Chronic pancreatitis (CP) is associated with impaired glucose tolerance and
with reduced hepatic sensitivity to insulin. We have previously shown that
in normal and sham operated rats, insulin suppresses hepatic glucose produ
ction, and this suppression is associated with a decrease in the hepatocyte
plasma membrane-bound quantity of the facilitative glucose transport prote
in GLUT2. The insulin-mediated reduction in membrane-bound GLUT2 is impaire
d in CP, and may play a role in the glucose intolerance associated with CP.
To determine whether GLUT2 is actively internalized and whether this mecha
nism is disordered in CP, livers from fed and fasting rats in whom CP had b
een induced 2-3 months earlier by pancreatic duct oleic acid infusion, and
in sham-operated (sham) rats, were fractionated to yield endosome (E)- and
plasma membrane (PM)-enriched fractions. Forty-five minutes after duodenal
intubation alone (fasting) or intubation plus duodenal feeding, livers were
removed, homogenized and ultracentrifuged, and microsomal pellets were sep
arated by sucrose density gradient ultracentrifugation. GLUT2 content of fr
actions was determined by Western blotting and scanning densitometry. The E
:PM ratio of GLUT2 increased from 0.68 +/- 0.11 (mean +/- SEM) in fasting s
ham livers (n = 8) to 1.04 +/- 0.09 in fed sham livers (n = 8; p < 0.05). H
owever, there was no change in the E:PM ratio of GLUT2 in CP livers after d
uodenal feeding (0.90 +/- 0.12 vs, 0.86 +/- 0.10; 12 = 8,8; p = NS). To tes
t our findings using confocal laser scanning microscopy, liver specimens fr
om fed and fasting CP and sham rats were minced, fixed in 4% paraformaldehy
de, sectioned, and stained with rabbit anti-rat GLUT2 antibody followed by
rhodamine-labeled secondary antibody. GLUT2 was quantified by mean pixel in
tensity in an 8 x 16-pixel area of PM and a 16 x 16-pixel area of cytosol (
CYT) in each of 30 random cells/field (400x) in each of three rats per grou
p. As in the fractionation study, duodenal feedings increased the CYT:PM ra
tio of GLUT2 from 0.75 +/- 0.01 in fasting sham liver to 0.86 +/- 0.01 in f
ed sham liver (p < 0.0001), while the CYT:PM ratio in CP remained unchanged
. We conclude that feeding induces a shift in GLUT2 from the plasma membran
e to the endosomal pool. The feeding-induced internalization of GLUT2 is ab
sent in livers from rats with CP and may play a role in the glucose intoler
ance associated with CP.