Measuring the balance between insulin synthesis and insulin release

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Abstract

The absolute rates of hormone synthesis and release were determined in purified pancreatic B cells. Newly synthesized proteins were labeled with L-[3,5-3H]tyrosine or L-[2,5-3H]histidine. When medium glucose was ≤ 10 mM, the production of insulin exceeded or equaled its release. Raising the glucose levels above 10 mM did not further increase the rate of insulin synthesis (67±10 fmol/103 cells/2 hour) but elevated that of insulin release up to 3-fold the production rates (181±10 fmol/103 cells/2 hour). In the presence of glucagon or of the phorbol ester 12-O-tetradecanoylphorbol 13-acetate the cells also released 3-fold more hormone that they synthesized; release was however reduced to 25% of the rate of production in the presence of epinephrine. It is concluded that glucose as well as hormonal regulators of islet B cells can influence, bi-directionally, the balance between the rates of insulin synthesis and release.

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