Reproductive ageing and the menopause.

This brief review describes early work initiated by Anne McLaren and John Biggers, in which they repeated on mice a very early experiment carried out by John Hunter on pigs, to test the effect of unilateral ovariectomy on subsequent breeding performance. This and subsequent experiments led to the conclusion that reproductive ageing in the female mouse was largely due to ageing changes in the uterus. As a result of these changes fewer implanted blastocysts are carried to term in the older females, with the result that the size of litters produced gradually drops and ceases altogether well before the expected time of death, thus leading to a period of reproductive inactivity at the end of life. Other organs undergo ageing changes but it appears to be those in the uterus which limit reproductive performance in the female. The somatic organs concerned in bringing the male gametes into the environment are still able to function effectively almost until the time of death so that males have a very short period of reproductive inactivity at the end of their lives. Due to the prenatal onset of meiosis in the germ cells, female mammals and some, but not all, other vertebrates are born with a finite crop of oocytes in the ovary, which cannot be increased after birth. Nevertheless, with the exception of women, female mammals appear to be able to produce ova well into old age, and have them fertilized. When examined after death the ovaries still contain oocytes so this is not a limiting factor in reproduction in old females. In women the situation is completely different. They also have an extended period of reproductive quiescence in middle and old age, the menopause, but, unlike other female mammals, this is not due to failure of the uterus but is caused by the ovary becoming depleted of oocytes in middle age. The reason women run out of oocytes before the end of life, whereas the other mammals which have been studied do not, is associated with the greatly extended lifespan of humans compared to other mammals of equivalent size. There is a linear relationship between longevity and body weight in mammals, small mammals have much shorter lives than large ones. This is probably associated with the increased production of free radical oxygen necessary to maintain body temperature in smaller animals. Heat is lost through the body surface which becomes relatively less as the animal increases in weight, so the smaller animal has to metabolise and thus produces more free radical oxygen to maintain body temperature. For reasons unknown this seems not to apply to humans. The menopause has thus evolved as a consequence of two adaptations: the prenatal onset of meiosis, common to all mammals and many other vertebrates and the greatly increased longevity of all humans, both male and female. In view of this dual origin it is unlikely to have evolved in response to an adaptive need to have grandmothers to help rear the young, as has been suggested!

Vascular and cellular changes in the decidualized endometrium of the ovariectomized mouse following cessation of hormone treatment: a possible model for menstruation.

Ovariectomized mice were prepared for decidualization with oestrogen and progesterone and arachis oil injected into the uterine lumen. Hormone injections were then stopped and uteri examined at intervals between 31 and 84 h after the last progesterone injection. At 31 and 35 h the stroma showed a normal decidual reaction. Between 45 and 79 h the stroma underwent a series of changes which started with the congestion of dilated blood vessels with swollen erythrocytes followed by breakdown of the vessel walls and extravasation of blood. At the same time the decidual cells showed typical apoptotic changes and there was invasion by leucocytes. An outer ring of stroma did not take part in the degenerative process and eventually a central core of blood cells and degenerating decidual cells became detached and was shed into the lumen. Animals treated in exactly the same way but with the omission of the decidual stimulus did not show such changes in the stroma. It is suggested that the changes in the endometrium resemble those of menstruation and support the suggestion that for menstruation to occur the stroma must be differentiated for implantation. This occurs during the cycle in women but does not occur in non-primates unless a decidual stimulus is applied to the uterus.

Effects of a long-acting progestin on reproductive function in female mice.

The duration of activity of a long-acting progestin, medroxyprogesterone acetate, was compared using three tests for progestational activity: the induction of stromal mitosis in the endometrium, implantation of blastocysts and inhibition of ovulation. The duration of activity was similar in each test and was longer when higher doses were given.

PIP: Three experiments were conducted to evaluate the duration of activity of a long-acting progestin, medroxyprogesterone acetate: 1) induction of stromal mitosis in the endometrium; 2) implantation of blastocysts; and 3) inhibition of ovulation. In the 1st experiment, randomly bred albino mice were ovariectomized and injected with MPA 1 week later. They were injected at various intervals with 20 ng estradiol-17B in 0.05 ml arachis oil and killed 24 hours later. In the 2nd experiment, male and female mice were mated and the day of finding a vaginal plug was assigned day 1 of pregnancy. On day 4, both ovaries were removed and MPA was injected to maintain the state in which implantation can be initiated by injection of estradiol-17B. Successful initiation is shown by implantation swellings 72 hours later; absence of implantation suggests that the progestin is no longer present at an effective level. In the 3rd experiment, female mice were given MPA before they were mated with male mice. Ovulation suppresson was determined by the difference in time before parturition between MPA-treated mice and untreated mice. The results of all experiments were similar. Effective levels of hormone were observed for 6 days in most animals and maintained for up to 8 days in some animals. Some animals exhibited sufficient progestational activity to allow blastocyst implantation 12 days after injection, while stromal mitosis could not be induced after 8 days. It appears that the state of epithelium, rather than the stromal cells' ability to undergo hormone-induced proliferation, allows implantation as shown by the epithelial mitosis which was still suppressed at 10 days. 1 mg MPA induced progestin activity similar to the physiological state of early pregnancy. Mating was inhibited by higher doses of progestin for unduly long periods.

Effects of an intra-uterine device on uterine cell division and epithelial morphology in ovariectomized mice treated with oestrogen and progesterone.

Silk threads placed in the uteri of ovariectomized mice increased cell proliferation in all tissues including regions of the uterus remote from the site of insertion. Many of the effects resembled those produced by oestrogens. An intra-uterine device (IUD) increased luminal and glandular mitosis and produced various degrees of luminal epithelial hyperplasia in untreated animals. In progesterone-treated mice bearing IUD's, luminal and stromal mitosis was increased. Epithelial morphology was not affected or luminal mitosis inhibited in oestrogen-treated animals with IUD's, but stromal and glandular mitosis was increased. After combined treatment with progesterone and oestrogen, stromal mitosis was suppressed at the contact site but was increased elsewhere. Both oestrogen and progesterone suppressed the luminal leucocytosis induced by the IUD. Despite this, the IUD prevented complete progestational differentiation of the luminal epithelium and closure of the lumen. The degree to which IUD-induced abnormalities were observed depended on the hormonal status of the animal at the time of sampling.

Changes in the endometrium of mice after the induction of implantation by actinomycin D.

Actinomycin D can induce a small number of implantations in pregnant mice undergoing progestin-induced delayed implantation following ovariectomy. However, the response of the uterus to the blastocyst is considerably retarded compared with the response observed when implantation is precipitated by oestradiol. With the electron microscope the attachment reaction between the trophoblast and uterine epithelium is evident about 48 h after administration of the drug. However, the differentiation of the luminal surface of the epithelial cells in areas of uterus distant from a blastocyst (2nd stage of closure), which normally accompanies implantation, and can be induced by oestradiol in progesterone-treated animals, is not seen. Thus actinomycin D, although allowing implantation to proceed, does not completely mimic the actions oestradiol on the progesterone-treated uterus.

Hormonal control of cell death in the luminal epithelium of the mouse uterus.

An attempt has been made to assess quantitatively the extent of cell death in the uterine epithelium after oestrogen treatment. [3H]Thymidine was injected into ovariectomized mice at an interval after oestrogen treatment when many of the luminal epithelial cells were in the S phase of mitosis. Uptake of [3H]thymidine was confirmed by autoradiography of sections of uterus and scintillation counting of trichloracetic acid-insoluble fraction of whole uterine horns. Radioactivity declined after the cessation of oestrogen treatment but remained high if treatment was continued. The decline appears to be correlated with the cell death previously demonstrated in histological sections of uteri under similar conditions.

Control of leucocyte infiltration into the decidualized mouse uterus.

Ovariectomized mice were treated with oestrogen and progesterone on a schedule to mimic early pregnancy. Decidualization was induced with oil and uteri were examined at various times after the last progesterone injection. The first morphological change detected in the uterus of decidualized mice following withdrawal of progesterone was infiltration of leucocytes into the stroma. This preceded overt tissue breakdown and extravasation of blood cells, and did not occur following withdrawal of progesterone without decidualization. It is suggested either that there is a release of a chemoattractant from decidual cells before any morphological changes are apparent or that the signal for attracting the leucocytes is released at the time of decidual induction, but that their migration is suppressed by progesterone.

Burst fracture of the fifth lumbar vertebra.

Burst fracture of the fifth lumbar vertebra is a rare injury. We report the cases of seven patients who were treated conservatively by immobilization for six to eight weeks in a body-jacket cast that included one lower extremity to the knee. The patients were allowed to walk ten to fourteen days after the injury. A thoracolumbosacral orthosis was worn for an additional three months. No patient had an injury to the sacral root. Two patients had mild lower lumbar motor-root deficits that resolved within one year. All patients had an occasional backache, and two had intermittent radicular-type pain in the distribution of the fifth lumbar or first sacral-nerve root. The degree of compromise of the spinal canal could not be directly related to the degree of neurological deficit; that is, a large compromise of the spinal canal did not necessarily result in a major loss of neurological function. There was no early or late loss of lordosis between the cephalad end-plate of the fourth lumbar vertebra and the cephalad aspect of the sacrum, and there were no signs of progressive collapse of the vertebral body in any patient. In our series, the burst fractures of the fifth lumbar vertebra were stable injuries that caused minimum neurological deficits, and treatment by immobilization in a body-jacket cast was effective.

Timing of the window of uterine sensitivity to decidual stimuli in mice.

The refractory period that follows the period of sensitivity to a decidual stimulus in ovariectomized hormone treated mice was investigated. Medroxyprogesterone acetate provided constant progestin concentrations and silastic implants containing oestradiol maintained constant nidatory oestrogen concentrations. The nidatory stimulus was provided by crushing the uterus with a haemostat or by the intrauterine instillation of arachis oil. The decidual response was assessed by measuring changes in uterine weight or by examining the stroma for the presence of alkaline phosphatase. Sensitivity to the oil was first observed approximately 14 h after the insertion of the oestradiol implant but this sensitivity had waned by 32 h and was absent at 40 h. Crushing the uterus initiated a decidual response in mice treated with progestin alone but if the oestradiol implant was inserted then the uterus was responsive to crushing 24 h after insertion but not at 45 h. The traumatic decidual cell reaction (crushing), although not requiring nidatory oestradiol for its successful initiation, was nevertheless subject to the refractoriness that followed oestradiol sensitivity.

Why do women menstruate? Historical and evolutionary review.

Theories regarding the significance of menstruation from the time of Aristotle to the present are reviewed, followed by a brief description of the evolutionary changes in the uterus. A specific duct for the transport of ova first appears in jawed fishes. Its important role in the evolution of internal fertilisation and the protection and nourishment of the embryo is followed through the vertebrate orders, amphibia, reptiles and mammals. The problems associated with the presence of a gamete or zygote of different genetic make up inside the maternal tract is stressed, and the mechanisms to overcome or modify the maternal inflammation reaction discussed. In egg laying reptiles and birds, the secretion of coverings around the embryo presumably shields the foreignness of the tissue, while in viviparous animals, the secretion of progesterone plays a major role in controlling the inflammatory reaction. In some mammals, for example the mouse, the invasiveness of the trophoblast is such that the blastocyst penetrates inside the wall of the endometrium. The stroma responds under the influence of progesterone, to undergo an implantation/decidual reaction which bears considerable resemblance to an inflammatory/granulation tissue reaction. A similar reaction occurs in women during the luteal phase in anticipation of a very invasive blastocyst. When there is no fertilisation the progesterone drops and the differentiated stromal tissue is shed with bleeding; menstruation.