No abstract

The polyamines have been under active investigation for nearly three decades. There is a great deal of evidence that they play an important role in gastrointestinal mucosal growth, but the mechanisms through which this role is carried out are still not fully explained. This review examines the role of the polyamines in the regulation of mucosal growth, the control of intracellular polyamine levels, the biosynthesis of the polyamines, and some known mechanisms of their action. Finally, we propose a model of polyamine action that reconciles the effects of various trophic agents and situations in which growth is stimulated along with concomitant changes in polyamine levels. It accounts for both humoral and gradient-oriented features of various adaptive responses of the gastrointestinal mucosa and is intended to provide a framework for the future investigation of the role of the polyamines in this tissue.

Direct exposure of small intestinal mucosal cells to luminal polyamines stimulates proliferation. This study tests the hypothesis that the protooncogenes c-fos, c-myc, c-jun, and junB are involved in the mechanism by which polyamines modulate mucosal growth. Studies were conducted in the IEC-6 cell line, derived from rat small intestinal crypt cells. Cells were grown in Dulbecco's minimal essential medium containing 5% dialyzed fetal bovine serum (dFBS) in the presence of absence of alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase, which is the rate-limiting enzyme for polyamine synthesis. Cellular polyamine levels, cell growth, and relative abundance of c-fos, c-myc, c-jun, and junB mRNAs, were measured at 1, 2, 4, 6, 8, and 12 days after initial plating. The intracellular polyamines, spermidine and spermine, and their precursor, putrescine, in DFMO-treated cells decreased significantly at 2 days and remained depleted thereafter. Although DFMO profoundly decreased growth and final cell number, both control and DFMO-treated cells entered a plateau phase by 6 days. In control cells, c-myc and c-jun mRNA levels significantly increased on days 4-6 and then returned to a basal level of expression, which was maintained thereafter. c-fos mRNA in quiescent cells after 24 h serum deprivation was significantly stimulated by 5% dFBS, although a steady-state level of c-fos mRNA was undetectable in control cells. Treatment with DFMO not only prevented increased expression of c-myc and c-jun protooncogenes at 4 days, but also significantly reduced steady-state levels of c-myc and c-jun mRNA between 6 and 12 days.(ABSTRACT TRUNCATED AT 250 WORDS)

We determined the development of the oxyntic gland mucosal gastrin receptor in rats killed at various times from 5 to 60 days after birth. Rats were weaned on the 18th day after birth. Newborn animals had no detectable gastrin binding, high serum gastrin levels (800-1,200 pg/ml), low antral gastrin levels (0.5-2.0 micrograms/g tissue), or high pH of gastric contents (pH greater than 5.0) and did not respond to pentagastrin. At the time of weaning, serum gastrin dropped to 600 pg/ml and reached adult levels (300 pg/ml) on day 40. Antral gastrin increased to 7.5 micrograms/g tissue on day 20 and reached adult levels (20 micrograms/g tissue) on day 22. Specific binding of gastrin was first detected on day 20 and reached the adult level of 4 fmol/mg protein on day 60. Pentagastrin significantly stimulated acid secretion on day 20 and DNA synthesis on day 25. Prevention of weaning through day 25 decreased the magnitude but did not prevent or delay the onset of the above changes. These results indicate that 1) the absence of a gastrin response in newborn rats is due to a lack of gastrin receptors, 2) development of gastrin receptor and biological sensitivity to gastrin appear at the time of weaning, and 3) the development that occurs with weaning is enhanced but not triggered by the shift to solid food.

Purpose: Exercise is becoming readily accepted as a beneficial adjunct therapy to maintain or enhance quality of life in breast cancer patients undergoing adjuvant chemotherapy. An essential precursor to these studies is to investigate whether exercise modulates the antitumor efficacy of chemotherapeutic agents. Experimental Design: Athymic female mice were transplanted with MDA-MB-231 breast xenografts and randomly assigned to one of four groups (n = 21 per group): (a) control, (b) exercise-only, (c) doxorubicin-only, or (d) exercise + doxorubicin. Exercise groups performed progressive treadmill running up to 18 m/min at 0% grade for 45 minutes, 5 d/wk for 8 weeks.Results: Tumor growth delay was significantly longer in the doxorubicin-only and exercise + doxorubicin groups compared with the control (median 42 versus 25 days, P = 0.0082; 36 versus 25 days, P = 0.029, respectively) and exercise-only groups (median 42 versus 25 days, P = 0.029; 36 versus 25 days, P = 0.080, respectively). There was no significant difference between the doxorubicin-only and exercise + doxorubicin groups (median 42 versus 36 days, P = 0.33), suggesting that moderate intensity exercise does not significantly influence doxorubicininduced tumor growth delay. Conclusion:These studies are essential to fully understand the safety and application of exercise as a supportive intervention in cancer control.

Epidermal growth factor (EGF) inhibits gastric acid secretion, but its effects on the growth of gut mucosa have not been examined. Fasted male rats were given six injections of EGF (10 micrograms/kg) over a 48-h period. The animals were killed and the incorporation of [3H]thymidine into various tissues was examined and compared to rats treated with NaCl, pentagastrin, and EGF plus secretin. EGF and pentagastrin significantly increased DNA synthesis of the oxyntic gland mucosa. Pentagastrin, but not EGF, stimulated DNA synthesis of duodenal and colonic mucosa as well. Neither peptide altered skin DNA synthesis. Secretin inhibited the effects of pentagastrin but not EGF. Chronic administration of EGF (5 days) caused significant increases in oxyntic gland mucosal DNA, RNA, and protein content. These results not only demonstrate that EGF is a trophic agent for the oxyntic gland mucosa but lend further support to the hypothesis that acid secretion and mitogenesis are the result of two separate mechanisms.

The trophic effects of the hormone gastrin-17 were examined on a human colon cancer cell line. LoVo cells were obtained from the American Type Culture Collection and grown in minimal essential medium in the presence of 10% bovine fetal serum. To demonstrate the trophic effect of gastrin, synchronization was necessary. The effect of gastrin was optimal after 26-h exposure to 0.6 mM thymidine. In the presence of serum the optimal dose of gastrin for stimulation of DNA synthesis was 7.2 X 10(-10) M. Under these conditions gastrin caused a 220% increase in [3H]thymidine incorporation. In the absence of serum the optimal dose of gastrin (3.6 X 10(-9) M) increased DNA synthesis approximately 200%. Twenty-four hours after gastrin treatment (1.8 X 10(-10) M gastrin 17) cell numbers increased 50.8% compared with control. At 48 h this increase was maintained at 44%. Maximum stimulation by gastrin occurred 7-8 h after release from synchronization and exposure to gastrin. This corresponded to the S phase of the cell cycle. Significant stimulation occurred a second time at 22-24 h, presumably during the second S phase in a still synchronous or partially synchronous cell population. These data demonstrate that physiological concentrations of gastrin-17 can stimulate the growth of a human cancer cell line and that some degree of synchronization may be necessary to demonstrate similar effects in other cell lines. Such cell lines may provide a source of rapidly growing cells in which the mechanisms of the trophic effect of gastrin can be examined.

Polyamines are necessary for the growth of eukaryotic cells and are supplied either by new synthesis or cellular uptake. To our knowledge, no information is available on polyamine uptake by gastrointestinal cells. In the current study, isolated villous enterocytes from the rat accumulated putrescine to an eightfold concentration gradient. Uptake was temperature dependent, saturable, and inhibited by 1 mM KCN. Kinetic analysis showed a Km of 1.23 X 10(-5) M and a Vmax of 2.60 X 10(-10) mol.10(6) cells-1.15 min-1. Enterocytes from the distal one-fourth of the gut showed the highest rate of uptake. Putrescine uptake was inhibited by cadaverine and spermine but not by the amino acids asparagine, AIB, or leucine. Sodium replacement by choline, lithium, N-methyl-D-glucamine, or tetramethylammonium significantly inhibited uptake, but replacement of Na+ by sucrose or mannitol was without effect. The inhibition observed was believed to be due to the ability of the cations to interact in some way with the carrier. Neither ouabain nor digitoxigenin had any effect on uptake. These data indicate that putrescine is accumulated by villous enterocytes by a carrier-mediated process that does not appear to involve Na+ contransport.