Progesterone Concentration in the Peripheral Plasma of Sheep During the Oestrous Cycle

Abstract

Using a protein-binding technique, progesterone concentrations in peripheral plasma (jugular vein) were measured throughout the oestrous cycle of 24 ewes. Examination of the specificity of the method by thin-layer chromatography indicated that interference from other steroids was not significant in sheep plasma. During the first 4 days of the cycle (days 0-3), plasma progesterone concentrations were below 0\m=.\4 ng./ml., increasing to a mean level of 1\m=.\5-2\m=.\5 ng./ml. between days 4 and 9, and remaining at this level for approximately 5 days, before declining rapidly on days 14 and 15 to reach a low level on the day before oestrus. The progesterone concentration on the day of oestrus was extremely low (0\m=.\1ng./ml.), and was of the same order as that found in the plasma of wethers and anoestrous or ovariectomized ewes. Three ewes, superovulated with pregnant mare serum gonadotrophin, showed marked elevation of peripheral progesterone concentration during the luteal phase of the cycle, the concentration being proportional to the number of corpora lutea formed.

The Role of Progesterone in Implantation in the Sheep

“…This test, -based on the competitive proteinbinding principle, responds to compounds other than progesterone, including 17IX-hydroxy-4-pregnen-3,20-dione and 20IX-hydroxy-4-pregnen-3-one. The results are more correctly "total plasma progestagen" levels although progesterone has been indicated as the dominant compound measured in plasma of non-pregnant sheep (Thorburn, Bassett, and Smith 1969). For convenience the results are referred to as plasma progesterone.…”

“…Plasma progesterone determinations in experiment 2 were performed on duplicate 2-ml aliquots of plasma by the competitive protein-binding method described by Basset and Hinks (1969) and Thorburn, Bassett, and Smith (1969). This test, -based on the competitive proteinbinding principle, responds to compounds other than progesterone, including 17IX-hydroxy-4-pregnen-3,20-dione and 20IX-hydroxy-4-pregnen-3-one.…”

Primordial Follicle Numbers in Ovaries and Levels of LH and FSH in Pituitaries and Plasma of Lambs Selected for and against Multiple Births

“…Peripheral plasma was assayed for progesterone by the competitive protein binding assay described by Thorburn et al (1969) and total oestrogens by the radioimmunoassay described by Abraham (1969). The peripheral plasma levels and anterior pituitary content of LH and FSH were determined by the radioimmunoassays reported by Goding et al (1969) and Salarnonsen et al (1973).…”

Development of Myometrial Electrical Activity during the First Half of Pregnancy in the Sheep

“…The results demonstrate that the uterus is not completely quiescent during the first half of pregnancy; myoelectrical activity steadily increases in amplitude during this period despite the presence of plasma progesterone levels comparable with those occurring during the luteal phase of the oestrous cycle Thorburn et al 1969).…”