Dual effects of n-alcohols on fluid secretion from guinea pig pancreatic ducts

Caffeine Inhibits Fluid Secretion by Interlobular Ducts From Guinea Pig Pancreas

OBJECTIVES

Caffeine is contained in coffee, tea, and numerous beverages and foods. We examined the direct effects of caffeine on the physiological function of pancreatic duct cells by using interlobular duct segments isolated from guinea pig pancreas.

METHODS

The rate of fluid secretion was continuously measured by monitoring the luminal volume of isolated duct segments. Changes in intracellular Ca concentration ([Ca]i) were estimated by microfluorometry in ducts loaded with Fura-2.

RESULTS

Both secretin-stimulated and acetylcholine (ACh)-stimulated fluid secretions were substantially and reversibly inhibited by relatively low concentrations of caffeine as low as 0.03 mM relevant to blood levels after ingestion of caffeine-containing beverages. Caffeine inhibited ACh-induced elevation of [Ca]i and secretin-induced fluctuation of [Ca]i. Caffeine abolished thapsigargin-induced intracellular Ca release but did not affect the entry of extracellular Ca. Caffeine (0.05 mM) abolished ethanol (1 mM)-induced fluid hypersecretion in secretin-stimulated pancreatic duct.

CONCLUSIONS

Low concentrations of caffeine directly inhibit pancreatic ductal fluid secretion stimulated by secretin or ACh and also ethanol-induced fluid hypersecretion. The inhibition by caffeine seems to be mediated by the blockade of intracellular Ca mobilization. Daily intake of caffeine may reduce the volume of pancreatic juice secretion.

Apoptotic damage of pancreatic ductal epithelia by alcohol and its rescue by an antioxidant

Alcohol abuse is a major cause of pancreatitis. However alcohol toxicity has not been fully elucidated in the pancreas and little is known about the effect of alcohol on pancreatic ducts. We report the molecular mechanisms of ethanol-induced damage of pancreatic duct epithelial cells (PDEC). Ethanol treatment for 1, 4, and 24 h resulted in cell death in a dose-dependent manner. The ethanol-induced cell damage was mainly apoptosis due to generation of reactive oxygen species (ROS), depolarization of mitochondrial membrane potential (MMP), and activation of caspase-3 enzyme. The antioxidant N-acetylcysteine (NAC) attenuated these cellular responses and reduced cell death significantly, suggesting a critical role for ROS. Acetaldehyde, a metabolic product of alcohol dehydrogenase, induced significant cell death, depolarization of MMP, and caspase-3 activation as ethanol and this damage was also averted by NAC. Reverse transcription-polymerase chain reaction revealed the expression of several subtypes of alcohol dehydrogenase and acetaldehyde dehydrogenase. Nuclear magnetic resonance spectroscopy data confirmed the accumulation of acetaldehyde in ethanol-treated cells, suggesting that acetaldehyde formation can contribute to alcohol toxicity in PDEC. Finally, ethanol increased the leakage of PDEC monolayer which was again attenuated by NAC. In conclusion, ethanol induces apoptosis of PDEC and thereby may contribute to the development of alcohol-induced pancreatitis.

Alcohols are inhibitors of Saccharomyces cerevisiae multidrug-resistance pumps Pdr5p and Snq2p

The effect of alcohols on cell membrane proteins has originally been assumed to be mediated by their primary action on membrane lipid matrix. Many studies carried out later on both animal and yeast cells have revealed that ethanol and other alcohols inhibit the functions of various membrane channels, receptors and solute transport proteins, and a direct interaction of alcohols with these membrane proteins has been proposed. Using our fluorescence diS-C3 (3) diagnostic assay for multidrug-resistance pump inhibitors in a set of isogenic yeast Pdr5p and Snq2p mutants, we found that n-alcohols (from ethanol to hexanol) variously affect the activity of both pumps. Beginning with propanol, these alcohols have an inhibitory effect that increases with increasing length of the alcohol acyl chain. While ethanol does not exert any inhibitory effect at any of the concentration used (up to 3%), hexanol exerts a strong inhibition at 0.1%. The alcohol-induced inhibition of MDR pumps was detected even in cells whose membrane functional and structural integrity were not compromised. This supports a notion that the inhibitory action does not necessarily involve only changes in the lipid matrix of the membrane but may entail a direct interaction of the alcohols with the pump proteins.

Diffusion-weighted MR imaging in the evaluation of pancreatic exocrine function before and after secretin stimulation

OBJECTIVES

To evaluate diffusion weighted MR imaging before and after secretin stimulation in the assessment of pancreatic exocrine function in the setting of chronic pancreatitis.

METHODS

Nine patients with severe chronic pancreatitis and sixteen patients without chronic pancreatitis but with a history of chronic alcohol consumption were enrolled in the chronic pancreatitis and risk groups, respectively. Thirty-eight patients without any pancreatic disease or history of alcohol consumption were included in the control group. Diffusion weighted images were obtained before and after secretin administration in all patients. The peak ADC values and times were determined and intergroup differences were compared. A receiver operating characteristic curve (ROC) was used to identify the cutoff values of the peak ADC times for discrimination of control group from risk and chronic pancreatitis groups.

RESULTS

In the control group, a peak increase in ADC value of 57-120% (median: 75%) was observed between 90 s and 4 min (median: 2 min) after administration of secretin (Pattern 1). In the risk group, in 13 patients, a peak increase of 52-150% was observed between 4 and 8 min (median: 7 min; Pattern 2). Peak times were significantly longer in risk group (p < 0.01). In three patients in the risk group, and in all patients in the chronic pancreatitis group, no ADC peak was observed within 10 min following secretin administration (Pattern 3). Using a peak time of 4 min as the cut-off value, a sensitivity of 100% and specificity of 94.7% were achieved in discriminating the control group from the combined risk and chronic pancreatitis groups.

CONCLUSION

Diffusion-weighted MR imaging before and after secretin administration could yield clinically useful information for detecting pathophysiologic alterations in the setting of chronic pancreatitis.