Changes in plasma oestradiol-17beta, progesterone, testosterone, LH and fertility after treatment with I.C.I. 80, 996.

Fifty heifers were twice injected with I.C.I. 80, 996 and inseminated 72 h and 96 h after the second administration. Twenty eight of them (56%) became pregnant. Changes in plasma oestradiol-17 beta, progesterone and LH concentrations around the oestrus following the second injection were similar to those occurring in spontaneous oestrus. The pattern of testosterone secretion resembled that of oestradiol;-17 beta. The highest testosterone concentration (135 +/- 24 pg/ml) was measured on the third day after treatment with I.C.I. 80, 996.     

Peripheral plasma levels of oestradiol-17 beta and progesterone in the bitch during the oestrous cycle, in normal pregnancy and after dexamethasone treatment.

Plasma oestradiol-17 beta concentrations in Labradors increased during pro-oestrus to an average maximal concentration of of 79-7 +/- 10-9 (S.D.) pg/ml, and then fell rapidly. In 6/7 bitches the peak occurred within 1 day of oestrus. No consistent changes in plasma oestradiol levels were observed during pregnancy and at parturition and the values were similar to those in late anoestrus. Plasma progesterone levels did not increase markedly during pro-oestrus. At oestrus, progesterone values rose and maximal concentrations, which varied from about 20 to about 55 ng/ml, were reached within a few days of the oestradiol peak. Plasma progesterone decreased in late pregnancy and in one of the three bitches studied in detail low or undetectable levels were reached 10 days before parturition. In the other two bitches an abrupt decrease in progesterone occurred just before parturition. Dexamethasone treatment (2 X 5 mg daily for 10 days) from Day 30 of pregnancy resulted in intrauterine death and resorption of the fetuses in the two bitches studied. Treatment from about Day 45 resulted in the birth of dead fetuses at Days 55 and 59 of pregnancy. The changes in plasma oestradiol levels were very small. No changes in plasma progesterone levels were seen when dexamethasone was given in late pregnancy, but an accelerated decline occurred after treatment in mid-pregnancy.     

Progesterone profile in buffaloes during various stages of oestrous cycle using radioimmunoassy technique

Investigation were carried out to study the norms of progesterone concentration in the blood serum of buffaloes during various phases of oestrous cycle. Twenty four animals (12 heifers and 12 cows) were used. The blood serum samples were stored at -20 degrees C until processed for progesterone assay. The progesterone concentrations were measured by the radioimmunoassay technique. The progesterone levels were 0.360 +/- 0.062 and 0.334 +/- 0.066 ng/ml on the day of oestrus in buffalo-heifers and buffalo-cows, respectively. The values were around 1 ng/ml till day 6, followed by a gradual increase to a peak average value of 4.888 +/- 0.399 and 5.119 +/- 0.415 ng/ml on day 15 of the cycle in heifers and cows, respectively. Thereafter, the progesterone concentration fell abruptly to a level similar to that at oestrus. The mean progesterone value a day before oestrus was 0.488 +/- 0.067 and 0.577 +/- 0.053 ng/ml in buffalo-heifers and buffalo-cows, respectively. The mean progesterone concentration of different days of the cycle (except day 16) did not differ significantly (P / -0.01) between heifers and cows.     

Plasma concentrations of gonadotrophins, preovulatory follicular development and luteal function associated with bovine follicular fluid-induced delay of oestrus in heifers

In Exp. 1, injections of 10 ml bovine follicular fluid (bFF, i.v. or s.c.), given twice daily for 3 days after injection of a luteolytic dose of PGF-2 alpha, delayed the onset of oestrus in 3 of 6 heifers to 8 or 9 days after PGF-2 alpha, as compared with 2 or 3 days after PGF-2 alpha in control heifers. Mean plasma concentrations of FSH and LH during the injection period were not different from those in saline-injected heifers. In Exp. 2, i.v. injections of 20 ml bFF twice daily for 3 days uniformly delayed oestrus to 8 days after PGF-2 alpha (N = 4) and injections of 20 ml bFF i.v. every 6 h for 24h on the day of PGF-2 alpha injection delayed oestrus to 5.0 +/- 0.6 days after PGF-2 alpha as compared with 2.8 +/- 0.3 days for control heifers. In both treatment groups, plasma concentrations of FSH were suppressed during the injection period and increased transiently after treatment, but plasma concentrations of LH during the injection period were not different from those of control heifers. Plasma levels of oestradiol in heifers given bFF remained basal for 2 or 3 days after treatment, then increased several days before the delayed oestrus, in a manner similar to that in control heifers, and elicited normal preovulatory surges of LH and FSH. Plasma concentrations of progesterone and the length of the next oestrous cycle were normal, indicating formation of functional corpora lutea. Therefore, bFF treatments appear to delay oestrus by selectively suppressing plasma FSH, without affecting LH, and delaying the development of the preovulatory follicle. These results suggest that FSH may be critical to support the growth and development of the preovulatory follicle after luteolysis in cows.     

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)     

The role of sub-optimal preovulatory oestradiol secretion in the aetiology of premature luteolysis during the short oestrous cycle in the cow

Premature regression of the corpus luteum, following the first post partum ovulation, is often preceded by sub-optimal preovulatory oestradiol secretion and accompanied by elevated levels of oxytocin receptors early in the luteal phase. We have investigated the role of preovulatory oestradiol in the control of subsequent oxytocin receptor concentration and activity by treating ovariectomised cows, over a simulated 48 h follicular phase, with high (600 microg per day) medium (300 microg per day) or low (150 microg per day) levels of oestradiol. These doses of oestradiol generated mean+/-S.E.M. plasma oestradiol concentrations of 12.1+/-1.0, 4.9+/-0.5 and 2.9+/-0.4 pg ml(-1), respectively. In Study 1 (n=4 per group), we found that by day 4 following oestrus there was a significant (P< 0.05) effect of the level of oestradiol on the inhibition of oxytocin binding activity measured in endometrial biopsy samples. This had fallen to mean+/-S.E.M. concentrations of 25+/-2 fmol per mg protein in the high group, 47+/-8 fmol per mg protein in the medium group and 65+/-12 fmol per mg protein in the low group. In Study 2, cows (n=3 per group) were treated with the same three levels of oestradiol followed by treatment with increasing levels of progesterone from days 3 to 6 following oestrus, generating mean+/-S.E.M. plasma concentrations of 2.17+/-0.18 ng ml(-1) by day 6. On day 6, there was a significant (P< 0.01) effect of the level of oestradiol on PGF(2alpha) release in response to oxytocin challenge. High, medium and low oestradiol groups exhibiting mean+/-S.E.M., increase plasma PGF(2alpha) metabolite concentrations of 10.0+/-2.2, 21.3+/-4.3 and 41.3+/-1.2 pg ml(-1), respectively, during the hour after oxytocin administration. From these results, we postulate that at the first post partum ovulation a low level of preovulatory oestradiol can result in the early generation of a luteolytic mechanism during the subsequent luteal phase due to impaired inhibition of oxytocin receptors allowing increased PGF(2alpha) release.     

Oxytocin infusion from day 10 after oestrus extends the luteal phase in non-pregnant cattle

Oestrus was synchronized in 8 cyclic heifers by progesterone treatment (PRID), after which the animals were monitored for one control cycle to measure the inter-oestrous interval. Osmotic minipumps containing saline (controls, N = 3) or oxytocin (N = 5) were implanted subcutaneously on Day 10 of the second cycle, and removed 12 days later. Jugular venous blood samples were collected daily for measurement of progesterone, and every 2 days for oxytocin. In addition, blood samples were taken every 10 min from 1 h before to 3 h after minipump insertion for measurement of plasma 15-keto-13,14-dihydroprostaglandin-F-2 alpha (PGFM) and every 30 min over the same period for measurement of progesterone and oxytocin. The lengths of the first untreated cycle in both groups of heifers were 20.2 +/- 0.56 (mean +/- s.e.m.) days compared with 25.4 +/- 0.81 days after oxytocin treatment (P less than 0.001). Oxytocin plasma concentrations in treated animals rose from less than 10 pg/ml to 70-500 pg/ml by 2 h after the start of oxytocin infusion and remained elevated until treatment was withdrawn. There was no increase in PGFM concentrations immediately after minipump insertion. Plasma progesterone concentrations were similar in treated and control animals but remained at mid-luteal levels for an average of 5 days longer in treated heifers. It is concluded that continuous administration of oxytocin can extend the luteal life-span in cattle.     

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.     

Extension of oestrous cycles and prolonged secretion of progesterone in non-pregnant cattle infused continuously with oxytocin

The experimental objective was to evaluate how continuous infusion of oxytocin during the anticipated period of luteolysis in cattle would influence secretion of progesterone, oestradiol and 13,14-dihydro-15-keto-prostaglandin F-2 alpha (PGFM). In Exp. I, 6 non-lactating Holstein cows were infused with saline or oxytocin (20 IU/h, i.v.) from Day 13 to Day 20 of an oestrous cycle in a cross-over experimental design (Day 0 = oestrus). During saline cycles, concentrations of progesterone decreased from 11.0 +/- 2.0 ng/ml on Day 14 to 2.0 +/- 1.3 ng/ml on Day 23; however, during oxytocin cycles, luteolysis was delayed and progesterone secretion remained near 11 ng/ml until after Day 22 (P less than 0.05). Interoestrous interval was 1.6 days longer in oxytocin than in saline cycles (P = 0.07). Baseline PGFM and amplitude and frequency of PGFM peaks in blood samples collected hourly on Day 18 did not differ between saline and oxytocin cycles. In Exp. II, 7 non-lactating Holstein cows were infused with saline or oxytocin from Day 13 to Day 25 after oestrus in a cross-over experimental design. Secretion of progesterone decreased from 6.8 +/- 0.7 ng/ml on Day 16 to less than 2 ng/ml on Day 22 of saline cycles; however, during oxytocin cycles, luteolysis did not occur until after Day 25 (P less than 0.05). Interoestrous interval was 5.9 days longer for oxytocin than for saline cycles (P less than 0.05). In blood samples taken every 2 h from Day 17 to Day 23, PGFM peak amplitude was higher (P less than 0.05) in saline (142.1 +/- 25.1 pg/ml) than in oxytocin cycles (109.8 +/- 15.2 pg/ml). Nevertheless, pulsatile secretion of PGFM was detected during 6 of 7 oxytocin cycles. In both experiments, the anticipated rise in serum oestradiol concentrations before oestrus, around Days 18-20, was observed during saline cycles, but during oxytocin cycles, concentrations of oestradiol remained at basal levels until after oxytocin infusion was discontinued. We concluded that continuous infusion of oxytocin caused extended oestrous cycles, prolonged the secretion of progesterone, and reduced the amplitude of PGFM pulses. Moreover, when oxytocin was infused, pulsatile secretion of PGFM was not abolished, but oestrogen secretion did not increase until oxytocin infusion stopped.     

Pulsatile release of oxytocin into the circulation of the ewe during oestrus, mating and the early luteal phase

Two experiments were designed to investigate release patterns of oxytocin into plasma during oestrus and the early luteal phase. In Exp. 1, blood samples were collected from 5 ewes every 30 min for 10 h during 6 days around oestrus and the early luteal phase. During oestrus concentrations of oxytocin were generally low (1.27 +/- 0.54 pg/ml; mean +/- s.d.) but with occasional pulses up to 6 pg/ml. By Day 5 mean basal concentrations had risen to 4.5 +/- 2.1 pg/ml with a fluctuating release pattern. In Exp. 2, a method was developed for continuous blood sampling from conscious, unrestrained ewes. On the predicted day of oestrus following an untreated oestrous cycle, 8-ml blood samples were collected every minute for two 35-min periods (8 ewes: 16 sampling periods). For 6 ewes a ram was introduced to the pen for part of this time, and resulting behaviour was recorded. Additional blood samples were assayed for LH and progesterone to determine the stage of the cycle. Overall mean oxytocin concentrations ranged from 1.5 +/- 0.53 to 6.8 +/- 5.25 pg/ml in different animals. Ewes which were both in oestrus and exposed to the ram showed a pulsatile oxytocin release pattern consisting of low baseline concentrations with short-duration pulses superimposed (duration 1-4 min; amplitude 2.5-31.7 pg/ml; frequency 3.18/h). Coitus was not temporally associated with pulsatile release. However, the importance of the presence of the ram was indicated by total separation of 2 oestrous ewes from the ram until after experimentation. In these animals only 1 pulse of oxytocin was detected in 2.7 h of sampling. It is concluded that, although mean oxytocin concentrations at oestrus were low, short duration pulses were released into the plasma at this time. This effect may be dependent on the presence of a ram.     

Concentrations of oestradiol-17 beta in plasma and corpora lutea throughout pregnancy in the tammar, Macropus eugenii

Oestradiol-17 beta concentrations were measured by radioimmunoassay in peripheral blood samples from 10 tammar wallabies after their pouch young were removed to terminate embryonic diapause. Oestradiol concentrations rose from 8.3 +/- 1.2 pg/ml on Days 3 and 4 to peak of 15.8 +/- 2.9 pg/ml on Day 5, coincident with an increase in 'progesterone' concentrations, and then fell to 10.5 +/- 2.7 pg/ml on Day 7. No changes in oestradiol concentrations were associated with parturition. Five females came into oestrus and mated 9.8 +/- 6.1 h post partum; peak concentrations of plasma oestradiol (20.9 +/- 2.1 pg/ml) occurred around the time of mating. None of the females that did not mate up to the end of the experiment at Day 30 had a rise in plasma oestradiol concentrations. Corpora lutea contained 20-100 pg oestradiol during pregnancy. The highest ovarian oestradiol content (greater than 1200 pg) was measured in whole ovaries containing Graafian follicles from full-term pregnant females. The rise in oestradiol concentrations at Day 5 may be important in the termination of diapause. The post-partum increase in plasma oestradiol concentrations coincides with oestrus. The source of this oestrogen appears to be the preovulatory follicle.     

Development of progesterone dependency in the appearance of the nocturnal prolactin surge in immature rats

Basal concentrations of plasma prolactin in immature, Wistar-Imamichi strain rats at 25, 28 and 31 days of age were 5-12 ng/ml and no prolactin surges were observed in intact immature rats. Plasma progesterone values ranged from 5 to 9 ng/ml, while plasma oestradiol concentrations increased from 11 to 27 pg/ml between 25 and 31 days of age. When oestradiol was administered to ovariectomized 25- or 28-day-old rats by s.c. insertion of an implant, plasma prolactin concentrations at 05:00 and 12:00 h were similarly elevated 3 days after the operation. Oestradiol did not induce a nocturnal prolactin surge. The progesterone implants in ovariectomized rats at 28 days of age or on the first day of oestrus increased plasma prolactin values at 05:00 h. The magnitude of the progesterone-induced prolactin surge was greater when progesterone was given closer to the time of the first ovulation (about 34 days old). Pretreatment with oestradiol amplified the progesterone-induced prolactin surge. Mechanisms causing nocturnal prolactin surges are more sensitive to, and respond over a longer time period, to progesterone in pubertal rats than in adult animals. The results suggest that progesterone initiates the nocturnal surge of prolactin release and that oestradiol can amplify the effects of progesterone.     

Control of oestrus in cattle using progesterone coils

Four experiments were conducted to determine the effect of length of treatment, stage of cycle at start of treatment and administration of oestradiol benzoate or progesterone at the start of treatment with intravaginal progesterone coils on oestrous response and fertility. In Experiment 1, the number of heifers in oestrus was affected neither by injection of 5 mg oestradiol benzoate alone or with 200 mg progesterone nor by length of treatment. More heifers (P < 0.05) were in oestrus on day 2 after treatment following a 12-day treatment compared to a 9-day treatment.In Experiment 2, heifers between days 17 and 20 of the oestrous cycle received an injection of either 5 mg oestradiol benzoate alone or with 200 mg progesterone at the start of a 9-day treatment with progesterone coils. Neither the number of heifers in oestrus nor the pattern of onset were affected after treatment. In Experiment 3, heifers between days 0 and 3 of the oestrus cycle received progesterone coils for 9, 12 or 14 days. In addition, animals received (i) no further treatment, (ii) a gelatin capsule adhered to the coil containing 10 mg oestradiol benzoate (iii) a gelatin capsule adhered to the coil containing 200 mg progesterone. Following a 9- or 12-day treatment period heifers receiving the coil with the oestrogen capsule had a high oestrous response ( compared to , P < 0.05). When oestrogen was not given, there was a significant linear effect of duration of treatment on the number in oestrus (9 days, ; 12 days ; 14 days, ; P < 0.05).In Experiment 4, post-partum cows were used to compare a 9- and 12-day treatment period and half the animals in each group received either 5 mg oestradiol benzoate and 200 mg progesterone at the start of treatment or a 10 mg gelatin capsule adhered to the coil. The length of treatment affected the number of heifers in oestrus since were in oestrus after a 12-day treatment period compared with after a 9-day period (P < 0.001). There were no significant differences in the number of cows in oestrus after injection of oestrogen and progesterone ( ) or after the use of the gelatin capsule ( ).     

Plasma concentrations of progesterone, oestrogens, testosterone and LH-like activity during the oestrous cycle of the camel (Camelus dromedarius)

Peripheral plasma concentrations of progesterone, total oestrogens and testosterone (measured by RIAs) and LH (monitored by the mouse Leydig cell bio-assay) were measured in 8 female camels for a complete oestrous cycle (23.1 +/- 1.2 days). The absence of an LH surge and a low concentration of progesterone (less than 1 ng/ml) during oestrus (5 days) and throughout the cycle indicated a failure of spontaneous ovulation and absence of a subsequent luteal phase in this species. High concentrations of testosterone and oestrogens indicated that the oestrous cycle in the camel is mostly follicular and that the increasing values of the two hormones during follicular development (5 days) is probably the stimulus to behavioural oestrus.     

Relationships between insulin and glucose metabolism and pituitary-ovarian functions in fasted heifers

The effects of fasting between Days 8 and 16 of the estrous cycle on plasma concentrations of luteinizing hormone (LH), progesterone, cortisol, glucose and insulin were determined in 4 fasted and 4 control heifers during an estrous cycle of fasting and in the subsequent cycle after fasting. Cortisol levels were unaffected by fasting. Concentrations of insulin and glucose, however, were decreased (p less than 0.05) by 12 and 36 h, respectively, after fasting was begun and did not return to control values until 12 h (insulin) and 4 to 7 days (glucose) after fasting ended. Concentrations of progesterone were greater (p less than 0.05) in fasted than in control heifers from Day 10 to 15 of the estrous cycle during fasting, while LH levels were lower (p less than 0.01) in fasted than in control heifers during the last 24 h of fasting. Concentrations of LH increased (p less than 0.01) abruptly in fasted heifers in the first 4 h after they were refed on Day 16 of the fasted cycle. Concentrations (means +/- SEM) of LH also were greater (p less than 0.05) in fasted (11.2 +/- 2.6 ng/ml) than in control (4.7 +/- 1.2 ng/ml) heifers during estrus of the cycle after fasting; this elevated LH was preceded by a rebound response in insulin levels in the fasted-refed heifers, with insulin increasing from 176 +/- 35 pg/ml to 1302 +/- 280 pg/ml between refeeding and estrus of the cycle after fasting. Concentrations of LH, glucose and insulin were similar in both groups after Day 2 of the postfasting cycle. Concentrations of progesterone in two fasted heifers and controls were similar during the cycle after fasting, whereas concentrations in the other fasted heifers were less than 1 ng/ml until Day 10, indicating delayed ovulation and (or) reduced luteal function. Thus, aberrant pituitary and luteal functions in fasted heifers were associated with concurrent fasting-induced changes in insulin and glucose metabolism.     

Estradiol induces and progesterone inhibits the preovulatory surges of luteinizing hormone and follicle-stimulating hormone in heifers

Objectives were to determine: 1) whether estradiol, given via implants in amounts to stimulate a proestrus increase, induces preovulatory-like luteinizing hormone (LH) and follicle-stimulating hormone (FSH) surges; and 2) whether progesterone, given via infusion in amounts to simulate concentrations found in blood during the luteal phase of the estrous cycle, inhibits gonadotropin surges. All heifers were in the luteal phase of an estrous cycle when ovariectomized. Replacement therapy with estradiol and progesterone was started immediately after ovariectomy to mimic luteal phase concentrations of these steroids. Average estradiol (pg/ml) and progesterone (ng/ml) resulting from this replacement were 2.5 and 6.2 respectively; these values were similar (P greater than 0.05) to those on the day before ovariectomy (2.3 and 7.2, respectively). Nevertheless, basal concentrations of LH and FSH increased from 0.7 and 43 ng/ml before ovariectomy to 2.6 and 96 ng/ml, respectively, 24 h after ovariectomy. This may indicate that other ovarian factors are required to maintain low baselines of LH and FSH. Beginning 24 h after ovariectomy, replacement of steroids were adjusted as follows: 1) progesterone infusion was terminated and 2 additional estradiol implants were given every 12 h for 36 h (n = 5); 2) progesterone infusion was maintained and 2 additional estradiol implants were given every 12 h for 36 h (n = 3); or 3) progesterone infusion was terminated and 2 additional empty implants were given every 12 h for 36 h (n = 6). When estradiol implants were given every 12 h for 36 h, estradiol levels increased in plasma to 5 to 7 pg/ml, which resembles the increase in estradiol that occurs at proestrus. After ending progesterone infusion, levels of progesterone in plasma decreased to less than 1 ng/ml by 8 h. Preovulatory-like LH and FSH surges were induced only when progesterone infusion was stopped and additional estradiol implants were given. These surges were synchronous, occurring 61.8 +/- 0.4 h (mean +/- SE) after ending infusion of progesterone. We conclude that estradiol, at concentrations which simulate those found during proestrus, induces preovulatory-like LH and FSH surges in heifers and that progesterone, at concentrations found during the luteal phase of the estrous cycle, inhibits estradiol-induced gonadotropin surges. Furthermore, ovarian factors other than estradiol and progesterone may be required to maintain basal concentrations of LH and FSH in heifers.     

Decreased pulsatile LH secretion in heifers superovulated with eCG or FSH

This study was designed to test the hypothesis that treatment with super-ovulatory drugs suppresses endogenous pulsatile LH secretion. Heifers (n=5/group) were superovulated with eCG (2500 IU) or FSH (equivalent to 400 mg NIH-FSH-P1), starting on Day 10 of the estrous cycle, and were injected with prostaglandin F(2alpha) on Day 12 to induce luteolysis. Control cows were injected only with prostaglandin. Frequent blood samples were taken during luteolysis (6 to 14 h after PG administration) for assay of plasma LH, estradiol, progesterone, testosterone and androstenedione. The LH pulse frequency in eCG-treated cows was significantly lower than that in control cows (2.4 +/- 0.4 & 6.4 +/- 0.4 pulses/8 h, respectively; P<0.05), and plasma progesterone (3.4 +/- 0.4 vs 1.8 +/- 0.1 ng/ml, for treated and control heifers, respectively; P<0.05) and estradiol concentrations (25.9 +/- 4.3 & 4.3 +/- 0.4 pg/ml, for treated and control heifers, respectively; P<0.05) were higher compared with those of the controls. No LH pulses were detected in FSH-treated cows, and mean LH concentrations were significantly lower than those in the controls (0.3 +/- 0.1 & 0.8 +/- 0.1, respectively; P<0.05). This suppression of LH was associated with an increase in estradiol (9.5 +/- 1.4 pg/ml; P<0.05 compared with controls) but not in progesterone concentrations (2.1 +/- 0.2 ng/ml; P>0.05 compared to controls). Both superovulatory protocols increased the ovulation rate (21.6 +/- 3.9 and 23.0 +/- 4.2, for eCG and FSH groups, respectively; P>0.05). These data demonstrate that super-ovulatory treatments decrease LH pulse frequency during the follicular phase of the treatment cycle. This could be explained by increased steroid secretion in the eCG-trated heifers but not in FSH-treated animals.     

Hormone concentrations before and after semen-induced ovulation in the bactrian camel (Camelus bactrianus)

During the follicular phase of bactrian camels, basal concentrations of LH were 2.7 +/- 1.2 ng/ml. By 4 h after insemination peak values of 6.9 +/- 1.0 ng/ml occurred. In addition, a smaller LH peak (5.4 +/- 2.5 ng/ml) appeared 1 day before regression of the follicle began in unmated camels. During the follicular phase peripheral plasma progesterone values were low (0.36 +/- 0.28 ng/ml), but values increased to reach 1.73 +/- 0.74 ng/ml at 3 days and 2.4 +/- 0.86 ng/ml at 7 days after ovulation. Plasma oestradiol-17 beta concentrations were 26.8 +/- 9.0 pg/ml during the follicular phase and 30.8 +/- 5.1 pg/ml when the follicle was maximum size. Values fell after ovulation but rose to 29.8 +/- 6.5 pg/ml 3 days later.     

Peripheral plasma concentrations of oestradiol, progesterone, cortisol, LH and prolactin during the oestrous cycle in the cow, with emphasis on the peri-oestrous period

Interrelationships of circulating hormone levels and their implications for follicular development were studied throughout the oestrous cycle with emphasis on the perioestrous period in heifers and cows. The oestradiol level showed a major peak (45 pmol/1) before and coinciding with oestrus, and a second peak (27 pmol/1) around day 5–6 (day 0: day of first standing oestrus); it was low during the luteal phase of the cycle when progesterone was higher than 14 nmol/1 from day −12 to day −2. Large antral follicles, which had developed during the luteal phase, did not secrete significant amounts of oestradiol, degenerated after luteolysis, and were replaced by a newly developing follicle which became preovulatory. Parallel with this development the oestradiol level increased from the onset of luteolysis to reach a plateau about 26 h before the onset of oestrus. The interval between the onset of luteolysis and the onset of oestrus was 58 h; luteolysis proceeded at a slower rate in heifers than in cows. At 4.6 h after the onset of oestrus the maximum of the LH surge was recorded; the LH surge appeared to be postponed in the period October–December in comparison to the period August–September. The maximum of the LH surge was higher in heifers (45 μg/l) than in cows (30 μg/l), but its duration was similar (8.0 h). The oestradiol level decreased significantly from 6 h after the maximum of the LH surge, and standing oestrus (duration 18 h) was terminated almost at the same time as the return to basal values of oestradiol. Cortisol and prolactin levels did not show a peak during the peri-oestrus period. Cortisol fluctuated irrespective of the stage of the oestrus cycle and prolactin was significantly higher during the luteal phase.

The results of this study indicate that development of the preovulatory follicle starts in the cow at the onset of luteolysis, about 2.5 days before the preovulatory LH surge, and that oestradiol secretion by this follicle is possibly inhibited by the LH surge.     

Prolactin administration during the luteal and follicular phase of the oestrous cycle of gilts

In Exp. I infusions of prolactin (0.5 mg in 2 ml sterile saline) were repeated every 2 h for 36 h on Days 12-13 of the cycle. In Exp. II infusions of prolactin were administered from Days 17 to 19 (60 h) at 2-h intervals. Control gilts were given 2 ml sterile saline at similar intervals during the same period. Basal prolactin concentrations before initiation of infusions ranged from 1.3 +/- 0.1 to 5.6 +/- 2.2 ng/ml in both experiments. By 5 min after a prolactin infusion, mean plasma prolactin concentration ranged from 74.9 +/- 5.8 to 113.0 +/- 9.5 ng/ml, but then declined to approximately equal to 10 ng/ml just before the next infusion of prolactin. Administration of prolactin during the luteal phase of the oestrous cycle of the gilts had no effect on basal levels of progesterone, oestradiol or LH. During the follicular phase there were no differences (P greater than 0.05) between control and prolactin-treated gilt progesterone and LH concentrations, but oestradiol plasma values were decreased (P less than 0.05) on the 2nd and 3rd day of prolactin treatment. Our results would indicate that prolactin does not play a major role in the regulation of the oestrous cycle of the pig.