Per Ivar, Løseth Ole-Petter, Johansen Per Wiik, Glover Joel C, Matre Vilborg, Olstad Ole Kristoffer, Reppe Sjur, Gordeladze Jan O, Walaas S Ivar, Gautvik Kaare M
Institute of Basic Medical Science, Department of Biochemistry, University of Oslo, PO Box 1112 Blindern, N-0317 Oslo, Norway.
Eur J Endocrinol. 2005 May;152(5):791-803. doi: 10.1530/eje.1.01902.
The accepted function of the hypothalamic peptide, thyrotrophin-releasing hormone (TRH), is to initiate release of thyrotrophin (TSH) from the pituitary. A physiological role for TRH in lactating rats has not yet been established.
Tissues were prepared from random-cycling and lactating rats and analysed using Northern blot, real time RT-PCR and quantitative in situ hybridisation.
This study demonstrates that TRH receptor 1 (TRHR1) mRNA expression is up-regulated in the pituitary and in discrete nuclei of the hypothalamus in lactating rats, while proTRH mRNA expression levels are increased only in the hypothalamus. The results were corroborated by quantitative in situ analysis of proTRH and TRHR1. Bromocriptine, which reduced prolactin (PRL) concentrations in plasma of lactating and nursing rats, also counteracted the suckling-induced increase in TRHR1 mRNA expression in the hypothalamus, but had an opposite effect in the pituitary. These changes were confined to the hypothalamus and the amygdala in the brain.
The present study shows that the mechanisms of suckling-induced lactation involve region-specific regulation of TRHR1 and proTRH mRNAs in the central nervous system notably at the hypothalamic level. The results demonstrate that continued suckling is critical to maintain plasma prolactin (PRL) levels as well as proTRH and TRHR1 mRNA expression in the hypothalamus. Increased plasma PRL levels may have a positive modulatory role on the proTRH/TRHR1 system during suckling.
下丘脑肽促甲状腺激素释放激素（TRH）公认的功能是启动垂体促甲状腺激素（TSH）的释放。TRH在泌乳大鼠中的生理作用尚未明确。
从随机发情和泌乳大鼠制备组织，采用Northern印迹、实时逆转录聚合酶链反应和定量原位杂交进行分析。
本研究表明，泌乳大鼠垂体和下丘脑离散核中的促甲状腺激素释放激素受体1（TRHR1）mRNA表达上调，而proTRH mRNA表达水平仅在下丘脑升高。proTRH和TRHR1的定量原位分析证实了该结果。溴隐亭可降低泌乳和哺乳大鼠血浆中催乳素（PRL）浓度，也可抵消哺乳诱导的下丘脑TRHR1 mRNA表达增加，但对垂体有相反作用。这些变化局限于脑内的下丘脑和杏仁核。
本研究表明，哺乳诱导泌乳的机制涉及中枢神经系统中TRHR1和proTRH mRNAs的区域特异性调节，尤其是在下丘脑水平。结果表明，持续哺乳对于维持血浆催乳素（PRL）水平以及下丘脑proTRH和TRHR1 mRNA表达至关重要。哺乳期间血浆PRL水平升高可能对proTRH/TRHR1系统具有正向调节作用。
