Effect of intra-uterine beads alone, or combined with oestrogen treatment, on utero-ovarian venous plasma prostaglandin F2alpha and progesterone levels in the guinea-pig.

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The presence of beads in the guinea-pig uterus caused premature regression of the corpora lutea, and a corresponding decrease in utero-ovarian venous plasma levels of progesterone, by days 9-10 of the oestrous cycle. If the beads were placed in one horn only, premature luteal regression occurred only in the adjacent ovary. Induced luteal regression was preceded by an increased release of prostaglandin F2alpha (PGF2alpha) from the uterine horns which contained the beads. Oestradiol benzoate treatment of guinea-pigs carrying beads in one uterine horn overcame the unilateral effect and resulted in premature luteal regression in both ovaries. This was also associated with the early release of PGF2alpha from both uterine horns, though a difference in the timing of the release was apparent between the bead-containing (experimental) and control horns.