PubMed Health⌕ Search

Biomedical subjects

R Webb

Publications and source records attributed to R Webb.

At least 181 records · Page 10Linked to original sources
PubMed1986

Endocrine differences in rams after genetic selection for testis size.

Testis diameter and body weight were recorded from 6 to 76 weeks of age in ram lambs from two established lines selected for high (H) and low (L) testis size. While testis growth was greater in the H line up to 14 weeks of age (P less than 0.001), body weight was significantly lower, with the L line rams being 10 kg heavier by 76 weeks. There were no differences in plasma LH up to 20 weeks of age, but FSH concentrations were significantly lower at 14 and 20 weeks in the H line. Testosterone concentrations were not significantly higher in the H line from 6 to 20 weeks. In lambs castrated at birth, significantly higher FSH values were recorded from 6 to 20 weeks of age in the H line (P less than 0.001) whereas there was no difference in LH concentration at 6 and 10 weeks of age between the lines. At 14 and 20 weeks, however, the concentrations of LH were greater in the H than L line lambs (P less than 0.05). After hemicastration at 6 weeks of age, the rate of growth of the remaining testis in the L line lambs was significantly faster than in entire lambs of that line from 10 to 20 weeks (P less than 0.05 at 10 weeks to P less than 0.001 at 20 weeks). There was no difference in the rate of testis growth between the the entire and hemicastrated lambs from the H line from 6 to 12 weeks of age. It can be concluded that there is an underlying genetic difference in pituitary gland and/or hypothalamic activity in ram lambs from the two selected lines.

Animals↗
PubMed1986

A combined radioimmunoassay and immunocytochemical study of ovarian oxytocin production during the periovulatory period in the ewe.

Corpora lutea and follicles were taken from the ovaries of 12 ewes at intervals from the start of luteolysis until 3 days after ovulation. RIA analysis of the tissue oxytocin content showed that luteal oxytocin concentrations declined during luteolysis to reach basal values at about the time of the next ovulation. Oxytocin was first measurable in the walls of 3 out of 6 preovulatory follicles during the LH surge, with a small increase in concentration to 26.1 +/- 6.6 pg/mg before ovulation, and a further increase in the young corpus luteum to concentrations exceeding 1 ng/mg 2-3 days later. After the LH surge, oxytocin was also found in the follicular fluid at a concentration of 3.4 +/- 0.3 ng/ml. Using immunocytochemical techniques, oxytocin and neurophysin were first detected in the follicle wall immediately before ovulation, and were localized in the granulosa cells. After ovulation the stained cells initially formed strands which appeared to break down to clusters and then to individual cells as the corpus luteum matured. The immunocytochemical picture also suggested that neurophysin immunoreactivity increased within a few hours of ovulation but that processing to oxytocin may be delayed. Measurements of circulating oxytocin concentrations revealed a pulsatile release pattern throughout the follicular phase with the height of the pulses decreasing from 25 +/- 5 pg/ml during luteolysis to a minimum of 11 +/- 2 pg/ml during the LH surge.

Animals↗
PubMed1986

Variations in patterns of follicle development in prolific breeds of sheep.

Prolific breeds of sheep (Romanov, Finn and Booroola Romanov crosses heterozygous for the Booroola gene (F+) were compared with breeds of lower prolificacy (Ile-de-France, Finn X Scottish Blackface, Merino X Blackface and Booroola X Romanov not carrying a copy of Booroola gene (++] by in-vivo monitoring of follicular kinetics by ink labelling during the late luteal phase and follicular phase of the oestrous cycle followed by histological examination of the ovaries or follicle dissection. At each of 3 successive laparotomies, the 3 largest follicles of each ovary were measured and ink labelled. At the final laparotomy, around the beginning of oestrus, all ewes were ovariectomized. High ovulation rate was not associated with the total number of antral follicles in any of the breeds. However, there were more follicles greater than 2 mm in diameter in Romanov and Booroola X Romanov crosses (F+) compared to their respective controls. Such a feature was not observed in Finnish Landrace compared to Finn X Blackface and Merino X Blackface ewes. A more numerous population of recruitable follicles, together with a similar incidence of selection through atresia, were the features associated with the high ovulation rate of Romanov compared to Ile-de-France ewes. The high ovulatory potential of the Finn ewes resulted from a markedly reduced incidence of selection through atresia. Booroola X Romanov ewes carrying a copy of the Booroola gene (F+) appeared to possess features of both parental breeds, including high numbers of recruitable follicles, smaller follicular size when recruitment occurs and an extended time for recruitment. Booroola X Romanov (++) ewes, not carrying the gene, appeared to have lost part of the 'Romanov characteristics' of a more numerous population of recruitable follicles. The variability in the kinetics of preovulatory enlargement, seen in these breeds of sheep, demonstrates that there are a number of pathways through which high ovulation rate can be achieved and hence through which ovulation rate might be manipulated.

Animals↗
PubMed1985

The measurement of testosterone and oestradiol-17 beta using iodinated tracers and incorporating an affinity chromatography extraction procedure.

The development of sensitive radioimmunoassays (RIA) for testosterone and oestradiol-17 beta, utilising 125I-radioligands, is described. Use of an homologous bridge at the same site of attachment, for both the radioligand and the steroid-carrier protein conjugate employed in raising antibodies, normally results in a loss of assay sensitivity and precision. This was overcome in the oestradiol assay by utilising an heterologous configuration at the site of attachment (11 alpha vs 11 beta). In contrast, for testosterone, even though an homologous bridge and site of attachment was used for the radioligand and the steroid-carrier protein conjugate, a very sensitive assay with extremely high antibody titres (dilution of 1:2 X 10(6] was achieved. This finding was repeated with a different antiserum suggesting that the "bridge binding" phenomenon may be related to the position of attachment to the steroid molecule. In addition, an antibody-Sepharose 4B affinity chromatography extraction procedure has been developed for both oestradiol and testosterone. This approach allows the measurement of very low concentrations of steroids from large volumes of a variety of biological fluids. As antibody-linked Sepharose 4B uses high concentrations of antibody, steroids of similar structure are extracted from biological fluids. However, the cross-reactivity of these related steroids are very low in the RIA's, ensuring good specificity.

Animals↗
PubMed1985

Control of gonadotrophin release in Scottish Blackface and Finnish Landrace ewes during seasonal anoestrus.

The patterns of LH and FSH secretion were measured in 4 experimental groups of Finnish Landrace and Scottish Blackface ewes: long-term (18 months) ovariectomized ewes (Group 1), long-term ovariectomized ewes with an oestradiol implant, which has been shown to produce peripheral levels of approximately 5 pg/ml (Group 2), long-term ovariectomized ewes with an oestradiol implant for 18 months which was subsequently removed (surgery on Day 0) (Group 3) and short-term ovariectomized ewes (surgery on Day 0) (Group 4). LH and FSH concentrations were monitored in all groups at approximately weekly intervals, before and after Day 0. Finnish Landrace ewes in Groups 1, 2 and 3 had significantly higher mean FSH concentrations than did Scottish Blackface ewes (P less than 0.01). FSH and LH concentrations increased significantly in Groups 3 and 4, but values in Group 4 were significantly lower (P less than 0.01) than those in Group 1 ewes even up to 30 days after ovariectomy. In Group 3, LH concentrations increased to levels similar to those in Group 1. The pattern of LH release was, however, significantly different, with a lower LH pulse frequency (P less than 0.05), but higher pulse amplitude (P less than 0.05). This difference was maintained at least until 28 days after implant removal. We suggest that removal of negative feedback by ovariectomy demonstrates an underlying breed difference in the pattern of FSH secretion and that ovarian factors other than oestradiol are also involved in the negative-feedback control of hypothalamic/pituitary gland function. Furthermore, negative-feedback effects can be maintained for long periods, at least 28 days, after ovariectomy or oestradiol implant removal.

Anestrus↗
PubMed1984

Microcomputer control applied to the Vickers M85/86 microdensitometer.

An electronic interface for a Research Machines 380Z microcomputer and a Vickers M85/6 integrating microdensitometer is described, together with outlines of the control software. A typical applications programme, which may be written in several high-level languages, is outlined for the determination of a time course plot for enzyme activity in a tissue section. This system facilitates rapid accurate measurement and analysis of experimental data.

Computers↗
PubMed1983

Progesterone withdrawal without parturition.

It has been demonstrated that administration of 100 mg of trilostane (an inhibitor of 3 beta-hydroxysteroid dehydrogenase) to late pregnant sheep will rapidly lower circulating levels of progesterone and that delivery ensues. Our intention was to reduce the dose of trilostane in order to separate the latter two sequelae and thereby obtain insight into the relationship between progesterone and prostaglandin biosynthesis. At the dose chosen (10 mg) the treatment did not induce parturition in 4 chronically catheterized sheep during late pregnancy. Circulating progesterone concentrations declined precipitously in all ewes but recovered to near basal values by 24 h after administration of trilostane. Circulating concentrations of 13,14-dihydro-15-keto-prostaglandin F2 alpha rose slightly but significantly at 4-5 h after administration of trilostane but never reached values normally associated with labor. Plasma estradiol levels were unchanged by treatment. These results are consistent with the view that progesterone withdrawal must be of a critical magnitude and duration for prostaglandin biosynthesis to be sufficiently stimulated to induce labor in sheep during late gestation.

Animals↗
PubMed1983

Fertility of sheep given antisera to steroids during anoestrus.

The incidence of oestrus (6/46) and ovulation (14/46) in ewes given antisera to androstenedione, oestrone, oestradiol and testosterone either separately or as a mixture of these sera at the time of treatment with progestagen sponges alone or progestagen sponges followed by LH-RH was similar to that of control ewes (2/13 and 6/13 respectively). The number of corpora lutea (CL) recorded for those ewes that did ovulate was, however, greater in the antiserum-treated ewes (22 CL/14 ewes) than in the controls (6 CL/6 ewes) at the first ovulation after sponge withdrawal. This superiority persisted to the second ovulation (53 CL/42 treated ewes compared to 13 CL/13 controls). The results for groups treated with antisera did not differ amongst themselves.

Androstenedione↗
PubMed1982

Oxytocin in the fetal and maternal circulations during induced and spontaneous parturition in sheep.

Oxytocin has been measured in fetal and maternal plasma samples obtained serially from 6 sheep during late pregnancy, spontaneous labor and labor induced by intrafetal infusion of Synacthen (ACTH1-24). Fetal plasma contained significantly (P less than 0.001) greater concentrations of oxytocin than maternal plasma. Concentrations of oxytocin rose in maternal plasma during the later stages of spontaneous and induced labor, whereas concentrations in fetal plasma did not exhibit a consistent trend.

Animals↗
PubMed1982

Dobutamine: a hemodynamic evaluation in children with shock.

The hemodynamic effects of dobutamine were studied in 33 infants and children with cardiogenic or septic shock. Dobutamine was administered at doses of 2.5, 5.0, 7.5, and 10.0 micrograms/kg/minute. Significant increases above preinfusion values were observed in cardiac index, left ventricular stroke work index, and pulmonary wedge pressure. Significant decreases from preinfusion values were observed in systemic arteriolar resistance index. No significant differences occurred in heart rate, mean systemic arterial pressure, mean pulmonary arterial pressure, right atrial pressure, or pulmonary arteriolar resistance index. Analysis of the data also revealed significant effects of age and diagnosis on the hemodynamic responses. These data suggest that dobutamine is a useful drug in the pharmacologic management of children in shock, especially in children older than 12 months with cardiogenic shock not complicated by severe hypotension.

Adolescent↗
PubMed1982

Pulsatile release of oxytocin during the estrous cycle, pregnancy and parturition in sheep.

Oxytocin has been measured in peripheral plasma from chronically catheterized sheep both during estrus and the early luteal phase of the estrous cycle and also during pregnancy at 122-124 days gestation, 141-145 days gestation and during spontaneous labor at term. In each experiment, blood samples were collected at 5-min intervals for 120 min and also at 1-min intervals for 10 min. In pregnant and nonpregnant sheep, pulsatile patterns of oxytocin concentrations were found in the experimental periods. Mean concentrations of oxytocin were significantly higher in plasma obtained during the luteal phase of the cycle when compared to samples taken during estrus. Moreover, concentrations of oxytocin were increased with length of gestation and labor. It is concluded that oxytocin secretion is episodic in sheep during both the estrous cycle and pregnancy.

Animals↗
PubMed1982

Effect of progesterone withdrawal in sheep during late pregnancy.

The concentration of progesterone in the peripheral plasma of seven sheep during late pregnancy was reduced by injection of an inhibitor of 3 beta-hydroxysteroid dehydrogenase activity. Concentrations of progesterone were 10.0 +/- 1.0 (S.E.M) ng/ml (n = 6) before injection of the inhibitor, fell to 1.39 +/- 0.40 ng/ml (n = 6) 30 min after injection, and remained within this lowered range for 6 h after injection. By 20-24h and 30-35h after injection progesterone concentrations had recovered to 4.63 +/- 0.94 and 14.07 +/-4.17 ng/ml respectively (n = 6). Six out of seven ewes delivered prematurely 32.5 +/- 2.9h after injection. Delivery appeared to be normal, and was associated with increasing concentrations of 13, 14-dihydro-15-oxo prostaglandin F2 alpha in peripheral plasma. Concentrations of oestradiol-17 beta in peripheral plasma were slightly raised immediately before delivery, at which time progesterone concentrations were within the preinjection range. These data suggest that progesterone withdrawal is one mechanism that initiates increased prostaglandin F2 alpha secretion in the pregnant sheep.

Abortifacient Agents↗
PubMed1982

Distribution of 125I-labelled follicle-stimulating hormone and human chorionic gonadotrophin in the gonads of hypogonadal (hpg) mice.

Hypogonadal mice are deficient in LH releasing hormone (LH-RH), the releasing factor for LH and FSH, with a consequent failure of postnatal ovarian and testicular development. After intravenous injection of hypogonadal females with 125I-labelled human chorionic gonadotrophin (hCG), followed by autoradiography of semi-thin (1 micrometer) slices of the ovary, labelled hCG was found to be associated with interstitial cells and thecal cells with little or no labelling of granulosa cells. Labelled human FSH was associated solely with granulosa cells. Hypogonadal females, implanted for 5 days with a silicone elastomer capsule of oestrogen, showed a similar response to that of normal females with hCG labelling of the granulosa cells of the larger follicles as well as of the thecal cell layer. Furthermore, subcutaneous injection of hypogonadal females with LH-RH (50 ng), 12 times daily for 5 days, increased uterine weight and stimulated ovarian development with some large follicles binding hCG to both thecal and granulosa cells. Therefore stimulation of follicular development may possibly be associated with increased oestradiol concentrations. In the male, after injection of 125-I-labelled hCG, silver grains were associated with the interstitial cells alone in both hypogonadal and normal mice. Labelled human FSH was undetectable in semi-thin testicular sections, but the mode of injection (intravenous) not have allowed enough labelled hormone to reach the testis in order to resolve the question as to whether the hypogonadal or normal testis can bind FSH.

Animals↗