Abstract
Evidence for the role of cyclic AMP in animal virus infections was reviewed, as were current methods for the preparation of cell cultures and techniques for the extraction and assay of cyclic AMP. Preliminary experiments were undertaken to develop suitable methods for investigation of intracellular cyclic AMP during in vitro productive virus infections. Selected procedures were applied to study levels of cyclic AMP in cell cultures of continuous cell lines during viral replication. Parallel monolayer cultures of VERO and HEp-2 cells, maintained in the absence of serum, were treated with ethanol to release cyclic AMP. The cell material was assayed for cyclic AMP by competitive protein-binding assays, and for protein by the method of Lowry et al. (1951). No significant changes in levels of cyclic AMP were found during in vitro replication of herpes virus or polio virus. Additionally theophylline, potassium fluoride and cholera toxin were applied to cell cultures to raise intracellular cyclic AMP, while the replication of herpes virus, polio virus, Mengo virus and Semliki Forest virus was observed. All the virus infections were found to be susceptible to modulation by these reagents under some conditions, although some of the effects were considered to be due to cytotoxicity rather than specific enhancement or inhibition of viral infection. The apparent lack of cyclic AMP involvement during single cycle infections and the sensitivity of viruses to exogenous reagents which raise intracellular cyclic AMP is discussed with reference to reports of similar studies from other laboratories and investigations of more diverse subjects in biochemistry and virology.