Cytophysiological studies on isolated pancreatic islets in vitro.

Single, isolated pancreatic islets of mice and rats were incubated for varying time intervals (0.5-60) minutes with high (300 mg%) and low (50 mg%) levels of glucose. The structural integrity of islets decreased progressively with time regardless of glucose concentration. Degeneration of islets was greatest after 60 minutes of incubation. The total amount of insulin released from cytologically intact mouse islets incubated with high glucose levels was always greater than that with low glucose except following 30 seconds of incubation when no difference was observed. Peaks of insulin secretion noted after 2 and 15 minutes of incubation were correlated with light microscopic and fine structural changes indicative of active secretion in beta-cells, i.e., degranulation, granule margination. At 5 and 30 minutes of incubation many beta-cells contained enlarged Golgi zones and abundant profiles of swollen rough endoplasmic reticulum containing pale, amorphous granular material presumably indicating insulin synthesis. Emphasis is placed on the desirability of correlating physiological and biochemical studies of isolated pancreatic islets with cytologic examination.