Veterans Affairs Puget Sound Health Care System and Division of Gerontology and Geriatric Medicine, Department of Medicine, University of Washington School of Medicine, Seattle, Washington, USA.
Endocrinology. 2012 Sep;153(9):4111-9. doi: 10.1210/en.2012-1435. Epub 2012 Jul 9.
The blood-brain barrier (BBB) separates the central nervous system (CNS) from the peripheral tissues. However, this does not prevent hormones from entering the brain, but shifts the main control of entry to the BBB. In general, steroid hormones cross the BBB by transmembrane diffusion, a nonsaturable process resulting in brain levels that reflect blood levels, whereas thyroid hormones and many peptides and regulatory proteins cross using transporters, a saturable process resulting in brain levels that reflect blood levels and transporter characteristics. Protein binding, brain-to-blood transport, and pharmacokinetics modulate BBB penetration. Some hormones have the opposite effect within the CNS than they do in the periphery, suggesting that these hormones cross the BBB to act as their own counterregulators. The cells making up the BBB are also endocrine like, both responding to circulating substances and secreting substances into the circulation and CNS. By dividing a hormone's receptors into central and peripheral pools, the former of which may not be part of the hormone's negative feed back loop, the BBB fosters the development of variable hormone resistance syndromes, as exemplified by evidence that altered insulin action in the CNS can contribute to Alzheimer's disease. In summary, the BBB acts as a regulatory interface in an endocrine-like, humoral-based communication between the CNS and peripheral tissues.
血脑屏障（BBB）将中枢神经系统（CNS）与外周组织隔开。然而，这并不能阻止激素进入大脑，而是将进入大脑的主要控制转移到 BBB。一般来说，甾体激素通过跨膜扩散穿过 BBB，这是一种非饱和过程，导致大脑中的水平反映血液中的水平，而甲状腺激素和许多肽和调节蛋白则通过转运蛋白穿过，这是一个饱和过程，导致大脑中的水平反映血液中的水平和转运蛋白的特征。蛋白结合、脑向血液的转运和药代动力学调节 BBB 的穿透性。一些激素在中枢神经系统中的作用与在外周组织中的作用相反，这表明这些激素穿过 BBB 作为自身的反向调节剂。构成 BBB 的细胞也具有内分泌样特征，既能对外周循环中的物质做出反应，又能将物质分泌到循环和中枢神经系统中。通过将激素的受体分为中枢和外周池，前者可能不是激素负反馈循环的一部分，BBB 促进了可变的激素抵抗综合征的发展，例如有证据表明，中枢神经系统中胰岛素作用的改变可能导致阿尔茨海默病。总之，BBB 作为中枢神经系统和外周组织之间基于体液的内分泌样通讯的调节界面。
