Regulation of macrophage and granulocyte proliferation. Specificities of prostaglandin E and lactoferrin.

Hemopoietic colony-forming cells committed to macrophage differentiation (M-CFC) are selectively and differentially inhibited by prostaglandin E (PGE). A hierarchy of sensitivity was observed among murine CFC stimulated by colony-stimulating factors (CSF) which differ in their ability to initiate proliferation of morphologically distinct colony types, or stimulated by CSF provided by macrophage feeder layers. Inhibition of macrophage colony formation to 50 percent levels occurred with PGE concentrations between 10(-8) and 10(-9) M, and was still evident at 10(-10) -10(-11) M PGE concentrations. The growth of mixed colonies containing both macrophages and neutrophils was less sensitive to the inhibitory effects of PGE, however, the monocytoid component of these colonies was reduced in the presence of PGE. Neutrophil progenitor cell proliferation was not influenced by PGE concentrations below 10(-6) M, regardless of time of addition of PGE, whereas clonal macrophage expansion, as well as clone size, was sensitive to inhibition by PGE when added as late as 3 d after culture initiation. Prostaglandin F(2alpha), was not inhibitory to colony formation. Experimental evidence for a selective role of macrophage PGE in the regulation of macrophage colony formation was directly provided by utilizing resident peritoneal macrophages as a source of CSF for bone marrow target cell overlays. Simultaneous morphological analysis of colonies proliferating in bilayer culture in response to increasing concentrations of macrophages, and direct measurements of PGE synthesized by an identical number of macrophages maintained in liquid culture demonstrate that a specific decline in macrophage colony formation occurs coincident with a linear increase in macrophage PGE synthesis. Inhibition of macrophage PGE synthesis by indomethacin results in the specific enhancement of macrophage colony formation. Furthermore, macrophage PGE synthesis is induced by CSF preparations with the selective capacity to differentially stimulate macrophage proliferation, but not by those which preferentially stimulate granulocyte colony formation. In comparison to the effects of PGE on M-CFC, polymorphonuclear granulocyte-derived lactoferrin (LF) reduces macrophage production of colony-stimulating activities for macrophage, mixed macrophage- neutrophil and neutrophil colony formation. The ability of LF to reduce macrophage PGE synthesis, presumably by decreasing CSF production, suggests that LF and PGE can interact in the control of macrophage and granulocyte proliferation.

Role of prostaglandin E in the biphasic fever response to endotoxin.

Biphasic fevers were induced in sheep with intravascular infusions or injections of 4-10 mug (80-200 ng/kg) of endotoxin, whereas monophasic fevers were obtained with doses of 1-2/mug (20-40 ng/kg). A marked increase in arterial blood pressure invariably accompanied the onset of fever; the latency of responses to the higher and lower doses of endotoxins averaged 26 min and 42 min, respectively. Prostaglandin (PG) assays of plasma from the carotid artery and jugular vein during fever episodes revealed a surge of PGE and PGF coincident with the pressor response and the first phase of fever, but PG were not detected in plasma samples taken throughout the second phase of fever. PG measurements of arterial and venous plasma collected at a distal site (hind limb) showed a similar surge of PGE and PGF in association with the early fever response, indicating that intravascular PG synthesis and release represents a generalized systemic response to circulating endotoxin. Carotid arterial infusions of PGE(2) produced immediate monophasic fevers and pressor responses, whereas PGD(2) infusions produced an immediate pressor effect but no fever. Infusions of PGF(2alpha) or prostacyclin, however, evoked neither fever nor pressor effects. Intracarotid infusions of leukocyte pyrogen (LP) caused monophasic fevers with latent periods of 15-20 min but pressor responses were not seen and neither PGE nor PGF were detected in plasma samples from the carotid artery or jugular vein before or during fever. Indomethacin, a potent inhibitor of arachidonic acid metabolism, blocked fever responses to endotoxin and to LP. These findings implicate PGE as the mediator of the early phase of endotoxin fever and imply a role for another pyrogenic metabolite ofarachidonic acid in the mediation of the second phase of fever, i.e., the phase associated with circulating LP. It is possible that both pyrogenic metabolites are generated within the vascular compartment, reaching thermoregulatory centers of the brain by transfer across the blood-brain interface.

Inhibition of gastric acid secretion in the gastric brooding frog, Rheobatrachus silus.

The female gastric brooding frog Rheobatrachus silus broods its young in its stomach. A substance that inhibits gastric acid secretion in a toad stomach preparation in vitro appears to be secreted by the developing young. This substance has been identified as prostaglandin E2. Rheobatrachus silus may thus have developed a mechanism whereby prostaglandin secreted by the larvae inhibits acid secretion in the stomach of the female until the larvae have completed development and emerged as juvenile frogs by way of the female's mouth.

Limitation of excessive myelopoiesis by the intrinsic modulation of macrophage-derived prostaglandin E.

The clonal proliferation of the committed granulocyte-macrophage stem cell is controlled by a balance between mutually opposing factors, colony stimulating factor and prostaglandin E, both of monocyte-macrophage derivation. Increases beyond a critical concentration of colony stimulating factor within the local milieu of the mononuclear phagocyte induces the coincident elaboration of prostaglandin E, a self-regulated response which serves to limit the unopposed humoral stimulation of myelopoiesis.

Is thymosin action mediated by prostaglandin release?

Treatment of spleen cells derived from adult thymectomized mice with thymosin fraction 5 resulted in a rapid and dose-dependent stimulation of the release of immunoreactive prostaglandin E2. The release of prostaglandin E2 was associated with induction of theta antigen and was totally inhibited by indomethacin. In contrast, prostaglandin E2 release from spleen cells from intact donors was inhibited by treatment with fraction 5. The data support the concept that prostaglandin E2 mediates the effects of thymosin fraction 5 on lymphocytes.

An investigation into the role of prostaglandins in zebrafish oocyte maturation and ovulation.

This study explored the potential for ovarian-derived prostaglandins (PGs) to be involved in the regulation of oocyte maturation and ovulation in zebrafish. It was demonstrated that cultured vitellogenic follicles have the capacity to produce prostaglandin E(2) (PGE(2)) and PGF(2alpha) in response to arachidonic acid (AA) in a concentration-dependent manner, and that AA stimulates the in vitro production of 17beta-estradiol (E(2)). The production of AA-stimulated PGF(2alpha) was significantly reduced by treatment with the non-selective cyclooxygenase (COX) inhibitor, indomethacin (INDO). Treatment of full-grown follicles with AA did not induce oocyte maturation as assessed by germinal vesicle breakdown, but INDO significantly decreased the rate of spontaneous maturation. Using Real-Time PCR, it was shown that follicles of different developmental size classes (primary growth and pre-vitellogenic, early-vitellogenic, and mid- to full-grown vitellogenic) express enzymes that release (cytosolic phospholipase A(2) (cPLA(2)); phospholipase Cgamma1) or metabolize (COX-1, COX-2, and prostaglandin synthase-2) AA to PG metabolites. The expression of cPLA(2) was found to be significantly greater in full-grown follicles compared to follicles of the pre- and early-vitellogenic stages. In vivo studies demonstrated that breeding groups of zebrafish exposed to 100 microg/L INDO exhibited reduced spawning rates and clutch sizes compared with control and 1 microg/L INDO exposed fish. In other studies, it was shown that naturally spawning groups of females exhibit increased ovarian levels of PGF(2alpha), E(2), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (a maturation-inducing hormone in zebrafish) near the time of ovulation compared with non-breeding females. Collectively, these experiments indicate that the AA pathway in zebrafish ovaries is involved in the regulation of oocyte maturation and ovulation and a non-selective inhibitor of COX disrupts these processes.

Modulation of alveolar macrophage-driven fibroblast proliferation by alternative macrophage mediators.

Tissue fibrosis results, in part, from an interaction between growth regulatory molecules released by mononuclear phagocytes and fibroblasts. In the chronic interstitial lung disorders, alveolar macrophages, the mononuclear phagocytes of the lung, are known to spontaneously release two growth factors for fibroblasts, fibronectin and alveolar macrophage-derived growth factor (AMDGF) that together stimulate nonreplicating lung fibroblasts to divide. In addition to these two primary growth promoting signals, alveolar macrophages are able to release other mediators that may have a potential role in modulating lung fibroblast replication in response to these primary signals, including interferon gamma (IFN gamma), prostaglandin E2 (PGE2), and interleukin 1 (IL-1). To evaluate this possibility, we examined the effect of each of these other mediators on lung fibroblast replication in response to fibronectin and AMDGF in serum-free, defined medium. IFN gamma had no effect on fibroblast replication. In contrast, PGE2 resulted in a dose-dependent inhibition of fibroblast replication in response to fibronectin and AMDGF with 50% of the maximum inhibition observed at a PGE2 concentration of less than 10 ng/ml. IL-1, while not active as a primary growth promoting signal, at concentrations of 4-10 U/ml, augmented fibroblast replication in response to fibronectin and AMDGF by 10 to 15%. Temporally, the growth augmenting effect of IL-1 occurred early in the G1 phase of the cell cycle. These data indicate that lung fibroblast replication in response to two of the primary growth promoting signals spontaneously released by alveolar macrophages in the interstitial lung disorders, while uninfluenced by IFN gamma, can be inhibited by PGE2 and modestly augmented by IL-1. Understanding the relevant fibroblast growth modulatory signals within the alveolar microenvironment in the chronic interstitial disorders may lead to rational therapeutic strategies designed to interrupt the fibrotic process.

Role of prostaglandin E2 in mediating the effects of pH on the hydroosmotic response to vasopressin in the toad urinary bladder.

Acidosis inhibits the hydroosmotic response to vasopressin. Since prostaglandins are known to modulate vasopressin-stimulated water flow we investigated the role of endogenous prostaglandin E2(PGE2) production in the pH-dependent response of the toad urinary bladder to vasopressin. Graded acidification of the serosal medial resulted in a progressive decline in vasopressin-stimulated water flow from 26.6 +/- 0.5 mg/min at pH 8.4 to 1.7 +/- 0.6 at pH 6.9. In these bladders basal PGE2 synthesis increased from 5.09 +/- 0.51 pmol/min per g hemibladder at pH 8.4 to 18.8 +/- 2.8 at pH 6.9. The addition of that concentration of PGE2 produced by the bladder at pH 7.4 (4 nM) to bladders at pH 8.4 resulted in 62-71% of the inhibition usually seen at pH 7.4; these data suggest that basal PGE2 production per se and not other products of prostaglandin synthesis or other pH-dependent events is responsible for the effect of acidosis. Preincubation with prostaglandin synthesis inhibitors reversed in major part the effect of serosal acidification on the response to submaximal concentrations of vasopressin and completely abolished the effect of pH on near maximal concentrations of the hormone. An increase in PGE2 synthesis after vasopressin was not seen at any pH. These studies establish that increased basal PGE2 synthesis plays a critical role in the pH dependence of the hydroosmotic response to vasopressin and demonstrate that factors that modulate the response to vasopressin may exert this effect by changing the basal rate of prostaglandin synthesis.

Modulation of keratinocyte proliferation in vitro by endogenous prostaglandin synthesis.

To understand the relationship between the proliferation of epidermis and its arachidonic acid metabolism, we studied human keratinocytes grown in vitro at confluent or nonconfluent densities. Keratinocyte cultures incubated with [14C]arachidonic acid synthesized prostaglandin (PG)E2 PGD2, PGF2 alpha, and small quantities of 6-keto-F1 alpha. Nonconfluent cultures, however, synthesized fourfold more PGE2 than did confluent cultures. When proliferation was studied using [3H]thymidine incorporation into DNA, it was found that this increased synthesis of PGE2 was accompanied by a fourfold increase in the rate of proliferation. When PGE2 synthesis was inhibited by indomethacin, the rate of proliferation of nonconfluent cultures was decreased 40%, while the rate of proliferation of confluent cultures was unchanged. Addition of 1 ng/ml of PGE2, but not PGF2 alpha, PGD2, or a stable analog of PGI2 to the indomethacin-treated nonconfluent cultures restored the initial rate of proliferation. These results suggest that PGE2 is a growth-promoting autocoid for epidermis. The synthesis of PGE2 by epidermis may be enhanced in wound healing and disease states where epidermal continuity is disrupted.

Inhibition of sodium transport by prostaglandin E2 across the isolated, perfused rabbit collecting tubule.

This study was designed to examine whether prostaglandin E2 can directly affect sodium transport across isolated perfused rabbit renal collecting tubules. Changes in transepithelial potential and isotopic sodium fluxes in response to peritubular prostaglandin E2 were measured. In addition, changes in transepithelial potential of the outer medullary collecting tubule in response to prostaglandin E2 were also measured. With few exceptions, all rabbits received 5 mg/day desoxycorticosterone acetate for 4-11 days before experimentation. The results of the experiments show that: (a) prostaglandin E2 inhibits the negative transepithelial potential in the cortical collecting tubule as well as the outer medullary collecting tubule; (b) prostaglandin E2 inhibits net sodium transport out of the lumen by inhibiting efflux while backflux is unaffected; (c) prostaglandin E2 produces this inhibition within 15 min, and the effects are dose dependent and reversible. These results suggest that prostaglandin E2 may modulate sodium transport in vivo and may contribute to the final regulation of sodium excretion.

Apical-basolateral membrane asymmetry in canine cortical collecting tubule cells. Bradykinin, arginine vasopressin, prostaglandin E2 interrelationships.

The studies reported here were designed to determine if there is an apical-basolateral asymmetry to the release of prostaglandins by or to the biochemical effects of prostaglandins on the renal collecting tubule. Canine cortical collecting tubule (CCCT) cells were isolated by immunodissection and seeded at supraconfluent densities on Millipore filters. The resulting confluent monolayer of CCCT cells: (a) developed and maintained a transcellular potential difference of 1 mV (apical side negative); (b) exhibited a permeability to inulin that was the same as that obtained with similar monolayers of Madin-Darby canine kidney (MDCK) cells; and (c) released adenosine 3',5'-cyclicmonophosphate (cAMP) in response to arginine vasopressin (AVP) added to the basolateral but not the apical surface of the monolayer. These results indicate that confluent monolayers of CCCT cells on Millipore filters have characteristics of asymmetry that are seen with intact collecting tubules. Moreover, PGE2 added to either side of the CCCT cell monolayer crossed the monolayer at the same slow rate as inulin, which demonstrated the feasibility of examining the sidedness of the effects of and the release of PGE2. Although AVP caused cAMP release only when added to the basolateral side of CCCT cells, AVP caused the release of PGE2 when added to either the apical or basolateral surface. This result implies that there are at least two AVP receptor systems, one coupled to cAMP synthesis and one to PGE2 formation. In contrast to the results observed with AVP, bradykinin caused PGE2 release only when added to the apical surface of CCCT cells, which suggested that urinary but not blood borne kinins elicit PGE2 formation by the canine collecting tubule. PGE2 was released in comparable amounts on each side of the monolayer in response both to AVP and to bradykinin. High concentrations (greater than or equal to 10(-8) M) of PGE2 added to either side of the monolayer caused the release of cAMP. However, at concentrations (10(-10) - 10(-12) M) at which PGE2 had no independent effect on cAMP release, PGE2 inhibited the release of cAMP, which normally occurred in response to AVP. This inhibition occurred with PGE2 added to either the apical or basolateral surface of the CCCT cell monolayer. PGE2 (10(-11) M) also inhibited the AVP-induced accumulation of intracellular cAMP by CCCT cells seeded on culture dishes. This inhibition was only observed when the cells were preincubated with PGE2 for greater than or equal to 20 min. Our results are consistent with the concept that inhibiton by prostaglandins of the hydroosmotic effect of AVP is due to inhibition of AVP-induced cAMP production. This inhibition does not appear to involve a direct physical interaction of PGE2 with the AVP receptor which is coupled to adenylate cyclase, since CCCT cells must be preincubated with PGE2 for 20 min for the inhibition to be observed, and since PGE2 added to the apical surface of CCCT cells inhibits cAMP release in response to AVP acting from the basolateral surface.

Role of endogenous prostaglandin E2 in erythropoietin production and dome formation by human renal carcinoma cells in culture.

Studies were carried out on the role of endogenous prostaglandin E2 (PGE2) in erythropoietin (Ep) production and dome formation in primary monolayer cultures of a human renal carcinoma from a patient with erythrocytosis that has been serially transplanted into BALB/c athymic nude mice. The metabolism of [14C]arachidonic acid (14C-AA) by cultured renal carcinoma cells, which were plated in 25-cm2 flasks at a density of 2 X 10(4) cells/cm2 and grown for 6, 12 (confluence, 13 X 10(4) cells/cm2), 16, 24, and 30 d in Eagle's minimum essential medium (MEM) supplemented with 10% fetal bovine serum, was examined by using radiometric thin-layer chromatography (TLC). TLC revealed PGE2 to be the major metabolite of 14C-AA produced by the cultured cells throughout the 30 d of cultivation. In addition, the cultured cells at each time period were incubated for 24 h in 5 ml of serum-free Eagle's MEM and the levels of PGE2 and Ep in the incubated media were measured via radioimmunoassay. PGE2 levels in the serum-free media incubated with the cultured cells grown for 6 d were significantly (P less than 0.001) elevated (174 +/- 2.5 pg/ml, n = 5), compared with the unincubated control media (1.5 +/- 0.19 pg/ml, n = 5) and gradually decreased at each time period to 97.6 +/- 4.4 pg/ml (n = 5) at 30 d. On the other hand, the levels of Ep in the incubated media of the cells grown for 6 d were 11.5 +/- 0.52 mU/ml (n = 5) compared with 7.6 +/- 0.62 mU/ml (n = 5) in the control media. However, after the cultured cells became confluent, the levels of Ep in the incubated media showed a marked increase to 222.9 +/- 5.26 mU/ml (n = 5) at 30 d of cultivation. Multicellular hemicysts (domes) developed after the cultured cells reached confluence and their numbers increased with increasing time in confluence in parallel with the increase in Ep. Meclofenamate (MF) (3 X 10(-6)-3 X 10(-5) M), a prostaglandin synthesis inhibitor, produced a significant dose-related decrease in PGE2, Ep, and dome formation without producing a significant effect on cell viability in the 30-d cells. This inhibitory effect of MF on Ep production and dome formation was completely abolished by the addition of 10(-8) M PGE2 to the incubation medium. In conclusion, endogenous PGE2 plays an important role in supporting and/or stimulating Ep production and dome formation in cultured renal carcinoma cells.

Inhibition of spleen cell cytotoxic capacity toward tumor by elevated prostaglandin E2 levels in mice bearing Lewis lung carcinoma.

The capacity to generate cytotoxic cells toward Lewis lung carcinoma (LLC) in mixed cultures of stimulator LLC and responder spleen cells of LLC-bearing C57BL/6 mice was monitored during the course of tumor growth. The cytotoxic response of mice bearing tumors that were not yet palpable was enhanced. However, as palpable tumors developed and tumor growth progressed, their cytotoxic capacity became suppressed. Concurrent with this decline in cytotoxic capacity, there was an increase in systemic immunoreactive prostaglandin E2 (PGE2) concentrations in tumor-bearing mice. Administration of indomethacin, a prostaglandin synthesis inhibitor, to LLC-bearing mice prevented the rise in PGE2 concentrations and the suppression in cytotoxic capacity toward LLC. A relationship between the elevated immunoreactive PGE2 levels, suppression in cytotoxic capacity, and progressive tumor growth was indicated when administration of indomethacin to tumor-bearing mice also reduced the rate of tumor development.

Prostaglandin E2 production by EL 4 leukemia cells from C57BL/6 mice: mechanism for tumor dissemination.

Murine EL 4 leukemia cells contained and secreted prostaglandin E2 (PGE2). PGE2 was secreted into the culture media during in vitro growth, as well as into plasma during growth in the peritoneum of inbred C57BL/6 mice. For the study of the role of PGE2 in tumor dissemination, migration of EL 4 cells out of glass capillary tubes was used as an in vitro model for tumor spread in a host. PGE2 enhanced the in vitro migration of EL 4 cells while indomethacin, a prostaglandin synthesis inhibitor, reduced the extent of migration. When EL 4 cells were allowed to migrate into medium containing both indomethacin and PGE2, the cells exhibited an enhanced migration ability suggesting an extrinsic effect on cells by PGE2. The participation of tumor-derived PGE2 in promoting tumor spread in a host was supported by demonstration that EL 4 cells grown in indomethacin-treated mice secreted less PGE2 and had reduced in vivo dissemination ability. These results indicated that tumor spread was promoted by tumor-derived PGE2. The extent of migration and dissemination can be reduced by prostaglandin synthesis inhibitors such as indomethacin.

Prostaglandin E2 regulation of tumoristatic factor production by macrophage-like P388D1 cells.

Macrophage-like P388D1 cells, when stimulated with lipopolysaccharide (LPS), produced a factor(s) whose activity was inhibitory to growth of Lewis lung carcinoma cells. Indomethacin, a prostaglandin-synthesis inhibitor, augmented the production of tumoristatic activity by LPS-stimulated P388D1 cells, whereas exogenous prostaglandin E2 (PGE2) suppressed its secretion. These results suggest that P388D1 cells regulate their antitumor abilities by producing PGE2, which inhibits production of soluble factor(s) with tumoristatic activities.

Role of prostaglandin E1 and copper in angiogenesis.

The interstitial fluid of MTW9A and Walker carcinomas and their ethanol extract induced strong angiogenic response in the rabbit (New Zealand White) corneal test. The fluid collected in vivo was rich in E-type prostaglandins, and prostaglandin E1 (PGE1) in particular was strongly angiogenic at the lowest dose as compared with the angiogenic responses of prostaglandins E2, I2, and F2 alpha. Neoplastic fibroblasts also induced a strong angiogenic response, but in indomethacin-treated rabbits neovascularization failed to occur. Copper was concentrated in the cornea during PGE1-induced neovascularization, and copper-deficient rabbits were unable to mount an angiogenic response in the corneal test. Ceruloplasmin, the copper carrier of plasma, was found to be angiogenic at high doses. In indomethacin-treated rabbits, however, ceruloplasmin at the same high doses failed to induce angiogenesis. The experiments are interpreted to indicate that angiogenesis is the end result of a sequence of events, two of which are PGE1 production and copper mobilization in the tissue where neovascularization occurs.

Enhancement of Lewis lung carcinoma cell migration by prostaglandin E2 produced by macrophages.

The role of macrophages in tumor metastasis was examined by using migration of a cloned metastatic Lewis lung carcinoma (LLC) variant, LLC-C4, out of glass capillary tubes as an in vitro model for dissemination of tumor cells from a primary tumor mass. Macrophages, derived from LLC tumors of C57BL/6 mice or from peritoneal exudates of mice given injections of complete Freund's adjuvant, enhanced tumor cell migration through an indomethacin-sensitive mechanism. Resident peritoneal macrophages did not produce a tumor migration-enhancing activity but could be induced to do so by preincubation with LLC-C4 cells or their culture supernatants. The capacity of macrophages to enhance LLC-C4 migration corresponded to their secretion of prostaglandin E2. Addition of similar concentrations of prostaglandin E2 to the migration medium of LLC-C4 cells enhanced their migration out of the capillary tubes. These results suggest that macrophages, following exposure to tumor cells or their products or following stimulation with complete Freund's adjuvant, secrete elevated amounts of prostaglandin E2 which in turn may enhance tumor dissemination.

T-cell recruitment from the thymus to the spleen in tumor bearing mice: phenotypical alteration and recruitment of thymocytes raised in a tumor bearing state.

Intrathymic events in mice bearing methylcholanthrene induced fibrosarcoma (MBS-1) were examined using mainly flow cytometric analysis. Ten days after tumor inoculation, the number of whole thymocytes was remarkably decreased. Surface phenotypical analysis by flow cytometry showed that the proportion of thymocytes with a low density of peanut agglutinin (PNAlow thymocytes), which is about 30% in normal mice, was increased to 70%. Histologically, the greater part of the thymus was occupied by the cortex. Moreover, the ratio of proliferating cells was increased in the PNAhigh cells. These findings in in vivo experiments suggested that a tumor bearing state would alter phenotypical characteristics of cortical thymocytes (PNAhigh, Thy 1high, H-2low) to medullary type (PNAlow, Thy 1low, H-2high). To support this hypothesis, in vitro experiments were performed using cultured thymic lymphoma EL4 cells, which possessed an immature thymus cell phenotype. Addition of serum from MBS-1 bearers to the culture medium of EL4 cells differentiated their phenotypical characteristics to the medullary type. Thus, it is assumed that factors in tumor bearers induce a massive migration of thymocytes by altering of phenotypes.

Relationships of prostaglandin E and natural killer sensitivity to metastatic potential in murine mammary adenocarcinomas.

The levels of two prostaglandins (prostaglandins E and F) have been determined in a series of murine mammary lesions ranging from preneoplastic, hyperplastic alveolar nodules to highly metastatic adenocarcinomas. A highly positive correlation was seen between high levels of prostaglandin E and high tumorigenicity and metastatic potential. In addition, spontaneous metastasis of two highly metastatic tumors was partially inhibited by p.o. administration of indomethacin from the time of s.c. tumor transplantation until removal of the primary tumor at a limited size. Further, mammary tumor cells of differing metastatic potential were susceptible to polyinosinic-polycytidylic acid activated spleen lymphocytes in vitro. Cells of metastatic tumor lines (410.4 and 66) were more resistant to killing than were cells of two non-metastatic tumor lines (168 and 410). The sensitivity of all target cells was increased when endogenous prostaglandin synthesis was prevented by the addition of indomethacin (1 microM) but was not affected by the lipoxygenase inhibitor nordihydroguaiaretic acid.

Role of prostaglandins in the production of hypercalcemia by tumors.

This report summarizes the data from two animal and cell culture systems that serve as models that show how certain malignant tumors produce hypercalcemia by means of a humoral mechanism. Studies with the HSDM1 murine fibrosarcoma and the VX2 carcinoma in the rabbit have led to the conclusion that these two tumors produce hypercalcemia in the host by means of a mechanism that utilizes prostaglandin E2 as the mediator between the neoplasm and bone. Analogous or identical mechanisms may operate in a small number of human tumors.