Preovulatory LH Discharge Research Articles

Onset of oestrus and periovulatory events in sheep exposed to 5 and 14 days of CIDR treatment with and without eCG

The present study supports that 5-day short-term CIDR treatments without administration of eCG are equally effective for inducing oestrus behaviour, preovulatory LH discharge and ovulation in sheep than classical protocols based on 14-day treatments plus eCG at CIDR withdrawal. However, the implementation of a 5-day protocol without eCG for fixed-time artificial insemination would be adapted to a later timing of ovulation (p<.05).

Onset of estrus and preovulatory LH surge and ovulatory efficiency in sheep after short-term treatments with progestagen-sponges and progesterone-CIDRs.

The present study supports that short-term (7-days) protocols based on progestagen-impregnated sponges and progesterone-loaded CIDRs are equally effective to induce ovulatory response in sheep. There were no significant differences in the onset of estrus behavior (32.0±6.0 and 33.8±4.0hr after device withdrawal for sponges and CIDRs, respectively; p>0.05) and preovulatory LH discharge (5.1±2.1 and 5.8±3.3hr after onset of estrus behavior for sponges and CIDRs, respectively; p>0.05). These features are similar to previously described for classical long-term (12-14days) treatments. Hence, short-term CIDR-based protocols may be implemented using the same time-intervals for insemination than sponge-based and long-term protocols.

The influence of azaperone treatment at weaning on reproductive function in sows: ovarian activity and endocrine profiles during the weaning-to-ovulation interval

Azaperone can reduce stress caused by weaning and relocation of breeding sows, but its effects on reproductive processes are still poorly understood. The primary aim of this study was to describe and compare the endocrine and ovarian activity in ultrasonographically monitored second parity sows, with or without azaperone treatment at weaning (2 mg/kg BW i.m.). The intervals from weaning to the onset of estrus and ovulation were both greater (P<0.05) in azaperone-treated (n=12) than in control sows (n=12) by ~12 h. Mean daily growth rates of identified antral follicles were less (P<0.05) in azaperone-treated than in control sows (1.08±0.17 v.1.23±0.18 mm/day; mean±SD) and treated animals exceeded (P<0.05) controls in the mean ovulation rate (13.7±1.3 v. 12.6±1.2). A transient suppression of cortisol release was observed in the treatment group (at 10 and 30 min after azaperone injections) but circulating cortisol concentrations were variable in both groups of sows for the remainder of the study. The preovulatory rise in LH and estradiol secretion was delayed (P<0.05), and the duration of the LH surge was greater (P<0.001) in azaperone-treated sows compared with their control counterparts. The amplitude of episodic fluctuations in serum cortisol concentrations was correlated with the number of stillborn piglets in control sows (r=0.63, P=0.04). The amplitude and concentration of the preovulatory rise in estradiol secretion were negatively correlated with ovulatory response and litter size (r=−0.63 to −0.82, P<0.05), whereas the time at which the LH surge ended was directly related to the number of live-born piglets (r=0.82, P=0.002) in azaperone-treated animals. The present results indicate that administration of azaperone at weaning had a profound effect on preovulatory LH secretion as well as growth kinetics and estrogenicity of ovarian antral follicles. However, the causative associations among various characteristics of the preovulatory LH discharge, ovarian and adrenal steroid secretion post-weaning, and reproductive variables in sows remain equivocal.

Induction of superovulation in cyclic heifers: The inhibitory effect of large doses of PMSG

In two different experiments, superovulation was attempted with a PMSG-PG treatment; a bovine anti-PMSG serum was injected at estrus. After 2500, 5000 and 7500 IU of PMSG injected during the luteal phase, the mean ovulation rates were respectively 16.2 ± 7.7, 3.2 ± 2.1, and 1.4 ± 0.6 in the first experiment (17 heifers) and 18.3 ± 12.6, 8.5 ± 8.2, and 2.2 ± 2.3 in the second (19 heifers). The estradiol-17β and progesterone patterns and the observations of the ovaries on the day of estrus (Day 0) by ultrasonic echography and on Day 8 by endoscopy show that the ovaries were highly stimulated and suggest that the inhibition observed with the largest doses reflects the absence of the preovulatory LH discharge or its effect.

Reversal of beta-endorphin-induced blockade of ovulation and luteinizing hormone surge with prostaglandin E2.

We examined the effects of intraventricular (Ivt) administration of beta-endorphin (beta E) on preovulatory LH release, ovulation, and the mechanism that may be involved in opioid action. Female rats were implanted with permanent cannulae in the third ventricle of the brain and were allowed to recover 4-day estrous cyclicity. Intrajugular cannulae were placed on the morning of proestrus. Thereafter, they received Ivt either saline (2 microliter) or beta E (10 micrograms/2 microliter) at 1300, 1430, and 1600 h. In addition, at 1600, 1700, and 1800 h, they were injected Ivt with either vehicle (cerebrospinal fluid or saline) or one of the following compounds: epinephrine (15.3 micrograms), norepinephrine (15.3 micrograms), or prostaglandin E2 (6 micrograms). Blood samples for LH measurements were taken 0, 10, 30, and 60 min after the additional injections at 1600 and 1700 h. beta E blocked the preovulatory LH surge and ovulation. Administration of the opiate receptor antagonist naloxone (2 mg/kg) reversed these effects. Epinephrine stimulated a small discharge of LH only after a second E injection in the beta E-treated rats, but this was insufficient to restore ovulation. On the other hand, prostaglandin E2 reversed the beta E blockade of the LH surge and ovulation. These studies suggest that beta E blocks ovulation and the LH surge primarily by suppressing either the influx or adrenergic expression of the spontaneous neurogenic stimuli responsible for the preovulatory LH discharge and not by evoking a general decrease in the secretory response of the LHRH neurons.

Inhibitory influence of the nuclei of the posterior hypothalamus on the pro-oestrous surge of LH.

The effect of transecting caudal afferents to the medial basal hypothalamus on the pro-oestrous surge of LH was studied in cyclic female rats. Rats with transverse cuts placed just in front of the mammillary bodies and caudal to the ventromedial hypothalamic nucleus showed an earlier time of onset of pro-oestrous surge of LH. Conversely, rats with transverse cuts placed 2 mm more caudally or with cuts along the lateral edges of the hypothalamus showed no altered release of LH. Advanced release of LH occurred also in rats in which the ventral premammillary nuclei or the posterior hypothalamic nuclei were bilaterally destroyed but not in those sham operated or with lesions in the dorsal premammillary nuclei. The number of ova ovulated was higher in rats bearing lesions of any of these nuclei but enhanced LH release was seen only in animals with lesions of the posterior hypothalamic nuclei. Electrochemical stimulation (anodic d.c., 100 microA, 15 s) applied at noon of pro-oestrus to the ventral premammillary nucleus, dorsal premammillary nucleus or posterior hypothalamic nucleus prevented ovulation and the preovulatory discharge of LH. It is concluded that inputs from nuclei of the posterior hypothalamus are inhibitory for LH release and could participate in determining the timing and magnitude of the pro-oestrous surge of the hormone.

Action of PMSG on follicular populations in the heifer.

The short-term action of PMSG on the population of growing follicles in cattle was studied using histological methods. On Day 7 of a synchronized oestrous cycle 10 Friesian heifers were unilaterally ovariectomized. The remaining ovary was immediately stimulated by an injection of PMSG (2000 i.u.) and was removed 48 h after the preovulatory discharge of LH. Control animals did not receive any injection of PMSG. In all ovaries, follicles greater than 70 micron diameter were counted, measured and checked for atresia. The mitotic index in granulosa cells of follicles of different sizes was estimated in both ovaries of all the PMSG-injected animals. Unilateral ovariectomy alone had no significant effect on follicular populations. In the interval between PMSG injection and removal of the second ovary (148 +/- 22.7 h), PMSG significantly increased the number of normal preantral follicles but did not change the number of normal antral follicles. The mitotic index doubled in preantral and early antral follicles but remained unchanged in large antral follicles. PMSG stimulated slightly the growth of the antrum in large antral follicles but did not stimulate its formation in preantral follicles. The incidence of atresia among antral follicles, particularly the largest ones (diam. greater than 1.7 mm), was significantly reduced after PMSG, suggesting some 'rescue' of follicles from atresia.

Effects of progestagen treatments and PMSG on the induction of the preovulatory LH discharge in ewes

The characteristics of the induced preovulatory LH discharge were compared in ewes after treatment for 12 days with intravaginal sponge pessaries impregnated with 40 mg Fluorogestone Acetate or with subcutaneous ear implants containing varying quantities of Norgestomet. In Experiment 1, ewes were treated with intravaginal sponges or implants alone. In Experiment 2, ewes received similar treatments and 500 IU pregnant mares' serum gonadotropin (PMSG) i.m. at the time of sponge or implant removal. The duration of the LH discharge and an estimate of the total LH discharged were similar among treatment groups within the same experiment. Overall, the onset of LH release occurred approximately 8 h earlier in ewes treated with implants, whether or not PMSG was used. Use of PMSG, in conjunction with implant or sponge treatments, shortened the mean interval from sponge or implant removal to the onset of LH release from 41 to 28 h and doubled the estimated total LH discharged, compared with treatments using sponges or implants alone.

Anomalies in ovarian function of peulh ewes

The ovarian activity of 8 Niger Peulh ewes was followed for 2 1 2 years by assaying the levels of progesterone in blood plasma sampled daily and by endoscopic observation. Although the ewes did not experience seasonal anestrus, their cycles were not regular. Most animals had persistent corpora lutea at some stage, but particularly in June. This resulted in cycles averaging 49.9±6.8 days in length instead of the normal 16.9±0.1 days. Intervals between successive luteal phases lasted 4–15 days as compared with 2.3±0.06 days seen in normal cycles. This occurred in most ewes at least once during the period from December to April. In these cases, the preovulatory discharge of LH was delayed until 7.5±1.8 days after the fall in the level of progesterone. The incidence of these anomalies suggests that the ewes had 69% of the ovulations and 56% of the behavioral estrus as compared to ewes that cycled regularly.

EFFECTS OF AN INTERMITTENT LIGHTING SCHEDULE ON THE TIME OF EGG-LAYING AND THE LEVELS OF LUTEINIZING HORMONE, PROGESTERONE AND CORTICOSTERONE IN THE PLASMA OF THE DOMESTIC HEN

The use of a complex lighting schedule consisting of five blocks of light and five alternating periods of darkness every 24 h completely abolished the normal pattern of egg-laying characteristic of the domestic hen. Animals tended to lay continuously and not in clutch sequences. Ovipositions were not restricted to an 8- to 10-h period of the day, instead they occurred at any time of the solar day with slightly more occurring during the hours of darkness. The preovulatory discharge of LH was not restricted to an 8- to 10-h 'open period' and the interval between the peak values of LH in the plasma and the time of lay of the corresponding egg was 32.3 h, i.e. identical to the interval found using a normal lighting schedule of 14 h light: 10 h darkness. There were some indications that minor fluctuations in the concentrations of LH in plasma occurred rhythmically with the changes in illumination, but the concentrations of progesterone showed only a single, preovulatory peak. The concentrations of corticosterone in the plasma were high and showed marked fluctations but this did not appear to affect either the levels of progesterone or the time of ovulation.

Duration of oestrus, ovulation rate, time of ovulation and plasma LH, total oestrogen and progesterone in Galway adult ewes and ewe lambs.

The mean duration of oestrus, ovulation rate, duration of the preovulatory LH discharge, time interval between sponge removal and beginning of the LH discharge, total LH discharged, maximum LH value observed and the concentration of progesterone in the peripheral plasma during the luteal phase of the oestrous cycle was similar in Galway adult ewes and 8-month-old ewe lambs after treatment with intravaginal sponges containing 30 mg cronolone for 12 days and injection of 500 i.u. PMSG. The interval between sponge removal and the onset of oestrus was shorter for adults than for ewe lambs; the interval between the onset of oestrus and the beginning of the LH discharge was longer in adults. During the period 12-36 h after sponge removal the mean plasma total oestrogen concentration was significantly higher in lambs than in adults. In a separate study of the time of ovulation in Galway ewe lambs given the same progestagen-PMSG treatment, ovulation did not occur in any lamb before 17 h after the onset of oestrus and the majority ovulated close to the end of oestrus.

Dual action of electrochemical stimulation of the bed nucleus of the stria terminalis on the release of LH.

The effect of stimulation of the bed nucleus of the stria terminalis (BNST) on ovulation and LH release was studied in unanesthetized, freely moving rats. Electrochemical stimulation (anodic d.c., 100 microA/30 sec) was applied at 11.30 h through chronically implanted monopolar, stainless steel electrodes. Serial blood samples were obtained by way of a plastic cannula implanted in the jugular vein. Stimulation on the day of proestrus prevented ovulation and the preovulatory discharge of LH when the stimulus was applied to the lateral part of the BNST but advanced the surge of LH in those rats stimulated in the medial part of the nucleus. In ovariectomized estrogen-primed rats stimulation in the medial part of the BNST produced LH release but no effect was seen when the stimulus was applied in the lateral part. It is concluded that the BNST is part of a dual system with antagonistic effects on LH secretion.

Plasma progesterone levels throughout the oestrous cycle and release of LH at oestrus in sheep with different ovulation rates

The concentrations of progesterone in the peripheral plasma throughout the oestrous cycle and the preovulatory LH discharge were examined in Finnish Landrace, Galway and Fingalway (Finnish Landrace X Galway) ewes. Progesterone levels were significantly higher in Finnish Landrace ewes during the luteal phase of the cycle (Days 10--13) than in Galways of Fingalways in which the concentrations were similar. Luteal-phase progesterone levels were almost 50% higher during December than during October in all three breeds. The relationship between the number of CL and plasma progesterone was not a simple linear function. All aspects of the preovulatory LH discharge were similar in the three breeds with the exception of the timing of the LH release in relation to the onset of oestrus. This occurred earliest in the Galway and latest in the Finnish Landrace while the Fingalway was intermediate.

TEMPORAL CHANGES IN THE HYPOTHALAMIC AND SERUM LUTEINIZING HORMONE-RELEASING HORMONE (LH-RH) LEVELS AND THE CIRCULATING OVARIAN STEROIDS DURING THE RAT OESTROUS CYCLE

Cycling female rats were sacrificed at various times during the 4-day oestrous cycle. LH-RH in the medial basal hypothalamus (MBH) and serum LH-RH, LH, oestradiol (Oe2), and progesterone were analyzed by radioimmunoassays. The MBH LH-RH content was lowest at 19.55-20.15 h during pro-oestrus but increased gradually through oestrus and dioestrus I to significantly higher values at noon of dioestrus II, and then decreased precipitously at 18.00 h. Although serum LH levels remained basal from midnight of pro-oestrus through dioestrus II, serum LH-RH levels were significantly elevated at 12.00 and 21.00 h on oestrus (vs. the midnight pro-oestrus levels) and declined between 15.00 and 22.00 h of dioestrus I. In conjunction with high Oe2 titres, LH-RH in the MBH and serum declined initially during pro-oestrus between 14.07-14.45 h and then increased abruptly between 14.55-15.55 h; the pre-ovulatory rise in serum LH was observed from 16.05 h onwards. LH-RH activity in the MBH and serum receded gradually to the early afternoon levels by 19.55-24.00 h while the peak in serum LH was observed at 17.05-18.05 h. These studies suggested that the hypersecretion of the MBH LH-RH (synthesis + release) may be responsible for the pre-ovulatory discharge of LH.

Suppression of serum LH-RH and LH in rats by an inhibitor of norepinephrine synthesis

Monoamine synthesis inhibitors have been used extensively to unravel the role of neurotransmitters in the hypothalamic regulation of pituitary LH release (Coppola, Leonardi & Lippmann, 1966; Kordon & Glowinski, 1972; Kalra, P.S. & McCann, 1973). Inhibition of tyrosine hydroxylase by α-methyl-paratyrosine (Corrodi & Hansen, 1966) or dopamine-β-hydroxylase by sodium diethyldithiocarbamate (Goldstein, Anagonste, Lauber & McKereghan, 1964) blocked the preovulatory discharge of LH and ovulation (Kalra & McCann, 1974). These pharmacological agents and a brain norepinephrine depletor, U-14,624 (1-phenyl-3-(2-thiazolyl)-2 thiourea (Johnson, Boukma & Kim, 1970), have been shown to suppress the release of pituitary LH induced by ovarian steroids (Kalra, Kalra, Krulich, Fawcett & McCann, 1972; Kalra, P.S. & McCann, 1973). These results were viewed as evidence for the involvement of a hypothalamic norepinephrine system in controlling LH release as suggested by Sawyer (1952). A single intraventricular injection of 6-hydroxydopamine to deplete norepinephrine and dopamine (Kostrzewa & Jacobowitz, 1974) reduced the LH-RH content of the hypothalamus (Kalra, 1975), but little other information is available to show that the depletion of brain catecholamines, and specifically norepinephrine, by these drugs results in modification of LH-RH secretion. In the present study the inhibition of pituitary LH release by the norepinephrine depletor, U-14,624, was investigated in ovariectomized rats.

The sensitivity of the ovulation rate of Finnish Landrace and Blackface ewes to exogenous oestrogen.

Variation in ovulation rate among different sheep breeds or crosses has been found to be related to the characteristics of the preovulatory discharge of LH, but there is no marked association with the concentration of LH during the oestrous cycle (Land, Pelletier, Thimonier & Mauléon, 1973). Studies of the oestrogen-induced discharge of LH in ovariectomized ewes indicated that breeds with high ovulation rates may be less sensitive to the positive and negative feed-back effects of oestrogen than are those with low ovulation rates. It was postulated that a low sensitivity of gonadotrophin release to the inhibitory effects of gonadal steroids may enable ewes which normally shed large numbers of eggs to tolerate higher concentrations of plasma oestrogen before the release of gonadotrophins is reduced (Land, Wheeler & Carr, 1976). Breed differences in follicular development and ovulation rate would therefore be compatible with similar LH concentrations. Alternatively, animals of a high-ovulation breed might catabolize the steroid produced more rapidly, or might produce less per follicle, than those of a breed in which fewer follicles developed; Bindon, Blanc, Pelletier, Terqui & Thimonier (1975) found no differences in the peripheral plasma oestrogen concentrations of ewes of breeds with differing ovulation rates.

The effects of nutrition on the reproductive performance of Finn x Dorset ewes. II. Post-partum ovarian activity, conception and the plasma concentration of progesterone and LH.

After lambing forty-five ewes were allocated to three groups, two of sixteen and one of thirteen ewes. The lambs of the two groups of sixteen ewes were weaned on Day 1 after lambing and the ewes were fed a diet of 100% (Group H) or 50% (Group R) of maintenance energy requirements. The thirteen ewes in the third group (Group L) suckled twin lambs and were fed freely. During the first 3 weeks after lambing, oestrus was observed for 11/16 (Group H) and 8/16 (Group R) ewes; of the ewes which had shown oestrus in the two groups, ovulation occurred in 5/8 and 5/7 respectively. Only 1/13 Group-L ewes showed oestrus and ovulated during the same period. The mean plasma concentrations of progesterone and LH were unaffected by the treatments and were around 0-4 and 1-5 ng/ml, respectively. Restricted feeding had no effect on oestrus, ovulation or the hormone levels during the oestrus cycle following synchronization. The onset of oestrus and the start of the preovulatory discharge of LH were 3 and 6 hr later, respectively, in the lactating ewes (Group L) than in those in Groups H and R. Ewes in Group L also had a higher ovulation rate, 2-8 +/- 0-2 versus 2-1 +/- 0-2 (P less than 0-05). Restricted feeding reduced the number of ewes lambing; only 1/11 ewes in Group R, considered to have conceived because of the presence of high progesterone levels 17 days after mating, subsequently lambed compared with 6/12 in Group H and 5/9 in Group L.

Changes of hypothalamic LH-RF content during the rat estrous cycle.

Anti-LH-RF serum was produced in rabbits by synthetic LH-RF-BSA conjugate prepard with bis-diazotized benzidine. Employing this antiserum, a radioimmunoassay for LH-RF was established with the assay range from 0.8 to 10 ng/ml. Acid extracts of hypothalami from 4 day cycling rats through various stages of the estrous cycle particularly in the afternoon of proestrus were measured for their LH-RF contents. The hypothalamic LH-RF content was high at 10:00 on the day of proestrus and declined until 17:00 and thereafter, the content gradually increased to reach the basal level. Serum LH showed the highest level at 17:00 on the day of proestrus and fell at 21:00 on the same day. Accompaning this change of serum LH level, pituitary LH content began to decrease at 17:00 of proestrus. These results indicate that LH-RF released in the afternoon of proestrus may participiate to stimulate the preovulatory discharge of LH in the rat.

Comparison of the induced preovulatory LH discharge in lactating and dry sheep during seasonal anoestrus.

To determine if the effect of lactation on the induced preovulatory LH discharge in sheep has an effect on fertility 12 lactating ewes and 12 nonlactating ewes were treated during seasonal anestrus. 6 of each type of ewe were treated with a procedure usually used to induce fertility out of season: administration of 40 mg of flurogestone acetate via vaginal sponge and intramuscular injection of 600 I.U. of PMSG at time of sponge withdrawal. To avoid excessive superovulation the remaining 6 ewes of each type received lesser amounts of the stimulants and 50 micrograms of estradiol benzoate 24 hours after sponge withdrawal. Blood samples were taken for plasma LH determination by radioimmunoassay. Corpora lutea were counted on Day 10 after sponge withdrawal. All of the sheep except 1 came into estrus. The interval between sponge withdrawal and onset of estrus was significantly shorter in the nonlactating than the lactating animals (p less than .01). Estrogen injection did not alter the onset of estrus. The discharge of LH induced in the lactating ewes was only 65% of that in the nonlactating animals which is a highly significant difference (p less than .01). Maximum LH concentration and observed LH release duration were significantly greater in the nonlactating ewes (p less than .05). The lower LH release in lactating ewes compared with dry ewes does not appear to limit ovulation and may be associated with reduced fertility. Further research is needed.

COMPARISON OF THE INDUCED PREOVULATORY LH DISCHARGE IN LACTATING AND DRY SHEEP DURING SEASONAL ANOESTRUS

During seasonal anoestrus in Île-de-France sheep, progestagen treatment with vaginal sponges associated with an intramuscular injection of PMSG induces oestrus and ovulation in dry and lactating females (42 days post partum). The fertility after artificial insemination, expressed as the percentage of treated ewes which subsequently lamb, is lower in lactating ewes at the induced oestrus than in the non-lactating ewes (35% versus 70%, Colas, Brice, Courot & Cottier, 1971). The present experiment was designed to investigate the effect of lactation on the induced preovulatory LH discharge since it may have an effect on fertility. In April, during the period of seasonal anoestrus, twelve non-lactating ewes (Groups 1 and 2) and twelve lactating ewes (Groups 3 and 4) were submitted to the various treatments shown in Table 1. The conditions of treatment for animals in Groups 1