Seale et al , 2002 Isolation and characterization of a homologue of mammalian prolactin-releasing peptide.pdf (original) (raw)
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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.
Biological research, 2012
Here we show the cloning and characterization of a novel homolog of prepro C-RFa cDNA from Cyprinus carpio. The deduced preprohormone precursor of 115 amino acids leads to a mature bioactive peptide of 20 amino acids with identical sequence to other teleost C-RFa. Modeling of the mature C-RFa peptide highlighted signifi cant similarity to homologous human PrRP20, specifi cally the conserved amphipathic system defi ned by the C-terminal alpha-helix. Clearly, the synthetic C-RFa peptide stimulated prolactin release from primary cultured fi sh pituitary cells. For the fi rst time, signifi cant variation was shown in C-RFa mRNA and protein levels in the hypothalamus and pituitary between summer-and winter-acclimatized carp. Furthermore, C-RFa protein distribution in carp central nervous tissue was visualized by immunodetection in fi bers and cells in hypothalamus, olfactory tract, cerebellum and pituitary stalk. In conclusion, we demonstrated the structure conservation of C-RFa in teleosts and mammals and immunopositive cells and fi bers for C-RFa in brain areas. Finally, the increase of C-RFa expression suggests the participation of this hypothalamic factor in the mechanism of modulation in PRL expression in carp.
General and Comparative Endocrinology, 1986
The effects of estradiol-17P (EJ and thyrotropin-releasing hormone (TRH) on prolactin (PRL) release were investigated using the organ-cultured rostra1 pars distalis (RPD) of the tilapia, Oreochromis mossambicus. Spontaneous PRL release into hyperosmotic medium increased in a dose-related manner following Ez pretreatment in vitro. In addition. TRH stimulated a dose-related increase in PRL release from E,-preincubated RPD's, but had no effect on tissues not previously exposed to E,. The maximal PRL response, nearly three times control levels, occurred at 50 nM TRH. Higher doses of TRH were less effective in stimulating PRL release. These findings indicate that TRH may be an important hypothalamic prolactin-releasing factor in the tilapia. Furthermore, the marked potentiation of the action of TRH on PRL release following exposure to Ez suggests that there may be a shift in the control of PRL secretion with changes in the reproductive state of the tilapia. o 1986 Academic Press, Inc.
General and Comparative Endocrinology, 2005
Gonadotropin-releasing hormone (GnRH) is a potent stimulator of prolactin (PRL) secretion in various vertebrates including the tilapia, Oreochromis mossambicus. The mechanism by which GnRH regulates lactotroph cell function is poorly understood. Using the advantageous characteristics of the teleost pituitary gland from which a nearly pure population of PRL cells can be isolated, we examined whether GnRH might stimulate PRL release through an increase in phospholipase C (PLC), inositol triphosphate (IP 3), and intracellular calcium ðCa 2þ i Þ signaling. Using Ca 2þ i imaging and the calcium-sensitive dye fura-2, we found that chicken GnRH-II (cGnRH-II) induced a rapid dose-dependent increase in Ca 2þ i in dispersed tilapia lactotrophs. The Ca 2þ i signal was abolished by U-73122, an inhibitor of PLC-dependent phosphoinositide hydrolysis. Correspondingly, cGnRH-II-induced tPRL 188 secretion was inhibited by U-73122, suggesting that activation of PLC mediates cGnRH-IIÕs stimulatory effect on PRL secretion. Pretreatment with 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), an inhibitor of Ca 2+ release from intracellular stores, impeded the effect of cGnRH-II on Ca 2þ i. To further address the possible involvement of intracellular Ca 2+ stores, IP 3 concentrations in the tilapia rostral pars distalis (RPD containing 95-99% PRL cells) was determined by a radioreceptor assay. We found that GnRH-II induces a rapid (<5 min) and sustained increase in IP 3 concentration in the RPD. Secretion of tPRL 188 in response to cGnRH-II was suppressed by Ca 2+ antagonists (TMB-8 and nifedipine). These data, along with our previous findings that show PRL release increases with a rise in Ca 2þ i , suggest that GnRH may elicit its PRL releasing effect by increasing Ca 2þ i. Furthermore, the rise in Ca 2þ i may be derived from PLC/IP 3-induced mobilization of Ca 2+ from intracellular stores along with influx through L-type voltage-gated Ca 2+ channels.
General and Comparative Endocrinology, 2004
Exposure to cortisol inhibits prolactin (PRL) release from the tilapia pituitary within 10-20 min through a plasma membraneassociated, non-genomic pathway. In the present study, in vitro effects of cortisol on the release and mRNA levels of two PRLs (PRL 188 and PRL 177 ) and growth hormone (GH) were examined in the organ-cultured pituitary of the Mozambique tilapia, Oreochromis mossambicus. The PRL release was significantly greater in hyposmotic (300 mOsmolal) than in hyperosmotic (350 mOsmolal) medium during the 2-8 h of incubation. The mRNA levels of two PRLs, as estimated by RNase protection assay, were increased after 8 h in hyposmotic medium. Cortisol (200 nM) inhibited the release of two PRLs under hyposmotic conditions within 1 h, and the inhibitory effects lasted for 24 h. Cortisol also reduced the gene transcription of both PRLs during 2-8 h of incubation but not after 24 h. No effect of cortisol was observed on PRL release or on its mRNA levels under hyperosmotic condition. There was no significant effect of medium osmolality on the release or mRNA levels of GH during 8 h of incubation. However, GH release was significantly stimulated by cortisol after 4 h, and the effect lasted for 24 h under both hyposmotic and hyperosmotic conditions. Cortisol also caused a significant increase in GH mRNA levels at 8 and 24 h. These results suggest that cortisol inhibits PRL release from the tilapia pituitary through non-genomic and also through transcriptional pathways, while stimulating GH release through classical genomically mediated glucocorticoid actions.
General and Comparative Endocrinology, 2003
The effect of estradiol-17b (E 2 ) implants on the in vitro secretion of prolactin (PRL) and its modulation by vasoactive intestinal peptide (VIP) in a marine teleost, sea bream (Sparus aurata L.), was determined. Experiments were conducted during winter and spring. During winter, fish (n ¼ 130, body weight 50-70 g) were randomly divided into 2 groups; control and E 2 treated (10 mg/kg, wet weight). Fish were sacrificed after 7 days treatment and in vitro pituitary cultures in Ringer bicarbonate supplemented with increasing doses (0-200 nM) of VIP were carried out for 18 h. Culture medium was analysed by PAGE and secreted PRL quantified by densitometry. Fish treated with E 2 secreted significantly more PRL ðP < 0:05Þ in vitro than control fish. In E 2 primed fish VIP caused a dose-dependent inhibition of PRL secretion in vitro. VIP had no detectable effect on the secretion of PRL from control pituitaries. Treatment with E 2 had a different effect during spring; PRL secretion was significantly decreased ðP < 0:01Þ compared with the control fish. Anatomical evidence of abundant VIP immunoreactive nerve fibres in neurohypophysial (NH) tissue penetrating the rostral pars distalis provide further evidence supporting an action for VIP in the regulation of PRL cells. In conclusion, the responsiveness of PRL in the pituitary gland varied with season. Moreover, in the sea bream VIP appears to modulate PRL secretion from E 2 primed pituitary glands.
Peptides, 2002
The quantitative distribution of corticotropin-releasing hormone (CRH) in the brain and pituitary of the fish Oreochromis mossambicus (tilapia) was studied following the validation of a radioimmunoassay. Compared to the pituitary content, the brain contained 20 times more CRH. Eighty percent of the total brain content was located outside the hypothalamus, particularly in the telencephalon. Substantial amounts of CRH were also present in other regions devoid of hypophysiotropic neurons, such as the vagal lobe and optic tectum. Telencephalic and pituitary CRH co-eluted with the tilapia CRH 1-41 standard on reverse phase HPLC. In vitro CRH release by the telencephalon amounted to 5% of its content per hour, whereas release from the pituitary was negligible. We conclude that CRH in the brain of tilapia regulates pituitary and non-pituitary related functions, probably as a neurotransmitter or neuromodulator.
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.
Endocrinology, 2014
LPXRFamide (LPXRFa) peptides have been characterized for their ability to inhibit gonadotropin (GTH) release in birds and stimulate growth hormone (GH) release in frogs. However, their involvement in regulating the reproductive hypothalamo-pituitary-gonadal axis in mammals and fish is inconclusive. To study the role of LPXRFa peptides in the regulation of GTH secretion, we cloned tilapia LPXRFa and LPXRF receptor (LPXRF-R). Processing of the tilapia preproLPXRFa liberated three mature LPXRFa peptides that varied in size and post-translational modifications. Phylogenetic analysis of LPXRFa and the closely related RFamide peptide PQRFa showed clear clustering of each peptide sequence with its orthologs from various vertebrates. Signal-transduction analysis of the tilapia LPXRF-R in COS-7 cells showed clear stimulation of CRE-dependent luciferase activity, whereas the human NPFFR1 showed suppression of forskolin-induced CRE-dependent activity in this system. Administration of the tilap...
Ouabain, a cardiac glycoside and inhibitor of Na + , K + -ATPase, is now believed to be a steroid hormone in mammals. We have recently identiWed ouabain immunoreactivity in the plasma of the tilapia, a euryhaline teleost. Changes in plasma concentrations of immunoreactive ouabain (20-40 pM) in response to salinity change were well correlated with the changes in plasma osmolality and cortisol. Our previous studies have shown that cortisol rapidly inhibits prolactin (PRL) release from the tilapia pituitary by suppressing intracellular Ca 2+ ([Ca 2+ ] i ) and cAMP. In the present study, low doses of ouabain (10-1000 pM) inhibited PRL release dosedependently during 2-24 h of incubation. There was no eVect on growth hormone (GH) release, except for a signiWcant increase at 1000 pM during 8-24 h of incubation. SigniWcant dose-related increases in PRL release were observed at higher doses of ouabain (100-1000 nM), whereas signiWcant inhibition was seen in GH release at 1000 nM during 2-24 h of incubation. Ouabain at 1-100 pM had no eVect on Na + , K + -ATPase activity of the pituitary homogenate. The enzyme activity was inhibited by higher concentrations of ouabain, 10% at 1 nM, 15% at 10 nM, 28% at 100 nM, and 45% at 1000 nM. Ouabain also attenuated stimulation of PRL release by the Ca 2+ ionophore, A23187, and by a combination of dibutyryl cAMP and a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthin. Intracellular Ca 2+ concentrations were monitored in the dispersed PRL cells with the Ca 2+ -sensitive dye, fura-2. Ouabain at 1 nM reversibly reduced [Ca 2+ ] i within seconds, whereas 1 M ouabain increased [Ca 2+ ] i . A rapid reduction in [Ca 2+ ] i was also observed when PRL cells were exposed to 1 M cortisol, whereas there was no consistent eVect at 1 nM. These results suggest that ouabain at physiological concentrations rapidly inhibits PRL release from the tilapia pituitary by suppressing intracellular Ca 2+ and cAMP metabolism. The stimulation of PRL release by high concentrations of ouabain (100-1000 nM) may result from an increase in [Ca 2+ ] i , and subsequent depolarization due to the inhibition of Na + , K + -ATPase activity.