Ultrastructural changes in the pars intermedia of the goldfish kept in calcium-free environments

The PAS-positive-calcium-sensitive (Ca-s) cells of the pars intermedia (PI) were studied in goldfish kept in fresh water (FW), deionized water (DW), 1/3 sea water (SW) and 1/3 Ca-free SW. Ultrastructural studies show that Ca-s cells of control goldfish kept in FW have a low activity with elongated or deeply indented nuclei. This activity is slightly reduced after 19 days in 1/3 SW. A considerable stimulation of most Ca-s cells is noted in goldfish kept in DW for 20 or 40 days. The stimulation is similar in 1/3 Ca-free SW, but it affects sometimes a smaller percentage of cells and may be less marked in peripheral areas of the PI. Exocytotic figures are more numerous in Ca-s cells of goldfish in 1/3 Ca-free SW than in DW. A basal lamina is rarely present and direct contacts between PI cells and nervous tissue are frequent, although a single synaptic contact with a type B fiber was observed. MSH cells are not affected in goldfish kept in DW. They are stimulated in 1/3 Ca-free SW: the physiological significance of this response remains unclear. Few agranular (Agr) cells are scattered in the PI. Evident changes are not observed in the different environments. The present ultrastructural data support the hypothesis that the Ca-s cells of the PI secrete a factor involved in calcium regulation in some teleosts.     

Response of calcium-sensitive cells in the pars intermedia of the goldfish adapted to diluted sea water with different calcium and magnesium contents

Summary Goldfish kept in diluted Ca-free sea water (SW) (23 or 30 %) or in Ca-Mg-deficient SW (23 %) have a limited survival, release large amounts of mucus, and show spasmodic seizures. Plasma calcium decreases. The PAS-positive calcium-sensitive (Ca-s) cells of the pars intermedia show a low activity in diluted SW and in 23 % Mg-free SW. In diluted Ca-free SW, Ca-s cells are stimulated, but cell hypertrophy is not uniform and often restricted to an area adjacent to the proximal pars distalis. Nuclear hypertrophy is significant in the reactive area, although less pronounced or even absent at the periphery of the lobe. Mitotic activity occurs in the Ca-s cells of goldfish gradually adapted to diluted Ca-free SW and Ca-Mg-deficient SW, and sacrificed after 19 and 28 days, respectively. A general stimulation of the Ca-s cells, which remains less intense than that in goldfish kept in deionized water (DW), appears unable to ensure the survival of the goldfish in an isosmotic Ca-free environment containing Mg²⁺ (0.1, 12 or 16.8 mM). These data are compared with those obtained in the eel kept in Ca-free SW.     

Response of prolactin cells to environmental calcium in the eel (Anguilla anguilla L.)

Prolactin (PRL) cell activity was investigated in eels kept in fresh water (FW), deionized water (DW) supplemented or not with Ca (2 mM), in Ca-enriched FW (10 mM), in normal (Ca 3.4 mM) or Ca-free 1/3 sea water (SW), and in SW (Ca 10.2 mM) or Ca-free SW (Ca 0.15 mM). Light-microscopic studies, including measurement of the nuclear area and cell height, showed that PRL cell activity, reduced in DW, is not affected by Ca supplementation. Activity is reduced in Ca-enriched FW, in 1/3 SW and in SW, conditions inducing an increase in the plasma sodium level. The lack of calcium in saline environments partly suppresses the nuclear atrophy occurring in SW. There is no significant correlation between external or total plasma calcium concentration and PRL cell activity. In artificial Ca-free SW, eels show a rapid increase in plasma osmolarity and sodium levels; there is a significant negative correlation between these two plasma values and the nuclear area or cell height of PRL cells. As in some other teleosts, plasma osmolarity and plasma sodium seem to play a more important role than external or internal calcium in controlling PRL secretion. This correlation is not apparent in eels kept in SW, having unstimulated PRL cells but active calcium-sensitive (Ca-s) cells in the pars intermedia.     

The Calcium-sensitive Cells of the Pars Intermedia in the Eel

In the pituitary, the PAS-positive calcium-sensitive (Ca-s) cells of the pars intermedia appear less active in seawater (SW)- than in freshwater (FW)-adapted eels. The kinetics of their response during adaptation to SW or readaptation to FW was investigated. Morphometric studies show that transfer to SW induces a rapid nuclear atrophy which accentuates in eels kept for several weeks in SW. Readaptation to FW stimulated the Ca-s cells after 2–10 days; after 1 or 2 months, the cells tend to be similar to those of eels kept in FW. Plasma calcium decreases slightly but significantly in SW eels. The response of the Ca-s cells is not modified by an ovine prolactin treatment inducing hypercalcemia, hypernatremia and stimulation of the corpuscles of Stannius. Minor changes occurring in the MSH cells remain difficult to interpret; the short stimulation during readaptation to FW may be related to a stress effect and/or to release of other peptides present in the MSH cells of fish.     

Ultrastructural changes in the calcium-sensitive (PAS-positive) cells of the pars intermedia of eels kept in deionized water and in normal and concentrated sea water

Summary The ultrastructure of the calcium-sensitive (Ca-s) (PAS-positive) cells of the pars intermedia was investigated in eels kept in hypo and hyperosmotic environments. Although the cells were moderately active in fresh water (FW), they were highly stimulated in deionized water (DW) and displayed an enlarged Golgi apparatus, a distinct rough endoplasmic reticulum, few secretory granules, some microtubules and an extended area of contact with the basal lamina that separates nervous and glandular tissues. Some mitosing cells were seen. A similar picture was observed in eels kept in sea water (SW) for 45 days, returned to FW and subsequently to DW for 21 days. In SW (30 and 33), and particularly in concentrated SW (50, 60 and 63), the Ca-s cells were inactive. Their granules were significantly smaller than in eels kept in FW, and the area of contact with the basal lamina was greatly reduced. However, signs of granule-release were seen in eels adapted to 50 and 60 SW. Nerve fibers rarely contacted the Ca-s cells and did not synapse with them. The ultrastructural data support the hypothesis that the Ca-s cells of Anguilla, like those of Carassius, are involved in ionic regulation. MSH cells were not greatly affected by the present experiments.     

Calcium-sensitive cells of the pars intermedia and osmotic balance in the eel

Summary The structure of the PAS-positive calcium-sensitive (Ca-s) cells of the pars intermedia was investigated in eels kept in deionized water (DW) or fresh water (FW) supplemented with Ca²⁺ or Mg²⁺. Ca²⁺ (2mM) reduces considerably the response to DW; plasma osmolarity, Na⁺ and Ca²⁺ levels are not significantly affected. In eels adapted to DW for 21 or 28 days, showing highly stimulated Ca-s cells, an addition of CaCl₂ for 2 days inhibits the release of granules, but does not immediately block their synthesis and the mitotic activity. The nuclear area is reduced, osmolarity and plasma sodium increase, but the rise in calcium is not always significant. Magnesium, at a 10-fold greater concentration than in FW (2 mM), slightly inhibits the release of secretory granules without reducing other indicators of stimulation. In Ca-enriched FW, the Ca-s cells appear inactive. These data show that the PAS-positive cells in the pars intermedia of the eel are calcium-sensitive, similar to those of the goldfish; their role in calcium regulation is briefly discussed.     

Effect of pimozide on the cytology of the eel pituitary

Pimozide, a specific blocker of dopaminergic receptors, was injected for 4 to 9 days in freshwater (FW) eels or eels acclimated to sea water (SW), for 10 to 30 days. The daily dose was 100 or 200 microgram/100 g. In FW, pimozide induces a nuclear hypertrophy in the prolactin (PRL) cells of eels; these elongated cells increase in height. The amount of erythrosinophilic granules in the cytoplasm, initially reduced, increases. Plasma electrolyte values are not modified: only the plasma sodium level slightly rises with the higher dose. In SW, PRL cells appear less active. After 10 days, this hypoactivity is not yet fully evident; pimozide stimulates PRL cells without affecting electrolyte values. After 1 month in SW, PRL cells are stimulated with pimozide and a slight regranulation may occasionally occur. The response in SW is never as marked as it is in FW; a high dose is not more effective than a low one. The higher dose significantly raises Na+, Ca2+ and Cl- plasma levels. These data suggest that prolactin synthesis and release increase with pimozide. They corroborate the hypothesis of a hypothalamic inhibitory control on PRL secretion mediated through dopaminergic fibers in the eel, but other factors may also be involved in this regulation in addition to the effect of salinity.     

Specific effect of calcium ions on the calcium-sensitive cells of the pars intermedia in the goldfish

Summary Cytological changes in the calcium-sensitive (Ca-s) cells (formerly termed PAS-positive cells) of the pars intermedia were investigated in the goldfish after adaptation to deionized water (DW), with or without addition of sodium, potassium and magnesium. These ions were added as chloride salts at concentrations similar to those present in fresh water (FW). The marked stimulation of the Ca-s cells is not inhibited in DW supplemented with Na⁺ (0.35 mM/1), K⁺ (0.05 mM/1), and Mg²⁺ (0.2mM/1) for a period of 24 days. The inhibition of the response to DW with calcium chloride (2 mM/1) is reproduced with calcium formiate (2 mM/1). These data show that chloride ions are not responsible for the regression of the Ca-s cells observed in goldfish kept in DW supplemented with calcium chloride. The effect of calcium ions on the Ca-s cells appears to be specific. These results support the hypothesis that the Ca-s cells synthesize a factor (hypercalcin?) involved in calcium regulation, and that its release is influenced by the calcium content of the environment. The role of the pars intermedia in calcium metabolism is strengthened by the present results. Biochemical data suggest the presence of a hypercalcemic factor in the pituitary of fish (Parsons et al. 1978) and are in agreement with the present cytological findings.     

Differential Effect of Sodium and Magnesium on the Pituitary of Goldfish Adapted to Calcium-Free Environments

Adaptation to deionized water (DW) affects several cell types in the goldfish. The pars intermedia PAS-positive cells are highly stimulated. Their low response or the absence of changes in goldfish kept in 1/3 Ca-free seawater (SW) and in Ca-free SW-adapted eels, respectively, suggest that sodium and/or magnesium are interfering. To test this hypothesis, young goldfish were adapted to DW supplemented or not with sodium (50 and 140 mM) for 8 and 16 days or with magnesium (16.5 and 50 mM) for 16 and 30 days. Cytological and morphometric studies of the pituitary showed that prolactin (PRL) cell activity was reduced by sodium. Thyrotropic (TSH) cells were stimulated. The activity of melanocyte-stimulating (MSH) cells increased in DW + Na+. Stimulation of the pars intermedia PAS+ cells in DW was partly inhibited by adding sodium; the cellular and nuclear areas increased only moderately, the endoplasmic reticulum (ER) was not conspicuous and mitotic activity disappeared. In DW + Mg²⁺ the activity of PRL, TSH and MSH cells tended to be lower after a long-term adaptation. The response of the PAS+ cells was as high as that noted in DW; complete degranulation, enlargement of the ER and important mitotic activity. Differential responses to Na+ and Mg²⁺ are not due to pH differences in the solutions. External sodium is able then to reduce the response of the PAS+ cells in a Ca-free environment, while magnesium is not inhibitory. Other cell types are also affected by high levels of Na+ and Mg²⁺.     

Two isoforms of the Na+/K+/2Cl- cotransporter are expressed in the European eel (Anguilla anguilla)

Two cDNA isoforms of the NKCC1 secretory cotransporter have been isolated from the European eel. The NKCC1a isoform exhibited mRNA expression in a wide range of tissues in a similar fashion to mammals, whereas NKCC1b was expressed primarily in the brain. The effect of freshwater (FW) to seawater (SW) transfer on NKCC1a expression was dependent on the developmental stage. In non-migratory yellow eels, NKCC1a mRNA expression in the gill was transiently up-regulated 4.3-fold after 2 days but also subsequently by 2.5-6-fold 3 weeks after SW transfer. Gill NKCC1a expression was localised mainly in branchial chloride cells of SW acclimated yellow eels. In contrast to yellow eels, NKCC1a mRNA abundance was not significantly different following SW acclimation in silver eel gill. NKCC1a mRNA abundance decreased in the kidney following SW acclimation and this may correlate with lower tubular ion/fluid secretion and urine flow rates in SW teleosts. Kidney NKCC1a mRNA expression in silver eels was also significantly lower than in yellow eels, suggesting some pre-acclimation of mRNA levels. NKCC1a mRNA was expressed at similar low levels in the middle intestine of FW- and SW-acclimated yellow or silver eels, suggesting the presence of an ion secretory mechanism in this gut segment.     

Effects of Hypophysectomy and Prolactin Replacement on Eel Kidney Structure During Adaptation to Sea Water

After 20 to 50 days in sea water (SW), regressive changes of the kidney occur at the same rate in intact and hypophysectomized eels (Anguilla anguilla). In SW, ovine prolactin (oPRL) increases plasma electrolytes and restores a fresh water (FW) kidney structure; cell height and nuclear area increase in main segments of the nephron: first (P1) and second proximal (P2), distal (D) and initial collecting (C) tubules. A differentiation of new tubules also occurs. This effect is less intense after hypophysectomy and greater in FW. A dose of 10 μg/g body weight/day for 10 days in SW produces some harmful renal effects, barely detected at 6 μg/g/day. The kidney plays a minor role in osmotic adjustment in SW when PRL secretion is reduced (intact eels) or suppressed (hypophysectomized); PRL treatment reverses effects of SW adaptation. An inhibition of gill sodium extrusion may explain the high blood sodium level; however, kidney histological changes suggest a renal participation, perhaps through reduced water permeability as in Platichthys.     

The effects of progesterone, prostaglandin F2α and oxytocin on the calcium-activation of the uterus

The relationship between “activator-calcium” (A-Ca), progesterone (P), prostaglandin F2α (PGF2α) and oxytocin (Oxy) has been examined in 100 uterine strips of 34 pregnant and 100 strips of 34 post partum rabbits. At the 25th day of gestation, uterine P was 13.9±1.3 ng/g, while within 3–12 hours post partum 3.3±0.3 ng/g tissue (P<0.001). Uterine strips, mounted isometrically in Krebs' solution, sustained maximum excitability in a steady state when exposed every 30 seconds for 4 seconds to an electric field of 12 V/5 cm (a.c.). The maximally contracting muscles were then rinsed at intervals of 6 minutes with Ca-free Krebs.In Ca-free Krebs, the post partum uterus lost 31% of its Ca and 96% of its excitability in a short 25 minutes, while the pregnant uterus lost 30% of its Ca and 93% of its excitability in 50 minutes (P<0.001). Since the extracellular space is 30% in the uterus, this 30% Ca, lost by both muscles, most probably was extracellular Ca and the small A-Ca fraction which is presumably “bound” more strongly at the membrane systems of the P-dominated pregnant, than the non-dominated post partum uterus. The significantly faster and more complete recovery from Ca-deficiency and inexcitability of the pregnant than the post partum uterus (P<0.001), at different levels of external Ca, further substantiates this premise. So does the demonstration that exposure to Ca-free Krebs increases ⁴⁵Ca-efflux 400% in the post partum and only 110% in the pregnant uterus (P<0.001). Exposure to 100 ng/ml PGF2α in normal Krebs has a similar effect on the ⁴⁵Ca-efflux of the post partum uterus, while the response of the pregnant uterus is indistinct (P<0.001).These highly significant differences between the post partum and the pregnant uteri in their Ca-efflux explain the higher threshold (P<0.001) and lower “sensitivity” to PGF2α and Oxy (P<0.001) of the pregnant than the post partum uterus. The already very highly significant differences between the two muscles, in threshold and sensitivity to these two most potent oxytocics, were increased still further by rendering the uterine strips Ca-deficient. All together, these findings substantiate the early contention (1–7,18,19) that uterine function at the cellular level is regulated by opposing actions of the suppressor P and the intrinsic stimulant PG or other oxytocic agents on threshold, excitability and the Ca-activation of the contractile process.     

Osmoregulation in North American eels (Anguilla rostrata LeSueur) on land and in freshwater: effects of the corpuscles of Stannius

Hypercalcemia, hypomagnesia and hypophosphatemia were observed in freshwater (FW) eels (Anguilla rostrata LeSueur) after removal of the corpuscles of Stannius. These changes did not occur if Stanniectomized (CSX) eels were removed from FW and placed on land for 12 days but did occur after the eels were returned to FW. Therefore, changes in plasma electrolyte concentrations after CSX depended upon the branchial and/or integumental influx of ions. Plasma Na⁺, Cl⁻ and osmolal concentrations decreased gradually in both sham-operated (SHM) and CSX eels on land (12 days) and in FW (12 days). Plasma K⁺almost doubled in both SHM and CSX eels after 4 days on land, remained elevated, and fell abruptly to normal within a day after the eels were returned in FW. After 2 days on land, urine flow rates in SHM and CSX eels had decreased by approximately 85%, osmolar clearance by 50% and positive free-water clearance by more than 90%. Body weights did not decrease when eels were on land so it was concluded that the reduced but continuous renal loss of water was counterbalanced by the integumental uptake of condensed water. Accepted: 21 October 1998     

Freshwater to seawater acclimation of juvenile bull sharks (<Emphasis Type="Italic">Carcharhinus leucas</Emphasis>): plasma osmolytes and Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase activity in gill,rectal gland,kidney and intestine

This study examined the osmoregulatory status of the euryhaline elasmobranch Carcharhinus leucas acclimated to freshwater (FW) and seawater (SW). Juvenile C. leucas captured in FW (3 mOsm l^–1 kg^–1) were acclimated to SW (980–1,000 mOsm l^–1 kg^–1) over 16 days. A FW group was maintained in captivity over a similar time period. In FW, bull sharks were hyper-osmotic regulators, having a plasma osmolarity of 595 mOsm l^–1 kg^–1. In SW, bull sharks had significantly higher plasma osmolarities (940 mOsm l^–1 kg^–1) than FW-acclimated animals and were slightly hypo-osmotic to the environment. Plasma Na⁺, Cl^–, K⁺, Mg²⁺, Ca²⁺, urea and trimethylamine oxide (TMAO) concentrations were all significantly higher in bull sharks acclimated to SW, with urea and TMAO showing the greatest increase. Gill, rectal gland, kidney and intestinal tissue were taken from animals acclimated to FW and SW and analysed for maximal Na⁺/K⁺-ATPase activity. Na⁺/K⁺-ATPase activity in the gills and intestine was less than 1 mmol Pi mg^–1 protein h^–1 and there was no difference in activity between FW- and SW-acclimated animals. In contrast Na⁺/K⁺-ATPase activity in the rectal gland and kidney were significantly higher than gill and intestine and showed significant differences between the FW- and SW-acclimated groups. In FW and SW, rectal gland Na⁺/K⁺-ATPase activity was 5.6±0.8 and 9.2±0.6 mmol Pi mg^–1 protein h^–1, respectively. Na⁺/K⁺-ATPase activity in the kidney of FW and SW acclimated animals was 8.4±1.1 and 3.3±1.1 Pi mg^–1 protein h^–1, respectively. Thus juvenile bull sharks have the osmoregulatory plasticity to acclimate to SW; their preference for the upper reaches of rivers where salinity is low is therefore likely to be for predator avoidance and/or increased food abundance rather than because of a physiological constraint.     

Water metabolism in the eel acclimated to sea water: from mouth to intestine

Eels seem to be a suitable model system for analysing regulatory mechanisms of drinking behavior in vertebrates, since most dipsogens and antidipsogens in mammals influence the drinking rate in the seawater eels similarly. The drinking behavior in fishes consists of swallowing alone, since they live in water and water is constantly held in the mouth for respiration. Therefore, contraction of the upper esophageal sphincter (UES) muscle limits the drinking rate in fishes. The UES of the eel was innervated by the glossopharyngeal-vagal motor complex (GVC) in the medulla oblongata (MO). The GVC neurons were immunoreactive to an antibody raised against choline acetyltransferase (ChAT), an acetylcholine (ACh) synthesizing enzyme, indicating that the eel UES muscle is controlled cholinergically by the GVC. The neuronal activity of the GVC was inhibited by adrenaline or dopamine, suggesting catecholaminergic innervation to the GVC. The AP and the commissural nucleus of Cajal (NCC) in the MO projected to the GVC and were immunoreactive to an antibody raised against tyrosine hydroxylase (TH), rate limiting enzyme to produce catecholamines from tyrosine. Therefore, it is likely that activation in the AP or the NCC may inhibit the GVC and thus relaxes the UES muscle, which allows for water to enter into the esophagus. During passing through the esophagus, the imbibed sea water (SW) was desalted to approximately 1/2 SW, which was further diluted in the stomach and arrived at the intestine as approximately 1/3 SW, almost isotonic to the plasma. Finally, from the diluted SW, the eel intestine absorbed water following the Na⁺–K⁺–2Cl⁻ cotransport (NKCC2) system. The NaCl and water absorption across the intestine was regulated by various factors, especially by peptides such as atrial natriuretic peptide (ANP) and somatostatin (SS-25 II). During desalination in the esophagus, however, excess salt enters into the blood circulation, which is liable to raise the plasma osmolarity. However, the eel heart was constricted powerfully by the hyperosmolarity, suggesting that the hyperosmolarity enhances the stroke volume to the gill, where excess salt was extruded powerfully via Na⁺–K⁺–2Cl⁻ cotransport (NKCC1) system.     

Classes and mechanisms of calcium waves

The best known calcium waves move at about 5–30 μm/s (at 20°C) and will be called fast waves to distinguish them from slow (contractile) ones which move at 0.1-1 μm/s as well as electrically propagated, ultrafast ones. Fast waves move deep within cells and seem to underlie most calcium signals. Their velocity and hence mechanism has been remarkably conserved among all or almost all eukaryotic cells. In fully active (but not overstimulated) cells of all sorts, their mean speeds lie between about 15–30 μm/s at 20°C. Their amplitudes usually lie between 3–30 μM and their frequencies from one per 10–300 s. They are propagated by a reaction diffusion mechanism governed by the Luther equation in which Ca²⁺ ions are the only diffusing propagators, and calcium induced calcium release, or CICR, the only reaction; although this reaction traverses various channels which are generally modulated by IP₃ or cADPR. However, they may be generally initiated by a second, lumenal mode of CICR which occurs within the ER. Moreover, they are propagated between cells by a variety of mechanisms. Slow intracellular waves, on the other hand, may be mechanically propagated via stretch sensitive calcium channels.     

Early Effects of Neonatal Rat Desympathization on Secondary Heart Rhythms

Neonatal Wistar rats for the first 3 weeks of life were injected intraperitoneally with isobarine every other day. The single doze was 40 mg/kg. Control animals were injected with saline. Degenerative changes in sympathetic ganglia were evident as early as in the 10-day old animals and increased by 18–19 days. The heart rate in the desympathized animals was lower than in control from 10–11 to 18–19 days, but by the end of the 3rd week the differences were eliminated. The same occurred with respiration rate. At same terms there was an essential decrease of amplitude of the heart rate high-frequency fluctuations synchronous with respiration and of the periodogram slow waves with the period about 1 min. Using the method of fast Fourier transform, the power spectra of heart rate fluctuations (secondary heart rhythms) in 5 frequency ranges (0–0.01, 0.01–0.03, 0.03–0.1, 0.1–1.0, and 1.0–2.5 Hz) were calculated. Desympathization leads to a decrease of the fluctuation power in all ranges, but in the ultralow-frequency range this decrease is the least pronounced, which suggests the presence of non- sympathetic mechanisms in their genesis. The greatest changes occur in the middle-frequency area. In all cases, differences from control values increase from the 10–11th to the 18–19th days, after which a tendency for restoration is observed, in spite of an enhancement of processes of degeneration of sympathetic neurons. This indicates an activation of the compensatory mechanisms, due to which consequences of desympathization are partially smoothed at distant terms of studies.     

Protoplast culture and plant regeneration ofPinellia ternata

A study was undertaken to develop a protoplast regeneration system for pinellia. A yield of 19 29 x 10⁵ protoplasts/g F. W. could be obtained from cell suspension cultures incubated in a digestion enzyme solution with 2% cellulase Onzuka R-10, 10% pectinase (Sigma), 0.01% pectolyase Y23. K8P and modified MS media were used to culture protoplasts in: a) liquid, b) liquid-solid double layer, or c) agarose embedded protoplast culture. The former two were conducive to colony formation from protoplast-derived cells. The frequency of cell division was about 8% after 3 days in culture. Gradually adding fresh medium of lower osmotic pressure into the medium for protoplast culture favored cell division. Calli (1–2 mm in diameter) formed after 30–40 days in culture. The calli transferred onto medium supplemented with KT (0.5 mg 1^–1) and NAA (0.2 mg 1)^–1) could regenerate plants after 40–50 days. Of 47 plantlets transplanted into plots, 29 flowered and were fertile.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - NAA -naphthaleneacetic acid - KT kinetin - CH casein hydrolysate     

Feeding habitat and silvering stage affect lipid content and fatty acid composition of European eel Anguilla anguilla tissues

Lipids, particularly fatty acids (FAs), are major sources of energy and nutrients in aquatic ecosystems and play key roles during vertebrate development. The European eel Anguilla anguilla goes through major biochemical and physiological changes throughout its lifecycle as it inhabits sea- (SW), and/or brackish- (BW) and/or freshwater (FW) habitats. With the ultimate goal being to understand the reasons for eels adopting a certain life history strategy (FW or SW residency vs. ‘habitat shifting’), we explored differences in lipid content and FA composition of muscle, liver and eyes from eels collected across Norwegian SW, BW and FW habitats, and at different lifecycle stages (yellow to silver). FW and SW eels had a higher lipid content overall compared to BW eels, reflecting differences in food availability and life history strategies. SW eels had higher proportions of certain monounsaturated FAs (MUFAs; 18:1n-9, 20:1n-9), and of the essential polyunsaturated FAs 20:5n-3 (eicosapentaenoic acid, EPA) and 22:6n-3 (docosahexaenoic acid) than FW eels, reflecting a marine-based diet. In contrast, the muscle of FW eels had higher proportions of 18:3n-3, 18:2n-6 and 20:4n-6 (arachidonic acid), as is typical of FW organisms. MUFA proportions increased in later stage eels, consistent with the hypothesis that the eels accumulate energy stores prior to migration. In addition, the decrease of EPA with advancing stage may be associated with the critical role that this FA plays in eel sexual development. Lipid and FA information provided further understanding of the habitat use and overall ecology of this critically endangered species.     

Relative antidipsogenic potencies of six homologous natriuretic peptides in eels

Atrial natriuretic peptide (ANP) exhibits a potent antidipsogenic effect in seawater (SW) eels to limit excess Na(+) uptake, thereby effectively promoting SW adaptation. Recently, cardiac ANP, BNP and VNP and brain CNP1, 3 and 4, have been identified in eels. We examined the antidipsogenic effect of all homologous NPs using conscious, cannulated eels in both FW and SW together with parameters that affect drinking. A dose-response study (0.01-1 nmol/kg) in SW eels showed the relative potency of the antidipsogenic effect was in the order ANP ≥ VNP > BNP = CNP3 > CNP1 ≥ CNP4, while the order was ANP = VNP = BNP > CNP3 = CNP1 = CNP4 for the vasodepressor effect. The minimum effective dose of ANP for the antidipsogenic effect is much lower than that in mammals. ANP, BNP and VNP at 0.3 nmol/kg decreased drinking, plasma Na(+) concentration and aortic pressure and increased hematocrit in SW eels. The cardiac NPs induced similar changes in drinking, aortic pressure and hematocrit in FW eels, but aside from BNP no change in plasma Na(+) concentration. CNPs had no effect on drinking, plasma Na(+) concentration and hematocrit but induced mild hypotension in both FW and SW eels, except for CNP3 that inhibited drinking in SW eels. These results show that ANP, BNP and VNP are potent antidipsogenic hormones in eels in spite of other regulatory factors working to induce drinking, and that CNPs are without effects on drinking except for the ancestor of the cardiac NPs, CNP3.