Summary
We have previously suggested that mechanisms other than reduced lipoprotein lipase
(LPL) activity might contribute to the defect in plasma removal of very low density
lipoprotein (VLDL)-triglyceride (TG) observed in insulin-deficient rats. To further
evaluate this phenomenon, removal rates of TG in nonfractionated plasma, as well as
in isolated lipoprotein fractions obtained from insulin-deficient and control rats,
were compared in a new, sensitive in vivo bioassay system (estradiol-treated male rats with a consistently low endogenous VLDL-TG
pool). Removal of TG in nonfractionated plasma from insulin-deficient rats was slower
than that of control rats: 3.0 ± 0.3 vs 1.6 ± 0.2 min (P < 0.001). No difference was
found in removal rate of isolated VLDL-TG (2.5 ± 0.3 vs 2.6 ± 0.4 min), or in removal
rates of TG carried in other lipoprotein fractions. We next determined the effect
of injection into normal rats of aliquots of dialyzed lipoprotein-free (D > 1.215)
plasma from insulin-deficient and control rats on the removal rate of normal VLDL-TG,
and found that lipoprotein-free plasma from insulin-deficient rats significantly (P
< 0.01) prolonged removal of normal VLDL-TG (4.3 ± 0.4 to 6.8 ± 0.7 min). This same
fraction did not interfere with the in vitro hydrolysis of normal VLDL-TG by postheparin LPL. Thus, a factor in the D > 1.215
plasma fraction of insulin-deficient rats is present which interferes with the rate
of removal of TG from plasma, unrelated to inhibition of LPL activity.
Key-Words:
Experimental Insulin Deficiency
-
Very Low
-
Density Triglycerides
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Rat Plasma
