No description available.

No description available.

No description available.

The involvement of a steroid in the feedback systems controlling the hypothalamic-adenohypophyseal axis may be inferred if a reduction in the biologically active fraction of the steroid through antibody binding results in an alteration in the secretion of gonadotrophins. The present studies examined the effects of active immunization against bovine serum albumin (BSA) conjugates of four steroids known to be secreted by the sheep ovary (oestradiol-17p, oestrone, androstenedione and testosterone) on the release of LH and FSB in the non-pregnant ewe. Groups of five adult ewes were actively immunized against 17p-oestradiol6-(0-carboxymethyl)oxime-BSA (E2 6-BSA), oestrone-6-(O-carboxymethyl)oxime-BSA (E1-6-BSA), testosterone-3-(O-carboxymethyl)oxime-BSA (T-3-BSA), androstenedione-114-hemisuccinyl-BSA (A-11-BSA) and BSA (controls). The concentrations of LH and FSH were measured in samples of jugular venous blood taken from all animals during anoestrus and during the breeding season. The ewes were laparotomized during the breeding season and samples of jugulat venous and ovarian venous blood obtained for subsequent steroid analysis. The macroscopic appearance of the ovaries was noted and the ovaries removed. Ovine LH and FSB and oestradiol-17p(oestradiol), oestrone, androstenedione, testosterone and progesterone were all measured by specific radioimmunoassays. The binding of tritiated steroids by plasma was determined after the removal of unbound steroid by dextran-charcoal absorption and after equilibrium dialysis. The presence of elevated LH levels together with the absence of behavioural oestrus and the inhibition of ovulation in four of the five oestradiol-immunized ewes served to confirm the widely accepted concept of action of oestradiol on LH secretion in the ewe. Furthermore, multiple ovarian follicular development was evident in the four anovulatory oestradiol immunized ewes and reflected the elevated circulating levels of LH. A marked similarity between the oestradiol-immunized animals and the ewes immunized against T-3-BSA was apparent in terms of an elevated plasma level of LH, the absence of behavioural oestrus and the inhibition of ovulation accompanied by multiple follicular development. These findings coupled with the presence of significant oestradiol antibody titres and the failure of exogenous oestradiol to alter LH secretion during anoestrus in the testosterone-immunized animals led to the conclusion that immunization against T-3-BSA produced a non-specific reduction in the level of biologically active oestradiol. Active immunization against E1-6-BSA produced plasma levels of LH greater than those found in ovariectomized-hysterectomized animals. A further anomalous finding in the present study was the absence of follicular stimulation in the oestrone-immunized ewes in response to the elevated circulating levels of gonadotrophins. The effects of active immunization against E1-6-BSA in the ewe could not be satisfactorily explained at the present time. Active immunization against -A-11-BSA produced an increased frequency of spontaneous discharges of LH during anoestrus and an elevation in the plasma level of LH during the luteal phase of the oestrous cycle. Furthermore, the positive feedback action of oestradiol on LH secretion during anoestrus was delayed or absent in those ewes with high androstenedione antibody titres. Since the plasma binding of oestradiol was unaltered and oestrous cycles of normal length occurred in the androstenedione-immunized ewes, it is postulated that androstenedione, or its extra-ovarian metabolites, could modulate the feedback actions of oestradiol on LH secretion in the ewe. Exogenous oestradiol exerts a dual action on the release of FSH in an oestrou d and ovariectomized-hysterectomized ewes in a manner similar to the negative and positive feedback actions of this steroid on LH secretion. A significant elevation in the plasma concentration of FSH was observed in the two oestradiol immunized ewes with the highest titres of oestradiol antibodies. It is suggested that in these animals, the level of biologically active oestradiol was sufficiently reduced to lift the inhibitory control of FSH secretion. The presence of normal plasma FSH levels in the three remaining oestradiol-immunized animals suggests that incomplete neutralization of circulating oestradiol had left sufficient biologically active oestradiol available to exert an inhibitory action on FSH secretion. In contrast, a reduction in the levels of biologically active androstenedione and testosterone in the ewes immunized against A-11-BSA and T-3-BSA failed to produce an elevation in the plasma level of FSH. In fact, a significant reduction in the plasma concentration of FSH was present in the androstenedione immunized animals. It is tentatively suggested that androgens may enhance the release of FSH by a direct action on the anterior pituitary. In the light of recent evidence suggesting that FSH may enhance the aromatization of androgens to oestrogens by the ovary, it is postulated that the increased secretion of androgens by the ovary in response to LH may enhance the release of FSH. The elevated level of FSH would in turn lead to increased secretion of oestradiol thereby resulting in the suppression of LH and FSH secretion. The problems associated with the evaluation of the antibody specificity and the degree to which the biological actions of steroids are neutralized in the actively immunized animal emphasize the need for caution in the extrapolation of the findings described in the present studies to physiological events in the intact animal. The proposed action of androgens on the release of FSH awaits further examination.

Factors affecting the composition of plasma, amniotic fluid, allantoic fluid, fetal urine and fetal ruminal and abomasal fluid were studied. Effects of laboratory conditions and experimental procedures on plasma composition were examined in goats and sheep. It took animals 1-2 weeks to adapt to the laboratory and 3-6 weeks of handling to adjust to prolonged procedures such as repeated venepuncture. Surgical insertion of uterine catheters was associated with changes in feed intake and plasma composition which were present after operation for up to seven days in sheep and 12 days in goats. Gestational changes in fetal fluid composition were examined in goats. Amniotic fluid composition was similar to that in sheep but differences in allantoic fluid composition were observed. It was not possible to say whether these differences were related to species differences in hormone production. during pregnancy because exogenous progesterone was given in an attempt to reduce the high incidence of postoperative abortion encountered in goats. Gestational changes in the composition of ruminal and abomasal fluid were studied in sheep. Values for sodium and potassium concentrations and osmolality of the amniotic, ruminal and abomasal fluids suggested that amniotic fluid was modified during its passage between the amniotic sac and the rumen. Effects of fetal adrenocorticotrophin and corticosterone infusion on the composition of allantoic fluid and fetal urine were studied in sheep. Results were consistent with an hypothesis that fetal corticosteroids act on ion pumps in the chorioallantois and fetal kidneys to alter the sodium and potassium concentrations of allantoic fluid and fetal urine. Changes in blood composition during the first 12 hours of life were observed in lambs and kids using a non-surgical method of catheterising the aortas and venae cava. Marked changes in composition occurred as breathing was established and after sucking. Effects of hypothermia and haemorrhage on blood composition were also reported. Finally, the 'chronic' approach to fetal physiology was critically evaluated. In this work the term 'chronic' has been used to describe the continuous study of conscious, catheterised animals.

Streptococcus uberis is a common cause of bovine mastitis and the lipoprotein MtuA has been shown to be essential for growth in milk and virulence. The enzymes responsible for processing lipoproteins in other Gram positive bacteria are lipoprotein diacylglyceryl transferase (Lgt) which acts to anchor lipoproteins to the membrane and lipoprotein signal peptidase (Lsp) which cleaves the signal peptide. S. uberis mutants containing lesions in lgt and lsp uncovered several novel phenotypes. A number of additional proteins were shown to be present in extracellular fractions prepared from lgt- and lgt-/lsp- mutants when compared to the equivalent fraction prepared from wild type bacteria. Atypical processing of MtuA and other lipoproteins within the signal peptide was shown to occur, indicating the presence of an activity capable of shaving such proteins from the membrane in the absence of Lgt and Lsp activity. MtuA was shown to be released into the extracellular space by Wetern blot; the size closely resembled that of wild type protein in both the lgt- and lgt-/lsp- mutants. A metallopeptidase that can be inhibited by phosphoramidon and metal ion chelating agents may be responsible for the activity that results in these proteins being alternatively processed. MtuA in the lsp- mutant had a molecular weight that corresponded to full length MtuA and remained localised in the membrane as seen in the wild type. During late log phase a second form of MtuA with a lower molecular weight was detected. A mutant containing insertions in both lsp and the gene encoding the S. uberis homologue to the Enterococcus faecalis was studied. Enhanced expression of pheromone (eep) suggested that this metallopeptidase was also able to cleave the signal peptide of MtuA.

No description available.

Trypanosomiasis, whether it affects an or domestic animals, continues to be one of the post baffling problems which has confronted medical and veterinary parasitologists. Surra is the most important of all the animal trypanososiases since it, has extremely wide geographical distribution and affects, a wide variety of mammals. The causative organism T : noaoma (Trypenozoon) evens i (Tev nsi) was the first trypanosome to have been recorded from a mammal, but many fundamental aspects of the parasite such as morphology, taxonomy and phylogeny are not parlectly understood. Hitherto, a cycle of development has not been demonstrated in an invert ate vector mnd the parasite is believed to be transmitted non-cyclically. Only a few attempts have been made to culture the parasite in bloodagar medium. Comparatively little work has been carried out on the immunology of T. evansi. Certain Immunological tests, e.g., indirect haemagglutination, agglutination, precipitation and fluorescent antibody tests have been demonstrated in experimental T. evansi infections, but an Important immunological aspect, antigenic variation, has not yet been investigated in this species. The present study is concerned with the establishment of antigenic variation of T. evansi in the mouse host and subsequent comparison of the antigenic types of the first natural relapse populations. The findings on antigenic variation in to evansi have been compared with similar studies in other species of the subgenus Trypanozoon. Furthermore, the importance of the 'recurrent antigenic type', which was observed In these fnvestigations, has been evaluated with respect to the immunlogical classification of salivariaa trypanosoms. Pleomorphisa was experimentally induced in an old monomorphic laboratory strain of T. evansi and attempts were made to culture both monomorphic and experimentally developed pleomorphic strains. Subsequently, the transmission of monomorphic and experimentally developed plaomorphic strains of T. evansi employing Glossina moraitans, Stomoxys calcitrans and Ornithodoros moubata was investigated. In view of the similarity between pleomorphic strains of T. evansi and those of trypanosoma (Trypanosoon) brucei, the systematic position of T. evansi has been discussed. The current concept on the phylogeny of T. evansi is critically reviewed and a different opinion on the subject is presented. During these studies the effect of environmental temperature on T. evansi infection was also studied and clone populations were set up to ctaractariss 3 strains of T. evansi. The thesis embodies observations on each of these aspects and the relevant literature, together with the present state of knowledge concerning T. evansi , has been reviewed.

No description available.

No description available.