Incidence Of Ovulation Research Articles

Delta-9-tetrahydrocannabinol attenuates luteinizing hormone release induced by electrochemical stimulation of the medial preoptic area.

Despite diverse pharmacological actions, drugs commonly used for blocking ovulation in the rat have not been observed to exert differential effects on the LH response to preoptic stimulation, thus suggesting blocking action above the final hypothalamic GnRH pathway. To determine if ovulatory blockade by delta-9-tetrahydrocannabinol (THC) is consistent with that scheme, LH surges evoked by preoptic stimulation were contrasted with those elicited during blockade by atropine (ATR), a classic ovulation-blocking agent with which other drugs have been compared. THC (10 mg/kg) or ATR (350 mg/kg) treatment before the proestrous critical period uniformly blocked LH release and ovulation in sham-stimulated rats. Preoptic stimulation evoked LH surges after both drug treatments (p less than 0.001), peak levels increasing with the intensity of stimulation (p less than 0.05). However, both maximum LH concentration (p less than 0.05) and total integrated LH release (p less than 0.01) were lower in THC-blocked rats. Inspection of the oviducts revealed no difference in the incidence of ovulation or the number of ova discharged. The reduced LH response during THC blockade was not attributable to variation in the extent or locus of histologically determined stimulation sites. These results distinguish THC from ATR and, by extension, other blocking drugs that do not overtly affect the LH response to preoptic stimulation. Thus, ovulatory blockade by THC may involve a different mechanism, which likely includes inhibitory action within the preoptic-to-tuberal GnRH pathway.

Ovarian and endocrine responses of Merino ewes to treatment with PMSG and/or FSH-P

An experiment was conducted to investigate the effects of different superovulatory regimes, including pregnant mare serum gonadotrophin (PMSG) and follicle-stimulating hormone (FSH-P) on steroidogenesis, oestrus, ovulation and premature luteal regression in sheep. Thirty mature Merino ewes were treated in the breeding season with intravaginal progestagen pessaries and 1200 IU PMSG (Group 1), 15 mg FSH-P (Group 2) or a combination of 700 IU PMSG and 11 mg FSH-P (PMSG/FSH-P; Group 3) to induce superovulation. After treatment with FSH-P alone, the incidence of oestrus was lower than after treatment with PMSG alone (6/10 vs. 10/10, P < 0.05) and the incidence of ovulation was lower than after treatment including PMSG (7/10 vs. 20/20, P < 0.05). However, there were no differences in the mean time to onset of oestrus (24.7 ± 2.3 h after pessary withdrawal) or the time to onset of ovulation (48–54 h after pessary withdrawal) between the treatment groups. The total ovarian response (corpora lutea + large follicles) was higher ( P < 0.05) following stimulation with PMSG alone (17.1 ± 1.9) than with FSH-P (8.3 ± 12.5). However, the numbers of corpora lutea present on Day 6 (Day 0 = pessary withdrawal) were not affected by the exogenous gonadotrophin treatment (PMSG, 11.4 ± 1.8; FSH-P, 7.2 ± 2.5; PMSG/FSH-P, 11.1 ± 2.1; not significant). The mean pre-ovulatory peripheral plasma peak level of oestradiol-17β (E 2) per follicle was higher following treatment with PMSG than with either of the other two regimes (PMSG, 23.2 ± 0.8 pg ml −1; FSHP, 10.8 ± 0.6 pg ml −1; PMSG/FSH-P, 13.9 ± 0.4 pg ml −1; P < 0.05). Moreover, E 2 peaked earlier in the ewes treated with PMSG than with FSH-P or PMSG/FSH-P (7.6 ± 2.1 h vs. 33.7 ± 1.5 h and 24.8 ± 0.5 h respectively; P < 0.01). There were no differences detected in the peak levels of luteinizing hormone (LH) (8.6 ± 1.1 ng ml −1) or the mean time to LH peak (32 ± 1.4 h) between the ewes treated with the different exogenous gonadotrophins. Three ewes (one treated with PMSG alone and two with PMSG/FSH) had premature luteal regression by Day 6. In each case, a secondary peak of E 2 secretion was observed 36–44 h after pessary withdrawal. These ewes each displayed a second oestrus on Days 5–6 and a mild superovulatory response at this oestrus. It is concluded that in sheep PMSG is highly steroidogenic in comparison with FSH-P. A combination of moderate doses of PMSG and FSH-P is a suitable superovulation regime for Merino ewes as it induces a consistently high superovulatory response without the secretion of excessive E 2 levels. Perturbation of the periovulatory endocrine events may result in premature luteal regression.

Ovulatory activity in native Thai goats

Ovarian activity was observed in native Thai goats run either alone, continuously with males, or intermittently with males at 56-day intervals between June 1985 and July 1986. Overall, the incidence of ovulation was highest in October and December (78.8%) and lowest in June (54.3%), with some does ovulating at every observation. The presence of males, either continually or intermittently, significantly increased the proportion of does ovulating throughout the year. The ovulation rate varied throughout the year, with the highest rate occuring in October 1985 (1.9) and the lowest rate in May and July 1986 (1.3). The implications of the study are discussed.

Follicular size at the time of human chorionic gonadotropin administration predicts ovulation outcome in human menopausal gonadotropin-stimulated cycles

The objectives of this study were: (1) to correlate follicle size by transvaginal sonography with ovulation outcome in cycles of controlled ovarian hyperstimulation with human menopausal gonadotropins; (2) to determine if follicular size on the day of human chorionic gonadotropin (hCG) administration predicts the incidence of ovulation; and, if so, (3) to derive a mathematical model that predicts the number of expected ovulations in any given cycle of controlled ovarian hyperstimulation. A retrospective analysis. Forty-nine consecutive patients undergoing 122 cycles of controlled ovarian hyperstimulation were studied in a tertiary care setting. Follicular size and evidence of ovulation were determined sonographically. The main outcome measure was the rate of ovulation per follicle size. The percentages of follicles measuring less than or equal to 14 mm, 15 to 16 mm, 17 to 18 mm, 19 to 20 mm, and greater than 20 mm on the day of hCG administration that subsequently ovulated were 0.5%, 37.4%, 72.5%, 81.2%, and 95.5%, respectively. (1) Follicular size on the day of hCG administration correlates with the incidence of ovulation. (2) The expected number of ovulations in any given controlled ovarian hyperstimulation cycle can be predicted with 95% confidence using the accompanying equation.

Importance of behavioural stimuli in ram-induced ovulation in seasonally anovular Corriedale ewes

Three groups of about 65 seasonally anovular Corriedale ewes were penned and exposed to rams on November 4, 1989. A fourth group ( n=64) was maintained in a 3-ha paddock and also exposed to rams on the same date. The sexual behaviour exhibited by rams in contact with penned ewes was recorded during nine simultaneous observation sessions lasting 2 h each. Five days after ram introduction, incidence of ovulation and ovulation rate were higher ( P < 0.01) in adult than in 1.5-year-old ewes. Among penned adult ewes, a greater ( P < 0.05) incidence of ovulation was recorded in ewes maintained in contact with rams and oestrous ewes (95.8%) than in ewes exposed to either rams with or without recent experience with oestrous ewes (68.7 and 57.1%, respectively). The fourth group, exposed to rams in field conditions, exhibited a lower ( P < 0.05) incidence of ovulation (31.9%) than any other group. No differences among treatments were detected in 1.5-year-old ewes. The incidence of ovulation was associated ( r=0.99, P<0.05) with the sexual behaviour displayed by the rams. It was concluded that the sexual behaviour of the rams plays an important role in ram-induced ovulation and that the continuous presence of oestrous ewes is necessary for the maximum efficacy of the technique in Corriedale ewes.

Response of anovular Corriedale ewes to teasing in spring

Two hundred and forty adult Corriedale ewes were randomly allocated to four experimental groups. Early short (ES) and early long (EL) teased ewes were introduced to adult vasectomized Corriedale rams on September 12. Group EL remained in continuous contact with the rams for the following 25 d while group ES was reisolated after 5 d. Late short (LS) teased ewes were exposed to vasectomized rams during the last 5 d of the experiment while the control group (T) remained continuously isolated from rams. Response of anovular ewes to 5 d of ram contact was quite similar in the early (22.7%) and late (21.8%) teased groups when 11.7 and 8.3% of ewes were spontaneously ovulating. Incidence of ovulation remained fairly constant (around 10%) in group T, declined ( P < 0.0025) in group ES from 35 to 15% and increased ( P < 0.001) in group EL from 28.3 to 60.3%. These trends were associated with differences between groups in maintaining and initiating ovarian activity. Most ovarian activity found in EL ewes after 25 d of ram contact started when the small proportion of ewes responding immediately to the introduction of the males displayed oestrus and were mounted by the rams 17 to 25 d after their introduction.

Pattern of follicular growth and resumption of ovarian activity in post-partum beef suckler cows

The ovaries of 18 post-partum beef suckler cows were examined daily, using ultrasound, from Day 5 post partum until a normal oestrous cycle was completed. Periods of growth and regression of medium-sized (5-9 mm) follicles were identified before one medium follicle became dominant (single large follicle greater than or equal to 10 mm). The mean (+/- s.e.m.) number of days from parturition to detection of the first post-partum dominant follicle was 10.2 +/- 0.5. The first post-partum dominant follicle ovulated in 2/18 (11%) cows. The interval from calving to first ovulation (mean +/- s.e.m. = 35.9 +/- 3.3 days) was characterized by the growth and regression of a variable number (mean = 3.2 +/- 0.2; range 1-6) of dominant follicles. The maximum diameter of the dominant follicle increased as the cows approached first ovulation (P less than 0.05). Behavioural oestrus was not detected in 16/18 (89%) cows at first ovulation. Following first ovulation, the length of the subsequent cycle was short (mean = 9.7 +/- 0.5 days; range 8-15 days) in 14/18 (78%) cows and was characterized by the development and ovulation of a single dominant follicle. During oestrous cycles of normal length (mean = 20.6 +/- 0.5 days; range 18-23 days) one (N = 2), two (N = 7) or three (N = 8) dominant follicles were identified. The growth rate, maximum diameter or persistence of non-ovulatory dominant follicles before first ovulation or during oestrous cycles were not different (P greater than 0.05). These data show that, in beef suckler cows, follicular development and formation of a dominant follicle occur early after parturition and the incidence of ovulation of the first dominant follicle is low. The number of dominant follicles that develop before first ovulation is variable; first ovulation is rarely associated with oestrus and short cycles are common after first ovulation. It is concluded that prolonged anoestrus in post-partum beef suckler cows is due to lack of ovulation of a dominant follicle rather than delayed development of dominant follicles.

Temporal relationship between the onset of oestrus, the preovulatory LH surge and ovulation in farmed fallow deer, Dama dama

A study was conducted to determine the timing of ovulation relative to the onset of oestrus and the preovulatory LH surge in fallow deer. Mature fallow does were randomly allocated to two treatments (N = 10 per treatment) designed to synchronize oestrus on or about 17 May. Does assigned to Group 1 (prostaglandin-induced oestrus) each initially received single intravaginal CIDR [Controlled Internal Drug Release] devices for 13 days followed by an i.m. injection of 750 mg cloprostenol on Day 12 (15 May) of the subsequent luteal cycle. Does assigned to Group 2 (progesterone-induced oestrus) each received CIDR devices for 13 days, with withdrawal occurring on 15 May. All does were run with crayon-harnessed bucks (10:1 ratio) from the start of synchronization (18:00 h 15 May). Ten does (5 per group) were blood sampled via indwelling jugular cannulae every 2 h for 72 h from cloprostenol injection or CIDR device withdrawal and the plasma was analysed for concentrations of progesterone and LH by radioimmunoassay. Does within each treatment were randomly allocated to an ovarian examination time of 12, 16, 20 or 24 h after the onset of oestrus. Laparoscopy was repeated at 12-h intervals until ovulation was recorded. The ovaries of does failing to exhibit oestrus were examined 72 and 86 h after cloprostenol injection or CIDR device withdrawal. A total of 17 does were observed to exhibit oestrus at a mean (+/- s.e.m.) interval from treatment of 44.6 +/- 3.6 h for Group 1 (N = 9) and 34.1 +/- 2.5 h for Group 2 (N = 8).(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive performance of Coopworth ewes following oral doses of zearalenone before and after mating

The reproductive performance of Coopworth ewes after administration of zearalenone was determined in two trials. In Trial I, zearalenone was administered to groups of 33 ewes at rates of 0, 1.5, 3.0, 6.0, 12.0 and 24.0 mg/ewe/day for 10 days, starting on Day 7 of the oestrous cycle before mating. There was a linear decline (P less than 0.001) in ovulation rate with dose of zearalenone; also cycle length decreased and duration of oestrous increased with increasing dose levels. Reductions in the incidence of ovulation and in fertilization were seen only at doses of 12 and 24 mg. In Trial 2, groups of 50 ewes were given the same range of doses of zearalenone for 10 days, starting 5 days after mating to entire rams. There was no effect of zearalenone treatment after mating on pregnancy rate or embryonic loss. These results indicate that the effects of zearalenone, administered orally, on ewe reproduction, at the dose levels examined, were restricted to ewes exposed before mating. Intakes of zearalenone of 3 mg/ewe/day or more during this period would be reflected as depressed ovulation rates and lower lambing percentages.

The Abnormal Response of Polycystic Ovarian Disease Patients to Exogenous Pulsatile Gonadotropin-Releasing Hormone: Characterization and Management*

Pulsatile GnRH administration for induction of ovulation is often ineffective in polycystic ovarian disease (PCOD) patients. To clarify and correct the endocrine mechanisms underlying this deranged response we gave pulsatile GnRH (5 micrograms, iv, every 60 min) to idiopathic hypogonadotropic hypogonadism (IHH) patients with primary amenorrhea for 19 cycles and to PCOD patients for 24 cycles before (pre-A) and for 25 cycles after (post-A) GnRH analog suppression. Compared to IHH, pre-A cycles were characterized by elevated LH, estradiol, and testosterone; reduced luteal phase progesterone; and low ovulatory (38%) and pregnancy rates (8%). Conversely, LH, estradiol, and follicular phase testosterone levels were lower in post-A than in pre-A cycles, while luteal phase progesterone was higher; the endocrine pattern of post-A cycles closely resembled the one of IHH cycles. The ovulatory and pregnancy rates of PCOD patients improved remarkably in post-A cycles (90% and 38%, respectively). Excessive body weight was associated with a lower incidence of ovulation in both pre-A (15%) and post-A cycles (75%). A worse endocrine pattern and a lower ovulatory rate (50%) were obtained when a second consecutive post-A cycle occurred without repeating GnRH analog suppression. No signs of even mild ovarian hyperstimulation and no multiple pregnancies were recorded in the post-A cycles. We conclude that in PCOD 1) deranged pituitary sensitivity, excessive ovarian androgen secretion, and obesity critically affect folliculogenesis and ovulation; 2) pituitary-gonadal suppression with a GnRH analog markedly improves the endocrine and clinical responses to pulsatile GnRH ovulation induction; 3) optimal results can be achieved only when each pulsatile GnRH cycle is preceded by GnRH analog suppression; and 4) pulsatile GnRH is highly effective and safe for ovulation induction, provided that PCOD subjects are pretreated with a GnRH analog.

Ovarian cyclicity and serum progesterone and luteinizing hormone in fine-wool ewes supplemented with alfalfa or pinto beans

Effects of season and supplementation on the incidence and rate of ovulation and hormone profiles in multiparous, nonlactating ewes were investigated under range and drylot conditions during anestrus (February through August). Ninety ewes received one of six nutritional treatments: 1) range forage, 2) range forage plus 0.33 kg·hd −1·d −1 pinto beans, 3) 0.45 kg·hd −1·d −1 alfalfa pellets, 4) dry lot plus 1.33 kg·hd −1·d −1 prairie hay only, 5) pinto beans or 6) alfalfa pellets at rates used on the range and prairie hay. Supplemented ewes were heavier (P < 0.05) than ewes fed range forage or prairie hay during most of the study. Seasonality of ovulation, in terms of incidence and rate, was not affected (P > 0.40) by supplementation in range ewes. The ovulation rate tended to be highest in prairie hay plus pinto bean drylot ewes in February (P = 0.21) and in prairie hay plus alfalfa pellet and prairie hay plus pinto bean ewes in March (P = 0.13) compared with prairie hay ewes. Generally, seasonality of ovulation was not influenced by supplementation (P > 0.40). The incidence of ovulation approached zero for drylot ewes in April, May, June and July, while it was 43, 27, 35 and 21% for range ewes, in those same months. Supplementation did not affect serum progesterone during the estrous cycle. Luteinizing hormone (LH) concentrations were similar (P > 0.50) among drylot treatment groups before a 50-ug gonadotropin releasing hormone (GnRH) challenge. Pinto bean supplementation enhanced serum LH response to GnRH (P < 0.10).

HCG-induced ovulation in two rabbit breeds: Effects of dose, season and sexual behaviour

This study demonstrates that human gonadotrophin hormone (hCG), induces a high incidence of ovulation in rabbits and that the number of ova shed is comparable to that in naturally-mated controls. Both strains studied (A1066 of California origin; A1077 of New-Zealand origin) respond similarly to hCG and the difference in the number of oocytes ovulated is the same as when mated naturally: the does of the California strain produce on the average 2 ova more than the New Zealand does. This method may be suitable for testing the ovulating ability of any new strains at an early age. HCG has been observed to be active in all seasons and whatever the sexual behaviour (lordosis or not). This suggests that lack of ovulation following natural mating in non-receptive does may be caused by a lack of discharge of LH (with, perhaps, added seasonal effects) rather than to a lack of mature follicles in the ovary. HCG induced a number of ovulations that were not related to the female's sexual behaviour. The receptive does had only an average of 0.6 ova (not significant) more than the non-receptive ones. The hCG optimal doses are about 10 IU for California does and 25 IU for New Zealand does of 20 weeks old.

Year and season effects on oestrus and ovarian activity in ewes of different breeds and crosses

The dates of onset and cessation of ovulation and oestrus and the duration of the ovulatory, oestrous, anovulatory and anoestrous seasons were determined for Suffolk, Rambouillet, Dorset, Finnish Landrace and reciprocal F 1 crosses between the last three breeds in a study which extended over 3 years. Ovulation rate, duration of oestrus and cycle length were also examined. Among the purebreds the major source of variation in these traits could be attributed to differences between the Rambouillet and the remaining breeds. Rambouillet ewes commenced and ceased ovarian and oestrous activity earlier than the Finn; first ovulation also occurred earlier in the Rambouillet than in the Suffolk and the duration of ovarian activity was longer for the Rambouillet than for either of these breeds. The oestrous season was 27 days shorter for the Rambouillet than for the Dorset, due to a higher incidence of ovulation without oestrus in the Rambouillet. The anoestrum was between 27 and 65 days longer for the Rambouillet than for any of the other purebreds. The period of anovulation was longest for the Suffolk breed. There was little evidence for heterosis in the duration of the breeding and non-breeding seasons. The repeatability of components of the breeding season was generally low. Ovulation rate increased slightly from early to mid-season and then declined significantly as the breeding season advanced, in all breeds.

Menstrual cycles in rhesus monkeys (Macaca mulatta) are unaffected by a single dose of the anesthetics ketamine and xylazine administered during the midfollicular phase at laparoscopy.

To identify an anesthetic regimen that produces more complete relaxation and analgesia than ketamine hydrochloride (Ketaset®) alone, a combination of ketamine (15 mg/kg body weight) and the hypnotic xylazine (Rompun®, 0.33 mg/kg) was evaluated. Since the desired experimental application required that the anesthetic not interfere with normal hormonal events during the menstrual cycle, this combination administered on day 6 of the cycle was tested to determine whether hormonal surges, incidence of ovulation, or cycle length would be altered relative to the use of ketamine alone. In five of six animals, ketamine plus xylazine had no effect on the occurrence of timely surges of estrogen, luteinizing hormone (LH), or follicle-stimulating hormone (FSH), or on ovulation as determined by the presence of a corpus luteum at laparoscopy and normal serum concentrations of progesterone. There were no significant differences between the cycle during treatment and previous cycles in the same animal for length of the menstrual cycle (26.0 ± 2.3 [5] days; X̄ ± S.D. [n] or luteal phase (13.4 ± 2.4 [5] days). Likewise, these values did not differ from those of ten control monkeys treated with ketumine only on day 5 or 6 of the cycle (incidence of ovulation, 10/10; cycle length, 27.9 ± 1.8 [10]; luteal phase length, 15.1 ± 1.4 [10], P > 0.05). Patterns of circulating progesterone were not altered by the addition of xylazine anesthesia. These findings indicate that xylazine, given in the midfollicular phase, did not alter ovulatory events or menstrual cycle characteristics in rhesus monkeys. Ketamine plus xylazine apparently provides anesthesia appropriate for laparoscopy.

Effect of LH-RH Analogue Treatment on Egg Maturation (Ovulation) in Lake Trout Brood Stock

Abstract Brood-stock females of lake trout (Salvelinus namaycush) were injected with luteinizing hormone-releasing hormone analogue des-Gly10 [D-Ala6]LH-RH-ethylamide (LH-RHa) in an attempt to induce advanced final egg maturation (ovulation). Experimental fish were divided into three groups: 49 control fish received a saline injection; 45 fish received 10 μg LH-RHa/kg body weight; and 46 fish received 20 μg LH-RHa/kg body weight. Fish in all groups received a single intraperitoneal injection. Data obtained 4 d post injection were inconclusive but appeared to indicate that LH-RHa injection was exerting a positive effect on advanced final egg maturation. Data collected on day 8 postinjection confirmed this observation. By this time, only 53% of the saline-injected controls had ovulated, whereas 91 and 98% ovulation had occurred in the 10- and 20-μg LH-RHa/kg groups, respectively. Both LH-RHa treatment groups showed a significantly greater (P < 0.05) incidence of ovulation than the control group.

Reproductive seasonality of the jenney

Reproductive seasonality was studied in 12 jennies in southern Wisconsin for 12 mo. The proportion of jennies ovulating differed (P < 0.05) among months due primarily to a lower proportion ovulating during December (64%) than during the other months (82 to 100%). Of 114 interovulatory intervals, eight were considered prolonged (>35 d) due to persistent corpus luteum (two intervals) and a follicular-related anovulatory period (six intervals). Four of the six follicular-related anovulatory periods were attributed to seasonal effects. The anovulatory season in these four jennies occurred in winter, was relatively short (39 to 72 d), and was terminated by a long period (17 to 41 d) of estrous behavior in the continued presence of large follicles (>20 mm). The prolonged estrus accounted for the lower incidence of ovulations during December and seemed similar to the transition between anovulatory and ovulatory seasons in mares. There was a significant effect of month on length of the interovulatory interval, even after removal of the eight prolonged intervals, due primarily to shorter intervals during May to September (means, 23.0 to 24.3 d) than during October to April (25.0 to 27.3 d). Length of estrus differed significantly among months due primarily to shorter periods during May to October (means, 5.7 to 6.9 d) than during November to April (7.4 to 15.2 d). These results indicated that this species is subjected to seasonal effects on reproductive function. However, contrary to the literature, the dramatic partitioning of the year into ovulatory and anovulatory seasons, as occurs in mares, was absent (eight jennies) or limited (four jennies).

Hormonal dissociation of ovulation and maturation of oocytes: Ovulation of immature amphibian oocytes by prostaglandin

AbstractProstaglandin involvement in ovulation and maturation of amphibian (Rana pipiens) ovarian follicular oocytes was investigated using in vitro‐cultured ovarian follicles. Exposure of follicles to PGF2α during culture stimulated variable but generally low levels of ovulation without concomitant induction of maturation. Addition of PGF2α to cultured follicles markedly enhanced the incidence of ovulation in follicles exposed to progesterone or frog pituitary homogenate (FPH). Onset of the ovulatory process was further accelerated following addition of PGF2α to FPH‐treated follicles. PGE, in contrast to PGF2α, exhibited no stimulatory effects on ovulation and consistently inhibited ovulation induction by FPH and progesterone. Cytological analysis of follicles undergoing ovulation revealed that ovulation of immature oocytes induced by PGF2α varied markedly from that seen following FPH or progesterone stimulation of follicles in vivo or in vitro. Immature oocytes in contrast to maturing oocytes were typically ovlulated with follicle cells still attached to the vitelline membrane. The observations indicate that PGF2α effected follicle rupture and contraction of the follicular epithelium and theca without prior separation of the follicle cells from the oocyte. Selective inhibitors of steroid synthesis (cyanoketone) and protein synthesis (cycloheximide) inhibited FPH‐induced ovulation and maturation. PGF2α reversed the inhibitory effects of cyanoketone and cycloheximide on FPH‐induced ovulation but not maturation of oocytes. Neither prostaglandins alone or in combination with progesterone or FPH induced ovulation of oocytes following removal of the follicular epithelium. Ovulatory effects of PGF2α appear to be mediated through the follicular epithelium. Results indicate that ovulation and maturation of amphibian oocytes can be induced independently of each other by separate classes of hormones. Normal synchronization of ovulation and maturation of oocytes may require the combined action of prostaglandins and steroids acting within different follicular compartments.

Blockade of first ovulation in pubertal rats by delta-9-tetrahydrocannabinol: requirement for advanced treatment due to early initiation of the critical period.

Successful blockade of ovulation in pubertal rats by delta-9-tetrahydrocannabinol (THC) required earlier treatment during proestrus than was required in adults under the same conditions. Only 1 of 8 adult rats ovulated after treatment with THC (10 mg/kg body weight, i.p.) at 1400 h proestrus, whereas 77% of pubertal rats released full sets of ova following similar treatment during proestrus of the first or second vaginal cycle. When treatment of pubertal rats was advanced to 1300 h, only 2 of 10 THC-treated rats exhibited full ovulation, an incidence significantly lower than the 80% ovulation rate observed in vehicle-treated animals (p less than 0.05). To determine whether the requirement for earlier THC treatment in pubertal rats was related specifically to THC or reflected possible age-associated differences in timing of the critical period, the ovulation-blocking efficacy of atropine sulfate (ATR) was tested in pubertal rats for comparison with that of THC. The serum concentrations of luteinizing hormone (LH) during the first proestrus (1200-1900 h) were determined in pubertal rats that remained untreated. The incidence of ovulation in rats treated with ATR (350 mg/kg, s.c.) at 1400 h proestrus was not significantly reduced from that in vehicle-treated rats; however, after ATR treatment at 1300 h, only 2 of 11 animals released full sets of ova whereas all vehicle-treated rats ovulated (p less than 0.025). The mean serum LH concentration in untreated pubertal rats was not significantly increased over baseline at 1300 h proestrus, but was markedly elevated by 1400 h (1009 +/- 375 ng/ml; p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nutritional environment and ram effect on breeding season in range sheep

Effects of season, nutritional environment, and presence of rams on incidence and rate of ovulation in fine-wool sheep in southern New Mexico were investigated over 14 months (February 1983–March 1984). Number of corpora lutea (CL) were observed each month by laparoscopy in random samples from six ewes in each subgroup. Seasonality of ovulation in fine-wool sheep managed on range was much more marked than in animals managed on alfalfa hay in drylot. Incidence of ovulation approached zero in range-managed ewes during May, June, and July (8%, 0%, 4%) but was higher (P<0.05) in the alfalfa-drylot group (42%, 17%, 75%), respectively. Although the incidence remained lower (P<0.05) in August in range-managed than in drylot ewes (50% and 83%, respectively), both groups were ovulating at a high rate during September through January. Incidence of ovulation dropped dramatically both years in the range-managed group in February compared with that of the alfalfa-drylot group (48% and 36% vs 100% and 83%). Mean ovulation rate per ewe ovulating did not differ (P>0.10) between nutrition groups within the 14 months. Body weight was related to CL number during periods of seasonal transition only. Continuous or intermittent presence of a ram had no real effect on either incidence or rate of ovulation during the transitional months. Nutritional environment can affect seasonality of breeding in fine-wool range sheep. This effect may not be consistently modified by presence of rams.

Indomethacin inhibition of ovulation in the cow.

Indomethacin or saline was administered via intramuscular, intrauterine or intraovarian routes to dairy cows, within 24 h after standing oestrus was first observed. The incidence of ovulation was determined at slaughter. All of the saline-treated cows (18/18) ovulated. Ovulation was not blocked after intramuscular injection (0/6) or intrauterine infusion (0/6) of indomethacin. In all cows, ovulation was blocked after intraovarian injection (6/6) of indomethacin. These findings add support to the hypothesis that prostaglandins play an essential role in ovulation in the cow as in many other mammalian species.