کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
9113097 1156207 2005 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Physiological concentrations of ouabain rapidly inhibit prolactin release from the tilapia pituitary
موضوعات مرتبط
علوم زیستی و بیوفناوری بیوشیمی، ژنتیک و زیست شناسی مولکولی علوم غدد
پیش نمایش صفحه اول مقاله
Physiological concentrations of ouabain rapidly inhibit prolactin release from the tilapia pituitary
چکیده انگلیسی
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 Ca2+ ([Ca2+]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 2-24 h 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 Ca2+ ionophore, A23187, and by a combination of dibutyryl cAMP and a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthin. Intracellular Ca2+ concentrations were monitored in the dispersed PRL cells with the Ca2+-sensitive dye, fura-2. Ouabain at 1 nM reversibly reduced [Ca2+]i within seconds, whereas 1 μM ouabain increased [Ca2+]i. A rapid reduction in [Ca2+]i was also observed when PRL cells were exposed to 1 μM 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 Ca2+ and cAMP metabolism. The stimulation of PRL release by high concentrations of ouabain (100-1000 nM) may result from an increase in [Ca2+]i, and subsequent depolarization due to the inhibition of Na+, K+-ATPase activity.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: General and Comparative Endocrinology - Volume 143, Issue 3, 15 September 2005, Pages 240-250
نویسندگان
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