Glutathione-mediated preservation and enhancement of isolated perifused islet function

It has been shown that myocardial tissue function may be better preserved if antioxidants are incorporated into the reoxygenation medium at the end of the ischemic period following isolation of the organ. Although isolated pancreatic islets are prone to ischemic-reperfusion injury, it is not clear if antioxidants have a role in the preservation of their function. The purpose of the present study, therefore, was to examine the effect of the addition of glutathione (GSH) to a physiologic incubation medium on pancreatic islet response to glucose stimulation. Islets isolated by microdissection were preperifused at the rate of 1 ml/min for 1 hr at 37 degrees C, with Krebs-Ringer bicarbonate (KRB) buffer containing 1% albumin, 5.5 mM (basal) glucose without (control) or with 10 mM glutamine or 10 mN GSH and maintained at pH 7.4 by continuous gassing with 95/5% O2/CO2. After preperifusion, basal effluent samples were taken on ice for 20 min. The perifusion was then continued for 20 min with the KRB containing 27.7 mM glucose alone, followed by another 20 min of basal glucose washout. Solutions were changed using a stopcock and all effluent perifusate samples obtained were stored frozen at -20 degrees C until radioimmunoassay for insulin. Total insulin output in the control group increased from a basal 11.45 +/- 3.18 to 29.23 +/- 7.08 ng/6 islets/20 min (P < 0.001, n = 5) when the glucose concentration was raised to 27.7 mM. During a 20-min washout, insulin secretion was still significantly raised and did not return to the prestimulation basal rate. In the glutamine-treated islets, insulin output increased from 7.23 +/- 0.94 to 16.83 +/- 2.25 ng/6 islets/20 min (P < 0.001, n = 5) with 27.7 mM glucose stimulation and the significantly raised washout basal rate of secretion did not return to the prestimulation level. GSH treatment not only caused an enhanced 27.7 mM glucose stimulation (8.46 +/- 1.99 to 38.72 +/- 11.51 ng/6 islets/20 min, P < 0.001, n = 6) of insulin output but also completely restored the basal rate of insulin secretion to the prestimulation level within the 20-min washout perifusion. In conclusion, these data show that incubation of isolated islets with GSH enhanced their secretory response to glucose stimulation and preserved their functional integrity.