22 research outputs found

    Prolactin secretion during the transitional phase and the relationship to onset of reproductive season in Mares

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    The goal of this study was to determine the temporal relationship between changes in equine prolactin secretion and the onset of reproductive function in spring as marked by the first ovulation, and to examine the effect of short-term treatment with the dopamine agonist bromocriptine on prolactin secretion and time of ovulation. Eight anestrous mares were kept under 16L:8D starting on 15 December, and fourteen anestrous mares were kept under natural photoperiod. Seven mares under natural photoperiod and three mares under artificial photoperiod were treated with bromocriptine from 19 February to 3 March (Day 50 to Day 62). Ovarian activity and plasma prolactin concentration were monitored every other day from 6 February (Day 37) until 1 wk after the first ovulation. Mares under artificial photoperiod ovulated earlier than mares under natural photoperiod, at Day 80 ± 8.8 and Day 114 ± 4.8, respectively. Bromocriptine treatment tended to decrease plasma prolactin concentration during treatment but did not affect the day of first ovulation. A significant increase in plasma prolactin concentrations preceded the first ovulation in mares ovulating after 17 April (Day 107), but no change in prolactin secretion was observed in mares ovulating before 4 April (Day 94), suggesting that an increase in prolactin secretion is not a prerequisite for onset of reproductive function in the mare

    Dopaminergic regulation of gonadotrophin secretion in seasonally anoestrous mares

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    We have previously demonstrated that daily administration of the dopamine D2 antagonist, sulpiride, during seasonal anoestrus, effectively advances the mean time of onset of the breeding season in mares. The purpose of this study was to examine the effect of sulpiride administration on pulsatile FSH and LH secretion in seasonally anoestrous mares, follicular development, time of first ovulation and the fertility at the first ovulation. Fourteen anoestrous mares were selected based on progesterone concentrations < 1 ng ml(-1) for 3 weeks and largest follicle diameter < 20 mm. Starting 30 January, eight seasonally anoestrous mares were treated daily with sulpiride until the first ovulation of the year, and six untreated control mares were maintained under the same environmental conditions. Ovarian activity was monitored and plasma samples were collected every other day. On days 1, 11 and 21 of treatment, plasma samples were collected every 15 min for 11 h in six treated and six control mares. Mares were bred during the first oestrus. Mean time of first ovulation was significantly advanced in sulpiride-treated mares compared with control mares. Pregnancy rate 18 days after ovulation was similar between groups. Mean FSH pulse frequency on the first day of treatment and mean plasma FSH concentrations on day 11 of treatment were significantly higher in sulpiride-treated mares compared with control mares. No significant difference was observed between groups for parameters of LH pulsatile secretion. The results of this study suggest that dopamine inhibits FSH pulsatile secretion in seasonally anoestrous mares

    Evidence for opioidergic inhibition of oxytocin release in periparturient mares

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    In the horse mare, the onset of parturition is associated with an increase in oxytocin secretion, and it has been suggested that the onset of parturition may be triggered by endogenous oxytocin release. To test the hypothesis that oxytocin secretion is regulated by endogenous opioids in the periparturient period, we have 1) characterized oxytocin secretion in response to vaginocervical stimulation and 2) determined the effect of naloxone, an opioid antagonist, on oxytocin secretion induced by vaginocervical stimulation in prepartum mares and in postpartum mares at estrus and diestrus. During the last 2 months of pregnancy, the first diestrus and subsequent estrus post partum, a total of 66 vaginocervical stimulations were performed. Mares were pretreated with naloxone (0.5 mg/kg iv) or saline, administered 20 min before vaginocervical stimulation on subsequent days, using a randomized switchback design in which mares served as their own controls. Plasma was collected from 30 min before until 30 min after stimulation and was analyzed for oxytocin concentrations. Vaginocervical stimulation resulted in a significant increase in oxytocin secretion in all mares. Between Days 30 and 20 prepartum, the total amount of oxytocin secreted (calculated as area under the curve for 0 to 10 min after vaginocervical stimulation) was significantly greater in naloxone-treated than in saline-treated mares. From Day 20 prepartum until parturition, the differences between naloxone and saline-treated mares tended to decrease with approaching parturition, and were no longer statistically different. Peak plasma oxytocin concentrations were greater in naloxone-treated mares than in saline-treated mares during the entire prepartum period. During the postpartum period, total amount of oxytocin secreted following vaginocervical stimulation tended to be greater than during the prepartum period, and stimulated oxytocin secretion was significantly greater in naloxone-treated mares than in saline-treated mares. In conclusion these data suggest that endogenous opioids suppress oxytocin secretion pre and post partum. It appears that opioid inhibition is not limited to the prepartum period, tends to decrease gradually towards parturition and is reinstated after foaling

    Histopathology of liver dicrocoeliosis in cattle

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    International audienc

    Histopathology of liver dicrocoeliosis in cattle

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    International audienc

    Effect of progesterone on prostaglandin F2 alpha secretion and outcome of pregnancy during cloprostenol-induced abortion in mares

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    Objectives-To determine the role of progesterone in the regulation of endogenous prostaglandin F-2 alpha (PGF(2 alpha)) secretion during cloprostenol-induced abortion and to investigate use of progestins to prevent prostaglandin-associated abortion. Animals-16 pregnant mares. Procedure-To induce abortion, cloprostenol (250 mu g/d) was administered daily until fetal expulsion or for up to 5 days. In experiment 1, 8 mares, 98 to 153 days' pregnant, received progesterone (300 mg/d) at 24-hour intervals for 5 days, starting 18 hours after the first cloprostenol administration. In experiment 2, 8 mares, 93 to 115 days' pregnant, received altrenogest (44 mg/d) at 24-hour intervals, starting 12 hours after the first cloprostenol administration. Historic control mares, 82 to 102 days' pregnant, received cloprostenol (250 mu g/d) daily until fetal expulsion. Results-in control mares, fetal expulsion occurred after 2 to 3 cloprostenol administrations and was associated with significant increases in PGF(2 alpha) secretion. Abortion did not occur in 5 of 8 progesterone-treated mares and 8 of 8 altrenogest-treated mares, and endogenous PGF(2 alpha) secretion was inhibited, compared with values in aborting mares. Conclusion-Circulating progestogen concentrations may have a role in the outcome of pregnancy during prostaglandin-induced abortion. Altered prostaglandin secretion may be a reflection] of a direct effect of progesterone or may be caused by the abortion process. Clinical Relevance-Progestogens might be useful for prevention of abortion in mares in which pregnancy is at risk owing to diseases that are associated with excess prostaglandin secretion
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