EVIDENCE THAT THE ACCUMULATION OF 5-HYDROXYTRYPTAMINE IN THE LIVER BUT NOT IN THE BRAIN MAY CAUSE THE HYPOGLYCEMIA INDUCED BY 5-HYDROXYTRYPTOPHAN

Experiments were undertaken to determine whether the site of the hypoglycemic action of 5-hydroxytryptophan (5-HTP), a direct precursor of 5-hydroxytryptamine (5-HT), was in the CNS or in the liver. The fall in blood glucose followed the rapid increase in the amount of 5-HT both in the brain and liver after 5-HTP injection into pargyline-treated and nontreated mice. Carbidopa, an inhibitor of peripheral aromatic amino acid decarboxylase, prevented the elevation of 5-HT levels in the liver of both pargyline-treated and non-treated mice. In contrast, carbidopa did not prevent but rather enhanced the elevation of 5-HT levels in the brain of both groups of mice. Corresponding to the prevention of 5-HT elevation in the liver, the fall in blood glucose was prevented by carbidopa. The accumulation of 5-HT in the liver but not in the brain evidently causes the hypoglycemia induced by 5-HTP.