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The aim of the study was to investigate the influence of diarrheic infections during the early postnatal phase of calves on the concentrations of hormones controlling reproduction and metabolism. Blood samples were collected from 20 male and female calves via jugular vein catheters every 15 min for 6 hr at Days 3, 9, and 21 of life. The animals were classified into three groups. Group 1 (controls): healthy calves (n = 9). Group 2: calves affected with diarrhea at Day 9 (n = 7). Group 3: calves with diarrhea at Days 3 and 9 (n = 4). Infections occurred spontaneously and were mainly due to E. coli infections. All affected calves had recovered at Day 21. Mean GH concentrations in the calves in Groups 2 and 3 compared to control calves had increased by Day 3 (P<0.01; P<0.001). Cortisol levels of calves in all groups were highest at Day 3 and decreased thereafter (P<0.001). Cortisol concentrations were lower at Day 3 in animals in Groups 2 (P<0.001) and 3 (P<0.05) than in controls. Pulsatile LH release was detectable at Days 9 and 21 only in healthy calves. Insulin increased at Day 9 during diarrhea. The results indicate that cortisol concentrations decreased whereas GH concentrations were increased before diarrhea was observed. The onset of pulsatile LH release was delayed in diarrheic calves. It is concluded that diarrhea exerts effects upon the release of reproductive and metabolic hormones in early postnatal calves.

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To evaluate new therapeutical concepts for male subfertility, we tested the effects of exogenous recombinant bovine growth hormone (rbGH) on various endocrine and metabolic parameters both in blood and in seminal plasma of bulls. Sperm quality was assessed morphometrically and by monitoring the number of successful artificial inseminations (AIs) defined as non-return rates (NRR). Aliquots of 450 semen samples were used from each bull and each experimental period (4 wk before, 14 weeks during and 6 wk after treatment). Six out of ten sires (average age 8.4 years) were treated every two weeks with 640-mg depot formulated rbGH (Eli Lilly). Four bulls received vehicle only. Blood plasma bGH, IGF-I, insulin and glucose concentrations were increased with rbGH treatment. In seminal plasma there was no effect of rbGH treatment on fructose and citrate or on testosterone concentrations. With one exception, rbGH-treated bulls had greater IGFBP-3 concentrations in seminal plasma. Motility of spermatozoa after freezing and thawing was increased compared with pretreatment rates. Most interestingly, the number of successful AIs was increased by an average of 6.0% NRR when ejaculates from rbGH-treated bulls were used.

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Semen from three stallions was collected weekly for six months (December through May) to determine semen parameters and hormones (testosterone and estradiol-17 beta) in seminal plasma. Once a month three ejaculates were collected at intervals of one hour and examined accordingly. Testosterone and estradiol-17 beta were also determined in peripheral blood plasma (V. jugularis) collected twice a week. Semen parameters (volume, gel-free volume and sperm concentration) were clearly influenced by season. The testosterone concentration in peripheral blood plasma was lowest during December whereas in seminal plasma testosterone concentration gradually increased throughout the experimental period. Testosterone concentrations in seminal plasma were only one tenth of those in peripheral blood. Estradiol-17 beta in blood plasma was highest in April and May whereas no significant differences occurred in seminal plasma. Average monthly concentrations of estradiol-17 beta in blood and seminal plasma were in the range of 27.4 pg/ml to 45.3 pg/ml. Collection of three successive ejaculations led to a significant decrease of ejaculate volume as well as sperm concentration. Ejaculation frequency did not influence testosterone in seminal plasma whereas the concentration of estradiol-17 beta decreased significantly in the second and third ejaculate. The results indicate that estradiol-17 beta in the stallion's semen may be bound to spermatozoa or is accumulated in seminal plasma.

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A leucine/valine substitution at amino acid position 127 was identified by the polymerase chain reaction and restriction fragment length polymorphism in the bovine growth hormone gene. Genotyping was performed in 84 AI bulls of three different breeds, in which plasma concentrations of growth hormone (GH) and insulin-like growth factor I (IGF-1) were also measured. Gene frequencies of variants L (leucine) und V (valine) were 0.80/0.20 (Black and White), 0.90/0.10 (Brown), 0.71/0.29 (Simmental). Hormone concentrations were measured during different physiological conditions (normal feeding, fasting, realimentation) in the majority of animals. Generally, genotype LL was associated with higher concentrations of GH than LV. This difference was significant in Black and White bulls (P < 0.05). In contrast, IGF-1 concentrations were higher in LV than in LL animals. This was most pronounced in mature, realimented Simmental bulls. We conclude that the various GH alleles influence the circulating concentrations of GH and IGF-1.

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SUMMARY: Blood plasma levels of growth hormone (bGH) and of free fatty acids (FFA) were measured in repeated samples drawn every 15' for bHG, every 1 h for FFA one day after morning feeding and after 3 days of severe feed restriction of 7 young (< 2 years) and 14 old (> 5 years) bulls. The numerous data were condensated by the PULSAR program of Merriam and Wachter (1982) to mean level, average baseline concentration, number, average amplitude and average duration of secretory peaks. Young bulls had higher values for all of these parameters except peak duration and increased these after fast except for peak duration, baseline and integral while mature bulls reacted little to food restriction. FFA plasma levels were higher in young bulls under normal feeding when mature bulls had more frequent peaks. After feed restriction mature bulls increased the mean plasma level to the increased level of young bulls but decreased the peak frequency. The milk protein yield breeding values are related significantly to mean level, integral and the peak duration of plasma bGH levels but in different directions in young and in mature bulls. ZUSAMMENFASSUNG: Beziehungen zwischen Alter, Futterstatus, Milchzuchtwert und Plasmaspiegel von Wachstumshormon (GH) und Freien Fettsäuren (FFA) bei Stieren Blutplasmaspiegel von Wachstumshormon (GH) und Freien Fettsäuren (FFA) wurden in wiederholten Proben gemessen, die im Falle von GH alle 15 min. und im Falle von FFA jede Stunde einen Tag nach Morgenfütterung, nach drei Tagen starker Futterrestriktion bei sieben jungen (weniger als zwei Jahre) und 14 alten (über fünf Jahre) Stieren gezogen worden waren. Die zahlreichen Daten wurden mit Hilfe des Computerprogrammes von Merriam und Wachter (1982) kondensiert zu durchschnittlichen Plasmaspiegel, durchschnittliche Basiskonzentration, Zahl, durchschnittliche Amplitude und durchschnittliche Dauer von Sekretionsspitzen und Integral. Die Jungstiere hatten für alle diese Parameter höhere Werte, außer der Dauer von Sekretionsspitzen und nahmen mit Ausnahme von dieser, von Basisspiegel und Integral nach Futterrestriktion zu, während Altstiere auf diese sehr wenig reagiert haben. FFA-Plasmaspiegel waren bei jungen Stieren höher unter Normalfütterung, während alte Stiere häufiger Sekretionsspitzen zeigten. Nach Futterrestriktion steigerten Altstiere den mittleren Plasmaspiegel auf den angestiegenen Spiegel junger Stiere, aber verminderten die Häufigkeit der Sekretionsspitzen. Milchprotein-Zuchtwerte sind signifikant mit mittlerem Plasmaspiegelwert, Integral und Dauer der Sekretionsspitzen bei Plasma GH korreliert, aber in verschiedener Richtung bei jungen und bei Altstieren.

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Yolk sac development was investigated in 69 ovine and 10 bovine embryos from the blastocyst stage to the 7th week of gestation. Light and electron microscopical findings are reported. The yolk sac in sheep and cattle is composed of an enlarged sac-like portion lying below the embryo and two ends which follow the elongated course of the trophoblast. In sheep, an open connection exists between the intestines and the yolk sac up to a crown-rump length (CRL) of 9 mm. It is closed by 12 mm CRL. The wall of the yolk sac is especially well vascularized in the enlarged, sac-like portion. Primary erythropoiesis occurs within the blood capillaries. In the blastocyst, the yolk sac entoderm is made up of elongated, flat cells. It becomes cuboidal in the 3 mm embryo (ovine) and later columnar. The up to 20 microns tall cells stain darkly and contain numerous light-colored vesicles. At 4.5 mm CRL light cells appear between the dark ones. Both cells are rich in rough endoplasmic reticulum (rER). The increased staining of the darker cells is due to an osmophilic cytoplasm and numerous, often parallel lamella of rER. The rER of the light cells is enlarged to irregularly-shaped cisternae, which nearly fill the entire cytoplasm and give them a rounded appearance. The dark cells contain polygonal nuclei, whereas those in the light cells are round with one or two nucleoli. The oval mitochondria have only a few peripheral cristae. Golgi fields are not very common. Cells of the entoderm are connected to one another over zonulae occludentes. They possess microvilli on the luminal surface and are supported by a basement membrane. From 5 mm CRL onwards (ovine), the yolk sac entoderm folds itself between the capillaries, thereby becoming stratified. The intercellular space between the cells expands as projections between neighboring cells interlock. Canaliculi arise between adjacent epithelia. The wall of the yolk sac thickens as a result of this infolding and the densely packed capillaries. Infoldings are especially predominant in the sac-like portion of the yolk sac, and only suggested in the ends. Involution of the yolk sac begins in the peripheral end segments and proceeds centripetally. Numerous glycogen particles appear in the yolk sac entoderm cells of the ovine fetus at a CRL of 36 mm, and by a CRL of 42 mm, the sac-like portion has also begun to show signs of degeneration. Mesenchyme is very sparse within the wall of the yolk sac throughout the entire period of development.(ABSTRACT TRUNCATED AT 400 WORDS)

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Twenty-five heifers and cows with follicular cysts (high level of total oestrogens, low level of progesterone in plasma) were treated with 20 or 50 micrograms buserelin i.m. 5-84 weeks after parturition. Two hours after medication an increased LH release was observed in all animals. In contrast to LH, FSH concentration was not increased in all cows. Twelve days after treatment a high progesterone concentration in plasma could be determined in 17 of 25 treated animals. Twenty cows showed oestrous symptoms 23.5 +/- 9.6 days after medication. The oestrous cycle was prolonged in 10 cows. Nineteen cows were inseminated and 14 cows became pregnant after 1-4 (phi 1.7 +/- 0.9) inseminations (73.6% of all inseminated cows and 56% of all treated cows). The differences in conception rate and in services per conception after treatment with 20 or 50 micrograms buserelin in favour of the higher dosage cannot be attributed to the medication.

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Ten nonlactating buffalo were superovulated with 3000 IU PMSG. Luteolysis was induced with 500 microg Cloprostenol (PG) 60 and 72 h after PMSG. Five buffalo were alloted for natural mating and five were bred by artificial insemination 60 and 84 h after the first PG treatment. Since four buffalo developed pyometra, only 6 of 10 underwent embryo collection successfully 180 to 190 h after PG. Three buffalo yielded only one morula each, while the remaining three yielded a total of two, three and four morulae and/or blastocysts as well als zero, one and three unfertilized ova, respectively. Six of the ten buffalo were assigned to an intensive blood collection regimen. Mean concentrations of progesterone (ng/ml) increased from 1.9 at PMSG stimulation to 4.8 at induction of luteolysis and decreased to a nadir of 0.2 about 72 h after PG treatment. The preovulatory surge of LH occurred 36 +/- 9 h after PG and was low in magnitude (7.3 +/- 1.3 ng/ml). Stimulation of 3 to 12 follicles resulted in concentrations of estradiol-17beta exceeding 5 pg/ml within 48 h after PMSG treatment and reaching a maximum of 32 +/- 11 pg/ml about the time of the preovulatory surge. Only in two individuals did concentrations decrease below 5 pg/ml within the following 12 h. In the other four buffalo 3 to 10 unovulated structures remained palpable, secreting estradiol-17beta far exceeding the preovulatory concentrations. The fast appearing, low magnitude LH surges were key problems resulting from PMSG treatment. They caused unovulated endocrinologically active follicles. High estrogen levels during the early luteal period may activate subclinical uterine infections, which in turn may negatively affect embryonic development.

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The investigations were carried out in herds of high yielding cows (n = 265) that showed fertility problems. The first interest was to find out whether clinical findings could be confirmed by progesterone analyses. It was found that the clinical defined diagnoses could be confirmed by 3 progesterone determinations in blood plasma taken in a 7 days interval. In that way diagnoses and therapeutic measures were better to be taken and controlled. From 16 cows out of the controlled herds ovarian cystic disorders have been defined. After treatment with one GnRH injection the animals showed FSH and LH release as suggested but the FSH release seemed to be different in cows, that showed progesterone levels less than 1 ng at the moment of treatment. These investigations show that clinical findings can better by understood when combined with progesterone determination. By that way cystic disease in cows can be determined. Cows who show clinical disorders of this kind seem to have problems in their hypothalamo-hypophyseal regulations.

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Using the biotin-streptavidin amplification technique, highly sensitive specific second-antibody enzyme immunoassays for determining LH in bovine plasma with long (48 h) and short (4 h) incubation periods were developed. Biotin was linked to bLH by the N-hydroxysuccinimide method and the product (biotinyl-bLH) used to bridge between streptavidin-peroxidase and the immobilised bLH antibody in competitive tests. The assays were validated and their performance compared with a radioimmunoassay currently in use. The sensitivities of the long and short incubation enzyme immunoassays (8 pg and 15 pg/well, respectively) were superior to that of 5-day incubation radioimmunoassay (100 pg/tube). Plasma interference in both assays were acceptable and volumes of 5 to 40 microliters gave parallel standard curves and comparable LH levels, 10-20 microliters plasma was sufficient to measure LH baseline levels by the long incubation enzyme immunoassay. The mean recovery of added standard bLH to plasma samples containing different endogenous LH was greater than 90% (range 91.7-112) in both assays. The intra- and inter-assay variations of both assays were less than 10 and 17%, respectively. When both enzyme immunoassay and radioimmunoassay were used to measure LH in cyclic cows, the basal levels measured by enzyme immunoassay were lower than that measured by radioimmunoassay. Enzyme immunoassay offers an attractive alternative to the lengthy radioimmunoassay in current usage, with an added advantage of employing non-isotopic label.

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The two-wave hypothesis for follicular development during the bovine estrous cycle was tested by ultrasonically monitoring individual follicles in 10 heifers during an interovulatory interval. A dominant follicle was defined as one that reached a diameter of at least 11 mm. Subordinate follicles were defined as those that appeared to originate from the same follicular pool as a dominant follicle. A dominant follicle and its cohorts were defined as a wave. Two waves during an interovulatory interval were identified in 9 of 10 heifers. The first wave was first identified, retrospectively, on a mean of Day 0.2 +/- 0.1 (ovulation = Day 0) and gave origin to a dominant anovulatory follicle and a mean of 1.4 +/- 0.3 identified subordinates. The dominant follicle reached maximum diameter (mean, 15.8 +/- 0.8 mm) on an average of Day 7 and then decreased (P less than .04) by Day 11. The subordinate follicles increased in diameter for a few days and then regressed. The second wave was first identified on a mean of Day 10.0 +/- 0.4 and gave origin to the ovulatory follicle and a mean of 0.9 +/- 0.3 subordinates. One of the 10 heifers had 3 waves of follicular activity characterized by an anovulatory wave emerging on Day 0, another anovulatory wave emerging on Day 10, and an ovulatory wave emerging on Day 16. Results strongly supported the two-wave hypothesis but also indicated that a minority of interovulatory intervals in this heifer population may have 3 waves of follicular activity.

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Blood samples were collected frequently from permanent catheters placed in the aorta and caudal vena cava of 36 heifers in order to monitor the release pattern of LH, FSH, progesterone, oestradiol-17 beta, oxytocin, PGF-2 alpha, PGE-2 and PGI-2 (determined as its 6-keto-PGF-1 alpha metabolite). The frequency of secretory bursts of both gonadotrophins and progesterone was similar in early pregnant and cyclic animals, whereas the amplitude of LH and progesterone increased between 2 and 4 weeks of gestation. Concentrations of circulating oestradiol-17 beta and oxytocin were already lower at Days 4-7 in pregnant than in cyclic animals. Oestradiol-17 beta originated after Day 14 from the uterus rather than the ovary. A sustained release of oxytocin most probably from the posterior pituitary gland and a concomitant decrease of progesterone occurred in about two-thirds of pregnant animals during Days 19-23. Insemination could induce releases of PGF-2 alpha lasting up to 2 h. In addition, basal concentrations of PGF-2 alpha during the first 6 days after oestrus were approximately 2-fold higher in inseminated than in non-inseminated cyclic heifers. A parallel increase of PGF-2 alpha and PGI-2 occurred between Days 30 and 33 of gestation. Early embryonic mortality resulted, at least up to Day 35, in 4-7 concomitant secretory bursts of PGF-2 alpha and luteal oxytocin. There was a delay of 20-26 h between the first and second release. The present results from in-vivo experiments point towards major endocrine changes in cattle within a few days after conception, resulting in an early inhibition of follicular oestradiol-17 beta and luteal oxytocin facilitating the suppression of luteolytic releases of PGF-2 alpha.

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A simple direct enzymeimmunoassay (EIA) on microtiter plates for plasma progesterone using the second antibody coating technique and horseradish peroxidase (HRP) as the enzyme label (EIA-HRP) is described and compared with an identical EIA procedure which employed alkaline phosphatase (AP) as the enzyme label (EIA-AP). The assays used antiserum raised against progesterone-7-carboxyethlthioether-BSA in rabbits. Both systems were further compared with the conventional direct progesterone radioimmunoassay (RIA) in regular use. The enzymes HRP and AP were coupled to progesterone-6 beta-hydroxy-hemisuccinate by a mixed anhydride method. While the precision of EIA-HRP was comparable to RIA, the sensitivity in terms of the lowest detection limit obtained in EIA-HRP was about 10 times better than that seen in RIA. Progesterone estimates from plasma samples in EIA-HRP showed good correlation (r = 0.94) with the RIA values and the levels measured in the two systems were identical. Progesterone estimates from plasma samples in EIA-AP were at least three times higher than those obtained by either EIA-HRP or RIA. Thus, only the EIA-HRP but not the EIA-AP was suitable for the reliable direct measurement of progesterone in plasma.

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The re-establishment of the positive feedback action of oestradiol-17 beta on both gonadotrophins was assessed in 20 dairy cows receiving three challenges once every 20 days from parturition through day 55 post partum (pp). One mg oestradiol-17 beta-benzoate dissolved in 5 ml oil was given im every 5 days to groups of 5 cows each. Blood was collected from the jugular vein every 3-12 h from 2 days before until 2 days after the injection. No effect of oestradiol-17 beta on the LH release was exerted at parturition or day 5 pp. A stimulation of LH release started to occur in the majority of cows by day 10 pp. Two types of preovulatory like surges could be elicited: low magnitude LH releases lacking any concomitant FSH increase and parallel high magnitude LH and FSH surges. No cow expressed heat when exhibiting a weak LH surge before day 30 pp and only 30% thereafter. All cows showed oestrus when exhibiting parallel high magnitude LH/FSH surges after day 20 pp but only 40% on days 10 and 15 pp. Progesterone concentrations greater than 0.5 ng/ml prevented the positive feedback action of oestradiol on LH and FSH. An initial negative feedback on FSH was exerted throughout the entire post-partum period comprising the luteal phase. We conclude from these results that a certain minimum threshold frequency of endogenous LH secretion is necessary to allow oestradiol-17 beta to evoke its unimpaired stimulatory feedback action after an initial period of pituitary refractoriness during the early puerperal anoestrus and acyclic period.

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Pulsatile LH and FSH release from the pituitary gland of 8 post-partum dairy cows was assessed in series of frequent bleedings (every 20 min for 12 h) performed in about weekly intervals from day 4 through day 32 post partum (pp). The frequency of short-term secretion of LH increased during individually varying time periods (1.5-5 weeks) from about 1 pulse/4 h to about 1 pulse/1.25 h prior to the re-establishment of luteal function. FSH pulses (average frequency 1 pulse/2 h) were always released concomitantly with LH, but extra FSH pulses occurred in between. Interpulse intervals of LH and FSH (80 +/- 4 vs 82 +/- 7 min) merged prior to the resumption of cyclicity. LH and FSH pulse frequencies remained slightly slower during this first periovulatory period pp than during pro-oestrus and oestrus of regular cycles; also, with one exception, no visible signs of oestrus were expressed. Despite low progesterone concentrations during the first luteal phase there was strong negative feedback mainly on LH, thus considerably prolonging the intervals between consecutive LH pulses (up to 620 min) whereas FSH release remained much faster (up to 270 min interpulse interval). LH interpulse intervals tended to be longer during short compared to normal length cycles post partum (420 +/- 107 vs 285 +/- 51 min) in the presence of only slightly altered FSH release (154 +/- 37 vs 107 +/- 7 min).(ABSTRACT TRUNCATED AT 250 WORDS)

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Short-term secretion patterns of LH, FSH, progesterone and oestradiol-17 beta were evaluated throughout complete oestrous cycles of 6 heifers. Frequent blood samples (in 20-min intervals for 12 continuous h) were taken every 3-5 days from indwelling jugular catheters. There was a high incidence of concomitant LH and FSH pulses ranging from 72% at luteolysis to 83-100% during the luteal phase. Almost the same total number of LH and FSH pulses occurred during the early luteal phase (7.0 vs 7.4/12 h, respectively), however, there was an average of one additional FSH pulse in between the synchronous LH/FSH ones during the mid- and late luteal phase (6.9 FSH vs 3.4 LH pulses/12 h). Basal LH and FSH concentrations remained unchanged from the early until the late luteal period. During and after luteolysis frequency of LH and FSH release (14.5 vs 10.5 pulses/12 h) increased considerably as well as basal concentrations and magnitude of LH pulses. Secretion of both gonadotrophins persisted very frequently (13.3 LH and 10.7 FSH pulses/12 h) during pro-oestrus and oestrus when basal FSH concentrations and FSH pulse maxima approached a nadir. During the mid-luteal phase 45% of pulsatile progesterone occurred concomitantly with each coinciding LH/FSH pulse and 44% of pulsatile progesterone happened after additional single FSH pulses. Distinct short-term changes of oestradiol concentrations were not observed in the jugular vein but concentrations fluctuated randomly ranging from 2-6 pg/ml throughout the luteal period. Prior to and during heat mean concentrations of oestradiol were approximately 2-fold higher (P less than 0.05) than during the other periods of the cycle. It is concluded that the frequency of pulsatile LH release is modulated to a much greater extent than FSH by negative feedback of ovarian steroids. Some pulsatile progesterone secretion resulting from the stimulation of FSH (and LH) is still detectable in the jugular vein whereas of oestradiol-17 beta is not. The additional frequent monitoring of FSH might be more appropriate reflecting pituitary and hypothalamic function than only measuring LH.

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Short-term secretion patterns (derived from samples collected from jugular vein cannulae every 20 min for 12 h) of LH, FSH, progesterone, oestradiol-17 beta, oestrone and prolactin were studied every 30 days during gestation in heifers. LH pulse frequency and amplitude was greater during the early (months 1-3) and end (months 8-9) than during mid-gestation when pulsatile LH secretion was almost abolished. The frequency of pulsatile FSH release, which was already twice as fast than of LH during early pregnancy, did not change throughout the whole gestation period. Mean, basal and maximal progesterone concentrations were highest during the first 3 months of gestation, were slightly reduced during mid-gestation and decreased further during the last 2 months preceding parturition. Pulses of progesterone occurred concomitantly with the parallel LH/FSH as well as the separate FSH pulses. Average oestradiol-17 beta concentrations during the first months of gestation were slightly higher than during the mid-luteal phase of the cycle and exceeded during mid-gestation concentrations measured at oestrus. Free oestrone could be detected as early as day 60 of pregnancy. Frequency and amplitude of short-term changes of oestrone increased after the 5th month. Discontinuous secretion of oestrone as well as oestradiol-17 beta was only arbitrarily but never consistently correlated with either each other or with pulsatile gonadotrophin release. Apart form an occasional coincidence with pulsatile release of other hormones prolactin concentrations seemed to depend rather on the season of the year and time of the day than on the individual pregnancy stage.(ABSTRACT TRUNCATED AT 250 WORDS)

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The role of PRL in the control of corpus luteum (CL) function was examined in hyperprolactinemic and euprolactinemic female rhesus monkeys with hypothalamic lesions in which ovulatory menstrual cycles were induced by the pulsatile administration of GnRH, in intact postpartum monkeys nursing their infants, as well as in animals treated with bromocriptine. In the lesioned monkeys, neither markedly elevated nor undetectable (bromocriptine-suppressed) PRL levels influenced the time courses of postovulatory plasma progesterone concentrations compared to those in monkeys with normal PRL concentrations. Plasma progesterone concentrations in the hyperprolactinemic monkeys, however, did not decline to undetectable levels at the end of the luteal phase, as is the case in normal animals, but remained slightly elevated for extended periods, a pattern characteristic of lactating animals. In both lesioned and postpartum animals, bromocriptine administration or removal of suckling infants from the latter resulted in complete functional luteolysis. These observations suggest that PRL does not play a significant role in the control of the CL of the menstrual cycle, but that in high concentrations, this hormone can partially maintain previously established CL.

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