The effect of oxytocin on the plasma glucagon response to insulin-induced hypoglycaemia in man

Abstract

The presence of the classical neurohypophyseal hormone oxytocin has recently been described in the human pancreas in considerably higher concentrations than those found in peripheral plasma. Evidence in animals and man suggests that oxytocin can directly stimulate the secretion of glucagon from pancreatic islets. In order to investigate a possible paracrine role for oxytocin in the regulation of glucagon secretion we have studied the effect of oxytocin on the plasma glucagon response to insulin-induced hypoglycaemia in 10 lean fasted male subjects. Intravenous insulin tests were performed in random order with or without oxytocin infusion (2 U bolus injection; 111 mU/min for 2 hours). Blood sugar nadir occurred at the onset of symptoms (time S) with no significant differences between oxytocin and saline infusions (saline S = 24 +/- 2.3 min; oxytocin S = 23.3 +/- 2.7 min). There was no significant change in peripheral plasma oxytocin concentrations during saline infusion. During the oxytocin infusion plasma oxytocin concentrations rose from 1.05 +/- 0.1 (mean +/- SEM) pmol/l to a peak of 632 +/- 179 pmol/l and remained elevated throughout the study. Peak plasma glucagon concentrations occurred at S + 10 mins with no significant differences in peak values (saline 200 +/- 26.3 pg/ml; oxytocin 207 +/- 23.6 pg/ml) between saline and oxytocin infusions. The data suggest that oxytocin at concentrations up to 6.3 X 10(-10) M has no effect on the decline or recovery of blood glucose concentrations or on the plasma glucagon response to insulin-induced hypoglycaemia.