Ingestive Peptides and the Blood–Brain Barrier

ABSTRACT The passage of substances such as leptin, ghrelin, and insulin across the blood–brain barrier (BBB) has emerged in the last decade as a major mechanism by which the central nervous system (CNS) and gastrointestinal (GI) tract communicate. Saturable transport systems in the brain or blood directions exist for many of these substances, and others cross by nonsaturable transmembrane diffusion. The transporters are them selves regulated and dysregulation results in disease. For example, the immune regulation of insulin transport could explain the insulin resistance of sepsis and the impaired transport of leptin as an early cause of the leptin resistance seen in obesity.