Evidence for priming and inhibitory effects of glucose on insulin secretion from isolated islets of Langerhans.

Biphasic insulin secretion from perifused rat islets of Langerhans was affected in three ways by the islet glucose environment prior to stimulation. (i) The secretory response to glucose was diminished if the basal concentration of glucose in the medium was reduced from 5.5 to 2.7 mmol/l for 2 h prior to stimulation. First phase secretion was affected more than the second. (ii) Secretion was potentiated if islets had been previously exposed to a stimulatory concentration of glucose of 22.2 mmol/l. Again first phase secretion was particularly affected and there was a positive correlation between the magnitude of the secretory response and the duration of the initial stimulus. (iii) In contrast, both phases of secretion were proportionately reduced if islets had been previously exposed to stimulatory concentrations of glucose of 8.3 mmol/l.