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RUTH DEANESLY

The pioneer work of Klein on unilaterally pregnant rabbits, rats and hamsters (Klein, 1933, 1935, 1938) established the role of the pregnant uterus in maintaining, independently of the foetuses, the histological structure and function of the corpora lutea of pregnancy. If the pregnant horn were removed from unilaterally pregnant animals in mid-pregnancy, degeneration of the corpora lutea followed, the progestational proliferation in the sterile horn broke down and a fresh ovulation took place.

From these, and from hypophysectomy experiments on the pregnant rat, a predominant role is often attributed to placental luteotrophins in animals where the corpora lutea persist for long periods or nearly till the end of pregnancy. This assumption has been tested by repeating Klein's experiments on the pregnant ferret.

The ferrets were from Mr Hammond's colony at the School of Agriculture, Cambridge. Normal pregnancies could be induced by

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RUTH DEANESLY

In guinea-pigs ovariectomized before implantation, where conceptuses continue to develop for some days, partial and finally complete haemorrhagic degeneration of the decidua takes place, usually terminating pregnancy by Day 16 or earlier. This can be prevented by exogenous progesterone (Deanesly, 1972). In pregnant rats, termination of pregnancy following ovariectomy is well known, but its immediate effect on the conceptuses does not appear to have been described. To compare their reactions with those in the guinea-pig, 6- to 9-day pregnant rats (vaginal plug, Day 0) were ovariectomized under ether anaesthesia and killed up to 2 days later, or after a longer interval if given progesterone. The 6- to 12-day conceptuses, fixed in Bouin's fluid and weighed from 70% alcohol, were compared with those from normal animals at corresponding ages. All were sectioned serially in the sagittal plane at 7 μm,

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RUTH DEANESLY

Summary.

In the guinea-pig, an ovarian or exogenous progestagen is not required for ovo-implantation, but the lack of it in females, ovariectomized 3, 4 or 5 days after mating, affects embryonic growth and development from about Day 12. Between 14 and 16 days after mating, the placenta and embryo undergo very rapid differentiation. This stage has been studied in a large series of embryos to see how they were affected by the progestagen deficiency. Growth of the embryonic swelling was slowed down but there was much variation, some embryos not getting beyond the 14-day stage and others surviving and differentiating normally up to Day 15 or 16.

The duration of embryonic viability in groups of ovariectomized mothers was tested by beginning administration of progesterone on Day 13, 14, 15 or 16. In the last group only two out of thirteen embryos survived. In the untreated series only five out of eighteen ovariectomized mothers contained live embryos on Day 16.

From the general variability and from a study of the embryos, it appeared that arrest of embryonic development and death was not caused at any precise time or stage by uterine compression but was more probably due to nutritional deficiencies associated with the absence of the ovarian progestagen.

In further experiments it was shown that pregnancy could continue after about Day 21, or even earlier, in the absence of the ovaries or of exogenous hormones. Both this and the normal differentiation of some embryos in ovariectomized mothers up to Day 16, indicate early production of sex hormones by the placenta.

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RUTH DEANESLY

Guinea-pigs were from the colony at the Institute. Examination of the animals and operative and histological techniques were the same as in previous work (Deanesly, 1967).

In the first group (Table 1, Group 1), one uterine horn was removed from four females; one of these failed to mate and another had no corpora lutea on the side of the sterile horn. Such animals are omitted from Table 1. For Group 2, a small piece of one Fallopian tube was removed without disturbance of the vascularization of the uterus or ovary, and for Group 3 one uterine horn was severed or ligatured near the middle. Ovaries were sectioned serially at 7 μ after fixation in Bouin's fluid, and one in six sections were mounted. Two diameters at right angles were measured ( × 27) across the largest sections of each corpus

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RUTH DEANESLY

Summary.

Sixty adult female guinea-pigs were treated with reserpine for a study of its effects on the ovaries and reproductive cycle. In the guinea-pig, as in the rat, it will inhibit ovulation, but whereas reserpine, acting through the hypothalamus and pituitary, is luteotrophic and lactogenic in the rat, in the guinea-pig it is neither, but has an inhibitory action on the development and function of the corpus luteum.

Reserpine does not interfere with ovo-implantation in the guinea-pig but later, at 14 to 15 days pregnant when an embryo is more vulnerable and requires a greater supply of progesterone, reserpine causes abortion.

After reserpine treatment, most follicles were unable to respond by ovulation to purified sheep luteinizing hormone, which will induce ovulation in the normal guinea-pig.

Apart from considerations of dosage, species differences in the reactions of the ovaries to reserpine are probably connected with differences in the hypothalamic-hypophysial neuro-secretory paths.

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RUTH DEANESLY

Summary.

In guinea-pigs absorbing 0·1 mg or more progesterone daily from solid, subcutaneous tablets, follicles grow and regress normally as do existing corpora lutea, but ovulation is completely inhibited. The uterus, in the absence of cyclic changes, is continuously stimulated by ovarian oestrogens in progesterone-treated animals. It enlarges, sometimes becoming enormous, and shows various pathological changes. These are absent from the uteri of ovariectomized animals treated with progesterone. Five males which absorbed 0·26 to 1·7 mg progesterone daily for 30 to 64 days had normal reproductive organs.

Testosterone propionate, similarly administered, also inhibits ovulation; additionally it leads to a reduction in follicle growth and ovary size. Both steroids showed steady, slow rates of absorption as determined from tablet weights before and after implantation.

Ergocornine, which is said to inhibit corpus luteum secretion in rats, had no such effect on corpora lutea in non-pregnant and pregnant guinea-pigs, when injected in solution.

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RUTH DEANESLY

Summary.

If all corpora lutea are removed by unilateral ovariectomy from a guinea-pig 4 or 5 days after mating, a fresh ovulation will occur in the remaining ovary about a week later and pregnancy can continue to term. If a single pregnancy corpus luteum persists after unilateral ovariectomy, there is no ovulation and pregnancy is maintained.

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RUTH DEANESLY

Summary.

Earlier experiments on guinea-pigs are said to demonstrate the essential participation of small amounts of progesterone at normal oestrus.

The guinea-pig vagina shows an elaborate proliferation just before oestrus, with stratified epithelial cells at the base, which eventually cornify, and loosely arranged mucified cells next to the lumen. Attempts with different hormones to reproduce this transitory condition in spayed females have shown that it is slow to develop but can be induced by 6 to 12 μg oestradiol benzoate spread over 3 to 4 days. This is enough for full vaginal oestrus including cornification and, in some females, mating. There was no evidence from these experiments of pre-ovulatory progesterone being a significant factor at oestrus.

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RUTH DEANESLY

A.R.C. Institute of Animal Physiology, Babraham, Cambridge

(Received 3rd March 1975)

At the end of the meiotic prophase, oocytes are enclosed by adjacent cells to form primordial follicles. Agreement is lacking on the origin of these cells, sometimes seen as epithelial, but in papers on man (Sauramo, 1954), the mouse (Peters & Pedersen, 1967), the rabbit (Peters et al., 1965) and the ferret (Deanesly, 1970) they have been clearly described as stromal cells which have ramified among the oocytes from the earliest stages of ovarian development. At first these cells are flattened but they become cuboid and their nuclei enlarge—a transition readily seen in the rabbit and ferret (see Deanesly, 1970: Figs 20 and 21).

Recently, it has been suggested by Byskov & Lintern-Moore (1973) and Peters (1973) that the rete tubules within the mouse ovary contribute cells to the formation of follicles and differentiate into granulosa cells. For

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RUTH DEANESLY

Summary.

Progesterone deficiency in the pregnant guinea-pig, ovariectomized before implantation, retards growth of the conceptuses and embryos and terminates pregnancy on or before Day 16.

In a fresh investigation, conceptuses from ovariectomized, 12- to 16day pregnant females were examined in serial sections, and from Day 12 a conspicuous degeneration of part of the decidua occurred, interfering with the normal development of the adjacent placenta. This degeneration undoubtedly contributed to the retardation of the conceptus during the following days, when very active embryonic differentiation was normally taking place. It was the total collapse of the decidua with massive haemorrhage, almost always on Day 16, which abolished surviving pregnancies. Similarly in the unmated guinea-pig, the traumatic deciduoma breaks down at the end of the 16-day cycle, when the corpora lutea regress before the next oestrus.

Decidual degeneration could be prevented in ovariectomized females if progesterone was given sufficiently early in pregnancy. In other developing conceptuses, however, in which progesterone had been deferred till later, an area of decidual degeneration, no longer in contact with the placenta, could persist for some days.

The rôle of the decidua in early pregnancy is discussed.