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Biomedical subjects

R V Short

Publications and source records attributed to R V Short.

At least 19 recordsLinked to original sources
PubMed1978

When a conception fails to become a pregnancy.

Other contributors to this symposium have analysed in great detail the many components that go to make up reproductive success, so it is fitting to conclude with some thoughts about the aetiology of reproductive failure. Firstly, there are occasions when reproduction can be too successful, so that a density-dependent mechanism for inducing early embryonic mortality may be a most valuable protective mechanism. This is particularly true for polytocous species, where it may be necessary to achieve some regulation of litter size by differential embryonic mortality. Even in monotocous species some degree of embryonic mortality may also be advantageous as a way of prolonging the interval between successive births, for if one infant follows too hard upon the heels of another, the normal growth and development of both offspring will be permanently impaired. Embryonic mortality is also likely to be an effective insurance mechanism against the production of genetically defective offspring, because the absence of haploid gene expression will protect the spermatozoon from maternal immunological surveillance systems. With these concepts in mind, it is interesting to look at the nature and extent of embryonic loss in man and animals.

Animals↗
PubMed1977

Acceptability of an oral contraceptive that reduces the frequency of menstruation: the tri-cycle pill regimen.

The frequency of menstruation was reduced to once every three months in 196 women by the continuous administration of the oral contraceptive pill, Minilyn, for 84 days (tri-cycle regimen). No pregnancies occurred. One hundred and sixty-one women (82%) welcomed the reduction in the number of periods with the associated freedom from menstrual and premenstrual symptoms, and many found the tri-cycle regimen easier to follow. Weight gain of more than 2 kg, irregular cycle control, especially in the first three months, breast tenderness, and headaches were the main side effects. Menstrual loss was unchanged or reduced in all but seven women. The doctors and nurses on the clinic staff were less enthusiastic about this regimen than the volunteers themselves.

Adolescent↗
PubMed1977

Changes in breast sensitivity at puberty, during the menstrual cycle, and at parturition.

Sensitivity to pain and touch was measured in the nipple, areola, and cutaneous breast tissue of prepubertal boys and girls, postpubertal men and nuliparous women before and after delivery. Before puberty there were no differences between the sexes, but after puberty the tactile sensitivity of all areas of the women's breast was significantly greater than the men's. Tactil sensitivity of all areas also varied during the menstrual cycle, with maximal sensitivity at midcycle and at menstruation; the mid-cycle peak was absent when the women were taking oral contraceptives. But the most dramatic changes occured within 24 hours of parturition, when there was a great increase in breast sensitivity. This may be the key event for activating the suckling-induced discharge of oxytocin and prolactin and inhibiting ovulation during lactation.

Adult↗
PubMed1977

Absence of hCG-like activity in the blood of women fitted with intra-uterine contraceptive devices.

Blood was obtained at various stages of the menstrual cycle from 201 women fitted with intra-uterine contraceptive devices (IUDs), and plasma levels of hCG were determined by radioimmunoassay. Urine samples were obtained from 117 of these women and tested, before and after sephadex gel filtration, in a haemagglutination inhibition test for pregnancy (Pregnosticon). Plasma hCG was undetectable (less than 25 MLU/ml) in all but one of the 201 women and, in this instance, the hCG-assay appeared to be measuring a midcycle peak of LH, as evidenced by high plasma FSH levels. All unextracted urines gave negative results in the Pregnosticon test but, after extraction, 18 of the 117 urines gave positive reactions, most of these being from women at midcycle or in the luteal phase. We conclude that the IUD does not permit the development of the embryo to a point where it is capable of secreting measurable amounts of hCG. Recent claims to the contrary are probably due to cross-reaction of LH or non-specific interference in the assays used for measuring hCG.

Adolescent↗
PubMed1977

Ovulation in prenatally androgenized ewes.

The ovarian activity of prenatally androgenized ewes was studied by measuring plasma progesterone concentrations in daily samples of peripheral blood, and by examining the ovaries at laparotomy. Ewes that were exposed to testosterone between days 30 and 80, 50 and 100 or 70 and 120 of foetal life by implanting their mothers with 1 g testosterone, failed to show regular overt oestrous cycles, although some of them ovulated, whereas ewes exposed to testosterone between days 90 and 140 of foetal life had normal oestrous cycles. The incidence of ovulatory failure appeared to increase with age in ewes treated between days 50 and 100 or days 70 and 120 of foetal life.

Animals↗
PubMed1976

Lactation--the central control of reproduction.

We are used to thinking of lactation as a consequence of reproduction but we tend to forget that, in many marsupials and placental mammals, lactation serves the equally important function of spacing-out the interval between successive births. In primitive human communities, the duration of the birth interval was all-important for the survival of the young, and lactational amenorrhoea lasting up to two years was nature's most effective form of contraception. Today, particularly in urban areas, lactational amenorrhoea is short, even in those women who still breast-feed their babies, and this has been one of the major factors responsible for the recent rapid growth of the human population. There is still much speculation about the way in which lactation and nutritional status may act in concert to suppress reproductive activity. Afferent stimuli from the nipple are an essential component of the reflex and it is possible that, in addition to a generalized central inhibition, they may initiate secretory surges of prolactin that have a direct inhibitory action on the ovary itself. The evidence for these various mechanisms of action is discussed.

Amenorrhea↗
PubMed1976

Effects of time zone changes on performance and physiology of airline personnel.

This study is the second of a series of experiments describing the effects of time zone changes on the performance and menstrual cycle changes in a group of 16 female airline personnel. Four groups of four subjects each spent 4 d in the isolation unit of the University of Manchester. One group acted as control; the other three groups were subjected to two 8-h retardations in time, representing Westerly flight. All groups were required to complete an identical battery of workload tasks. In addition, the effects of a therapeutic preparation (mepiprazole hydochloride) were studied in a double-blind experiment. The results of the study confirmed previous experiments in that there was impaired performance in individuals subjected to time zone changes when work was carried out in local time, but the results were difficult to compare with those obtained in Easterly shifts. The therapeutic agent appeared to have little influence on the effect of time zone changes upon subjects, although they reported favourably on its use.

Adult↗
PubMed1976

Effects of testosterone implants in pregnant ewes on their female offspring.

Pregnant ewes were implanted with 1 g testosterone between days 30-80, 50-100, 70-120 or 90-140 of gestation. Ewes treated between days 30-80 and 50-100 showed increased aggressive behaviour and clitoral enlargement, whereas this was not seen in the day 70-120 or 90-140 groups. Although the implants released similar amounts of testosterone at all stages of gestation, plasma testosterone concentrations were lower in the day 70-120 and 90-140 groups. The increased testosterone clearance in late gestation could be a result of increased placental aromatization. Masculinization of the genital tubercle was complete in female lambs in the day 30-80 group, partial in the day 50-100 and 70-120 groups, and absent in the day 90-140 group. These results therefore suggest that the 'critical period' for masculinization of the external genitalia is between days 40 and 50 of foetal life. In contrast to this anatomical masculinization, one aspect of behavioural masculinization had a later critical period, since female lambs of 30-80, 50-100 and 70-120 day groups adopted male-like urination postures, whereas the day 90-140 offspring showed the normal female pattern.

Abnormalities, Drug-Induced↗