title: Acidic digestion in a teleost: postprandial and circadian pattern of gastric pH, pepsin activity, and pepsinogen and proton pump mRNAs expression.
abstract: Two different modes for regulation of stomach acid secretion have been described in vertebrates. Some species exhibit a continuous acid secretion maintaining a low gastric pH during fasting. Others, as some teleosts, maintain a neutral gastric pH during fasting while the hydrochloric acid is released only after the ingestion of a meal. Those different patterns seem to be closely related to specific feeding habits. However, our recent observations suggest that this acidification pattern could be modified by changes in daily feeding frequency and time schedule. The aim of this study was to advance in understanding the regulation mechanisms of stomach digestion and pattern of acid secretion in teleost fish. We have examined the postprandial pattern of gastric pH, pepsin activity, and mRNA expression for pepsinogen and proton pump in white seabream juveniles maintained under a light/dark 12/12 hours cycle and receiving only one morning meal. The pepsin activity was analyzed according to the standard protocol buffering at pH 2 and using the actual pH measured in the stomach. The results show how the enzyme precursor is permanently available while the hydrochloric acid, which activates the zymogen fraction, is secreted just after the ingestion of food. Results also reveal that analytical protocol at pH 2 notably overestimates true pepsin activity in fish stomach. The expression of the mRNA encoding pepsinogen and proton pump exhibited almost parallel patterns, with notable increases during the darkness period and sharp decreases just before the morning meal. These results indicate that white seabream uses the resting hours for recovering the mRNA stock that will be quickly used during the feeding process. Our data clearly shows that both daily illumination pattern and feeding time are involved at different level in the regulation of the secretion of digestive juices.
authors.affiliation: Instituto de Ciencias Marinas de Andalucía (ICMAN-CSIC). Apartado Oficial, Puerto Real, Cadiz, Spain. manuel.yufera@icman.csic.es
authors.forename: Manuel
authors.initials: M
authors.lastname: Yúfera
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Moyano
authors.forename: Antonio
authors.initials: A
authors.lastname: Astola
authors.forename: Pedro
authors.initials: P
authors.lastname: Pousão-Ferreira
authors.forename: Gonzalo
authors.initials: G
authors.lastname: Martínez-Rodríguez
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D004063:Digestion / Q000502:physiology*; D005399:Fishes; D005744:Gastric Acid / Q000378:metabolism*; D005745:Gastric Acidity Determination; D005753:Gastric Mucosa / Q000378:metabolism*; D010434:Pepsin A / Q000378:metabolism*; D020116:Pepsinogen A / Q000235:genetics; D010802:Phylogeny; D019518:Postprandial Period; D017494:Proton Pumps / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D017494:Proton Pumps; D012333:RNA, Messenger; D020116:Pepsinogen A; D010434:Pepsin A