The effect of estradiol on the production and secretion of complement component 3 by the rat uterus and surgically induced endometriotic tissue*†*Supported by grants HD-20025 and HD-06274 (C.R.L.) from the National Institutes of Health, Bethesda, Maryland; and the Mellon Foundation, New York, New York.†Presented at the 45th Annual Meeting of The American Fertility Society, San Francisco, California, November 13 to 16, 1989

The Inflammatory Feed-Forward Loop Triggered by the Complement Component C3 as a Potential Target in Endometriosis

The complement system is a major component of humoral innate immunity, acting as a first line of defense against microbes via opsonization and lysis of pathogens. However, novel roles of the complement system in inflammatory and immunological processes, including in cancer, are emerging. Endometriosis (EM), a benign disease characterized by ectopic endometrial implants, shows certain unique features of cancer, such as the capacity to invade surrounding tissues, and in severe cases, metastatic properties. A defective immune surveillance against autologous tissue deposited in the peritoneal cavity allows immune escape for endometriotic lesions. There is evidence that the glandular epithelial cells found in endometriotic implants produce and secrete the complement component C3. Here, we show, using immunofluorescence and RT-qPCR, the presence of locally synthesized C3 in the ectopic endometriotic tissue, but not in the eutopic tissue. We generated a murine model of EM via injection of minced uterine tissue from a donor mouse into the peritoneum of recipient mice. The wild type mice showed greater amount of cyst formation in the peritoneum compared to C3 knock-out mice. Peritoneal washings from the wild type mice with EM showed more degranulated mast cells compared to C3 knock-out mice, consistent with higher C3a levels in the peritoneal fluid of EM patients. We provide evidence that C3a participates in an auto-amplifying loop leading to mast cell infiltration and activation, which is pathogenic in EM. Thus, C3 can be considered a marker of EM and its local synthesis can promote the engraftment of the endometriotic cysts.

Immunological Basis of the Endometriosis: The Complement System as a Potential Therapeutic Target

Endometriosis (EM) is a chronic disease characterized by the presence and proliferation of functional endometrial glands and stroma outside the uterine cavity. Ovaries and pelvic peritoneum are the most common locations for endometrial ectopic tissue, followed by deep infiltrating EM sites. The cyclic and recurrent bleeding, the progressive fibrosis and the peritoneal adhesions of ectopic endometrial glands, may cause different symptoms depending on the origin involved. EM is a frequent clinical condition affecting around 10% of women of mainly reproductive age, as well as in post-menopausal women and adolescents, especially with uterine anomalies. The risk of developing EM depends on a complex interaction between genetic, immunological, hormonal, and environmental factors. It is largely considered to arise due to a dysfunction of immunological surveillance. In fact, women with EM exhibit altered functions of peritoneal macrophages, lymphocytes and natural killer cells, as well as levels of inflammatory mediators and growth factors in the peritoneal fluid. In EM patients, peritoneal macrophages are preponderant and highly active compared to healthy women. Peritoneal macrophages are able to regulate the events that determine the production of cytokines, prostaglandins, growth factors and complement components. Several studies have shown alteration in the regulation of the complement activation, leading to chronic inflammation characteristic of EM. Aberrant regulation/activation of the complement system has been observed in the peritoneal cavity of women affected by EM. Thus, complement inhibition may represent a new approach for the treatment of EM, given that a number of complement inhibitors are under pre-clinical and clinical development. Such an intervention may provide a broader therapeutic control of complement-mediated inflammatory damage in EM patients. This review will focus on our current understanding of the role of complement activation in EM and possible modalities available for complement-based therapy.

The role of immune and oxidative pathways in menstrual cycle associated depressive, physio-somatic, breast and anxiety symptoms: Modulation by sex hormones

OBJECTIVE

To examine whether 1) immune and nitro-oxidative stress (IO&NS) biomarkers are associated with premenstrual syndrome (PMS); and 2) changes in IO&NS biomarkers during the menstrual cycle (MC) are associated with PMS symptoms and plasma estradiol and progesterone.

METHODS

This longitudinal study examined 41 women who completed the Daily Record of Severity of Problems (DRSP) rating scale during 28 consecutive days and assayed plasma levels of complement C3 and C4, highly sensitive C-reactive protein (hsCRP), haptoglobin (Hp), advanced oxidation protein products (AOPP), lipid hydroperoxides (LOOH), nitric oxide metabolites (NOx), total radical-trapping antioxidant parameter (TRAP), sulfhydryl (-SH) groups and the activity of paraoxonase (PON)1 at days 7 (D7), 14 (D14), 21 (D21) and 28 (D28) of the MC. MC Associated Syndrome (MCAS) was diagnosed when the summed DRSP score during the MC is >0.666 percentile.

RESULTS

All biomarkers, except hsCRP, showed significant alterations during the MC. Arylesterase (AREase) was lowered at D28, while LOOH increased at D14 and C4 at D21 in MCAS. Total DRSP scores were predicted by the combined effects of C4 (positively) and AREase and malondialdehyde (MDA) (both inversely associated). Progesterone lowered levels of LOOH, AOPP and C3 and estradiol lowered levels of Hp while both sex hormones increased 4-(chloromethyl)phenyl acetate (CMPA)ase and AREase activities and levels of -SH groups.

CONCLUSION

PMS/MCAS is not accompanied by a peripheral inflammatory response. Lowered MDA and antioxidant defenses and increased C4 may play a role in MC symptoms while sex hormones may have a protective effect against oxidative stress toxicity.

Resveratrol and endometrium: a closer look at an active ingredient of red wine using in vivo and in vitro models

Resveratrol is a natural phytoestrogen with antiproliferative properties present in red wine, grapes, and berries. Published reports on the effects of resveratrol in human endometrial function are limited. The objective of this study was to investigate the expression of estrogen receptor α (ESR1), Ki-67 (a proliferative marker), aryl hydrocarbon receptor (AhR), and members of the cytochrome P450 superfamily of enzymes (CYP1A1 and CYP1B1) in an in vitro and vivo assay. Alkaline phosphatase assay of estrogenicity was used to compare estrogen activity of different concentrations of resveratrol to estradiol (E2) and diethylstilbestrol (DES), using Ishikawa cell culture. Immunohistochemical expression of ESR1 and Ki67, and reverse transcriptase polymerase chain reaction of AhR, CYP1A1, and CYP1B1 were analyzed from xenograft implants of human endometrial tissue in ovariectomized immunodeficient RAG-2-γ(c) mice, after 30 days of treatment with subcutaneous pellets of E2, E2 plus progesterone (P4), or E2 plus resveratrol (6, 30, or 60 mg) for 30 days. Compared to E2, resveratrol acted as an agonist and antagonist of estrogen in low and high concentrations, respectively, when combined with E2. Xenografts of human endometrial tissues in RAG-2 mice exhibited reduced expression of ESR1 and proliferative activity (Ki67) with 60 mg of resveratrol. This study suggests that resveratrol, at high doses, has the potential benefit to reduce proliferation of human endometrium through ESR1.

Plasma C3a-des-Arg levels in women with and without endometriosis

PROBLEM

The lack of a reliable method for early non-invasive detection of endometriosis often results in delayed diagnosis. The aim of this study was to test the hypothesis that the plasma concentration of complement factor C3a (anaphylatoxin) can be used as a non-invasive test in the diagnosis of endometriosis.

METHOD OF STUDY

The C3a concentration was analyzed using ELISA in 160 patients with (n = 109) or without (n = 51) endometriosis during menstruation (n = 49), follicular phase (n = 55), and luteal (n = 56) phase.

RESULTS

Plasma C3a concentration was comparable between patients with [102 (27-2213) ng/mL] and without [105 (32-2340) ng/mL] (P = 0.84) endometriosis, also when assessed separately during menstruation, follicular phase, and luteal phase.

CONCLUSION

We found no difference in C3a levels between women with and without endometriosis and did not confirm our hypothesis that plasma C3a levels can be used as diagnostic test for endometriosis.

Levels of complement components iC3b, C3c, C4, and SC5b-9 in peritoneal fluid and serum of infertile women with endometriosis

OBJECTIVE

To assess whether complement components iC3b, C3c, C4, and SC5b-9 may be involved in the pathogenesis of endometriosis.

DESIGN

Prospective, experimental trial.

SETTING

Medical university.

PATIENT(S)

112 women infertile women undergoing laparoscopy.

INTERVENTION(S)

Venipuncture and laparoscopic peritoneal fluid collection.

MAIN OUTCOME MEASURE(S)

Peritoneal fluid and serum iC3b, C3c, C4, and SC5b-9 levels were measured by the enzyme-linked immunosorbent assay (ELISA) method.

RESULT(S)

Higher levels of C3c, C4, and SC5b-9 complement components were found in the serum compared with the peritoneal fluid, but the levels of iC3b were higher in the peritoneal fluid. We observed higher concentrations of C3c, C4, and SC5b-9 in the peritoneal fluid and serum of women with endometriosis compared with healthy women. However, the levels of iC3b in both peritoneal fluid and serum were statistically significantly lower than in the control group.

CONCLUSION(S)

The impairment of the mechanisms involved in the regulation of activation of complement system may be an important factor in the pathogenesis of endometriosis and endometriosis-associated infertility.

Effect of the immunomodulator leflunomide on the induction of endometriosis in an experimental rat model

The effect of immunomodulator leflunomide on the development of an experimental endometriosis model was assessed by surgically transplanting autologous fragments of endometrial tissue onto the inner surface of the abdominal wall and arterial cascades of the small intestines. Leflunomide was found to affect the development of endometriosis negatively and seemed to interfere with the growth and maintenance of the uterine explant in this experimental rat model.

Effect of peroxisome proliferator-activated receptor-gamma agonist rosiglitazone on the induction of endometriosis in an experimental rat model

OBJECTIVE

To assess the effect of the peroxisome proliferator-activated receptor (PPAR)-gamma agonist rosiglitazone on the induction of endometriosis in a rat model.

METHODS

Endometriosis was surgically induced in 28 rats by transplanting an autologous fragment of endometrial tissue onto the inner surface of the abdominal wall. Group I was assigned as control and no medication was administered. Starting 3 days before the operation and continuing for 4 weeks, 0.2 mg/kg/d rosiglitazone was administered to the study group orally. Four weeks later rats were killed and ectopic uterine tissues were evaluated morphologically and histologically. Scoring systems were used to evaluate preservation of epithelia.

RESULTS

Four rats in the study group and one rat in the control group died of complications related to surgery. There was a significant difference in post-treatment spherical volumes (64.00 mm3 [interquartile range (IQR): 354.42] vs 41.60 mm3 [IQR: 37.87], P = .018) and explant weights (77.97 mg [IQR: 431.27] vs 47.24 mg [IQR: 43.01], P = .005) between control and rosiglitazone-treated groups. The epithelia were found to be preserved significantly better in the control group when compared with the roziglitazone-treated group (2.00 [IQR:2.00] vs 0.00 [IQR:2.25], P = .014).

CONCLUSIONS

Rosiglitazone was found to affect the induction of endometriosis negatively in this experimental rat model and seemed to interfere with the growth and maintenance of the uterine explant.

Human endometriotic xenografts in immunodeficient RAG-2/gamma(c)KO mice

OBJECTIVE

The purpose of this study was to create a novel animal model for studies of endometriosis.

STUDY DESIGN

To facilitate the study of the transplantation of endometriosis into immunodeficient RAG-2/gamma(c)KO mice, endometriosis biopsy specimens were collected from 19 women by laparoscopic surgery and grafted subcutaneously into the mice, which were treated subsequently with estradiol and progesterone to create 28-day artificial cycles. The grafts were collected during the first, second, and fourth cycles and were evaluated histologically for evidence of bleeding and immunocytochemically for estrogen receptor and progesterone receptor.

RESULTS

Biopsy specimens that contained endometrium-like glands were well accepted (>90% success). These grafts maintained glandular morphologic condition, estrogen receptor, and progesterone receptor; bled after progesterone withdrawal; and formed chocolate cysts. However, biopsy specimens that lacked glands or that consisted of peritoneal adhesions and stroma were accepted poorly <5% success) and failed to show evidence of estrogen receptor, progesterone receptor, or cyclic bleeding.

CONCLUSION

Human endometriosis transplanted into RAG-2/gamma(c)KO mice can provide a model for endometriotic bleeding.

Gene expression profiling of the effects of castration and estrogen treatment in the rat uterus

The development and functions of female reproductive tissues are regulated by the actions of two major sex steroid hormones, estrogen and progesterone. To investigate estrogen-dependent gene expression in the rat uterus, we studied the effect of ovariectomy with or without estrogen treatment on the uterine expression of 3000 genes using cDNA microarrays. Many genes were regulated by either treatment, but only few were reciprocally regulated by these contrasting treatments. The present study confirms previous findings and identifies several genes with expressions not previously known to be influenced by estrogen. These genes include follistatin-related protein, Thy-1 glycoprotein, alpha-fodrin, CD24, immediate early response 5, insulin-like growth factor-binding protein 2, growth response protein CL-6 (INSIG-1), ladinin1, class I major histocompatibility complex heavy chain, lactadherin, ezrin, and Fas-activated serine/threonine kinase. Because of their function as regulators of proliferation and apoptosis, CD24, insulin-like growth factor-binding protein 2, and Fas/Fas ligand were examined further by immunohistochemical expression and tissue localization analysis. Our analysis confirms a contrasting regulation of these gene products by ovariectomy and estrogen treatment. The present study identifies novel mediators of estrogen actions in the uterus and provides genome-wide expression data from which novel hypotheses regarding uterine function can be generated.

Suppression of natural killer cell activity by splenocyte transplantation in a rat model of endometriosis

BACKGROUND

One immune characteristic of endometriosis is a decrease in natural killer (NK) cell activity. This study was performed to determine whether an abnormal immune reaction in an endometriosis animal model could be transferred to an animal of the same species.

METHODS

An endometriosis model was prepared using 8 week old female rats by grafting a small section of one uterine horn onto the mesentery, followed 4 weeks later by removal of the spleen and remaining uterine horn. Splenocytes, that had been depleted of macrophages were injected via the tail vein, and NK cell activity of splenocytes was determined 4 days later. The uterus was simultaneously investigated immunohistochemically for immune cells. There was a control group (untreated; group 1), a control-splenocyte injection group (group 2), an experimental endometriosis model group (group 3) and an endometriosis model splenocyte injection group (group 4).

RESULTS

Splenocyte NK cell activity was decreased in group 3 to 42.0% of that of group 1 and in group 4 to 38.9%. Immunohistologically, the number of NK cells in groups 3 and 4 markedly decreased to 62.0 and 55.1% of group 1 respectively.

CONCLUSION

It was demonstrated that abnormal immunity caused by allograft of immune cells could recur in an endometriosis rat model.

Using rats as a research model for the study of endometriosis

Although there are disadvantages of extrapolating data across species, the rat model may be used to study events involved in the pathogenesis and pathophysiologies of endometriosis or novel therapeutic approaches for this disorder that are not accessible in humans. Rat endometriotic tissues are similar to human lesions in vivo, and rat endometriotic tissues and cells perform in a similar manner as human endometriotic tissues and cells in organ explant culture and isolated cell culture. The rat model permits studies of mechanisms and regulators in a controlled manner free from confounding influences such as individual patient variation and environmental influences. The primary method used for induction of endometriosis in rats has been autotransplantation of uterine squares (implants) into the peritoneal cavity. Beyond mere growth of endometrium in ectopic locations, rats with endometriosis display similar symptoms, including a reduction in fertility and fecundity, and the endometriotic implants react similarly to therapeutics as those of humans with the disease. Similar alterations in gene expression and protein production have been observed in endometriotic tissues from rats and humans that may, in part, be causative agents involved in the pathogenesis or pathophysiologies of endometriosis.

Endometrial anomalies in women with endometriosis

Endometriotic lesions are defined by extrauterine growth of endometrial glands and stroma. Retrograde menstruation with subsequent attachment, invasion, and neovascularization are believed to give rise to the endometriotic lesions. As most women exhibit some degree of retrograde menstruation, some other unidentified factor(s) must render certain women susceptible to attachment and growth of ectopic endometrial tissue. A variety of theories have been proposed to account for this susceptibility, including genetic predisposition, aberrant immunological response, and an altered peritoneal environment. Ectopic endometriotic lesions are histologically similar to their putative eutopic precursors, yet significant biochemical differences exist between these two tissues. Less information is available regarding differences between eutopic endometrium from women with or without endometriosis. This report describes anomalies in structure, proliferation, immune components, adhesion molecules, proteolytic enzymes and inhibitors, steroid and cytokine production and responsiveness, and gene expression and protein production that have been identified in eutopic endometrium from women with endometriosis.

Induction of the angiogenic factor VEGF in the uterus by the antiprogestin onapristone

Onapristone (also referred to as ZK 98,299) is an antiprogestin that shares a number of structural similarities to mifepristone (RU-486) and other drugs in this class. While investigating the actions of antiprogestins on steroid hormone induced gene expression of angiogenic factors such as vascular endothelial growth factor (VEGF), we noted that onapristone alone induces VEGF transcript levels in the immature, ovariectomized rat uterus. In addition, onapristone induces expression of c-fos mRNA, which is induced by estrogens but not progestins in this target tissue. This induction of VEGF and c-fos by onapristone is inhibited by the antiestrogen ICI 182,780, but not by the antiprogestin RU-486. Both transcripts are very rapidly induced by onapristone, with maximal mRNA levels observed 3-6 h after in vivo administration of the drug. This time course is similar to that for induction of these genes by estrogenic hormones. Dose-response studies show that both these genes are maximally induced by a 2.5 mg/kg dose of onapristone following intra peritoneal injection. These results indicate that onapristone rapidly upregulates several genes normally under estrogenic regulation in the immature rat uterus. Importantly, this is the first report of the induction of a major angiogenic factor by an antiprogestin. Since an increase in vascularity increases tumor expansion and metastasis, the induction of angiogenesis and its regulatory factors such VEGF may be an important end-point to consider in the development and use of antiprogestins for the treatment of neoplastic disease.

Increased expression of complement component 3 in human ectopic endometrium compared with the matched eutopic endometrium

OBJECTIVE

To compare the gene expression of complement component 3 (C3) in human eutopic and ectopic endometrium.

DESIGN

A prospective, controlled study.

SETTING

Academic hospital.

PATIENT(S)

Women with documented endometriosis.

INTERVENTION(S)

Eutopic and ectopic endometrial tissues were collected simultaneously at laparoscopy.

MAIN OUTCOME MEASURE(S)

Detection of C3 messenger RNA (mRNA) by in situ hybridization and C3 protein by immunohistochemistry and Western blot.

RESULT(S)

Expression of C3 mRNA increased in ectopic endometrium compared with that in the matched eutopic endometrium. The quantitative analysis of C3 mRNA by grain count (mean +/- SE) showed 175.60 +/- 40.02 and 39.97 +/- 8.17 grains per micron2 in ectopic and eutopic glands, respectively, and 67.65 +/- 29.82 and 15.02 +/- 5.80 grains per micron2 in ectopic and eutopic stroma, respectively. Expression of C3 mRNA in ectopic glands was significantly higher than that in eutopic glands. The pattern of immunoreactive staining of C3 protein was consistent with that of C3 mRNA. A higher level of C3 protein in ectopic endometrium than eutopic endometrium was detected by immunohistochemistry and Western blot.

CONCLUSION(S)

Expression of C3 mRNA and protein significantly increased in human ectopic endometrium compared with that in the matched eutopic endometrium.

Basic research in endometriosis

A more thorough understanding of the mechanisms associated with the cause and pathophysiology of endometriosis may help in the development of new diagnostic and therapeutic methods for the management of endometriosis. Research has begun to enhance our understanding of endometriosis by demonstrating the differences and similarites between eutopic and ectopic endometrium, and by characterizing the peritoneal environment. Animal models have been developed and validated to conduct studies that are ethically impossible in women. Recently, cell culture models, using purified populations of cells from endometriotic lesions, have provided an appropriate in vitro endometriosis model to study the language by which cells communicate; to evaluate the biochemical effects of steroids, growth factors, pharmacological agents and immunomodulatory agents on the cells; and to study the effects of endometriosis on reproduction.

Endometriosis: the host response

There is abundant evidence of altered immune function in endometriosis. The task that remains is to attempt a synthesis from the accumulated data, to try to make some sense of the observed phenomena and to fit them into a conceptual framework; this might permit the formulation and testing of hypotheses. Evidently, eutopic endometrium does not engender an immune response in normal subjects, otherwise the endometrium would be subject to autoimmune destruction. It has also been established that the overwhelming majority of women regurgitate menstrual debris into the peritoneal cavity. Why does this lead to endometriosis in some, but not in others? There are several possible explanations. The uterus might act as a privileged site, i.e. be exempt from immune effector mechanisms. This would certainly be conducive to the reproductive goal, the survival of the fetal allograft. Endometrium would then not enjoy the immunologic tolerance of most other tissues, and upon leaving the uterus and entering an immunocompetent environment would be subject to immune attack. In normal subjects, this could consist of elimination of menstrual debris without further sequelae. An altered response, characterized by the production of antibody that could mask receptors for cytotoxic or phagocytic effector cells, would permit persistence of ectopic endometrium. The alternative to this hypothesis is that the uterus is not a privileged site, and that the organism is normally tolerant to endometrial antigens. Menstrual debris would be eliminated intraperitoneally without loss of tolerance due to the presence of homeostatic mechanisms including suppressor T cells and suppressive cytokines. In endometriosis, this tolerance breaks down, as is the case in several autoimmune disorders, causing a chronic inflammatory response with the release of toxic factors and, eventually, peritoneal scarring. Finally, the role of cell adhesion molecules, including the integrins, is only just being explored. The behaviour of these molecules in ectopic endometrium differs from that in eutopic endometrium, and it remains to be seen whether regurgitated endometrial debris from normal subjects is different from that of endometriosis sufferers. It seems that this will be an area of intense investigation in the immediate future.

Immunohistochemical markers of uterine receptivity in the human endometrium

The factors responsible for the initial interaction between maternal and fetal epithelium leading to the establishment of pregnancy remain poorly understood. Temporal and spatial expression of specific endometrial peptides in response to ovarian steroids is thought to contribute to the development of a period of uterine receptivity, whereby the endometrium becomes hospitable to the implanting blastocyst. The failure to establish receptivity may account for a significant percentage of the cases of infertility in the female, especially affecting women with luteal phase deficiency, leiomyomata uteri, endometriosis, habitual abortion, and unexplained infertility. In addition, despite increasing global experience with advanced reproductive technologies, the majority of In Vitro Fertilization (IVF) attempts remain unsuccessful, most likely on the basis of implantation failure. In this article, we review the concepts involved in the study of uterine receptivity in the human, highlight potential immunohistochemical (IHC) markers that have recently been discovered, and discuss how IHC assessment of the endometrium is a potentially valuable method for the evaluation of the receptive endometrial state. Using this approach we have examined several new potential markers of uterine receptivity. Endometrial progesterone receptors and one of the integrin cell adhesion molecules appear to undergo changes in expression around the time of implantation, and may be sensitive indicators of the receptive state. Further, these markers are delayed in women with infertility and luteal phase deficiency. These studies illustrate the utility of IHC diagnosis for the evaluation of endometrial function.

Time-related effects of RU486 treatment in experimentally induced endometriosis in the rat

OBJECTIVE

To evaluate the time-dependent effect of the progesterone antagonist RU486 on experimentally induced endometriosis in the rat.

DESIGN

Endometriosis was induced by implanting endometrium onto the peritoneal side wall. Size of the implants was measured before and after treatment.

PARTICIPANTS

Fifty-two adult female Sprague-Dawley female rats weighing 200 to 225 g.

SETTING

Departmental research laboratory of university hospital.

INTERVENTION

Animals treated with RU486 or vehicle only for 2, 4, 6, or 8 weeks.

MAIN OUTCOME MEASURES

Size of the implant was measured before and after treatment; relative change in size of the implants was calculated.

RESULTS

There was not a statistically significant difference between the treatment groups and the control groups. There was no regression of endometriosis in any of the treatment groups.

CONCLUSIONS

RU486 administered for 8 weeks in the rat model was not effective therapy for endometriosis.

The effect of peritoneal macrophage-derived factor(s) on ovarian progesterone secretion and LH receptors: the role of calcium

Macrophages and their secretory products, cytokines, play an integral role in many reproductive processes. In this study we examined the effect of conditioned media from cultured human peritoneal macrophages on progesterone production by granulosa cells and the role of calcium in this process. Macrophages were pretreated with various concentrations of a calcium channel blocker (verapamil) or a calcium ionophore (A23187). Macrophage-conditioned media (MCM) or cell-free media that contained calcium channel modifiers were added at three dose levels to cultured porcine granulosa cells. Progesterone production and LH receptor content were determined. Macrophage-conditioned media alone elevated basal progesterone production, but significantly attenuated granulosa cell LH receptor content. These effects were neither potentiated nor suppressed by pretreating macrophages with verapamil. However, production of the LH receptor lowering factor(s) appeared to be suppressed by calcium ionophore. We conclude that (1) one or more factors produced by macrophages have a net stimulatory effect on basal progesterone production and these factor(s) may not be calcium-dependent and (2) macrophage-derived secretory products reduce granulosa cell LH receptor content. The production of these factor(s) may be calcium-dependent.