Biomedical subjects

P Prunet

Publications and source records attributed to P Prunet.

At least 37 records · Page 2Linked to original sources

PubMed1998

Activation of gene transcription by tilapia prolactin variants tiPRL188 and tiPRL177.

In the tilapia species Oreochromis niloticus, the pituitary releases two forms of prolactins (tiPRL188 and tiPRL177). The binding parameters and the activation of tiPRL-induced JAK2/Stat5 signalling pathway were analysed using a mammalian cell line transiently transfected with the tiPRL receptor (tiPRLR). Our data indicate that the tiPRLR is able to mediate transcriptional activation of the PRL responsive element. At nanomolar concentrations, tiPRL188 activates gene transcription whereas at micromolar concentrations it inhibits luciferase transcription from the lactogenic responsive element. This is consistent with a model of receptor dimerisation. In contrast, the activation by tiPRL177 was only reached at high (microM) concentrations. The transcriptional activities induced by tiPRL177 and tiPRL188 are discussed in the context of the physiology of these hormones.

Amino Acid Sequence↗

PubMed1998

Isolation and functional analysis of the histone H3 promoter from atlantic salmon (Salmo salar L.).

The histone H3 (sH3) promoter of Atlantic salmon (Salmo salar) was cloned via polymerase chain reaction using primers designed from the rainbow trout (Oncorhynchus mykiss) promoter sequence. A comparison of the nucleotide sequence with the equivalent sequences from rainbow trout and sockeye salmon (Oncorhynchus nerka) revealed a high degree of conservation. In vivo expression analysis of the sH3 promoter was carried out in both rainbow trout and zebrafish (Danio rerio) embryos. A direct comparison of the sH3 promoter with the viral RSV promoter in rainbow trout resulted in stronger expression of the sH3 promoter. Furthermore, lacZ expression directed by the sH3 promoter was ubiquitous in several different cell types in developing zebrafish embryos. These results suggest that the sH3 promoter will be useful in transgenic studies in Atlantic salmon.

Animals↗

PubMed1997

Effect of confinement stress on circulating levels of growth hormone and two prolactins in freshwater-adapted tilapia (Oreochromis niloticus).

The aim of the present study was to assess a potential link between confinement stress and prolactin (PRL), the hormone responsible for adaptation to a hypoosmotic environment in freshwater-adapted tilapia (Oreochromis niloticus). The effect of stress on plasma levels of the two tilapia PRL forms, tiPRLI (or tiPRL188) and tiPRLII (or tiPRL177), was examined along with the effects on plasma levels of cortisol and growth hormone (GH). In a preliminary study, various sampling protocols (immediate sampling; sampling one by one; anesthesia at 0.5, 1, 2 ml/liter phenoxyethanol) were tested for their ability to modify basal plasma PRL and cortisol. In fish sampled within 1 min of capture (immediate sampling), no changes in the plasma levels of these hormones were observed, whereas when fish were sampled one at a time, PRL levels did not change but cortisol levels were modified. The immediate sampling protocol was used to study the effects of 1 hr confinement stress, which induced a large increase in plasma cortisol levels as well as increases tiPRLI and tiPRLII levels with kinetics similar to those of cortisol. In contrast, plasma tiGH levels significantly decreased after 1 hr confinement. When this stress situation was removed, plasma cortisol and tiPRL levels decreased and plasma GH levels increased. Two and one-half hours later, values were not significantly different from those measured in control fish. In tilapia exposed to 24 hr confinement stress, similar changes in hormone levels were observed. However, after 24 hr confinement, only cortisol levels were significantly different from those measured in control fish. None of these stress conditions significantly changed plasma chloride levels. Together, these results indicate that both PRL and GH have important roles in the adaptive response of freshwater-adapted tilapia to confinement stress.

Animals↗

PubMed1996

Plasma prolactin, cortisol, and thyroid responses of the brown trout (Salmo trutta) exposed to lethal and sublethal aluminium in acidic soft waters.

Brown trout, with indwelling dorsal aortic cannulae, were exposed to various concentrations of aluminium (Al; 50 micrograms liter-1, 100% mortality over 48 hr; 25 micrograms liter-1, 50% mortality over 120 hr; 12.5 micrograms liter-1, 0% mortality over 120 hr) in acidic (pH 5.0) soft water. The plasma concentrations of prolactin (PRL), cortisol, thyroxine (T4), and triiodothyronine (T3) were monitored. Plasma PRL concentrations were transiently depressed (to less than 20% of resting concentrations) after 12 hr in trout in the two highest water Al concentrations, but were unchanged in the trout exposed to 12.5 micrograms liter-1 Al. Plasma cortisol concentrations were elevated in response to all water Al levels and remained elevated in trout in the lethal conditions. The sublethally exposed trout showed a recovery in plasma cortisol concentrations by 120 hr. Plasma T4 concentrations were significantly elevated in trout exposed to both the lethal and the sublethal Al concentrations (from mean resting concentrations of 1-2 ng ml-1 to peaks of 8.9 and 9.0 ng ml-1 in the 50 and 12.5 micrograms liter-1 Al groups, respectively), although a recovery in plasma concentrations was evident in the sublethally exposed trout from 72 hr onwards. Plasma T3 concentrations were relatively stable in the trout exposed to the two highest doses of Al, whereas the trout under the lowest, sublethal, Al conditions exhibited a sustained (12-72 hr) elevation in plasma T3 concentrations (from a mean resting concentration of 0.9 ng ml-1 to a peak of 4.2 ng ml-1 at 48 hr). No clear relationship was apparent between the plasma PRL concentrations and the previously reported ionoregulatory status of the trout.

Aluminum↗

PubMed1995

Expression cloning of a cDNA encoding a fish prolactin receptor.

By using an expression cloning strategy, we isolated a single positive clone encoding a tilapia prolactin (PRL) receptor. Tilapia PRL188 was used to screen a freshwater tilapia kidney expression library transfected in COS cells. The tilapia PRL receptor is a mature protein of 606 amino acids. The extracellular domain is devoid of the tandem repeat units present in birds and has two pairs of cysteine residues, a Trp-Ser-Xaa-Trp-Ser motif, and two potential N-glycosylation sites. The cytoplasmic domain contains 372 amino acids, including box 1, a sequence previously shown to be important for signal transduction in mammalian species. Thus, the general structure is similar to the long form of mammalian PRL receptors; however, amino acid comparisons reveal a rather low identity (approximately 37%). Northern blot analysis shows the existence of a single transcript in osmoregulatory tissues and reproductive organs. This localization is in agreement with known functions of PRL in teleosts.

Amino Acid Sequence↗

PubMed1995

Apical structures of "mitochondria-rich" alpha and beta cells in euryhaline fish gill: their behaviour in various living conditions.

BACKGROUND: One of the characteristic features of the two types (alpha and beta) of "mitochondria-rich" (chloride) cells in the gill epithelium of freshwater fishes is the presence in their apical region of tubulovesicular structures. A further analysis of the ultrastructural features of these apical elements as well as that of their modifications under various living conditions should help to understand better the respective rôle of both alpha and beta cells in these conditions. METHODS: Atlantic salmon (Salmo salar) maintained in fresh water as well as tilapia (Oreochromis niloticus) maintained either in fresh water or in deionized water or in 20% saltwater were examined. Measurements of surface areas of apical structures in the various living conditions were also performed. RESULTS: In the alpha cells of freshwater fishes, the apical structures consisted of isolated vesicles containing a filamentous material resembling that coating the apical surface. They were closely related to the apical plasma membrane and did not penetrate the region containing the tubular system. When fishes were transferred to deionized water, the number of the apical membrane folds increased significantly, as did the number and size of apical structures which became elongated. In saltwater-adapted fishes, the apical structures showed a tendency to collapse and took the appearance of flattened and slightly curved elements. These observations tended to indicate that in alpha cells the apical structures were extensions of the apical plasma membrane and thereby might be implicated in sodium uptake when fishes are placed in fresh or deionized water and in chloride excretion when they are transferred to salt water. In beta cells, the apical structures were usually separated from the apical plasma membrane by a zone rich in cytoskeleton elements. They penetrated deeply into the supranuclear region, where they intermingled with the elements of the tubular system. They consisted mainly of tubular elements that contained a material resembling that present in the trans tubular Golgi network from which they might originate. The apical structures remained unaltered in beta cells whatever the medium (fresh or deionized water) in which the fish was placed. CONCLUSIONS: The alpha cells which are usually thought to be mainly involved in chloride excretion when fishes are transferred into seawater might also be implicated in sodium uptake in freshwater living conditions. The rôle of beta cells, in contrast, still remains to be established.

Animals↗

PubMed1995

Absence of a tiGH effect on adaptability to brackish water in tilapia (Oreochromis niloticus).

The aim of this study was to investigate the possible role of growth hormone in the adaptation of tilapia (Oreochromis niloticus) to brackish water and to analyze its interactions with prolactin in this process. Plasma levels of growth hormone do not change upon transfer to brackish water. Treatment of intact tilapia in fresh water with growth hormone prior to transfer did not enable the fish to preadapt to brackish water: the duration of the hydromineral imbalance after transfer was the same in treated animals and controls. The major osmoregulatory role of prolactin in fresh water led us to test the hypothesis that prolactin might antagonize the effect of growth hormone on adaptation to brackish water. Growth-hormone-treated hypophysectomized animals, however, exhibited no increased osmoregulatory capacity as compared to hypophysectomized controls, confirming the absence of a growth-hormone-related osmoregulatory effect. When prolactin and growth hormone were coinjected, growth hormone also proved unable to oppose the Na+ retaining effect of prolactin, in both brackish and fresh water. Surprisingly, hypophysectomized animals adapt better to brackish water than do sham-operated animals. This result is discussed in light of the effects of prolactin and cortisol on osmoregulation in brackish water and we suggest that an important event which allows O. niloticus to adapt to hyperosmotic environment is the reduction of plasma PRL upon transfer to brackish water.

Adaptation, Physiological↗

PubMed1995

Regulation of gill prolactin receptors in tilapia (Oreochromis niloticus) after a change in salinity or hypophysectomy.

Prolactin (PRL) receptors in gill tissue have been analyzed in tilapia (Oreochromis niloticus) after transfer from fresh water (FW) to brackish water (BW). This study has indicated the presence of only one class of tilapia PRL (tiPRL) receptor whatever the salinity. After transfer, however, the percentage of specific binding of the two forms of tiPRL (tiPRLI and tiPRLII) increased significantly. Scatchard analysis of tiPRLI binding indicated an increase in receptor affinity, an effect which was not accompanied by any change in receptor specificity. Transfer to BW also caused the number of tiPRL receptors to increase rapidly, remaining high in fish adapted to BW for 28 days. Based on the sharp reduction in plasma tiPRLI and tiPRLII levels after transfer to BW, one possible explanation may be that tiPRL itself is an important factor regulating the number of free receptors. This hypothesis finds support in the fact that the number of tiPRL receptors also increased in hypophysectomized fish reared in FW. However, the absence of change in receptor affinity after hypophysectomy suggested that yet other factors are involved in tiPRL receptor regulation during the transfer from FW to BW. The paradoxically high numbers of tiPRL receptors in the gills of BW-adapted tilapia, even though PRL is known to be a FW-adapting hormone, is discussed with regard to the environment in which tilapia live.

Animals↗

PubMed1994

Effects of growth hormone on gill chloride cells in juvenile Atlantic salmon (Salmo salar).

Experiments were performed to investigate the effects of ovine growth hormone (oGH) on both the ultrastructural features of chloride cells and the ability of gills to extrude Na+ after transfer into seawater. February presmolts and June parrs of the Atlantic salmon (Salmo salar) were implanted with oGH. In such animals, spontaneously showing a poor ability to adapt themselves to seawater life, GH significantly increased gill Na(+)-K(+)-adenosinetriphosphatase activity as well as gill sodium efflux into seawater. When examined by electron microscope, two types of chloride cells (alpha- and beta-types) were identified in control parrs and presmolts. GH treatment induced an increase in size and number of alpha-cells that displayed an extensive tubular system, while the beta-cells, thought to be specific to freshwater life, decreased in number. There was, concomitantly, an increase in number of accessory cells associated with the apical portion of the alpha-cells and, as a result, the formation of extensive shallow junctions between these cell types. Such functional and ultrastructural modifications that mimicked those naturally occurring during the last steps of the smoltification strongly suggest that GH stimulates the differentiation of freshwater chloride cells toward a seawater type.

Animals↗

PubMed1994

Evidence that two tilapia (Oreochromis niloticus) prolactins have different osmoregulatory functions during adaptation to a hyperosmotic environment.

Two forms of prolactin (tiPRLI and tiPRLII), with only 69% sequence identity, have been previously described in the cichlid fish tilapia (Oreochromis species). In the present study we have attempted to investigate the biological activity of these two prolactin forms during adaptation to a hyperosmotic environment. For this purpose, we have developed two highly sensitive (sensitivity: 0.05 ng/ml) and specific (cross-reactivity < 0.04%) radioimmunoassays for tiPRLI and tiPRLII, using recombinant hormones. When fish were directly transferred from fresh to brackish water, the measured levels of plasma tiPRLI and tiPRLII dropped abruptly until 12 h after transfer. Thereafter, plasma tiPRLII remained stable (around 0.5 ng/ml) until the end of the experiment, whereas plasma tiPRLI continued to decrease to undetectable levels. These different patterns of change are reflected in the calculated ratio of plasma tiPRLII to tiPRLI, which increased from 2-3 in fresh water-adapted fish to over 10 in fish which had spent 3 days or more in brackish water. The pituitary contents of tiPRLI and tiPRLII varied in a qualitatively similar fashion after transfer to brackish water. The tiPRLI content dropped continuously after 12 h, reaching one-twelfth of its initial level after 2 weeks. The pituitary tiPRLII content, on the other hand, did not decrease significantly until day 7, and after a 2-week exposure to brackish water it had only decreased by 50%. When injected into tilapia adapted to brackish water, both ovine prolactin and recombinant tiPRLI induced a clear dose-dependent ion-retaining effect. In contrast, the effect induced by tiPRLII treatment was markedly smaller and not dose-dependent. Northern blot analysis of tiPRL mRNAs using either a tiPRLI or a tiPRLII cDNA probe indicated the presence of two mRNAs differing in size: a 1.7 kb mRNA coding for tiPRLI and a 1.3 kb mRNA coding for tiPRLII. After transfer to brackish water, levels of the two mRNAs decreased similarly. The present study indicates that, in O. niloticus, the two forms of prolactin have different osmoregulatory roles during adaptation to brackish water. Accordingly, their synthesis are differentially regulated after transfer to a hyperosmotic environment, presumably at a post-transcriptional level.

Adaptation, Physiological↗

PubMed1994

Characterization of a single prolactin (PRL) receptor in tilapia (Oreochromis niloticus) which binds both PRLI and PRLII.

In tilapia, there are two forms of prolactin (PRL) whose effects on sodium and chloride movements differ and depend on the living environment of the fish. To see whether different receptors or the same receptor mediates these different effects, we have characterized the specific binding of both forms of tilapia (ti)PRL in two osmoregulatory organs, the gill and kidney. Two recombinant tiPRLs were used for this analysis. The recombinant hormones had the same properties as the native hormones in a tilapia gill radioreceptor assay. Specific binding to gill and kidney membranes was increased by optimizing the quality of the tissue preparations (physiological state of fish, membrane preparation) and the incubation conditions (pH, salt concentrations, temperature, time). Under these optimized conditions, we detected only one class of high affinity PRL receptor in gill and kidney. Its binding affinity was higher for tiPRLI than for tiPRLII in both gill and kidney (for tiPRLI the respective affinity values were 2.9 and 2.3 x 10(10) per M, for tiPRLII they were 1.9 and 0.5 x 10(10) per M). In competition studies, tiPRLI was more potent, followed by tiPRLII and ovine (o)PRL. tiGH and oGH did not significantly displace either tiPRL. The receptor we have characterized thus recognizes quite specifically both tiPRLs.

Animals↗

PubMed1993

Effects of prolactin on alpha and beta chloride cells in the gill epithelium of the saltwater adapted tilapia "Oreochromis niloticus".

Tilapia (Oreochromis niloticus), 21 g average body weight, were divided into two groups. A group was maintained in fresh water, whereas another group was adapted for 2 weeks to 20% salt water. Among the latter, fishes were injected every 2 days for a week with tilapia prolactin (ti-PRL I). Gills were prepared for electron microscopy in order to determine the types and surface areas of chloride cells in each experimental condition. Two types of chloride cells, the alpha and beta cells were easily distinguished on the basis of their location and ultrastructural features in the gills of freshwater fishes, while only one type of cell, the saltwater alpha cells presumably derived from the transformation of the freshwater alpha cells, were encountered in saltwater adapted animals. After PRL injection of saltwater adapted fishes, small chloride cells, which displayed ultrastructural features similar to those of beta cells in freshwater tilapia, reappeared in interlamellar regions of the gills. In the same experimental conditions, the voluminous saltwater alpha cells showed a tendency to resume ultrastructural features more characteristic of the freshwater alpha cells from which they were derived. These observations tend to indicate that prolactin behaves as a "freshwater adapting hormone" and that beta cells are specifically involved in fish adaptation to freshwater living conditions.

Adaptation, Physiological↗

PubMed1992

The effects of confinement stress on circulating prolactin levels in rainbow trout (Oncorhynchus mykiss) in fresh water.

Rainbow trout were confined for 48 hr, during which time water quality either was allowed to deteriorate (resulting in elevated NH3, elevated free CO2, and reduced dissolved O2) or was maintained at preconfinement levels. Fish were removed and blood samples taken at 0, 2, 4, 8, 24, and 48 hr after the onset of confinement from both stressed (confined) and unstressed (unconfined) fish. Plasma cortisol and plasma prolactin (PRL) levels were determined using specific RIAs. Chronic confinement of rainbow trout, accompanied by a decline in water quality, resulted in significant elevation of plasma cortisol, maintained for the period of confinement. Plasma PRL levels were significantly lower in stressed fish, by up to 60% relative to control fish, during the first 24 hr of confinement. The stress of confinement alone, in the absence of deterioration in water quality, produced similar results, with the change in prolactin levels being less rapid but more prolonged under these conditions.

Animals↗

PubMed1992

Absence of direct regulation of prolactin cells by estradiol-17 beta in rainbow trout (Oncorhynchus mykiss).

The effects of estradiol-17 beta (E2) implants on plasma prolactin (PRL) concentrations, pituitary PRL content and pituitary PRL mRNA levels were examined in rainbow trout (Oncorhynchus mykiss). Intact immature fish treated with 1 mg estradiol-17 beta did not show significant changes in both PRL mRNA levels and pituitary PRL content after 3 days of treatment. In a similar experiment, no changes were observed in plasma PRL levels followed during 7 days. Similarly, lack of estradiol-17 beta effect on plasma PRL levels and on final PRL pituitary content was observed in ovariectomized female rainbow trout treated during 48 days with 25 mg estradiol-17 beta and in mature male fish over a 3-week treatment period. Localization of estradiol receptor (ER) mRNAs in the pituitary was carried out by Northern blot analysis using a full-length rainbow trout estrogen receptor (rtER) cDNA as a probe. The rostral pars distalis of the pituitary which contained mostly PRL cells showed the lower amount of rtER mRNA when compared to other parts of the pituitary. Moreover, two mRNAs of different size (3.5 and 1.4 kb) were detected in different parts of the pituitary. Further hybridization experiments using probes containing part of the rtER cDNA (E domain or C and D domains) indicated that the small-sized mRNA (1.4 kb) probably encodes a truncated ER protein lacking hormone binding domain or an ER-related protein. Thus, only the 3.56 kb mRNA appeared to be involved in the regulation of pituitary function by estradiol. In situ hybridization analysis allowed a more precise localization of this rtER mRNA in the pituitary.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Effect of somatostatin on prolactin in rainbow trout (Oncorhynchus mykiss) pituitary cells in primary culture.

To study the control of prolactin secretion in fish, an in-vitro technique using a monolayer cell culture system of rainbow trout pituitary glands was developed. Such secretion was characterized by measurement of both prolactin release and prolactin mRNA content using a trout prolactin cDNA as a probe. This cell culture technique, already used to study the regulation of gonadotrophin secretion in rainbow trout, was further validated by measuring total DNA and protein content. Both parameters appeared to be stable after 2 days of culture. Studying the effect of somatostatin (SRIF) on prolactin cells indicated that a maximal inhibitory effect (62%) was observed after 24 h of treatment. Significant inhibition of prolactin release was obtained for SRIF doses ranging from 50 nM to 1 microM. However, in the same experiment, SRIF was much more potent as an inhibitor of growth hormone release. Short-term (< 12 h) incubation with SRIF did not induce a significant change in prolactin release, whereas growth hormone release was reduced at as early as 1 h after SRIF exposure. SRIF did not have a significant effect on total prolactin content or prolactin mRNA levels, suggesting the absence of an effect on prolactin synthesis. No increase in the magnitude of the inhibitory effect of SRIF was observed when using pituitary cells from immature, mature male or mature female trout. When comparing effects on primary cultures containing cells from the whole pituitary with a prolactin cell-enriched population, SRIF appeared to have the same inhibitory effect on prolactin release, supporting a direct action of SRIF on prolactin cells. These results provide further support for SRIF being a prolactin-inhibiting factor in rainbow trout and acting as a modulator of a dominant stimulatory control of prolactin release.

Actins↗

PubMed1991

Plasma prolactin and cortisol concentrations of stressed coho salmon, Oncorhynchus kisutch, in fresh water or salt water.

Juvenile coho salmon, Oncorhynchus kisutch, adapted to fresh water or seawater were either acutely handled or continuously stressed by severe confinement. Chronic stress, independent of external salinity, caused a gradual increase in the concentration of circulating prolactin that persisted for 1 to 5 days but lagged behind the cortisol response which peaked much more rapidly and remained elevated. Acutely stressed fish showed a rapid, more transient increase in plasma cortisol titer with no apparent effect on prolactin. Confinement appeared to be more stressful to fish in salt water than to those in fresh water, as judged by their sodium regulatory ability, hormone profiles, and mortality. Stress always elevated plasma prolactin concentrations, regardless of medium or developmental stage.

Animals↗

PubMed1991

Production and purification of biologically active recombinant tilapia (Oreochromis niloticus) prolactins.

Recombinant expression vectors carrying tilapia prolactin-I or -II (tiPRL-I or tiPRL-II) cDNA were constructed and the tiPRL-I and II proteins were produced in E. coli as inclusion bodies. These inclusion bodies were dissolved in 6 mol urea/l. Refolding of the proteins was followed by SDS-PAGE under non-reducing conditions so as to visualize the oxidized state of the molecules. Proteins tiPRL-I and tiPRL-II were purified by gel filtration and ion-exchange chromatography. The N-terminal sequence and bioactivities of both purified proteins were then analysed. Recombinant tiPRL-I and tiPRL-II induced a significant rise in plasma calcium levels as well as in mucocyte density in the abdominal skin epithelium. When tested on kidney membrane, both proteins exhibited potency in competing with 125I-labelled tiPRL-I for binding sites, but tiPRL-I seemed to be more potent than tiPRL-II in competing for these sites. The results obtained for the biological activities tested suggest that both recombinant prolactins were correctly refolded and had retained the full biological activity previously observed with the natural hormone preparations extracted from the animals.

Animals↗

PubMed1990

Ultrastructural features of mitochondria-rich cells in stenohaline freshwater and seawater fishes.

In order to elucidate the functional significance of accessory cells in freshwater fishes, such as the rainbow trout, which displays a poor adaptability to seawater life, a search for such cells was performed in two stenohaline freshwater fishes: the loach and the gudgeon. Accessory cells were never encountered in these species; but, in contrast, two types of chloride cells were observed consistently that strikingly resembled the alpha- and beta-cells previously described in the guppy, a freshwater-adapted euryhaline fish. The alpha-cell, a pale and elongated chloride cell, was located at the base of the secondary lamellae in close contact with the arterioarterial pillar capillary. Darker, ovoid chloride cells resembling the beta-cell were found exclusively in the interlamellar region of the primary epithelium facing the central venous sinous. The latter cells frequently formed multicellular complexes linked together by deep, narrow, apical junctions. In another experiment, a stenohaline seawater fish, the turbot, was adapted to diluted 5% saltwater and to fresh water. In seawater, the gill epithelium contained only one type of chloride cell, always associated with accessory cells. Due to numerous cytoplasmic interdigitations between the accessory cells and the apical portion of the chloride cell, there was a noticeable increase in the length of the shallow apical junction, sealing off the intercellular space between the two cell types. In 5% saltwater, there was a decrease in the number of these interdigitations and a concomitant decrease in the length of the shallow apical junction. In fresh water, chloride cells were partially or completely separated from the outside medium by modified accessory cells. It is thus concluded that accessory cells are found exclusively in fish living in seawater or preadapted to seawater and that they probably are involved in the formation and modulation of paracellular pathways for ionic excretion. In contrast, the respective roles of the two types of chloride cells observed in freshwater fishes are still to be determined.

Adaptation, Physiological↗