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Biomedical subjects

E D Watson

Publications and source records attributed to E D Watson.

At least 19 recordsLinked to original sources
PubMed2006

Seasonal changes in ovarian activity: lessons learnt from the horse.

The annual reproductive cycle in the horse involves a reduction in ovarian activity during short days. The absence of ovulatory activity during winter has important consequences for an equine industry eager to breed mares early during the year. The anovulatory season results from a reduction in the secretion of pituitary gonadotropin that is in turn triggered by the inhibitory effects of short photoperiod on the hypothalamus-pituitary axis. Recent studies have provided evidence that the response of the ovaries to endocrine stimuli during the anovulatory season is affected not only by circulating concentrations of trophic hormones but also by locally produced growth factors that are putative modulators of follicular responses to gonadotropins. The present review summarises current knowledge on ovarian dynamics during the equine anovulatory season and the regulatory mechanisms involved at both systemic and local levels.

Animals↗
PubMed2006

Temporal relationship between proliferating and apoptotic hormone-producing and endothelial cells in the equine corpus luteum.

The temporal relationship between endothelial cell death, vascular regression and the death of hormone-producing cells in the mare has not been established. To determine the dynamics of cell proliferation and death throughout the luteal phase, corpora lutea were studied at the early, mid- and late luteal phase, and after treatment with cloprostenol in the mid-luteal phase to induce premature luteolysis. Changes in cell proliferation and apoptosis were investigated utilising specific markers (phosphorylated histone-3 and activated caspase-3 respectively). Histone-3 positive cells were most abundant during the early luteal phase, and were mainly present in endothelial cells. Histone-3 activity significantly increased in hormone-producing cells 36 h after cloprostenol treatment. Frequency of activated caspase-3 staining peaked on day 14, and was induced by 36 h after cloprostenol administration in mid-luteal phase. However, cell death occurred simultaneously in the endothelial and hormone-producing cells. These results show that a subset of hormone-producing cells enter the early stages of cell division around luteolysis, while the majority of cells are undergoing cell death. Natural and induced functional and structural luteal regression in the mare can be at least partially attributed to simultaneous apoptosis of endothelial and hormone-producing cells. However, there is no evidence that endothelial cell death is the trigger for naturally occurring luteolysis.

Animals↗
PubMed2005

Investigation and management of a cluster of cases of equine retained fetal membranes in Highland ponies.

Four at-risk Highland ponies on the same premises all retained their fetal membranes in the same breeding season. The ponies were treated with a combination of oxytocin, infusion and distension of the allantochorionic sac with fluid, gentle traction in one case, and supportive therapy. The possible causes of the condition were investigated with clinicopathological tests and analyses of the herbage for its species composition and fungal contamination. No obvious possible causative abnormalities were identified apart from a low total serum calcium level in one case. No fescue grass was found and no pathogenic fungi were detected.

Animals↗
PubMed2005

Expression of mRNA encoding insulin-like growth factor binding protein-2 (IGFBP-2) during induced and natural regression of equine corpora lutea.

The insulin-like growth factors, IGF-I and -II, have been shown to play a key role in luteal function in some species. The IGF binding proteins, IGFBP-2 and -3, have been shown to inhibit binding of IGF-I and -II to bovine luteal cells and decrease progesterone production. We have recently shown that equine follicles have the genetic capacity to produce IGFBP-2, and that levels decrease in healthy preovulatory follicles. In the present study expression of mRNAs encoding IGFBP-2, as well as the rate-limiting steroidogenic enzyme, P450scc, were studied in equine corpora lutea to investigate whether IGFBP-2 might be involved in luteolysis. Corpora lutea were collected from mares in mid-luteal phase (day 10), at early regression (day 14), late regression (day 17), and 12 and 36 h after intramuscular administration of the PGF(2alpha) analogue, cloprostenol (0.5 microg/kg). During early natural regression, and 12 h after administration of cloprostenol on day 10, steady state levels of mRNAs encoding P450scc had decreased significantly compared with day 10 of dioestrus (P < 0.001). Levels of mRNA encoding IGFBP-2 increased significantly between mid-diestrus and early (P < 0.01) and late (P < 0.001) regression, and 36 h after cloprostenol administration (P < 0.001). We conclude that the genetic capacity for increased IGFBP-2 production in the early stages of natural luteolysis in the mare may act to sequester IGF-I in the CL, assisting in inhibition of progesterone production. However the delay in increase in mRNA encoding IGFBP-2 after cloprostenol administration, combined with the sharp fall in expression of P450scc mRNA, suggests that the luteolytic action of a pharmacological dose of cloprostenol may not be mediated via IGFBP-2 in the mare.

Animals↗
PubMed2004

Insulin-like growth factors-I and -II and insulin-like growth factor-binding protein-2 in dominant equine follicles during spring transition and the ovulatory season.

The period between seasonal anoestrus and cyclicity is characterized in many mares by cyclical growth and regression of large dominant follicles. The insulin-like growth factor (IGF) system plays a key role in follicular growth and regression; therefore, we hypothesized that changes in the IGF system and its binding proteins would modulate onset of cyclicity in mares. Ovaries were obtained from pony mares on the day after detection of an actively growing 30 mm transitional anovulatory follicle, and also at the second or third oestrus of the breeding season on the day after the preovulatory follicle reached 30 mm in diameter. Size of dominant follicles at the time of removal was similar in transition (32 +/- 0.8 mm) and at oestrus (34 +/- 0.6 mm). IGF-I mRNA was present in granulosa cells, with low thecal expression, whereas IGF-II mRNA was confined to the theca layer. Expression of IGF-I and -II mRNAs, and intrafollicular concentrations of oestradiol, were lower (P < 0.01; paired t test) in transitional anovulatory follicles than in preovulatory follicles. Messenger RNA encoding IGFBP-2 was present in both theca and granulosa layers. Steady-state concentrations of mRNA encoding IGFBP-2 mRNA increased (P < 0.001) in theca in preovulatory follicles. Intrafollicular concentrations of IGFBP-2 were higher (P < 0.001) in transitional than in preovulatory follicles. The similarity in circulating concentrations of IGF-I in transitional and cyclic mares, suggested that the somatotrophic axis is not involved in transition from anovulatory to ovulatory cycles. The results suggest that the increased expression of IGF-I and -II mRNAs in preovulatory follicles, along with the decrease in IGFBP-2 concentrations, could increase the bioavailability of intrafollicular IGF in large follicles during the breeding season, and support our hypothesis that intrafollicular IGF bioavailability must exceed a threshold level before ovulation can occur.

Animals↗
PubMed2003

Association of uterine edema with follicle waves around the onset of the breeding season in pony mares.

During spring transition, when estrus may be exhibited for prolonged periods, it is important for veterinarians and stud farm personnel to be able to predict whether a large follicle will ovulate or regress. It is thought that the presence of ultrasonically detectable uterine edema indicates that a follicle will ovulate, however, there is little evidence to support this. In the present study, 16 mares were regularly examined by transrectal ultrasonography to follow growth and regression of follicles from seasonal anestrus in February until second ovulation. Blood samples were collected daily for measurement of estradiol concentrations when a large ovarian follicle was present. Estrous-like uterine edema was detected during 7 of 11 (64%) anovulatory follicle waves, in 12 of 14 (86%) mares before their first ovulation, and in 100% of mares before their second ovulation. Uterine edema was first detected 43+/-6.7 days before first ovulation. Large anovulatory follicles tended to be present for longer periods of time than ovulatory follicles. Uterine edema was present for a significantly greater proportion of time in the presence of a large follicle at second ovulation than at first ovulation (P<0.05) or for anovulatory follicles (P<0.01). Peak plasma estradiol concentrations and mean plasma estradiol concentrations were significantly higher (P<0.001) when a dominant preovulatory follicle was present compared with a dominant anovulatory follicle, but there was no difference in estradiol concentrations between first and second ovulations. It was apparent, therefore, that uterine edema was not a reliable indicator of follicular steroidogenic competence, or of whether the follicle would ovulate.

Animals↗
PubMed2003

Angiogenesis and vascular endothelial growth factor expression in the equine corpus luteum.

Precise pharmacological control of the corpus luteum is important in the manipulation of the oestrous cycle in mares. Angiogenesis plays a key role in the growth and regression of the corpus luteum; therefore, influencing the vasculature of the corpus luteum may offer a novel method for controlling its lifespan. In the present study, changes in angiogenesis and vascular expression of endothelial growth factor (VEGF) were evaluated throughout the luteal phase and after PGF(2alpha)-induced luteolysis. Corpora lutea were collected from mares in the early luteal phase (days 3-4), mid-luteal phase (day 10), early regression (day 14), late regression (day 17), and at 12 and 36 h after administration of PGF(2alpha) on day 10 of the oestrous cycle. Immunohistochemistry was used to localize Von Willebrand factor and Ki67 in endothelial and proliferating cells, respectively. VEGF mRNA and protein were localized by in situ hybridization and immunohistochemistry. The proliferation index of endothelial cells was intense in the early luteal phase. The early and mid-luteal phases were characterized by a dense network of capillaries. The microvasculature started to regress by day 14. After administration of PGF(2alpha), vasodilation was observed after 12 h, but after 36 h, luteal degeneration was accompanied by a significant decrease in vascularity. VEGF mRNA and protein were expressed mainly in the luteal cells during the early and mid-luteal phases and expression declined at early regression (day 14). However, immunostaining for VEGF protein was high in late luteal regression (day 17) and 36 h after PGF(2alpha) administration. These findings indicate a close temporal association between VEGF expression and angiogenesis in the equine corpus luteum during its functional lifespan.

Animals↗
PubMed2003

Analysis of atresia in equine follicles using histology, fresh granulosa cell morphology and detection of DNA fragmentation.

Follicular atresia has been examined previously by various biochemical and histological methods. The aim of this study was to compare, for the first time, detection of granulosa cell apoptosis by biochemical DNA analysis and microscopic examination of fresh granulosa cell morphology with the established method of detecting atresia by histology in equine follicles. DNA extracted from granulosa cells was examined by staining with ethidium bromide and end-labelling with [(32)P]dideoxy-ATP, which labels the free 3'-end of DNA fragments. In 25 of 26 follicles (96%) there was agreement between end-labelling and staining of DNA with ethidium bromide (P < 0.001). Granulosa cell apoptosis was distinguished more easily in the end-labelled samples than by staining with ethidium bromide. Histological atresia and apoptosis as detected by biochemical DNA analysis were significantly correlated (P < 0.02) with 20 of 22 follicles (91%) receiving corresponding classifications with the two methods. No follicles with granulosa cell apoptosis as detected by biochemical DNA analysis were histologically viable, but some of the histologically early atretic follicles did not display DNA laddering. Stereomicroscopic evaluation of morphology of the fresh granulosa cells was significantly correlated (P < 0.001) with the histological findings, with 29 of 33 follicles (88%) receiving corresponding classifications. There was a potential error in determining follicle health by biochemical DNA analysis only, as both histologically early and late atretic follicles in some cases did not show DNA laddering. Thus, if relying solely on biochemical detection of apoptosis, severely atretic follicles could wrongly be classified as healthy follicles.

Animals↗
PubMed2002

Concentrations of inhibin, progesterone and oestradiol in fluid from dominant and subordinate follicles from mares during spring transition and the breeding season.

Dominant and subordinate follicles were collected from mares on the day after the dominant follicle reached 30 mm in diameter, to investigate regulation of folliculogenesis during spring transition and the breeding season. Concentrations of oestradiol-17beta, progesterone and inhibin A, but not inhibin isoforms with pro- and alpha C-immunoreactivity, were significantly higher in preovulatory follicles than in dominant anovulatory transitional follicles. Steroidogenic activity was regained gradually in the dominant follicles of successive anovulatory waves through spring transition. The dominant follicles, during both spring transition and cyclicity, contained higher concentrations of oestradiol, progesterone and inhibin A, but not inhibin pro- and alpha C-isoforms, than subordinate follicles. The results indicate that high follicular levels of oestradiol, progesterone and inhibin A are associated with continued follicle growth and ovulation. The low concentrations of oestradiol and progesterone in transitional follicles indicate that the deficiency in steroidogenesis exists early in the steroidogenic pathway. The similarity in patterns of follicular hormones in spring transition and during cyclicity strongly suggests that the mechanism of dominance is the same in both types of follicle.

Animals↗
PubMed2002

Chemoattractant properties of conditioned medium from equine corpora lutea collected at various stages of the oestrous cycle.

This study investigated the chemotactic activity of equine CL at different stages of the oestrous cycle. The purpose of this was to ascertain whether luteal tissue itself contributes to the massive influx of leucocytes around the time of natural and induced luteal regression. Corpora lutea were collected at different stages of dioestrus and after treatment with PGF2alpha. Culture medium harvested after incubation of luteal tissue for 20 h was chemotactic for both polymorphonuclear and mononuclear cells in late dioestrus (before functional regression) as well as after natural and induced luteal regression. By contrast, midluteal tissue showed no chemotactic activity. This is the first report of the ability of equine luteal tissue actively to recruit inflammatory cells in vitro and supports our earlier findings that this infiltration starts prior to functional luteolysis. We hypothesise that this early influx of inflammatory cells may play an active role in luteal regression. Further research is needed to identify the specific chemotactic factor(s).

Animals↗
PubMed2002

Cell death during natural and induced luteal regression in mares.

In mares, little information is available on the type of cell death that occurs during natural and induced luteal regression. Corpora lutea were collected from mares in the early luteal phase, days 3-4 (n = 4); mid-luteal phase, day 10 (n = 5); early regression, day 14 (n = 4); late regression, day 17 (n = 4); and 12 and 36 h (n = 3 per group) after PGF2alpha administration on day 10. Histological and ultrastructural sections were examined and TUNEL was used to detect DNA fragmentation. In early luteal regression, there were more pyknotic luteal cells and extracellular round dense bodies compared with the mid-luteal phase. By late regression, there was a significant decline (P < 0.01) in the number of round dense body clusters and a marked accumulation of lipid. Twelve and 36 h after PGF2alpha administration, changes were similar to those seen in natural regression, but there was also a marked infiltration of neutrophils. Accumulation of lipid was not apparent until 36 h after PGF2alpha administration. Ultrastructural examination revealed rarefaction and distortion of the mitochondrial cristae in most of the luteal cells by the mid-luteal phase. Luteal cells showed shrinkage, accumulation of lipid with foamy appearance, and disruption in both smooth endoplasmic reticulum and mitochondria during natural and induced regression. Some luteal cells showed fragmented or pyknotic chromatin characteristic of apoptosis. Other luteal cells showed crenation of the nuclear membrane and shrinkage of the nucleus, features not characteristic of apoptotic cell death. In late regression, capillaries were obstructed by swollen endothelial cells and round dense bodies. These results show that structural regression may be initiated as early as the mid-luteal phase, and is clearly visible by day 14 in natural regression and 12 h after induced regression. Apoptosis did appear to be involved in luteolysis in the equine corpus luteum, but non-apoptotic changes were also observed in some luteal cells during regression. Accumulation of lipid was a late feature of luteal regression.

Analysis of Variance↗
PubMed2002

Plasma FSH, inhibin A and inhibin isoforms containing pro- and -alphaC during winter anoestrus, spring transition and the breeding season in mares.

Ten mares were studied from February (winter anoestrus) to their second ovulation in the breeding season to investigate the relationship between resumption of ovarian cyclicity in the spring and circulating concentrations of FSH, inhibin A and inhibin isoforms containing pro- and -alphaC immunoreactivity. An additional four mares were studied during one oestrous cycle. Growth and regression of ovarian follicles were monitored by transrectal ultrasonography. The frequency of blood sampling varied from three times a week to once a day, depending on the follicular activity present. Concentrations of FSH, oestradiol, inhibin A and pro- and -alphaC isoforms were low during deep winter anoestrus when minimal follicular activity was present in the ovaries. During spring transition, an increase in FSH concentration preceded the emergence of each follicular wave. Concentrations of inhibins were significantly higher (P < 0.05) during growth of anovulatory follicles in spring transition than during winter anoestrus. Plasma concentrations of oestradiol and inhibin A were significantly higher (P < 0.001, P < 0.05, respectively) during the growth of preovulatory follicles than during the growth of transitional anovulatory follicles, but concentrations of inhibin pro-alphaC isoforms did not differ between the two types of follicle. During the oestrous cycle, there was a significant inverse relationship (P < 0.001) between concentrations of FSH and the inhibins. Plasma inhibin pro-alphaC isoforms, but not inhibin A, reached a peak on the day of ovulation. The results strongly indicate that FSH regulates growth of spring anovulatory and preovulatory follicles. Inhibins are likely to contribute to negative feedback on the release of FSH from the pituitary gland both during the transitional period and the breeding season in mares.

Analysis of Variance↗
PubMed2002

Characterization of morphology and angiogenesis in follicles of mares during spring transition and the breeding season.

The mare is a seasonal breeder and undergoes a period of ovarian transition in spring between winter anoestrus and cyclicity. During spring transition LH concentrations are low and many mares have successive large anovulatory follicular waves which reach the size of preovulatory follicles. Follicular angiogenesis is essential for growth and health of preovulatory follicles. The aim of the present study was to investigate the morphology and vascularity of transitional anovulatory follicles. On gross inspection, the wall of transitional follicles was visibly less well vascularized than that of preovulatory follicles. Histologically, it could be seen that the theca was only poorly developed in transitional follicles. Immunostaining for factor VIII showed that there were significantly (P < 0.05) fewer blood vessels in the theca of transitional follicles. There was substantially less (P < 0.001) proliferative activity, measured by immunostaining for Ki67, in the endothelial cells and granulosa cells of transitional follicles compared with preovulatory follicles. Preovulatory follicles had a heavy band of immunostaining in the theca for vascular endothelial growth factor (VEGF), whereas staining was sparse in the transitional follicles. It was concluded that the poor vascularity and development of the theca layer in transitional follicles could be related to low circulating LH, and possibly other trophic hormones, and are likely to be the key factors in explaining the steroidogenic incompetence of transitional anovulatory follicles.

Anestrus↗
PubMed2001

The effect of a GnRH antagonist on endocrine and seminal parameters in stallions.

Relatively little is known about endocrine control of reproduction in the stallion, but gonadotropins are thought to be central in regulating spermatogenesis and libido. The ability to effectively antagonise GnRH, and thereby gonadotropins, is therefore important both in further investigations of hormonal control of reproduction in stallions, and for clinical applications. In the present study four pony stallions were treated with a potent GnRH antagonist, Antarelix. Their libido, seminal parameters, and hormonal profiles were compared with those recorded before administration of the antagonist. Plasma concentrations of gonadotropins, testosterone and estradiol decreased by 48 h after antagonist administration, with estradiol and FSH being most consistently suppressed, and remained at reduced concentrations for 4 weeks. Spermatozoal motility, numbers and morphology were not significantly affected by treatment, but increasing numbers of round spermatogenic cells were seen in the ejaculate as the trial progressed. Libido was assessed by the time taken for the stallions to regain an erection in the presence of a mare after ejaculation (refractory period). The refractory period increased significantly after treatment. When the stallions were castrated 8 weeks after antagonist treatment, histological evidence of testicular degeneration was present. We concluded that use of this antagonist showed promise as a valuable research tool in modulating changes in circulating hormone concentrations in stallions. Reversibility of the effects on libido and testicular changes need further investigation.

Animals↗
PubMed2001

Effect of insemination time of frozen semen on incidence of uterine fluid in mares.

Ninety five mares were inseminated with frozen semen either within 12 h before ovulation or within 8 h after ovulation. The effect of preovulatory versus postovulatory insemination (AI) on the subsequent detection of uterine fluid was studied. The overall pregnancy rate was 43% and this was not significantly influenced by preovulatory or postovulatory insemination. When mares were first examined 12 h after AI, 18 of 52 mares (35%) had accumulated uterine fluid. However, when mares were first examined 18 to 24 h after AI, only 6 of 43 mares (14%) had uterine fluid. Presence of intrauterine fluid significantly lowered pregnancy rates. Timing of insemination did not affect incidence of uterine fluid. Serum concentrations of estrogen and progesterone at time of insemination did not influence uterine clearance or pregnancy rates, but both hormones were higher at preovulatory than at postovulatory inseminations. We concluded that there was no evidence that postovulatory inseminations would predispose mares to persistence of uterine fluid after AI.

Animals↗
PubMed2001

Immunohistochemical study of the distribution of adrenergic and peptidergic innervation in the equine uterus and the cervix.

Little is known about neurogenic regulation of uterine contractility in mares. The present study investigated the distribution of adrenergic and peptidergic nerves in the mare uterus. Samples from the uterine horn, body and cervix were collected from 18 cyclic mares for immunohistochemistry. The uterus was well supplied with adrenergic nerves. A large number of tyrosine hydroxylase- and dopamine beta-hydroxylase-immunoreactive nerve bundles and fibres were present in the myometrium and endometrium in all regions of the uterus and cervix. These adrenergic nerve bundles and fibres travelled parallel to the muscle layers and were often associated with blood vessels. The density of peptidergic nerves was less than that of adrenergic nerves, but the pattern of distribution was similar. Neuropeptide Y-immunoreactive nerve fibres were the most abundant, whereas vasoactive intestinal polypeptide- and calcitonin gene-related peptide-immunoreactive nerve fibres were less frequently seen. Substance P-immunoreactive nerve fibres were the most sparse. Peptidergic nerves were distributed among the smooth muscle layers and near endometrial glands and were often associated with blood vessels in all regions of the uterus. The density of peptidergic nerve fibres was similar in the uterine horn and body but was slightly denser in the cervix. These findings indicate that uterine innervation may have an important role in controlling reproductive functions in mares.

Animals↗