IN-VITRO REGULATION OF INSULIN RELEASE AND BIOSYNTHESIS OF FETAL-RAT PANCREATIC-CELLS EXPLANTED ON PREGNANCY DAY 16

Although the morphological development of the fetal pancreatic B cell has been studied in considerable detail, knowledge about the functiona l maturation, particularly in early stages of development, is still po or. The present paper describes a method for monolayer culture of feta l rat islet cells which allows a study of the regulation of insulin bi osynthesis, release and content during critical stages of embryonic an d fetal development. Suspensions of pancreatic cells were prepared fro m rat fetuses on pregnancy day 16 and cultured for 3 days. During the initial 2 days cultures were performed in the presence of 5 or 15 mmol /l glucose. During this initial period culture at 5 mmol/l glucose was carried out in the presence or absence of either 10 mmol/l nicotinami de (NA) or 5 or 100 ng/ml nerve growth factor (NGF). After changing th e media the cells were further exposed for 24 h to either 5 or 15 mmol /l glucose or 15 mmol/l glucose plus 5 mmol/l theophylline before meas uring the insulin concentration in the culture medium. Cells that had initially been cultured for 2 days in 5 mmol/l glucose showed an incre ased insulin release, when subsequently cultured in 15 mmol/l glucose for 24h. Theophylline potentiated the response and caused a decrease i n cellular insulin content. Cells initially cultured in the presence o f 15 mmol/l glucose showed unchanged insulin release during the subseq uent 24-hour exposure to 15 mmol/l glucose, irrespective of the presen ce or absence of theophylline. The presence of NGF (100 ng/ml) during the initial 2-day culture period increased the insulin release in the presence of 15 mmol/l glucose and theophylline during the subsequent 2 4-hour culture period as compared to cells cultured in the absence of NGF. When cells were first exposed to either NA or NGF followed by exp osure to 5 mmol/l glucose alone in the last, 24-hour culture period, t here was an increased insulin content. Rates of insulin biosynthesis s is remained unchanged irrespective of the glucose concentration in the culture medium. It is concluded that, already in early fetal developm ent, B cells show glucose stimulation of insulin release albeit less p ronounced than in the postnatal state.