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      A 66-kDa protein of bovine hypophyseal Pars tuberalis induces luteinizing hormone release from rat Pars distalis

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          Abstract

          In this study, evidence for a factor secreted by bovine hypophyseal pars tuberalis that stimulates luteinizing hormone (LH) release from rat pars distalis cells is shown. The secretion products of bovine pars tuberalis cells into the culture medium were assayed on dispersed rat pars distalis cells in 30 min incubations and superfusion experiments. The culture medium from pars tuberalis total cell populations, added at a dose of 6 μg per tube, induced the greater LH release from pars distalis cells, without effect on follicle stimulating hormone (FSH) release. After pars tuberalis cells separation on a discontinuos Percoll gradient, only the culture medium of cells from 50 and 60% strength Percoll were able to release LH from rat pars distalis cells. Therefore, cell fractions from 50 and 60% strenght Percoll were cultured together. To elicit maximal LH release (6 times the basal output), with the addition of 2 μg of pars tuberalis protein was required, suggesting that these cells produce the factor or factors which affect pars distalis gonadotrope cells. After applying the pars tuberalis culture medium on 12% SDS-PAGE, the band with biological activity was that of 66-kDal. Fifty ng protein of its eluate released almost 9 times the basal output of LH from pars distalis cells. Results suggest a modulating effect of a protein from the bovine pars tuberalis on rat cultured gonadotrope cells from the pars distalis.

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          Most cited references 30

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          A Rapid and Sensitive Method for the Quantitation of Microgram Quantities of Protein Utilizing the Principle of Protein-Dye Binding

           M. Bradford (1976)
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            Prolactin suppresses luteinizing hormone secretion and pituitary responsiveness to luteinizing hormone-releasing hormone by a direct action at the anterior pituitary.

            In pathological or experimental hyperprolactinemia, the elevated circulating levels of PRL are the usual cause of the impairment in gonadotropic function. The present study was undertaken to determine whether PRL could suppress basal LH secretion and LHRH-stimulated LH release by a direct action at the anterior pituitary. Anterior pituitaries from ovariectomized rats were incubated in medium 199 alone or in medium 199 containing ovine PRL, and basal and the LHRH-stimulated LH release were followed for 2 or 3 h in vitro. Ovine PRL at 40 and 80 micrograms/ml suppressed basal LH release by 41% and 72%, respectively, at 2 h of incubation. This suppressive effect of both concentrations of PRL continued to the third hour of incubation. LHRH at 5 ng/ml increased the release of LH from pituitaries incubated in medium alone by 57%, 61%, and 107% at 1, 2, and 3 h of incubation, respectively. However, in the pituitaries treated with 40 micrograms/ml ovine PRL, the stimulatory effects of LHRH were diminished at all time points measured. Pretreatment of anterior pituitaries with ovine PRL for 6 h significantly inhibited by 81% the LHRH (5 ng/ml) stimulation of LH release at 2 h of incubation. On the other hand, inhibition of endogenous PRL release by 10(-6) M bromocriptine enhanced the stimulatory effects of 5 ng/ml LHRH by 2.5-fold at 2 h of incubation. The inhibitory effects of PRL on basal and stimulated LH secretion appeared unique, since neither BSA nor vasopressin could elicit similar suppressive effects on LH. These results suggest that in anterior pituitaries exposed to elevated levels of PRL, LH secretion and pituitary responsiveness to LHRH could be impaired. This phenomenon may contribute in part to the antigonadotropic effects of PRL.
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              Cleavage of structural proteins during the assembly of the head bacteriophage T4

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                Author and article information

                Journal
                biocell
                Biocell
                Biocell
                Sociedad Latinoamericana de Microscopía Electrónica.; Centro Regional de Investigaciones Científicas y Tecnológicas (Mendoza, Argentina) (Mendoza, Mendoza, Argentina )
                0327-9545
                1667-5746
                December 2008
                : 32
                : 3
                : 211-218
                Affiliations
                San Luis orgnameUniversidad Nacional de San Luis orgdiv1Facultad de Química, Bioquímica y Farmacia orgdiv2Laboratorio de Biología de la Reproducción (LABIR) Argentina
                Article
                S0327-95452008000300001 S0327-9545(08)03200300001

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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                Figures: 0, Tables: 0, Equations: 0, References: 24, Pages: 8
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