One of the characteristic functions of the liver is hepatic regeneration. In an experimental animal (e.g., rats), when liver tissue is affected by an agent (e.g., viral infection, chemical toxin), or removed surgically (up to 70%), the remnant liver spontaneously undergoes cell division to regenerate the organ. Such proliferative reactions are ceased when the whole organ is restored. Several methods to elucidate this complex phenomenon became available in the 20th century, and various studies have been performed in many laboratories. As a result, many factors that promote hepatocyte proliferation, as well as some growth inhibitors, were confirmed. Among these, serotonin (5-HT: 5-hydroxytryptamine) was recently identified as a promising hepatocellular growth-promoting factor. In this review, we attempt to integrate the intracellular signal transduction pathway for 5-HT-induced hepatocyte proliferation in primary cultures of adult rat hepatocytes and discuss the physiological significance of 5-HT in liver regeneration in vivo.
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