1. Sepsis is associated with marked changes in cardiac muscle protein synthesis. Such changes may be the result of altered transcription of specific myofibrillar protein mRNAs.
2. In order to investigate myofibrillar protein gene expression, a rat model of sepsis was used. Adult rats were given a single sub-lethal dose of lipopolysaccharide by the intraperitoneal route. At various times thereafter, rats were killed and ventricular muscle was removed. RNA was extracted and transferred to nylon membranes. Changes in expression of mRNA for α- and β-myosin heavy chain, α-actin, cardiac troponin C and carbonic anhydrase III were detected by Northern hybridization.
3. After treatment with lipopolysaccharide, mRNA for β-myosin heavy chain increased to 260% of control values at 24 h and reached a maximum of 310% at 48 h. α-Myosin heavy chain mRNA levels fell to 72% of control values at 24 h. mRNA levels for α-actin, cardiac troponin C and carbonic anhydrase III remained unchanged.
4. In order to investigate the role of tumour necrosis factor-α in this process, some rats were pretreated with monoclonal antibody against tumour necrosis factor-α before receiving lipopolysaccharide. Such animals showed an absence of tumour necrosis factor-α bioactivity in plasma, but changes in myocardial protein mRNA levels were no different from those seen in animals receiving lipopolysaccharide alone.
5. The reduction in protein synthesis in cardiac muscle in sepsis does not appear to be the result of reduced expression of genes for structural or soluble muscle protein. Rather there is a paradoxical increase in β-myosin heavy chain expression, which may represent a protective mechanism. Tumour necrosis factor-α does not appear to be involved in the mediation of these changes.
