Changes in prostaglandin secretion by the regressing bovine corpus luteum

Secretion of prostaglandins (PGs) by the regressing corpus luteum (CL) was investigated in the cow. Six cows were implanted with microcapillary dialysis membranes of a microdialysis system (MDS) into the CL during Days 8-9 (Day 0 = estrus), and a prostaglandin (PG) F2alpha analogue (Estrumate) was injected intramuscularly (i.m.) to induce luteolysis. Acute increases in intraluteal release of PGF2alpha and PGE2 were observed during the first 4 h, followed by decreases over the next 8 h. Intraluteal release of both PGs gradually increased again during the period 48-72 h. Concentrations of PGF2alpha in ovarian venous plasma (OVP) were 4-13 times higher than those of jugular venous plasma (JVP) (P < 0.001) during the period of the experiment, and increased from 24 h after treatment with Estrumate (P < 0.05). Cyclooxygenase (COX)-2 mRNA expression increased (P < 0.05) at 2 and 24 h after treatment with Estrumate. The results indicated that local release of PGF2alpha and PGE2, and COX-2 mRNA expression were increased by Estrumate in the regressing CL at the later stages of luteolysis. Thus, luteal secretion of PGs may be involved in the local mechanism for structural rather than functional luteolysis.     

FSH receptors in the bovine corpus luteum

Binding of follicle stimulating hormone (FSH) to a crude membrane fraction of bovine corpus luteum (CL) has been detected. This binding meets the usual criteria for a receptor based on specificity, time course of reaction and association constant (Ka = 8.5 x 10(10)M(-1)). Physiological studies with CL removed from heifers at specific times after estrus indicate that day-6 CL had the highest FSH binding. However, a correlation with physiological function was not obvious since some functional mid-cycle CL were high in progesterone and luteinizing hormone (LH) receptor but had nondetectable FSH receptor. Conversely, some late-cycle CL had low progesterone and LH receptor but significant quantities of FSH receptor.     

Luteotropic and luteolytic mechanisms in the bovine corpus luteum

The function of the corpus luteum (CL) is a key element in many reproductive processes including ovulation, length of the estrous cycle, recognition of pregnancy and embryo survival in all mammalian species. The main function of the CL is to produce progesterone which acts on its tissues to prepare them for successful pregnancy. The CL is controlled by numerous biological compounds which provide luteotropic support during the estrous cycle and pregnancy and for inducing luteolysis at the end of the cycle The purpose of this paper is to review the mechansims responsible for controlling the endocrine function of this tissue in the bovine ovary.     

Biosynthesis of retinal in bovine corpus luteum

Bovine corpus luteum tissue was sliced and incubated with beta-[15,15'-(3)H]carotene. The conversion of radioactive beta-carotene into radioactive retinal was substantiated utilizing column chromatography, thin-layer chromatography, high-speed liquid chromatography, and a derivative formation. Lowering of the incubation temperature to 20 degrees C or boiling the tissue eliminated the conversion of beta-carotene to retinal. In addition, other carotenoids and possible oxidation products of beta-carotene in the corpus luteum were investigated. Our results indicate that the bovine corpus luteum possesses the ability to synthesize retinal in situ, which may play a role in reproductive functions.     

Lipoprotein lipase activity in the bovine corpus luteum during the estrous cycle and early pregnancy.

Lipolytic activity measured at pH 8.6 in bovine corpora lutea exhibited classical properties of lipoprotein lipase (LPL) in terms of serum and heparin stimulation and NaCl inhibition. LPL activity was measured in 23 corpora lutea collected at different stages of the estrous cycle and early pregnancy. The LPL activity in cyclic corpora lutea (mumole FA released/hr/100 mg acetone powder) was low at Days 4-8 of the estrous cycle (3.1 +/- 1.5: mean +/- SE) and at Days 19-20 (1.6 +/- 0.6). However, high activity of the enzyme was found at Days 12-15 of the cycle (11.8 +/- 1.8); these concentrations were significantly (P less than 0.01) elevated over those found at Days 4-8 and 19-20. The enzyme activity began to decline at Days 16-18 of the estrous cycle (5.1 +/- 1.7). Low enzyme activity was found in the corpora lutea removed from two cows at Day 22 of pregnancy. Progesterone concentrations were measured in 16 of the 23 corpora lutea and a good correlation (r = 0.75, P less than 0.01) was found between lipoprotein lipase and progesterone concentrations of the tissue. The data suggest that LPL may be involved in controlling the transfer of fatty acids, including arachidonic, from plasma lipoproteins to luteal tissue.     

Immunohistochemical localization of prolactin in functioning and regressing corpus luteum of pituitary autotransplanted rats

In an attempt to shed light on the intimate mechanism by which prolactin (PRL) switches from supporting corpus luteum (CL) progesterone secretion (P) to promote structural regression of the CL, day 2 (metestrous) autopituitary transplanted (APTr) rats were used. In APTr rats the CL is under the only control of PRL since an almost complete absence of LH and FSH exist. The experimental group was given bromocriptine (CB-154: 0.4 mg/day) on days 12, 13 and 14 of the cycle and 0.25 ml of ethanol from day 15 to day 21. The control group was given CB-154 from day 12 to day 21. Rats were hemiovariectomized on day 12 to assess the morphological characteristics of the active CL. PRL and P were determined by RIA on days 12, 15 and 22. On day 12, both PRL and P levels were higher than 80 ng/ml (luteotrophic action of PRL). On day 15, due to treatment with CB-154, the levels of both hormones had fallen below 7 ng/ml (functional luteolysis). On day 22, PRL levels were again high (greater than 50 ng/ml) in the shortly CB-154-treated rats and low (less than 5 ng/ml) in the controls; the P levels were lower than 5 ng/ml in both groups. PRL-induced structural luteolysis in the experimental group (hyperprolactinemic) was assessed by the structural characteristics and by the CL weight loss on day 22 in comparison with that exhibited by control rats. The immunohistochemical staining of both endogenous and total PRL in the lutein cells showed that the internalization of PRL is not modified by the functional state of the CL, nevertheless the intracellular redistribution of the internalized hormone varied in relation with the PRL action on the CL (luteotrophic, day 12 vs luteolytic, day 22). These results seem to indicate that intracellular mechanisms rather than receptor content determine CL response to PRL.     

Expression of costimulatory molecules in the bovine corpus luteum

Background  

Bovine luteal parenchymal cells express class II major histocompatibility complex (MHC) molecules and stimulate class II MHC-dependent activation of T cells in vitro. The ability of a class II MHC-expressing cell type to elicit a response from T cells in vivo is also dependent on expression of costimulatory molecules by the antigen presenting cell and delivery of a costimulatory signal to the T cell. Whether bovine luteal parenchymal cells express costimulatory molecules and can deliver the costimulatory signal is currently unknown.     

Immune cell-endothelial cell interactions in the bovine corpus luteum

Early embryonic mortality accounts for a substantial portionof reproductive failure in agriculturally important livestock,including the dairy cow. The maintenance of early pregnancyrequires a fully functional corpus luteum (CL) that is not susceptibleto regression following fertilization, yet the cellular mechanismsof luteal regression are not clearly understood. Immune-cellaccumulation within the CL at the time of regression is a well-documentedphenomenon in a variety of species. In the dairy cow, immune-cellaccumulation precedes luteal regression by several days andcoincides with an increase in expression of the chemokine monocytechemoattractant protein 1 (CCL2), suggesting that immune-mediatedevents promote tissue destruction. Recent studies indicate thatendothelial cells comprising the CL are a primary source ofCCL2 secretion. Moreover, although uterine-derived prostaglandinF₂ (PGF) initiates luteal regression in the cow, PGF does notdirectly provoke CCL2 secretion by luteal endothelial cells.Instead, PGF-induced luteal regression is thought to requirecooperative interaction among immune cells, endothelial cells,and steroidogenic cells of the CL to further promote CCL2 secretion,enhance immune-cell recruitment, and eliminate luteal tissue.This brief review focuses on putative interactions between immunecells and endothelial cells derived from the bovine CL thatresult in enhanced CCL2 expression and the elaboration of otherinflammatory mediators (for example, cytokines), which perpetuateluteal regression. Fundamental knowledge of immune-endocrineinteractions within the reproductive system of cows has relevanceto other CL-bearing mammals, including humans and endangeredanimals, particularly in the development of methods to controland/or improve fertility. Thus, it is a timely topic for thissymposium concerning ecological immunology and public health.     

Production of enkephalins by the human and bovine corpus luteum

In search of early pregnancy factors, we detected by radioimmunoassay the presence of enkephalin in bovine and human corpus luteum. In vitro met-enkephalin release by bovine corpus luteum is about 0.5 to 1 pmole/mg of fresh tissue/24 hrs. The content of the fresh tissue is between 0.7 and 1.9 pmoles per gram of human tissue, and 0.9 pmoles for bovine tissue. Furthermore, we determined the presence of leu-enkephalin and met-enkephalin Arg-Gly-Leu to. The ratios observed confirm a pro-enkephalin A expression in the ovary. Opiates or opioid-like peptides are present in the female genitalia at the time of early embryo development. The roles of these opioid peptides is discussed in term of ovum transport, granulosa cell physiology and early pregnancy factors.     

Expression of costimulatory molecules in the bovine corpus luteum

Background  

A major event in the post-meiotic development of male germ cells is the formation of the acrosome. This process can be perturbed in C57BL/6 mice by administration of the small molecule miglustat (N-butyldeoxynojirimycin, NB-DNJ). The miglustat-treated mice produce morphologically abnormal spermatozoa that lack acrosomes and are poorly motile. In C57BL/6 mice, miglustat can be used to maintain long-term reversible infertility. In contrast, when miglustat was evaluated in normal men, it did not affect spermatogenesis. To gain more insight into this species difference we have now evaluated the reproductive effects of miglustat in rabbits, in multiple mouse strains and in interstrain hybrid mice.     

Ultrastructural studies of the bovine Graafian Follicle and corpus luteum

Summary Ovaries were obtained from normal adult dairy cows at all days of the estrous cycle. The largest Graafian follicle and corpus luteum were excised and prepared for electron microscopic study.In the follicle wall, membrana granulosa cells contained granular endoplasmic reticulum and mitochondria with villous or lamellar cristae. The theca interna cells during proestrus and estrus contained ribosomes separated from endoplasmic reticulum. The latter during these periods assumed tubular and tortuous shapes. Mitochondria during these periods assumed rounded shapes, were occasionally cup-shaped, and developed tubular cristae.In the corpus luteum, the large luteal cells during metestrus and diestrus contained an abundance of agranular, tubular, branching membranes of endoplasmic reticulum and Golgi apparatus. Mitochondria were large, with tubular cristae, but smaller mitochondria, with irregular or villous cristae, were also present. Transitional bodies of the latter mitochondria to another form were observed. Cup-shaped and annular mitochondria were present during diestrus. In the small luteal cells, large vesicular membrane formations were present and often associated with lipid bodies. The cells were lipid-laden. Lysosomes and granular bodies were present during luteal regression.The observed features of the granulosa cells are related to protein synthesis, those of the pre-ovulatory theca interna cells and metestrus-diestrus large luteal cells to steroid synthesis, and those of the small luteal cells to lipid storage.This investigation was supported by a General Research Support Grant to the College of Veterinary Medicine, University of Minnesota, and Research Grant No. GM-07009, of the United States Public Health Service. Approved for publication as Scientific Journal Series Paper No. 6344, Minnesota Agricultural Experiment Station. The work reported is taken from the senior author's Ph. D. thesis.     

Gonadotropin-releasing hormone-induced alteration of bovine corpus luteum function

Two experiments were conducted to evaluate effects of gonadotropin-releasing hormone (GnRH) on the function of the bovine corpus luteum during the estrous cycle. In Experiment 1, 10 beef heifers were assigned randomly into two groups; each heifer served as her own control. Heifers in Group I (n = 5) were injected i.v. with vehicle (saline) on Day 2 of the cycle (Day 0 = day of estrus) followed by an i.v. injection of 100 micrograms GnRH on Day 2 of the subsequent estrous cycle. Group II (n = 5) heifers were treated similarly except injections were given on Day 10 of the estrous cycle. All heifers were bled via the jugular vein at 15 min intervals beginning 30 min prior to injection and for 3 h after injection. Blood samples were also taken on alternate days after injection through Day 16 of the cycle. Gonadotropin-releasing hormone caused a significant release of luteinizing hormone (LH) on both treatment days with the peak occurring at 15 to 30 min postinjection. Treatment with GnRH on either Day 2 or 10 caused a reduction in serum progesterone levels on Days 12, 14 and 16 of the cycle (Group I, control 3.99, 3.97; 4.07 vs. treated 2.63, 3.45, 2.87; Group II, control 3.18, 3.82, 4.13 vs. treated 2.50, 2.82, 3.17 ng/ml, respectively; common SE = 0.24 p less than 0.03). Length of the estrous cycle did not differ between groups (Group I, control 20.7 vs. treated 20.9; Group II, control 20.7 vs. treated 21.1 days, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in the proteome of functional and regressing corpus luteum during pregnancy and lactation in the rat

The corpus luteum (CL) is an exquisitely regulated transitory endocrine gland necessary for the onset and maintenance of pregnancy in mammals. Most of the data on the mechanisms of CL differentiation at the molecular level come from genomic studies, but direct protein data are scarce. Here we have undertaken a differential expression proteomic approach to identify, in an unbiased way, those proteins whose levels change significantly in the rat CL as it evolves from functionality during pregnancy to regression after parturition. Moreover, we have compared the regressing CL with the newly formed functional CL that coexist during lactation under the same endocrine environment. We have defined a "proteomic signature" of CL functionality, which is constituted by a set of 24 proteins with a few differences between pregnancy and lactation. Most of these markers are new and are involved in microtubule assembly, retinoic acid transport, and Raf kinase signaling cascade; 10 are enzymes that define a ketogenic metabolic landscape, demonstrating, for the first time, the prevalence of de novo cholesterol synthesis in luteal cells. The "proteomic signature of regression," on the other hand, is composed of nine proteins, one of which is 20alpha-hydroxysteroid dehydrogenase and two, ferritin and gamma-actin, are new. The discovery of unpredictable new actors in the differentiation process of CL reported here will contribute to new hypotheses that explain the complex female reproductive function at the protein level. It will also open new doors to research on each identified protein by relating them to cellular differentiation.