Effect of fasting on luteal function, leptin and steroids concentration during oestrous cycle of the goat in natural photo-status

The effect of fasting during oestrous cycle on the occurrence of oestrous and concentration of leptin and steroid hormones was investigated in goats. Sixteen Ardi goats of 10-12 month of age were split into two groups (control and fasting). Oestrous was synchronized with intravaginal progesterone sponges and detected 24h after sponge removal. Blood samples were collected at the days 5, 10, 15 of each cycle. Fasting of mature goats twice for 4 days starting on day 10 of two successive oestrous cycles inhibited oestrous behaviour and resulted in reduced concentration of leptin, progesterone and testosterone with different timing. Day 5 of the second cycle showed significant decrease in the plasma level of leptin (1.6+/-0.15 ng/ml) and progesterone (1.6+/-0.1 ng/ml) as compared to control group (3.2+/-0.15 ng/ml and 4.1+/-0.2 ng/ml, respectively). Testosterone started to decrease from day 10 of the second cycle (35.0+/-12.0 pg/ml) as compared to control group (65.0+/-15.0 pg/ml); the decrease in this hormone was significant in day 15 of the second cycle (65.0+/-16.0 pg/ml) as compared to the control (320.0+/-50.0 pg/ml). These data suggest that fasting-induced inadequate corpus luteum function, hence, lowering progesterone plasma level may partly be more leptin-dependent than the following decrease in plasma level of testosterone.     

Effect of pinealectomy on heat-induced endocrine changes in female rats

Exposure of pinealectomized rats to high ambient temperature (35 degrees C; PXH) brought about a diminution in pituitary weight and LH content when compared to their sham-operated peers (35 degrees C) or to pinealectomized controls (22 degrees C). Serum corticosterone level of PXH rats was significantly depressed while heat or pinealectomy alone had no effect. Mean oestrous cycle length was prolonged and blood serum progesterone was increased in the heat-exposed rats. However, the extended oestrous cycles and elevated serum progesterone levels of heat-exposed rats were depressed or abolished by pineal ablation. Thus, the pineal appears to exert a moderating effect on heat-induced endocrine changes in female rats. No changes were noticed in uterine and ovarian weights corrected for body weights either on the day of vaginal opening, at occurrence of the oestrous phase expressed as percentage of total oestrous cycle, or in N-acetyltransferase and hydroxyindole-O-methyltransferase activities.     

Effect of high progesterone concentrations during the early luteal phase on the length of the ovulatory cycle of goats

The effect of exogenous progesterone exposure early in the oestrous cycle on the duration of the interovulatory interval was studied in dairy goats. A controlled intravaginal drug release (CIDR-G) device was inserted for 5 days starting at day 0 (D0 group, n=6) or day 3 (D3 group, n=5) postovulation. A third group was composed of untreated control goats (control group, n=7). Daily transrectal ultrasound was carried out during the interovulatory interval to assess the ovarian dynamics. Oestrous behaviour was checked twice a day and serum progesterone levels were assayed in daily jugular blood samples. Treated goats showed two different responses. In three D0 goats and one D3 goat, progesterone concentrations fell immediately after CIDR withdrawal and this was followed by oestrus and ovulation between days 8 and 11 (short cycles). In the other three D0 goats and in four D3 goats the treatment significantly reduced the interovulatory interval (18.3+/-0.3 and 18.5+/-0.3 days, respectively) (shortened cycles) compared with the control group (20.0+/-0.2 days; P<0.05), but the intervals with progesterone concentrations over 1 ng/ml were not different (15.7+/-0.3, 15.8+/-0.7 and 16.0+/-0.5 days for D0, D3 and control goats, respectively). In all D0 goats with a short cycle response, the ovulatory follicle arose from the first follicular wave but in the D3 goat with a short cycle it arose from the second follicular wave. These results showed that premature progesterone exposure early in the ovulatory cycle of the goat affected its length inducing short or shortened cycles. The effect of progesterone could either affect luteotropic support of the corpus luteum (CL) and/or stimulate a premature release of the luteolysin.     

The effects of stress and of ACTH administration in hormone profiles, oestrus and ovulation in pigs

Hormone concentrations and oestrous cycle patterns were studied in five chronically cannulated gilts. During oestrous cycles that were unaffected by stress, plasma oestrogen concentrations remained at basal luteal phase levels (10 to 30 pg/ml) until plasma progesterone had decreased to less than 2 ng/ml. The pre-oestrus surge of oestrogen ranged from 40 to 80 pg/ml. Plasma corticoid concentrations varied randomly and were not related to oestrogen, progesterone concentrations, or the stage of the oestrous cycle. There was, however, evidence of a positive relationship between elevated corticoid levels and observed stressful events. The stress of surgery or illness acting during the follicular phase of the oestrous cycle delayed the onset of oestrus, and corticoid levels were frequently elevated on these occasions. Elevated plasma corticoid concentrations in response to ACTH treatment were associated with either a change in the timing of or a suppression of the pre-oestrus LH peak. Altering the timing of the LH peak resulted in the formation of large partially luteinized ovarian cysts, while suppressing LH interfered with follicular development and led to small ovarian cysts. These experiments suggest that stress acting via the adrenal gland may play a role in the aetiology of infertility in sows.     

Influence of repeated rectal ultrasound examinations on hormone profiles and behaviour around oestrus and ovulation in dairy cattle

Frequent rectal ultrasound is often used to assess time of ovulation. This study investigated whether frequent rectal ultrasound examination, affects behavioural oestrus and peri-ovulatory hormone profiles (LH, oestradiol and progesterone). Additionally, the relation between peri-ovulatory hormone profiles, oestrous behaviour and time of ovulation was studied. Oestrus was synchronised in two consecutive cycles of Holstein Friesian cattle (parity from 1 to 6; n = 24 cycles). In 12 of these cycles, time of ovulation was assessed by three-hourly rectal ultrasound (assessment of ovulation time with ultrasound group: UG) the other half served as controls (n = 12; no assessment of ovulation time group: CG). There were no significant differences between the onset of oestrus (33.8 +/- 1.6 h), duration of oestrus (13.4 +/- 0.9 h) or intensity of oestrous behaviour (1047 +/- 180 points) between UG and CG treated animals. Furthermore, LH, oestradiol and progesterone profiles were similar between UG and CG. For UG, ovulation took place 30.2 +/- 1.9 h after onset of oestrus. This interval had the largest variation (21 h) of all parameters studied, ranging between 19 and 40 h after onset of oestrus. The smallest variation (6 h) was found in the timing of ovulation in relation to the LH-peak; ovulation took place 25.3 +/- 0.6 h (range: 21.5-27.5 h) after the peak in LH. This study demonstrated that repeated rectal ultrasound does not alter behavioural oestrus or peri-ovulatory hormone profiles and is therefore a useful tool for assessing time of ovulation. Further research, using ultrasound, can now be carried out to find predictors for time of ovulation.     

Resumption of oestrous behaviour and cyclic ovarian activity in suckling and non-suckling ewes

In Préalpes de Sud ewes after an autumn lambing, the mean post-partum interval to first LH surge was 10 +/- 1 days and 17 +/- 1 days for non-suckling and suckling ewes, respectively. Post-partum interval to first luteal phase, estimated from plasma progesterone concentrations, was similar in non-suckling and suckling ewes (27 +/- 1 days and 28 +/- 5 days, respectively). Interval to first oestrus was shorter in non-suckling (22 +/- 2 days) than in suckling ewes (35 +/- 2 days) but these first oestrous periods were followed by short luteal phases in 60% (12/20) of non-suckling ewes and in only 7% (2/29) of suckling ewes. Finally, suckling slightly postponed the resumption of the first oestrus followed by a normal oestrous cycle (37 +/- 1 days versus 31 +/- 2 days) because progesterone, essential for oestrus expression, was secreted mainly during normal luteal phases in 70% (21/30) of suckling ewes and during short cycles in 95% (21/22) of non-suckling ewes. Therefore, the primary consequence of suckling is to regulate the conditions of resumption of cyclic ovarian activity after parturition.     

Effects of abdominal vagotomy on serum LH concentrations in female rats

Vagotomy on the morning of pro-oestrus did not prevent the pro-oestrous LH surge and rats became oestrous on the following day. However, vagotomized rats then exhibited a period of acyclicity which lasted for 20.4 +/- 1.3 (s.e.m.) days. Food intake and body weight also declined after vagotomy. During the first week after vagotomy, afternoon LH surges generally did not occur, a pattern which was similar in animals pair fed with vagotomized rats. However, pair-fed rats showed oestrous cycles while vagotomized rats were acyclic. At 7 days after vagotomy, LH surges were induced by oestradiol benzoate and progesterone treatment of ovariectomized rats. Vagotomy suppressed the post-ovariectomy increase in serum LH at 7 and 21 days after surgery. These results, combined with those of other studies, suggest impairment of LH release in vagotomized rats.     

Episodic secretion of gonadotrophins and ovarian steroids in jugular and utero-ovarian vein plasma during the follicular phase of the oestrous cycle in gilts

Blood samples were collected simultaneously from the jugular and utero-ovarian veins of 13 gilts from Days 11 through 16 of the oestrous cycle. A luteolytic dose (10 mg) of PGF-2 alpha was given on Day 12 to facilitate the natural occurrence of luteolysis and standardize the associated decrease in concentrations of progesterone. The mean interval from PGF to oestrus was 5.5 +/- 0.7 days (mean oestrous cycle length = 17.5 +/- 0.7 days). Mean concentrations, pulse amplitudes and pulse frequencies of oestradiol and progesterone were greater (P less than 0.05) in the utero-ovarian than jugular vein. Secretory profiles of LH and FSH were similar (P greater than 0.05) in plasma collected simultaneously from both veins. Based on these data, temporal relationships among hormonal patterns of FSH and LH in the jugular vein and oestradiol and progesterone in the utero-ovarian vein were examined. Concentrations of progesterone declined (P less than 0.05) between Days 12 and 14, while all secretory variables for oestradiol increased (P less than 0.05) from Day 12 through 16 of the oestrous cycle. The pulsatile secretion of FSH remained relatively constant during the experiment. However, both pulse amplitude and mean concentration tended (P less than 0.2) to be lower on Day 16 compared with Day 12. The episodic secretion of LH shifted from a pattern characterized by high-amplitude, low-frequency pulses to one dominated by numerous pulses of diminishing magnitude between Days 13 and 14. From Days 14 to 16 of the oestrous cycle, 91% of all oestradiol pulses were temporally associated with gonadotrophin pulses composed of both FSH and LH episodes. However, pulses of oestradiol (52%) not associated with an episode of LH and/or FSH were observed on Days 12 and 13. These data demonstrate that during the follicular phase of the pig oestrous cycle substantial oestradiol production occurred coincident with luteolysis and before the shift in the episodic secretion of LH. The pool of follicles which ovulated was probably the source of this early increase in the secretion of oestradiol. Therefore, we propose that factors in addition to FSH and LH are involved in the initial selection of follicles destined to ovulate during the early stages of the follicular phase of the pig oestrous cycle. In contrast, high-frequency, low-amplitude pulses composed of LH and FSH were the predominant endocrine signal associated with oestradiol secretion during the second half of the oestrous cycle.(ABSTRACT TRUNCATED AT 400 WORDS)     

Male-induced short oestrous and ovarian cycles in sheep and goats: a working hypothesis

The existence of short ovulatory cycles (5-day duration) after the first male-induced ovulations in anovulatory ewes and goats, associated or not with the appearance of oestrous behaviour, is the origin of the two-peak abnormal distribution of parturitions after the "male effect". We propose here a working hypothesis to explain the presence of these short cycles. The male-effect is efficient during anoestrus, when follicles contain granulosa cells of lower quality than during the breeding season. They generate corpora lutea (CL) with a lower proportion of large luteal cells compared to small cells, which secrete less progesterone, compared to what is observed in the breeding season cycle. This is probably not sufficient to block prostaglandin synthesis in the endometrial cells of the uterus at the time when the responsiveness to prostaglandins of the new-formed CL is initiated and, in parallel, to centrally reduce LH pulsatility. This LH pulsatility stimulates a new wave of follicles secreting oestradiol which, in turn, stimulates prostaglandin synthesis and provokes luteolysis and new ovulation(s). The occurrence of a new follicular wave on days 3-4 of the first male-induced cycle and the initiation of the responsiveness to prostaglandins of the CL from day 3 of the oestrous cycle are probably the key elements which ensure such regularity in the duration of the short cycles. Exogenous progesterone injection suppresses short cycles, probably not by delaying ovulation time, but rather by blocking prostaglandin synthesis, thus impairing luteolysis. The existence, or not, of oestrous behaviour associated to these ovulatory events mainly varies with species: ewes, compared to does, require a more intense endogenous progesterone priming; only ovulations preceded by normal cycles are associated with oestrous behaviour. Thus, the precise and delicate mechanism underlying the existence of short ovulatory and oestrous cycles induced by the male effect appears to be dependent on the various levels of the hypothalamo-pituitary-ovario-uterine axis.     

Do cyclic female goats respond to males with an increase in LH secretion during the breeding season?

The male effect is currently only used during seasonal or lactational anoestrus because the response is thought to be blocked in cyclic females by periods of elevated progesterone. In this study, we tested whether cyclic, female goats would respond to male exposure with an increase in pulsatile LH secretion. During May (breeding season; Southern Hemisphere) the cycles of 16 Australian Cashmere goats were synchronised using intravaginal progesterone pessaries. Pessary insertion was staggered to produce groups in their early luteal (EL; n=8) and late luteal phases (LL; n=8). The LL group was retrospectively subdivided into mid-luteal (ML; n=4) and late luteal (LL; n=4) groups due to differences in oestrous cycle length that emerged during the study. Male exposure stimulated an increase in LH pulse frequency in the EL and LL groups (P<0.01) but not in the ML group (P>0.1). This increase was accompanied by an increase in basal and mean concentrations of LH in the LL group (P<0.05) but not in EL (P<0.1) or ML (P>0.1) group. There was no effect of male exposure on LH pulse amplitude (P>0.1). Progesterone concentrations differed among all groups on the day of male exposure (P<0.05) and declined significantly over the 12-h sampling period in the LL group (P<0.05). Prolactin concentrations declined in the EL group but did not change significantly in the ML or LL group. In conclusion, male exposure induced an increase in pulsatile LH in goats in the early and late luteal phases of the oestrous cycle. The high concentrations of progesterone in females in the mid-luteal phase appeared to block the male effect.     

Effect of stress on the course of oestrous cycle and the release of luteinizing hormone; the role of endorphin in these processes

It has been postulated that stress induces discorrelations of the hypothalamo-pituitary and pituitary gonadal axis. In our experiments on the effect of stress on the reproductive physiology in rats and sheep we applied mild electrical footshocking of short or prolonged duration. Foot-shocking applied with some breaks during 9 h within one a day (15th day of the oestrous cycle) induced in ewes acceleration of the release of LH. Prolonged footshocking applied with some breaks during 3 days in cycling sheep caused disturbances in the circadian rhythm of the cortisol secretion, disturbances in the release of LH and led to the blockade of ovulation. Disturbances in the course of oestrous cycle occurred not only during the current cycle but also during two subsequent cycles. Rats exposed to relatively long-term stressful situation (24 h) during dioestrous displayed marked changes in the length of this phase in three subsequent post-stress oestrous cycles. To follow the neurohormonal background of the stress-induced disturbances in LH release and in the course of oestrous cycle in sheep the concentrations of beta-endorphin (beta-END) in the infundibular and paraventricular nuclei as well as in the pituitary gland under physiological and stress conditions were determined, while in rats the metabolism of brain serotonin was investigated. Footshocking in rats induced significant decrease in 5-HT concentrations in the fronto-parietal brain cortex, hippocampus, striatum, medial basal hypothalamus and the preoptic-anterior hypothalamic area. These results allow to suggest that the decline in brain 5-HT under stress conditions has some associations with the impairments in the course of oestrous cycle. Measurements of the beta-END in perfusates of medial basal hypothalamus (nucl. infundibularis) in sheep evidenced significant increase of this opioid under stress conditions and it was postulated that this increase might be the main cause of the stress-induced impairments in the course of oestrous cycle and inhibition of LH-release. In addition, it was found that beta-END suppressed the secretion of cortisol and attenuated some noxious consequences of general nature for organism.     

Progesterone blockade of the positive feedback effects of 17β oestradiol in the ewe

Ovariectomized ewes (n = 24) were treated with implants that resulted in circulating concentrations of progesterone and 17β-oestradiol similar to those seen in intact ewes in the luteal phase of an oestrous cycle. Progesterone implants were left in for 10 days, and 17β-oestradiol implants for 14 days. Twelve of these ewes received daily injections of 17β-oestradiol in oil (i.m.) at doses sufficient to cause a surge release of luteinizing hormone (LH) in the absence of progesterone. The other 12 ewes were treated daily with vehicle (oil). Following progesterone withdrawal on Day 10, each group of 12 ewes was divided into three subgroups. Ewes in each subgroup of the groups treated daily with 17β-oestradiol or vehicle, received an injection of either 17β-oestradiol (oil i.m.), gonadotrophin-releasing hormone (GnRH) (saline, i.v.) or vehicle, 24 h after progesterone withdrawal. Following progesterone withdrawal, no LH surge was detected in ewes treated with vehicle. Surge secretion of LH was detected in ewes of all other groups. The data suggested that in progesterone-treated ewes, daily exposure to stimulatory doses of 17β-oestradiol did not desensitize the hypothalamic pituitary axis to the positive feedback effects of 17β-oestradiol. Daily exposure to 17β-oestradiol did not suppress pituitary responsiveness to GnRH. It was concluded that circulating concentrations of progesterone, similar to those seen during the luteal phase of an oestrous cycle in intact ewes, may prevent all necessary components of the LH surge secretory mechanism from responding to 17β-oestradiol.     

Luteinizing hormone secretion in hypophysial stalk-transected pigs given progesterone and pulsatile gonadotropin-releasing hormone

This study was conducted to determine whether progesterone inhibits luteinizing hormone (LH) secretion in female pigs by a direct action on the pituitary gland. Eight ovariectomized, hypophysial stalk-transected gilts were given 1-microgram pulses of gonadotropin-releasing hormone iv every 45 min from Day 0 to 12. On Days 5-12, each of four gilts received either progesterone or oil vehicle im at 12-hr intervals. Serum progesterone concentrations in steroid-treated gilts reached 70 +/- 6.8 ng/ml (mean +/- SE) by Day 8 and remained elevated thereafter, whereas serum progesterone concentrations in oil-treated controls were less than 1 ng/ml for the entire study. Daily serum LH concentrations were not different between gilts treated with progesterone or oil. The 1-microgram pulses of gonadotropin-releasing hormone reliably evoked pulses of LH in both treatment groups. The LH pulse frequency and amplitude, assessed from samples collected every 15 min for 6 hr on Day 12, were similar for progesterone- and oil-treated gilts. These results provide evidence that progesterone does not act at the pituitary gland to alter LH secretion in pigs.     

Effect of continuous infusion of oxytocin on length of the oestrous cycle and luteolysis in cattle

In Exp. I oxytocin (60 micrograms/100 kg/day) was infused into the jugular vein of 3 heifers on Days 14-22, 15-18 and 16-19 of the oestrous cycle respectively. In Exp. II 5 heifers were infused with 12 micrograms oxytocin/100 kg/day from Day 15 of the oestrous cycle until clear signs of oestrus. Blood samples were taken from the contralateral jugular vein at 2-h intervals from the start of the infusion. The oestrous cycle before and after treatment served as the controls for each animal. Blood samples were taken less frequently during the control cycles. In Exp. III 3 heifers were infused with 12 micrograms oxytocin/100 kg/day for 50 h before expected oestrus and slaughtered 30-40 min after the end of infusion for determination of oxytocin receptor amounts in the endometrium. Three other heifers slaughtered at the same days of the cycle served as controls. Peripheral concentrations of oxytocin during infusion ranged between 155 and 641 pg/ml in Exp. I and 18 and 25 pg/ml in Exp. II. In 4 our of 8 heifers of Exps I and II, one high pulse of 15-keto-13,14-dihydro-prostaglandin F-2 alpha (PGFM) appeared soon after the start of oxytocin infusion followed by some irregular pulses. The first PGFM pulse was accompanied by a transient (10-14 h) decrease of blood progesterone concentration. High regular pulses of PGFM in all heifers examined were measured between Days 17 and 19 during spontaneous luteolysis. No change in length of the oestrous cycle or secretion patterns of progesterone, PGFM and LH was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma progesterone and LH concentrations in ewes after injection of an analogue of prostaglandin F-2alpha

Plasma progesterone and LH concentrations were monitored throughout a natural oestrous cycle in 12 Clun Forest ewes and compared to those following treatment with a single i.m. injection of 100 microng ICI 80,996, an analogoue of prostaglandin F-2alpha, given during the luteal phase of the cycle. After injection of the analogue there was a high degree of synchrony in the return of oestrus (440 +/- 1-9 h; mean +/- S.E.M.) and the timing of the LH peak (48-5 +/- 2-0 h) from injection. There were no significant differences in the plasma progesterone concentrations or in the height and duration of the preovulatory LH peak between control and treatment cycles. The technique offers the possibility of controlled ovulation in the ewe.     

Short and long phases of progesterone secretion during the oestrous cycle of the African elephant (Loxodonta africana)

Serum samples were collected from 3 mature female African elephants once each week for 15-18 months. Circulating concentrations of progesterone, oestradiol and LH were determined by radioimmunoassay (RIA). The LH RIA was validated by demonstrating parallel cross-reaction with partly purified elephant LH pituitary fractions. Changing serum progesterone concentrations indicated an oestrous cycle length of 13.3 +/- 1.3 weeks (n = 11). The presumed luteal phase, characterized by elevated serum progesterone values, was 9.1 +/- 1.1 weeks (n = 11). Two abbreviated phases of progesterone in serum lasting 2-3 weeks were observed in 2 elephants, indicating short luteal phases. Oestradiol concentrations in serum were variable, with no clear pattern of secretion. More frequent blood samples were collected during periovulatory periods and 9 distinct LH peaks were detected; all were followed by rises in serum progesterone concentrations. Periovulatory changes in progesterone and LH in sera correlated with external signs of oestrus and mating behaviour.     

Plasma progesterone and gonadotrophin concentrations and ovarian activity in post-partum dairy cows

Plasma progesterone concentrations in jugular vein blood samples collected every other day after calving from 13 Friesian dairy cows indicated that ovarian cyclic activity was initiated by 16.6 +/- 1.1 (s.e.m.) days post partum, except for 1 cow which did not resume cyclic activity until Day 98 post partum. Rectal palpation of the ovaries indicated that a developing follicle was recognizable at a mean time of 15.7 +/- 2.0 days after calving. During the first oestrous cycle after parturition there was a significantly shorter period when plasma progesterone levels were elevated than during the next 2 cycles. Concentrations of progesterone, LH, FSH and prolactin were determined for 4 cows, in blood samples taken every 6 h from 2 to 36 days post partum. Tonic LH release was lower during the first 10 days than subsequently, but the lack of change in pattern for FSH suggests dissimilar control mechanisms for these hormones during this time. Three cows showed evidence of a resumption of ovarian cyclicity during the sampling period: in 2 there was an initial LH surge of a magnitude which would normally give rise to ovulation, followed 4 days later by an increase in plasma progesterone lasting only 5 and 9 days. This progesterone was considered to be of follicular origin. A second LH surge was followed by the presence of a corpus luteum.     

Characteristics and regulation of the ovarian cycle in vervet monkeys (Chlorocebus aethiops)

This study was designed to evaluate the timecourse of ovarian and pituitary endocrine events throughout the menstrual cycle in the vervet monkey, and whether circulating luteinizing hormone (LH) or the uterus regulates the functional lifespan of the vervet corpus luteum. Daily saphenous blood samples were collected from adult females (1) during spontaneous menstrual cycles (n = 7), and (2) during cycles in which a gonadotropin-releasing hormone antagonist (acyline) was administered for 3 days at midluteal phase (n = 3), and (3) for 30 days following recovery from hysterectomy (n = 4). Estradiol (E) and progesterone (P) levels were assayed using electrochemoluminescent assays. Gonadotropin levels were measured by radioimmunoassay using reagents developed for the assay of follicle-stimulating hormone and LH in macaques. Spontaneous cycles exhibited a midcycle E rise (476+/-49 pg/ml), engendering an LH surge, 12+/-1 days after onset of menses, followed by a luteal phase with peak P levels of 4.7+/-0.9 ng/ml. Histologic evaluation of the ovaries at late follicular phase or early luteal phase revealed the presence of a single, large Graafian follicle or developing corpus luteum, respectively. Acyline treatment caused a significant (P<0.05) decline in P levels (2.9+/-0.5 vs 0.5+/-0.3 ng/ml, 0 vs 48 h post-treatment) and premature menstruation compared with untreated controls (P<0.05). Hysterectomy had no apparent effect on the monthly pattern or levels of circulating E or P. Thus, the characteristics and regulation of the ovarian cycle in vervets appear similar to those in women and macaques, with cyclicity dependent on pituitary gonadotropin hormones and independent of a uterine luteolytic factor.     

Monitoring ovarian function and pregnancy in Eld's deer (Cervus eldi thamin) by evaluating urinary steroid metabolite excretion

Direct radioimmunoassays (RIA) for urinary oestrone conjugates and pregnanediol-3 alpha-glucuronide (PdG) were used to study ovarian activity patterns and pregnancy in Eld's deer. In 2 does, urinary metabolite patterns were compared to temporal patterns of plasma LH, oestradiol-17 beta and progesterone. Preovulatory LH peaks occurred coincident with behavioural oestrus, and plasma progesterone secretion paralleled PdG excretion. Although plasma oestradiol-17 beta levels fluctuated between 5 and 10 pg/ml throughout the oestrous cycle, no preovulatory oestrogen surge was observed. Based on PdG excretion, non-conception oestrous cycles averaged 21.5 +/- 2.1 days (+/- s.e.m., n = 65); however, 2 of 13 does exhibited prolonged oestrous cycles (30.1 +/- 4.4 days; range 14-62 days, n = 14) characterized by sustained PdG excretion. Excluding these 2 females, the mean oestrous cycle was 18.5 +/- 0.3 days (range 14-23 days, n = 51). Behavioural oestrus (12-24 h duration) was observed in 42 of 65 cycles (64.6%), and always corresponded with intercyclic troughs in PdG excretion (2-5 days duration). Mean gestation duration (n = 10) was 33.5 +/- 0.4 weeks. PdG concentrations increased (P less than 0.05) by Week -32 (3rd week of gestation), plateaued between Weeks -31 and -25, increased (P less than 0.05) markedly by Week -22 and then rose steadily until parturition, declining (P less than 0.05) rapidly thereafter. Mean excretion of oestrone conjugates remained low until Week -30, increased (P less than 0.05) steadily to Week -24 (P less than 0.05) and then returned to baseline by Week -17. Increased (P less than 0.05) oestrone conjugates concentrations were detected again by Week -4 followed by a rapid increase to peak pregnancy levels by Week -1, declining (P less than 0.05) precipitously after parturition. The results confirm that the Eld's deer is seasonally polyoestrous with onset (January-March) and cessation (August-October) of regular, cyclic ovarian activity coinciding with increasing and decreasing daylengths, respectively. Urinary PdG excretion accurately reflects cyclic ovarian activity and markedly elevated concentrations of this metabolite provide an accurate index of pregnancy. The simultaneous monitoring of oestrone conjugates appears useful for estimating the stage of pregnancy and predicting parturition onset.     

Induction of precocious puberty in ewe lambs by pulsatile administration of GnRH

Circhoral administration (250 ng/h, i.v.) of GnRH induced a preovulatory-like surge of LH and subsequent luteal function in 4 of 4 ewe lambs 1 month before expected date of puberty. Within 12h of the start of pulsatile delivery of GnRH, mean concentrations of immunoactive and bioactive LH increased significantly (P less than 0.05) and the LH surge occurred by 1.8 +/- 0.6 days of treatment. Mean concentrations of serum progesterone were elevated significantly (P less than 0.001) 3 days after the surge. The biopotency of LH (bioactive LH/immunoactive LH) before the GnRH-induced surge of LH did not differ from LH biopotency in ewe lambs receiving circhoral delivery of saline (0.41 +/- 0.05 and 0.46 +/- 0.04, respectively). Biopotency of LH declined markedly at the GnRH-induced LH surge (0.25 +/- 0.04), but biopotency of serum LH was significantly augmented (P less than 0.05) during the period of luteal activity (0.70 +/- 0.07). Regular oestrous cycles were observed in 3 of 4 ewe lambs after the 10-day GnRH treatment period. These results indicate that pulsatile delivery of GnRH is effective in inducing precocious puberty in ewe lambs. Increase in LH biopotency does not appear to be required in the pubertal transition to reproductive cyclicity in this species. Augmented LH biopotency may be important in support of luteal function after first ovulation.