Our previous studies had suggested a link between bile salt stimulation of colonic epithelial proliferation and the release and oxygenation of arachidonate via the lipoxygenase pathway. In the present study, we examined the role of reactive oxygen versus end products of arachidonate metabolism via the cyclooxygenase and lipoxygenase pathways in bile salt stimulation of rat colonic epithelial proliferation. Intracolonic instillation of 5 mM deoxycholate increased mucosal ornithine decarboxylase activity and MIHthymidine incorporation into DNA. Responses to deoxycholate were abolished by the superoxide dismutase mimetic Cull (3,5 diisopropylsalicylic acid)2 (CuDIPS), and by phenidone or esculetin, which inhibit both lipoxygenase and cyclooxygenase activities. By contrast, indomethacin potentiated the response. Phenidone and esculetin suppressed deoxycholate-induced increases in prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and 5,12, and 15-hydroxyeicosatetraenoic acid (HETE), whereas CuDIPS had no effect. Indomethacin suppressed only PGE2. Deoxycholate (0.5-5 mM) increased superoxide dismutase sensitive chemiluminescence 2-10-fold and stimulated superoxide production as measured by cytochrome c reduction in colonic mucosal scrapings or crypt epithelium. Bile salt-induced increases in chemiluminescence were abolished by CuDIPS, phenidone, and esculetin, but not by indomethacin. Intracolonic generation ofreactive oxygen by xanthixanthine oxidase increased colonic mucosal ornithine decarboxylase activity and V3Hjthymidine incorporation into DNA approximately twofold. These effects were abolished by superoxide dismutase. The findings support a key role for reactive oxygen, rather than more distal products of either the lipoxygenase or cyclooxygenase pathways, in the stimulation of colonic mucosal proliferation by bile salts.

Deoxycholate (DOC), chenodeoxycholate, 12-0-tetradecanoyl phorbol-13-acetate (TPA), or 1-oleoyl-2-acetyl-glycerol (OAG) activated colonic epithelial protein kinase C as reflected by translocation from the soluble to the particulate cell fraction. Activation of protein kinase C was correlated with stimulation of enhanced proliferative activity of colonic mucosa and reactive oxygen production. TPA and OAG, but not DOC, directly activated soluble protein kinase C in vitro. However, DOC rapidly increased labeled inositol phosphate and diacylglycerol accumulation in colonic epithelial cells. Retinoic acid inhibited protein kinase C activity and suppressed DOG-, TPA-, and OAG-induced increases in reactive oxygen production. The results support a role for protein kinase C in the stimulation of colonic epithelial proliferative activity and reactive oxygen production induced by bile acids, TPA and OAG. In contrast to TPA and OAG, which activate protein kinase C directly, bile acids appear to activate protein kinase C indirectly by increasing the diacylglycerol content of colonic epithelium.

kovian Langevin equation seems valid. The main complication in this approach for activated chemical reactions is the evaluation of the friction, which in the barrier region is expected to be quite different than the more familiar viscosity-based friction from the Stokes-Einstein f o r m~l a .~ In fact, the ab initio evaluation of this "excited-state" friction may be difficult, taking on aspects of and becoming mixed up with entropy concepts that depend on a full knowledge of the vibrational state distribution of the solvent/solute system in the barrier regionz6 Hidden somewhere in the evaluation of this friction is the connection between quantum and (26) Courtney, S. H.; Fleming, G. R.; Khundkar, L. R.; Zewail, A. H. J.

We report the observation at high resolution of seven vibronic bands that appear within ϳ200 cm −1 of the electronic origin in the S 1 -S 0 fluorescence excitation spectrum of 4,4Ј-dimethylaminobenzonitrile ͑DMABN͒ in a molecular beam. Surprisingly, each band is found to be split into two or more components by a ͑coordinated͒ methyl group tunneling motion which significantly complicates the analysis. Despite this fact, high quality ͓͑Observed− Calculated͒ ഛ 30 MHz͔ fits of each of the bands have been obtained, from which the rotational constants, inertial defects, torsion-rotation interaction constants, methyl group torsional barriers, and transition moment orientations of DMABN in both electronic states have been determined. The data show that DMABN is a slightly pyramidalized ͑ϳ1°͒ but otherwise ͑heavy-atom͒ planar molecule in its ground S 0 state, and that its electronically excited S 1 state has both a more pyramidalized ͑ϳ3°͒ and twisted ͑ϳ25°͒ dimethylamino group. Large reductions in the methyl group torsional barriers also show that the S 1 ← S 0 electronic transition is accompanied by significant charge transfer from the nitrogen atom to the ‫ء‬ orbitals of the aromatic ring. Thereby established is the participation of all three vibrational coordinates in the dynamics leading to the "anomalous" emissive behavior of DMABN in the condensed phase.

No abstract