The control of ornithine decarboxylase activity during liver regeneration

Abstract

The effect of amino acids and growth hormone on rat liver ornithine decarboxylase activity was investigated in an attempt to elucidate the mechanisms that control the activity of this enzyme during the early stages of liver regeneration. A single administration of casein hydrolyzate to intact rats produces a marked increase in liver ornithine decarboxylase activity. The casein effect is abolished by puromycin or actinomycin, is not modified by adrenalectomy and is slowed down by hypophysectomy. Histidine also causes a rapid increase in the activity of the enzyme but the amino acid effect is blocked by puromycin, is not inhibited by actinomycin, and is entirely absent in hypophysectomized rats. Growth hormone injections increase ornithine decarboxylase activity in normal or regenerating liver. The action of the hormone is only slightly inhibited by doses of actinomycin that prevent any increase in the specific activity of nuclear or cytoplasmic rapidly labeled RNA. 8-Azaguanine injection or small doses of actinomycin do not block the initial increase in ornithine decarboxylase activity occurring shortly after partial hepatectomy. The possibility that a post-transcriptional mechanism is involved in the control of ornithine decarboxylase activity during liver regeneration is discussed in detail.