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Secretion and Hepatic Extraction of Insulin in Nondiabetic, Obese, Aged Subjects
Author(s) -
BONORA ENZO,
COSCELLI CARLO,
BUTTURINI UGO
Publication year - 1983
Publication title -
journal of the american geriatrics society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.992
H-Index - 232
eISSN - 1532-5415
pISSN - 0002-8614
DOI - 10.1111/j.1532-5415.1983.tb05742.x
Subject(s) - insulin , medicine , endocrinology , c peptide , beta cell , peripheral , glucose tolerance test , pancreatic hormone , insulin resistance , catabolism , metabolism , islet
Considerable evidence suggests that glucose tolerance deteriorates with age, in spite of a generally normal insulin response to the oral glucose tolerance test (OGTT). However, several metabolic events besides pancreatic secretion are known to influence the peripheral insulin concentration. Thus, C‐peptide is considered a more reliable index of beta cell activity than insulin. Moreover, the simultaneous assay of C‐peptide and insulin in peripheral blood provides a noninvasive method to estimate the hepatic removal of insulin. In this study, insulin and C‐peptide responses to the OGTT were evaluated in a group of 12 nondiabetic, obese, aged subjects and in a group of 12 sex‐ and weight‐matched young controls. Compared with younger subjects, older subjects showed significantly higher glucose levels and incremental areas in spite of comparable concentrations of C‐peptide and insulin. Ratios of C‐peptide to insulin, both in the fasting state and after glucose load, did not differ in elderly and young subjects. The results suggest that the higher glucose levels in the aged are not due to decreased insulin secretion by the beta cell or to alterations in the hepatic catabolism of insulin. The discrepancy of normal insulin concentrations and elevated glucose levels may be interpreted as the result of an age‐related decrease in insulin sensitivity. However, the differences in glucose concentrations in old and young subjects also might be due to (1) an age‐related reduction in the size of those tissues that dispose of very large amounts of glucose or (2) an age‐related impairment in those gastrointestinal factors that promote the uptake of orally administered glucose by the liver.