A possible role for insulin in the altered capability for hepatic enzyme adaptation during aging.

The pattern of change in the concentration of immunoreactive insulin in portal vein blood during a 7-hour period following intragastric administration of glucose to fasted, male Sprague-Dawley rats is modified both in magnitude and time course of response as rat age increases from 2- to 24-months. This alteration in the control of insulin levels probably is not the consequence of modifications in the availability of administered glucose to the pancreas. A similar modification in the control of insulin secretion also is evident when pancreatic islets isolated from fasted rat donors aged 2- to 24-months are perifused with glucose in vitro. This may represent the first demonstration of an altered response of aging animals which is expressed in the same way in an isolated in vitro system.