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R. V. SHORT

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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Y. Gao and R. V. Short

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 and T. MANN

Summary.

We have studied the antlers and male reproductive organs of thirteen roebucks, shot at approximately monthly intervals throughout the year. The roebuck is a seasonally breeding mammal that is in rut from mid-July to mid-August. Antlers `in velvet' begin to develop in January, and the velvet is shed in March or April. The animal then remains in `hard horn' until November or December, when the antlers are cast.

The testes are at their most inactive state in January, when there is no spermatogenic activity and a very low content of testosterone. By mid-February, the testicular testosterone content has risen considerably, and primary spermatocytes are to be seen in the enlarging seminiferous tubules. The testosterone content of the testis remains high until the beginning of the rut, but falls precipitously towards the end. Spermatogenesis is not finally completed until April or May, and, although it continues for several weeks after the end of the rut, there is a highly significant decline in testis tubular diameter that coincides with the fall in testosterone content. Thus spermatogenesis and androgenesis are closely related at the beginning and end of the sexual cycle, suggesting that fsh and lh secretion by the pituitary gland normally go hand-in-hand.

The seminal vesicles secrete fructose, sorbitol, inositol and citric acid. Although there is a significant correlation between testicular testosterone and vesicular fructose and citric acid, the correlation coefficients are not high. This is probably because the seminal vesicles do not respond until some weeks after the onset of testosterone production in the spring, and their secretion declines less rapidly than testicular testosterone after the end of the rut.

These endocrine changes are in accord with the seasonal changes in antler growth, which are known to be under endocrine control. Shedding of the velvet occurs soon after the testicular testosterone levels have risen in the spring, and casting of the antlers in late autumn coincides with extremely low testicular testosterone levels.

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S. P. COUDERT and R. V. SHORT

Summary.

Inoculation of Corynebacterium pyogenes or Vibrio foetus into the uterine lumen of ewes on the 10th day of the oestrous cycle resulted in a prolongation in the life of the corpus luteum in six out of eleven animals. In three animals, the corpora were still fully functional on Day 21 of the cycle, as judged by their progesterone concentration, as well as the progesterone concentration in ovarian vein blood.

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Y. Gao and R. V. Short

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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P. D. ROSSDALE and R. V. SHORT

The length of pregnancy in the mare is known to be influenced both by the genotype of the foetus and the environment of the mother. The heritability of gestation length is 36% (Rollins & Howell, 1951), and male foetuses are carried longer than females (Uppenborn, 1933; Mauch, 1937). Mares mated between December and May have pregnancies that are on average 10 days longer than those of mares mated at other times of the year. This seasonal influence alone accounts for 44% of the observed variance in gestation length, and it appears to to be independent of nutritional factors (Howell & Rollins, 1951).

In addition to these genetical and environmental factors that control the day of parturition, there appear to be other environmental factors that can even influence the hour of birth.

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R. V. SHORT and K. YOSHINAGA

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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Y. Gao and R. V. Short

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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M. J. TAYLOR and R. V. SHORT

Summary.

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.