Effect of phosphate omission on arginine-induced insulin and glucagon release by the isolated perfused rat pancreas

Relationships between energy level and insulin secretion in isolated rat islets of Langerhans. Manipulation of [ATP]/[ADP][Pi] by 2-deoxy-D-glucose

Perifusion of islets with nominally phosphate-free buffer containing increasing concentrations of 2-deoxy-D-glucose (2.5 to 10 mM) produced increments in high alpha-ketoisocaproic acid-induced secretion of insulin beyond those observed in the absence of the sugar analogue. 3-O-methyl-D-glucose, a poorly metabolized sugar, was without effect. Insulin release evoked by 40 mM KCl was not altered by 2-deoxyglucose. The concentration of intracellular inorganic phosphate was lower in islets perifused with 2-deoxyglucose and declined to a lower level after addition of 20 mM alpha-ketoisocaproic acid. The enhancement of alpha-ketoisocaproic acid-induced hormone secretion by 2-deoxyglucose was not seen in islets perifused with medium containing 1.5 mM phosphate; instead a small inhibition was observed. It is postulated that conditions which lower intracellular [Pi] facilitate, either directly or indirectly, hormone release although the mechanism of this effect remains to be elucidated.

Influence of inorganic phosphate on glucose-induced insulin release in vitro

The effect of various extracellular phosphate concentrations on glucose induced insulin secretion has been investigated in two experimental systems the isolated perfused rat pancreas and the isolated rat pancreatic islets incubated in vitro. In both systems, total insulin secretion in response to 16.7 mmol/l glucose increased as extracellular phosphate concentration increased from 0 to 3.6 mmol/l. In perfusion experiments insulin secretion was significantly reduced at 4.8 mmol/l phosphate. In incubation experiments insulin secretion was inhibited only at 9.6 mmol/l phosphate concentration. When IBMX 1 mmol/l was used in incubation experiments glucose induced insulin secretion increased as extracellular phosphate increased from 0 to 3.6 mmol/l, but was also inhibited at 4.8 mmol/l.

Effect of phosphate omission on the glucose-induced insulin release in vitro in fed and fasted rats

Isolated perfused rat pancreases from fed and 20-h fasted rats were used to investigate the effect of phosphate omission on the insulin response to 16.7 mmol/l glucose. The insulin response to continuous glucose stimulation was biphasic. Both phases were significantly reduced when pancreases were perfused in the absence of extracellular phosphate in fasted, but not in fed rats.

Effect of phosphate on the arginine-induced insulin release by the isolated perfused rat pancreas

The isolated perfused rat pancreas was used to investigate the effect of extracellular phosphate on the arginine-induced insulin release. In the absence of any metabolic substrate, the insulin response to arginine was monophasic. In the absence of phosphate in the medium, the insulin release as unaffected until the 15th minute of the stimulation period, but was significantly augmented from that time onward. In the presence of oleic acid in the perfusate, the insulin response to arginine was also monophasic but occurred earlier than in controls. In this conditin, phosphate omission resulted in an increase of the insulin response to arginine from the 3rd minute of the stimulatory period onward. In the presence of glucose 5.5 mM in the medium the insulin response to argnine was biphasic and was not affected by extracellular phosphate omission.

Effect of phosphate omission on glucose-induced insulin release in vitro

In the isolated perfused rat pancreas, omission of extracellular phosphate (H2PO-4) significantly reduces the insulin secretion in response to 16.7 mM glucose.