Portal and Peripheral Vein Immunoreactive Insulin Concentrations Before and After Glucose Infusion

Catheterization of the portal vein via the umbilical vein was performed under local anesthesia in twelve nondiabetic subjects prior to exploratory laporatomy for a variety of conditions. Immunoreactive insulin (IRI) in simultaneously obtained portal and peripheral vein plasma was determined before, during, and after a two-minute glucose infusion (25 gm.). Two phases of insulin secretion were apparent from portal vein IRI concentrations. A rapid secretory phase beginning one minute after start of the infusion and lasting three to four minutes was followed by a slower secretory phase beginning approximately ten minutes after start of the glucose infusion. The absolute amount of “big” insulin (proinsulin-like material) in the portal vein was similar during the first phase and the early part of the second phase of insulin secretion. A significant positive correlation between portal vein and peripheral vein IRI responses to glucose was noted.