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R. G. EDWARDS

Summary.

Normal serum from male and female rabbits aged 1 o weeks or more possessed complement-fixing activity when mixed with rabbit semen, washed or epididymal spermatozoa, and the non-dialysable fraction of seminal plasma obtained from semen, but not with seminal plasma obtained from a vasectomized buck. Sera from younger animals did not have this activity. The active fraction in seminal plasma originated in the spermatozoa. Absorption with epididymal spermatozoa reduced the activity in two sera considerably, and slightly in a third. Other tests, i.e. passive cutaneous anaphylaxis (PCA) in the guinea-pig, precipitation tests, and agglutination or immobilization of spermatozoa in vitro, did not indicate the presence of antibody-like activity in normal sera.

Five rabbits were injected twice with rabbit semen in adjuvant. The serum of one, and possibly another, of these rabbits possessed complement-fixing activity against seminal plasma from a vasectomized buck, and also showed a slight rise in titre against epididymal spermatozoa after the injections. Positive PCA against spermatozoa and seminal plasma could not be demonstrated in sera from any of the five rabbits, although precipitins against seminal plasma, and agglutinating and immobilizing antibodies against epididymal and ejaculated spermatozoa were found in sera from two of the rabbits. Agglutination and immobilization of spermatozoa were probably caused by antibodies against seminal plasma.

The presence of natural complement-fixing activity in serum against spermatozoa, and the failure to induce significant amounts of antibodies against spermatozoa as judged by the absence of PCA and precipitins, or by a definite rise in complement-fixing titre, is discussed in relation to the characteristics of the immunological tests employed. The results are also briefly discussed in relation to the clonal selection theory of antibody formation, and to other natural antibody systems.

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R. G. EDWARDS

Summary.

The antigenicity of whole rabbit semen or of bull semen in egg yolk citrate and the distribution of antibodies in the serum and in the reproductive tract were studied following either two intramuscular injections with adjuvant or several intravaginal depositions (artificial inseminations) into female rabbits.

Repeated artificial insemination of non-pregnant does with bull semen in egg yolk citrate induced only serum antibodies against egg yolk in two out of five rabbits. Repeated insemination of pregnant does led to serum antibodies against egg yolk, bull seminal plasma, and bull spermatozoa in three out of four rabbits, and to vaginal antibodies against egg yolk and bull seminal plasma in two of these rabbits. The cause of the increased response during pregnancy is not known. After the intramuscular injections of bull semen in egg yolk citrate and adjuvant, antibodies against egg yolk, bull seminal plasma, and bull spermatozoa were found in the serum and throughout the tract.

Repeated insemination of pregnant and non-pregnant rabbits with rabbit semen failed to induce any antibodies. Intramuscular injections with adjuvant into five rabbits led to the presence of sperm agglutinins in the sera of all five rabbits, and to sperm-immobilizing antibodies, a precipitin against seminal plasma, and complement-fixing antibodies against seminal plasma from a vasectomized buck in two of the rabbits. No antibodies could be detected in the tract. Experiments with homologous semen were complicated by the presence of natural complement-fixing activity in rabbit serum against rabbit spermatozoa, and by a heat-stable factor in the uterus causing agglutination of rabbit spermatozoa.

The results are discussed in relation to (a) the non-antigenicity of homologous spermatozoa in rabbits, as compared with the antigenicity of homologous spermatozoa in other species, and (b) the passage of heterologous antigens or of antibodies against these antigens between the serum and the genital tract. It is concluded that intramuscular injection of antigen induces systemic antibodies which then enter the tract, whereas artificial insemination leads to the formation of local tract antibodies and to the passage of antigen into the systemic circulation.

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R. G. EDWARDS

The following experiment was performed to study cleavage in one- and two-celled rabbit eggs after removal of the zona pellucida. Adult rabbits were killed between 18 and 30 hr after natural mating. Under sterile conditions, the one- and two-celled eggs were flushed from the Fallopian tubes with Hanks' salt solution buffered with tris-citrate buffer. They were washed twice, then transferred into a 1% solution of Pancreatin (L. Light & Co) or the protease Pronase (Calbiochem) (Mintz, 1962) for between 5 and 30 min to remove the albumen coat and the zona pellucida. Pronase was more efficient than Pancreatin especially in digesting the albumen layer, although it was seldom that either enzyme removed the zona completely. The remaining part of the zona pellucida was removed by drawing the eggs in and out of a fine Pasteur pipette until the zona split and the egg could be drawn gently out. Examples
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R. G. EDWARDS

Follicular fluid is composed partly of secretions from the follicle, and partly of exudates from plasma. Its composition reflects changes in the secretory processes of the granulosa layer and theca interna, and alterations in the components of plasma due to physiological or pathological processes. The presence of follicular fluid in so many species testifies to its potential importance in ovarian physiology, including steroidogenesis, growth of the follicle and ovulation, and maturation of the oocyte and its transport to the oviduct. The fluid can be collected easily, especially as the follicle enlarges, and there has been prolonged interest in its composition and functions.

The source of the fluid in Graafian follicles was discussed widely in early debates, some authorities maintaining that it was produced within the follicle, whereas others believed it to be a transudate of plasma. Such a debate is now spurious, for various components of the fluid almost certainly

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S. Edwards and G. R. Foxcroft

Summary. The timing and dosage of oestradiol benzoate injected after weaning was critical with respect to the pattern of behavioural oestrus and the ovarian stimulation achieved; treatment on the day of weaning (Day 0) and Day 1 with 60 μg oestradiol benzoate/kg body wt produced poor ovulatory responses and abnormal oestrous behaviour. Treatment on Day 2 with 30 μg oestradiol benzoate/kg resulted in consistent oestrus and ovulatory responses although the ovulation rates (10·6 ± 1·1 in 3-week and 12·2 ± 1·7 in 5-week weaned sows) were below those expected in fertile untreated sows weaned at these times. The timing of the preovulatory LH surge (53·6 ± 2 h after oestradiol benzoate) was closely synchronized in all sows and a similar synchronous rise in plasma progesterone concentrations 100 ± 4 h after oestradiol benzoate suggests a similar synchrony of ovulation. The magnitude of the LH and FSH responses to oestradiol benzoate were similar to those that occur in untreated sows and similar differences also existed in gonadotrophin secretion related to the length of lactation.

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S. Edwards and G. R. Foxcroft

Summary. Plasma concentrations of LH, FSH, prolactin, oestradiol-17β and progesterone were determined in 18 multiparous sows at 4-h intervals for 15–18 days around weaning at 3 or 5 weeks post partum. Sampling at 10-min intervals for 6 h occurred every 2 days throughout the same period. Shortening lactation significantly reduced the preovulatory LH surge and altered the pattern of FSH release. However, there was no significant effect on ovulation rate or interval from weaning to oestrus between groups. Weaning was consistently associated with a significant rise in basal LH concentrations whilst FSH secretion remained unaffected. Lactation length did not appear to affect the characteristics of episodic LH secretion before weaning, nor were any consistent changes in LH secretion apparent until the preovulatory rise in LH. Plasma prolactin values declined rapidly at weaning and remained low thereafter. These results indicate that the 'trigger' controlling the return to cyclic ovarian activity after weaning in the pig is complex, but it is suggested that lactational anoestrus and anovulation result primarily from a lack of LH stimulation to the ovary.

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EVERETT D. WILSON and R. G. EDWARDS

Summary.

The length of gestation and the duration of parturition were similar in mice that had mated during natural oestrus and in those with large numbers of full-term foetuses following superovulation. After superovulation many offspring die at parturition, but by giving every possible assistance to the offspring at birth, mean litter size was raised from 6·8 to 10·7 living young (controls that mated during natural oestrus gave birth to 6·2 living young). The mortality rate after birth was high in large litters, and offspring weighing less than 0·7 g at birth survived less than 24 hr. When one-half of the large litters which included offspring weighing 0·7 g or more were fostered on to control females, mortality was reduced to control levels and the offspring grew at the same rate whether a superovulated or control mother was suckling. The overall fecundity of superovulated mice was lower than controls because (a) 11 out of 137 of them died, (b) more than one-half of them failed to implant any embryos.

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R. G. EDWARDS, L. C. FERGUSON and R. R. A. COOMBS

Summary.

Antigens on the membrane of human spermatozoa have been investigated using the mixed agglutination and mixed antiglobulin reactions. The spermatozoal membrane was shown to possess 'speciesspecific' antigens in common with red cells which probably correspond to antigens on other tissue cells of the body.

The A and B blood group iso-antigens have been shown on the spermatozoa of secretors but not on the spermatozoa of non-secretors. The presence of the iso-antigens M, N and Tja was established; however, the sex-linked antigen Xga could not be shown on the spermatozoa.

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J. SWANSON BECK, R. G. EDWARDS and M. R. YOUNG

Summary.

The immune fluorescence technique has been used to study reactions between serum and spermatozoa from several species of mammals.

Normal serum from adult guinea-pigs, rabbits, mice and men stained the acrosomes of homologous and heterologous spermatozoa, staining being most intense with rabbit and guinea-pig spermatozoa. Staining was weak with sera from rabbits up to 3 weeks of age, and could be removed by heating or Seitz-filtering the sera. Sera from immature guinea-pigs likewise lost most of their staining capacity on heating. Differences in the intensity of staining appeared to be determined chiefly by the species of spermatozoa rather than by the species of serum.

Serum from guinea-pigs immunized with homologous spermatozoa stained the surface of homologous sperm tails, in addition to the acrosomal staining. A slight cross-reaction probably occurred between this serum and the tails of hamster spermatozoa, but not with spermatozoa from other species. Immunization of rabbits with homologous spermatozoa failed to produce any tail staining.

The two reactions between serum and spermatozoa, i.e. with acrosomes and tails, are discussed in relation to the isoantigenicity of spermatozoa, and to induced aspermatogenesis following the injection of testis or spermatozoa and adjuvant.

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D. E. Walters, R. G. Edwards and M. L. Meistrich

Summary. All the available data relating to pregnancy and multiple implantations from Bourn Hall Clinic are used to assess the accuracy of two statistical models of implantation. The simple binomial model was found to be incapable of describing both the pregnancy rates and the incidence of multiple implantations, whereas a two-parameter model, incorporating both patient and embryo variability, provided a good fit to the data. The estimates obtained for the two parameters in the second model suggested that 36% of the embryos could implant, and that 43% of patients were capable of sustaining implantation. The Maximum Likelihood method of constructing 95% confidence limits on the estimates of the parameter values is demonstrated.