Biomedical subjects

Takashi Yada

Publications and source records attributed to Takashi Yada.

10 recordsLinked to original sources

PubMed2006

Effects of acid water exposure on plasma cortisol, ion balance, and immune functions in the "cobalt" variant of rainbow trout.

This study was undertaken to examine physiological responses to acidification of environmental water in the "cobalt" variant of rainbow trout (Oncorhynchus mykiss), which exhibits malformation of the pituitary, by following changes in plasma levels of cortisol and electrolytes, blood pH, gill Na(+), K(+)-ATPase activity, and immune functions after exposure to acid water (pH 4.5). Resting levels of plasma cortisol and lysozyme were significantly lower in the cobalt variant than in the normal trout, whereas plasma ceruloplasmin was significantly higher in the cobalt variant, suggesting that some endocrine factors, lacking or deficient in the cobalt variant, are important for the regulation of its immune functions. Blood pH was slightly but significantly lower in the cobalt variant at rest. After exposure to acid water for 24 h, both the normal trout and cobalt variant showed a significant elevation in plasma cortisol, although the increased level in the cobalt variant was still lower than that in the normal trout transferred to neutral water. No differences were seen in blood pH, plasma electrolytes, and gill Na(+), K(+)-ATPase activity between the normal trout and the cobalt variant, indicating that the cobalt variant regulates ion balance when exposed to acid water, despite malformation of the pituitary. Although the normal trout showed a reduction in plasma lysozyme level after acid exposure, there was no significant change in the cobalt trout. Adverse effects of pituitary malformation on ion balance and immune functions may be compensated by extrapituitary factors in the cobalt variant when it is exposed to acid water.

Animals↗

PubMed2005

Medaka receptors for somatolactin and growth hormone: phylogenetic paradox among fish growth hormone receptors.

Somatolactin (SL) in fish belongs to the growth hormone/prolactin family. Its ortholog in tetrapods has not been identified and its function(s) remains largely unknown. The SL-deficient mutant of medaka (color interfere, ci) and an SL receptor (SLR) recently identified in salmon provide a fascinating field for investigating SL's function(s) in vivo. Here we isolated a medaka ortholog of the salmon SLR. The mRNA is transcribed in variable organs. Triglycerides and cholesterol contents in the ci are significantly higher than those in the wild type, providing the first evidence of SL's function in suppressing lipid accumulation to organs. Interestingly, phylogenetic comparisons between the medaka SLR and growth hormone receptor (GHR), which is also isolated in this study, in relation to GHRs of other fish, suggested that all GHRs reported from nonsalmonid species are, at least phylogenetically, SLRs. An extra intron inserted in medaka and pufferfish SLRs and flounder and sea bream GHRs also supports their orthologous relationship, but not with tetrapod GHRs. These results may indicate lineage-specific diversification of SLR and GHR functions among fish or just an inappropriate naming of these receptors. Further functional and comparative reassessments are necessary to address this question.

Amino Acid Sequence↗

PubMed2005

Cortisol stimulates growth hormone gene expression in rainbow trout leucocytes in vitro.

Extrapituitary expression of the growth hormone (GH) gene has been reported for the immune system of various vertebrates. In the rainbow trout (Oncorhynchus mykiss), GH mRNA could be detected in several lymphoid organs and leucocytes by reverse transcriptase-polymerase chain reaction (RT-PCR). To understand the control of GH expression in the fish immune system, mRNA levels for two distinct GH genes (GH1 and GH2) in trout leucocytes isolated from peripheral blood were quantified using a real-time PCR method. Both GH mRNAs could be detected in trout leucocytes, although their levels were extremely low compared to those in pituitary cells. The levels of GH2 mRNA in leucocytes were several times higher than those of GH1, while no difference was observed between GH1 and GH2 mRNA levels in the pituitary. Administration of dibutyryl cyclic AMP and cortisol produced a significant elevation of GH mRNA levels in trout leucocytes, although the levels were unchanged by T3. GH1 and GH2 mRNA levels showed similarities in responses to those factors. The effect of cortisol on GH mRNA appears biphasic; a dose-depending elevation of GH gene expression was observed in leucocytes treated with cortisol at below 200 nM, however, cortisol had no effect at 2000 nM. Cortisol-treated leucocytes showed no significant change in the mRNA level of beta-actin or proliferative activity during the experiments. Our results thus show that, at the low levels, GH gene expression in trout leucocytes is regulated by cortisol, which has been known as a regulatory factor of GH gene expression in pituitary cells, and suggest a physiological significance of paracrine GH produced in the fish immune system.

Actins↗

PubMed2004

In vitro effects of cortisol on the release and gene expression of prolactin and growth hormone in the tilapia, Oreochromis mossambicus.

Exposure to cortisol inhibits prolactin (PRL) release from the tilapia pituitary within 10-20min through a plasma membrane-associated, 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 (300mOsmolal) than in hyperosmotic (350mOsmolal) medium during the 2-8h of incubation. The mRNA levels of two PRLs, as estimated by RNase protection assay, were increased after 8h in hyposmotic medium. Cortisol (200nM) inhibited the release of two PRLs under hyposmotic conditions within 1h, and the inhibitory effects lasted for 24h. Cortisol also reduced the gene transcription of both PRLs during 2-8h of incubation but not after 24h. 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 8h of incubation. However, GH release was significantly stimulated by cortisol after 4h, and the effect lasted for 24h under both hyposmotic and hyperosmotic conditions. Cortisol also caused a significant increase in GH mRNA levels at 8 and 24h. 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.

Animals↗

PubMed2004

Effects of prolactin and growth hormone on plasma levels of lysozyme and ceruloplasmin in rainbow trout.

In vivo and in vitro effects of prolactin (PRL) and growth hormone (GH) on plasma levels of lysozyme and ceruloplasmin were examined in the rainbow trout (Oncorhynchus mykiss). Hypophysectomy had no effect on the plasma lysozyme level. Implantation of PRL- or GH-containing cholesterol pellets increased the lysozyme level in a dose-related manner. After hypophysectomy and sham operation, plasma ceruloplasmin was elevated above the level in intact fish, suggesting inflammation caused by the surgery. PRL or GH treatment significantly attenuated the increased level of ceruloplasmin in the operated fish. Expression of lysozyme mRNA was detected in the leucocytes isolated from the peripheral blood by RT-PCR. In vitro administration of PRL or GH showed no effect on the proliferation of isolated leucocytes or on the total protein content; however, lysozyme activity in the medium increased in a dose-related manner. These results suggest that PRL and GH directly stimulate lysozyme production without affecting the proliferation of leucocytes, and the attenuated ceruloplasmin level increased in response to inflammation.

Animals↗

PubMed2004

Effects of prolactin and growth hormone on proliferation and survival of cultured trout leucocytes.

The in vitro effects of prolactin (PRL) and growth hormone (GH) on the proliferation and survival of leucocytes isolated from the blood of the rainbow trout (Oncorhynchus mykiss) were examined, with special reference to the immunosuppression by cortisol. Both PRL and GH induced a mitogenic effect in trout leucocytes. Contrary, the frequencies of annexin V-positive apoptotic cells and propidium iodide-positive dead cells were decreased by the administration of PRL, but were uninfluenced by GH. Administration of cortisol suppressed the mitotic activity and induced cell death of leucocytes. PRL inhibited the decrease in mitosis and the increase in cell death due to cortisol. GH significantly assisted recovery of cortisol-suppressed mitosis but did not influence the survival of leucocytes. These results suggest that PRL and GH are involved in the maintenance of specific immune functions in fish through a prevention of immunosuppression by cortisol.

Animals↗

PubMed2002

Relationships between obesity and metabolic hormones in the "cobalt" variant of rainbow trout.

The "cobalt" variant of rainbow trout (Oncorhynchus mykiss) lacks most of the pars intermedia of the pituitary, and shows significant obesity with an enlarged liver and a fat accumulation in the abdominal cavity. Plasma levels of growth hormone, prolactin, and somatolactin were significantly lower in the cobalt variant than those in the normal trout. In contrast, plasma insulin level was four times higher than that in the normal. Plasma levels of total protein, free cholesterol, and triacylglycerol were higher in the cobalt, while those of glucose and fatty acids were not different from the normal levels. In the white muscle, red muscle, liver, and mesenteric fat, the cobalt showed higher contents of triacylglycerol than the normal fish. There was no significant difference in tissue contents of phosphatidylcholine between the two groups of the trout, except for that in the mesenteric fat, exhibiting significantly lower content than in the normal fish. Activity of triacylglycerol lipase in the liver in vivo was lower in the cobalt than that in the normal trout, while there was no significant difference between the two in the cultured liver slices. Desacetyl-alpha-MSH stimulated lipolysis of triacylglycerol similarly in the cultured liver slices from the normal trout and from the cobalt variant. Results from this study suggest that the lack of pars intermedia and the increased plasma level of insulin are involved in a depression of lipid mobilization and obesity in this variant of rainbow trout.

Animals↗

PubMed2002

Effects of insulin-like growth factors (IGF-I and -II) on growth hormone and prolactin release and gene expression in euryhaline tilapia, Oreochromis mossambicus.

We investigated in vitro effects of insulin-like growth factors (IGF-I and -II) on growth hormone (GH) and prolactin (PRL) release and gene expression in euryhaline tilapia, Oreochromis mossambicus. Pituitaries were removed from freshwater-acclimated adult males and incubated for 2-24h in the presence of human IGF-I or -II at doses ranging from 1-1000 ng/ml (0.13-130 nM). IGF-I at concentrations higher than 10 ng/ml and IGF-II higher than 100 ng/ml significantly inhibited GH release after 8, 16, and 24h. No effect of IGFs was seen during the first 4h of incubation. IGFs at the same concentrations also significantly attenuated GH gene expression after 24h, although no effect was seen at 2h. By contrast, PRL(188) release was stimulated significantly and in a dose-related manner by IGF-I at concentrations higher than 10 ng/ml and by IGF-II at concentrations higher than 100 ng/ml within 2h. No stimulation was observed after 4h. Similarly, both IGFs at concentrations higher than 10 ng/ml increased PRL(177) release within 2h. However, no significant effect of IGF-I or -II was observed on mRNA levels of both PRLs after 2 and 24h at all concentrations examined. These results clearly indicate differential regulation of GH and PRL release and synthesis by IGFs in the tilapia pituitary, i.e., rapid-acting, stimulatory effects of IGFs on PRL release and slow-acting, inhibitory effects on GH release and synthesis.

Animals↗

PubMed2002

Interaction between endocrine and immune systems in fish.

Diseases in fish are serious problems for the development of aquaculture. The outbreak of fish disease is largely dependent on environmental and endogenous factors resulting in opportunistic infection. Recent studies, particularly on stress response, have revealed that bidirectional communication between the endocrine and immune systems via hormones and cytokines exists at the level of teleost fish. Recently information on such messengers and receptors has accumulated in fish research particularly at the molecular level. Furthermore, it has become apparent in fish that cells of the immune system produce or express hormones and their receptors and vice versa to exchange information between the two systems. This review summarizes and updates the knowledge on endocrine-immune interactions in fish with special emphasis on the roles of such mediators or receptors for their interactions.

Animals↗

PubMed2002

Hypophysectomy depresses immune functions in rainbow trout.

As the immune system is known to be influenced by the endocrine system, the effects of hypophysectomy on immune functions were examined in the rainbow trout (Oncorhynchus mykiss). Superoxide anion (O2-) production, accompanied by phagocytosis, was significantly decreased in leucocytes isolated from the head kidney 7 days after hypophysectomy. Significant reduction was also observed in plasma immunoglobulin (Ig) M levels, whereas no change was observed in plasma lysozyme activity. The number of Ig-secreting leucocytes in peripheral blood had decreased after hypophysectomy, although total leucocyte number was not affected. The percentage of Ig-producing leucocytes as assessed by flow cytometry using a monoclonal antibody to trout IgM showed significant reduction in the head kidney. However, hypophysectomy did not affect the number of Ig-producing leucocytes in spleen, thymus or peripheral blood. By RT-PCR, expression of two growth hormones (GH I and II) and prolactin (PRL) mRNA was detected in lymphoid tissues, such as head kidney, spleen, thymus and intestine, as well as in leucocytes from blood and head kidney, indicating the local production of these hormones. These results indicate important roles of hypophyseal hormones produced not only in the pituitary, but also in the lymphoid tissues, in the maintenance of the immune functions in trout.

Analysis of Variance↗