30 ORGAN CULTURE OF FETAL RAT PANCREAS: EFFECT OF CCK AND INSULIN ON AMYLASE ACTIVITY

Abstract

In fetal rats, just before birth, there is a dramatic increase in pancreatic amylase activity. Besides the well demonstrated role of corticosteroids in this process, in vivo studies have suggested that CCK, a trophic hormone for the pancreas in adult rats, might also be involved (Werlin, Biol Neonate 1983; 44: 287-94). Since in vivo studies cannot rule out an indirect maternal effect through corticosteroid secretion, we studied the direct effect of CCK on fetal rat pancreas in organ culture. Furthermore, the role of insulin, another important hormone for the exocrine pancreas in adult rats, was checked by using streptozotocin (STZ). Pancreata from 20 day-old rat fetuses were cultured in a serum-free medium (SFM) for 6 days, with or without dexamethasone 3.10−6M (DXM) and/ or CCK8 2.10−6M. In the presence of these two hormones, and with or without insulin (0.1 U/ml), cultures were exposed to STZ 10−7M for the first day of culture. Pancreatic explants were assayed for proteins and amylase on days 0, 2, 4, 6. Amylase specific activity (ASA) was expressed as percentage of day 0. With SFM alone, almost all the ASA disappeared by day 2 (17.7 % ± 12.5), but was partially but significantly maintained when CCK (48.6% ± 8.8) or DXM (47.9% ±14.4) was added. The DXM effect was significantly maintained for 6 days but not the CCK effect which lasted only 2 days. On day 2 of culture the latter was dose-dependent with a maximum occuring between 10 md 10−10M and was inhibited by asperlicin 10 μM. A combination of CCK and DXM gave the best results in maintenance of ASA (87.4 % ± 21.8 on day 2; 81.9% ± 15.9 on day 4; 62.2% ± 10.3 on day 6). When cultures in this optimal medium (CCK + DXM) were exposed to streptozotozin for the first day of culture, a significant decrease of the ASA was found on days 4 (63.2% ± 21)and 6 {47.6% ± 12.8). This difference was corrected when, in the same protocol, insulin was added for the complete time of culture. Conclusions: CCK, like DXM, is important in the prenatal development of the pancreas in the rat. Its action on ASA is different from and additive, but not synergistic, to that of DXM. The effect of STZ, corrected by insulin, suggests also a role for this hormone. The paracrine effect of insulin on exocrine pancreas, well demonstrated in the adult rat, might be already efficient in the fetus.