The effect of the intracervical administration of FSH or LH on the levels of hyaluronan, COX2, and COX2 mRNA in the cervix of the nonpregnant ewe.

During the periovulatory period, the cervix relaxes in response to changes in circulating concentrations of reproductive hormones. The present study investigated the role of gonadotrophins in cervical function by examining the expression of cyclooxygenase-2 (COX2) and COX2 mRNA and the concentration of hyaluronan (HA) in the cervix, after intracervical treatment with either FSH or LH. Eighteen ewes were assigned to four groups.

The "Ram Effect": A "Non-Classical" Mechanism for Inducing LH Surges in Sheep.

During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the "ram effect" in ewes that had a "precocious" LH surge (starting within 6 hours), a "normal" surge (between 6 and 28h) and "late» surge (not detected by 56h).

Insulin signalling and glucose transport in the ovary and ovarian function during the ovarian cycle.

Data derived principally from peripheral tissues (fat, muscle and liver) show that insulin signals via diverse interconnecting intracellular pathways and that some of the major intersecting points (known as critical nodes) are the IRSs (insulin receptor substrates), PI3K (phosphoinositide kinase)/Akt and MAPK (mitogen-activated protein kinase). Most of these insulin pathways are probably also active in the ovary and their ability to interact with each other and also with follicle-stimulating hormone (FSH) and luteinizing hormone (LH) signalling pathways enables insulin to exert direct modulating influences on ovarian function. The present paper reviews the intracellular actions of insulin and the uptake of glucose by ovarian tissues (granulosa, theca and oocyte) during the oestrous/menstrual cycle of some rodent, primate and ruminant species.

The "ram effect": new insights into neural modulation of the gonadotropic axis by male odors and socio-sexual interactions.

Reproduction in mammals is controlled by the hypothalamo-pituitary-gonadal (HPG) axis under the influence of external and internal factors such as photoperiod, stress, nutrition, and social interactions. Sheep are seasonal breeders and stop mating when day length is increasing (anestrus). However, interactions with a sexually active ram during this period can override the steroid negative feedback responsible for the anoestrus state, stimulate luteinizing hormone (LH) secretion and eventually reinstate cyclicity.

Plasma and ovarian oestradiol and the variability in the LH surge induced in ewes by the ram effect.

The proportion of anoestrous ewes ovulating after exposure to a sexually active ram is variable mainly due to whether an LH surge is induced. The aim of this study was to determine the role of oestradiol (E2) in the ram-induced LH surge. In one study, we measured the plasma concentrations of E2 in ewes of different breeds before and after the 'ram effect' and related these patterns to the presence and latency of the LH surge, while another compared ovarian responses with the 'ram effect' following exposure to rams for 2 or 12 h.

The effects of intravenous, glucose versus saline on ovarian follicles and their levels of some mediators of insulin signalling.

Background: A short-term increase in food intake and specifically dietary energy can stimulate folliculogenesis and increase ovulation rate in ewes. The mechanism appears to involve the insulin-glucose metabolic system and its interaction with FSH signalling pathways in the granulosa cells of ovarian follicles. This experiment was designed to investigate the interaction between these two systems in the granulosa cells of ovarian follicles.

The interaction between photoperiod and nutrition and its effects on seasonal rhythms of reproduction in the ewe.

In sheep, the seasonal patterns of reproductive activity are driven primarily by the annual photoperiodic cycle, but can also respond to other environmental factors, such as nutrition, yet little is known about the mechanisms underlying this interaction. This study was designed to define the interaction between photoperiodic and nutritional cues on seasonal patterns of ovarian activity, and to determine if there is a central interaction between these cues. Groups of Ile-de-France ewes were maintained in two nutritional states (restricted and well fed) under a simulated annual photoperiod of 8-16 h of light per day over two breeding seasons.

The infusion of glucose in ewes during the luteal phase increases the number of follicles but reduces oestradiol production and some correlates of metabolic function in the large follicles.

Short-term nutritional supplementation stimulates folliculogenesis in ewes probably by insulin-mediated actions of glucose in the follicle. The aim of this study was to determine the effect of glucose on follicle number and granulosa levels of Aromatase P450 and phosphorylated Akt and AMPK. Twelve Ile-de-France ewes were allocated to two groups; one (n=7) infused with saline and the other (n=5) with glucose (10mM/h) for 72h in the luteal phase.

The effect of an intracerebroventricular injection of metformin or AICAR on the plasma concentrations of melatonin in the ewe: potential involvement of AMPK?

Background: It is now widely accepted that AMP-activated protein kinase (AMPK) is a critical regulator of energy homeostasis. Recently, it has been shown to regulate circadian clocks. In seasonal breeding species such as sheep, the circadian clock controls the secretion of an endogenous rhythm of melatonin and, as a consequence, is probably involved in the generation of seasonal rhythms of reproduction.

An analysis of the relationship between plasma urea and ammonia concentration in dairy cattle fed a consistent diet over a 100-day period.

Measurement of plasma urea concentration is often used to identify a risk of dietary nitrogen-associated infertility. However, the use of plasma urea concentration in this way relies on it being an effective predictor for other potential toxic products associated with nitrogen metabolism (such as plasma or uterine ammonia). Recent research has shown that dietary nitrogen-associated infertility can be produced by diets which elevate plasma ammonia concentration without markedly increasing plasma urea concentration.

The effects of the prostaglandin E analogue Misoprostol and follicle-stimulating hormone on cervical penetrability in ewes during the peri-ovulatory period.

Two experiments in parous Welsh Mountain ewes determined the pattern of natural cervical relaxation over the peri-ovulatory period and investigated FSH and Misoprostol as cervical relaxants to facilitate transcervical passage of an insemination pipette into the uterine cavity. Following synchronisation of oestrus using progestagen sponges and PMSG (500 IU) the depth of cervical penetration was determined using a modified cattle insemination pipette as a measuring device. Penetration of the cervix was least at the time of sponge removal and increased to a maximum at 72 h after sponge removal and then declined.

The expression of prostaglandin endoperoxide synthase 2 messenger RNA and the proportion of smooth muscle and collagen in the sheep cervix during the estrous cycle.

The use of transcervical artificial insemination in sheep is limited because of the anatomy of the cervix, which restricts the passage of an inseminating pipette into the uterine lumen. There is a degree of natural cervical relaxation at estrus that enables greater penetration with an inseminating pipette. We hypothesize that this relaxation may be regulated by cervical prostaglandin synthesis and remodeling of the cervical extracellular matrix.

Long-term suppression of reproductive function by a single dose of gonadotropin-releasing hormone antagonists in a sheep model.

Objective: To determine the effect of single long-acting doses of GnRH antagonists on reproductive function in a sheep model.

Design: Observational, model study.

Setting: University-affiliated research unit.

A review of the effects of supplementary nutrition in the ewe on the concentrations of reproductive and metabolic hormones and the mechanisms that regulate folliculogenesis and ovulation rate.

This paper discusses the phenomenon of nutritional flushing in ewes whereby increased nutrition stimulates folliculogenesis and ovulation rate. In addition the paper reviews recent findings on the effects of increased levels of nutrition on the blood concentrations of reproductive and metabolic hormones in the ewe and some of the intraovarian changes that take place in response to nutritional stimulation. Finally, in the paper, we propose a model of the physiological mechanism for the nutritional stimulation of folliculogenesis and we review how closely the model fits recent published and unpublished evidence examining the mechanism of flushing.

The anatomy of the sheep cervix and its influence on the transcervical passage of an inseminating pipette into the uterine lumen.

The anatomy of the sheep cervix is highly variable between animals and may explain the differing success of transcervical AI between individuals. This study aims to quantify the variation in cervical morphology between ewes and investigate the relationship between cervical anatomy and cervical penetration. Two series of reproductive tracts were collected.

Glucose-stimulated insulin response in pregnant sheep following acute suppression of plasma non-esterified fatty acid concentrations.

Background: Elevated non-esterified fatty acids (NEFA) concentrations in non-pregnant animals have been reported to decrease pancreatic responsiveness. As ovine gestation advances, maternal insulin concentrations fall and NEFA concentrations increase. Experiments were designed to examine if the pregnancy-associated rise in NEFA concentration is associated with a reduced pancreatic sensitivity to glucose in vivo.

Heat stress and seasonal effects on reproduction in the dairy cow--a review.

In dairy cows inseminated during the hot months of the year, there is a decrease in fertility. Different factors contribute to this situation; the most important are a consequence of increased temperature and humidity that result in a decreased expression of overt estrus and a reduction in appetite and dry matter intake. Heat stress reduces the degree of dominance of the selected follicle and this can be seen as reduced steroidogenic capacity of its theca and granulosa cells and a fall in blood estradiol concentrations.