Effects of oral glucose administration on preproinsulin mRNA in rats in vivo.

An experiment was performed to examine whether the acute increase in insulin release induced by oral glucose ingestion is associated with alterations in pancreatic preproinsulin mRNA (PImRNA) levels. Rats either fed ad libitum or after overnight fast were used. Fasted rats were administered glucose orally in a conscious, unrestrained state. Pancreatic RNA was extracted and the relative level of PImRNA was determined by dot blot analysis with a cloned rat preproinsulin I cDNA probe. In fasted animals PImRNA levels decreased compared with those of fed animals and showed no significant changes after acute glucose administration, while blood glucose and plasma insulin increased rapidly to maximum values at 15 min after glucose administration. Although the transcription rate was not directly measured in this experiment, it is possible that the rapid increase in insulin release from the beta cell under physiological conditions is controlled by post-transcriptional regulations.