Effect of glucose on insulin biosynthesis and beta cell ultrastructure in cultured fetal rat pancreas.

Pancreatic rudiments from 14-day fetal rats were cultured whole for 8 days in medium containing 5.5 or 16.5 mmol glucose/l (1G or 3G medium). Rudiments grown in 3G medium (3G cells) contained more DNA and insulin than those grown in 1G medium (1G cells) but there was no alteration in the insulin/DNA ratio or the fractional area of the rudiment occupied by insulin-containing cells. Morphometric analysis of ultrastructure revealed that the beta cells grown in 3G medium were smaller and had smaller nuclei than those grown in 1G medium. The size of exocrine cell nuclei in 1G or 3G medium was similar. Insulin granules occupied a greater proportion of the cytoplasmic volume in rudiments grown in 3G medium although the mean absolute volume of insulin granules per cell grown in 1G and 3G media was similar. Hence the residual cytoplasmic volume (cell--nucleus and granules) of 3G cells was less than that of 1G cells. Insulin granules from 3G cells had smaller granule sacs and cores than those from 1G cells. It is concluded that glucose stimulates the growth of rat fetal pancreas in vitro and has important effects on beta cell ultrastructure.