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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. The present study investigated the changes in prostaglandin endoperoxide synthase 2 (PTGS2) mRNA expression and the proportion of smooth muscle and collagen in the sheep cervix during the estrous cycle. Sheep cervices were collected at four stages of the estrous cycle: prior to the LH surge, during the LH surge, after the LH surge, and during the luteal phase. The expression of cervical PTGS2mRNA was determined by in situ hybridization, and the proportion of smooth muscle and collagen in the cervix was investigated by Masson trichrome staining. The expression of PTGS2mRNA in the sheep cervix was greatest prior to the LH surge, when estradiol concentrations were also greatest. The increase in PTGS2mRNA expression was associated with an increase in the proportion of collagen in the sheep cervix. We propose that prior to the LH surge, estradiol may stimulate PTGS2mRNA expression and hence prostaglandin E2synthesis in the sheep cervix to regulate cervical relaxation, most likely through the rearrangement of collagen bundles within the cervical extracellular matrix.

Based upon very large differences in the steroid content of blood obtained by concurrent cannulations of both ovarian veins, Shaikh and Harper (1972) have implied that one member of a pair may act predominantly as the steroid-secreting ovary. To test this hypothesis, estradiol, testosterone, and progesterone were measured by radioimmunoassay in the ovarian venous plasma of six rabbits in which right and left ovarian veins were cannulated concurrently and in eight others in which right and left ovarian veins were cannulated successively. The duration of blood collections ranged from 5 to 20 min/ovary and the resultant calculated amounts of whole blood obtained/ovary/h ranged between 54 and 252 ml. In most cases, paired ovaries secreted comparable amounts of steroid. Relative to steroid concentration, the highest ratios obtained between right and left ovarian veins were 1.0–3.0 for estradiol, 1.0–1.6 for testosterone, and 1.0–1.8 for progesterone. The highest ratios of secretion rate/ovary/h ranged from 1.0 to 3.0 for estradiol, 1.0 to 1.4 for testosterone, and 1.0 to 1.5 for progesterone. These results are in sharp contrast to those reported by Shaikh and Harper and fail to support their hypothesis of marked differential secretion rates by the two ovaries.

This experiment was designed to examine gonadotropin requirements for the induction and maintenance of persistent ovarian follicles in sheep. At the time of prostaglandin (PG) treatment on the tenth day of an induced estrous cycle, 8 ewes (with one ovary autotransplanted to the neck) received an injection of a GnRH antagonist ([Ac-d-Nal1, d-4-C-1-Phe2, d-Trp3, d-Arg6, d-Ala10] GnRH.HOAc; 50 μg/kg s.c.), and continuous hourly injections of exogenous ovine LH (equivalent to 1.25 μg NIH-oLH-S26) began simultaneously with this first antagonist injection (time zero). Antagonist was given three times at 3-day intervals. On Day 6, LH injections were stopped in 4 ewes (group 2) but continued in 4 other ewes (group 1) until the end of the 10-day experiment. Ovarian vein blood was sampled daily every 15 min for a 2-h period around two injections of exogenous LH (this sampling included group 2 after Day 6). Additional jugular and ovarian vein blood samples were collected every 8 h throughout the experiment.Daily ultrasound examination revealed the presence of at least one large follicle (range 4- to 7.5-mm diameter) from Day 3 to Day 10 in all ewes, but no new growing follicles (> 2 mm) were detected for at least 6 days. After Day 2, secretion of estradiol was positively correlated with that of inhibin (r= 0.83, p< 0.001), whereas FSH concentrations were inversely related to inhibin (r= -0.71, p< 0.001) and estradiol (r= -0.81, p< 0.001). In the absence of an LH surge, estradiol and androstenedione secretion (range 5–20 ng steroid/min) was maintained from Day 1 to Day 8 in group 1; but in group 2, secretion decreased abruptly when the LH injections stopped. Thus, continued low-amplitude, high-frequency LH pulses were required to maintain estradiol secretion when concentrations of FSH were < 0.5 ng/ml. However, estradiol and androstenedione secretion decreased (and FSH concentrations increased) between Days 8 and 10 in the ewes that received continued LH injections (group 1), showing that atresia in estrogenic follicles was not due to a lack of gonadotropin availability but to changes within the follicle.For the first 3 days after administration of PG, androstenedione secretion was greater than that of estradiol (p< 0.05), but from Day 4 to 6 the secretion rates were similar (p< 0.1), suggesting that aromatase may be limiting in the first 3 days whereas provision of androstenedione precursors was altered as the follicle persisted. In group 2 on Days 7 and 8 when hourly LH injections had stopped, neither androstenedione nor estradiol secretion increased after one test injection of LH; in contrast, androstenedione but not estradiol secretion increased after a second LH test injection 1 h later, suggesting that secretion of androstenedione is controlled by repeated exposure to LH.In conclusion, persistent estrogenic follicles were produced in the follicular phase in sheep by treatment with a combination of GnRH antagonist and hourly pulses of LH. Secretion of estradiol was dependent on continued hourly LH pulses of approximately 1 ng/ml and the follicles remained estrogenic for 8 days, after which time the ability to secrete estradiol and androstenedione declined even with continued LH injections.

Three groups of intact hinds (n = 10–18) and one group of ovariectomized hinds were treated with progesterone by mean of Controlled Internal Drug Releasing (CIDR) devices for 13 days (device removal = Day 0). Group 1 served as controls; group 2 received injections of 4 mg recombinant bovine interferon- α1l twice daily from Days 13 to 21; group 3 was run with a stag from Days 0 to 3, and all hinds were subsequently diagnosed pregnant; group 4 (ovariectomized) was treated with CIDR devices and estradiol to mimic steroid secretion during the estrous cycle. Progesterone profiles were determined from thrice-weekly plasma samples from Days -13 to 28. Rectal temperature was measured in a subset of groups 1 and 2 from Days 9 to 21. Oxytocin-induced prostaglandin F2αrelease was measured in a subset of groups 1, 2, and 4 on Days 2, 4, 10, 16, and 18.Data are presented as means ± SEM. Exogenous interferon delayed luteolysis ( 28 vs. 21.2 ± 0.55 days, p< 0.0005) and induced transient pyrexia after the first injection (39.89 ± 0.11 vs. 38.88 ± 0.19°C, p< 0.0005). Incidence of oxytocin-induced PGF2. release in control hinds was greater on Days 2 and 18 than on Days 4 and 10 (8/8 and 7/8 vs. 3/8 and 0/8, respectively; p< 0.05) and was greater in control than in interferontreated hinds on Days 16 and 18 (5/8 and 7/8 vs. 1/8 and 1/8, respectively; p< 0.05). Profiles of plasma progesterone concentration and oxytocin sensitivity in steroid-treated ovariectomized hinds did not differ from those in control hinds. These results suggest that steroid-controlled uterine oxytocin sensitivity is important in luteolysis and is suppressed by the administration of interferon, the putative embryonic pregnancy recognition signal in red deer.

A radioimmunoassay for ovine LH is described in which the plasma values are lower than those reported in most other radioimmunoassay studies. Simultaneous measurements of estrogen and LH in the ovarian venous effluent of sheep were performed by radioimmunoassay. Levels of both hormones were elevated during the follicular phase. The first rise in estrogen levels was detected 1 day before the LH rise. The measurement of LH in the peripheral and ovarian venous blood collected from the same sheep at the same time (± 5 min) indicated no significant lowering of LH in the ovarian venous effluent when compared to jugular levels.

Insheep, 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. At the end of the first breeding season, half of the animals of each group were ovariectomized (OVX) and fitted subcutaneously with estradiol implants. Low nutritional status shortened the season of ovarian activity, determined from the pattern of progesterone concentrations, by modifying the timing of seasonal transitions between periods of ovarian activity and anestrus. The same results were observed for the seasonal rhythm of neuroendocrine activity, assessed in the OVX ewes, from the pattern of luteinizing hormone concentrations. These results were then confirmed for neuroendocrine activity induced by a photoperiodic treatment. We conclude that nutrition centrally modulates the interpretation of photoperiod to affect seasonal reproductive transitions. The mechanisms of this interaction are discussed in the paper.