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Department of Veterinary Anatomy, University of Bristol, Bristol, BS1 5LS
(Received 22 May 1974)
Hydroxysteroid dehydrogenases (HSD's) acting at the 3α, 3β and 16β positions have been demonstrated histochemically in the trophoblast of the established placenta of the pig and 17β-HSD has been identified in the maternal placental epithelium (Christie, 1968; Dufour & Raeside, 1969). This 17β-HSD is also found in the uterine epithelium of the interlocular and unoccupied parts of the pregnant uterus but is absent from the non-pregnant uterus (Flood, unpublished). The object of the present study was to determine the time of appearance of these enzymes.
Eight gilts and one sow were killed at 10, 12(2), 13(2), 14, 15, 16 and 19 days of gestation. The day after first service was regarded as day 0. The uteri were removed within 10 min of slaughter and in the case of the gilt killed at 10 days' gestation, ten
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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.
