Ca. Bernal et al., THE DURATION OF FEEDING ON A SUCROSE-RICH DIET DETERMINES VARIABLE IN-VITRO EFFECTS OF INSULIN AND FRUCTOSE ON RAT-LIVER TRIGLYCERIDE-METABOLISM, Journal of nutritional biochemistry, 6(8), 1995, pp. 422-430
The aim of the present study was to investigate under controlled condi
tions the in vitro metabolic effects of fructose and insulin on the tr
iglyceride formation by the isolated perfused livers obtained from hyp
ertriglyceridemic rats that had been fed a sucrose-rich diet for a lon
g-term (15 week) period as compared with those fed sucrose for a short
-term (3 week) period. Our findings indicate a significantly higher in
crease in triglyceride formation by perfused livers of rats fed the su
crose-rich diet for a long-term period in the presence of oleate as a
triglyceride-forming substrate (15 weeks, 6-fold increase; 3 weeks, 2-
fold increase). Though the contribution of net triglyceride secretion
to this increase in triglyceride formation was about twice as high at
both durations of feeding on a sucrose-rich diet, a strikingly elevate
d liver triglyceride accumulation was recorded for a long-term period
(15 week, 10-fold increase; 3 week, 4-fold increase). The addition of
fructose in the perfusate further increased the output of triglyceride
s from livers of animals fed the sucrose diet at both durations of fee
ding. Despite this finding, long-term sucrose led to even higher hepat
ic triglyceride storage under the present experimental conditions (mu
mol/liver at 15 week; 318.2 +/- 17.2 vs. 63.0 +/- 10.0 at 3 week; P <
0.001). Insulin in the presence of fructose promoted synthesis of live
r triglycerides at both durations of feeding an the sucrose-rich diet.
However, different insulin responses have been observed, showing an i
ncrease (3-fold) in triglyceride storage only in rats fed the sucrose
diet for 3 weeks and an inhibition (32%) on the net triglyceride outpu
t only in animals fed the sucrose diet for 15 weeks. Our findings indi
cate important differences in the in vitro effects of fructose and ins
ulin on hepatic triglyceride formation characterized by an imbalance b
etween secretion and storage depending on the duration of feeding on t
he sucrose-rich diet. Thus care should be taken when generalizing conc
lusions on the effects of nutrients or hormones in this nutritionally
induced hyperlipemic experimental animal model, since variable metabol
ic milieu may emerge at different durations of feeding on the diet.