Regulation of corpus luteum function

The effects have been studied of different ovulation inductionregimens [either domiphene citrate or buserelin in combinationwith human menopausal gonadotrophin (HMG)] on the circulatingconcentrations of progesterone, oestradiol, relaxin and humanchorionic gonadotrophin (HCG) during the first trimester ofpregnancy. Ovulation induction with clomiphene resulted in elevatedconcentrations of gonadotrophins in both phases of the cycle,while during ovulation induction with buserelin, gonadotrophinconcentrations were elevated in the follicular phase only. Theconcentrations of all corpus luteum products were greater inclomiphene pregnancies compared with spontaneous pregnancies,but only oestradiol and relaxin concentrations were greaterin clomiphene pregnancies compared with buserelin pregnancies.The concentrations of HCG were significantly reduced in clomiphenepregnancies compared to natural pregnancies. Relaxin concentrationswere significantly higher from 7 weeks gestation in buserelincompared with spontaneous pregnancies, while progesterone, oestradioland HCG concentrations were not consistently different. Consistentassociations were found between relaxin and HCG concentrationsin spontaneous pregnancies and between the concentrations ofrelaxin and both progesterone and oestradiol in pregnanciesachieved after ovulation induction. These data suggest that(i) given the similarity in the circulating concentrations ofHCG, the relatively lower circulating gonadotrophin concentrationsduring the luteal phase of the cycle of conception result inreduced circulating concentrations of oestradiol and relaxin;while in the case of relaxin this effect is partially reversible,there is no evidence that this is so for oestradiol; (ii) synthesisof progesterone in the corpus luteum is less affected by lowerconcentrations of gonadotrophins during the luteal phase; (iii)ovulation induction with clomiphene results in pregnancies withlower concentrations of HCG, suggesting that trophoblast functionmay be impaired; and (iv) corpus luteum function is linked withplacental steroidogenesis.     

Structure and function of the hamster corpus luteum during the estrous cycle

Luteal cell structure and function were studied by electron microscopy in conjunction with measurement of progesterone production by corpora lutea which were isolated and incubated in vitro on successive days of the four-day hamster estrous cycle. Granulosal cells were primarily responsible for the formation of the corpus luteum. Agranular endoplasmic reticulum and lipid droplets developed during luteinization of granulosal cells on the first post-ovulation day (day 1). Luteal cell hypertrophy on day 2 resulted from dilation of tubular agranular endoplasmic reticulum and swelling of mitochondria with tubular cristae. Plasma progesterone levels on the first two days of the cycle appeared to be correlated with luteal activity as corpora lutea were demonstrated to synthesize progesterone during this interval. Luteolysis occurred on day 3 with a reduction in luteal cell size accompanied by condensation of the agranular endoplasmic reticulum, regressive changes in the mitochondria, and a marked drop in luteal progesterone synthetic activity. On day 4, extensive phagocytic activity and luteal cell autolysis indicated an advanced involutional state. The short but functional luteal phase in the cyclic hamster does not appear to involve the production of 20α-hydroxy-pregn-4-en-3-one as occurs in the rat. This progestin was not detectable in plasma or luteal tissue before or after incubation at any time during the cycle. Possible mechanisms regulating luteal cell development and regression during the estrous cycle are discussed.     

Involvement of leukocytes and cytokines in the ovulatory process and corpus luteum function

The role of leukocytes and cytokines in ovarian physiology isnow established, although the function of each cell type andcytokine remains to be determined in detail. Current knowledgeof these effects on follicle development, ovulation, luteinizationand luteotrophic process and luteolysis is reviewed. It is possiblethat further research will help to unravel some of the clinicalmysteries in ovarian function, including polycystic ovary syndrome,premature menopause, ovulatory disorders, and luteal phase defect.Furthermore, the increasing use of cytokines and their antagonistsin clinical practice may have significant effects upon reproductivefunction.     

Mechanisms of life span determination in Caenorhabditis elegans

Molecular analysis of several gerontogenes of Caenorhabditis elegans has led to the discovery of at least two life span-controlling pathways. An insulin-like signaling cascade consisting of proteins encoded by the genes daf-2, age-1, akt-1, akt-2, daf-16 and daf-18 regulates dauer diapause, reproduction, and longevity. This pathway regulates all three processes systemically. daf-12 interacts with it, affecting dauer diapause and longevity. Life span extension mediated by this pathway probably results from the activation of an enhanced life-maintenance program, which is normally operative during dauer diapause. A different mechanism is specified by the clock genes clk-1, clk-2, clk-3 and gro-1, which regulate metabolic activity and the pace of many temporal processes including longevity. There is some controversy as to whether the life span extension observed in these mutants requires the activity of daf-16. All known gerontogenes appear to confer resistance to environmental stress, usually multiple stress factors, including oxidative stress, high temperature, and exposure to ultraviolet radiation. Caloric restriction extends longevity substantially, and may act by activating the enhanced life-maintenance program.     

Relationship of luteal blood flow and corpus luteum function in pseudopregnant rats

An experiment was conducted to examine whether blood flow to corpora lutea may regulate luteal function as judged from plasma levels of progesterone (P) in mature pseudopregnant rats. 141Ce-labeled microspheres (14.1 +/- 0.8 micrometer diam) were used to measure cardiac output and organ and tissue blood flow in rats on days 6, 8, 10, and 12 of pseudopregnancy and in proestrus following luteal regression. The mean arterial blood pressure and cardiac output were similar among all groups of rats. Although a significant (P less than 0.05) decrease in plasma P was observed in rats on day 12 of pseudopregnancy, no change in luteal blood flow or distribution of ovarian blood flow to the corpora lutea was seen at this stage of pseudopregnancy when compared to day 8 or 10 of pseudopregnancy. However, a significant decrease (P less than 0.05) in luteal blood flow was seen in proestrous rats. Because a decrease in plasma progesterone preceded the decrease in luteal blood flow, it was concluded that physiological luteal regression may not be initiated by a reduction of blood flow to the corpus luteum.     

Recovery of corpus luteum function after prolonged deprivation from gonadotrophin stimulation

Three women with hypogonadotrophic hypogonadism, all desiringpregnancy, participated in a prospective open study attemptingto assess the ability of the human corpus luteum to recoverafter 7 days of deprivation from gonadotrophin stimulation.Follicular growth was induced by gonadotrophins. An endogenousluteinizing hormone (LH) surge was induced by the s.c. injectionof a gonadotrophin-releasing hormone agonist For luteal support,10 mg/day oral medroxyprogesterone acetate were given for 7days, after which a single i.m. injection of human chorionicgonadotrophin (HCG) was administered. Monitoring during thefollicular phase consisted of daily measurements of serum oestradiol,LH and follicle stimulating hormone (FSH) concentrations, andof follicular growth by trans-vaginal ultrasonography. Duringthe luteal phase, monitoring consisted of measurements of serumconcentrations of LH, FSH, oestradiol, progesterone, 17-hydroxy-progesteroneand -HCG. Ovulation and luteinization occurred in two patients,demonstrated by transient marked increases in serum progesteroneand 117-hydroxy-progesterone concentrations which decreasedto basal pre-ovulatory values and increased again followingthe administration of HCG 7 days later. In the third patient,ovulation and luteinization did not occur, and the subsequentadministration of HCG did not result in an increase in progesteroneconcentration. Of the two patients who ovulated, one conceivedand the second had a luteal phase of 15 days duration. Our preliminaryresults suggest that the human corpus luteum can be ’rescued‘and can function normally after 7 days of deprivation from gonadotrophinstimulation in patients with hypogonadotrophic hypogonadism.     

Local uterine regulation of the corpus luteum

In order to determine if the well known uterine inhibition of the guinea pig corpus luteum is a local effect, a series of partial hysterectomies were performed. Some groups were subjected to one-half or three-fourths hysterectomies alone, while in others one ovary was also removed on either the side retaining some or the side losing all uterine tissue. In addition, two groups in which all ovarian and uterine tissue was preserved were subjected to unilateral or bilateral complete surgical separation of all communicating structures between uterus and ovary. Sham-operated, totally hysterectomized, and unilaterally ovariectomized groups were used as controls. In all groups in which an ovary left in the animal was separated from direct contact with its uterine horn, the estrous cycles became long and erratic, or were arrested completely due to the persistance of active corpora lutea in those ovaries. However, corpora lutea regressed normally in all ovaries left in their normal relationship to a uterine horn. These results indicate that the uterine regulatory factor does reach the ovary by some local route.     

Mitochondrial function as a determinant of life span

Average human life expectancy has progressively increased over many decades largely due to improvements in nutrition, vaccination, antimicrobial agents, and effective treatment/prevention of cardiovascular disease, cancer, etc. Maximal life span, in contrast, has changed very little. Caloric restriction (CR) increases maximal life span in many species, in concert with improvements in mitochondrial function. These effects have yet to be demonstrated in humans, and the duration and level of CR required to extend life span in animals is not realistic in humans. Physical activity (voluntary exercise) continues to hold much promise for increasing healthy life expectancy in humans, but remains to show any impact to increase maximal life span. However, longevity in Caenorhabditis elegans is related to activity levels, possibly through maintenance of mitochondrial function throughout the life span. In humans, we reported a progressive decline in muscle mitochondrial DNA abundance and protein synthesis with age. Other investigators also noted age-related declines in muscle mitochondrial function, which are related to peak oxygen uptake. Long-term aerobic exercise largely prevented age-related declines in mitochondrial DNA abundance and function in humans and may increase spontaneous activity levels in mice. Notwithstanding, the impact of aerobic exercise and activity levels on maximal life span is uncertain. It is proposed that age-related declines in mitochondrial content and function not only affect physical function, but also play a major role in regulation of life span. Regular aerobic exercise and prevention of adiposity by healthy diet may increase healthy life expectancy and prolong life span through beneficial effects at the level of the mitochondrion.     

Extracellular matrix of the human cyclic corpus luteum

Extracellular matrix regulates many cellular processes likely to be important for development and regression of corpora lutea. Therefore, we identified the types and components of the extracellular matrix of the human corpus luteum at different stages of the menstrual cycle. Two different types of extracellular matrix were identified by electron microscopy; subendothelial basal laminas and an interstitial matrix located as aggregates at irregular intervals between the non-vascular cells. No basal laminas were associated with luteal cells. At all stages, collagen type IV alpha1 and laminins alpha5, beta2 and gamma1 were localized by immunohistochemistry to subendothelial basal laminas, and collagen type IV alpha1 and laminins alpha2, alpha5, beta1 and beta2 localized in the interstitial matrix. Laminin alpha4 and beta1 chains occurred in the subendothelial basal lamina from mid-luteal stage to regression; at earlier stages, a punctate pattern of staining was observed. Therefore, human luteal subendothelial basal laminas potentially contain laminin 11 during early luteal development and, additionally, laminins 8, 9 and 10 at the mid-luteal phase. Laminin alpha1 and alpha3 chains were not detected in corpora lutea. Versican localized to the connective tissue extremities of the corpus luteum. Thus, during the formation of the human corpus luteum, remodelling of extracellular matrix does not result in basal laminas as present in the adrenal cortex or ovarian follicle. Instead, novel aggregates of interstitial matrix of collagen and laminin are deposited within the luteal parenchyma, and it remains to be seen whether this matrix is important for maintaining the luteal cell phenotype.     

Glucocorticoid effects on memory function over the human life span

Glucocorticoids (GCs), produced by the stress-responsive hypothalamic-pituitary-adrenal axis, are well recognized for their regulatory role in peripheral metabolism. GCs are also known to regulate various brain functions, with well-described effects on human cognition. Increased GC exposure in humans-including exposure to the endogenous GC, cortisol-at levels associated with stress, decreases memory and learning function. These results extend evidence from in vitro studies of synaptic and cell function and evidence from animals indicating the GCs can regulate substrates of memory function. While considerable evidence details these effects in adult humans and animals, relatively less is know about the effect of GCs on cognitive function in children and older adults. Investigators have suggested that children, particularly preschool-aged children, may be vulnerable to adverse consequences of increased GC secretion resulting from stress and neuropsychiatric diseases such as depression. Adverse GC effects on memory substrates and memory function in the adult have also fostered concern that age-related changes, including changes in GC receptors and changes in circulating cortisol levels, could lead to age-related increases in the adverse effect of GCs on brain function. Investigators have reported an association between age-related increases in cortisol levels and age-related memory decline, but this association may or may not be due to a direct effect of cortisol on memory substrates. A number of possible treatment approaches to prevent or remediate adverse GC-induced effects are under development. In general, the use of safe and effective agents for blocking adverse GC effects on brain functions including memory may offer benefits to individuals suffering acute and chronic stressors and could prevent brain changes relevant to stress, aging, and stress-related neuropsychiatric diseases.     

Discovery of LH-regulated genes in the primate corpus luteum

Circulating LH is essential for the development and function of the primate corpus luteum (CL) during the menstrual cycle. However, the cellular and molecular processes whereby LH controls luteal structure and function are poorly understood. Therefore, studies were initiated to identify gene products that are regulated by gonadotrophin in the monkey CL. Rhesus monkeys either were untreated (controls, CTRL; n = 3) or received the GnRH antagonist Antide (ANT; 3 mg/kg body weight, n = 3) to inhibit pituitary LH secretion on day 6 of the luteal phase in spontaneous menstrual cycles. The CL was removed 24 h later. RNA was extracted and converted to cDNA. The CTRL and ANT cDNA were differentially labelled with fluorescent dyes (Cy3-CTRL and Cy5-ANT) and hybridized onto microarrays containing 11,600 human cDNA. The selected cDNA were analysed further via semi-quantitative RT-PCR (a) to validate the microarray results and (b) to determine if their expression varies in the CL (n = 3/stage) between the mid (day 6-8), late (day 14-16), or very late (day 18-19, menses) luteal phase of the natural cycle. After normalization of the fluorescence data, 206 cDNA (1.8% of the total) exhibited > or = 2-fold change in expression after ANT. Of the 25 cDNA exhibiting a > or = 6-fold change, 6 were up-regulated and 19 were down-regulated. Twenty-two of these 25 cDNA were validated by RT-PCR as differentially expressed in the ANT group, relative to the CTRL group, and 11 of 25 changed (P < 0.05) correspondingly in the late-to-very late luteal phase. Thus, we have identified gene products that are regulated by gonadotrophin in the primate CL that may be important in luteal regression during the menstrual cycle.     

Immunolocalization of glutaredoxin in the human corpus luteum.

Glutaredoxin (Grx) is a small protein with oxidoreductase activity which is involved in the cellular defence against oxidative stress. Corpus luteum (CL) regression has been related to the generation of reactive oxygen species (ROS). We have studied the presence of glutaredoxin in the human ovary during the ovulatory cycle using polyclonal antibodies developed against recombinant human Grx. Immunostaining was only detected between days 15 and 23 of the cycle and was localized exclusively in the corpus luteum. Grx-positive cells corresponded to granulosa-derived luteal cells (GLC) whereas the remaining luteal cell types were not immunostained. In general, Grx immunoreactivity was parallel to the functional activity of the CL. Most GLC were immunostained on days 15-16 of the cycle, whereas on days 17-19 immunoreaction was found mainly at the inner and outer aspects of the granulosa lutein layer (GLL). After this stage only isolated GLC showed Grx immunoreactivity and no reaction was found from day 23 of the cycle onward. In two CL of pregnancy that were also studied, isolated GLC showed Grx immunoreactivity. Loss of Grx immunoreactivity was coincident with the appearance of morphological signs of structural luteolysis, such as shrinkage of the GLL and the presence of apoptotic cells. These data suggest that Grx, as a cellular antioxidant, plays an important role in the mechanisms of human CL development.     

Immunolocalization of bcl-2 in the human corpus luteum

The mechanisms of luteal regression and rescue in women areunknown but forms of programmed cell death may be involved.The proto-oncogene bcl-2 is an important inhibitor of apoptosisbut has not previously been described in the human corpus luteum.Immunohistochemical localization of bcl-2 protein was investigatedin human corpora lutea obtained from women undergoing surgeryduring endocrine monitored menstrual cycles as well as fromwomen who had been treated with human chorionic gonadotrophin(HCG) to prolong the luteal phase. Bcl-2 was found to be localizedin granulosa-lutein, theca-lutein (as identified by co-localizationof P450_{17-hydroxylase}) and the endothelial cells around someblood vessels. Immunoblotting demonstrated the presence of asingle band of MW 26 kDa. There was no apparent change in eitherthe intensity of immunostaining or the histological localizationduring the normal luteal phase or following treatment with humanchorionic gonadotrophin. The product of the proto-oncogene bcl-2is present in the human corpus luteum. It is unlikely that bcl-2expression alone is responsible for prolongation of the lifespanof the corpus luteum in early pregnancy although it is possiblethat the action of the bcl-2 gene present is modified by changesin other members of the bcl-2 family. apoptosis/bcl-2/corpus luteum/granulosa/17-hydroxylase     

Cell proliferation and vascular morphology in the marmoset corpus luteum

Luteal formation is associated with angiogenesis and low progesterone production. Maximal mid-luteal phase progesterone production is concurrent with extensive vascularization, and luteolysis occurs when steroidogenesis decreases. Angiogenic cell proliferation and vascular changes have not been examined in the marmoset. The aim of this study was to examine vascular morphology throughout the luteal phase by identifying: (i) von Willebrand factor VIII antigen (vW)-immunopositive endothelial cells; (ii) Ki67-positive proliferating cells; and (iii) bromodeoxyuridine-positive proliferating cells. Marmoset corpora lutea were examined throughout the cycle, and natural regression was compared with induced luteolysis after administration of a prostaglandin F(2alpha) analogue or gonadotrophin-releasing hormone (GnRH) antagonist. Steroidogenic and endothelial cells were positive for proliferation markers. Endothelial cell proliferation was highest during luteal formation, then decreased and remained low during the luteal phase and functional regression, however endothelial cell proliferation increased during structural regression. Endothelial cell proliferation was unchanged by induced regression. The area of vW immunostaining was highest during luteal formation, decreased thereafter and remained constant during the luteal phase and regression. Distribution of immunostaining indicated the presence of an extensive capillary network, but during structural regression the numbers of capillaries decreased and numbers of microvessels increased. These results suggest that vascular changes are concurrent with changes in the functional status of the marmoset corpus luteum.