Immediate-Early Protooncogene Expression and Liver Function Following Various Extents of Partial Hepatectomy in the Rat

Abstract

Immediate–early protooncogenes (IEP) are thought to play an important role in hepatocyte replication. Whether the extent of their expression correlates with the strength of the proliferative stimulus and subsequent regenerative activity has yet to be documented in vivo. Data are also lacking with respect to the level at which liver disease is associated with biochemical evidence of hepatic dysfunction. Thus, the objectives of this study were to determine whether a correlation exists between IEP gene mRNA expression and varying extents of partial hepatectomy (PHx) and to document the extent of resection required to result in increases in serum bilirubin levels. Eighty-nine adult, male Sprague-Dawley rats underwent either sham surgery or 20%, 35%, 55%, 70% or 90% PHx. Postoperatively, rats were killed (N = 3–6/group) at 15 and 30 mins and 8 and 24 hrs for c-fos, c-jun, and c-myc mRNA expression by northern blot analyses. Rats killed at 24 hrs also had hepatic regenerative activity documented by [³H]thymidine incorporation into hepatic DNA and serum bilirubin determinations. While c-fos mRNA expression at 15 mins and c-myc mRNA expression at 8 hrs after PHx did not correlate with the extent of PHx (r² = 0.478 and 0.018, respectively), a weak correlation existed between c-jun mRNA expression at 30 mins and the extent of PHx (r² = 0.662, P < 0.05). In terms of IEP mRNA expression and hepatic regenerative activity, a strong correlation existed between c-fos mRNA expression and [³H]thymidine incorporation (r² = 0.851, P < 0.01) but not c-jun or c-myc mRNA expression. Compared to sham operated controls, [³H]thymidine incorporation was 2.0×, 3.4×, 3.2×, 7.8×, and 2.2× increased following 20%, 35%, 55%, 70%, and 90% PHx, respectively. Serum bilirubin levels remained unchanged until 70% PHx, when they increased from baseline values of 0.54 ± 0.05 mg/dl to 1.02 ± 0.15 mg/dl (P < 0.05). A further increase occurred following 90% PHx (1.83 ± 0.30 mg/dl, P < 0.01). In conclusion these findings indicate that c-fos mRNA expression 15 mins after PHx correlates with hepatic regenerative activity but not the strength of the regenerative stimulus and that hepatic parenchymal loss of 55–70% must occur prior to the detection of elevated serum bilirubin levels. The results also indicate that relative to a 70% PHx, 90% PHx is associated with decreased rather than increased hepatic regenerative activity.