The original corpora lutea were examined and measured in twenty-one guinea-pigs still in the luteal phase 55 to 116 days after hysterectomy. Most corpora lutea had regressed to less than half their average maximum volume after 70 days and all had regressed after 80 days. The luteal phase may last for 150 days or more, although ovulation may sometimes occur spontaneously between 79 and 90 days after hysterectomy. Possible reasons for the prolonged anoestrus are discussed.
In previous experimental work, existing hysterectomy corpora lutea remained unaffected for 14 to 18 days by induced corpora lutea in the same ovaries. In a fresh series killed 51 to 72 days after hysterectomy, the original corpora lutea had regressed in six out of nine females and, except for a remnant, had disappeared in another, while the induced corpora lutea remained large 21 to 33 days after ovulation. It was concluded that the original corpora lutea regressed according to their age, asynchronously with the induced ones, as in similar experiments on hysterectomized sheep. No uterine luteolytic hormone could be involved, but a more active metabolism in the more recent corpora lutea might be postulated.
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