Endocrine profiles during the estrous cycle and pregnancy in the Baird's tapir (Tapirus bairdii)

Serum samples were collected 1–3 times weekly from two Baird's tapirs (Tapirus bairdii) for 6 months in 1987–1988, and for more than 3 consecutive years beginning in 1989 to characterize hormone patterns during the estrous cycle and pregnancy. Based on serum progesterone concentrations, mean (±SEM) duration of the estrous cycle (n = 20) was 30.8 ± 2.6 days (range, 25–38 days) with a luteal phase length of 18.1 ± 0.4 days (range, 15–20 days). Mean peak serum progesterone concentrations during the luteal phase were 1.35 ± 0.16 ng/ml, and nadir concentrations were 0.19 ± 0.03 ng/ml during the interluteal period. Distinct surges of estradiol preceded luteal phase progesterone increases in most (14/20) cycles. Gestation length was 392 ± 4 days for three complete pregnancies. Mean serum progesterone concentrations increased throughout gestation and were 1.83 ± 0.13, 2.73 ± 0.13, and 4.30 ± 0.16 ng/ml during early, mid- and late gestation, respectively. Serum estradiol concentrations began to rise during mid-gestation, increasing dramatically during the last week of pregnancy. Patterns of serum estriol and estrone secretion during pregnancy were similar to that observed for estradiol. In contrast to progesterone and estrogens, serum cortisol concentrations were unchanged during pregnancy or parturition. Females resumed cycling 16.2 ± 2.0 days after parturition (n = 4) and, on two occasions, females became pregnant during the first postpartum estrus. These data suggest that the tapir cycles at approximately monthly intervals and that increases in serum progesterone are indicative of luteal activity. The interluteal period is relatively long, comprising approximately 40% of the estrous cycle. During gestation, progesterone concentrations are increased above luteal phase levels, and there is evidence of increased estrogen production during late gestation. The absence of increased cortisol secretion at the end of gestation suggests that this steroid does not play a major role in initiating parturition in this species. © 1994 Wiley-Liss, Inc.     

Periovulatory time courses of plasma estradiol and progesterone in the Japanese monkey (Macaca fuscata)

Periovulatory time courses of plasma estradiol and progesterone were determined in 21 menstrual cycles of 20 Japanese monkeys. Both steroids were measured by radioimmunoassay. Ovulation was detected by serial laparoscopic observations of the ovaries. Three of the 21 cycles were anovulatory cycles. In the remaining 18 ovulatory cycles, a preovulatory estradiol peak occurred on day 12.2±1.4 (range 10–15) of the menstrual cycle. The estradiol concentration at the peak was 431±199 (range 210–930) pg/ml. The time interval between the estradiol peak and ovulation was within 48 hr; the shortest interval was 10–13 hr and the longest 32–48 hr. Although the progesterone levels began to increase slightly (0.6–1.4 ng/ml) before ovulation, they did not show a continuous increase but decreased once before ovulation. The increase in progesterone with development of the corpus luteum after ovulation was very gradual during the first 2 days after ovulation. Subsequently, in 13 of 18 ovulatory cycles the progesterone levels rose rapidly and reached a maximum, 4.0±1.2 (range 2.3–5.7) ng/ml, 4–8 days after ovulation. In 5 of the 18 cycles, the progesterone levels did not rise at all or did not exceed 2.0 ng/ml even if they showed more or less an increase. In the 5 cycles, the length of the luteal phase was 8.2±1.6 (range 6–10) days, which was significantly shorter than that of the former 13 cycles with 14.0±1.1 (range 13–16) days.     

Salivary progesterone for the assessment of the ovarian function in the capuchin monkey (Cebus apella)

Salivary and plasma progesterone were measured in normally cycling (n=10) and castrated (n=4) femaleCebus monkeys (Cebus apella). During the follicular phase, progesterone levels in saliva ranged between 0.05 and 1.40 ng/ml and in the luteal phase they increased to between 0.22 and 4.70 ng/ml. These values represented on average 6.5 and 3.2% of those values measured in plasma, for the follicular and luteal phases, respectively. The regression analysis of the steroid concentrations in both fluids showed a highly significant correlation (r=0.8985,n=180,P<0.0001). Ovariectomized monkeys had consistently low salivary (0.37±0.02 ng/ml) and plasma (4.70±0.25 ng/ml) progesterone, showing a low, but significnat, correlation coefficient (r=0.2592,n=58,P=0.047). The ratio of plasma/salivary progesterone was significantly higher in the luteal phase (31.09±1.65) than in the follicular phase (23.06±2.26) and in castrated monkeys (16.00±1.38). The free fraction of progesterone constituted 5.3±0.2% of the total plasma progesterone during the follicular phase and 3.3±0.1% during the luteal phase. Ovariectomized monkeys showed a significantly higher percentage of free progesterone in plasma (7.7±0.1%). In contrast, free progesterone made up 64.4 and 70.9% of the total salivary progesterone for the follicular and luteal phases, respectively. The proportion of free progesterone in castrated animals was within the range observed in cycling animals. We suggest that the levels of progesterone in the saliva of capuchin monkey follow a pattern similar to that for plasma progesterone, reflecting the free steroid fraction. Thus, the measurement of such steroid in saliva may offer a valuable alternative to plasma determinations for the assessment of the ovarian function inCebus and probably other New World monkey species.     

The relationship between plasma progesterone and the timing of ovulation and early embryonic development in the marmoset monkey (Callithrix jacchus)

Levels of progesterone in peripheral plasma samples showed a mean (± S.E.M.) ovarian cycle length of 28 ·63 ± 1·01 days ( n = 19).
The preovulatory, or follicular phase (mean ± S.E.M. length: 8·25 ± 0·30 days, n = 56) was defined as that period of the cycle during which progesterone levels remained below 10 ng/ml. The postovulatory, or luteal phase (mean ± S.E.M. length: 19·22 ± 0·63 days, n = 48) was defined as the remaining period of the cycle during which levels remained between 10 ng/ml and 150 ng/ml.
The day of ovulation (day 0) was defined as that preceding the day on which progesterone levels first exceeded 10 ng/ml (day l), at the onset of the luteal phase. Oocytes and preim-plantation embryos recovered from the reproductive tract provided supporting evidence for the timing of ovulation.
The short follicular phase indicated that follicular growth may be initiated during the previous luteal phase. The long luteal phase may be related to the extended period of preim-plantation development.     

Progesterone concentrations during estrous cycle of dairy cows exposed to electric and magnetic fields

Sixteen multiparous nonpregnant lactating Holstein cows (each weighing 662 ± 65 kg in 150.4 ±40 day of lactation) were confined to wooden metabolic cages with 12:12 h light:dark cycle during the experiment. The cows were divided into two sequences of eight cows each and exposed to electric and magnetic fields (EMF) in an exposure chamber. This chamber produced a vertical electric field of 10 kV/m and a uniform horizontal magnetic field of 30 μT at 60 Hz. One sequence was exposed for three estrous cycles of 24 to 27 days. During the first estrous cycle, the electric and magnetic fields were off; during the second estrous cycle, they were on; and during the third estrous cycle, they were off. The second sequence was also exposed for three 24 to 26 days estrous cycles, but the exposure to the fields was reversed (first estrous cycle, on; second estrous cycle, off; third estrous cycle, on). The length of each exposure period (21 to 27 days) varied according to the estrous cycle length. No differences were detected in plasma progesterone concentrations and area under the progesterone curve during estrous cycles between EMF nonexposed and exposed periods (2.28 ±0.17 and 2.25 ± 0.17; and 24.5 ± 1.9 vs. 26.4 ± 1.9 ng/ml, respectively). However, estrous cycle length, determined by the presence of a functional corpus luteum detected by concentrations of progesterone equal to or more than 1 ng/ml plasma, was shorter in nonexposed cows than when they were exposed to EMF (22.0 ± 0.9 vs. 25.3 ± 1.4 days). Bioelectromagnetics 19:438–443, 1998. © 1998 Wiley-Liss, Inc.     

Evaluation of progesterone and 20-oxo-progestagens in the plasma of Asian (Elephas maximus) and African (Loxodonta africana) elephants

The corpus luteum of African elephants produces high amounts of 5α-reduced progesterone metabolites (5α-pregnane-3,20-dione and 5-α-pregnane-3α-ol-20-one), whereas progesterone itself is quantitatively less important, and plasma levels of progesterone during the estrous cycle in elephants are considerably lower than those of other mammals. The objective of this study was to compare the concentration of progesterone in plasma of Asian and African elephants as determined by specific progesterone assays with those of total immunoreactive progestagens containing a 20-oxo-group (20-oxo-P). These metabolites were determined by an enzyme immunoassay using an antibody against 5-α-pregnane-3β-ol-20-one, 3HS:BSA. Plasma of non-pregnant Asian (n = 4) and African (n = 4) elephants was collected at weekly intervals for periods of 8–15 months and at random intervals during pregnancy in one Asian elephant. High-performance liquid chromatography separation of plasma samples of both species demonstrated that in the 20-oxo-P assay, 5α-pregnane-3,20-dione makes up ˜60% of the total immunoreactive material. The progesterone and 20-oxo-P values during the estrous cycle showed a parallel pattern and were significantly correlated (P < 0.001; Asian: r = 0.80; y = 3.76 × –0.10; African: r = 0.75; y = 2.66 × –0.08). Progesterone and 20-oxo-P values in Asian and African elephants were <0.15 ng/ml during the follicular phase (weeks –4 to 0) of the estrous cycle; progesterone values during the luteal phase (weeks 2–9) were 0.60 ± 0.03 and 0.53 ± 0.03 ng/ml, and the 20-oxo-P values were 2.19 ± 0.16 and 1.48 ± 0.12 ng/ml, respectively. The 20-oxo-P values of the pregnant animal, although slightly higher, were comparable to those of non-pregnant elephants during the luteal phase. Total immunoreactive 20-oxo-P values are about three times higher than those of progesterone during the luteal phase, and 5α-pregnane-3,20-dione is the major immunoreactive 20-oxo-P in the plasma of Asian and African elephants. Zoo Biol 16:403–413, 1997. © 1997 Wiley-Liss, Inc.     

The influence of prolactin (PRL) on progesterone secretion by porcine luteal cells in vitro

Porcine luteal cells were obtained from corpora lutea on the 5th, 13th and 17th days of the estrous cycle. The cells were suspended at a concentration of 5 × 10⁴ cells/ml in Eagle's medium with 2% human serum albumin. These cells were incubated with or without 0.01, 0.1, 1 or 10 μg/ml porcine prolactin. The amount of progesterone in cultures was estimated by a radio-immunological method after 30 min, 3 h and 6 h of culturing.Luteal cells obtained on the 5th day of the estrous cycle and incubated without prolactin secreted 71.24 ± 21.91 ng progesterone/ml of medium, whereas under the influence of prolactin at 0.01, 0.1, 1 and 10 μg/ml, 39.06 ± 13.33, 44.31 ± 12.69, 44.88 ± 16.85 and 51.62 ± 15.01 ng progesterone/ml (P<0.01) were secreted. Luteal cells from the 13th day of the estrous cycle incubated without prolactin secreted on average 70.72 ± 9.21 ng progesterone/ml of medium, whereas under the influence of different prolactin doses 50.75 ± 8.52, 46.54 ± 7.13, 43.30 ± 6.78 and 41.68 ± 7.21 ng progesterone/ml (P<0.01) were secreted.Prolactin did not change progesterone secretion by luteal cells obtained on the 17th day of the estrous cycle. An influence of the incubation time on progesterone secretion by these cells was observed: after 30 min of incubation the cells secreted 8.83 ± 2.95 ng/ml, after 3 h 8.12 ± 2.57 ng/ml and after 6 h 6.86 ± 1.91 ng/ml, irrespective of the amount of PRL added.The results suggest that prolactin plays a role in the luteolysis of the corpus luteum.     

Serum profiles of luteinizing hormone,progesterone and total estrogens during the canine estrous cycle

Serum levels of LH, total estrogen and progesterone were measured daily by radioimmunoassay during proestrus, estrus and early diestrus in five beagle bitches. Occurrence of the LH peak relative to the onset of estrus was quite variable ranging from 3 days before to 7 days after the onset of estrus. Serum LH levels were elevated for 3 days with a peak value of 25 ± 2 ng/ml reached 2.4 days after the start of estrus. LH levels were ≤ 2 ng/ml when measured at other times during the estrous cycle. Estrogen titers ranged from 84 ± 39 pg/ml at 9 days before the LH peak to 175 ± 15 pg/ml coincident with the LH peak. A broad estrogen peak was evident beginning 5 days before and continuing for 5 days after the LH peak. An estrogen surge was seen in 4 of 5 dogs immediately preceding or coincident with the LH peak suggesting that LH release in the bitch is triggered by a sharp elevation in estrogen levels. Serum progesterone levels rose from ≤ 5 ng/ml before the LH peak to 46 ± 6 ng/ml 6 days afterwards.     

Repeatability of blood serum progesterone levels in dairy heifers on day 7 of the estrous cycle

Thirty normally cycling dairy heifers were used to determine the repeatability of blood serum progesterone levels on Day 7 ± 0.25 d of the estrous cycle. The experimental group consisted of 16 Holsteins and 14 dairy crossbreds ranging in age from 18 to 24 months. Day of the estrous cycle was determined from twice daily observations for standing heat (Day 0). Serum progesterone levels for Day 7 ± 0.25 d were determined by radioimmunoassay from blood samples collected by jugular venipuncture over three to four consecutive estrous cycles. Levels of blood serum progesterone for Day 7 ± 0.25 d ranged from 0.57 to 6.03 ng/ml. Least square means for the Holstein (2.74 ng/ml) and dairy crossbred (3.38 ng/ml) groups were different (P<0.006). The repeatability for levels of blood serum progesterone on Day 7 of the estrous cycle was low (0.0115).     

Ovarian cycle approach by rectal temperature and fecal progesterone in a female killer whale,Orcinus orca

This study aimed to validate the measurements of body temperature and fecal progesterone concentrations as minimally invasive techniques for assessing ovarian cycle in a single sexually mature female killer whale. Rectal temperature data, fecal and blood samples were collected in the dorsal position using routine husbandry training on a voluntary basis. The correlations between rectal temperature and plasma progesterone concentration and between fecal and plasma progesterone concentrations were investigated. Fecal progesterone metabolites were identified by a combination of high‐performance liquid chromatography and enzyme immunoassay. Plasma progesterone concentrations (range: 0.2–18.6 ng/ml) and rectal temperature (range: 35.3–35.9°C) changed cyclically, and cycle lengths were an average (±SD) of 44.9±4.0 days (nine cycles) and 44.6±5.9 days (nine cycles), respectively. Rectal temperature positively correlated with the plasma progesterone concentrations (r=0.641, P<0.01). There was a visual trend for fecal progesterone profiles to be similar to circulating plasma progesterone profiles. Fecal immunoreactive progestagen analysis resulted in a marked immunoreactive peak of progesterone. The data from the single killer whale indicate that the measurement of rectal temperature is suitable for minimally invasive assessment of the estrous cycle and monitoring the fecal progesterone concentration is useful to assess ovarian luteal activity. Zoo Biol 30:285–295, 2011. © 2010 Wiley‐Liss, Inc.     

Competitive protein binding assay of progesterone without chromatography

A competitive protein binding assay for the measurement of progesterone in human plasma without chromatographic separation of steroids and recovery evaluation in individual samples is described. It is based on the specificity of the progesterone binding plasma protein (PBP) of the pregnant guinea pig. A dried petroleum ether extract of plasma was incubated with ³H-progesterone and 1600 fold diluted pregnant guinea pig plasma. Bound radioactivity was measured with a dextran coated charcoal suspension technique. Plasma progesterone concentration was obtained by comparison with a standard curve and correction for extraction separately measured for each batch of petroleum ether. The sensitivity was 100 pg. Recovery experiments for progesterone and competing steroids added to plasma respectively showed the accuracy and the specificity of the method. However comparison of the results from assays with and without chromatographic separation of steroids, showed that in the latter-case the specificity was good only for plasmas containing more than 1ng/ml of progesterone. Concentration of progesterone in plasma from men was 0.46±0.14 ng/ml (mean ± S.D) and from post menopausal women 0.30± 0.13 ng/ml.Between days 1 and 13 and days 16 and 22 of the normal menstrualcycle the concentrations were respectively 0.81 ± 0.38 and 12.50 ± 2.96 ng/ml. The variations of the progesterone concentration during pregnancy are also shown.     

Cyclic changes in the circulating and urinary levels of ovarian steroids in the adult female owl monkey (Aotus trivirgatus).

Circulating levels of oestrone and progesterone were measured by radioimmunoassays in plasma samles from 5 female owl monkeys on 60 consecutive days. Both steroids exhibited cyclic fluctuations and based on nadir to nadir intervals the ovarian cycle was estimated to be 15.92 +/- 0.26 days. Levels of oestrone and pregnanediol-3 alpha-glucuronide were also measured in daily urine samples. The fluctuations of urinary steroids reflected those observed in plasma. Ketamine sedation had no effect on the length of the cycle. Peak values of plasma progesterone and oestrone were 250.48 +/- 11.37 and 3.59 +/- 0.066 ng/ml respectively. There was no clear hormonal distinction between the follicular and luteal phase of the cycle in these owl monkeys.     

Ovarian function in crossbred beef heifers treated with dexamethasone

Each of 32 crossbred beef heifers was brought from pasture on day 16 of its estrous cycle and assigned randomly to one of four treatment groups as follows: Field Control (FC), Field Dexamethasone (FD), Pen Control (PC), and Pen Dexamethasone (PD). Field groups were kept in a 0.8-ha field and pen groups were kept in 4.6-x 9.8-m pens in a pole barn during the trial. Dexamethasone (DEX) groups received 20 mg of DEX on cycle day 16 and 30 mg daily on days 17 through 20. Control heifers received an equal volume of physiological saline solution on corresponding cycle days. Average treatment cycle lengths (±SD) for control heifers in FC and PC groups were 21.1 ± 2.8 and 21.6 ± 1.8 days, respectively, and were not significantly different. Average time from progesterone decline (<1 ng/ml) to estrus was two days for each of the control groups. Four DEX-injected heifers had not shown estrus by day 44 of the treatment cycle. Progesterone had declined for two of these heifers by cycle day 18 and remained below 1 ng/ml past cycle day 48. The other two showed a decline in plasma progesterone by cycle days 18 and 32, respectively, and a progesterone rise by day 42 without having been detected in estrus. The remaining 12 DEX heifers had an average cycle length of 29.4 days. Four extended cycles resulted from extended CL function, five from an extended period from progesterone decline to estrus and three from a combination of these factors. These observations suggest that the administration of pharmacological doses of glucocorticoid during the late diestrus or early proestrus may result in altered ovarian function.     

Plasma luteinizing hormone during the breeding cycle of the female ring dove

Plasma luteinizing hormone (LH) levels in serial blood samples of female ring doves (Streptopelia risoria) were measured by radioimmunoassay method. Our findings indicate the following pattern of LH levels: LH increases during early courtship which reaches a peak (5.43 ± 0.79 ng/ml) during the nesting period. LH declines following egg-laying (3.77 ± 0.33 ng/ml) and again after hatching (2.23 ± 0.28 ng/ml). It remains high in females which laid infertile eggs initially and subsequently showed a further laying. The results are compared with published data on plasma estrogens and progesterone in the dove's breeding cycle.     

A controlled internal drug-release dispenser containing progesterone for control of the estrous cycle of ewes

Experiments were conducted to evaluate a controlled internal drug-release (CIDR) dispenser containing progesterone to control the estrous cycle of ewes. After insertion of CIDR dispensers into the vaginae of ovariectomized ewes (Experiment 1; n = 11), the mean plasma progesterone rose from 0.74 ± 0.2 ng/ml to a peak of 5.5 ± 1.0 ng/ml within 2 h and then declined to 3.0 ± 0.5 ng/ml by 48 h. This was followed by a more gradual decline to 1.7 ± 0.3 ng/ml at the time of removal 12 or 14 d later. Following removal, the levels declined to baseline within 4 h. In Experiment 2, a 12- or 14-d treatment with CIDR dispensers was initiated in ewes 2, 9 and 16 d after synchronization of the estrous cycle with fluorogestone acetate (FGA)-impregnated intravaginal sponges. An intramuscular (i.m.) injection of 500 IU pregnant mare serum gonadotropin (PMSG) was given at the time of removal of the FGA sponge or CIDR dispenser. Based on plasma progesterone profiles, CIDR dispensers inserted 9 or 16 d after FGA sponge removal delayed the onset of a new estrous cycle until they were withdrawn. Following withdrawal, ovulation was effectively synchronized in all treatment groups and accompanied by development of functionally active corpora lutea with a normal lifespan. In Experiment 3, comparison of the mating response of ewes after treatment with CIDR dispensers (n = 192) or FGA sponges (n = 194) showed that 92% and 91% of the treated ewes, respectively, were marked by the ram within 72 h. Fertility and litter size of ewes bred at the synchronized and followup estrus were similar for both treatments. These results indicate that treatment of ewes with CIDR dispensers containing progesterone maintains plasma levels of progesterone within the range found during the normal estrous cycle. The CIDR dispenser is effective in synchronizing the estrous cycle of adult ewes and offers a promising alternative to the FGA-impregnated intravaginal sponge.     

Characteristics of the oestrous cycle of Iberian red deer (Cervus elaphus hispanicus) assessed by progesterone profiles

This study examines the length of the oestrous cycle in 16 Iberian red deer females assessed by means of changes in progesterone concentrations, along with the changes in the profile of this hormone. Samples were collected three occasions per week from the week after calving (15 May to 15 June) up to May of the following year. The oestrous cycle lasted 19.57+/-0.29 days (range 10-27 d) calculated in 130 oestrous cycles examined. Progesterone titres did not rise above 0.5 ng/ml in the follicular phase, except in four samples. The maximum peak in progesterone concentration during the luteal phase remained above 1 ng/ml in most cases. Twenty-five percent of the individuals studied (4 out of 16) showed an oestrous cycle lasting shorter than the mean (15.2+/-0.30 days) before the start of the reproductive season, followed by a period of sexual inactivity. The standard progesterone profile in natural oestrous cycles rose from basal levels to those above 0.5 ng/ml four days after onset of oestrus, reached a peak of 1.71+/-0.07 ng/ml and then declined to less than 0.2 ng/ml after day 20. Following the rapid decline of progesterone after day 14, the concentration remained around the baseline level of 0.1 to 0.2 ng/ml during the immediate pre- and post-ovulatory phase of the cycle.     

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; X? ± 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.     

Uptake and effects of ovarian steroids in the early pig embryo: In vitro and in vivo studies

The role of ovarian steroids in the preimplantation pig embryo was studied in vivo and in vitro. Twenty gilts were treated three times daily on days 1 to 4 after insemination with either 25, 100, 250, or 1000 mg progesterone in oil, and 17 gilts were injected with corresponding amounts of sesame oil (controls). All gilts were slaughtered 5 days after insemination and the embryos were recovered. Oviduct and plasma progesterone content were significantly (P<0.001) higher in gilts treated with 750 mg of exogenous progesterone per day. After 750 mg progesterone, oviduct progesterone content was twice as high as control levels, while after 3000 mg progesterone per day the levels in oviduct and uterus exceeded those of controls by five and seven times, respectively. In gilts treated with 750 mg progesterone per day, plasma progesterone levels were 177.4 ± 22.1 ng/ml ($\text{x}\text{±}\text{SD}$) on day 3 and 186.4 ± 69.2 ng/ml on day 5 and resembled values found in superovulated pigs with more than 40 ovulations. Excessive plasma progesterone values of 1014.6 ± 840.4 ng/ml on day 3 and 473.2 ± 197.2 ng/ml on day 5 were found after treatment with 3000 mg of progesterone per day. Treatment with up to 750 mg of exogenous progesterone per day, did not affect embryonic development, but 3000 mg per day resulted in a significantly (P<0.001) higher percentage of retarded and degenerate embryos compared to controls (71.8% versus 3.2%).In addition, the amount and specificity of uptake of ³H-labelled progesterone and estradiol-17 beta by pig blastocysts recovered from superovulated gilts were investigated after 6 hrs in vitro culture. The uptake of ³H-progesterone was 131.9 ± 56.9 counts per million (cpm) per 10 blastocysts, corresponding to 1.1 fmoles progesterone. The uptake was non-specific for it was only slightly reduced in the presence of a 100-fold excess of unlabelled progesterone (20.1%) or estradiol-17 beta (27.0%). The uptake of ³H-estradiol-17 beta was 133.9 ± 74.12 cpm per 10 blastocysts, corresponding to 1.3 fmoles estradiol-17 beta. The uptake was significantly (P<0.01) reduced by 67.7% in the presence of a 100-fold excess of unlabelled estradiol-17 beta. Apparent specific binding was 0.87 fmoles estradiol-17 beta per 10 blastocysts or 72.5 fmoles estradiol-17 beta per mg protein. The uptake was only slightly reduced in the presence of a 100-fold excess of unlabelled progesterone (23.3%). This significant inhibition could be determined after 2 hrs in vitro culture. There was no competitive inhibition after 20 min. of culture.Uptake by unfertilized ova and degenerate embryos recovered on day 5 was significantly smaller (51.8 ± 10.3 cpm per 10 eggs; P<0.001) than by blastocysts recovered on the same day. No competitive inhibition could then be determined. In vivo, preimplantation pig embryos seem to be rather insensitive to high progesterone levels. Excessive amounts of progesterone probably can be metabolized to a great extent. Progesterone seems to be taken up rather non-specifically by the pig embryo. The uptake and binding of estradiol-17 beta seems to be more specific. Studies are in progress to investigate the physiological role of estradiol-17 beta uptake in early embryonic development.     

Serum luteinizing hormone levels in cattle under various reproductive states

Serum lutinizing hormone (LH) levels in cattle during various reproductive states were measured by radioimmunoassay. A sharp LH peak observed at estrus (22.72 ± 5.68 ng/ml) was about 26 times higher than at other stages of the cycle (0.87 ± 0.06 ng/ml). LH levels during the first 90 days of pregnancy (0.75 ± 0.15 ng/ml) were similar to those of the estrous cycle, except during estrus, while those during the second (0.22 ± 0.07 ng/ml) and third trimesters of pregnancy (0.22 ± 0.08 ng/ml) were significantly lower. Higher levels than those of the cycling cows, except during estrus, were seen in ovariectomized cows (2.21 ± 0.56 ng/ml). Levels of LH in cows with cystic follicles (2.00 ± 0.49 ng/ml) were higher than the levels in the cycle. LH levels in bulls (1.29 ± 0.39 ng/ml) were comparable to that of estrous cows. Serum LH of calves increased with age from 1.00 ± 0.32 ng/ml (less than 30 days of age), to 2.30 ± 0.83 ng/ml (181 to 210 days of age), and the level after 151 days was significantly higher than that of the cyclic cows, except during estrus.     

Plasma Progesterone Assays in Superovulated Cattle

Plasma progesterone was measured in 14 normally cycling heifers and cows subjected to non-surgical recoveries of embryos. A radioimmunoassay (RIA) method was used for progesterone determination. The average progesterone concentration increased from 7.5 to 11.6 ng/ml in 8 of the animals following treatment with PMSG on day 8–12. Six animals had a decrease from 5.0 ± 2.1 to 3.9 ± 2.5 ng/ml. The overall increase was from 6.4 ± 2.7 ng/ml to 8.3 ± 4.8 ng/ ml. Prostaglandin F2a-analogue (cloprostenol) treatment resulted in a sharp decrease in plasma progesterone followed by a rapid increase to an average of 46.8 ng/ml on day 16. A high degree of variability in this peak value was observed, and it was not correlated with the number of corpora lutea. The superovulatory cycle was generally prolonged. The heat following the superovulatory treatment was silent, and a typical ovarian resting period was observed during which the progesterone concentration remained low and the ovaries small.