Body weight, oestrous and ovarian activity in local Burundian ewes and goats after parturition in the dry season
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Journal Article Cell types and hormonal mechanisms associated with mid-cycle corpus luteum function Get access Milo C. Wiltbank Milo C. Wiltbank Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Animal Science, Volume 72, Issue 7, July 1994, Pages 1873–1883, https://doi.org/10.2527/1994.7271873x Published: 01 July 1994 Article history Received: 14 July 1993 Accepted: 27 February 1994 Published: 01 July 1994
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Series Preface Cellular Aspects of Corpus Luteum Function Control of Luteolysis Uterine Responses to the Corpus Luteum Interaction Between the Embryo and the Corpus Luteum Prolactin and the Corpus Luteum Luteal Function after Ovulation Induction by Pulsatile Luteinizing Hormone-Releasing Hormone The Abnormal Luteal Phase Contraception in the Luteal Phase Index.
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The synthesis of progesterone by the corpus luteum is essential for the establishment and maintenance of early pregnancy. Regulation of luteal steroidogenesis can be broken down into three major events; luteinization (i.e., conversion of an ovulatory follicle), luteal regression, and pregnancy induced luteal maintenance/rescue. While the factors that control these events and dictate the final steroid end products are widely varied among different species, the composition of the corpus luteum (luteinized thecal and granulosa cells) and the enzymes and proteins involved in the steroidogenic pathway are relatively similar among all species. The key factors involved in luteal steroidogenesis and several new exciting observations regarding regulation of luteal steroidogenic function are discussed in this review.
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Angiogenesis is important for the formation and development of the corpus luteum and for maintenance of luteal function. Blood vessel regression is an important physiological phenomenon in the corpus luteum, which is associated with tissue involution during structural luteolysis. Angiogenesis actively occurs during the early luteal phase and is completed by the mid‐luteal phase. Perivascular cells (pericytes) increase in number from the early luteal phase to the mid‐luteal phase, suggesting that blood vessels are gradually stabilized until the mid‐luteal phase. In the corpus luteum undergoing luteolysis, blood vessels and pericytes decrease in number, which is related to structural involution. In the corpus luteum of early pregnancy, the number of blood vessels with pericytes increases, suggesting that angiogenesis occurs again, accompanied by blood vessel stabilization. These changes in vasculature of the corpus luteum are regulated by the collaboration with vascular endothelial growth factor, which is involved in proliferation of vascular endothelial cells, and angiopoietins, which are involved in stabilization of blood vessels. This review focuses on angiogenesis, blood vessel stabilization and blood vessel regression during the divergent phases of luteal formation, luteal regression and luteal rescue by pregnancy. (Reprod Med Biol 2008; 7 : 91–103)
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Summary. The cellular composition of CL from 6 cows on ∼Day 12 of the oestrous cycle, after synchronization with cloprostenol, was studied by ultrastructural morphometry. Point-count measurements of volume density (mean ± s.d.) showed that large luteal cells occupied 40·2 ± 7·0% of the luteal tissue, and small luteal cells 27·7 ± 6·3%. Of the total of 393·4 ± 52·0 × 103 cells per mm3 of luteal tissue, large luteal cells made up only 3·5% and small luteal cells 26·7%, a ratio of 1:7·6. Endothelial cells/pericytes, at 52·3%, were the most numerous cell type. The mean volume per large luteal cell was 29·6 ± 6·3 × 103 μm3, while that of small luteal cells was 2·7 ± 0·4 × 103 μm3. In spherical form, these volumes would represent mean diameters of 38·4 μm and 17·2 μm respectively, and are consistent with published measurements on dispersed luteal cells. However, the values for cell numbers are much higher than published values based on luteal tissue dispersion, suggesting that dispersion may result in substantial and possibly selective losses of luteal cells. Keywords: corpus luteum; oestrous cycle; cow; morphometry; luteal cells
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To examine possible mechanisms involved in resistance of the ovine corpus luteum to the luteolytic activity of prostaglandin (PG)F2α, the enzymatic activity of 15-hydroxyprostaglandin dehydrogenase (PGDH) and the quantity of mRNA encoding PGDH and cyclooxygenase (COX-2) were determined in ovine corpora lutea on Days 4 and 13 of the estrous cycle and Day 13 of pregnancy. The corpus luteum is resistant to the action of PGF2α on Days 4 of the estrous cycle and 13 of pregnancy while on Day 13 of the estrous cycle the corpus luteum is sensitive to the actions PGF2α. Enzymatic activity of PGDH, measured by rate of conversion of PGF2α to PGFM, was greater in corpora lutea on Day 4 of the estrous cycle (P < 0.05) and Day 13 of pregnancy (P < 0.05) than on Day 13 of the estrous cycle. Levels of mRNA encoding PGDH were also greater in corpora lutea on Day 4 of the estrous cycle (P < 0.01) and Day 13 of pregnancy (P < 0.01) than on Day 13 of the estrous cycle. Thus, during the early estrous cycle and early pregnancy, the corpus luteum has a greater capacity to catabolize PGF, which may play a role in the resistance of the corpus luteum to the actions of this hormone. Levels of mRNA encoding COX-2 were undetectable in corpora lutea collected on Day 13 of the estrous cycle but were 11 ± 4 and 44 ± 28 amol/μg poly(A)+ RNA in corpora lutea collected on Day 4 of the estrous cycle and Day 13 of pregnancy, respectively. These data suggest that there is a greater capacity to synthesize PGF2α, early in the estrous cycle and early in pregnancy than on Day 13 of the estrous cycle. In conclusion, enzymatic activity of PGDH may play an important role in the mechanism involved in luteal resistance to the luteolytic effects of PGF2α.
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Regression of the corpus luteum (CL) is characterized by a decay in progesterone (P4) production (functional luteolysis) and disappearance of luteal tissues (structural luteolysis). In mares, structural luteolysis is thought to be caused by apoptosis of luteal cells, but functional luteolysis is poorly understood. 20α-hydroxysteroid dehydrogenase (20α-HSD) catabolizes P4 into its biologically inactive form, 20α-hydroxyprogesterone (20α-OHP). In mares, aldo-keto reductase (AKR) 1C23, which is a member of the AKR superfamily, has 20α-HSD activity. To clarify whether AKR1C23 is associated with functional luteolysis in mares, we investigated the expression of AKR1C23 in the CL in different luteal phases. The luteal P4 concentration and levels of 3β-hydroxysteroid dehydrogenase (3β-HSD) mRNA were higher in the mid luteal phase than in the late and regressed luteal phases (P<0.05), but the level of 3β-HSD protein was higher in the late luteal phase than in the regressed luteal phase (P<0.05). The luteal 20α-OHP concentration and the level of AKR1C23 mRNA were higher in the late luteal phase than in the early and mid luteal phases (P<0.05), and the level of AKR1C23 protein was also highest in the late luteal phase. Taken together, these findings suggest that metabolism of P4 by AKR1C23 is one of the processes contributing to functional luteolysis in mares.
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We have reported that angiogenesis is important for development of the corpus luteum and maintenance of luteal function. To maintain progesterone production for successful pregnancy, not only high vascularization but also adequate blood flow in the corpus luteum is necessary to provide luteal cells with large amounts of cholesterol needed for progesterone synthesis and for the delivery of progesterone to the circulation. The present study was undertaken to investigate a relationship between angiogenesis and blood flow in the human corpus luteum throughout the menstrual cycle and during early pregnancy. Changes in numbers of blood vessels were examined in the corpus luteum during the menstrual cycle [early stage of the early luteal phase:1–2 days after ovulation (D1–2), late stage of the early luteal phase:D3–4, mid-luteal phase:D5–8, late luteal phase:D10–14, with day 1 being the day of ovulation confirmed by urinary LH] and in early pregnancy (6–8 weeks). The number of blood vessels in the corpus luteum, determined by immunohistochemistry for CD34, expressed per 100 luteal cells was used as a vascular index. Vascular index significantly increased from the early stage to the late stage during the early luteal phase. Vascular index in the late stage of the early luteal phase was the same level as that in the midluteal phase, and significantly decreased in the late luteal phase. In the corpus luteum of early pregnancy, vascular index was significantly larger than that in the mid-luteal phase, suggesting that angiogenesis is activated again by pregnancy. Changes in blood flow impedance in the preovulatory follicle and in the corpus luteum were assessed by transvaginal color and pulsed Doppler ultrasound during the menstrual cycle and in early pregnancy. Blood flow impedance was expressed as resistance index (RI), which was calculated from curves fitted to flow velocity waveforms according to the formula (ratio between the systolic peak velocity and end-diastolic velocity). Color flow was detected in the follicular wall and in the peripheral area of the corpus luteum. RI in the preovulatory follicle rapidly declined after ovulation. Then, RI in the corpus luteum further declined from the early stage to the late stage during the early luteal phase. RI in the corpus luteum of the mid-luteal phase was the same level as the late stage of the early luteal phase, and thereafter increased in the late luteal phase. In the corpus luteum of early pregnancy, RI remained the same level as the mid-luteal phase until 7 weeks of gestation. In conclusions, the present study showed the change in luteal blood flow throughout the menstrual cycle and during early pregnancy. The change in luteal blood flow is closely associated with angiogenesis and blood vessel regression during the divergent phases of luteal formation, luteal regression, and luteal rescue by pregnancy. (platform)
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The epidermal growth factor (EGF) concentration and its binding characteristics in bo-vine corpus luteum (CL) during the estrous cycle (early: Days 3-5, mid-: 8-12, late stage: 15-18) were determined. The EGF concentrations in corpus luteum tissue, evaluated by a radioreceptor assay using human placenta, were 3.0 ± 0.7 ng/g in early luteal phase, 43.9 ± 2.2 ng/g in mid-luteal phase and 18.6 ± 2.7 ng/g in late luteal phase. Specific EGF receptors were present in bovine corpus luteum of all luteal phases. TGFα, but not IGF-I, FGF and NGF competitively displaced EGF binding. The binding affinity of luteal EGF receptors differed between the luteal stages and decreased significantly from early (Kd=0.8 ± 0.04 nM) to mid-luteal stage (Kd=1.6 ± 0.34 nM, P<0.05). The binding capacity of luteal EGF receptor at different luteal stages were similar (early stage; Bmax=35.1 ± 5.7 fmol/mg protein, mid-luteal stage; Bmax=46.3 ± 4.0 fmol/mg protein, late stage; Bmax=35.1 ± 5.7 fmol/mg protein, all values mean ± SEM). These results suggest that EGF plays a physiological role for the regulation of luteal function during the estrous cycle.
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