Induction of rat alpha-1-acid glycoprotein by phenobarbital is independent of a general acute-phase response.

Phenobarbital (PB) induces transcription of the alpha 1-acid glycoprotein (AGP) gene, one of the major positive acute-phase proteins, the expression of which is controlled by a specific combination of glucocorticoids and cytokines. This raises questions as to the involvement of glucocorticoids and cytokine pathways in the PB-mediated effect on AGP gene expression. We found that the pattern of whole-serum proteins in PB-treated rats differed markedly from that observed during a typical acute inflammatory response (in turpentine-treated rats): levels of some positive acute-phase proteins (APP) increased slightly (alpha 1-acid glycoprotein, haptoglobin, hemopexin and T-kininogen), while levels of alpha 2 macroglobulin, the most sensitive marker of the acute-phase reaction, decreased. Among the negative APP, neither albumin nor prealbumin decreased while CBG increased. The cytokines involved in AGP gene regulation (mainly IL1, IL6 and TNF alpha) do not therefore seem to mediate the effect of PB on acute-phase protein expression. Glucocorticoid involvement is also ruled out by the observed enhancement of the effect of PB on AGP expression in adrenalectomized animals. Our results suggest that phenobarbital acts on AGP expression by a mechanism independent of the inflammatory pathway.