Hyperplasia and cystic dilatation of the extrahepatic biliary ducts is a usual secondary change in mice bearing large grafts of dependent pituitary tumors which secrete thyroid-stimulating hormones (TSH) and probably also gonad-stimulating hormones. Occasionally, rupture of the common duct following excessive dilatation is the immediate cause of death. Autonomous pituitary tumors (those not requiring for growth absence of the thyroid) do not cause these changes in the common duct, even through such tumors secrete TSH and possibly gonad-stimulating hormones.

The available evidence suggests that this change in the biliary tract is related to some hormone of the pituitary.

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Work performed under Contract No. W-7405-eng-26 for the Atomic Energy Commission.

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