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W. TAYLOR
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D. E. WRIGHT
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SUMMARY

[7α-3H]Progesterone was administered to two groups of mice. The localization of radioactivity in tissues was examined by autoradiography and by liquid scintillation counting. Particular attention was paid to the distribution of radioactivity in the liver and biliary system. The greatest amount of administered steroid was taken up by the liver, rapidly secreted into the biliary system and excreted into the gastrointestinal tract. Other tissues, including the uterus, did not take up any appreciable amount of radioactivity, and the autoradiographs showed that radioactivity was not associated with any particular region of hepatic and other cells. The biological half-life of radioactivity in the blood was 11 min in animals given labelled progesterone intravenously.

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D. PAULINE ALEXANDER
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H. G. BRITTON
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V. H. T. JAMES
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D. A. NIXON
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R. A. PARKER
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E. MARELYN WINTOUR
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R. D. WRIGHT
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SUMMARY

From the left adrenal of ten sheep foetuses and four lambs aged from 110 days after conception to 14 days after birth, adrenal venous blood was collected and assayed for cortisol, corticosterone and aldosterone. These steroids were secreted at all ages but the rate of secretion was greatly increased toward term and after birth. The increase coincided with morphological changes in the adrenal gland. At no stage was the rate significantly increased by corticotrophin, and in two young foetuses it was not decreased by dexamethasone. In two foetuses and one lamb, angiotensin II did not increase the rate of secretion of any of the three steroids significantly, and the blood pressure was raised only in the lamb. It is probable that the secretion of the steroids was maximal under the conditions of the experiments.

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J. R. BLAIR-WEST
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A. BRODIE
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J. P. COGHLAN
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D. A. DENTON
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C. FLOOD
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J. R. GODING
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B. A. SCOGGINS
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J. F. TAIT
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S. A. S. TAIT
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E M. WINTOUR
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R. D. WRIGHT
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SUMMARY

The effect of sodium depletion on the conversion of corticosterone to aldosterone has been examined in vivo using the adrenal transplants of two sheep. [3H]Corticosterone was infused continuously directly into the adrenal gland via the carotid artery over a period of 30 min. and the total adrenal effluent was collected via the jugular vein in six consecutive 5-min. samples. The conversion of [3H]corticosterone to [3H]aldosterone and the endogenous output of aldosterone was measured in each sample using a double isotope derivative method and the specific activity of the aldosterone calculated. Radioactive conversion of B → aldosterone reached equilibrium within 10 min. of the start of infusion and remained constant over a period of 10–25 min. Aldosterone secretion was also constant during the first 25 min. of infusion.

In the same sheep the mean percentage conversion increased as aldosterone secretion rose over a range of 2–12 μg./hr. With more severe sodium depletion, i.e. with aldosterone secretion rates of 12–16 μg./hr., conversion decreased to that found in the sodium replete state. The specific activity of the aldosterone was constant throughout the mildly deplete range (2–12 μg./hr.) but fell with severe sodium depletion. In the sodium replete range (0–2 μg./hr.) before the introduction of a parotid fistula, the specific activity was the same as in the mildly deplete state. After the introduction of a parotid fistula the specific activity increased as the secretion decreased from 2 to 0 μg.

The validity of the approach and interpretation of the results in terms of the biosynthetic pathways involved are discussed.

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