EFFECTS OF GLUCOSE AND AMINO-ACIDS ON INSULIN, GLUCAGON AND ZYMOGEN GRANULE SIZE OF FETAL RAT PANCREAS GROWN IN ORGAN-CULTURE

Foetal rat pancreatic rudiments explanted on day 14 of gestation were grown for 6 days in organ culture in medium containing glucose (5.5 (1G) or (16.5 (3G) mmol/l) and amino acids at the 'physiological' (1AA) or seven times the 'physiological' (7AA) concentration. Cultures were also performed in medium to which zinc sulphate had been added at 10-7 to 10-5 mol/l concentration. At the end of the period of culture the diameters of insulin, glucagon and zymogen granule profiles in the rudiments were compared with those in normal 20-day foetal pancreas by quantitative morphology. The β cell volume, the number of granules per β cell, the insulin granular volume fraction and the area of insulin granule core and halo were also measured under selected experimental conditions. Zymogen granule profiles were largest in vivo, intermediate in diameter when grown in 1G x 7AA medium and smallest in 1G x 1AA medium. The mean diameter of glucagon granule profiles remained constant for growth in vivo, in 1G x 1AA medium or in 1G x 7AA medium. Insulin granule profiles were largest in 1G x 7AA medium, smallest in 3G x 1AA medium and of intermediate diameter in vivo. Amino-acid enrichment increased the diameter of insulin granules and glucose enrichment decreased it. The addition of zinc to the culture medium had no effect on insulin granule diameter. In 1G x 7AA cultures the β cells were of similar size to those in vivo, but there were 29% fewer insulin granules per cell. The increased size of the insulin granules in 1G x 7AA cultures resulted in the insulin granule volume fraction in 1G x 7AA being 17.6 compared with 10.8% in vivo. Insulin granule cores were made larger by amino-acid enrichment of the culture medium but they were unaffected by glucose. The haloes were larger in 7AA medium and smaller in 3G medium. Glucose and amino-acid enrichment had a significant interaction on halo area, the mean area in 3G x 7AA medium being less than would have been expected from the summation of the effects of the two conditions.