Regulation of acute phase gene expression following surgery and endotoxin administration in the anesthetized pig

The hepatic acute phase response (APR) reflects an organism's integrated response to stress. This APR results in augmented synthesis and secretion of specific procoagulants and antiproteases and a complementary decrease in the synthesis and secretion of several constitutive proteins, such as albumin. The cytokines tumor necrosis factor (TNF) or interleukin-6 (IL-6) have been identified as proximal mediators of the APR in response to endotoxin stress. The authors hypothesized that TNF, IL-6, or both would be the proximal mediators of the APR in response to anesthesia and surgical stress.

The effects of a standardized surgical stress on the APR in pigs under general anesthesia with sodium pentobarbital and ketamine hydrochloride was investigated. Acute phase gene transcription was assayed in nuclei from serial liver biopsies obtained before and after 2.5 h of surgical stress, and after endotoxin administration. Tumor necrosis factor and IL-6 mRNA levels in this liver tissue were examined by Northern blot hybridization, and simultaneous plasma levels of these cytokines were measured using bioassays.

The transcription rates of three positive acute phase genes--chymotrypsin inhibitor, inter-alpha-trypsin inhibitor and beta-fibrinogen--increased seven-, six-, and twofold, respectively (P < 0.05), and the transcription rate of albumin, a negative acute phase gene, decreased to 34% of baseline (P < 0.01) during the 2.5 h of anesthesia and surgical stress. During this initial 2.5 h, plasma concentrations of TNF and IL-6 did not change. Hepatic IL-6 mRNA expression was never observed, and TNF mRNA expression was undetectable in six of seven pigs. Subsequent 10-micrograms/kg endotoxin administration caused 20- and 100-fold increases in plasma concentrations of TNF and IL-6, respectively (P < 0.01), and were associated with substantial hepatic expression of the TNF and IL-6 mRNAs. These increments in cytokines were not associated with any further increase in the acute phase gene transcription rates. Thus, the APR was initially regulated at the transcriptional level during surgical stress independent of, and not augmentable by, an endotoxin-provoked increase in either plasma levels or hepatic mRNA expression of TNF or IL-6.

Surgical stress induced hepatic acute phase gene transcription within 2.5 h in the absence of either systemic or local (hepatic) increases in TNF or IL-6. Subsequent endotoxin-induced increases in TNF or IL-6 did not alter this surgical stress-induced acute phase gene transcription.