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R. DEANESLY

Luteinizing hormone (Ovine, nih-lh-s7 from the National Institutes of Health, Bethesda, U.S.A.) has been administered subcutaneously in normal saline (0·5 mg/ml) to female guinea-pigs for a study of its effects on ovulation and the cycle.

The animals were examined daily for vaginal changes; the first day of vaginal closure after oestrus (corresponding in general to the morning of the vaginal plug in mated females), was recorded as Day 0 and the following days as (luteal) Days 1, 2, etc. In most experiments a single dose of lh was given; the ovaries were examined at autopsy, and one or both sectioned serially after fixation in Bouin's fluid. Preliminary tests in cyclic females showed that 200 μg lh would stimulate ovulation within 24 hr and also follicular luteinization.

Fifteen unmated non-parous females with a regular cycle of about 16

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R. DEANESLY

Summary.

In guinea-pigs, low doses of oestradiol benzoate, given immediately after mating, inhibit pregnancy. This is not due to retention of eggs in the Fallopian tubes but to their expulsion. It is suggested on present evidence that the term 'tube-locking' should be dropped, unless it is clearly shown that eggs are detained in the Fallopian tubes beyond the usual period.

Once the fertilized eggs have passed normally into the uterus, implantation is not prevented by as much as 30 or 50 μg oestradiol in the guinea-pig, but later stages of development may be affected and the corpora lutea regress completely, either because of a failure of the placental luteotrophic hormone at about 10 days post coitum (p.c.) or through a direct effect of oestrogen on the secretion of pituitary gonadotrophins. In animals which aborted or resorbed their embryos, oestrus returned about Day 16.

Implantation was not inhibited by 20 μg oestradiol in guinea-pigs ovariectomized on Day 5 and injected on Days 6 and 7 p.c.

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R. DEANESLY

Summary.

The rapid decidualization of the endometrial stroma, which begins while the guinea-pig blastocyst is still passing through the uterine epithelium, has been compared in serial sections with the decidualization following thread traumatization in the same or similar uteri. In both cases there are localized alkaline phosphatase reactions, but blastocyst implantation leads to formation of a decidua which within the first 24 hr, is more organized and differentiated than the corresponding traumatic deciduoma. The passage of the guinea-pig blastocyst through the uterine epithelium does not involve cell destruction or phagocytosis and the decidual changes in the stroma must be attributed to specific blastocyst activity.

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R. DEANESLY

Summary.

Ovo-implantation in the guinea-pig on the 6th to 7th day post coitum is not affected by ovariectomy on days 3 to 7 p.c. If the ovaries are removed on the 2nd day after mating, however, implantation does not occur unless at least one injection of progesterone is given. In the ovariectomized guinea-pigs, the embryos develop normally for several days but may regress after day 14 unless progesterone is supplied, permitting further growth. No evidence was found of delayed implantation.

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R. DEANESLY

Summary.

Unilaterally sterilized guinea-pigs were mated and the sterile uterine horn traumatized 0 to 7 days later by the passage of two or more threads which were left in situ. The animals were killed 3 to 7 days after traumatization and the endometrial reactions studied histologically. Although deciduomata developed in uteri traumatized 4 to 7 days after mating, those traumatized up to 3 days after mating and killed up to 5 days later showed little reaction and contrasted markedly with the corresponding horns in which fertilized eggs were becoming implanted. This difference, not affected by exogenous progesterone treatment, indicates that the fertilized eggs have a specific capacity to induce changes in the endometrium, while it is non-reactive to other stimuli.

Traumatization of both uterine horns did not completely inhibit ovoimplantation or subsequent pregnancy.

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R. B. HEAP and R. DEANESLY

Plasma progesterone concentrations in the pregnant guinea-pig are greater than in many species (Heap & Deanesly, 1966; Heap, Perry & Rowlands, 1967) and far higher than those found in the normal cycle (Table 1). The present experiments were intended to compare the effects of subcutaneous progesterone tablets on plasma progesterone levels after ovariectomy with those in normal, non-pregnant and pregnant females.

The ovaries are essential for pregnancy in most guinea-pigs between about Days 14 and 28 (Deanesly, 1963) but from about Day 28 pregnancy will continue normally without exogenous hormones owing to the production of placental progesterone. In this study it was decided to use females in the 1st month of pregnancy when the actual production of progesterone by the placenta is far less than that of the ovary and is well below that reached in later stages (Heap

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R. DEANESLY and J. S. PERRY

Summary.

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.