In vitro modulation of ornithine decarboxylase (ODC) activity by caerulein and cycloheximide in freshly prepared pancreatic acini

137 IN VITRO MODULATION OF ORNITHINE DECARBOXYLASE (ODC) ACTIVITY BY CAERULEIN AND CYCLOHEXIMIDE IN FRESHLY PREPARED PANCREATIC ACINI. Dub6 M, Morisset J. Centre de Recherche sur les M6canismes de S6cr6tion, Universit6 de Sherbrooke, Sherbrooke, QuEbec, Canada, J1K 2R1. Among the initial biochemical reactions involved in the initiation of pancreatic growth or are the induction of ODC mRNA expression and ODC activity. Such events were observed in vivo in normal pancreas, after caerulein-induced pancreatitis and in AR42J pancreatic tumor cells in response to the CCK agonist caerulein and the growth factors IGF-I, EGF and FGF. These same trophic agents are also associated with growth of acinar cells in monolayer culture but the induction of ODC activity has never been documented under these conditions. This study was performed to set up an ODC activity assay in freshly prepared pancreatic acini and evaluate its induction by caerulein. Results: We first looked at the effect of incubation time at 37°C; to our surprise, ODC activity was significantly increased after 1 (566%), 2 (2560%) and 3h (5914%) when compared to freshly prepared acini kept at room T °. These increases in ODC activity were not inhibited by cycloheximide 10 pM which inhibited protein synthesis by 60% but significantly increased by 364% and 278% above their respective controls after 2 and 3 h. A dose-response curve of caerulein (10 -12 -108M) indicates that 10-1° and 10 -~1 M caerulein increased ODC activity by 21% and 45% (significant) respectively after 2 h of incubation. At 10.8 M caerulein, ODC activity was significantly reduced by 76% below control value in parallel with a 63% decrease in protein synthesis. These data indicate for the first time in vitro that 1) increases in ODC activity are time and To-dependent and resistant to inhibition of protein synthesis and 2) caerulein can increase ODC activity in a very narrow range of concentrations 10-1~ -10-1° compatible with maximal secretion but not growth, 3) cycloheximide stimulate ODC through a mechanism distinct from its inhibitory effect on protein synthesis. Funded by NSERC Canada.

GASTRIN RELEASING PEPTIDE (GRP) HAS DIFFERENT EFFECTS ON HUMAN GASTRIC AND DUODENAL MUSCLE IN VITRO Dfiring B 1, Mandrek K 2, Lfidtke FE 1, Lepsien G 1, Golenhofen K 2. 1Dept of General Surgery, University of G6ttingen, W-3400 G6ttingen, FRG. 2Dept of Physiology, University of Marburg, W-3550 Marburg, FRG. Isolated muscle strips from human stomach and duodenum were investigated in conventional organ baths. Mechanical activity was measured under isometric conditions. Preparations were taken from the circular and longitudinal layers of fundus, corpus and antrum. Preparations from the duodenum (8-20 cm distal to the pylorus) were cut circularly or longitudinally. It has been reported that porcine GRP induced activation of gastric smooth muscle of rat and dog in vitro and influenced gastric emptying in cats and dogs. GRP-like immunoreactivity has also been described for the human stomach and duodenum with maximum values in the fundic muscle. Application of GRP (10 -9 to 10-7 mol/1) caused a concentration-dependent increase of the mechanical activity in all stomach strips, the height and the pattern of contraction was similar to the acetylcholine (ACh) responses (10 -7 to 10-5 mol/1). Longitudinally cut duodenal strips were also excitable by GRP. Circularly cut duodenal strips, however, showed no responses to GRP. Both layers were excitable by ACh. The most prominent effect of GRP on longitudinal duodenal strips near the jejunum was a tonically appearing activation, which could reach up to 150% of the maximum ACh(10 -6 mol/1)-induced activation. Only the smaller part of the tonic activity could be inhibited by nifedipine. The greater, nifedipine-resistant part could be suppressed by sodium nitroprusside or papaverine, i.e. it is a "specific tonic" contraction (K. Mandrek, K. Golenhofen, Prog. Clin. Biol. Res. 327 (1990) 463-481). GRP might play a role in the control of gastric emptying and duodenal transit.