Levels of progesterone were determined by competitive protein-binding techniques and oestrogens by radio-ligand binding techniques in the uterine and peripheral plasma of parturient ewes. Uterine progesterone levels began a continuous decline 4 to 5 days ante partum whereas jugular levels only declined 1 or 2 days ante partum. Peripheral plasma progesterone levels were significantly elevated in ewes carrying multiple fetuses compared to those in ewes with a single fetus. A similar but non-significant difference existed in the uterine plasma. Adrenalectomized and adrenalectomized-ovariectomized ewes had lower progesterone levels in the peripheral blood but not lower uterine levels than did control ewes. Ovariectomy did not affect progesterone levels. Oestrone and oestradiol values were lower in the uterine venous concentrations of adrenalectomized and adrenalectomized-ovariectomized ewes. A depression of oestrogen values before birth was not noted in ovariectomized ewes. It is concluded that the maternal adrenal has a definite rôle in oestrogen biosynthesis in pregnant sheep.
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