RESUMO
In many euryhaline fish, prolactin (PRL) plays a key role in freshwater adaptation. Consistent with this function, the present study showed a remarkable reduction in pituitary PRL content of silver sea bream abruptly transferred to low salinity (6ppt). This reduction in pituitary PRL content followed closely the temporal changes in serum osmolality and ion levels. Serum osmolality, Na(+) and Cl(-) levels of silver sea bream abruptly transferred to hyposmotic salinity (6ppt) were markedly reduced 2h after the transfer. The decline in pituitary PRL content lagged behind the serum changes implying that reduction in pituitary PRL content is a response to the drop in serum ion levels and osmotic pressure. Silver sea bream pituitary cells were dispersed and exposed to a medium with reduced ion levels and osmolality in vitro, and PRL released from pituitary cells was significantly elevated. In hyposmotic exposed anterior pituitary cells, cell volume exhibited a 20% increase when exposed to a medium with a 20% decrease in osmolality. The enlarged pituitary cells did not shrink until the surrounding hyposmotic medium was replaced, a phenomenon suggesting an osmosensing ability of silver sea bream PRL cells for PRL secretion in response to a change in extracellular osmotic pressure. The decrease in pituitary PRL content in vivo and stimulated pituitary PRL release in vitro under reduced osmolality together suggest hyposmotic exposure triggers PRL release from the pituitary.
Assuntos
Hipófise/efeitos dos fármacos , Hipófise/metabolismo , Prolactina/metabolismo , Animais , Western Blotting , Cloretos/sangue , Cloretos/farmacologia , Concentração Osmolar , Dourada , Sódio/sangue , Sódio/farmacologiaRESUMO
The present study aims to investigate potential regulatory effect of different growth-related hormones including growth hormone (GH), human insulin-like growth factor-I (hIGF-I), thyroxine (T(4)), triiodothyronine (T(3)) and cortisol, on insulin-like growth factor-I (IGF-I) mRNA expression of hepatocytes isolated from silver sea bream. By using real-time PCR, IGF-I mRNA expression profiles of hepatocytes in response to individual hormones were determined in vitro. Hepatocytes incubated with GH at concentrations of 10-1000 ng/mL showed significantly higher IGF-I expression, but the elevation was attenuated at high concentration of GH (1000 ng/mL). IGF-I expression remained unchanged in hepatocytes after incubation with hIGF-I. Hepatocytes incubated with T(4) at concentration of 1000 ng/mL exhibited a significant elevation in IGF-I expression, whereas no difference in IGF-I expression was demonstrated in hepatocytes after incubation with T(3). Upon incubation with cortisol (1-1000 ng/mL), IGF-I expression was significantly decreased in hepatocytes in a dose-dependent manner. Our study demonstrated that GH, T(4), and cortisol had direct modulatory effects on IGF-I expression in fish hepatocytes in vitro.
Assuntos
Hormônio do Crescimento/farmacologia , Hepatócitos/efeitos dos fármacos , Hepatócitos/metabolismo , Hidrocortisona/farmacologia , Fator de Crescimento Insulin-Like I/genética , Dourada/genética , Tiroxina/farmacologia , Animais , Sequência de Bases , Primers do DNA/genética , Expressão Gênica/efeitos dos fármacos , Glucosefosfato Desidrogenase/genética , Humanos , Fator de Crescimento Insulin-Like I/farmacologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas Recombinantes/farmacologia , Dourada/crescimento & desenvolvimento , Dourada/metabolismo , Tri-Iodotironina/farmacologiaRESUMO
In this study, the induction of metallothionein (MT) and glucose-6-phosphate dehydrogenase (G6PDH) gene expression in response to exposure to cadmium (Cd(2+)) was investigated in silver sea bream (Sparus sarba) in vivo. In addition, a primary hepatocyte culture has been developed from silver sea bream liver in order to assess the changes in gene expression of MT and G6PDH in hepatocytes directly exposed to Cd(2+) in vitro. The sea bream metallothionein gene was cloned and characterized for the development of real-time PCR assays for quantification of MT transcript abundance. G6PDH gene expression was quantified using a real-time PCR assay developed using sequence information from a previously cloned silver sea bream G6PDH gene. In both in vivo and in vitro experiments, MT mRNA was highly inducible following Cd(2+) treatment. In addition, Cd(2+) exposure caused the upregulation of G6PDH mRNA expression and this suggests the possibility of the involvement of G6PDH in the defense against Cd(2+)-induced oxidative stress in cells. It is likely that the defense system of silver sea bream to Cd(2+) stress includes upregulation of G6PDH in addition to metallothionein.