Midgut Gland Tissues Research Articles

Spatial distribution of digestive proteinases in the midgut of the Pacific white shrimp (Litopenaeus vannamei) indicates the existence of endo-ectoperitrophic circulation in Crustacea.

The effect of dietary protein concentration on the spatial distribution of digestive proteinases in the shrimp Litopenaeus vannamei indicates the existence of endo-ectoperitrophic enzyme circulation in this species. Samples recovered from the midgut gland tissues, stomach contents, three different portions of the midgut and feces were used for quantitative and qualitative analyses of the composition and distribution of the digestive proteinases. Animals were divided into three different groups: (1) animals (controls) fed with a commercial 35% protein diet, (2) animals fed with a commercial diet supplemented with ovalbumin to a final protein concentration of 60%; (3) animals fed with an 80% protein diet. Quantitative determinations using different substrates and zymograms showed that increasing protein concentration in the diet alters the distribution of proteinases along the digestive tract. Composition of proteinases in the midgut gland, stomach contents, midgut sections and feces were similar, but not identical. Chymotrypsin and trypsin paralogues were identified in all enzyme sources in a concentration gradient along the midgut in the control shrimp, the expected distribution supporting the existence of a recycling mechanism. The occurrence of a peritrophic membrane in other Decapoda suggests that endo-ectoperitrophic circulation of digestive enzymes and nutrients may also occur in other crustaceans and also extends beyond the Insecta.

Food utilization of two pelagic crustaceans in the Greenland Sea: Meganyctiphanes norvegica (Euphausiacea) and Hymenodora glacialis (Decapoda, Caridea)

Large pelagic crustaceans from Greenland Sea waters, the northern krill Meganyc- tiphanes norvegica (Euphausiacea) and the decapod shrimp Hymenodora glacialis (Caridea), were captured in depths down to 1500 m and studied with respect to their physiological food utilization abilities. Both species showed distinct differences in the amount of total lipids (TLs), lipid class and fatty acid (FA) compositions as well as proteolytic enzyme activities. In M. norvegica, the overall amount of TLs and storage lipids was much lower than in H. glacialis, and triacylglycerols formed the major lipid fraction with a mean of 48% TLs. Major FAs comprised the trophic markers 20:1(n-9) and 22:1(n-11), indicating the ingestion of calanid copepods. Additionally, the FAs 22:6(n-3), 18:1(n-9) and 16:0 prevailed. In H. glacialis, TLs (mean = 44% dry mass) were about twice as high as in krill, with wax esters comprising up to 89% TLs. H. glacialis seems to accumulate these lipids as energy reserves to survive periods of food limitation. Moreover, high lipid levels, particularly wax esters, also help to maintain neutral buoyancy. The major FA in H. glacialis was 18:1(n-9); other dominant FAs were 20:1(n-9) and 22:1(n-11), typical of calanid copepods, as well as the diatom trophic marker 16:1(n-7). Both species showed omnivorous feeding behaviour with a strong tendency towards carni- vory. Total proteolytic activities in midgut gland tissue were higher in M. norvegica than in H. glacialis. In M. norvegica, proteinases were dominated by serine proteinases, whereas cysteine proteinases formed the major group in H. glacialis. High proteolytic activity in M. norvegica indicates a high digestive potential for proteins and efficient utilization of prey. The presence of different pro- teinase classes in both species may be due to different group-specific enzyme expression patterns between euphausiids and caridean decapods. Both species follow highly deviating life strategies, as reflected by their specific lipid and enzymatic characteristics.

Behavioral, physiological, and cellular responses following trophic transfer of toxic monoaromatic hydrocarbons

The trophic transfer of monoaromatic hydrocarbons to predatory organisms feeding upon contaminated marine animals is not well reported within the scientific literature. Branched alkylbenzenes (BABs) unresolved by gas chromatography have been reported to be principal toxic components of bioaccumulated hydrocarbons in the tissues of some wild mussel, Mytilus edulis, populations with poor health status. Mussels, M. edulis, contaminated with a commercial mixture of BABs were fed to shore crabs, Carcinus maenas, for 7 d, and effects upon the behavior, heart rate, hemolymph cellular viability, and immune response of the crabs were assessed. Accumulation of BABs in crab midgut gland tissue was quantified by gas chromatography-mass spectrometry, and the presence of BABs in crab urine was detected spectrophotometrically using ultraviolet fluorescence spectroscopy. Analysis of crab tissues and urine revealed a proportion of the BABs was transferred from the mussel tissues to the crabs, but the majority was not present 3 d after consumption of the mussels and may have been metabolized, excreted, or both. The results do not support the hypothesis that BABs are likely to be biomagnified, at least by crabs, in the marine environment. Alterations to measured cellular and physiological responses of crabs fed BAB-exposed mussels were not significant. Consumption of contaminated mussels was shown to cause highly significant abnormal behavior that, in the wild, may affect the feeding ability of crabs and make them more vulnerable to predation.

Role of the midgut gland in purine excretion in the robber crab, Birgus latro (Anomura: Coenobitidae)

White fecal strands of Birgus latro are composed of small spherules of uric acid with a mean diameter of 1.6 ± 0.6 μm. Large numbers of membrane-bound spherules with concentric lamellae are present in the R cells of the midgut gland, so we suggest that lengths of white feces are produced by coordinated secretion of these spherules into the lumen of the midgut gland tubules. There are four cell types in the tubules with embryonic (E) cells at the distal tip, B cells in a narrow band at the distal end and R cells making up the bulk of the tubules and gland. F cells are sparsely scattered among the R cells. Midgut gland tissue was assayed for activities of xanthine dehydrogenase and xanthine oxidase, the two forms of xanthine oxidoreductase. Contrary to previous reports, we found that the midgut gland of B. latro contains only high activities of xanthine dehydrogenase. If proteinase inhibitors were omitted from the assays, however, significant activity of xanthine oxidase was measured, a result we regard as an artifact attributable to the partial conversion of xanthine dehydrogenase to xanthine oxidase by endogenous proteinases. R cells were demonstrated to contain peroxisomes, which may be involved in lipid metabolism rather than synthesis of uric acid. J. Morphol. 241:227–235, 1999 © 1999 Wiley-Liss, Inc.

Role of the midgut gland in purine excretion in the robber crab, Birgus latro (Anomura: Coenobitidae).

White fecal strands of Birgus latro are composed of small spherules of uric acid with a mean diameter of 1.6 +/- 0.6 microm. Large numbers of membrane-bound spherules with concentric lamellae are present in the R cells of the midgut gland, so we suggest that lengths of white feces are produced by coordinated secretion of these spherules into the lumen of the midgut gland tubules. There are four cell types in the tubules with embryonic (E) cells at the distal tip, B cells in a narrow band at the distal end and R cells making up the bulk of the tubules and gland. F cells are sparsely scattered among the R cells. Midgut gland tissue was assayed for activities of xanthine dehydrogenase and xanthine oxidase, the two forms of xanthine oxidoreductase. Contrary to previous reports, we found that the midgut gland of B. latro contains only high activities of xanthine dehydrogenase. If proteinase inhibitors were omitted from the assays, however, significant activity of xanthine oxidase was measured, a result we regard as an artifact attributable to the partial conversion of xanthine dehydrogenase to xanthine oxidase by endogenous proteinases. R cells were demonstrated to contain peroxisomes, which may be involved in lipid metabolism rather than synthesis of uric acid.

Extracellular and intracellular ionic changes in crayfish Astacus astacus exposed to nitrite at two acclimation temperatures

Freshwater crayfish, Astacus astacus, were exposed to two concentrations of ambient nitrite (0.5 and 1.0 mM) at two acclimation temperatures (6°C and 16°C) for 1 week. The concentration of nitrite in the haemolymph increased with increasing temperature and ambient level of nitrite. The haemolymph/water concentration ratio was the same at the two ambient nitrite concentrations but increased with temperature. Haemolymph nitrite reached concentrations that were 12 and 16 times higher than the water values at 6°C and 16°C, respectively. Nitrite accumulation induced a decrease in the haemolymph chloride concentration that far exceeded the rise in haemolymph [NO 2]. Haemolymph sodium concentration decreased significantly but less than haemolymph chloride. A large decrease in muscle tissue potassium concentration was seen in nitrite-exposed animals at both temperatures. In midgut gland tissue, the potassium concentration tended to increase, suggesting that the K + efflux mechanism that was stimulated in muscle tissue was absent (or less affected) in midgut gland tissue, and that part of the potassium lost from muscle may have been taken up by the midgut gland.

Physiological Diversity in Metabolism in Marine and Terrestrial Crustacea

Two aspects of metabolic adaptation to increased terrestrialism are considered: (1) respiratory adaptations as reflected by comparative cytochrome c oxidase activity in tissues of crabs from aquatic and terrestrial habitats, and (2) thermal acclimation patterns in cytochrome c oxidase activity in tissues from these crabs. Enzymatic assays were done spectrophotometrically on gill, muscle, and mid-gut gland tissues from two aquatic species, Libinia emarginata and Callinectes sapidus , and the terrestrial Ocypode quadrata . Cytochrome c oxidase was chosen for this study since it is generally believed that the more aerobic the cells or tissues become, the more fully developed the cytochrome system will be. This enzyme is also thought to have a role in thermal acclimation. In gill tissue the activity of cytochrome c oxidase is enhanced with the advent of aerial respiration. Enzymatic activity of gill tissue from Ocypode quadrata was significantly greater than it was in tissue from the aquatic species. No correlation was observed with increased terrestrialism and enzymatic activity of muscle or mid-gut gland tissue. The thermal acclimation patterns of tissues of these three species of crabs indicate a clear-cut tendency for less enzymatic adaptation to temperature at the tissue level as these crabs evolve toward a land habitat.

Ribonucleotide phosphohydrolases in the clam, Meretrix meretrix lusoria (Gmelin)

1. 1. Phosphohydrolytic activity was studied in the homogenized mid-gut gland tissue, using nucleotides (5′-AMP, 3′-AMP, 5′-IMP and GMP) and β-glycerophosphate as substrates. 2. 2. For nucleotides there were two optima of pH (8·5–9·7, 4·0–4·2). For β-glycerophosphate the activity was restricted to the alkaline region (pH 9·5).