Secretory activity and trophic effects of epidermal growth factor in the rat pancreas

Intravenously administered human epidermal growth factor in the rat. Biliary excretion and influences on pancreatic secretion

BACKGROUND/AIM

Epidermal growth factor (EGF) is known to exert mitogenic effects in different tissues, including the digestive tract and pancreas. EGF is also found in high concentrations in pancreas. Infusion of human EGF has been shown to induce proliferation of cells in exocrine pancreas, and to increase the thickness of the small intestine. The aim of this study was to investigate the influence of intravenously administered human EGF on pancreatic and biliary secretions in the rat.

MATERIALS AND METHODS

Rats were fasted overnight and were given human EGF intravenously, either as a bolus dose of 5 microg or as a continuous infusion in increasing doses from 0.5 to 10 microg/h. Bile and pancreatic juice were either collected together or separately. The concentration of human EGF in bile and pancreatic juice was measured.

RESULTS

After a bolus dose of EGF increased bile/pancreatic secretion was seen after 60 and 90 min when the bile and pancreatic secretions were not separated. Continuous infusion of EGF increased the joint secretion rate of bile and pancreatic juice in a dose-dependent manner. No effect on secretion rate was seen when bile and pancreatic juice were collected separately. After intravenous infusion of human EGF a 1,000-fold increase of human EGF excretion was found in bile but not in pancreatic juice.

CONCLUSION

Intravenously administered human EGF was excreted in high concentrations in bile and increased the secretion rate of pancreatic juice when collected together with bile. The results suggest that EGF, at least partly, exerts its effect on the pancreas and the proximal gastrointestinal tract after excretion with bile and stimulates pancreatic secretion via this route.

Effect of sodium nitroprusside and 8-bromo cyclic GMP on nerve-mediated and acetylcholine-evoked secretory responses in the rat pancreas

The effects of sodium nitroprusside (SNP) and 8-bromo-guanosine 3'5' cyclic monophosphate (8-Br-cyclic GMP) on nerve-mediated and acetylcholine (ACh)-evoked amylase secretion, tritiated choline ([3H]-choline) release and on intracellular free calcium concentration ([Ca2+]i) in the isolated rat pancreas were investigated. Electrical field stimulation (EFS; 10 Hz) and ACh (1 x 10(-5) M) caused large increases in amylase output from pancreatic segments. The response to ACh was blocked by atropine (1 x 10(-5) M) whereas the EFS-evoked response was markedly reduced but not abolished. In contrast, pretreatment with tetrodotoxin (1 x 10(-6) M) abolished the secretory effect of EFS. Either SNP (1 x 10(-3) M) or 8-Br-cyclic GMP (1 x 10(-4) M) inhibited amylase secretion compared to basal. Combining either SNP or 8-Br-cyclic GMP with EFS resulted in a marked decrease in amylase output compared to EFS alone. In contrast, either SNP or 8-Br-cyclic GMP had no significant effect on the amylase response to ACh. When extracellular Ca2+ concentration ([Ca2+]o) was elevated from 2.56 mM to 5.12 mM, SNP failed to inhibit the response to EFS. EFS stimulated the release of 3H from pancreatic segments preloaded with [3H]-choline. Either SNP or 8-Br-cyclic GMP had no effect on basal 3H release but significantly reduced the EFS-evoked response. In fura-2 loaded acinar cells, SNP elicited a small decrease in [Ca2+]i compared to basal and had no effect on the ACh-induced [Ca2+]i peak response. Nitric oxide may modulate the release of endogenous neural ACh in response to EFS in the rat pancreas.

Effects of epidermal growth factor (EGF) on fetal islet B cells in vitro

ABSTRACT. It has been reported that when the rat fetus is treated with streptozotocin (STZ) in vivo, islet B cells are destroyed but later recover. To investigate the process of the recovery of B cells after in vitro treatment of the fetal pancreas with STZ and the role of epidermal growth factor (EGF) in the recovery of B cells, we measured the level of insulin released from the cultured fetal pancreas and examined it histologically. As a result, we immunohistologically confirmed the regeneration of B cells in the pancreas that had been cultured for 48 hr after destruction of islet B cells by STZ treatment. An immunohistologic study using proliferating cell nuclear antigen (PCNA) showed that without the addition of EGF, the cell division index was significantly higher in the STZ-treated group (STZ group) than in the untreated group (intact group), whereas with the addition of EGF, the cell division index increased in both groups, but EGF did not have a significant cell division-promoting effect on the pancreas in the STZ group. The addition of EGF caused a significant decrease in the concentration of insulin in culture medium in both groups. These results indicate that EGF has a cell growth-promoting effect on intact fetal pancreas in vitro but has the effect of inhibiting the release of insulin, and thus suggest that EGF does not trigger the regeneration of islet B cells.

Effects of epidermal growth factor on neonatal pancreatic growth in the guinea pig

CONCLUSION

EGF and/or transforming growth factor-alpha (TGF-alpha) are likely to be important in the rapid pancreatic growth that occurs in the neonatal guinea pig.

BACKGROUND

Rapid pancreatic growth is observed during the neonatal period in the guinea pig. The growth factors that are involved are not known but may include members of the EGF family.

METHODS

Mini-osmotic pumps were implanted on the day of birth for continuous infusion of EGF (30 microgram/d). Pancreatic DNA, RNA, and protein contents were determined at 4 and 15 d, along with wet weights of the pancreas, duodenum, jejunoileum, colon, and gallbladder. Pancreatic EGF and TGF-alpha concentrations were measured in adult controls, in control neonates at 1, 4, 8, and 15 d, and also at 4 and 15 in guinea pigs receiving either EGF or the cholecystokinin receptor antagonist devazepide (25 nmol/kg/h).

RESULTS

EGF infusion significantly increased the weight of the stomach and duodenum at 4 d and all the gastrointestinal organs, including the pancreas, at 15 d. Exogenous EGF increased pancreatic DNA, RNA, and protein content at 4 and 15 d. Endogenous EGF and TGF-alpha concentrations in the pancreas were significantly higher at birth than in adults (P < 0.001) and P < 0.01, respectively) and declined during the first 2 wk postpartum. At 15 d, EGF concentrations remained significantly higher than adult levels (P < 0.01), but TGF-alpha concentrations had declined to adult values. Infusion of EGF decreased concentrations of endogenous EGF in the pancreas at 4 and 15 d (both P < 0.05) and decreased TGF-alpha concentrations at 4 d (P < 0.001). Devazepide infusion caused a significant decrease in endogenous pancreatic EGF concentrations at 15 d (P < 0.05).

Effect of basic fibroblast growth factor on cholecystokinin-induced amylase release and intracellular calcium increase in male rat pancreatic acinar cells

Isolated rat pancreatic acinar cells were used to investigate the effect of basic fibroblast growth factor (bFGF) on both amylase secretion and intracellular free calcium concentration ([Ca2+]i) in response to the calcium-mobilizing secretagogue cholecystokinin-octapeptide (CCK-8). Our data show that bFGF inhibited CCK-8-induced amylase release in a concentration-dependent manner and decreased the CCK-8-induced rise in [Ca2+]i. This inhibitory effect of bFGF on both amylase secretion and [Ca2+]i increase in response to CCK-8 was reverted when acinar cells were pretreated with 100 microM tyrphostin A25, a tyrosine kinase inhibitor. Tyrphostin A25 also inhibited Ca2+ influx induced by CCK-8. These results show that bFGF inhibits CCK-8-induced pancreatic response by a tyrosine kinase-dependent mechanism. A role for tyrosine phosphorylation in capacitative Ca2+ entry is suggested.