Abstract
In order to determine whether endogenous somatostatin has an inhibitory action on insulin and glucagon secretion, the isolated rat pancreas was perfused with 10Mm theophylline, which strongly stimulated somatostatin release, under pretreatment or simultaneous administration of 8.3, 16.7Mm glucose and 20Mm arginine with 4.4Mm glucose. 1) In the infusion of 10Mm theophylline with 8.3Mm glucose, the first phase at the time corresponding with that of insulin release elicited by 8.3Mm glucose alone was suppressed by endogenous somatostatin stimulated by theophylline. 2) During the infusion of 16.7Mm glucose for 35 min, 10Mm theophylline was interposed at from 15 to 25 min intervals. Its addition caused a rapid increase in somatostatin. Only at 15 min 30 sec and 16 min, insulin concentration went down and reached the levels of 70 and 74 per cent of the 15-min value, respectively. 3) During the infusion of 20Mm arginine with 4.4Mm glucose for 35 min, 10Mm theophylline was added to the perfusate from 15 to 25 min. The addition of theophylline caused an increase in somatostatin and decrease in glucagon. At 15 min 30 sec and 16 min, the levels of glucagon were 63 and 75 per cent of 15-min value, respectively. These results seem to support the idea that endogenous somatostatin suppresses glucose-induced insulin and arginine-induced glucagon secretion. However, the possibility of a direct effect of theophylline on the changes in insulin and glucagon secretion could not be excluded.
