Isolated hepatic cholinergic denervation impairs glucose and glycogen metabolism.

BACKGROUND

Hepatic innervation plays an essential role in insulin extraction and glucose production, but the specific role of hepatic cholinergic innervation remains unclear. We sought to establish a model of isolated hepatic cholinergic denervation (IHCD), and to assess whether glycogen storage or the control of net hepatic glucose production (HGP) was altered by IHCD.

MATERIALS AND METHODS

Sprague-Dawley rats underwent either hepatic vagotomy or sham operation. Liver tissue was stained for vesicular acetylcholine transporter (VAChT) and (nonspecific neural) protein gene product 9. 5 (PGP) for verification of IHCD. Liver glycogen content was quantified in fed and fasted IHCD or sham-operated animals. HGP was determined after single-pass isolated liver perfusion, during which a 30-min 12 ng/ml glucagon infusion was begun after equilibration, and after 10 min, a 200 microU/ml insulin infusion was added.

RESULTS

Uniform staining of PGP and absence of VAChT staining in hepatic vagotomized rats demonstrated the validity of our model. Glycogen content of sham-operated livers (n = 8) increased from 6.0 +/- 1.7 in the fasting state to 10.6 +/- 1.8 mg/g liver, after feeding (P < 0.05). IHCD livers (n = 8) showed no comparable increase (3.5 +/- 0.6 to 4.0 +/- 0.7 mg/g liver). Perfusion with glucagon alone resulted in less HGP in IHCD livers (n = 12) compared with sham-operated livers (n = 10) (integrated HGP 3.3 +/- 0.3 mg/g liver min(-1) vs 5.1 +/- 0.5 mg/g liver min(-1), P < 0.05). Insulin infusion revealed impaired responsiveness to insulin after IHCD; the ratio of HGP in the final 10 min of perfusion (glucagon and insulin) to HGP in the initial 10 min (glucagon alone) was 90.3 +/- 2.4% for IHCD livers versus 68.1 +/- 4.4% for sham-operated controls, respectively (P = 0.0002).

CONCLUSIONS

Our study shows that IHCD results in significant impairment in liver glycogen storage and impaired hepatic sensitivity to glucagon and, possibly, to insulin. We conclude that hepatic cholinergic integrity is essential to normal hepatic glucose metabolism.