Effect of osmotic pressure on prolactin release in rainbow trout: In vitro studies

Gonnet, F.; Prunet, Patrick; Tonon, Marie Christine; Dubourg, P.; Kah, Olivier; Vaudry, Hubert

doi:10.1016/0016-6480(88)90013-5

Cited by 20 publications

(5 citation statements)

References 38 publications

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“…It is well established that PRL acts as a hyperosmoregulatory hormone in teleost fish in which it increases plasma Na + concentrations and Ca 2 + uptake (Hasegawa et al 1986;Fargher and McKeown 1989). Adaption of euryhaline fishes, i.e., 0. mykiss to freshwater results in release of PRL into the blood (Gonnet et al 1988) and in gill tissue PRL appears to be bound to areas with osmotically active cells (McKeown et al 1987). Here for the first time, we report that PRL specifically stimulates PGE 2 synthesis in trout gills.…”

Section: Discussionmentioning

confidence: 67%

Arachidonic acid metabolism in gill homogenate and isolated gill cells from rainbow trout, Oncorhynchus mykiss: the effect of osmolality, electrolytes and prolactin

Beckman¹,

Mustafa²

1992

Fish Physiol Biochem

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An assay method based on thin layer chromatography to study the arachidonic acid (AA) metabolism in gill tissues was optimized and the effect of osmotically different incubation mediums on AA metabolism was evaluated. Rainbow trout gill tissues metabolize AA into PGE2 in highest concentration followed by PGD2, PGF2α and 6-keto-PGF1α (the stable metabolite of PGI2) among the prostanoids tested. Approximately 40% of PGE2 is synthesized within the first minute of incubation and is directly dependent on the substrate concentration (AA). As in mammalian tissues, PGE2 synthesis in fish gills is inhibited by the cyclooxygenase inhibitor indomethacin. PGE2 synthesis in gill homogenate and isolated gill cells incubated in trout Ringer was 0.45 and 1.9 ng/mg protein, respectively, and increased to 8.9 and 4.3 ng/mg protein, respectively, when incubated in KPO4 buffer, due to a ten-fold increase in the free AA. The hydroxy acid synthesis of the gill homogenate was higher (13%), and that of the isolated gill cells incubated in KPO4 buffer was lower (44%) compared to gill homogenate and cells incubated in trout Ringer. Gill homogenate incubated in 50 mM phosphate buffer with increasing sodium or potassium concentrations (up to 250 mM) exhibited a concentration-dependent increase in PGE2 synthesis (220% and 72%, respectively). Prolactin stimulated the PGE2 synthesis up to 30% while PGD2, PGF2α and 6-keto-PGF1α synthesis was not affected. This effect of prolactin was maximal when PGE2 synthesis was estimated 30 minutes after prolactin addition and diminished after two hours. These results suggest that rainbow trout gills possess the ability to metabolize AA through the cyclooxygenase and lipoxygenase pathways. PGE2 synthesis may be under the influence of ion balance and prolactin availability, indicating the probable involvement of AA metabolites in the regulation of ion balances across the gill membrane.

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Section: Discussionmentioning

confidence: 67%

Arachidonic acid metabolism in gill homogenate and isolated gill cells from rainbow trout, Oncorhynchus mykiss: the effect of osmolality, electrolytes and prolactin

Beckman¹,

Mustafa²

1992

Fish Physiol Biochem

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“…Transfer from fresh water to seawater results in a transient decrease in plasma GH levels, a dramatic and permanent decrease in PRL levels (12), and a concomitant transient increase in cortisol and melatonin levels (46). In rainbow trout, adaptation to salinity is under control by a number of chemical (neurotransmitters, neuropeptides) and physical (osmotic pressure) factors (24,47). PRL levels are low in the pituitary and high in plasma, as long as fish are maintained in fresh water, whereas the opposite holds true in fish maintained in salt water (12,24).…”

Section: Melatonin Modulates Prl Release By Trout Lactotropesmentioning

confidence: 99%

Melatonin Modulates Secretion of Growth Hormone and Prolactin by Trout Pituitary Glands and Cells in Culture

et al. 2003

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In Teleost fish, development, growth, and reproduction are influenced by the daily and seasonal variations of photoperiod and temperature. Early in vivo studies indicated the pineal gland mediates the effects of these external factors, most probably through the rhythmic production of melatonin. The present investigation was aimed at determining whether melatonin acts directly on the pituitary to control GH and prolactin (PRL) secretion in rainbow trout. We show that 2-[125I]-iodomelatonin, a melatonin analog, binds selectively to membrane preparations and tissue sections from trout pituitaries. The affinity was within the range of that found for the binding to brain microsomal preparations, but the number of binding sites was 20-fold less than in the brain. In culture, melatonin inhibited pituitary cAMP accumulation induced by forskolin, the adenyl cyclase stimulator. Forskolin also induced an increase in GH release, which was reduced in the presence of picomolar concentrations of melatonin. At higher concentrations, the effects of melatonin became stimulatory. In the absence of forskolin, melatonin induced a dose-dependent increase in GH release, and a dose-dependent decrease in PRL release. Melatonin effects were abolished upon addition of luzindole, a melatonin antagonist. Our results provide the first evidence that melatonin modulates GH and PRL secretion in Teleost fish pituitary. Melatonin effects on GH have never been reported in any vertebrate before. The effects result from a direct action of melatonin on pituitary cells. The complexity of the observed responses suggests several types of melatonin receptors might be involved.

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“…Recent studies using a perifusion technique revealed that reduced osmotic pressure stimulated PRL release from the tilapia pituitary only for a few hours (Grau et al 1986 and from the rainbow trout pituitary for less than 1 hour (Gonnet et al 1988). Gonnet et al (1988) suggested that the temporal increase in the hormone secretion by hypotonic medium may be a result of physical modification of the outer cell membrane and not necessarily specific to PRL cells. It is highly probable, therefore, that apparent stimulation of GH release by hypotonic medium for the first 3 days may also be due to mechanical modification.…”

Section: Discussionmentioning

confidence: 99%

Growth hormone secretion during longterm incubation of the pituitary of the Japanese eel, Anguilla japonica

Suzuki

Kishida

Hirano

1990

Fish Physiol Biochem

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Growth hormone (GH) secretion from organ-cultured pituitaries of the eel (Anguilla japonica) was studied during incubation in a defined medium for 2 weeks, using a homologous radioimmunoassay which does not distinguish between the two molecular forms of eel GH. The total amount of GH secreted increased gradually during the incubation period; so that the amount of GH released on day 14 was about 30 times greater than that on day 1. On day 14, the proportion of GH released relative to the total amount of GH present (the sum of GH released into the medium and residual content in the pituitary) was 96% and the amount produced on day 14 was 4 times greater than the content in the unincubated pituitary. Somatostatin (SRIF, 1.8 × 10(-7) M) inhibited the increase in GH release. On day 7, the proportion of GH released by pituitaries treated with SRIF (28%) was less than that released by the control pituitary (91%). There was no significant difference in GH release between the pituitaries incubated in isotonic medium (300 mOsm) and those in hypotonic medium (240 mOsm) for 2 weeks except for the first 3 days, when the pituitaries in hypotonic medium secreted significantly greater amounts of GH than those incubated under isotonic condition. Hypertonic medium (350 mOsm) had no effect on GH release except for significant inhibition on days 6 and 14. When secretion of the two forms of GH (GH I and II) was examined after separation by polyacrylamide gel electrophoresis followed by densitometry, slightly more GH I tended to be secreted than GH II during the culture period, although the effects of SRIF and osmolality of the media on GH I release were similar to those on GH II. It is concluded that GH secretion and production in the eel is mainly under the inhibitory control of hypothalamus, and that osmolality has a minimum influence on the GH release.

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Effect of osmotic pressure on prolactin release in rainbow trout: In vitro studies

Cited by 20 publications

References 38 publications

Arachidonic acid metabolism in gill homogenate and isolated gill cells from rainbow trout, Oncorhynchus mykiss: the effect of osmolality, electrolytes and prolactin

Arachidonic acid metabolism in gill homogenate and isolated gill cells from rainbow trout, Oncorhynchus mykiss: the effect of osmolality, electrolytes and prolactin

Melatonin Modulates Secretion of Growth Hormone and Prolactin by Trout Pituitary Glands and Cells in Culture

Growth hormone secretion during longterm incubation of the pituitary of the Japanese eel, Anguilla japonica

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