BACKGROUND
It is well known that the concentration of serum proinsulin and the ratio of proinsulin/total insulin (P/I) are elevated in type 2 diabetes. Proinsulin is produced by the ribosome in pancreatic beta cells, undergoes maturation in Golgi body and exists in the form of secretory granules. Immature granules possess disproportionately large amount of proinsulin. When there is increased demand of insulin caused by diabetes, higher level of proinsulin is secreted from immature granules of dysfunctioning beta cells. Thus, the elevated concentration of proinsulin and the increased ratio of P/I are considered to be the markers of pancreatic dysfunction and predictors for the future development of diabetes. The elderly-onset type 2 diabetes is also thought to develop due to both dysfunction of insulin secretion by impaired beta cell with aging and increased insulin resistance in peripheral tissue due to less muscle mass and more fat. However, it is still controversial as to which mechanism is predominant in the development of type 2 diabetes. METHODS: We measured the levels of fasting blood glucose, serum proinsulin and specific human insulin by using radioimmunoassay kit, and calculated the P/I ratio and insulin sensitivity index in normal adults (40