Follicular, hormonal, and pregnancy responses of early postpartum suckled beef cows to GnRH, norgestomet, and prostaglandin F2alpha.
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Cycling (n = 16) and noncycling (n = 24), early postpartum, suckled beef cows of three breeds were assigned randomly to three treatments: 1) 100-microg injection of GnRH plus a 6-mg implant of norgestomet administered on d -7 before 25 mg of PGF2alpha and implant removal on d 0 (GnRH+NORG); 2) 100 microg of GnRH given on d -7 followed by 25 mg of PGF2alpha on d 0 (GnRH); or 3) 2 mL of saline plus a 6-mg implant of norgestomet administered on d -7 followed by 25 mg of PGF2, and implant removal on d 0 (NORG). All cows were given 100 microg of GnRH on d +2 (48 h after PGF2alpha). Blood sera collected daily from d -7 to d +4 were analyzed for progesterone and estradiol-17beta, and ovaries were monitored daily by transrectal ultrasonography to assess changes in ovarian structures. Luteal structures were induced in 75% of noncycling cows in both treatments after GnRH, resulting in elevated (P < .01) progesterone on d 0 for GnRH+NORG-treated cows. Concentrations of estradiol-17beta (P < .01) and LH (P < .05) were greater on d +2 after GnRH for cows previously receiving norgestomet implants. Pregnancy rates after one fixed-time AI at 16 h after GnRH (d +2) were greater (P < .05) in GnRH+NORG (71%) than in GnRH (31%) and NORG (15%) cows. Difference in pregnancy rate was due partly to normal luteal activity after AI in over 87% of GnRH+NORG cows and no incidence of short luteal phases. The GnRH+NORG treatment initially induced ovulation or turnover of the largest follicle, induction of a new follicular wave, followed later by increased concentrations of estradiol-17beta and progesterone. After PGF2alpha, greater GnRH-induced release of LH occurred in GnRH+NORG cows before ovulation, and pregnancy rates were greater after a fixed-time AI. (+info)
The effect of the angiogenesis inhibitor TNP-470 on luteal establishment and function in the primate.
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Angiogenesis during luteal development is probably essential for normal lutein cell function. Since the angiogenesis inhibitor TNP-470 inhibits pregnancy in mice, the current study investigated its effects on the establishment and function of the primate corpus luteum. Regularly ovulating macaques were treated with TNP-470 (6 mg/kg), i.v. in three doses, 48 h apart. Serum progesterone concentrations, as indicators of treatment effect, were normal in four macaques where treatment commenced at the onset of the ovulatory progesterone rise, and in five of eight in which treatment commenced a few days before ovulation. In the other three the normal progesterone rise was absent. To investigate the direct effect on luteal angiogenesis of a daily dose over a longer period, four marmosets received 18 mg/kg/day of TNP-470 i.v. for 9 days starting at ovulation. On day 10, luteal cell proliferation was determined by nuclear bromodeoxyuridine incorporation. Luteal microvasculature was examined using immunocytochemical factor VIII staining, and endothelial cell and luteal function assessed by in-situ hybridization of insulin-like growth factor binding protein-3 mRNA and plasma progesterone concentrations respectively. None of these parameters were affected by the TNP-470 treatment. The results show that, with the treatment regimens employed, TNP-470 had no significant effect on the expression of the differentiated state of the primate corpus luteum. (+info)
26-cholesterol hydroxylase in rat corpora lutea: A negative regulator of progesterone secretion.
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From a subtracted cDNA library of rat luteal tissue, where cDNA fragments in functional luteal tissue were subtracted from those in regressing luteal tissue, a cDNA clone corresponding to 26-cholesterol hydroxylase (P450(C26)) was obtained. It is known that P450(C26) catalyzes the conversion of cholesterol to 26-hydroxycholesterol, which blocks cholesterol utilization in the cell, and that 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD) catalyzes the conversion of progesterone to an inactive steroid, 20alpha-dihydroprogesterone (20alpha-OHP). Thus, using pseudopregnant rats as a model, physiological cooperation of P450(C26) and 20alpha-HSD in the reduction of progesterone release toward the end of the luteal phase was evaluated. Levels of P450(C26) and 20alpha-HSD mRNA were examined in corpora lutea from pseudopregnant rats by Northern blot or reverse transcription-polymerase chain reaction or both. P450(C26) mRNA was ubiquitously expressed in corpora lutea, and its expression increased toward the end of pseudopregnancy, while 20alpha-HSD was expressed in all corpora lutea on Day 16 (Day 0 = the day of after cervical stimulation) but not detected before Day 10. An inhibitor of 20alpha-HSD, STZ26 (D-homo-16-oxa-4-androstene-3,16alpha-dione), was administered at various doses to rats from Day 12 to 20, effectively suppressing the elevation of 20alpha-OHP in a dose-dependent manner but not the depletion of progesterone completely. The expression of P450(C26) mRNA was increased as STZ26 dose increased, which negatively correlated with the progesterone levels. These results strongly suggest that P450(C26) cooperated with 20alpha-HSD in the reduction of progesterone release from the rat luteal tissue at the end of the functional luteal phase. (+info)
Prostaglandin F(2alpha) induces a rapid decline in progesterone production and steroidogenic acute regulatory protein expression in isolated rat corpus luteum without altering messenger ribonucleic acid expression.
(36/1885)
With interest in steroidogenic acute regulatory protein (StAR) involvement in the luteolytic process, we studied changes in serum progesterone levels and the concomitant expression of StAR mRNA and protein (37-, 32-, and 30-kDa forms) in postovulatory Day 7 corpora lutea (CL) isolated from rats 1 h after injection with prostaglandin F(2alpha) (PGF(2alpha), n = 6) or saline (n = 6). Serum progesterone levels were determined by RIA, StAR and beta-actin mRNA expression by Northern analysis, and StAR and beta-actin protein expression by Western analysis. Adrenal, brain, and spleen from control animals were used as positive and negative controls for StAR expression. Scanning optical densitometry measurements were standardized by dividing the signal strength from each StAR autoradiogram lane by that from the corresponding beta-actin autoradiogram lane. ANOVA was used for significance testing, with alpha set at 0.05. The 37-, 32-, and 30-kDa forms of StAR protein were expressed in all adrenal samples, whereas only the 37- and 30-kDa forms were found in CL. Serum progesterone levels and expression of the 30-kDa and 37-kDa forms of the StAR protein in CL were all found to be significantly lower in the PGF(2alpha)-treated than the saline-treated group. StAR mRNA expression was not significantly different in the saline- and PGF(2alpha)-treated rats. The rapid decline in StAR protein expression that accompanies PGF(2alpha) induced luteolysis, therefore, does not result from significant decline in mRNA expression. (+info)
Preliminary results on the role of embryonic human chorionic gonadotrophin in corpus luteum rescue during early pregnancy and the relationship to abortion and ectopic pregnancy.
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The precise mechanisms by which corpus luteum (CL) function is modulated during early pregnancy are not known. Evidence in failed pregnancies (ectopic, abortions), shows that factors other than human chorionic gonadotrophin (HCG) could be involved in its regulation. The objective of this study was to investigate the dynamics of beta-HCG, progesterone and oestradiol production in early pregnancy and its relation to embryonic quality and topographic localization. Plasma concentrations of progesterone, oestradiol and beta-HCG were studied between days +12 and +21 after an in-vitro fertilization (IVF) embryo transfer in 11 intrauterine pregnancies, 10 intrauterine abortions and seven tubal pregnancies. Tubal pregnancies and abortions were grouped according to doubling time (DT) of HCG. Results showed that oestradiol concentrations were apparently reduced in both ectopic pregnancies and abortions compared with normal pregnancies. The fall in oestradiol concentrations was seen in ectopic pregnancies with an abnormal DT for HCG and in all abortions. When the ectopic pregnancy had a normal DT, oestradiol and progesterone concentrations were normal. In abortions, the fall in oestradiol and progesterone concentrations was less influenced by the DT of HCG. These findings suggest that corpus luteum function depends on an adequate DT of HCG more than an absolute value, and with normal trophoblastic tissue the site of implantation does not affect CL function. (+info)
Targeted disruption of CDK4 delays cell cycle entry with enhanced p27(Kip1) activity.
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The mechanism by which cyclin-dependent kinase 4 (CDK4) regulates cell cycle progression is not entirely clear. Cyclin D/CDK4 appears to initiate phosphorylation of retinoblastoma protein (Rb) leading to inactivation of the S-phase-inhibitory action of Rb. However, cyclin D/CDK4 has been postulated to act in a noncatalytic manner to regulate the cyclin E/CDK2-inhibitory activity of p27(Kip1) by sequestration. In this study we investigated the roles of CDK4 in cell cycle regulation by targeted disruption of the mouse CDK4 gene. CDK4(-/-) mice survived embryogenesis and showed growth retardation and reproductive dysfunction associated with hypoplastic seminiferous tubules in the testis and perturbed corpus luteum formation in the ovary. These phenotypes appear to be opposite to those of p27-deficient mice such as gigantism and gonadal hyperplasia. A majority of CDK4(-/-) mice developed diabetes mellitus by 6 weeks, associated with degeneration of pancreatic islets. Fibroblasts from CDK4(-/-) mouse embryos proliferated similarly to wild-type embryonic fibroblasts under conditions that promote continuous growth. However, quiescent CDK4(-/-) fibroblasts exhibited a substantial ( approximately 6-h) delay in S-phase entry after serum stimulation. This cell cycle perturbation by CDK4 disruption was associated with increased binding of p27 to cyclin E/CDK2 and diminished activation of CDK2 accompanied by impaired Rb phosphorylation. Importantly, fibroblasts from CDK4(-/-) p27(-/-) embryos displayed partially restored kinetics of the G(0)-S transition, indicating the significance of the sequestration of p27 by CDK4. These results suggest that at least part of CDK4's participation in the rate-limiting mechanism for the G(0)-S transition consists of controlling p27 activity. (+info)
Corpus luteum development and function in cattle with episodic release of luteinizing hormone pulses inhibited in the follicular and early luteal phases of the estrous cycle.
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The influence of episodic LH pulses before and subsequent to ovulation on size and function of the corpus luteum (CL) in cattle was examined. Treatments were 1) control; 2) LHRH antagonist starting 2 days before the preovulatory LH surge (Antagonist [Ant] -2); 3) LHRH antagonist at initiation of the preovulatory LH surge (Ant 0); and 4) LHRH antagonist starting 2 days after the preovulatory LH surge (Ant 2). Treatments with an LHRH antagonist were continued until 7 days after the preovulatory surge. Diameter of the CL and concentrations of progesterone were monitored during the luteal phase that ensued after treatment. Maximum average diameters of CL were 9.5, 17.5, 21.6, and 28.8 mm for females from the Ant -2, Ant 0, Ant 2, and control groups, respectively (P < 0. 01). Compared with those in control animals, concentrations of progesterone in plasma were less (P < 0.01) in animals in which release of LH pulses was inhibited by treatment with antagonist. Arbitrary units under the curve for concentrations of progesterone during the luteal phase of the estrous cycle for Ant -2, Ant 0, Ant 2, and control groups were 19.6, 41.6, 43.6, and 142.2, respectively. There was no difference in circulating concentrations of progesterone (P > 0.1) among antagonist-treated groups. In conclusion, episodic release of LH pulses before, during, and after the time of the preovulatory surge of LH may stimulate development and function of the CL in cattle. (+info)
Tumor necrosis factor alpha receptors in microvascular endothelial cells from bovine corpus luteum.
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There is sufficient evidence to prove that tumor necrosis factor alpha (TNFalpha) modulates bovine corpus luteum (CL) function. Our previous study demonstrated that functional TNFalpha receptors are present on luteal cells in bovine CL throughout the estrous cycle. The purpose of the present study was to identify the presence of functional TNFalpha receptors on the microvascular endothelial cells derived from developing bovine CL. TNFalpha receptors were analyzed by a radioreceptor assay using (125)I-labeled TNFalpha on two types of cultured endothelial cells. One has a cobblestone appearance (CS cells), and the other has a tube-like structure (TS cells). (125)I-Labeled TNFalpha binding was maximal after incubation for 30 h at 37 degrees C, and the specificity of binding was confirmed. A Scatchard analysis showed the presence of two binding sites (high- and low-affinity) for TNFalpha receptors on both CS and TS cells. The dissociation constant (K(d)) values and concentrations of the high-affinity binding sites for TNF receptors were similar for CS and TS cells. However, K(d) values and concentrations of the low-affinity binding sites in CS cells were significantly higher than those in TS cells (P < 0.05 or lower). The expression of TNF receptor type 1 (TNF-RI) mRNA was determined in both cell types. Furthermore, TNFalpha significantly stimulated prostaglandin E(2) and endothelin-1 secretion by both CS and TS cells (P < 0.05 or lower). These results indicate the presence of two types of TNF receptors and the expression of TNF-RI mRNA in the endothelial cells derived from bovine CL, and suggest that TNFalpha plays two or more roles in regulating the secretory function of the endothelial cells. (+info)