Abstract
A study was made on the insulin secretion of the perfused rat pancreas in response to a slowly rising glucose concentration. The pancreas with the proximal portion of the duodenum was removed from male Wistar rats (250-300g) by the modified method of Grodsky. The perfusate was a Krebs Ringer bicarbonate buffer containing 4.5% dextran (MW 60, 000). The flow rate was adjusted to 2 ml per min and the buffer was equilibrated in a mixed gas of 95%02 and 5 % CO2. When the glucose solution (1000 mg/100 ml) was added to the fluid reservoir (B in figure) containing 60 ml of 50 mg/100 ml glucose at a constant rate of 2 ml per min, the glucose concentration in the medium increased at a rate of 20 mg/100 ml per min. Insulin response to the slow-rise stimulus of glucose was divided into two phases. During the early phase (0-5 mim) the insulin secretion rapidly increased and in the late phase (15-20 min) it reached approximately the maximal level. When alprenolol (1.25μg/min), one of beta adrenergic blocking agents, had been added to the perfusate, the early phase of insulin secretion was not suppressed, but the late phase tended to be inhibited. Phlorizin (100μg/min) having a competitive inhibition of glucose transport through the cell membrane suppressed the early phase of insulin secretion, although the late phase of insulin response increased in phloridin addition. 2-deoxy-Dglucose (100μg/min) suppressed both the early phase and the late phase of insulin secretion in response to the slowly rising rate of glucose. The substances which inhibit insulin secretion act upon different sites of glucose transport and metabolism. These substances were shown to affect different inhibitory insulin responses to the slow-rise stimulus of glucose. The present experimental methods were useful to analyse the mechanism of insulin secretion.
