Effects of changes in sodium balance on prostaglandin synthesis and prostaglandin E2 9-ketoreductase activity in the rat kidney

The in vitro synthesis of prostaglandins E2 and F2 alpha by renal cortex, medulla and papilla was measured in normal rats and in rats receiving either a low or a high sodium intake for 14 days. The production of both prostaglandins was unchanged in the cortex. In the medulla, both low and high sodium intakes led to a similar decrease in prostaglandin E2 synthesis in vitro, but prostaglandin F2 alpha synthesis was unchanged. In the papilla, a low sodium intake increased prostaglandin E2 synthesis. The activity of prostaglandin E2 9-ketoreductase, a cytosolic enzyme catalysing the conversion of prostaglandin E2 to prostaglandin F2 alpha, was unchanged in cortical preparations. In medullary slices, prostaglandin E2 9-ketoreductase activity was decreased by both sodium depletion and loading. In the papilla, prostaglandin E2 9-ketoreductase activity was slightly decreased by sodium loading and increased with sodium depletion. These results obtained in the rat are at variance with findings in the rabbit. The role played by prostaglandin E2 9-ketoreductase in the regulation of prostaglandin biosynthesis during changes of sodium balance remains controversial.     

Indomethacin, prostaglandin E2 and transmission at the frog neuromuscular junction

The effects of indomethacin on transmission at the frog neuromuscular junction were studied using intra- and extracellular voltage recordings. The drug had two dose-dependent effects on spontaneous and evoked quantal acetylcholine release. Low doses (less than or equal to 30 microM) irreversibly decreased and high doses (greater than or equal to 300 microM) reversibly increased release. Indomethacin also increased the latencies of evoked responses by increasing synaptic delays and usually increasing nerve action potential conduction times. Low doses are thought to inhibit cyclo-oxygenase specifically. To determine whether this single action might account for the presynaptic effects of the drug, other treatments that affect prostaglandin concentrations were also studied: 1) potassium 5,8,11,14-eicosatetraynoate (3 microM) and phenylbutazone (80 micron or 1 mM), two additional, molecularly different synthesis inhibitors; 2) prostaglandin E2 (30 nM-30 microM); and 3) sodium arachidonate (30 nM-30 microM), the essential fatty acid precursor of prostaglandin E2. Each treatment altered transmission, but perturbations in endogenous prostaglandin concentrations cannot account for all of their presynaptic effects.     

NADH-dependent prostaglandin E2-9-ketoreductase activity and prostaglandin synthesis in the Brattleboro rat kidney: effects of the antidiuretic hormone

The activity of prostaglandin (PG)E2-9-ketoreductase (9KR), an enzyme catalyzing the conversion of PGE2 to PGF2 alpha, was significantly increased in glomerular and cortical homogenates of diabetes insipidus (DI) rats, as compared to normal Long Evans (LE) rats, and did not change with ADH treatment. Medullary 9KR was similar in the three groups and papillary 9KR was increased, but not significantly, in both groups of DI rats. Km values for PGE2 and NADH were compared in the various compartments of the kidney. Levels of 9KR were not correlated with the PGE/PGF ratio in urine or supernatants. The synthesis of PGE2 and PGF2 alpha by isolated glomeruli was increased in DI rats. This was not reversed by ADH treatment, PGE2 synthesis increasing even further, especially in the presence of arachidonic acid. In contrast, medullary slices produced significantly less PGs in DI than in LE rats and returned to normal with ADH treatment. Papillary slices produced similar quantities of prostaglandins in all groups. The results do not support the concept that the alterations in PG synthesis observed in DI rat are related only to changes in 9KR activity, but do not exclude the possibility that the enzyme participates in the regulation of PG biosynthesis.     

The effect of inhibition of prostaglandin synthesis on urinary sodium excretion in the conscious dog.

Studies were performed to determine the effect of decreased endogenous release of renal prostaglandins on urinary sodium excretion. Two structurally dissimilar inhibitors of prostaglandin synthesis were employed, and studies were performed in conscious dogs allowed to recover from prior surgical instrumentation. Either meclofenamate (2 mg/kg) or the competitive prostaglandin inhibitor RO 20-5720 (1 mg/kg) was given to seven unanesthetized dogs undergoing a water diuresis. The administration of either prostaglandin inhibitor did not alter glomerular filtration rate, renal plasma flow, urinary volume, or potassium excretion. Sodium excretion, however, increased from 32 to 130 mueq/min (P less than 0.02). Essentially, the entire increase in sodium excretion was due to an increase in urinary sodium concentration from 7.7 to 28.3 meq/liter (P less than 0.02). On a different day, the same animals were studied before and after administration of the diluent of the prostaglandin inhibitor. No change was noted in sodium excretion or any other parameter. Thus, these findings suggest that prostaglandin inhibition in the conscious dog is associated with a natriuresis without a change in urinary volume or potassium excretion during water diuresis. This may indicate that the natruiresis was due to diminished sodium reabsorption beyond the distal tubule.     

Effect of synthesis inhibitors of thromboxane A2 and prostaglandin E2 on the regulation of sodium and water

The aim of this study was to evaluate the response to water deprivation in rats during development in the presence and in the absence of either benzylimidazole or acetaminophen (10 mg/kg of each), inhibitors of the synthesis of thromboxanes and other arachidonic acid metabolites. Whereas water deprivation induced an increment in urine osmolality both in control and vehicle-treated animals, this response was blocked by benzylimidazole and acetaminophen in the 5-day-old rats. No effect was observed in the older rats. Benzylimidazole also increased sodium excretion in the newborn rat. To assess the effect of benzylimidazole on epithelial cells deprived of the influence of hemodynamic factors, sodium transport and water flow were studied in the frog skin and in the toad bladder, respectively. In the frog skin epithelium, benzylimidazole (10(-4) M) inhibited the vasopressin-stimulated (100 mU/ml) sodium transport and in the toad bladder it decreased the vasopressin-stimulated (5 mU/ml) hydroosmotic flow. Our results suggest that thromboxanes are necessary for a full development of the response to vasopressin in sensitive epithelia. In the rat, thromboxanes and other arachidonic acid metabolites appear to play a role in the neonate but not in the older animal.     

Endogenous prostaglandin E2 mediates inhibition of rat thick ascending limb Cl reabsorption in chronic hypercalcemia.

The hypothesis that endogenous PGE2 mediates defective thick ascending limb (TAL) Cl reabsorption (percent delivered load: FRCl%) in rats with vitamin D-induced chronic hypercalcemia (HC) was tested by measuring FRCl% in loop segments microperfused in vivo in HC and control rats treated acutely with indomethacin (Indo) or its vehicle, and obtaining the corresponding outer medullary [PGE2]. Microperfusion conditions were developed in which FRCl% was exclusively furosemide sensitive. To determine the cellular mechanism, tubules were perfused acutely with forskolin (FSK), cAMP, or the protein kinase C inhibitor staurosporine (SSP). Outer medullary [PGE2] in HC rats was 9 to 10 times greater than control and could be normalized by Indo. FRCl% was 20% lower in HC rats infused with vehicle, and Indo, FSK, and cAMP returned FRCl% to normal despite sustained HC. Indo or FSK had no effect on FRCl% in control rats and Indo did not prevent inhibition of FRCl% by luminal PGE2 (1 microM). Luminal SSP (10(-7), 10(-8) M) in HC did not return FRCl% to control values. We conclude that impaired TAL FRCl% in HC occurs at a pre-cAMP site and is due to endogenous PGE2 and not to HC.     

Glomerular and tubular adaptive responses to acute nephron loss in the rat. Effect of prostaglandin synthesis inhibition.

These studies, using in vivo micropuncture techniques in the Munich-Wistar rat, document the magnitude of changes in glomerular and tubular function and structure 24 h after approximately 75% nephron loss (Nx) and compared these results with those obtained in sham-operated rats. The contribution of either nephron hypertrophy or renal prostaglandin to these adjustments in nephron function was also explored. After acute Nx, single nephron GFR (SNGFR) was increased, on average by approximately 30%, due primarily to glomerular hyperperfusion and hypertension. The approximately 45% reduction in preglomerular and the constancy in postglomerular vascular resistances was entirely responsible for these adaptations. Although increases in fluid reabsorption in proximal convoluted tubules correlated closely with increase in SNGFR, the fractional fluid reabsorption between late proximal and early distal tubular segments was depressed. Nephron hypertrophy could not be substantiated based on either measurements of protein content in renal tissue homogenates or morphometric analysis of proximal convoluted tubules. However, acute Nx was associated with increased urinary excretory rates per functional nephron for 6-keto-PGF1 alpha and TXB2. Prostaglandin synthesis inhibition did not affect function in control nephrons, but this maneuver was associated with normalization of glomerular and tubular function in remnant nephrons. The results suggest that enhanced synthesis of cyclooxygenase-dependent products is one of the earliest responses to Nx, and even before hypertrophy the pathophysiologic effects of prostaglandin may be important contributors to the adaptations in remnant nephron function.     

Tubular prostaglandin E2 production and its role in urinary hypotonicity after release of ureteral occlusion in the rat

1. In order to explore the involvement of endogenous prostaglandin E2 (PGE2) in the urine concentration defect after ureteral occlusion, PGE2 production by isolated collecting ducts in vitro and effects of indomethacin on urine osmolality in vivo were examined. 2. Twenty-four hours ureter obstruction caused increased PGE2 production by the medullary collecting ducts, which was maintained at a high level on the day after release of obstruction (0.8 +/- 0.2 pg/mm normal, 8.1 +/- 0.9 pg/mm 24 h obstruction, and 6.6 +/- 1.0 pg/mm post-obstruction, mean +/- SEM). An enhanced PGE2 production was also observed for papillary collecting duct on the day after release of 24 h ureteral occlusion (3.9 +/- 0.5 pg/mm normal and 7.7 +/- 1.2 pg/mm post-obstruction). 3. Administration of indomethacin to the unilateral post-obstructive rats slightly raised the urine osmolality of the post-obstructed kidney (from 339 +/- 17 to 390 +/- 22 mosmol/kg H2O), while it had a greater effect on the contralateral intact kidney (from 1569 +/- 138 to 2567 +/- 198 mosmol/kg H2O). 4. Our data may indicate that the urine concentration defect after 24 h ureteral occlusion is ascribable mainly to a mechanism other than increased endogenous PGE2.     

Altered prostaglandin synthesis and impaired sodium conservation in the kidneys of old rats.

1. The aim of this investigation was to study the role of prostaglandins in the impaired Na+ conservation of the ageing kidney. 2. We measured the urinary excretion of thromboxane B2, 6-keto-prostaglandin F1 alpha and prostaglandin E2 in young (3-4 months) and old (20-21 months) rats after 12, 24 and 36 h of Na+ deprivation. In a separate protocol, we measured prostanoid synthesis by isolated glomeruli, cortical homogenates, medullary slices and papillary slices from young and old rats in basal conditions and after 15 days of dietary Na+ deprivation. 3. In the acute study, urinary excretion of 6-keto-prostaglandin F1 alpha and prostaglandin E2 decreased in young but not in old rats. Urinary excretion of prostaglandin E2 was lower in old rats, but did not vary significantly with Na+ deprivation. 4. In old rats, thromboxane B2 synthesis was increased in all the portions of the kidney except the medulla. Production of 6-keto-prostaglandin F1 alpha was elevated in glomeruli and tended to increase in the cortex. Prostaglandin E2 synthesis was also elevated in the cortex. Thromboxane B2 synthesis tended to increase in the medulla and was enhanced in the papilla. After Na+ deprivation, only glomerular prostaglandin E2 synthesis increased in young rats. In old rats, cortical and papillary synthesis of 6-keto-prostaglandin F1 alpha increased, whereas prostaglandin E2 synthesis did not change. 5. The results suggest increased thromboxane synthesis in the ageing kidney. Increased prostacyclin and prostaglandin E2 synthesis may be an attempt to counteract enhanced thromboxane production.(ABSTRACT TRUNCATED AT 250 WORDS)     

Urinary prostaglandin F2 alpha excretion is not pH-dependent in the conscious rat: implications for the urinary prostaglandin E2/prostaglandin F2 alpha ratio

1. The influence of urine pH on the urinary excretion of prostaglandin (PG) F2 alpha and the PGE2/PGF2 alpha ratio has been examined in the conscious rat. 2. The basal urinary PGF2 alpha excretion rate of 3.9 pmol/h (n = 23) did not vary with urine pH. In marked contrast, PGE2 excretion increased as the urine became more alkaline. The PGE2/PGF2 alpha ratio therefore progressively increased from 1.5 to 22 as the pH of the urine changed from pH 5.8 to pH 7.8. 3. The independence of PGF2 alpha excretion from urine pH: (a) excludes cyclo-oxygenase as a potential site of action for the pH-dependence of urinary PGE2 excretion; (b) suggests that the urinary PGE2/PGF2 alpha ratio measured in alkaline urine may be a more accurate reflection of the kidneys, ability to synthesize these two prostaglandins in vivo; (c) suggests that control of urine pH is required before the urinary PGE2/PGF2 alpha ratio can be employed as an index of PGE2 9-ketoreductase (EC 1.1.1.189) activity in vivo.     

The role of prostaglandin E2 receptors in the pathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder leading to bone and cartilage destruction. A substantial body of evidence suggests that prostaglandin E2 (PGE2) contributes to the pathogenesis of RA, and nonsteroidal anti-inflammatory drugs, inhibitors of the synthesis of PGE2 and other prostanoids, continue to be used in the treatment of this disease. To begin to understand the mechanism by which prostaglandins modulate the pathophysiology of this disease, we examined mice lacking each of the four known PGE2 (EP) receptors after generation of collagen antibody-induced arthritis, an animal model of RA. Homozygous deletion of the EP1, EP2, or EP3 receptors did not affect the development of arthritis, whereas EP4 receptor-deficient mice showed decreased incidence and severity of disease. These animals also showed reduced inflammation as assessed by circulating IL-6 and serum amyloid A levels. Joint histopathology of EP4(-/-) animals revealed reduced bone destruction, proteoglycan loss, and type II collagen breakdown in cartilage compared with EP4(+/+) mice. Furthermore, liver and macrophages isolated from EP4(-/-) animals produced significantly less IL-1 beta and IL-6 than control samples. Thus, PGE2 contributes to disease progression at least in part by binding to the EP4 receptor. Antagonists of this receptor might therefore provide novel agents for the treatment of RA.     

Long-term effects of aldosterone on kallikrein, prostaglandin E2 and sodium in rats

To assess the long-term effects of mineralocorticoids on the regulation of the synthesis or release of kallikrein and prostaglandin E2 in the renal kallikrein-kinin-prostaglandin E system, we studied the effects of chronic infusion of aldosterone (50 micrograms/kg/day) on urinary excretion of total and active kallikrein, and prostaglandin E2 for 10 days in conscious rats on regular intakes of sodium and on sodium loading with 1% NaCl as a drinking water. Chronic infusion of aldosterone induced a prompt and transient decrease in the ratio of sodium to potassium and a sustained increase in urinary prostaglandin E2 excretion in rats on regular diets, whereas urinary total and active kallikrein excretion did not increase significantly until the 4th day of aldosterone infusion. In rats loaded with sodium, aldosterone did not induce any changes in urinary total and active kallikrein excretion, whereas it induced similar changes in the ratio of sodium to potassium and urinary prostaglandin E2 excretion to those in rats on regular diets. Thus, the present results suggest that aldosterone might stimulate the synthesis or release of renal prostaglandin E2 independent of sodium balance. Furthermore, it is also suggested that aldosterone might stimulate the synthesis or release of kallikrein, at least partly, via the same pathway as sodium loading does.     

Indomethacin in vivo increases the sensitivity to Listeria infection in mice. A possible role for macrophage thromboxane A2 synthesis.

This paper demonstrates that in the presence of indomethacin, a cyclooxygenase inhibitor, 100% of the mice died when infected with live Listeria, whereas none of the animals died in the absence of the drug. The death of the animals correlated with the numbers of bacteria found extraperitoneally in the spleen and not with the Ia expression of the peritoneal macrophages. Increases in the spleen bacterial numbers between mice treated with either indomethacin or a specific thromboxane synthase inhibitor, OKY1581, and those not receiving either drug, were found as early as 2-4 h after infection. The differences in the initial increased bacterial spleen counts in the presence of indomethacin were reversed by administration of a stable thromboxane A2 analog or another potent vasoconstrictor, phenylephrine. Because thromboxane A2 does not regulate macrophage or T cell functions directly (Tripp, C.S., A. Wyche, E.R. Unanue, and P. Needleman, 1986, J. Immunol., In press; and Ceuppens, J.S., S. Vertessen, H. Deckmyn, and J. Vermylen, 1985, Cell Immunol., 90:458-463), but is probably generated at the site of an infection (Tripp, C.S., K.M. Leahy, and P. Needleman, 1985, J. Clin. Invest., 76:898-901), these data suggest an important role for the vasoconstrictive properties of thromboxane A2 in the regulation of immunity to Listeria infection.     

Interleukin-1 regulation of prostaglandin E2 synthesis by the papillary collecting duct

Interleukin-1 (IL-1) has been demonstrated to cause a natriuresis and diuresis in experimental animals. This effect is associated with an increase in prostaglandin E2 (PGE2) excretion and is prevented by pretreatment with cyclooxygenase inhibitors. Micropuncture studies have shown IL-1 inhibition of sodium reabsorption by the rat papillary collecting duct (PCD), a nephron segment capable of abundant PGE2 synthesis. The current study examined the effect of IL-1 on PGE2 synthesis by cultured PCD cells and the mechanism by which such regulation occurs. IL-1 markedly increased PCD cell PGE2 synthesis within 15 minutes of exposure in a dose-dependent manner. Preincubation with saturating concentrations of arachidonic acid abolished IL-1 stimulation of PGE2 synthesis. PCD cells labeled with tritiated arachidonic acid released significantly more arachidonic acid within 5 minutes of exposure to IL-1 as compared to control cells. These data demonstrate that IL-1 directly stimulates PGE2 synthesis by PCD cells and that this effect occurs by enhancement of arachidonic acid release.     

Predominant functional roles for thromboxane A2 and prostaglandin E2 during late nephrotoxic serum glomerulonephritis in the rat.

While much is known regarding acute nephrotoxic serum (NTS)-induced glomerular injury, the glomerular dynamics and pathophysiologic mediators of the more relevant chronic autologous phase remain poorly defined. Studies were performed in rats 14 d after injection of rabbit serum (n = 6), NTS in the absence (n = 6), or presence, of a cyclooxygenase inhibitor, ibuprofen (n = 6) or a thromboxane A2 (TxA2) receptor antagonist, L-670,596 (n = 5). A mesangial macrophage/monocyte infiltrate was noted with equal intensity in all NTS-treated rats. Glomerular generation rates of prostaglandin (PG) E2, PGF2a, and TxA2 in nephritic kidneys were dramatically increased as compared to controls. 2 wk after NTS, there was an increase in glomerular plasma flow rate (SNPF), attainment of filtration pressure disequilibrium, and augmentation of net transcapillary hydraulic pressure difference (delta P). Glomerular filtration rate (GFR), however, was reduced, due to a marked fall in the glomerular capillary ultrafiltration coefficient (Kf). Cyclooxygenase inhibition resulted in normalization of glomerular eicosanoid generation rates, amelioration of proteinuria, afferent vasoconstriction, and normalization of SNPF, delta P, Kf, and GFR. Selective antagonism of TxA2 also led to preservation of Kf, but was without effect on SNPF, thereby leading to elevated values for GFR. Thus, in contrast to the pathophysiologic role of arachidonate-lipoxygenase products in the early heterologous phase, PG-mediated vasodilatation and TxA2-induced reductions in Kf and GFR underlie glomerular functional changes during autologous mesangioproliferative glomerulonephritis.     

Reversal by methysergide of inhibition of insulin secretion by prostaglandin E in the dog.

These studies were designed to examine whether interrelationships exist between serotonin and prostaglandin E (PGE) during regulation of insulin secretion in dogs in vivo. In our studies serotonin was found to inhibit insulin responses to intravenous glucose. This inhibition was not reversed by complete adrenergic blockade provided through combined phentolamine and propranolol pretreatment. This property of serotonin is similar to that of PGE which also inhibits glucose-induced insulin secretion in vivo independently of adrenergic activity. To investigate whether these effects of serotonin and PGE are related, studies with methysergide (a serotonin antagonist) and indomethacin (a PGE synthesis inhibitor) were performed. Methysergide reversed the effects of both PGE and serotonin. In contrast, indomethacin did not diminish the inhibitory effect of serotonin upon insulin secretion. It is hypothesized that endogenous serotonin may play a role in the inhibitory effect of PGE upon insulin secretion in dogs in vivo.     

16,16-Dimethyl prostaglandin E2 reduced chenodeoxycholate-induced small intestinal mucosal injury in the rat

To determine whether prostaglandin may protect the small intestinal mucosa against bile acid-induced injury, we perfused in vivo rat jejunal segments with 5 mmol/L chenodeoxycholate with and without topical pretreatment with 2.6 mumol/L (1 microgram/ml) 16,16-dimethyl prostaglandin E2. Mucosal injury by chenodeoxycholate and its time sequence was assessed by using mannitol absorption and quantitative histology after 5, 15, 30, and 45 minutes of chenodeoxycholate perfusion. Forty-five-minute perfusion with chenodeoxycholate increased mannitol absorption from 0 to 0.9 nmol/min/cm, whereas prostaglandin pretreatment reduced this increase threefold (P less than 0.001). The increase in mannitol absorption coincided with progressive denudation of epithelial cells from intestinal villi. After 45 minutes exposure to chenodeoxycholate, an average of 50 micron of the cross-sectional surface of the villi tips was denuded of epithelial cells compared with only 25 micron denuded with prostaglandin pretreatment (P less than 0.01). These data indicate that topical administration of 16,16-dimethyl prostaglandin E2 reduces both the functional and morphologic small intestinal mucosal injury caused by chenodeoxycholate.     

Sympathoadrenomedullary system mediation of the prostaglandin E2-induced central inhibition of gastric acid output in rats

Mechanisms related to the gastric antisecretory action of i.c.v.-administered prostaglandins (PGs) were investigated in urethane-anesthetized rats with gastric fistula. The gastric acid output was enhanced by electrical stimulation of the left cervical vagus nerve after cutting the bilateral cervical vagus nerves. Intracerebroventricular administered PGE2 (0.05-0.5 microgram/animal) dose-dependently inhibited the vagally stimulated acid output whereas the same doses of PGE2 administered i.v. were without effect. The inhibitory effect of PGE2 (0.1 microgram/animal, i.c.v.) was more potent than the effects of the same doses of PGD2 and PGF2 alpha (PGE2 greater than PGD2 greater than PGF2 alpha). PGE2 (0.1 microgram/animal)-induced inhibition of the gastric acid output was abolished by splanchnicectomy, cutting the preganglionic splanchnic nerves under diaphragm, or by combined pretreatment with adrenalectomy and 6-hydroxydopamine (50 mg/kg i.v., 3 days before). This PGE2-induced inhibition was also abolished by pretreatment with phentolamine (5 mg/kg i.m.), but not by propranolol (5 mg/kg i.m.). These observations suggest that the i.c.v.-administered PGs, in particular PGE2, induces a central excitation of the sympathoadrenomedullary outflow and that the resultant activation of gastric alpha adrenoceptors inhibits the vagally stimulated gastric acid output.     

Enhancement by clofazimine and inhibition by dapsone of production of prostaglandin E2 by human polymorphonuclear leukocytes in vitro.

The effects of the antileprosy agents clofazimine and dapsone (1 to 10 micrograms/ml) on the spontaneous and stimulated release of prostaglandin E2 (PG E2) by human polymorphonuclear leukocytes (PMNL) in vitro have been investigated. PMNL were obtained from normal adult volunteers and three patients with leprosy (two borderline lepromatous and one subpolar lepromatous leprosy). The synthetic chemotactic tripeptide N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) at a concentration of 10(-7) M was used as the stimulant of PG E2 synthesis. None of the test agents at the concentrations used inhibited the binding of radiolabeled FMLP to PMNL. However, dapsone at 5 and 10 micrograms/ml inhibited the spontaneous and FMLP-induced release of PG E2 by PMNL. Clofazimine, on the other hand, significantly increased both the spontaneous and the FMLP-induced synthesis of PG E2 by PMNL. The enhancing effects of clofazimine on FMLP-mediated synthesis of PG E2 were particularly striking and were observed at concentrations of 1 to 10 micrograms of the drug per ml. Measurements of PMNL spontaneous and FMLP-induced synthesis of PG E2 in the presence of both clofazimine and dapsone (5 micrograms/ml) indicated that the two drugs are mutually antagonistic. PMNL from both normal control subjects and patients with leprosy were equally sensitive to these effects of clofazimine and dapsone. The immunostimulatory and immunosuppressive properties of dapsone and clofazimine, respectively, may be related to the opposite effects of these agents on PG E2 synthesis in human leukocytes.