Insulin-induced hypoglycemia stimulates both adrenaline and noradrenaline release from adrenal medulla in 21-day-old rats.

It has been well-established that insulin-induced hypoglycemia evokes preferential adrenaline release from the adrenal medulla in fasted adult rats. The present study examined the responsiveness to hypoglycemia in fasted 21-day-old and 8-week-old rats. The recovery of adrenaline in the chromaffin granule fraction prepared from the 8-week-old rat adrenal homogenate decreased 30 min after subcutaneous injection of 3 U/kg insulin, whereas the recovery of both adrenaline and noradrenaline was diminished in 21-day-old rats. In electron microscopy, omega-shaped profiles, indicative of exocytosis, were frequently observed in adrenaline- and noradrenaline-storing cells of 21-day-old rats. These results indicate that the responsiveness of the noradrenaline-storing cells to hypoglycemia in 21-day-old rats is different from that in young adult rats.