Dynamics of somatostatin release from isolated rat pancreatic islets

1. Introduction Isolated islets of Langerhans release somatostatin in response to glucose [l] , CAMP [2] , Lu-ketoisocaproic acid, glucagon and theophylline [3]. The aim of the present study was to investigate the interactions that might exist between the secretion of somatostatin and insulin, i.e., a possible D-cell/B-cell interrelationship. A static incubation system, as previously used [l-3], is of limited help for this purpose because it does not give information on the dynamics of the respective release processes. Therefore, the kinetics of somatostatin and insulin release from isolated rat islets were investigated in a perifusion system. 2. Materials and methods Fed, male Wistar rats (220-270 g) were used throughout the study. Bovine serum albumin was purchased from Behringwerke A. G., Marburg, FRG; 12SI-labeled porcine insulin (spec. act. 1 SO-200 mCi/ mg) from Farbwerke Hoechst A. G., Frankfurt, FRG; crystalline rat insulin from Serono, Freiburg, FRG; collagenase from Worthington Biochemical Co., USA. Islets were isolated from rat pancreas by collagenase 2 h after intraperitoneal administration of 0.6 ml pilocarpine hydrochloride (2% w/v), as previously described [4,5] and perifused for 90 min with Krebs- Ringer bicarbonate buffer (0.2 mg/ml BSA; 1000 KIU/ml Trasylol @), 2 mM or 25 mM glucose with or without 5 mM theophylline, pH 7.4,37”C), 0.9 ml/min flow rate, 300 islets/perifusion [6] . All perifusions were preceded by a preperifusion period of 30 min with 2 mM glucose. Insulin release into the medium was determined