Histamine modulates the interleukin-6-regulated acute phase protein synthesis in cultured murine hepatocytes

Influence of Histamine in a Liver Injury Model Induced by Propionibacterium acnes and Lipopolysaccharide

In normal mice, plasma histamine levels were 29.4+/-10.1 pmol/ml. When 0.1 microg of lipopolysaccharide (LPS) was intravenously injected into Propionibacterium acnes (P. acnes)-primed ICR mice, histamine levels increased remarkably to 61.2+/-15.9 pmol/ml (p<0.001). An increase was also observed in liver tissues. Oral administration of histidine at 200 mg/kg once daily for 5 d before intravenous LPS injection increased the plasma alanine aminotransferase (ALT) activity to 2936.5+/-356.3 IU/l, a significant change compared with the controls (2244.8+/-425.5 IU/l, p<0.05). The 24 h survival rate after LPS injection was 72.7% in the mice treated with 50 mg/kg of ranitidine, in contrast with 50% in the control group although the treatment did not significantly decrease the plasma ALT activity. On the other hand, 50 mg/kg of pyrilamine significantly reduced plasma ALT activity (p<0.001). The results suggested that histamine levels are related to hepatic damage in the P. acnes plus LPS induction of liver injury.

Increase in histamine synthesis by liver macrophages in CCl4-injured mast cell-deficient W/Wv mice

This study set out to examine the possible role of liver macrophages in histamine synthesis in the injured liver. The effects of the hepatotoxins Escherichia coli lipopolysaccharide (LPS) and CCl4 on histamine synthesis in the liver of mice were evaluated. C3H/HeJ mice were resistant to LPS in including histidine decarboxylase (HDC) in the liver compared with C3H/HeN mice and mast cell-deficient W/Wv mice. However, C3H/HeJ mice did respond strongly to another hepatotoxin, CCl4, leading to a significant increase in HDC activity. CCl4 also caused a marked increase in HDC activity and histamine levels in the liver of W/Wv mice. In addition, injection of CCl4 produced a large increase in the activity of HDC in the spleen and lung of W/Wv mice. HDC activity was confined to the nonparenchymal cells, with parenchymal cells expressing essentially no HDC activity. The CCl4-induced increase in HDC activity was confined, at least in part, to the liver macrophages. These results indicate that the macrophages are responsible for the increase in HDC-dependent histamine production in the liver caused by the injection of hepatotoxins. The possible role of histamine in liver regeneration after injury is discussed.

The acute phase response: general aspects

The acute phase response in a given individual represents the integrated sum of multiple, separately regulated changes. Although many of these changes commonly occur together in affected individuals, clinical experience indicates that not all of them occur in all individuals, indicating that they must be individually regulated. For example, febrile patients may have normal blood levels of CRP and vice versa, leukocytosis does not always accompany other acute phase phenomena, and many instances of discordance between levels of the various acute phase proteins are seen. Cytokines function as part of a complex regulatory network, a signalling language in which information is conveyed to cells by combinations, and perhaps sequence, of intercellular messenger molecules. The effects of combinations of cytokines are complex. To use a somewhat crude simile, individual cytokines can be thought of as words which bear informational content and which may, on occasion, communicate a complete message. More commonly, however, the actual messages received by cells probably resemble sentences, in which combinations and sequences of words convey information. Currently available data suggest that hepatocytes receive a complex mixture of humoral or paracrine signals during the acute phase response. These are integrated by multiple interacting signal transducing mechanisms to cause finely regulated changes in plasma protein synthesis. Regulation largely occurs by transcriptional control, but post-transcriptional mechanisms, including translational regulation, may also participate. Both the extracellular and intracellular mechanisms that mediate the response of the hepatocyte to inflammatory stimuli appear to be highly complex and involve multiple overlapping, concurrent and parallel pathways. Enough is known at present to conclude that IL-6 is a major participant in these plasma protein changes. Regulation of non-hepatocyte acute phase phenomena has not been delineated as thoroughly, but clearly involves a number of inflammation-associated cytokines.