Inhibition of the glycogen phosphorylase system during ochratoxicosis in chickens

Abstract

Graded doses of ochratoxin A incorporated into the diet (0, 0.5, 1.0, 2.0, 4.0, and 8.0 μg/g) of broiler chickens significantly (P < 0.05) inhibited activity of protein kinase, the initiator enzyme of the glycogen phosphorylase system, in the livers at all dose levels. Only the highest dose, 8.0 μg/g, significantly reduced the total activity of phosphorylase kinase, which is activated by protein kinase. The total activity of phosphorylase, which is activated by phosphorylase kinase, was unaltered by ochratoxin A at any level. Addition of ochratoxin A to liver extracts from control birds inhibited protein kinase but not phosphorylase kinase. When added to extracts of livers from control birds, cyclic adenosine 3',5'-monophosphate stimulated protein kinase but not phosphorylase kinase. The cyclic adenosine 3',5'-monophosphate had no effect when added to extracts from birds fed ochratoxin A. These results suggest that ochratoxin A affects primarily the cyclic adenosine 3',5'-monophosphate-dependent protein kinase which initiates the enzymatic cascade leading to glycogenolysis. Furthermore, these results confirm an earlier assignment on morphological criteria of the glycogenosis of ochratoxicosis as a type X glycogen storage disease.