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Basic fibroblast growth factor (bFGF) is a potent mitogen for various cell types. Induction of ornithine decarboxylase (ODC) activity is one of the early events triggered in proliferating cells. Our aim was to study the effect of bFGF on ODC activity and ODC mRNA expression in a pancreatic tumoral cell line, AR4-2J. Following kinetic and dose-response studies, we found that maximal stimulation (150 over control) of ODC activity occurred after 3 h of bFGF treatment (10−9M), the EC, being 20 p M.To elucidate the mechanism by which bFGF stimulates ODC activity, we measured the ODC mRNA levels by Northern blot hybridization using a 32P-labeled rat cDNA probe. In AR4-2J cells treated with bFGF at 10−9Mover 120 min, ODC mRNA expression was transiently increased by 71.6 at 60 min. Furthermore, bFGF was also able to stimulate ODC mRNA synthesis in the presence of cycloheximide. In conclusion, in AR4-2J cells of pancreatic origin, bFGF stimulates ODC gene transcription. This effect contributes to the stimulation of ODC enzymatic activity and to the proliferative effect of bFGF on this cell line.

Polyamines are polycationic molecules essential for cell growth and differentiation. Recent work has focused on cell polyamine-transport systems as a way to regulate intracellular polyamine levels. In this study, we demonstrate the presence of two different active transporters for putrescine and spermidine in a rat tumoral cell line (AR4-2J). The first has a Km of 3.1 microM and a Vmax of 3.7 pmol/15 min per micrograms of DNA for putrescine and the second a Km of 0.42 microM and a Vmax of 4.7 pmol/15 min per micrograms of DNA for spermidine. Competition studies performed between the polyamines confirm the difference between these two carriers; one has an equal affinity for the three main polyamines, and the other has a lower affinity for putrescine. Amino acids do not share this transport system, which is Na(+)-independent. Choline chloride inhibits selectively and in a dose-responsive manner the uptake of putrescine without affecting that of spermidine. These data demonstrate that AR4-2J cells possess two polyamine transporters; one is specific for aminopropyl groups (spermidine and spermine), and the other is choline-sensitive, but cannot discriminate between aminobutyl (putrescine) and aminopropyl groups.

A technique for preparing a suspension of dispersed functional acini from human pancreas has been developed. The changes in pancreatic enzyme secretion and accumulation of cellular cyclic AMP caused by various secretagogues have been studied. Ca2-mobilizing agents stimulated amylase release from human pancreatic acini. The relative potencies with which secretagogues increased amylase release were as follows: gastrin-releasing pep-tide's potency (Ec50, 0.1 ± 0.01 nM) was greater than bombesin 14's (Ec50, 0.2 ± 0.01 nM), which was greater than litorin's (Ec50, 0.6 ± 0.18 nM), which was greater than bombesin 9's (Ec50, 6 ± 0.1 nM). For CCK-peptides, the relative potencies were as follows: CCK-39's potency (Ec, 0.28 ± 0.15 pM) was equal to cerulein's (Ec50, 0.3 ± 0.07 μM). Both of these potencies were greater than CCK-8's (Ec50, 1.6 ± 0.1 pM), which was greater than that of CCK-4. Carbamyl choline was poorly potent (Ec50, >1 mM). The 12-0-tetradecanoyl-phorbol-13-acetate (TPA) was active from 0.1 nM to 0.1 μM. Neither secretin nor VIP increased amylase release from human pancreatic acini but they did cause an accumulation of cellular cyclic AMP, secretin (Ec50, 0.5 ± 0.2 nM) being more potent than VIP.