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Oestrogen induction of riboflavin-binding protein in immature chicks.

ABSTRACT: In hyperthyroid chicks, oestrogen-induced plasma accumulation of riboflavin-binding protein was diminished, whereas the reverse situation prevailed in hypothyroid birds. Under hyperthyroid conditions, higher concentrations of oestrogen were required to elicit a response comparable with that obtained in normal birds treated with lower concentrations of the hormone. Elevated hepatic cytochrome P-450 concentrations and decreased half-life of the induced protein in hyperthyroid animals suggest that higher catabolic rates of the inducer and induced protein are contributory factors to the diminished response.

SUBMITTER: Murthy US

PROVIDER: S-EPMC1165053 | biostudies-other | 1977 Sep

REPOSITORIES: biostudies-other

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Project description:A specific radioimmunoassay procedure was developed to monitor the plasma concentrations of thiamin-binding protein, a minor yolk constituent of the chicken egg. By using this sensitive assay, the kinetics of oestrogen-induced elaboration of this specific protein in immature chicks was investigated. After a single injection of the steroid hormone, with an initial lag period of 4-5h the thiamin-binding protein rapidly accumulated in the plasma, attaining peak concentrations around 75h and declining thereafter. A 4-fold amplification of the response was noticed during the secondary stimulation, and this increased to 9-fold during the tertiary stimulation with the steroid hormone. The magnitude of the response was dependent on the hormone dose, and the initial latent period and the duration of the ascending phase of induction were unchanged for the hormonal doses tested during both the primary and secondary stimulations. The circulatory half-life of the protein was 6h as calculated from the measurement of the rate of disappearance of the exogenously administered (125)I-labelled protein. Simultaneous administration of progesterone, dihydrotestosterone or corticosterone did not alter the pattern of induction. On the other hand, hyperthyroidism markedly decreased the oestrogenic response, whereas propylthiouracil-induced hypothyroidism had the opposite effect. The anti-oestrogen E- and Z-clomiphene citrates, administered 30min before oestrogen, effectively blocked the hormonal induction. alpha-Amanitin and cycloheximide administered along with or shortly after the sex steroid severely curtailed the protein elaboration. A comparison of the kinetics of induction of thiamin- and riboflavin-binding proteins by oestrogen revealed that, beneath an apparent similarity, a clear-cut difference exists between the two vitamin-binding proteins, particularly with regard to hormonal dose-dependent sensitivity of induction and the half-life in circulation. The steroid-mediated elaboration of the two yolk proteins thus appears to be not strictly co-ordinated, despite several common regulatory features underlying their induction.

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Oestrogen induction of riboflavin-binding protein in immature chicks.

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