LPA was originally reported to be a growth factor released from activated platelets and other injured cells. LPA and thrombin, another mitogen and well-known permeability-increasing agent in vitro, initiate similar cellular responses and signaling pathways such as mobilization of intracellular calcium, stimulation of phospholipase C and protein kinase C, formation of actin stress fibers, and contraction of fibroblasts. These known actions of LPA would link this phospholipid to an increase in endothelial permeability, as has been observed in endothelial cells from brain microvessels and human umbilical veins. In contrast, LPA decreases endothelial permeability in bovine endothelial cells from the lung and aorta. Thus, the effects of LPA on vascular permeability may be organ, tissue, or species specific.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.