The Kinetics of Insulin, C-Peptide, and Proinsulin in Normal and Diabetic Man
The accurate measurement of pancreatic insulin secretory rates is the key for our understanding of the hormonal regulation of glucose and other nutrients as well as our insight into the pathophysiology of diabetes and obesity. Unfortunately, our ability to study insulin secretion in detail has been hampered by the fact that after its secretion into the portal vein, insulin first traverses the liver before reaching the peripheral circulation [1–4]. It is well known that approximately 50% of the insulin delivered to the liver is extracted on the first pass. Furthermore, it has been suggested that the extraction of insulin by the liver may be altered by oral glucose ingestion [1, 4, 5], increases in serum insulin concentrations [3, 6, 7], as well as by a variety of other physiological factors . It has also been suggested that changes in hepatic insulin extraction may occur in obesity, diabetes, and insulin-resistant states [9–12]. Thus, because of the anatomic relationship of the systemic circulation to the site of insulin delivery into the portal circulation, the peripheral insulin concentration more directly reflects posthepatic insulin delivery rather than the secretion rate of insulin.
KeywordsObesity Carbohydrate Glucagon Hypoglycemia Proinsulin
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