Release of beta-endorphin by prostaglandin E2 to lower plasma glucose in streptozotocin-induced diabetic rats.

In the present study, Wistar rats, which received a streptozotocin injection to induce diabetes (STZ-diabetic rats), a model similar to insulin-dependent diabetes mellitus (IDDM) or type 1 diabetes mellitus, were used to investigate the effect of prostaglandin (PG) E2 on plasma glucose. Intravenous injection of PGE2 produced a dose-dependent lowering of plasma glucose level in fasting STZ-diabetic rats after 60 min. In addition to the blockade of this hypoglycemic effect by guanethidine (a noradrenergic nerve terminal-blocking agent), prazosin at a dose effective to block alpha1-adrenoceptors abolished the action of PGE2. An increase of plasma norepinephrine (NE) was also observed in STZ-diabetic rats receiving PGE2 injections. Participation of sympathetic stimulation by PGE2 may thus be speculated. Also, the plasma glucose-lowering effect of PGE2 was also blocked by pretreatment with naloxone or naloxonazine at doses sufficient to block opioid mu-receptor. Injection of PGE2 increased plasma beta-endorphin-like immunoreactivity (BER) in STZ-diabetic rats, and this action was abolished by prazosin. Bilateral adrenalectomy resulted in the loss of this PGE2 effect, and no increase was seen in plasma BER with PGE2 in STZ-diabetic rats. Therefore, beta-endorphin from the adrenal gland appears to be responsible for the lowering of plasma glucose in STZ-diabetic rats by PGE2 through an increase of NE release to activate alpha1-adrenoceptors.     

Stimulation of CFU-f formation by prostaglandin E2 is mediated in part by its degradation product, prostaglandin A2

Prostaglandins (PG) of the E series are known to rapidly undergo non-enzymatic dehydration in culture medium containing serum albumin to produce the cyclopentenone PGs of the A series. We investigated the actions of PGA1 and A2 in the in vitro calcifying fibroblastic-colony forming unit assay which can partially mimic the in vivo anabolic effects of PGE2. It was found that PGA1 and A2 both stimulated colony formation in a dose-dependent manner with a maximum at 10(-6) M and to a similar degree to PGE2. In contrast to PGE2, PGA1 and PGA2 both caused an inhibition of cAMP accumulation. Furthermore, the addition of protein kinase A inhibitors, H8 and H89, had no significant effect on the stimulation of colony number by PGE2. These data suggest that (a) the bone anabolic effects of PGE1 and E2 are, in part at least, mediated by their dehydration products PGA1 and A2 and (b) that they are mediated via pathways not necessarily involving the cAMP/protein kinase A cascade.     

Effect of captopril or enalapril on renal prostaglandin E2

Since one of the hypotensive mechanisms of angiotensin-converting enzyme inhibitor (ACEI) has been suggested to be mediated through the renal kinin-prostaglandin (PG) axis, the present study was designed to investigate the effect of captopril (C) or enalapril (E) on renal PGE2 excretion or synthesis. Wistar male rats (BW 200-250 g) were given orally captopril at 30 mg/kg/day or enalapril at 10 or 30 mg/kg for one week. Before and after ACEI, blood pressure (tail cuff method) as well as PRA and urinary PGE2 excretion was determined. Renopapillary slices were obtained from some of the rats including controls and incubated to determine PGE2 synthesis. C or E administration resulted in a blood pressure decrease of 21 to 36 mm Hg with an increase in PRA. Urine volume and sodium excretion increased after daily treatment with C or E at 30 mg/kg. Urinary PGE2 excretion increased 1.4-fold in response to C, but not to E. Papillary PGE2 synthesis demonstrated a marked decrease 2 h after in vivo administration of either ACEI compared to controls. However, when C or enalaprilat was added in vitro to renal slices obtained from controls, only C at 10(-5) M showed a significant 2-fold increase in renal PGE2 synthesis. These results suggest that (1) renal PGE2 synthesis may be dependent on circulating angiotensin II. (2) C, but not enalaprilat, has a direct stimulatory effect on renal PGE2 synthesis and (3) renal PGE2 may not be involved very much in the hypotensive effect of ACEI.     

Stimulation of CFU-f formation by prostaglandin E(2) is mediated in part by its degradation product, prostaglandin A(2)

Prostaglandins (PG) of the E series are known to rapidly undergo non-enzymatic dehydration in culture medium containing serum albumin to produce the cyclopentenone PGs of the A series. We investigated the actions of PGA(1) and A(2) in the in vitro calcifying fibroblastic-colony forming unit assay which can partially mimic the in vivo anabolic effects of PGE(2). It was found that PGA(1) and A(2) both stimulated colony formation in a dose-dependent manner with a maximum at 10(-6) M and to a similar degree to PGE(2). In contrast to PGE(2), PGA(1) and PGA(2) both caused an inhibition of cAMP accumulation. Furthermore, the addition of protein kinase A inhibitors, H8 and H89, had no significant effect on the stimulation of colony number by PGE(2). These data suggest that (a) the bone anabolic effects of PGE(1) and E(2) are, in part at least, mediated by their dehydration products PGA(1) and A(2) and (b) that they are mediated via pathways not necessarily involving the cAMP/protein kinase A cascade.     

Effects of ulcerative colitis activity on plasma and mucosal prostaglandin E2 concentration

The aim of this study was to determine effects of changes in ulcerative colitis activity on mucosal and plasma PGE2 concentrations measured with an EIA in 49 patients who underwent sigmoidoscopy. The disease was diagnosed in 37 patients. Twelve patients with normal colonic mucosa served as controls. Patients were divided into three groups depending on the changes of endoscopic picture during a three-month follow-up. Some laboratory markers of the disease activity, such as C-reactive protein, albumin, gamma-globulin and hemoglobin concentrations, sedimentation rate, and white blood and platelets counts, were also evaluated. Initial examination revealed a significant, positive correlation of mucosal and plasma PGE2 concentration with endoscopic score. Follow-up of patients without significant progression of mucosal changes revealed constant and close to normal concentration of mucosal PGE2. Plasma PGE2 was higher at the second examination, yet without significant difference. Improvement of endoscopic picture resulted in significant decrease of plasma and mucosal PGE2 concentrations. Worsening of mucosal changes reflected endoscopically was associated with significant increase of PGE2. There were no remarkable changes in the values of analyzed laboratory markers of the disease activity. These results indicate the usefulness of mucosal or plasma PGE2 measurement as a possible prognostic marker in patients with ulcerative colitis.     

A possible role of carbohydrate moieties in prostaglandin D2 and prostaglandin E2 receptor proteins from the porcine temporal cortex.

The binding activities of prostaglandins (PGs) D2 and E2 were measured after deglycosylation of P2 membranes prepared from the porcine temporal cortex in order to investigate the role of carbohydrate moieties in the receptor binding. PGD2 and PGE2 binding activities were significantly decreased by pretreatment with various exoglycosidases, such as neuraminidase for PGE2 binding, alpha-mannosidase and beta-galactosidase for PGD2 binding, and beta-N-acetylhexosaminidase for both. Further, peptide N-glycohydrolase F and endo-alpha-N-acetylgalactosaminidase, which are specific for the cleavage of N-glycan and O-glycan linkages, respectively, in glycoproteins were used. Pretreatment with either of them also reduced both PGD2 and PGE2 binding activities. The reduction was dependent on the pretreatment time and enzyme concentration. The time courses of the reduction were typically characterized by a marked increase in the nonspecific bindings. Scatchard plot analysis revealed that the reduction was caused by a decrease in the affinity rather than one in the maximal binding capacity. The specificity of the binding sites thereby shifted to be more nonspecific without affecting the order of the relative affinities among PGs for the binding sites. These results suggest that the carbohydrate moieties on PG receptor proteins of the brain are essential for the expression of their binding activities.     

Changes in human plasma catecholamines and dopamine-beta-hydroxylase produced by prostaglandin F2 alpha

Clinical research was conducted into the possible interrelationships between prostaglandin (PG) F2alpha and the human sympathetic nervous system. The study also permitted comparison of the relative sensitivity of 2 indicators of sympatho-adrenal activity: 1) the determination of circulating catecholamines, epinephrine and norepinephrine; and 2) analysis of plasma dopamine-8-hydroxylase activity. Intravenous PGF2alpha infusion was administered to college students 12-18 weeks pregnant to produce abortion; the results were compared to results from nonpregnant controls. Circulating norepinephrine but not plasma epinephrine or dopamine-8-hydroxylase levels were increased in response to the PG. There was no correlation between plasma epinephrine and plasma norepinephrine levels. Plasma dopamine-8-hydroxylase activity was found not to be significantly changed by pregnancy, administration of the analgesic and antiemetic, or the PG infusion. In fact, central venous dopamine-8-hydroxylase activity did not differ significantly from that of arterial blood. The PG did not affect cardiac output or maximal expiratory flow rate. It is suggested that the nausea and diarrhea accompanying PGF2alpha infusion may put stress on the sympathetic nervous activity causing the observed increase in plasma norepinephrine concentration. Since no changes in blood pressure, heart rate, central venous pressure, or cardiac output were observed, it is unlikely that PGF2alpha causes even slight impairment of sympathetic nervous system activity.     

Applications and limitations of measurement of 15-keto,13,14-dihydro prostaglandin E2 in human blood by radioimmunoassay

It has been anticipated that the inherent limitations of radioimmunoassays for prostaglandin E (PGE) would be obviated by assays for its major circulating metabolite, 15-keto, 13,14-dihydro PGE2) which has a longer half-life in blood. We examined the effects of PGE2 infusion and alterations in lipolysis in vivo, and of clotting, prolonged storage and hemolysis in vitro, on KH2-PGE2 immunoreactivity in unextracted human plasma and serum samples. Indeed KH2-PGE2 levels rose several hundred fold during infusions of PGE2 at doses which cause little or no increment in peripheral PGE levels. During stimulation of lipolysis by infusions of epinephrine, apparent KH2-PGE2 levels rose five-fold. However, the dilution curve of plasma obtained during stimulation of lipolysis was not parallel to the standard curve; furthermore, apparent KH2-PGE2 levels were correlated strongly with free fatty acid (FFA) levels, suggesting that FFA's cross-reacted in the RIA weakly but significantly due to their very high molar concentration in blood. Clotting and prolonged storage of samples, but not hemolysis, also caused marked apparent increments in KH2-PGE2 levels. Competition curves using dilutions of such samples were again not parallel to the standard curves in plasma or buffer, but resembled dilution curves of samples containing high levels of FFA. These results suggest that handling of human blood samples for KH2-PGE2 measurement must be carefully standardized to avoid significant artifacts which presumably are due in part to fatty acids released from triglyceride stores in vivo or from disrupted membrane phospholipids in vitro. Unextracted plasma appears to be unsatisfactory for use in this RIA.     

Prostaglandin E1 and F2alpha specific binding in bovine corpora lutea: comparison with luteolytic effects.

Preliminary characterization indicated the presence of separate prostaglandin (PG)E1 and (PG)F2alpha binding sites in membrane fractions prepared from bovine corpora lutea. These differ in the rate and temperature dependence of the specific binding. Equilibrium binding data indicate the apparent dissociation constants as 1.32 x 10(-9)M and 1.1 x 10(-8)M for PGE1 and PGF2alpha, respectively. Competition of several natural prostaglandins for the PGE1 and PGF2alpha bovine luteal specific binding sites indicates specificity for the 9-keto or 9alpha-hydroxyl moiety, respectively. Differences in relative ability to inhibit 3H-PG binding were found due to sensitivity to the absence or presence of the 5, 6-cis-double bond as well. Bovine luteal function was affected following treatment of heifers with 25 mg PGF2alpha as measured by reduced estrous cycle length, decreased corpus luteum size and significantly decreased plasma progesterone levels. In contract, treatment with 25 mg PGE1 resulted in cycle lengths comparable to those of non-treated herdmates with no apparent modification in corpus luteum size. However, plasma progesterone levels were increased significantly following PGE1 treatment compared to pretreatment values. In so far as data obtained in vitro on PGF2alpha relative binding affinity to the bovine CL can be compared to data obtained independently in vitro on PGF2alpha induced luteolysis in the bovine, PGF2alpha relative binding to the CL and luteolysis appeared to be associated. By similar reasoning, there was no apparent relationship between PGE1 relative binding affinity in the luteal fractions and luteolysis in estrous cyclic cattle.     

Factors regulating the production of prostaglandin E2 and prostacyclin (prostaglandin I2) in rat and human adipocytes.

The regulation of PGE2 (prostaglandin E2) and PGI2 (prostaglandin I2; prostacyclin) formation was investigated in isolated adipocytes. The formation of both PGs was stimulated by various lipolytic agents such as isoproterenol, adrenaline and dibutyryl cyclic AMP. During maximal stimulation the production of PGE2 and PGI2 (measured as 6-oxo-PGF1 alpha) was 0.51 +/- 0.04 and 1.21 +/- 0.09 ng/2 h per 10(6) cells respectively. Thus PGI2 was produced in excess of PGE2 in rat adipocytes. The production of the PGs was inhibited by indomethacin and acetylsalicylic acid in a concentration-dependent manner. The half-maximal effective concentration of indomethacin was 328 +/- 38 nM and that of acetylsalicylic acid was 38.5 +/- 5.3 microM. The PGs were maximally inhibited by 70-75% after incubation for 2 h. In contrast with their effect on PG production, the two agents had a small potentiating effect on the stimulated lipolysis (P less than 0.05). The phospholipase inhibitors mepacrine and chloroquine inhibited both PG production and triacylglycerol lipolysis and were therefore unable to indicate whether the PG precursor, arachidonic acid, originates from phospholipids or triacylglycerols in adipocytes. Angiotensin II significantly (P less than 0.05) stimulated both PGE2 and PGI2 production in rat adipocytes without affecting triacylglycerol lipolysis. Finally, it was shown that PGE2 and PGI2 were also produced in human adipocytes, although in smaller quantities than in rat adipocytes. It is concluded that the production of PGs in isolated adipocytes is regulated by various hormones. Moreover, at least two separate mechanisms for PG production may exist in adipocytes: (1) a mechanism that is activated concomitantly with triacylglycerol lipolysis (and cyclic AMP) and (2) an angiotensin II-sensitive, but lipolysis (and cyclic AMP)-independent mechanism.     

Separation of a population of human T lymphocytes that bind prostaglandin E2 and exert a suppressor activity

Prostaglandin E2 (PGE2) is a potent inhibitor of immune functions. Two possible mechanisms of PGE2-mediated suppression have been proposed: one is a direct inhibitory effect exerted on interleukin 2-producing T cells; the second is mediated by the activation of nonspecific suppressor T lymphocytes. We previously showed that PGE2 can directly activate human T lymphocytes to suppress lymphocyte proliferation and B lymphocyte maturation. Herein is described the binding of 10 to 30% of human peripheral blood T lymphocytes to insolubilized PGE2 coated to albumin-Sepharose. The T lymphocytes that bound PGE2 (PGE2(+] could be eluted by the addition of serum and gentle shaking of the beads. The following data indicated the specificity of the binding: i) T lymphocytes after an overnight incubation, a condition known to abolish sensitivity to PGE2, lost their affinity for PGE2; ii) preincubation of T lymphocytes with PGE2 blocked the binding; iii) PGE2(+) T cells bound PGE after a 24-hr incubation, whereas PGE2(-) T cells did not. Few T cells bound albumin, and only a small percentage (7 to 9%) bound 6-keto-prostaglandin F1 alpha-coated beads. Among PGE2(+) T cells, there was a slight increase in the percentage of OKT8+ cells. Although T cells that had no affinity for PGE2 (PGE2(-] proliferated as well as unseparated T lymphocytes when stimulated with mitogens or antigens, the proliferative response of the PGE2(+) subset was poor. Moreover, PGE2(+) T lymphocytes did exert a strong suppressor activity on mitogen- or allogeneic cell-induced lymphocyte proliferation as well as on pokeweed mitogen-driven B cell maturation into Ig-containing cells. PGE2(-) T lymphocytes were shown not to exert a significant suppressor activity in these assays. The PGE2(+) subset-mediated suppression was not secondary to a carry-over of PGE2 released from the beads, because its suppressor activity was not altered by the addition of an anti-PGE2 serum. Moreover, PGE2(-) T lymphocytes were not sensitive to the inhibitory activity on cell proliferation of PGE2. These results indicate that a given functional subset of peripheral blood T lymphocytes binds PGE2, and that at least some of them are activated into suppressor T cells. The relationship between the PGE2-activatable T suppressor subset and other functionally defined suppressor T cells remains to be clarified; it is suggested, however, that PGE2 can act as an immunoregulator through the activation of identifiable suppressor T cells.     

Effects of exogenous prostaglandin E1 on human plasma norepinephrine level and dopamine-beta-hydrolyxase activity.

Effects of exogenous PG E1 on the level of human plasma norepinephrine (NE), dopamine-beta-hydroxylase (DBH) activity, cAMP, cGMP, free fatty acids (FFA) as well as pulse rate and blood pressure were studied. Significant decreases of blood pressure and increases of pulse rate were observed after 20 min of the infusion of 0.05 microgram/kg/min of PG E1. The level of plasma NE increased by 174% (p less than 0.005) after the infusion. However, the increase of DBH activity was not significant. There was a tendency of increase of plasma level of FFA. These results suggested that the infusion of PG E1 caused an augmented sympathetic nervous activity due to systemic hypotension induced by PG E1.     

Effects of epidermal growth factor on serum zinc and plasma prostaglandin E2 levels of mice with pressure sores

This work was undertaken to study the effects of systemic application of EGF on the plasma PGE2 and serum zinc levels of mice with pressure sores. The pressure sores were made on the hind limb of the mice by bilateral sciatic nerve neurotomy. Mice were injected IP, 1 μg EGF daily for ten days, begining on the 21st day after operation. EGF administration increased the serum zinc and plasma PGE2 levels compared with controls. These results indicate that EGF can be effective on wound healing by elevating the serum zinc and plasma PGE2 concentrations together with other physiological roles in cellular events.     

Metabolism of prostaglandin glycerol esters and prostaglandin ethanolamides in vitro and in vivo.

Prostaglandin glycerol esters (PG-Gs) and prostaglandin ethanolamides (PG-EAs) are generated by the action of cyclooxygenase-2 on the endocannabinoids 2-arachidonylglycerol (2-AG) and arachidonylethanolamide, respectively. These novel eicosanoids may have unique pharmacological properties and/or serve as latent sources of prostaglandins at sites remote from their tissue of origin. Therefore, we investigated the metabolism of PG-Gs and PG-EAs in vitro and in vivo. PGE(2)-G was rapidly hydrolyzed in rat plasma to generate PGE(2) (t(1/2) = 14 s) but was only slowly metabolized in human plasma (t(1/2) > 10 min). An intermediate extent of metabolism of PGE(2)-G was observed in human whole blood (t(1/2) approximately 7 min). The parent arachidonylglycerol, 2-AG, and the more stable regioisomer, 1-AG, also were much more rapidly metabolized in rat plasma compared with human plasma. PGE(2)-EA was not significantly hydrolyzed in plasma, undergoing slow dehydration/isomerization to PGB(2)-EA. Both PGE(2)-G and PGE(2)-EA were stable in canine, bovine, and human cerebrospinal fluid. Human 15-hydroxyprostaglandin dehydrogenase, the enzyme responsible for the initial step in PG inactivation in vivo, oxidized both PGE(2)-G and PGE(2)-EA less efficiently than the free acid. The sterically hindered glyceryl prostaglandin was the poorest substrate examined in the E series. Minimal 15-hydroxyprostaglandin dehydrogenase oxidation of PGF(2 alpha)-G was observed. PGE(2)-G and PGE(2)-EA pharmacokinetics were assessed in rats. PGE(2)-G was not detected in plasma 5 min following an intravenous dose of 2 mg/kg. However, PGE(2)-EA was detectable up to 2 h following an identical dose, displaying a large apparent volume of distribution and a half-life of over 6 min. The results suggest that endocannabinoid-derived PG-like compounds may be sufficiently stable in humans to exert actions systemically. Furthermore, these results suggest that the rat is not an adequate model for investigating the biological activities of 2-arachidonylglycerol or glyceryl prostaglandins in humans.     

Effects of prostaglandin E2 and F2 alpha on peri-implantation development of mouse embryos in vitro.

The effects of exogenous prostaglandin (PG) E2 and F2 alpha on the morphology and lactate dehydrogenase (LDH) activities of pre-implantation mouse embryos in vitro were studied. A 24-hour exposure from 0.01 to 10 micrograms/ml of PGE2 at the 4-cell or morula stages had no effect on the morphology of embryos during the 144 hours in culture. Exposure to 10 micrograms/ml PGE2 at the blastocyst stage accelerated and enhanced spreading of the trophoblast in vitro. Embryos treated at 0.01 to 10 micrograms/ml PGE2 at various stages all showed a more rapid decline in LDH activity from morula to blastocysts. Treatment with 50 or 100 micrograms/ml PGE2 led to abnormal morphology of embryos in vitro. In contrast, continuous treatment with 0.01 to 100 micrograms/ml PGF2 alpha from 4-cell to early post-implantation (day 8) had no effect on the morphology of embryos, although breakdown of LDH was again accelerated. These results suggest that the peak of PGE2 secretion on day 4 of pregnancy in mice may enhance trophoblastic outgrowth, and the lower levels of PGE2 and PGF2 alpha secreted earlier in pregnancy modulate the development of pre-implantation mouse embryos.     

Serum and plasma stimulate prostaglandin production by alveolar macrophages

Fetal bovine serum (FBS) stimulated rabbit alveolar macrophages to synthesize prostaglandins (PG) and release lysosomal enzymes. This stimulatory action was not entirely due to the effect of foreign protein in FBS, since rabbit serum and plasma, both homologous and autologous, also induced release of PGs and lysosomal enzymes. Rabbit serum and plasma are less effective than FBS as a stimulus for PG release, with rabbit serum being more potent than plasma at the same concentration. Bovine serum albumin elicited a dose-dependent increase of arachidonic acid release by macrophages, but not of PG production. Hence, the fatty acid "trapping" effect of albumin in serum and plasma is not responsible for the PG stimulation. The PG stimulating factors were stable at 56 degrees C for 30 min., but lost half the activity after heating at 100 degrees C for 10 min. Gel permeation chromatography of FBS showed several peaks of PG stimulating and arachidonic acid releasing activity. The molecular weight of the major one (150,000 daltons) is similar to that of immunoglobulin G. Rabbit IgG, when added to the macrophage culture, stimulated release of arachidonic acid and PGs. However, the major stimulatory effect in serum or plasma is not all due to IgG, since removal of IgG by a Protein A-agarose column did not remove the stimulatory effect of FBS and rabbit serum. The possibility of other factors, such as complement fragments, is discussed.     

Binding of norgestrel to human plasma proteins.

Binding of [14, 15-3H](+/-)-norgestrel to human plasma proteins has been investigated. Norgestrel showed greater affinity to plasma than to human serum albumin indicating specific norgestrel binding protein(s) in the plasma. alpha1-acid glycoprotein showed high affinity for norgestrel when compared with human serum albumin. The binding protein was eluted at pH 5.8 by step by step elution on a DEAE-cellulose column. Norgestrel binding to plasma proteins was not affected at 60 degrees C. The optimal binding occurred between pH 7 and 8. Ligand specificity of the binding protein revealed that progesterone was able to compete for the norgestrel binding sites, whereas corticosterone, testosterone, oestradiol, and norethindrone acetate did not show much competition. The molecular weight of the binding protein was found to be approximately 43 000. Sucrose density gradient analysis indicated that norgestrel bound to a macromolecular component of sedimentation coefficient 2.9 S. The association constant (Kass) and dissociation constant (Kdiss) of norgestrel-binding plasma protein was found to be 1.4-10(6) M-1 and 0.7-10(-6) M respectively. The number of binding sites was 0.5-10(-9) mol/mg protein. Norgestrel-binding protein in the plasma appeared to be a protein different from human serum albumin, corticosteroid-binding globulin and sex-steroid-binding protein. This binding protein showed some similarities to alpha1-acid glycoprotein.     

Cardiovascular reactivity to arachidonic acid, prostaglandin E2, prostacyclin and bradykinin in carrageenan treated rats

In the rat, during carrageenan-induced peritonitis, the hypotensive activity of arachidonic acid, which depends on PG biosynthesis, is increased during the first hours, and thereafter is not modified. The vasodilator action of PGE2 is reduced during the first day while the actions of PGI2 and bradykinin are not modified. The concentrations of plasma albumin and haptoglobin, two inhibitors of PG biosynthesis are reduced during the first hours. Thereafter the concentration of haptoglobin is increased by 100% while the concentration of albumin remains diminished. During this peritonitis, no plasmatic inhibitory influence on PG synthesis is seen. The anti-inflammatory action of carrageenans does not depend on PG synthesis inhibition.     

Serum and plasma stimulate prostaglandin production by alveolar macrophages

Fetal bovine serum (FBS) stimulated rabbit alveolar macrophages to synthesize prostaglandins (PG) and release lysosomal enzymes. This stimulatory actions was not entirely due to the effect of foreign protein in FBS, since rabbit serum and plasma, both homologous and autologous, also induced release of PGs and lysosomal enzymes. Rabbit serum and plasma are less effective than FBS as a stimulus for PG release, with rabbit serum being more potent than plasma at the same concentration. Bovine serum albumin elicited a dose-dependent increase of arachidonic acid release by macrophages, but not of PG production. Hence, the fatty acid “trapping” effect of albumin in serum and plasma is not responsible for the PG stimulation. The PG stimulating factors were stable at 56°C for 30 min., but lost half the activity after heating at 100°C for 10 min. Gel permeation chromatography of FBS showed several peaks of PG stimulating and arachidonic acid releasing activity. The molecular weight of the major one (150,000 daltons) is similar to that of immunoglobulin G. Rabbit IgG, when added to the macrophage culture, stimulated release of arachidonic acid and PGs. However, the major stimulatory effect in serum or plasma is not all due to IgG, since removal of IgG by a Protein A-agarose column did not remove the stimulatory effect of FBS and rabbit serum. The possibility of other factors, such as complement fragments, is discussed.     

Phosphatidylethanolamide derivatives of prostaglandins E1 and E2.

Prostaglandins E1 (PGE1) and E2 (PGE2) have been coupled with the amine group of phosphatidylethanolamine (PE) by means of dicyclohexylcarbodiimide. These complexes basically mimic the relaxant and contractile effects of the corresponding free prostaglandins (PGs) on various smooth muscle preparations, but exhibit a delayed onset of action and a lower affinity for the PG receptors. The complexes are comparable with the free, parent PGs, in their intrinsic activities. The same holds true for the effects on blood pressure and on the motility of the uterus in situ. The PGE2-PE complex is hydrolysed to release obviously free PGE2 by cell-free homogenates prepared from various tissues, but not by blood plasma. The PGE2-PE complex is immunologically indistinguishable from the free PGE2.