Effects of acclimation salinity and in vitro medium osmotic pressure on the incorporation of3H-leucine into the two prolactins of the tilapia,Oreochromis mossambicus (original) (raw)
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Journal of Experimental Zoology, 1992
Prolactin (PRL) is thought to play a significant role in the freshwater (FW) adaptation of euryhaline teleost fishes, including the tilapia, Oreochromis mossambicus. Two PRLs (tPRL,,, and tPRL,77) have been characterized in the anteriormost portion of the tilapia pituitary, the rostra1 pars distalis (RPD; Specker et al., '85a,b; Yamaguchi et al., '88). Our studies were undertaken to determine whether the in vivo RPD content of tPRLlaa and tPRL,,, varied with environmental salinity. To this end, tilapia were reared from the period of yolk-sac absorption for 7 months or acclimated for 21 and 35 days in FW or seawater (SW). In a parallel study, we also examined whether the release of the 2 tilapia PRLs from the RPD of FW or SW tilapia might be differentially sensitive to changes in medium osmotic pressure during 18-20 hr incubations. In agreement with earlier work, we found that the smaller tPRL,,7 molecule was present in greater quantities in the RPD of FW tilapia compared to the content in RPD of SW fish. For the first time, we show here that the content of tPRL,,,, like that of tPRL177, is also significantly greater in the RPD of FW fish compared to the quantity in RPD of SW tilapia. Nevertheless, the relative content or ratio of the 2 PRLs in the pituitary was dependent on rearing salinity. Thus, the relative content or ratio of the larger tilapia PRL to smaller PRL (tPRL188/tPRL177) in the RPD of FW tilapia was significantly higher (1.51) than that seen in SW fish (0.751). This ratio was not altered after 18-20 hr in vitro incubations in hyposmotic or hyperosmotic medium, suggesting that the shift in ratios did not result from differential release by osmotic pressure. During 18-20 hr incubation in either hyposmotic or hyperosmotic medium, the RPD of FW tilapia released more of both forms of PRL than did the RPD of SW fish. Consistent with previous studies, reductions in medium osmotic pressure within the physiological range of the tilapia stimulated the release of both tPRLIa8 and tPRL177 from RPD of FW fish over levels observed during exposure to hyperosmotic medium. We report here, for the first time, that the reduction of medium osmotic pressure also stimulates the release of both tPRLIa8 and tPRL177 from RPD of SW fish. Throughout the experiments we did not observe differences between the release of tPRLla8 and tPRL177 under our incubation conditions. The transfer of FW-reared fish to SW and vice versa for 49 days altered the ratio of the 2 PRLs (tPRL,,a/tPRL177) to that observed in the RPD of SW-reared and FW-reared fish, respectively. Overall, our studies indicate that the processing of the 2 PRLs may be differentially sensitive to environmental salinity. o 1992 Wiley-Liss, Inc.
Two forms of prolactin (Prl), prolactin 177 (Prl 177 ) and prolactin 188 (Prl 188 ), are produced in the rostral pars distalis (RPD) of the pituitary gland of euryhaline Mozambique tilapia, Oreochromis mossambicus. Consistent with their roles in fresh water (FW) osmoregulation, release of both Prls is rapidly stimulated by hyposmotic stimuli, both in vivo and in vitro. We examined the concurrent dynamics of Prl 177 and Prl 188 hormone release and mRNA expression from Prl cells in response to changes in environmental salinity in vivo and to changes in extracellular osmolality in vitro. In addition, mRNA levels of Prl receptors 1 and 2 (prlr1 and prlr2) and osmotic stress transcription factor 1 (ostf1) were measured. Following transfer from seawater (SW) to FW, plasma osmolality decreased, while plasma levels of Prl 177 and Prl 188 and RPD mRNA levels of prl 177 and prl 188 increased. The opposite pattern was observed when fish were transferred from FW to SW. Moreover, hyposmotically induced release of Prl 188 was greater in Prl cells isolated from FW-acclimated fish after 6 h of incubation, while the hyposmotically induced increase in prl 188 mRNA levels was only observed in SW-acclimated fish. In addition, prlr2 and ostf1 mRNA levels in Prl cells from both FW-and SW-acclimated fish increased in direct proportion to increases in extracellular osmolality both in vivo and in vitro. Taken together, these results indicate that the osmosensitivity of the tilapia RPD is modulated by environmental salinity with respect to hormone release and gene expression. ) and SW to FW (triangles). Symbols represent mRNA levels from individual RPDs GS.E.M. (nZ8-10). Control fish were maintained in FW (FW-FW) or SW (SW-SW) and sampled on the same time course as fish subjected to salinity change. Expression levels are presented relative to the time 0 SW-SW group. Differences among groups were evaluated by two-way ANOVA. *, ***Significantly different from the corresponding FW-FW controls (open circles) at P!0 . 05, and 0 . 001 respectively by Student's t-test. †, † †, † † † Significantly different from the corresponding SW-SW controls (open triangles) at P!0 . 05 and 0 . 001 respectively by Student's t-test.
Seale et al, 2006 Disparate release of prolactin and growth hormone from the tilapia pituitary.pdf
In most teleost Wshes, prolactin (PRL) plays a key role in freshwater (FW) adaptation, whereas growth hormone (GH) is involved in seawater (SW) adaptation in salmonids and certain euryhaline species including the tilapia, Oreochromis mossambicus. Consistent with its osmoregulatory activity, PRL release increases in response to physiologically relevant reductions in extracellular osmolality. When dispersed PRL and GH cells from FW-acclimatized Wsh were incubated in media of varying osmolalities, PRL release increased signiWcantly in response to a 12% reduction in medium osmolality during 1 and 4 h of exposure. By contrast, cells from SW-acclimatized Wsh responded only to a 24% reduction in osmolality. Growth hormone release on the other hand increased whether medium osmolality was reduced or raised. Cell volume increased together with PRL release during the perifusion of dispersed PRL cells in direct proportion to the reduction in medium osmolality. Growth hormone release increased whether GH cell volume increased or decreased. In in vivo studies, circulating PRL levels increased as early as 1 h after the transfer of Wsh from SW to FW, whereas GH levels remained unchanged during 24 h of acclimatization. These results indicate that while PRL and GH cells are osmosensitive, the PRL cells respond to reductions in extracellular osmolality in a manner that is consistent with PRL's physiological role in the tilapia. While the rise in GH release following the reduction in osmolality is of uncertain physiological signiWcance, the rise in GH release with the elevation of medium osmolality may be connected to its role in SW adaptation.
Osmosensitive transcription factors in the prolactin cell of a euryhaline teleost
Comparative Biochemistry and Physiology, 2022
In euryhaline fish, prolactin (Prl) plays a key role in freshwater acclimation. Prl release in the rostral pars distalis (RPD) of the pituitary is directly stimulated by a fall in extracellular osmolality. Recently, we identified several putative transcription factor modules (TFM) predicted to bind to the promoter regions of the two prl isoforms in Mozambique tilapia, Oreochromis mossambicus. We characterized the effects of extracellular osmolality on the activation of these TFMs from RPDs, in vivo and in vitro. OCT1_PIT1 01, CEBP_CEBP 01 and BRNF_RXRF 01 were significantly activated in freshwater (FW)-acclimated tilapia RPDs while SORY_PAX3 02 and SP1F_SP1F 06, SP1F_SP1F 09 were significantly activated in seawater (SW)-counterparts. Short-term incubation of SW-acclimated tilapia RPDs in hyposmotic media (280 mOsm/kg) resulted in activation of CAAT_AP1F 01, OCT1_CEBP 01, AP1F_SMAD 01, GATA_SP1F 01, SORY_PAX6 01 and CREB_EBOX 02, EBOX_AP2F 01, EBOX_MITF 01 while hyperosmotic media (420 mOsm/kg) activated SORY_PAX3 02 and AP1F_SMAD 01 in FW-tilapia. Short-term incubation of dispersed Prl cells from FW-acclimated fish exposed to hyperosmotic conditions decreased pou1f1, pou2f1b, stat3, stat1a and ap1b1 expression, while pou1f1, pou2f1b, and stat3 were inversely related to osmolality in their SW-counterparts. Further, in Prl cells of SW-tilapia, creb3l1 was suppressed in hyposmotic media. Collectively, our results indicate that multiple TFMs are involved in regulating prl transcription at different acclimation salinities and, together, they modulate responses of Prl cells to changes in extracellular osmolality. These responses reflect the complexity of osmosensitive molecular regulation of the osmoreceptive Prl cell of a euryhaline teleost.
Comparative Biochemistry and Physiology, Part C
Comparative Biochemistry and Physiology Part C Toxicology & Pharmacology
Prolactin plays an essential role in ion uptake as well as reduction in ion and water permeability of osmoregulatory surfaces in euryhaline fish. Kryptolebias marmoratus is a euryhaline fish with unique internal selffertilization. In order to understand the effect of different salinities and environmental endocrine-disrupting chemicals (EDCs) on the regulation of prolactin (PRL) and prolactin receptor (PRLR) genes, the full-length sequences of PRL and two PRLR genes were cloned from K. marmoratus. The expression pattern of K. marmoratus PRL (Km-PRL) and PRLR (Km-PRLR1, Km-PRLR2) mRNAs was analyzed in different developmental stages (2 dpf to 5 h post-hatching) and tissues of hermaphrodite fish. To investigate the effects of salinity changes and EDC exposure, the mRNA expression pattern of PRL, PRLR1 and PRLR2 was analyzed in exposed fish. The Km-PRL mRNA in the hermaphrodite was predominantly expressed in the brain/pituitary, the Km-PRLR1 mRNA was highly expressed in the intestine, while the Km-PRLR2 mRNA was intensively expressed in the gills. The expression of the Km-PRL mRNA generally increased from stage 1 (2 dpf) to stage 3 (12 dpf) in a developmental, stage-dependent manner. It decreased in stage 4 (12 dpf) and the hatching stage (stage 5). Km-PRLR1 and Km-PRLR2 mRNAs showed a gradual increase in expression from stage 1 (2 dpf) to stage 4 (12 dpf) and decreased by stage 5 (5 h post-hatching). Also, both mRNAs of PRLR showed a different expression pattern after exposure to different salinity concentrations (0, 33, and 50 ppt) in juvenile fish. The expression of PRL mRNA was upregulated at 0 ppt, but was downregulated at a moderately higher salinity concentration (33 to 50 ppt). The Km-PRLR1 mRNA showed upregulation at freshwater stress (0 ppt) compared to other concentrations of salinity (33 ppt to 50 ppt). The Km-PRLR2 mRNA was marginally upregulated at freshwater stress (0 ppt), but was downregulated at a higher salinity concentration (50 ppt) and showed no significant change in expression at 33 ppt salinity. Interestingly, both mRNAs showed upregulation in the brain (e.g. Km-PRL) and intestine (e.g. Km-PRLR1) after EDC exposure. These findings suggested that Km-PRL and two Km-PRLR mRNAs would be useful in analyzing the effect of different salinities as well as the modulatory effect of EDC exposure on these gene expressions in K. marmoratus.
Effect of osmotic pressure on prolactin release in rainbow trout: In vitro studies
General and Comparative Endocrinology, 1988
To investigate a possible effect of osmotic pressure on prolactin (PRL) release in rainbow trout, we developed a technique for in vitro perifusion of trout pituitaries. Changes in osmotic pressure similar to those observed in fish plasma during transfer experiments did not induce significant modifications of PRL release. In contrast, high-amplitude variation of osmotic pressure resulted in clear modifications of PRL secretion: hyperosmotic medium caused a reduction in PRL release, while infusion of hyposmotic medium induced a transitory increase in PRL release. By using different concentrations of mannitol, we found that the modifications of prolactin secretion could not be ascribed to alterations of the ionic composition of the medium but actually resulted from variations in the osmotic pressure of the incubation medium. In further experiments osmotic pressure was decreased from 300 to 220 mOsm/kg or from 400 to 300 mOsm/kg; a similar transitory increase in PRL release was observed. Measurement of gonadotropin (GtH) in the perifusion effluent medium showed that PRL and GtH secretion followed similar patterns. Thus, our results suggest a possible mechanical effect of wide changes in osmotic pressure on pituitary cell membranes. These data indicate that the rainbow trout differs notably from nonsalmonid teleost species thus far studied in the lack of sensitivity of its PRL cells to osmotic pressure.
General and Comparative Endocrinology, 1973
A bioassay method for fish prolactin was developed based on the ability of prolactin to increase the plasma sodium concentration of intact Tilapia mossambica acclimated to sea water. The plasma, sodium concentration is linearly related to log dose of ovine prolactin. Homogenates of whole pituitary gland from fresh water T. mossambica give a parallel dose response. A significant elevation of plasma sodium is elicited by 4 @g/g body wt of ovine prolactin. The same amount (wet wt) of whole pituitary gland from freshwater T. mossnmbica has equal potency, indicating that the assay is much more sensitive to at least some teleost prolactins than to mammalian prolactins. The assay is unaffected by ACTH, dexamethasone, bovine growth hormone, porcine prolactin, or human chorionic somatomammo-498
Seale et al 2014 Effects of salinity and prolactin on tilapia intestine.pdf
Euryhaline teleosts are faced with significant challenges during changes in salinity. Osmoregulatory responses to salinity changes are mediated through the neuroendocrine system which directs osmoregulatory tissues to modulate ion transport. Prolactin (PRL) plays a major role in freshwater (FW) osmoregulation by promoting ion uptake in osmoregulatory tissues, including intestine. We measured mRNA expression of ion pumps, Na + /K + -ATPase a3-subunit (NKAa3) and vacuolar type H + -ATPase A-subunit (V-ATPase A-subunit); ion transporters/channels, Na + /K + /2Cl À co-transporter (NKCC2) and cystic fibrosis transmembrane conductance regulator (CFTR); and the two PRL receptors, PRLR1 and PRLR2 in eleven intestinal segments of Mozambique tilapia (Oreochromis mossambicus) acclimated to FW or seawater (SW). Gene expression levels of NKAa3, V-ATPase A-subunit, and NKCC2 were generally lower in middle segments of the intestine, whereas CFTR mRNA was most highly expressed in anterior intestine of FWfish. In both FW-and SW-acclimated fish, PRLR1 was most highly expressed in the terminal segment of the intestine, whereas PRLR2 was generally most highly expressed in anterior intestinal segments. While NKCC2, NKAa3 and PRLR2 mRNA expression was higher in the intestinal segments of SWacclimated fish, CFTR mRNA expression was higher in FW-fish; PRLR1 and V-ATPase A-subunit mRNA expression was similar between FW-and SW-acclimated fish. Next, we characterized the effects of hypophysectomy (Hx) and PRL replacement on the expression of intestinal transcripts. Hypophysectomy reduced both NKCC2 and CFTR expression in particular intestinal segments; however, only NKCC2 expression was restored by PRL replacement. Together, these findings describe how both acclimation salinity and PRL impact transcript levels of effectors of ion transport in tilapia intestine.
This study characterized the local effects of extracellular osmolality and prolactin (PRL) on branchial ionoregulatory function of a euryhaline teleost, Mozambique tilapia (Oreochromis mossambicus). First, gill filaments were dissected from freshwater (FW)-acclimated tilapia and incubated in four different osmolalities, 280, 330, 380, and 450 mosmol/kg H2O. The mRNA expression of Na ϩ /K ϩ -ATPase ␣1a (NKA ␣1a) and Na ϩ /Cl Ϫ cotransporter (NCC) showed higher expression with decreasing media osmolalities, while Na ϩ /K ϩ /2Cl Ϫ cotransporter 1a (NKCC1a) and PRL receptor 2 (PRLR2) mRNA levels were upregulated by increases in media osmolality. We then incubated gill filaments in media containing ovine PRL (oPRL) and native tilapia PRLs (tPRL177 and tPRL188). oPRL and the two native tPRLs showed concentration-dependent effects on NCC, NKA␣1a, and PRLR1 expression; Na ϩ /H ϩ exchanger 3 (NHE3) expression was increased by 24 h of incubation with tPRLs. Immunohistochemical observation showed that oPRL and both tPRLs maintained a high density of NCCand NKA-immunoreactive ionocytes in cultured filaments. Furthermore, we found that tPRL 177 and tPRL188 differentially induce expression of these ion transporters, according to incubation time. Together, these results provide evidence that ionocytes of Mozambique tilapia may function as osmoreceptors, as well as directly respond to PRL to modulate branchial ionoregulatory functions.