Regulation of distal esophageal mucosal blood flow: the roles of nitric oxide and substance P

BACKGROUND: An increase in esophageal mucosal blood flow (MBF) may be an important protective mechanism against mucosal injury from noxious agents that are ingested or refluxed. This study investigated the changes in MBF and the regulation thereof after intraluminal application of noxious chemical stimuli. The role, if any, of substance P (SP) and nitric oxide (NO), two potent vasodilatory substances, and the vascular distribution of SP in the distal esophagus were evaluated. METHODS: Esophageal MBF was measured in anesthetized dogs with a laser Doppler flow probe attached to manometry and pH probes. MBF was measured before and after topical application of HCl (2 ml; 1N) or capsaicin (2 ml; 0.5%) in the distal esophagus. The effects on MBF of intraarterial SP and bradykinin were also determined. Pharmacologic antagonists and denervation procedures were used to delineate the mechanisms that regulate MBF. RESULTS: Sequential luminal applications of hydrochloric acid (HCl) or a single application of capsaicin increased MBF (p < 0.01). Topical intraluminal lidocaine blocked the response to capsaicin (p > 0.2) but not to HCl (p < 0.05). Abrupt increases in MBF occurred with intraarterial SP or bradykinin (p < 0.01). Neither atropine nor truncal vagotomy blocked the increase in MBF from these peptides or noxious stimuli. The NO synthesis antagonist NG-nitro-L-arginine methyl ester (L-NAME) blocked the response to bradykinin and attenuated the response to HCl (p < 0.05). NG-nitro-L-arginine methyl ester did not affect the response to SP or capsaicin. A substance P antagonist blocked the effects of both capsaicin (p > 0.6) and SP (p > 0.1) but not that of HCl (p < 0.01) or bradykinin (p > 0.01). CONCLUSIONS: Intraluminal applications of HCl or capsaicin appear to stimulate increases in esophageal MBF by different mechanisms. HCl produces an adaptive response that appears dependent on the paracrine effect of NO. Capsaicin-sensitive neurons mediate vasodilation through SP neurotransmission, independent of extrinsic vagal or cholinergic innervation.     

Effect of protein kinase C inhibitors and activators on corneal re-epithelialization in the rat

PURPOSE: To examine the ability of protein kinase C (PKC) inhibitors and activators to influence the rate of corneal re-epithelialization in the rat. METHOD: Rat corneas with 3 mm diameter central epithelial abrasions were organ-cultured in control medium or in medium with inhibitors or activators of PKC. RESULTS: In control corneas, the defect was completely re-epithelialized by 25 hr. In the presence of the PKC inhibitors staurosporine (100 nM), sphinganine (50 mumol/l), or H-7 (100 mumol/l) there were significantly larger epithelial defects than in controls after 5-25 hr of incubation. Re-epithelialization rates were similar to control corneas when the incubation medium contained HA1004 (100 mumol/l), an analogue of H-7 that is a potent inhibitor of cyclic adenosine monophosphate- and cyclic guanosine monophosphate-dependent protein kinases and a weak inhibitor of PKC. Two PKC activators, 1-oleoyl-2-acetyl-sn-glycerol (OAG) and phorbol 12-myristate 13-acetate (PMA), were unable to enhance the rate of epithelial wound healing. CONCLUSIONS: Our results suggest that PKC activity is an important factor in regulating corneal epithelial wound healing, presumably by influencing cell migration. Moreover, the results with OAG and PMA suggest that PKC is maximally activated during re-epithelialization in this organ-culture assay.     

Osmoprotective compounds in the Plumbaginaceae: a natural experiment in metabolic engineering of stress tolerance

In common with other zwitterionic quarternary ammonium compounds (QACs), glycine betaine acts as an osmoprotectant in plants, bacteria, and animals, with its accumulation in the cytoplasm reducing adverse effects of salinity and drought. For this reason, the glycine betaine biosynthesis pathway has become a target for genetic engineering of stress tolerance in crop plants. Besides glycine betaine, several other QAC osmoprotectants have been reported to accumulate among flowering plants, although little is known about their distribution, evolution, or adaptive value. We show here that various taxa of the highly stress-tolerant family Plumbaginaceae have evolved four QACs, which supplement or replace glycine betaine-namely, choline O-sulfate and the betaines of beta-alanine, proline, and hydroxyproline. Evidence from bacterial bioassays demonstrates that these QACs function no better than glycine betaine as osmoprotectants. However, the distribution of QACs among diverse members of the Plumbaginaceae adapted to different types of habitat indicates that different QACs could have selective advantages in particular stress environments. Specifically, choline O-sulfate can function in sulfate detoxification as well as in osmoprotection, beta-alanine betaine may be superior to glycine betaine in hypoxic saline conditions, and proline-derived betaines may be beneficial in chronically dry environments. We conclude that the evolution of osmoprotectant diversity within the Plumbaginaceae suggests additional possibilities to explore in the metabolic engineering of stress tolerance in crops.