抗利尿ホルモンの甲状腺刺戟ホルモン (TSH) 放出作用に関する研究
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Hormonal regulation of anterior pituitary secretion as postulated in the form of neurosecretion transmitted from hypothalamic nuclei is a highly important problem in endocrinology. Among many factors postulated such as chemical mediators which seem to regulate anterior pituitary activity, the posterior pituitary hormone is thought to be one with considerable activity. Clinically and experimentally the direct stimulating effect of posterior pituitary hormone upon anterior pituitary secretion, such as ACTH release, is inferred from observations on the functional level of the peripheral target organ, e.g. that of the adrenal cortex in the case of ACTH, since direct measurement of anterior pituitary activity in the form of an hormonal assay of a given blood or plasma is still difficult to obtain. As regards the direct determination of TSH-like activity of plasma, a new release method using beef thyroid slices loaded with I<SUP>131</SUP> has been developed in our laboratory. (Tsuji, S. und Ogura, H. : Naunyn-Schmiedeberg's Arch. exp. Path. u. Pharmak., 238. 391, 1960) With this method we are now able to observe directly the secretory activity of the anterior pituitary with regard to TSH-production. It is well known that posterior pituitary hormone is composed of vasopressin (pitressin) and oxytocin. Maeda of our clinic recently demonstrated, that intramuscular administration of pitressin significantly enhances the TSH-like activity of plasma 30-60 minutes after injection. His conclusion was that pitressin exerts a direct stimulating effect upon the secretion of TSH from anterior pituitary. On the other hand, a view has been expressed that pitressin is not one simple antidiuretic substance but is possibly contaminated by other factors. In the author's laboratory, functional studies are going on, in search of chemical mediators liberated from the brain stem, which are thought to be concerned in the regulation of anterior pituitary activity. Clarifying the nature of posterior pituitary hormone, particularly of pitressin (Park, Davis), with regard to its TSH-releasing activity and antidiuretic effect is an interesting problem. Hence, the author tried to fractionate pitressin (Parke, Davis) by continuous paper electrophoresis and to examine the antidiuretic and TSH-releasing activity of separated fractions.<BR>Methods and results of experiments : <BR>1) The fractionating of pitressin was carried out in phosphate buffer of pH 7.73 by continuous paper-eletrophoresis. Pitressin was thus fractionated into 3 fractions, which were stained with Folin reagent. We named them B, A and C accrding to their distribution from the anode side.<BR>2) These fractions were collected separately and examined for antidiuretic activity by Van Dyke's method. It was faund that fraction C alone has antidiuretic activity.<BR>3) Each fraction was injected intramuscularly into normal male dogs, and blood samples were taken immediately before and 30, 60,120 minutes after administration for determination of plasma TSH-like activity. Increase of plasma TSH-like activity was observed in samples taken 30-60 minutes after injection of fraction A, similar but less and often a doubtful effect was seen with injection of fraction B, whereas fraction C showed almost no effect upon plasma TSH-like activity.<BR>4) Each fraction was given to rats of Wister strain and their effect upon thyroid function was studied on the following thyroid items : weight of thyroid, thyroid uptake of Psi, Seruum PBI<SUP>131</SUP> conversion ratio and T/S I<SUP>131</SUP> ratio. In this experimental series the most remarkable thyroid stimulating effect was observed in the group of rats which were treated with fraction A. In the group treated with fraction B, a similar but lesser effect was seen, whereas in the group treated with fraction C almost no change in thyroid function could be demonstrated. The results in rats correspond well with the findings made in dogs with regard to thyroid function.
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