TPH1 and fatty liver disease: Obesity associated with HFD induces liver steatosis and inflammation, increases platelet number and aggregation in the liver sinusoids 274, and increases TPH1 activity in the gut (duodenum, jejunum, and colon), which augments 5-HT release from the gut 222 and platelet-derived 5-HT to the hepatic portal vein 198.