Diurnal Rhythms of Tissue Components Related to Protein Metabolism in Normal and Virus-infected Chicks

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Abstract
Diurnal changes in protein metabolism were studied over a 72-hour incubation period in Newcastle disease virus-infected chicks. Protein, DNA, RNA and free amino acid levels were determined, where applicable, in liver, muscle and serum at 4 daily intervals. The data, which included non-infected controls, were plotted in relation to clock hours. Significant diurnal rhythms in all 3 tissues indicated the presence of periodicity. In the controls, liver DNA was highest in the evening but maximal values of RNA, protein and the free amino acids occurred during the day. While the free amino acid pool in the liver was significantly depressed by the Newcastle disease virus (NDV), in the serum there was an increase in values. The NDV also caused a significant desynchronization in relation to clock hours of the rhythmic patterns in the liver and to a lesser extent in muscle. The effect in the liver was noted within 12 hours post-inoculation. Serum patterns in the NDV chicks, however, remained synchronized during the incubation period of the disease cycle. The effect of these diurnal rhythms on experimental error was discussed.