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A novel full-length cDNA that encodes for the Atlantic cod (Gadus morhua L.) PepT1-type oligopeptide transporter has been cloned. This cDNA (named codPepT1) was 2,838 bp long, with an open reading frame of 2,190 bp encoding a putative protein of 729 amino acids. Comparison of the predicted Atlantic cod PepT1 protein with zebrafish, bird and mammalian orthologs allowed detection of many structural features that are highly conserved among all the vertebrate proteins analysed, including (1) a larger than expected area of hydrophobic amino acids in close proximity to the N terminus; (2) a single highly conserved cAMP/cGMP-dependent protein kinase phosphorylation motif; (3) a large N-glycosylation-rich region within the large extracellular loop; and (4) a conserved and previously undescribed stretch of 8-12 amino acid residues within the large extracellular loop. Expression analysis at the mRNA level indicated that Atlantic cod PepT1 is mainly expressed at intestinal level, but that it is also present in kidney and spleen. Analysis of its regional distribution along the intestinal tract of the fish revealed that PepT1 is ubiquitously expressed in all segments beyond the stomach, including the pyloric caeca, and through the whole midgut. Only in the last segment, which included the hindgut, was there a lower expression. Atlantic cod PepT1, the second teleost fish PepT1-type transporter documented to date, will contribute to the elucidation of the evolutionary and functional relationships among vertebrate peptide transporters. Moreover, it can represent a useful tool for the study of gut functional regionalization, as well as a marker for the analysis of temporal and spatial expression during ontogeny.

Studies with teleost larvae have reported poor performance associated with quantitative lipid imbalances in the diet. The present study examined the effect of dietary protein:neutral lipid ratio on fatty acid (FA) absorption efficiency and metabolism in larval Senegalese sole. In addition, the effect of lipid class (triolein (TRI) and l-3-phosphatidylcholine-1,2-di-oleoyl (PC)), carbon number and degree of saturation of the labelled NEFA, stearic acid (SA), oleic acid (OA) and DHA) was tested. FA absorption was determined by tube feeding [1-14C]-labelled lipids and NEFA after a single meal of either non-enriched Artemia (NEA) or Artemia enriched on a soyabean oil emulsion (EA), or after feeding these diets over an extended period of time (18 d). The tested dietary protein:lipid ratios had no short-term influence but long-term feeding of a diet higher in neutral lipid (EA) increased lipid accumulation within the gut epithelium and resulted in lower FA absorption (higher label evacuation and lower retention of dietary FA), which may partially explain the trend for lower growth observed with this diet. The lipids and NEFA, showed different digestive and metabolic properties, independent of feeding regime. FA absorption increased with unsaturation, being lowest for SA, followed by OA, and highest for DHA. In addition, sole larvae had a lower capacity to digest and absorb FA esterified to TRI, compared with PC, with the order of decreasing absorption being NEFA>PC>>TRI. Moreover, larvae appeared to discriminate between the source of OA, as this FA in the free form or esterified to PC was catabolised less than TRI.

The mRNA of the peptide hormone cholecystokinin (CCK) was isolated from juvenile Atlantic herring, Clupea harengus, by RT-PCR. The open reading frame encodes a 137 amino acid-long precursor protein. The peptide sequence of herring CCK-8, DYMGWMDF, is identical to that of higher vertebrates and elasmobranchs, and contains methionine in the sixth position from the C-terminus, which has not been reported previously in teleosts. Expression analysis by in situ hybridization shows that positive endocrine-like cells were mainly located in the pyloric caeca and to a less extent in the rectum of the juvenile. A few positive cells were also found in the pyloric portion of the stomach and the intestine. CCK cells were present in all the larvae examined from the day of hatching onwards. Although the CCK cells were scattered throughout the whole midgut, no signals were detected in either the foregut or the hindgut. Since herring larvae have a straight gut, the distribution pattern of CCK cells seems to be reflected in the anatomy of the gut.

The ontogenetic development of cholecystokinin-immunoreactive (CCK-IR) cells was studied in larval ayu, Plecoglossus altivelis. This species has a straight digestive tract during the larval phase. CCK-IR cells were present in all the larvae from the day of hatching (0 days after hatching, DAH). An immunoreaction to anti-trypsinogen antibody was also detected in the pancreas at this stage. The distribution pattern of the CCK-IR cells was quantified by recording the location of CCK-IR cells at 1, 16, and 76 DAH. Although the number of CCK-IR cells increased during development, the distribution pattern of CCK-IR cells did not change until 76 DAH. The CCK-IR cells were scattered throughout the midgut, with the exception of the regions adjacent to the pyloric and rectal sphincters. No CCK-IR cells were detected in the foregut or the hindgut. This distribution pattern differs from species with rotated digestive tracts, whose CCK-IR cells are only found in the anterior part of the midgut. CCK-IR cells seem to be located in regions where the ingested food is retained and thus can easily receive chemical signals from the food and the digestive process in order to control the release of the hormone.

The appearance and distribution of cholecystokinin (CCK)-producing cells were investigated in the digestive tract of developing larvae of cultured Atlantic halibut, Hippoglossus hippoglossus. The CCK-producing cells were detected immunohistochemically, by use of a primary antiserum against CCK cloned for the Japanese flounder, Paralichthys olivaceus. No CCK-immunoreactive (IR) cells were detected in first-feeding larvae (33 days after hatching, DAH). Forty-five DAH or 12 days after first feeding, there were a few scattered CCK-IR cells in the epithelium of the anterior midgut in about 30% of the examined larvae. All larvae older than 52 DAH had CCK-IR cells in the anterior midgut, particularly frequent in the most anterior region adjacent to the pyloric caeca. No CCK-IR cells were detected in the foregut, the hindgut, or the midgut posterior to the first curvature. The CCK-IR cells spanned the intestinal epithelium from the basal lamina to the lumen and were triangular in shape, with the nucleus in the basal part and a thin apex toward the lumen. The mechanisms controlling release of bile, pancreatic enzymes, and peristalsis during the 12 days between first feeding and the first detection of CCK-IR cells remain to be clarified.

Embryos and larvae of the African catfish Clarias gariepinus excrete significant quantities of urea. The present study focused on the potential urea-generating pathways during early development of this teleost; uricolysis, argininolysis and the ornithine-urea cycle (OUC). Uricase, allantoinase, allantoicase and ureidoglycollate lyase of the uricolytic pathway were expressed in all early life stages and in adult liver of C. gariepinus. Uricase activity increased in starved larvae compared with yolk-sac larvae. The key regulatory enzyme of the teleost OUC, carbamoyl phosphate synthetase III (CPSase III), was expressed predominantly in muscle of developing C. gariepinus larvae and showed negligible activity in the absence of its allosteric effector N-acetyl-L-glutamate. CPSase III and ornithine carbamoyl transferase activities increased in fed larvae compared with starved larvae. In contrast to the early developmental stages, adult C. gariepinus expressed only low and variable levels of CPSase III, suggesting that, under the experimental conditions employed, OUC expression is influenced by developmental stage in this species. The data indicate that early C. gariepinus life stages express the enzymes necessary for urea production by uricolysis, argininolysis and the OUC, and this may explain why urea tissue levels and urea excretion rates are substantial during the early development of this air-breathing teleost.

In diving, pulmonary mechanical function is limited by the increased density of the gas breathed. Breathing cold and dry gas may cause an additional increase in airways resistance. We have measured forced vital capacity, forced expired volume in 1 s (FEV1) and forced midexpiratory flow rate (FEF25%-75%) before and after breathing dry or humid gas at 29-32 degrees C during a standardized exercise intensity on a cycle ergometer at an ambient pressure of 3.7 MPa. The atmosphere was a helium and oxygen mixture with a density of 6.8 kg.m-3. Six professional saturation divers aged 26-37 years participated in the study. There were no significant differences in convective respiratory heat loss between the exposures. The mean evaporative heat loss was 67 W (range 59-89) breathing dry gas and 37 W (range 32-43) breathing humid gas, corresponding to water losses of 1.7 g.min-1 (range 1.5-2.2) and 0.9 g.min-1 (range 0.8-1.1), respectively. There was a significant reduction in FEV1 of 4.6 (SD 3.6)% (P < 0.05), and in FEF25%-75% of 5.8 (SD 4.7)% (P < 0.05) after breathing dry gas. There were no changes after breathing humid gas. By warming and humidifying the gas breathed in deep saturation diving bronchoconstriction may be prevented.

We have measured in 7 divers forced vital capacity (FVC), forced expired volume in 1 s (FEV1), and forced midexpiratory flow rate (FEF25-75%) before and after exposure to dry or humid breathing gas of 35.3 degrees-36.8 degrees C (air) when diving to pressures of 117-600 kPa. The response was compared with the subjects' reactivity to pharmacologic bronchoprovocation with methacholine. Baseline FEV1 and FEF25-75% decreased in accordance with increasing gas density. Relative to baseline, there was a significant reduction after the dives in FEV1 of 4.0 +/- 6.1% (P less than 0.05) and in FEF25-75% of 8.6 +/- 9.7% (P less than 0.01) with exposure to dry breathing gas. By analysis of variance the reduction in the lung function variables below baseline were related to the breathing gas characteristic (dry/humid) (P less than 0.01), bronchial hyperreactivity (P less than 0.02), and ambient pressure (P less than 0.02) independently of each other. There was no significant change in FVC after the exposures. Humid breathing gas was considered more comfortable than dry breathing gas, and the upper comfort limit for breathing gas temperature was higher with humid breathing gas. Convective respiratory heat loss was negligible in these experiments, indicating that dry gas itself had a significant bronchoconstrictive effect. Bronchial hyperreactivity may cause increased risk of development of bronchial obstruction and air trapping during diving.