Abstract
The role of the liver in the regulation of systemic insulin levels is not well understood.
The reported extraction rates vary between 0 to 85%, and extraction of a constant
fraction of 50% of the portally delivered insulin is generally assumed. In the present
study, we have investigated the role of the liver in the regulation of systemic insulin
levels in the normal rat. Insulin was infused into the portal vein of conscious and
freely moving rats in doses of 20, 40, 80 pmol/min during 15 min to mimic the gradual
release of insulin by the native endocrine rat pancreas. The profiles of plasma insulin
and glucose levels in the systemic circulation were compared to those obtained after
direct infusion into the systemic circulation. The effect of intraportal and direct
systemic infusion on plasma insulin and blood glucose levels were virtually similar
where 20 pmol/min was applied. But, these effects were different if the dose was 40
pmol/min, and this difference increased when the dose was increased to 80 pmol/min,
since hypoglycemia was less severe and normoglycemia was restored more rapidly with
portal than with systemic infusion. Thus, our results show that the fraction of intraportally
infused insulin reaching the systemic circulation decreases with higher doses of insulin.
This suggests that the liver contains adaptable mechanisms to reduce the systemic
insulin levels.
Key words
Portal Insulin - Systemic Insulin - Extraction - Liver - Pancreas
