The effect of nitric oxide (NO) donors on the release of mucus from a suspension of isolated gastric cells was investigated by using an enzyme-linked immunosorbent assay for rat gastric mucin. Isosorbide dinitrate (ISDN, 0.1-2 mM) produced a dose-related stimulation of mucus secretion, without affecting the viability of the isolated cells as determined by trypan blue exclusion or acid phosphatase release. In a comparable concentration range to that stimulating mucus release, ISDN elevated the guanosine 3',5'-cyclic monophosphate (cGMP) content of cell suspensions enriched with mucous cells. The nitrosothiol S-nitroso-N-acetylpenicillamine (0.3 mM), which spontaneously liberates NO, likewise stimulated mucus release, and this action was blocked by 10 microM oxyhemoglobin, which scavenges NO. Nitroprusside (1 mM), dibutyryl cGMP (0.01-1 mM), and the cGMP phosphodiesterase inhibitor M & B 22948 (0.1 mM) also increased mucus release. Thus generators of NO stimulate mucus secretion by rat gastric mucosal cells, which may reflect the elevation of intracellular cGMP. These findings, along with the presence of NO synthase in the gastric epithelial cells, suggest an effector role for NO in mediation of gastric mucus release.

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SUMMARY1. The rate of metabolism of glucose to lactate has been measured in a number of non-vascularly perfused preparations of rat jejunum in vitro. The glucose and lactate metabolism was measured simultaneously and under conditions such that the uptake of glucose and the appearance of lactate were linearly related to time.2. It is found that there is no difference between the rates at which rings of rat jejunum utilize glucose during the first 45 min of anaerobic or aerobic incubation. During the first 15 min of incubation between 60-70 % of the metabolized glucose was converted to lactate under aerobic conditions; this value increased to 80-90 % during the subsequent 30 min.During the period 0-15 min of incubation, lactate production was found to be higher under anaerobic than under aerobic conditions but after this initial period the rate of lactate production was the same under aerobic and anaerobic conditions.3. For segments of rat jejunum, maintained in vitro by the recirculation of nutrient fluid through the intestinal lumen, neither the rate of production of lactate, nor the utilization of glucose, was stimulated if the preparation was maintained under anaerobic rather than aerobic conditions. The direct delivery of gas into the intestinal lumen in the form of a stream of bubbles (segmented circulation) reduced both the utilization of glucose and the production of lactate under aerobic conditions. However, no effect on glucose metabolism was observed under anaerobic conditions. The finding of a Pasteur effect with the segmented-circulated preparation, but not with the simple recirculated preparation, is associated with the lower rate of aerobic lactate production in the former preparation. Reasons are given for supposing that under conditions of segmented circulation, the luminal compartment is better stirred, thereby increasing access of 02 to the tissue. P. J. HANSON AND D. S. PARSONS 4. A preparation of rat small intestine perfused through the vascular bed is described. With this preparation the rate of glucose utilization is significantly lower than that for recirculated preparations and the rate of lactate production is substantially less than that of the other preparations studied.5. With the preparation perfused through the vascular bed, and with glucose, 10 mm, present only in the vascular medium the addition of erythrocytes to the vascular infusate causes a significant reduction in both glucose utilization and in the rate of lactate production. The addition of erythrocytes to produce an haematocrit of 40 % (v/v) causes a greater reduction in glucose utilization and lactate production than is found for an haematrocrit of 15 %. About 10% of the lactate produced appears in the luminal contents. With an haematocrit of 15 %, the 02 consumption of the whole wall of the jejunum was found to be 6-4 ,mole 02 g dry wt.-' min-', equivalent to a value for the Qo. of 8 6 #d. 02 mg dry wt.-' hr-1.

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1. The metabolism and transport of glutamine and glucose were investigated in a preparation of rat small intestine perfused through the vascular bed in vitro and in situ. 2. With glucose (7.5mm) or glutamine (4.5mm) in the lumen, approx. 40% of the substrate taken up appears unchanged on the vascular side. When glutamine (1.5mm) is also added to the vascular perfusate, metabolism of glutamine is increased and there is uptake of glutamine from both the vascular bed and lumen. Orientation of substrate (vascular bed or lumen) influences the value of alanine production/glutamine utilization and lactate production/glucose utilization. 3. Deprivation of food and metabolic acidosis have no effect upon the utilization of glutamine by unit length of jejunum. In fed rats, glutamine utilization is 44% of glucose utilization, but in rats deprived of food it is 112% of glucose utilization. 4. Glucose utilization and lactate production are not significantly altered by the presence of glutamine in the vascular bed or lumen. 5. With glucose only in the vascular perfusate, glucose utilization is the same in jejunum and ileum. Glutamine metabolism in the ileum is 28% lower than in the jejunum. 6. Glutamine utilization is dependent on the concentration of glutamine in the vascular perfusate, but is not significantly affected by the absence of glucose. 7. Results are discussed in relation to the role of intestinal glutamine metabolism and with respect to some problems of the transepithelial movement of substrates that are both transported and metabolized.

ABSTRACT:Gastric absorption of feruloylquinic acid and di-O-caffeoylquinic acid analogs has never been investigated despite their potential contribution to the proposed beneficial health effects leading to reduced risk of type 2 diabetes. Using a cultured gastric epithelial model, with an acidic apical pH, the relative permeability coefficients (P app ) and metabolic fate of a series of chlorogenic acids (CGAs) were investigated. Mechanistic studies were performed in the apical to basal direction and demonstrated differential rates of absorption for different CGA subgroups. For the first time, we show intact absorption of feruloylquinic acids and caffeoylquinic acid lactones across the gastric epithelium (P app ϳ 0.2 cm/s). Transport seemed to be mainly by passive diffusion, because good linearity was observed over the incubation period and test concentrations, and we speculate that a potential carrier-mediated component may be involved in uptake of certain 4-acyl CGA isomers. In contrast, absorption of intact di-O-caffeoylquinic acids was rapid (P app ϳ 2-10 cm/s) but nonlinear with respect to time and concentration dependence, which was potentially limited by interaction with an efflux transporter and/or pH gradient dependence. For the first time, methylation is shown in gastric mucosa. Furthermore, isoferulic acid, dimethoxycinnamic acid, and ferulic acid were identified as novel gastric metabolites of CGA biotransformation. We propose that the stomach is the first location for the release of hydroxycinnamic acids, which could explain their early detection after coffee consumption.

Nitric oxide has been implicated in the regulation of blood flow, mucosal integrity and mucus secretion in the gastric mucosa. An antiserum directed against the C-terminal hexadecapeptide of rat brain nitric oxide synthase (NOS) and monoclonal antibodies to the neuronal and endothelial forms of NOS were used to establish the location of isoforms of NOS in rat gastric glandular mucosa. Antibodies to the neuronal form of NOS reacted with a band of 160 kDa on immunoblots of brain and gastric mucosa, and the addition of the hexadecapeptide inhibited recognition by the antipeptide antiserum. The antibody to endothelial NOS detected a band of 140 kDa on protein blots of samples of intestinal mesentery and gastric mucosa. Immunohistochemistry using these antibodies demonstrated that material related to neuronal NOS was present in surface cells of the gastric mucosa, and showed a similar localization to intense NADPH diaphorase activity. The antibody to endothelial NOS did not stain the surface of the gastric mucosa but recognized blood vessels in the lower region of the gastric glands and in the sub-mucosa. This study suggests that nitric oxide might act both as an intra- and inter-cellular messenger to regulate mucus release, and that the NOS present in surface cells is related more closely to the neuronal than to the endothelial isoform.