Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.4.1 (phosphodiesterase)
 18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ouabain, a cardiac glycoside and inhibitor of Na(+), K(+)-ATPase, is now believed to be a steroid hormone in mammals. We have recently identified 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 dose-dependently during 2-24 h of incubation. There was no effect on growth hormone (GH) release, except for a significant increase at 1000 pM during 8-24 h of incubation. Significant dose-related increases in PRL release were observed at higher doses of ouabain (100-1000 nM), whereas significant inhibition was seen in GH release at 1000 nM during 2-24h of incubation. Ouabain at 1-100 pM had no effect 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 microM ouabain increased [Ca(2+)]i. A rapid reduction in [Ca(2+)]i was also observed when PRL cells were exposed to 1 microM cortisol, whereas there was no consistent effect 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.
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PMID:Physiological concentrations of ouabain rapidly inhibit prolactin release from the tilapia pituitary. 1592 43

In grass carp, luteinizing hormone (LH) can act locally within the pituitary to regulate growth hormone expression. To test if LH receptor (LHR) expression in the carp pituitary can also serve as a target of modulation for LH actions, grass carp LHR was cloned and characterized by functional expression. In carp pituitary cells, LHR mRNA (lhr) level could be reduced by LH or human chorionic gonadotropin (hCG) but up-regulated by dopamine treatment. Dopamine-induced lhr expression occurred mainly in carp somatotrophs via the cAMP/PKA pathway coupled to pituitary D1 receptors. This stimulatory effect could be blocked by LHR activation by hCG, presumably through phosphodiesterase III activation. These findings provide evidence that lhr expression in the carp pituitary is under the differential control of LH and dopamine via modification of cAMP-dependent signaling mechanisms, which may play a role in regulating somatotroph responsiveness to the paracrine action of LH in carp species.
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PMID:Gene expression of luteinizing hormone receptor in carp somatotrophs differentially regulated by local action of gonadotropin and dopamine D1 receptor activation. 2360 2


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