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Biomedical subjects

R Webb

Publications and source records attributed to R Webb.

At least 163 records · Page 9Linked to original sources
PubMed1989

Neurosecretory-like material in 3rd- and 4th-stage Dirofilaria immitis larvae (Nematoda: Filarioidea).

Phase-interference microscopic examination of the infective, post-infective 3rd-stage and 4th-stage larvae of Dirofilaria immitis has identified a single cell body in each of the paired lateral amphidial nerves which undergoes characteristic morphological change during the development from 3rd- to 4th-stage larvae. Acetaldehyde-fuchsin staining of worm sections revealed fuchsinophilic material in the precise location of the amphidial nerve-cell bodies observed by phase-interference microscopy. This material was found in 70% of infective larvae recovered from mosquitoes and in 100% of larvae recovered from micropore chambers 24 h after implantation into BALB/C mice. In pre-moult larvae recovered at 42 h (Experiment 1) and at 48 h (Experiment 2) fuchsinophilic material was demonstrable, but no staining was observed in those larvae in which separation of the 3rd- and 4th-stage cuticles had occurred. No such material was observed in 4th-stage larvae recovered from chambers after 74 h, and in these larvae the amphidial nerve-cell bodies were not discernible. These cytological observations are consistent with a cycle of elaboration and release of neurosecretion associated with moulting in D. immitis.

Animals↗
PubMed1989

Characterization of a Synechococcus sp. strain PCC 7002 spontaneous mutant strain defective in accumulation of photosystem II core chlorophyll-protein complexes.

Two photosystem II-associated chlorophyll-protein complexes of Synechococcus sp. strain PCC 7002 were identified. Their polypeptide compositions were similar to those of chlorophyll-containing antenna complexes of other cyanobacteria. Strain GT8B did not possess the complex responsible for 695-nm fluorescence and was unable to grow photoautotrophically; hence, this complex is necessary for photosystem II function in vivo.

Chlorophyll↗
PubMed1989

Study of LH response to GnRH in the young male as a criterion of genetic merit for female reproduction in sheep.

A high and a low response line in sheep were selected on the basis of the mean concentration of LH in 10-week-old Finn-Dorset ram lambs after an i.v. injection of 5 micrograms GnRH. After 8 male generations the mean LH response of the high line was more than 5-fold that of the low line and the heritability of the selected trait was estimated at 0.44 +/- 0.015. Highly significant line differences in mean LH response to GnRH were also found in males at 20 weeks of age and females at 10 and 20 weeks of age and the genetic correlations between the four LH response traits appear to be close to unity. Large line differences in the mean FSH response to GnRH were also found in both males and females at 10 and 20 weeks of age. Selection had little effect on the physical characteristics of lambs. High-response line ewes entering their first breeding season at about 7 months of age showed oestrus earlier in the season and had higher ovulation rates and numbers of lambs born per ewe lambing than did low-response line ewes. In the second breeding season, at about 19 months of age, the only line difference was a higher ovulation rate early in the breeding season in high-line ewes. It is suggested that these changes may be mediated by a more rapid response in high-line ewes to increased GnRH stimulation at puberty or at the beginning of the breeding season.

Animals↗
PubMed1989

Ovarian response to hCG treatment during the oestrous cycle in heifers.

The aims of this study were to investigate whether treatment with a single ovulatory dose of hCG, between the day of oestrus and the end of the luteal phase, could induce extra ovulations in heifers and whether the presence of an existing corpus luteum (CL) affected the response. Heifers (N = 32) were injected with 1500 i.u. hCG or saline on a given day of the oestrous cycle. Treatments were repeated during subsequent cycles to provide a total of 71 observations, 57 of which followed an injection of hCG, given between Day 0 (oestrus) and Day 16, and 14 of which followed saline injections as controls. Ovulatory responses were noted by laparoscopy 2 days after hCG treatment. No heifers injected with saline produced additional CL. Of the hCG-treated cycles, 23 resulted in the formation of an additional CL, and this was significantly affected by the stage of the oestrous cycle when hCG was given; a greater response was observed during the early (Days 4-7) and late (Days 14-16) stages of the luteal phase than at the mid-luteal phase of the oestrous cycle. Two heifers were also treated with hCG on Days 17 or 18 of the oestrous cycle, but before oestrus; both had induced CL. There were no significant differences between the left-right orientation of the existing CL or the hCG-induced CL. These results demonstrate that the large, luteal-phase follicle of the cow is capable of ovulating in response to hCG and that the induced CL is not affected by the presence of an existing CL.

Animals↗
PubMed1989

Morphological and functional characterization of large antral follicles in three breeds of sheep with different ovulation rates.

Morphological and functional features of large ovarian follicles from three breeds of sheep, with different ovulation rates (Finnish Landrace N = 12, Finnish Landrace X Scottish Blackface N = 16, Merino X Scottish Blackface N = 16) were compared by integrating three techniques; ink labelling, in-vitro oestradiol production and morphological classification. The follicles were removed at two stages of the follicular phase, 1 (PG + 1) or 2 (PG + 2) days after PGF-2 alpha treatment and compared after monitoring their rates of growth with the use of ink labelling. After ovariectomy all follicles greater than or equal to 1 mm in diameter were dissected, and the 8 largest were incubated individually for 2 h to assess their ability to secrete oestradiol and testosterone. After incubation the follicles were processed for histological examination and checked for atresia. An analysis of the follicle population was based on in-vitro oestradiol secretion rates in all three breeds; an oestrogen-active population producing 500-8100 pg oestradiol/ml/h and an oestrogen-inactive population producing 0-499 pg oestradiol/ml/h. A comparison of the 3 approaches demonstrated agreement on 94.3 +/- 1.2% of occasions. Ink-labelling demonstrated that all follicles identified as oestrogen-active were increasing in size. Within oestrogen-active follicles significant correlations were detected between oestradiol production and testosterone production (r = 0.42), oestradiol production and granulosa cell number (r = 0.45) and between oestradiol production and mitotic index (r = -0.38). A regression model fitting breed, stage of atresia, granulosa cell number, in-vitro testosterone production and mitotic index demonstrated that granulosa cell number is a characteristic which contributes significantly to the variation of in-vitro oestradiol production in oestrogen-active and oestrogen-inactive follicles. There was no significant difference between breeds in the mean number of ink-labelled follicles growing from Day PG - 1 to Day PG + 1. There was a significant difference between the breeds in the number of ink-labelled follicles growing between Days PG + 1 and PG + 2 (Days 1 and 2 of the follicular phase), the number being similar to the ovulation rate for the breed. The majority of the oestrogen-active follicles had been recruited by Day PG - 1, although in the Finnish Landrace genotypes more than 30% were recruited on or after Day PG + 1 compared to less than 10% in Merino x Scottish Blackface ewes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Ethylene glycol intoxication: evaluation of kinetics and crystalluria.

Ethylene glycol and glycolate kinetics were studied in two cases of ethylene glycol intoxication with maximal ethylene glycol/glycolate concentrations of 40.9/26.8 and 56.4/22.4 mmol/liter, respectively. Both patients survived, but with prolonged renal failure, upon treatment with bicarbonate, ethanol, and hemodialysis. Glycolic acid was the major cause of the metabolic acidosis in both cases; lactate levels were only slightly elevated. Kinetic calculations showed that both ethylene glycol and glycolate were distributed in total body water with plasma half-lives of 8.4 and 7.0 hours, respectively. The half-life of ethylene glycol was increased more than 10-fold by ethanol treatment alone. Calcium oxalate monohydrate crystalluria was dominant in both cases, but in one was preceded by a short period with mainly dihydrate excretion; crystalluria was not present upon admission. Repetitive urine microscopy in search of needle- or envelope-shaped crystals should be performed when ethylene glycol intoxication is suspected.

Acidosis↗
PubMed1988

Survival of ovine embryos stored at 4 degrees C for 24 hours.

This study was conducted to ascertain if sheep embryos collected for transfer can be stored for short periods without freezing to allow for international transport. Of twelve Finnish Landrace ewes treated with equine follicle stimulating hormone (FSH), eleven ewes ovulated with a mean of 9.1 +/- 4.3 (SD) corpora lutea. Recovery rate from the nine ewes with normal corpora lutea was 68 +/- 27%, providing 61 morulae which were then cooled to 4 C and stored for 24 h while transporting them from Scotland to France. Romanov recipients received either 4 (n = 14) or 5 (n = 1) of these morulae. Fourteen of the recipients lambed, with a mean lambing rate of 2.1 +/- 0.8, representing 48.3% of embryos transferred. Cooling of embryos to 4 C and storing them in ovum culture medium for 24 h at 4 C may be a valuable technique for the handling and short-term storage of embryos.

Journal Article↗
PubMed1988

Qualitative variation in the immune response to ovarian follicular fluid proteins in cattle.

In two experiments 44 heifers were immunised with inhibin preparations of partially purified ovarian follicular fluid (PPFF) of ovine, porcine and equine origin in non-ulcerative Freund's adjuvant. In the first experiment 20 cattle were immunised with ovine PPFF1. In the second, a further 24 were immunised with either a different sheep PPFF (ovine PPFF2) or PPFF from pigs or horses. Large molecules of over 30 kDa initiated a strong immune response in some animals, but none in others, although there was no obvious relationship with the MHC Class I (BoLA) phenotype. Immunisation with ovine partly purified follicular fluid affected ovulation rate in some cattle, and only these cows produced detectable antibodies to an approximately 40 kDa protein. These data show that the immunological response of cattle to a mixture of antigens is highly variable between individuals and may explain the variation in the ovarian response to immunological manipulations of ovulation rate seen in this species.

Animals↗
PubMed1988

Steroid control of gonadotropin secretion and ovarian function in heifers.

The failure of anti-steroid treatments to induce multiple ovulations in cattle in a repeatable way, prompted us to examine the role of the gonadal steroids in the control of gonadotropin secretion in this species. A better understanding of the control of gonadotropin secretion in the cow would assist in the development of treatments to control prolificacy. Groups of six heifers were implanted with one of three sizes of estradiol (E2) implant on day 9 of a synchronized estrous cycle, and five control heifers received empty implants. All heifers were ovariectomized during the luteal phase of the subsequent estrous cycle and given progesterone-releasing intravaginal devices (PRID). Blood samples were taken every 10 min for 12 h with PRIDs and for 6 h after PRID withdrawal, for the measurement of LH and FSH concentrations. The two larger implant sizes (increasing E2 concentrations to 7.4 and 18.7 pg/ml plasma during the luteal phase of the cycle) decreased ovulation rate, the number of large follicles, and luteal weight. After ovariectomy, the three implant sizes produced E2 concentrations comparable with those during the luteal and follicular phases of the estrous cycle and at estrus (1.5, 4.4, and 10.5 pg/ml, respectively). E2 alone decreased mean LH and FSH concentrations and LH pulse amplitude, whereas progesterone alone reduced mean gonadotropin concentrations and LH pulse frequency. Only in the presence of progesterone did E2 decrease LH pulse frequency. Steroid concentrations which mimicked those of the luteal and follicular phases of the cycle produced luteal- and follicular-phase patterns of LH and FSH secretion. These results confirm that E2 and progesterone are important regulators of gonadotropin secretion in cattle, and question the role of inhibin in this respect.

Animals↗
PubMed1988

Interactions between inhibin, oestradiol and progesterone in the control of gonadotrophin secretion in the ewe.

Experiments were carried out to test the hypothesis that inhibin and oestradiol act synergistically to inhibit the secretion of FSH, to test for effects of progesterone, and to compare the FSH and LH responses to ovarian feedback. In Exp. 1, with 11 ovariectomized and 12 intact Romanov ewes during the anoestrous season, doses of oestradiol (administered by means of subcutaneous implants) that restored normal LH pulse frequencies were insufficient to restore normal concentrations of FSH. In Exp. 2, with 48 ovariectomized Welsh Mountain ewes during the breeding season, a factorial design with 4 ewes per cell was used to assess the responses in LH and FSH to 3 doses of oestradiol (s.c. implants) and 4 doses of bovine follicular fluid ('inhibin', 0.2-1.6 ml s.c. every 8 h). This was done initially in the absence of progesterone and then after 7 days of treatment with progesterone (s.c. implants). Analysis of variance revealed a significant synergistic interaction between oestradiol and inhibin on the plasma concentrations of FSH. Progesterone had little effect. In contrast, there was a significant synergistic interaction between oestradiol and progesterone on the concentrations of LH. 'Inhibin' also inhibited LH secretion but this effect was independent of the two steroids. We conclude that there are basic differences in the way that ovarian feedback acts to control the secretion of LH and FSH in the ewe. FSH secretion appears to be primarily controlled by the synergistic action of oestradiol and inhibin on the anterior pituitary gland, while the secretion of LH is inhibited during the follicular phase by an effect of oestrogen at pituitary level and during the luteal phase by the synergistic action of oestradiol and progesterone at the hypothalamic level. Inhibin, or another non-steroidal factor in follicular fluid, may also play a minor role in the control of LH secretion.

Animals↗
PubMed1988

Are differences in FSH concentrations involved in the control of ovulation rate in Romanov and Ile-de-France ewes?

Despite differences in FSH concentrations ranging from 1.5 ng/ml (Romanov ewes) to 4 ng/ml (Ile-de-France ewes) between the follicular and luteal phases, follicular growth (numbers of follicles growing, growth rates, maximum size reached) was morphologically similar between the two stages of the cycle. Injection of 750 i.u. hCG at Day 6 or 16 of the cycle triggered ovulation of 4.1 +/- 0.7 and 4.0 +/- 1.3 follicles in Romanov and 2.2 +/- 0.5 and 1.7 +/- 0.5 follicles in Ile-de-France ewes, respectively, demonstrating that functional differentiation was similar between the two stages of the cycle. As gonadotrophin environment differs between these two stages of the cycle, this suggests that there is a wide flexibility in the amount of gonadotrophins required to trigger terminal follicular growth and that ovarian requirements for gonadotrophins might work through thresholds. When Romanov and Ile-de-France ewes were given similar amounts of exogenous gonadotrophins (1250 i.u. PMSG, 750 i.u. hCG) after hypophysectomy, ovulation rates were close to the usual values (Romanov, 5.5 +/- 3.9; Ile-de-France, 1.4 +/- 0.5), demonstrating that differences in gonadotrophin concentrations during the follicular phase do not play a major role in the high ovulation of the Romanov compared to the Ile-de-France ewes.

Animals↗
PubMed1988

Changes in the feedback control of gonadotrophin secretion in ewes from lines selected for testis size in the ram lamb.

The dynamics of FSH and LH secretion were studied in sheep genetically selected for High (H) and Low (L) rates of testis growth. Gonadotrophin secretion had previously been shown to be affected in the ram lamb with H-line lambs more sensitive to steroid feedback than L. While there were significant differences in mean LH concentrations during the luteal and follicular phases of the oestrous cycle, mean LH values were essentially similar in the two lines in response to ovariectomy, the effect of oestradiol implants on the response to ovariectomy and the response to LHRH. However, the frequency of LH pulses in the H line was similar during both phases of the oestrous cycle, showing a surprising insensitivity to steroid feedback. By contrast, LH pulse frequency was markedly lower in the L-line ewes in the luteal than the follicular phase (0.6 vs 1.1 pulses/h) as expected from the literature. Mean FSH concentrations were significantly higher in the L-line ewes during the follicular phase of the oestrous cycle and after ovariectomy but no significant differences were detected at the other sampling periods. There were no differences in ovulation rate between the lines. It was concluded that selection for testis size had affected the feedback control of gonadotrophin release in the ewe, as in the ram, and hence the expression of the genes controlling this is not sex limited.

Animals↗
PubMed1987

Increasing ovulation rate and lambing rate in sheep by treatment with a steroid enzyme inhibitor.

Treatment of ewes with a 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) inhibitor (Epostane) resulted in a significant increase in both ovulation rate and in the mean number of lambs per ewe lambing. The progestagen sponge plus 3 beta-HSD inhibitor treatment also caused a significant increase in oestrous cycle duration of approximately 1.5 days. Treatment of ewes with the 3 beta-HSD inhibitor caused a significant decrease in peripheral progesterone concentrations, which were reduced even further when 3 beta-HSD inhibitor treatment was given to ewes after insertion of a progestagen sponge. However, mean oestradiol concentrations were significantly higher in the two treatment groups, both at the end of the luteal phase and during the follicular phase of the oestrous cycle. These results demonstrate that ovulation rate and the production of lambs per ewe lambing can be significantly increased by 3 beta-HSD inhibitor treatment.

Androstenols↗
PubMed1987

Reproductive and endocrine effects of active immunization against a testosterone conjugate in the heifer.

Yearling heifers were actively immunized against 8 mg testosterone-3-carboxymethyloxime-ovalbumin in Non-Ulcerative Freund's Adjuvant, with or without the addition of Corynebacterium parvum (Groups A and B, respectively; N = 4 for each group). After the priming injection, Groups A and B were boosted twice at 4-monthly intervals. Control heifers (N = 9) were not injected. All treated animals except one gave a measurable antibody response, and all responding animals became anoestrous and displayed ovarian cysts after the first booster injection. There were no apparent differences between treatments, and so results for Groups A and B were pooled. At 25 weeks after the second booster 3 of the 7 responding, anoestrous heifers resumed cyclicity; one with two consecutive double ovulations, and one with one double ovulation. The 3rd heifer showed 4 corpora lutea, then became anoestrus again. The 4 remaining acyclic heifers, and the control heifers, were intensively blood sampled; the anoestrous heifers showed significantly higher mean LH and significantly lower mean FSH concentrations and higher LH pulse frequency than did the control animals. These heifers remained anoestrous for 11 months after the second booster, at which point they were injected with GnRH and PGF-2 alpha; only 1 heifer resumed ovarian cyclicity. These results indicate that it is possible to increase ovarian activity in cattle by active immunization against testosterone, but that there is a high incidence of anoestrus.

Anestrus↗
PubMed1987

Active immunization of cattle against partly purified follicular fluid from sheep.

Yearling cross-bred heifers were injected with 0.4 or 4 mg total protein in non-ulcerative Freund's adjuvant (Groups A and C, respectively; N = 5 per group), or adjuvant with C. parvum (Groups B and D, respectively; N = 5 per group). Control heifers were not treated (N = 9). No antibodies were detected in heifers in Groups A and C and so these were excluded from the analysis. There was no effect of the treatment on Group B or D heifers after the priming or first booster injection. After a second booster injection one Group D heifer gave a triple ovulation, and two Group D heifers and one Group B heifer gave double ovulations, but for one oestrous cycle only. Group B heifers also showed a significant rise in FSH concentrations after the second booster injection. Group D heifers were given a third booster injection; there was an increase in the mean number of large follicles per heifer, and a decrease in oestrous cycle length, but no increase in ovulation rate. These results indicate that a transient increase in ovulation rate can be induced by actively immunizing cattle against partly purified follicular fluid from sheep.

Animals↗
PubMed1987

Effect of an inhibitor of 3 beta-hydroxysteroid dehydrogenase on progesterone concentrations and embryo survival in sheep.

The effect of an inhibitor of 3 beta-hydroxysteroid dehydrogenase on peripheral progesterone concentration during the luteal phase of the oestrous cycle and on embryo survival was determined in sheep. Following administration of 10, 50, 100 or 250 mg epostane (4,5-epoxy-17-hydroxy-4,17,dimethyl-3-oxo-androstane-2-carbonitrile) progesterone concentrations were significantly lower than control levels 4 h after injection, from 2.5 to 22 h, 1.5 to 24 h and 1 to 24 h after injection respectively. There appeared to be no effect on peripheral oestradiol concentrations. Adrenal progesterone production was small and not influenced by epostane treatment. Epostane was administered on day 9 of the oestrous cycle to cause a reduction in progesterone concentrations for approximately 12-18 h on day 9 only (group 1, 250 mg epostane on day 9), or a series of such reductions on 3 consecutive days (group 2, 50 mg epostane on days 9, 10 and 11) or a continuous reduction for 3 days (group 3, 250 mg epostane on days 9, 10 and 11). The proportion of ewes that were pregnant was significantly (P less than 0.05) lower in ewes treated to give a continuously low progesterone concentration for 3 days than in either controls or ewes in which progesterone concentration was reduced for less than 24 h (in controls and groups 1, 2 and 3 the proportion was 85, 92, 54 and 18% of ewes treated respectively). Embryo survival was not affected by administration of 250 mg epostane on days 9, 10 and 11 if luteal phase levels of progesterone were maintained by insertion of a silicone elastomer implant of the steroid.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxysteroid Dehydrogenases↗