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R. V. SHORT
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R. V. SHORT
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Summary.

  1. The following steroids were estimated in five samples of normal bovine follicular fluid, and in twenty-four samples of cyst fluid from cows with cystic ovaries: progesterone, 17α-hydroxyprogesterone, androstenedione, oestrone and oestradiol-17β. 20β-Hydroxypregn-4-en-3-one was also found in two samples of cyst fluid. No testosterone could be detected in any of the samples assayed.

  2. Oestradiol-17β was the major steroid present in all five samples of follicular fluid. The concentration of oestradiol-17β was significantly lower (P<0·01) in the cyst fluid.

  3. Many of the cyst fluid samples contained large amounts of progesterone, but little or no detectable 17α-hydroxyprogesterone, androstenedione, oestrone or oestradiol-17β. Histological examination of the cyst wall in a number of these cases showed atretic or luteinization changes. In one case where luteinization had occurred, 20β-hydroxypregn-4-en-3-one was also present in the cyst fluid.

  4. There was no obvious correlation between the behavioural characteristics of the 'cystic cows' and the nature or amount of the steroids present in the cyst fluid. Thus the steroid concentrations in nine 'cystic cows' with normal oestrous cycles did not differ significantly (P>0·05) from the concentrations in seven nymphomaniac cows.

  5. The absolute concentrations and relative amounts of the various steroids differed greatly, both between animals and within the same animal. It is therefore concluded that the cyst itself is not the primary defect in cystic ovarian disease. Both histologically and endocrinologically the cyst appears to be a degenerative structure. In the normal follicle, follicular growth and endocrine activity seem to accompany one another; in the cyst, on the other hand, follicular growth continues whilst endocrine activity is waning.

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J. HANKS
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R. V. SHORT
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Summary.

The uterus and ovaries of 617 elephants shot in Zambia were examined. Corpora lutea seem to be necessary for the development of the endometrial glands, and before conception can occur, a certain critical mass of luteal tissue has to be achieved by accumulating crops of cl from successive oestrous cycles. The elephant can be either monovular or polyovular, and ovulation is spontaneous. New ovulations do not occur during pregnancy, and the presence of an embryo prolongs the life of the cl. There is great variability in luteal size, small cl being commonest in non-pregnant animals and large ones in pregnant animals. The cl do not enlarge during gestation, and some of the smaller ones may regress. The number of cl in pregnant elephants varied with the age of the cow, the younger elephants having a significantly higher number. Larger cl ( > 20 mm in diameter) predominated in older animals. Very little progesterone appears to be secreted by the corpora lutea, and the hormone could not be detected in the peripheral blood during gestation. If progesterone is necessary for pregnancy, the elephant must be extremely sensitive to it, and may be forced to accumulate a large mass of relatively inactive cl before sufficient hormone is available to enable the animal to become pregnant.

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M. J. TAYLOR
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R. V. SHORT
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The ovaries of fetal and neonatal mules and hinnies were examined in order to study the development of the germ cells. Although migration of these cells into the fetal gonad and their subsequent mitotic divisions were apparently normal, most oogonia died in early neonatal life as they entered meiosis. This was thought to be due to the inability of the paternal and maternal sets of chromosomes to form homologous pairs. However, a few germ cells were able to enter meiosis and become oocytes, and possible mechanisms for this are discussed. These few surviving oocytes probably give rise to the occasional Graafian follicles found in the ovaries of adult mules, but it seems highly unlikely that the ova would ever be capable of normal fertilization and development.

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Y. Gao
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R. V. Short
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The intermittent use of an antigestagen could prove to be a very effective way of controlling the fertility of rats and mice in the wild. This concept was tested by giving paraffin wax blocks containing cereal grains and the antigestagen Mifepristone, RU486 (150 mg kg−1 block) to male and female laboratory rats and mice in a series of free-choice feeding experiments. There was no significant difference in the consumption of blocks with or without RU486, showing that it was completely palatable to rats and mice, and no aversion developed following refeeding. The average consumption of RU486 by rats was 11 mg kg−1 day−1; mice consumed 37 mg kg−1 day−1. All the females showed persistent oestrous vaginal smears throughout the treatment. When male and female rats and mice were given continuous access to treated paraffin blocks for 30 days, no conceptions occurred. At the end of this time, there was a significant increase in ovarian weight in the treated rats and mice, but no difference in testicular weight. Treated blocks were given to rats for 3 days every 21 days for a total of 115 days. Four dead litters were produced following the first antigestagen treatment on day 21, but no more litters were produced and no treated rats were pregnant when autopsied on day 115. Mice were initially treated for 3 days every 21 days, but some animals continued to produce live young on this schedule. The treatment period was therefore reduced to 3 days every 18 days and no more litters were produced and none of the treated females was pregnant at autopsy. The antigestagen RU486 shows considerable promise as a chemosterilant for the control of fertility in female rats and mice. Intermittent administration every 18 days (mice) or 21 days (rats) in free-choice feeding trials completely inhibited reproduction.

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Y. Gao
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R. V. Short
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Paraffin blocks containing either no steroid, 150 mg RU486 kg−1, 500 mg methyl testosterone kg−1 or 1500 mg methyl testosterone kg−1 were fed to wild mice (Mus musculus in addition to the standard laboratory diet in four large (3 m × 3 m) outdoor pens for six months over the summer. The RU486 bait was provided for only 3 days every 18 or 21 days, whereas the methyl testosterone bait was available continuously. From a foundation stock of 20 mice (nine male, eleven female) in each pen, the population had increased to 253 (control), 72 (RU486), 249 (low methyl testosterone concentration) and 103 (high methyl testosterone concentration) at the end of six months, when 17%, 4%, 32% and 13% of the mature females were pregnant in the respective treatment groups. There was little evidence of an increase in the incidence of injuries in the androgen-treated animals. Daily estimation of water consumption in the pens proved to be a good non-invasive way of monitoring population growth during the course of the experiment. Intermittent feeding with a low concentration of RU486 appeared to be much more successful in inhibiting reproduction than continuous feeding with a high concentration of methyl testosterone, and it therefore offers a new method for controlling feral mouse populations.

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R. V. SHORT
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K. YOSHINAGA
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Summary.

The Walker carcinosarcoma was inoculated into the uterine lumen of the following six groups of rats : (1) Normal oestrous cycles, (2) ovariectomized, (3) ovariectomized + 2 mg progesterone daily, (4) ovariectomized + 2 mg progesterone + 2 μg oestradiol-17β daily, (5) ovariectomized + 2 mg progesterone daily + a single injection of 0·2 μg oestradiol-17β on the day of tumour transplantation, and (6) pseudopregnant, Day 5.

Whilst the tumour grew well outside the uterus in all groups, tumour tissue only invaded the uterine wall in Groups 5 and 6. Growth was most marked in the pseudopregnant animals, where the tumour was actively invading the anti-mesometrial decidua. In Groups 3 and 5, the uterine lumen was full of extravasated blood and polymorphonuclear leucocytes, whereas in Groups 1, 2 and 4 the uterus appeared normal, with no signs of any tissue reaction.

It is concluded that the tumour behaves very like the blastocyst; its ability to survive within the uterus is hormone dependent, whereas it can develop outside the uterus irrespective of the hormonal environment. The mechanisms by which a hostile endometrium can destroy the tumour are not known.

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R. V. SHORT
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I. O. BUSS
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Summary.

Progesterone determinations were carried out on eleven corpora lutea obtained from six African elephants in various stages of the oestrous cycle and pregnancy. In no case was it possible to detect any progesterone whatsoever, even when using an extremely sensitive gas chromatographic technique, coupled with an internal isotope standard of 4C14-progesterone to correct for extraction losses.

The histological appearance of many of the corpora lutea in these elephants suggested that they might be degenerate structures. It is therefore postulated that the functional life of the elephant's corpus luteum may be relatively short, even though it persists structurally for long periods of time. However, we cannot entirely exclude the possibility that the elephant's corpus luteum never secretes progesterone at all.

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L. W. HOLM
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R. V. SHORT
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Summary.

Progesterone was determined in the peripheral blood of five cows exhibiting a prolonged gestation period of up to 92 days beyond the normal duration of pregnancy (285 days). The blood progesterone levels during the period of prolonged gestation were similar to those found in normal cows during mid-pregnancy; however, there was no sign of a fall in the progesterone level just prior to the expected date of delivery, which is so characteristic of normal cows. The significance of these findings is discussed in relation to the mechanisms that might initiate parturition in the cow.

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Y. Gao
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R. V. Short
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Three synthetic steroids were evaluated as potential chemosterilants for rodent control. Ethinyl oestradiol, methyl testosterone or Org 5933, a synthetic gestagen, were incorporated into paraffin blocks containing cereal grains and offered to laboratory rats and mice in addition to their standard laboratory diet. Ethinyl oestradiol (50 mg kg−1 paraffin block) was highly unpalatable to female rats, and the amount of steroid ingested was not sufficient to interfere with their oestrous cycles or inhibit ovulation. Methyl testosterone (5000 mg kg−1 paraffin block), although not as palatable as untreated blocks, was effective in inducing almost immediate infertility in female rats and mice at an ingested dose of about 35 μg g−1 body weight day−1. This infertility persisted throughout the duration of treatment, and lasted for several weeks after the cessation of treatment. Male rats became infertile after 3 months of treatment owing to suppression of spermatogenesis. Female rats developed a specific aversion to methyl testosterone when they were pregnant or lactating; it was therefore not possible to masculinize the brains of their female offspring. In mice, the androgen treatment induced high levels of aggression in the females so that they fought with males and with one another. One female died of her wounds. Org 5933 (4 mg kg−1 paraffin block) was highly palatable to female rats and mice, and at doses of about 420 ng g−1 body weight day−1 was effective in inhibiting ovulation in rats within 3 to 4 days after the start of treatment. This infertility persisted throughout the duration of treatment, and the animals conceived within 5 days of cessation of treatment. A dose of about 930 ng g−1 body weight day−1 was not completely effective in inhibiting ovulation in mice, but females that became pregnant during treatment gave birth to dead young. When the gestagen was given to female rats and mice in the last few days of pregnancy, the duration of gestation was significantly prolonged, and most young were born dead; some of the females also died in labour. The gestagen did not appear to inhibit lactogenesis, since the few animals that gave birth to live young reared them normally for the first 5 days of life. These results show that either methyl testosterone or Org 5933 in paraffin blocks could perhaps be used as a chemosterilant for the control of rat and mouse populations. The optimal strategy would be to use the chemosterilant when the population density of rodents was lowest, for example at the end of the winter, or following a poisoning campaign with conventional rodenticides, thereby preventing the survivors from reproducing and spreading genetic resistance to the poison.

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