Antioxidant capacity of 3D human skin EpiDerm model: effects of skin moisturizers.

The objective of this study was to determine the effects of skin moisturizers on total antioxidant capacity (TAC) of human skin using EpiDerm model. Three different skin moisturizers containing antioxidant ingredients (samples 1-3) or aloe vera extract were topically applied to EpiDerm units and incubated for 2 and 24 h to determine acute and longer-term effects of applied samples on TAC and glutathione peroxidase activity in medium and/or homogenized skin tissues. Total antioxidant capacity in medium and skin homogenates was enhanced (P < 0.0001) by gel containing antioxidant ingredients (sample 2) after 2 and 24 h of incubation. Total antioxidant capacity in medium was also enhanced (P < 0.001) by cream containing antioxidant ingredients (sample 3) after 24 h of incubation. Overall, TAC in medium was greater (P < 0.02) after 24 h than 2 h of incubation. Skin moisturizer cream with high antioxidant levels determined by using oxygen radical absorbance capacity testing (sample 1) and aloe vera extract did not affect TAC. Glutathione peroxidase activity was enhanced (P < 0.0001) in medium and skin homogenates by sample 2 but not by any other sample. These data demonstrate high potential of gel and cream (samples 2 and 3) containing antioxidant ingredients in enhancing antioxidant capacity of EpiDerm which will likely contribute to overall skin health. Results of this experiment will help to better understand mechanisms of effects of skin moisturizers containing antioxidant ingredients on skin function at the tissue level and to establish effective strategies for skin protection and clinical treatments of skin disorders and possibly healing wounds.

Neurotrophic Factors in the Treatment of Acute Brain Hypoxia Secondary to Cardiac Arrest: a Case Report.

Finding neuroprotective agents to counteract the deleterious effects of hypoxia on neuronal cells successfully is one of the most critical targets of clinical research since preclinical studies have identified potential neuroprotective strategies. In clinical practice, amantadine and piracetam are used with reasonable success. We present the cases of three patients with acute brain hypoxia secondary to cardiac arrest, to whom Cerebrolysin was added to the standard neuroprotective treatment regimen, leading to a notable improvement in functional outcome.

Myokine irisin-induced protection against oxidative stress in vitro. Involvement of heme oxygenase-1 and antioxidazing enzymes superoxide dismutase-2 and glutathione peroxidase.

Irisin is a recently discovered myokine reported as protective protein released from exercising skeletal muscles. Although myokines were recently reported to possess the antioxidizing properties, the impact of irisin on the functions of macrophages with respect to its anti-inflammatory potential has not been fully elucidated. Here, we determined the ability of irisin to interact with reactive oxygen species (ROS) in RAW 264.7 murine macrophages. The macrophages were pre-incubated with irisin (0 - 50 nM), some of which had undergone additional co-incubation with bacterial lipopolysaccharide (LPS) (100 ng/ml). Cell viability, the reactive oxygen species scavenging potential as well as the mRNA and protein expression of key oxidative stress factors such as superoxide dismutase 1 (SOD-1), superoxide dismutase 2 (SOD-2), glutathione peroxidase (GSH-Px), catalase 9 (Cat-9), nuclear factor (erythroid-derived 2)-like 2-related factor (Nrf2) and heme oxygenase-1 (HO-1) were evaluated. We found that irisin applied in a concentration of 50 nM significantly attenuated the production of harmful H2O2 and this effect appears to be mediated by a significant increase in the expression of key enzymes involved with antioxidative stress pathways including SOD, GSH-Px and Cat-9 predominantly observed after stimulation of these cells with LPS. We conclude that 1) irisin exhibits a potent antioxidant and anti-inflammatory activities in non-stimulated and LPS-stimulated isolated murine macrophages in vitro, and 2) this protective and antioxidative activity of irisin in vitro might be considered as an important component of protective action of this peptide in vivo, especially under condition of exercise.

New insight into the direct anti-inflammatory activity of a myokine irisin against proinflammatory activation of adipocytes. Implication for exercise in obesity.

A biological activity of myokine irisin, has been intensively investigated in the context of a browning process occurring in white adipose tissue, but its role as a modulator of immune response has been little studied. The aim of our study was to determine the impact of irisin (0 - 100 nM) on pro-inflammatory activation of adipocyte 3T3 L1 cell line. Irisin reduced in a concentration-dependent manner the expression and activity of major proinflammatory cytokines, e.g. tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6) expression and their secretion into cell medium. Moreover, irisin enhanced adiponectin synthesis reversing the effect of the lipopolysaccharide (LPS)-induced attenuation of this adipokine expression. The opposite effect was observed for leptin whose expression increased by LPS and this effect was suppressed by irisin application. A decreased phosphorylation and activation of nuclear factor kappa B (NFκB) in the presence of irisin suggests that mechanism of action irisin involves the inhibition of an inflammatory transcription factor. Irisin exerts also an inhibitory effect on macrophage migration toward chemoattractants present in adipocyte supernatants. Among the specific molecules secreted by adipocytes was monocyte chemotactic protein 1 (MCP-1) whose expression was suppressed by irisn. In majority of experiments irisin was effective in 100 nM concentration but in some of them the inhibitory effects occurred already in a concentration of 50 nM of this peptide. This study for the first time showed that adipocytes are directly affected by irisin and provides an evidence on anti-inflammatory action of irisin on fat cells.

Effects of time of day and the wingate test on appetite perceptions, food intake and plasma levels of adipokines.

It has been demonstrated that several aspects of adipose-related physiology including adipokine release, exhibit daily oscillations. Physical exercise exerts a strong influence on adipokine release and a possible reverse disruption of peripheral circadian clocks. The aim of this study was to establish the effects of time of day and the Wingate test on appetite perception, food intake and plasma levels of adipokines. Twenty-four moderately active non-smoking males (mean ± S.D. age: 27.1 ± 3.1 years; height: 1.79 ± 0.1 m; weight: 76.1 ± 11.7 kg) were recruited for this study and divided in two groups; one fed with an ad libitum test meal and another one without an ad libitum test meal. Each subject participated in the following studies performed at 11:00 and 23:00 hours on separate days: 1) Exercise study (ES): a 30-second Wingate Anaerobic Test (WAnT), and 2) sedentary study (SS). Subjects rated their appetite perceptions (hunger and prospective food consumption) on a 100-milimeter visual analogue scale (VAS) at baseline, after exercise, after test meal and during the postprandial/control period. At those time points blood samples were obtained for the measurement of plasma leptin, visfatin and apelin concentrations. Appetite perception and energy intake results at test meal decreased in response to WAnT in comparison with sedentary subjects. Time of day had no statistically significant effect on energy intake but the appetite perception score after test meal at 24:00 hours was statistically higher than that after test meal at 12:00 hours. No significant differences in the tested plasma adipokine concentrations between the trials existed at baseline, however, all plasma adipokine levels at 24:00 hours were higher than those at 12:00 hours. Plasma apelin concentrations after WAnT were significantly higher than its pre-exercise value at 12:00 hours, unlike those at 24:00 hours. Sedentary experiments showed a modest, yet significant, rise in plasma apelin levels after the test meal at 12:00 hours but not after the one at 24:00 hours. There were no significant changes in plasma leptin concentrations after exercise or test meal but a significant decrease in plasma visfatin concentrations after exercise intervention both at the 12:00 hours test and the 24:00 hours test has been observed. Test meals caused a significant rise in visfatin concentrations in sedentary, but not exercise series, in the daytime and nighttime tests. We conclude that time of day is an important aspect to consider in the relationships between exercise, metabolism and appetite. Further studies are needed to explain the specific mechanisms underlying the effects of acute exercise on postprandial physiology at different times of the day.

Sulfation in vitro of mucus glycoprotein by submandibular salivary gland: effects of prostaglandin and acetylsalicylic acid.

Enzymatic sulfation of mucus glycoprotein by rat submandibular salivary gland and the effect of prostaglandin and acetylsalicylic acid on this process were investigated in vitro. The sulfotransferase enzyme which catalyzes the transfer of sulfate ester group from 3'-phosphoadenosine-5'-phosphosulfate to submandibular gland mucus glycoprotein has been located in the detergent extracts of Golgi-rich membrane fraction of the gland. Optimum enzyme activity was obtained at pH 6.8 with 0.5% Triton X-100, 25 mM NaF and 4 mM MgCl2, using the desulfated glycoprotein. The enzyme was also capable of sulfation of the intact mucus glycoprotein, but the acceptor capacity of such glycoprotein was 68% lower. The apparent Km of the submandibular gland sulfotransferase for salivary mucus glycoprotein was 11.1 microM. The 35S-labeled glycoprotein product of the enzyme reaction gave in CsCl density gradient a 35S-labeled peak which coincided with that of the glycoprotein. This glycoprotein upon reductive beta-elimination yielded several acidic 35S-labeled oligosaccharide alditols which accounted for 75% of the 35S-labeled glycoprotein label. Based on the analytical data, the two most abundant oligosaccharides were identified as sulfated tri- and pentasaccharides. The submandibular gland sulfotransferase activity was stimulated by 16,16-dimethyl prostaglandin E2 and inhibited by acetylsalicylic acid. The rate of enhancement of the glycoprotein sulfation was proportional to the concentration of prostaglandin up to 2.10(-5) M, at which point a 31% increase in sulfation was attained. The inhibition of the glycoprotein sulfation by acetylsalicylic acid was proportional to the drug concentration up to 2.5.10(-4) M at which concentration a 48% reduction in the sulfotransferase activity occurred. The apparent Ki value for sulfation of salivary mucus glycoprotein in presence of acetylsalicylic acid was 58.9 microM. The results suggest that prostaglandins may play a role in salivary mucin sulfation and that this process is sensitive to such nonsteroidal anti-inflammatory agents as acetylsalicylic acid.

Enhancement of the lipid content and physical properties of gastric mucus by geranylgeranylacetone.

The effects of intragastric administration of geranylgeranylacetone (GGA) on the content, composition and physical properties of the mucus component of the gastric mucosal barrier were investigated. One group of rats received twice daily for 3 consecutive days a dose of 100 mg/kg body weight of GGA, while the control group was subjected to daily doses of the vehicle. Sixteen hours following the last dose, the animals were killed, and their stomach was cut open and subjected to measurements of the adherent mucus gel content, analysis of its lipids and molecular forms of elaborated mucin, and evaluation of the viscosity and H+ retardation capacity. The results revealed that GGA elicited a 62% increase in the adherent mucus gel and caused a marked decrease in the proportion of the lower molecular weight mucin. Furthermore, the mucus of the GGA group exhibited a 67% higher content of covalently bound fatty acids and contained 46% more total lipids which were greatly (143%) enriched in phospholipids. The physical measurements demonstrated that mucus elaborated in the presence of GGA also exhibited 2.3 times higher viscosity and had a 32% greater ability to retard the diffusion of H+ than the mucus of the control group. The results suggest that GGA exerts a profound effect on the lipid content and the properties of gastric mucus associated with the maintenance of the mucosal integrity.

Effects of human corticotropin releasing factor (CRF) on gastric and pancreatic secretion in vivo and in vitro.

Human CRF given IV inhibited dose-dependently pentagastrin- but not histamine-induced gastric acid secretion. When added to the incubation medium of the isolated gastric glands, CRF did not alter the formation of HCl under basal conditions or after stimulation with histamine or DBcAMP. CRF caused a small but significant increase in pancreatic HCO3 and protein secretion. It augmented CCK-induced pancreatic protein and secretin-induced HCO3 secretion in vivo but failed to affect basal or stimulated (CCK and urecholine) amylase release by the in vitro dispersed pancreatic acini. This study indicates that CRF inhibits gastric and stimulates pancreatic secretion in vivo but not in vitro and these effects are indirect involving, at least in part, alterations in the pancreatic circulation.

The importance of gastric secretion in the feedback control of interdigestive and postprandial pancreatic secretion in rats.

Previous studies demonstrated that pancreatic enzyme secretion in rats is stimulated by the diversion of pancreatic juice from the duodenum or by the inhibition of pancreatic proteinases in the intestinal lumen but little attention has been paid to the role of gastric secretion in this stimulation. This study, carried out on conscious rats with large gastric (GF) and pancreatic fistulas, confirms that diversion of pancreatic juice in rats with the GF closed results in the progressive stimulation of pancreatic secretion reaching the maximum similar to that induced by exogenous CCK. When the GF was kept open, the diversion resulted in only small increment in pancreatic secretion and this was accompanied by progressive increase in gastric acid outputs. Similar amounts of HCl (25-400 mumol/h) instilled intraduodenally (i.d.) in rats with the GF open fully reproduced the increase in pancreatic secretion observed after the diversion of pancreatic juice and this effect was completely abolished by the pretreatment with L-364,718, a specific CCK receptor antagonist. Pretreatment with omeprazole to suppress completely gastric acid secretion in the diverted state resulted in a decline in pancreatic secretion similar to that observed after opening the GF. Camostate given in graded doses (6-200 mg/kg) either i.d. or s.c. in rats with pancreatic juice returned to the duodenum caused a dose-dependent increase in pancreatic secretion, but after opening the GF or after omeprazole this increase was reduced by about 50% while after L-364,718 it was abolished. This study provides evidence that gastric secretion plays an important role in the pancreatic response to diversion of pancreatic juice or inhibition of luminal proteinases (but not to feeding) and the elimination of gastric acid reduces this response.

Role of cholecystokinin in the intestinal fat- and acid-induced inhibition of gastric secretion.

This study was designed to determine the role of cholecystokinin (CCK) in the inhibition of gastric HCl secretion by duodenal peptone, fat and acid in dogs with chronic gastric and pancreatic fistulas. Intraduodenal instillation of 5% peptone stimulated both gastric HCl secretion and pancreatic protein secretion and caused significant increments in plasma gastrin and CCK levels. L-364,718, a selective antagonist of CCK-A receptors, caused further increase in gastric HCl and plasma gastrin responses to duodenal peptone but reduced the pancreatic protein outputs in these tests by about 75%. L-365,260, an antagonist of type B receptors, reduced gastric acid by about 25% but failed to influence pancreatic response to duodenal peptone. Addition of 10% oleate or acidification of peptone to pH 3.0 profoundly inhibited acid secretion while significantly increasing the pancreatic protein secretion and plasma CCK levels. Administration of L-364,718 reversed the fall in gastric HCl secretion and significantly attenuated pancreatic protein secretion in tests with both peptone plus oleate and peptone plus acid. Exogenous CCK infused i.v. in a dose (25 pmol/kg per h) that raised plasma CCK to the level similar to that achieved by peptone meal plus fat resulted in similar inhibition of gastric acid response to that attained with fat and this effect was completely abolished by the pretreatment with L-364,718. We conclude that CCK released by intestinal peptone meal, containing fat or acid, exerts a tonic inhibitory influence on gastric acid secretion and gastrin release through the CCK-A receptors.

Role of endogenous nitric oxide in the control of gastric acid secretion, blood flow and gastrin release in conscious dogs.

Nitric oxide (NO) was shown to mediate gastric hyperemia following secretory stimulation but its role in the control of gastric secretion has not been clarified. Secretory studies were carried out on conscious dogs with chronic gastric fistula, Heidenhain pouch and esophageal fistula, while changes in gastric blood flow were measured in the mucosa of Heidenhain pouuch by laser Doppler flowmetry. Plasma gastrin was determined by radioimmunoassay. Infusion of NG-nitro-L-arginine (L-NNA) (bolus i.v. injection of 2.5 mg/kg followed by infusion of 0.5 mg/kg/h), a potent inhibitor of nitric oxide synthase, failed to affect basal gastric secretion or plasma gastrin level but suppressed an increase of this secretion induced by sham-feeding, ordinary meat feeding or i.v. infusion of bombesin (0.5 microgram/kg/h), pentagastrin (4 micrograms/kg/h) or histamine (40 micrograms/kg/h). In tests with feeding and bombesin infusion, L-NNA caused a significant and dose-dependent reduction in plasma gastrin levels. The inhibition by L-NNA of gastric acid secretory response to pentagastrin, histamine or feeding was accompanied by a decline in blood flow. Addition of L-arginine (bolus i.v. dose of 50 mg/kg followed by infusion of 5 mg/kg/h) significantly attenuated the L-NNA induced inhibition of gastric secretion and the reduction in plasma gastrin response as well as in the fall of gastric blood flow. We conclude that endogenous nitric oxide affects the gastric secretion and that this effect is mediated, at least in part, by the changes in the gastrin release and gastric blood flow.

Effects of growth hormone releasing factor on pancreatic secretion in vivo and in vitro.

Growth hormone releasing factor (GRF), a 44-residue peptide originally isolated from human pancreatic tumors, shows structural similarities to the members of the secretin-vasoactive intestinal peptide (VIP) peptides. This study was designed to determine the effects of human GRF (hGRF-(1-44] on pancreatic secretion in vivo in conscious dogs and in vitro in dispersed rat pancreatic acini. GRF given i.v. in graded doses in dogs caused a small but significant stimulation of pancreatic HCO3- and protein outputs and potentiated secretin- and cholecystokinin (CCK)-induced pancreatic HCO3- but not protein secretion. When given together with somatostatin, GRF failed to reverse the inhibitory action of this peptide on HCO3- and protein responses to secretin plus CCK in dogs. Studies in vitro dispersed rat pancreatic acini showed that GRF added to the incubation medium of these acini caused an increase in basal amylase release and shifted to the left the amylase dose-response curve to caerulein and urecholine but failed to affect the amylase response to VIP. This study indicates that GRF in vivo stimulates basal and augments secretin- or CCK-induced pancreatic HCO3- secretion and that this is probably due to direct stimulatory action of the peptide on pancreatic secretory cells.

Enhancement in gastric mucus gel qualities with colloidal bismuth subcitrate administration.

The effects of intragastric administration of an antiulcer drug, colloidal bismuth subcitrate, on the content, composition and physical properties of the mucus component of gastric mucosal barrier were investigated. The experiments were conducted with two groups of rats in which one group received twice daily for three consecutive days a dose of 100 mg/kg colloidal bismuth subcitrate, while the control group received saline. The animals were killed 16 h after the last dose, their stomachs dissected and the mucosa subjected to physicochemical measurements. The results revealed that colloidal bismuth subcitrate elicited a 49% increase in mucus gel dimension, while sulfo- and sialomucin content of the gel increased by 64 and 112%, respectively. The changes in mucus with colloidal bismuth subcitrate were accompanied by a 28% increase in H+ retardation capacity, 2.2-fold increase in viscosity, and a 26% increase in the gel hydrophobicity. The mucus elaborated in the presence of colloidal bismuth subcitrate exhibited 16% lower protein content and 68% higher content of carbohydrate than that of the control, displayed similar levels of total lipids and covalently bound fatty acids, but its phospholipid content was 32% higher. Furthermore, the mucus of the colloidal bismuth subcitrate group showed a marked increase in the proportion of the high molecular weight form of mucin. The results suggest that colloidal bismuth subcitrate is capable of the enhancement of mucus gel qualities associated with the maintenance of gastric mucosal integrity.

Gastrointestinal secretory, motor and circulatory effects of corticotropin releasing factor (CRF).

This study was designed to determine the effects of CRF on the gastrointestinal functions such as secretion, motility and circulation in dogs. CRF was found to inhibit dose-dependently gastric acid response to pentagastrin but not to histamine. CRF stimulated pancreatic bicarbonate and protein secretion under basal conditions and in response to secretin or cholecystokinin (CCK). This stimulation was accompanied by an increase in plasma levels of pancreatic polypeptide (PP), but not of secretin or gastrin. CRF caused a partial inhibition of the migrating motor complexes in fasted dogs and increased spike activity of the small bowel. These motor effects of CRF probably resulted from the action of the released PP on the intestinal smooth muscle. CRF is also a potent and selective stimulant of the mesenteric blood flow. This effect may be secondary to the stimulation of intestinal motility and metabolism.

Effects of basic fibroblast growth factor (FGF-2) on proliferation of human skin fibroblasts in type II diabetes mellitus.

Skin fibroblasts from patients with diabetes mellitus display abnormalities in cell proliferation. The use of exogenous growth factors on diabetic wounds has been found to stimulate fibroblast proliferation and facilitate wound healing. However, the results of application of FGF-2 alone to diabetic wounds in clinical trials have been disappointing. The objective of this experiment was to study the effects of FGF-2 and media supplements on in vitro proliferation of skin fibroblasts from patients with type II diabetes and nondiabetic controls, and to evaluate the association between fibroblast proliferation and cAMP production. Fibroblast cell lines (n = 5 from diabetic and n = 5 from control individuals) were cultured in DMEM + 20% FBS for 7 days. Cells were then counted, plated into 24-well plates at a concentration of 2 x 10(4) cells/well and incubated for 24 h in DMEM with serum. The next day, medium was changed to serum-free DMEM alone or DMEM with supplements (albumin, transferrin, insulin and hydrocortisone). Cells were cultured in the presence or absence of varying doses of FGF-2 (0, 0.3, 1, 3, 10 and 30 ng/ml) for 72 hrs then counted and medium was collected for cAMP radioimmunoassay. The doubling time for cell number tended to be greater (p < 0.2) for diabetic fibroblasts than for control fibroblasts. The addition of supplements to the medium reduced (p < 0.05) the doubling time for both fibroblast types. FGF-2 stimulated (p < 0.05) proliferation of diabetic fibroblasts only in medium containing supplements. In contrast, FGF-2 stimulated proliferation of control fibroblasts in medium with or without supplements. The maximal effects of FGF-2 on fibroblast proliferation were greater (p < 0.02) in medium with supplements than in medium without supplements. The K(D) of FGF-2 for fibroblast proliferation was greater (p < 0.06) for diabetic than for control fibroblasts, and lower (p < 0.02) for medium with supplements than for medium without supplements. Fibroblasts from patients with diabetes mellitus produced more (p < 0.05) cAMP than control fibroblasts. These results demonstrate that FGF-2 requires the presence of supplements to enhance proliferation of fibroblasts from patients with type II diabetes mellitus. In addition, fibroblasts from diabetic patients showed a greater K(D) for FGF-2 in terms of cell proliferation. These data suggest a defective FGF receptor or down-regulation of the FGF receptor-mediated cascade that leads to cell proliferation. Identifying methods of reducing the K(D) of FGF-2 in stimulating the proliferation of diabetic fibroblasts may improve the clinical response of diabetic wounds to FGF-2.

Role of nitric oxide in gastroduodenal alkaline secretion.

This study was designed to determine the involvement of nitric oxide (NO) in gastric and duodenal alkaline under basal conditions and in response to exogenous and endogenous stimulants in conscious dogs with Heidenhain pouches and duodenal loops. A topical application of HCl or capsaicin increased both gastric and duodenal alkaline secretion. A meat meal stimulated only duodenal alkaline secretion while gastric secretion was not significantly changed. The NO synthase inhibitor, NG-nitro-L-arginine (L-NNA), significantly inhibited basal gastroduodenal alkaline secretion and almost completely suppressed the alkaline responses to food, acid or capsaicin. L-arginine given alone did not affect significantly basal or stimulated gastroduodenal alkaline secretion but when given together with L-NNA partially reversed the inhibitory effects of L-NNA on this secretion. For the comparison, the administration of indomethacin to suppress the generation of prostaglandin biosynthesis, also reduced basal and stimulated alkaline secretion but this reduction was relatively smaller than that attained by the inhibition of NO synthase with L-NNA. Luminal application of nocloprost, a stable prostaglandin E2 analog, and glycerin trinitrate caused significant increase in both gastric and duodenal alkaline secretion but these responses were not affected by the administration of L-NNA or indomethacin. We conclude that endogenous NO together with prostaglandins plays a significant role in secretory alkaline response of gastroduodenal mucosa to acid, food and capsaicin.

Role of endogenous nitric oxide in the control of exocrine and endocrine pancreatic secretion.

L-Arginine (L-Arg), that is a substrate for nitric oxide (NO) synthase, stimulates the release of pancreatic islet hormones but the mechanism of this stimulation is unknown. The aim of this study was to determine the role of NO in the control of endocrine and exocrine pancreatic secretion in response to sham feeding (SF), ordinary meat feeding (F), duodenal perfusion with nutrients and i.v. infusion of gastrin releasing peptide (GRP) or urecholine in conscious dogs with chronic pancreatic fistulas. SF1 F, duodenal nutrient and GRP and urecholine resulted in the stimulation of pancreatic secretion reaching, respectively, 50%, 50%, 40%, 85% and 20% of maximal response to caerulein (200 pmol/kg-h i.v.). Infusion of L-Arg (50 mg/kg + 5 mg/kg-h i.v.) almost doubled the basal pancreatic protein secretion and significantly increased the secretory response to SF, F, and duodenal nutrient. After i.v. administration of L-NNA (2.5 mg/kg + 0.5 mg/kg-h), an inhibitor of NO synthase, the pancreatic secretory responses to SF, F, duodenal nutrient, GRP and urecholine were significantly inhibited by about 74%, 70%, 70%, 80% and 30%, respectively. When L-Arg was combined with L-NNA, the reduction in pancreatic secretion induced by L-NNA was significantly attenuated. SF resulted in a marked rise in plasma insulin and glucagon and this response was completely abolished by L-NNA infusion. Insulin and glucagon levels were 2-3 folds increased by F and L-NNA infusion inhibited these responses while the addition of L-Arg partly reversed this inhibition. Duodenal nutrient produced several fold increase in plasma insulin and glucagon levels that were significantly reduced by L-NNA and this reduction was partially reversed by L-Arg. GRP also caused moderate rise in plasma insulin and glucagon levels which were significantly reduced by L-NNA and this was partially restored by L-Arg. We conclude that SF, F, duodenal nutrient, GRP or urecholine stimulate both the exocrine and endocrine pancreatic secretion and that these effects are mediated, at least in part, through the NO pathway.

Nitric oxide and the interrelation between intestinal motility and pancreatic secretion in fasted and fed dogs.

Intestinal motility and pancreatic secretion show synchronous cyclic changes (MMC) that are interrupted by feeding. The aim of this study was to determine the possible implication of nitric oxide (NO) (that was proposed as nonadrenergic noncholinergic neurotransmitter) in the motor and secretory components of MMC in 5 conscious dogs equipped with monopolar electrodes implanted along the small bowel and pancreatic fistulas. In fasted dogs with typical MMCs, L-NNA (an inhibitor of NO synthase) (5 mg/kg-h i.v.) decreased the MMC interval from control value of 80 +/- 7 to 60 +/- 4 min while increasing significantly the slow waves with spikes and suppressing the phase III-related increase in pancreatic secretion. Infusion of L-arginine (L-Arg) (a substrate of NO synthase) (10 mg/kg-h i.v.) increased the MMC interval from control 79 +/- 7 to 96 +/- 8 min and reduced the slow waves spikes by about 25%. Pancreatic secretion showed significant increase to about 20%. CCK maximum. Similar but transient effects were observed when glyceryl trinitrate (GTN) (a donor of NO) (1 mg/kg-h) was administered. After ingestion of meal, the MMC cycles were replaced by irregular spike activity with an average of about 35% slow waves with spikes and pancreatic secretion rose to about 70% of CCK maximum. Infusion of L-Arg (10 mg/kg-h) reduced by about 90% the postprandial spike activity but failed to affect significantly the pancreatic secretion. Also, injection of GTN (1 mg/kg-h) reduced the spike activity but did not influence pancreatic secretion. L-NNA in fed dogs caused an initial increase in spike activity followed by phase III and about 60% inhibition of pancreatic secretion. L-NNA added to L-Arg infusion reversed in part both intestinal motility and pancreatic secretory effects of L-Arg infusion. We conclude that NO system exerts a tonic inhibitory influence on intestinal myoelectric activity by reducing the frequency of MMC pacesetter and by suppressing the postprandial activity but stimulates pancreatic secretion.

Feedback control of pancreatic secretion in rats. Role of gastric acid secretion.

Pancreatic secretion in rats is regulated by feedback inhibition of cholecystokinin (CCK) release by proteases in the gut lumen, but little is known about the role of gastric acid in this regulation. This study, carried out on conscious rats with large gastric fistulas (GF) and pancreatic fistulas, shows that diversion of pancreatic juice results in the progressive stimulation of pancreatic secretion only in rats with the GF closed. When the GF was kept open, the diversion resulted in only small increment in pancreatic secretion and this was accompanied by progressive increase in gastric acid outputs. Similar amounts of HCl instilled into the duodenum in rats with the GF open fully reproduced the increase in pancreatic secretion observed after the diversion of pancreatic juice. Pretreatment with omeprazole (15 mumol/kg) to suppress gastric acid secretion or with L-364,718 (5 mumol/kg) to antagonize CCK receptors in the diverted state, resulted in the decline in pancreatic secretion similar to that observed after opening the GF. CCK given s.c. (20-320 pmol/kg) failed to cause any significant rise in the post-diversion pancreatic secretion in rats with the GF closed, but stimulated this secretion dose-dependently when the GF was open. Camostate (6-200 mg/kg) in rats with pancreatic juice returned to the duodenum caused dose-dependent increase in pancreatic secretion, but after opening the GF or after omeprazole this increase was reduced by about 75%. This study provides evidence that gastric acid plays a crucial role in the pancreatic response to diversion of pancreatic juice or inhibition of luminal proteases, and that factors that eliminate gastric acid secretion reduce this response.

Antagonism of receptors for gastrin, cholecystokinin and GRP/bombesin in postprandial stimulation of exocrine pancreas in dogs.

Postprandial pancreatic secretion results from the interaction of neural and hormonal factors such as cholecystokinin (CCK), gastrin and gastrin releasing peptide (GRP), but their contribution to the net secretion is not established. Recent description of highly specific and potent hormonal receptor antagonists allows the determination of the physiological role of CCK, gastrin and GRP. In six dogs with chronic pancreatic fistulas, the blockade of CCK receptors by L-364, 718, gastrin receptors by L-365, 260 or GRP/bombesin receptors by nonapeptide RC-3095 failed to affect basal or sham-feeding induced pancreatic secretion indicating that none of these hormonal peptides plays a major role in this secretion. In contrast, the pancreatic response to ordinary feeding (which includes cephalic, gastric and intestinal phases), that was accompanied by a significant increment in plasma CCK and gastrin levels, was strongly inhibited (by over 50%) by L-364, 718 and slightly (by 20-30%) by L-365, 260 but not by RC-3095. Each antagonist was given at a dose that eliminated the secretory response to CCK, gastrin or GRP, respectively. We conclude that specific receptor antagonists are useful tools in assessing the physiological role of gut hormones in the control of pancreatic secretion and that none of the peptides tested appears to be involved in the cephalic phase. However, CCK plays a major role in the postprandial stimulation of pancreatic secretion.