The role of G proteins and protein kinase C in mediating muscarine receptor-linked prostanoid synthesis by the rat urinary bladder was investigated using the G protein activator, sodium fluoride (NaF); the protein kinase C activators, phorbol myristate (PMA) and phorbol dibutyrate (PDBU); the protein kinase C inhibitor, H7, and the parasympathomimetic, carbachol. NaF stimulated in vitro rat urinary bladder prostacyclin (PGI2) synthesis (EC50 = 6 mmol.l-1), an action inhibited by the presence of EDTA (10 mmol.l-1). Carbachol potentiated the stimulatory action of NaF. NaF (10 mmol.l-1)-stimulated PGI2 synthesis was inhibited by the calcium channel blockers verapamil, nifedipine and the protein kinase C inhibitor, H7, in concentration-dependent manners. Carbachol-stimulated PGI2 synthesis was also inhibited by H7. PDBU and PMA were without effect on de novo, NaF- or carbachol-stimulated urinary bladder PGI2 synthesis. Other prostanoids (PGF2 and PGF2 alpha) were stimulated to the ame degree as PGI2 by NaF, and inhibited equally by H7 and calcium channel blockers. Dibutyryl adenosine 3':5'-cyclic monophosphate was without effect on de novo or NaF-stimulated prostanoid synthesis. Since fluoride activates G proteins, these data indicate that: (1) muscarine receptor-prostanoid synthesis coupling is mediated by G proteins in the rat urinary bladder; (2) fluoride action is mediated by protein kinase C and not adenyl cyclase, probably through activation of phospholipase C and therefore the generation of the protein kinase C activator, diacyl glycerol; (3) activated protein kinase C may initiate Ca2++ mobilisation linked to prostanoid synthesis; and (4) the lack of effect of the phorbol esters on urinary bladder PGI2 synthesis, in contrast to that on other smooth muscle, indicates that in different smooth muscle tissues there are varying forms of protein kinase C.

Endogenous prostaglandin (PG) concentrations (6oxo PGF1 alpha, PGE, PGF2 alpha) have been measured by radioimmunoassay in the endometrium of women with objectively assessed menstrual blood loss (MBL). The concentration of PGE and "total" PG (6oxo PGF1 alpha + PGE + PGF2 alpha) was greater in the endometrium of those women with heavy menses (median MBL 152 ml (range 86,432) n = 16) than in those individuals with a normal menstrual loss (MBL 59 ml (18,78) n = 18). The concentrations of PGE and PGF2 alpha were similar in each group, but the concentration of 6oxo PGF1 alpha was significantly less than that of both PGE and PGF2 alpha. In 19 individuals, specimens of endometrium were incubated for 1 and 2 hours in modified 199 medium to assess PG release. There was a direct correlation between endogenous PG content and the production of 6oxo PGF1 alpha, PGE, PGF2 alpha and "total" PG in the first hour, which persisted for the second hour with PGF2 alpha and "total" PG. Endometrial PGs may play a role in the mechanism underlying menstruation; however the observed relationship between the prostanoids and MBL will vary with different experimental methods.

Prostaglandin (PG) I2 (measured as 6-keto-PGF1 alpha) was the major PG synthesized by homogenates of the aorta from male rats, followed by lesser quantities of PGF2 alpha and PGE2. The amounts of 6-keto-PGF1 alpha synthesized by homogenates of the vena cava, mesenteric artery and femoral artery were much less than synthesized by the aorta, and were similar to the amounts of PGF2 alpha and PGE2 synthesized. The amounts of 6-keto-PGF1 alpha synthesized by homogenates of the aorta were 30% lower in female rats than in male rats. The amounts of 6-keto-PGF1 alpha and PGF2 alpha synthesized by homogenates of the aorta from female rats were similar, but the amounts of PGE2 synthesized were lower. The amounts of 6-keto-PGF1 alpha synthesized by homogenates of the aorta and femoral artery of female rats were similar, but the amounts of 6-keto-PGF1 alpha synthesized by homogenates of the mesenteric artery and vena cava were lower and were similar to the amounts of PGF2 alpha and PGE2 synthesized. The amounts of 6-keto-PGF1 alpha synthesized by the vena cava were significantly lower (P less than 0.05) and the amounts of 6-keto-PGF1 alpha and PGF2 alpha synthesized by the femoral artery and aorta, respectively, were significantly higher (P less than 0.05) in female rats than in male rats. The total amount of 6-keto-PGF1 alpha, PGF2 alpha and PGE2 synthesized by the aortae of male and female rats did not differ, indicating that the higher output of 6-keto-PGF1 alpha from the aorta of male rats compared to female rats is not due to a higher concentration of PGH2 synthetase in the aortic tissue of male rats. However, the shift in the relative amounts of 6-keto-PGF1 alpha and PGF2 alpha synthesized by the aorta of female rats in favour of PGF2 alpha may be responsible for the lower output of 6-keto-PGF1 alpha from the aorta of female rats. Oestradiol and progesterone had no effect on the amounts of 6-keto-PGF1 alpha, PGF2 alpha and PGE2 synthesized by homogenates of the aorta and vena cava from intact and ovariectomized, female rats. However, ovariectomy increased the amounts of 6-keto-PGF1 alpha and PGE2 synthesized by the aorta and vena cava, respectively, an effect not reversed by oestradiol and progesterone treatment.

Platelet function was investigated in 15 patients with cystic fibrosis (CF) and in ten age-matched controls. Marked hyperaggregability of platelets to adrenaline, collagen and arachidonic acid was observed in platelet rich plasma (PRP) prepared from patients with cystic fibrosis. Thromboxane A2 (TXA2) release from these platelets was also markedly enhanced. Hyperaggregability and increased TXA2 release observed in patients with CF was not due to the higher platelet counts in these patients since hyperaggregability was observed even in those patients whose platelet counts were similar to those in controls. Platelet hyperaggregability and increased thromboxane release in these patients were also independent of their body weight and occurred despite supplementation with vitamin E. Hyperaggregability of platelets in CF may be clinically relevant since it may contribute to the pathogenesis of bronchoconstriction through the release of TXA2 and other bronchoconstrictor platelet products such as serotonin.

Prostaglandin (PG) I 2 (mesured as 6-keto-PGF 1α ) was the major PG synthesized by aortic homogenates from normotensive and hypertensive male rats, with lesser quantities of PGF 2α and PGE 2 . Homogenates of vena cave from the same rats synthesized PGI 2 and PGE 2 in similar quantities. PGF 2α synthesis by aortic homogenates was significantly higher in hypertensive than in normotensive male rats. A similar trend was seen in PGF 2α synthesis by homogenates of the vena cava. Separation of the aorta of normotensive and hypertensive, male rats showed that PGI 2 was the major PG synthesized by endothelial cells and smooth muscle, and that PGF 2α was the major PG synthesized by adventia. PGI 2 synthesis by smooth muscle and PGE 2 synthesis by endothelial cells were lower, and PGF 2α synthesis by endothelial cells and smooth muscle were higher in hypertensive than in normotensive, male rats. PGI 2 was the major PG released from the aorta of normotensive and hypertensive male rats, together with lesser quantities of PGE 2 and PGF 2α . Aortic PGF 2α output, but not PGI 2 and PGE 2 outputs, was significantly higher in hypertensive compared to normotensive, male rats.

The incidence of vascular disorders increases with age, and is also higher in men than in women. Since prostaglandin (PG)I2 produced by blood vessels has been proposed to have a protective function in the cardiovascular system, reduced vascular PGI2 production with age and lower vascular PGI2 production in males than in females may be causes for these increases in the incidence of vascular disorders. The production of prostaglandins by blood vessels has therefore been investigated in young (2 to 3 months) and old (12 to 14 months), male and female rats. The amounts of 6-keto-PGF1 alpha (reflecting PGI2 formation) synthesized by endothelial cell suspensions were significantly lower in old compared to young male rats, but did not differ between old and young female rats. The amounts of 6-keto-PGF1 alpha synthesized by homogenates of aortic smooth muscle were considerably higher in old compared to young, male and female rats. However, the basal output of 6-keto-PGF1 alpha from the perfused aorta in vitro did not change significantly with increase in age and, if anything, tended to be higher in the older rats, of both sexes. Furthermore, the basal output of 6-keto-PGF1 alpha from the aorta was significantly higher in young and old, male rats compared to young and old, female rats, respectively. Similar findings were observed regarding basal 6-keto-PGF1 alpha output from the perfused mesenteric arterial bed in vitro. The increases in output of 6-keto-PGF1 alpha from the mesenteric arterial bed in response to noradrenaline and angiotensin II were not diminished with age in either male or female rats. Consequently, PGI2 output from the blood vessels studied did not decrease with age, nor was it lower in male rats compared to female rats. The blood pressure was significantly higher in the old rats compared to the young rats. Also, the vascular output of PGF2 alpha, a vasoconstrictor, was higher in the old rats. The increase in blood pressure with age may therefore be connected with this increase in vascular PGF2 alpha production in both sexes.

The concentrations of PGF2 alpha, PGE2 and 6-oxo-PGF1 alpha were measured in human uterine tissues during the menstrual cycle. The concentrations of all PGs in endometrium were greater than in myometrium. PGF2 alpha, which was found in the greatest concentrations, was high in the mid-secretory phase in both endometrium and myometrium. The concentration of PGE2 did not vary during the menstrual cycle in either tissue. The biosynthetic capacity of endometrium to produce both PGF2 alpha and PGE2 was significantly greater in the mid than the late secretory phase in the presence of exogenous arachidonic acid. Also, in spite of low endogenous concentrations, both endometrium and myometrium were able to produce significant amounts of 6-oxo-PGF1 alpha during a 30 minute incubation. The possible significance of this late secretory decline in the capacity of the endometrium to produce PGF2 alpha and PGE2 is discussed.

A sensitive RIA for LTB4 (which cross-reacts 60% with 6-trans LTB4) has been developed with a minimal detectable mass of 7.4 X 10(-15) mole. The properties of a second RIA more specific for 6-trans LTB4 are also described. The latter has utility in the measurement of the enzymatic and non-enzymatic transformations of LTA4 and in the characterisation of inhibitors of LTA4 epoxide hydrolase. Conditions for the direct RIA of immunoreactive LTB4 in human plasma are described. Addition of calcium ionophore, A23187, to human blood increased basal immunoreactive LTB4 levels from less than 100pg ml-1 to 259 +/- 23ng ml-1 (mean +/- SEM, n = 16). Extraction and RPHPLC confirmed that greater than 90% of immunoreactive LTB4 co-eluted with synthetic and [3H]LTB4. Pharmacological characterisation of immunoreactive eicosanoids revealed that in vitro the NSAIDs: aspirin, indomethacin, flurbiprofen and benoxaprofen did not inhibit LTB4 but inhibited TXB2, consistent with cyclo-oxygenase inhibition whereas the prototype mixed inhibitor BW755c inhibited both LTB4 and TXB2. This experimental paradigm may be used in the clinical measurement of the bio-availability of novel agents that inhibit eicosanoid biosynthesis.

Prostaglandins including prostacyclin (PGI2) have been demonstrated to have choleretic properties in dogs and in this study the effect of PGI2 on bile flow in rats has been investigated. PGI2 at a dose of 250 ng kg-1 min-1 was infused into the mesenteric vein of biliary cannulated rats and bile samples were collected every 10 min. Administration of PGI2 did not produce any significant changes in bile flow and in the output of bile acids or sodium, potassium and bicarbonate as compared to controls infused with buffer alone. Similarly no differences in pancreatic juice flow or bicarbonate output were observed between PGI2 treated rats and controls. No hypotension was observed at this dose of PGI2 given intraportally indicating inactivation by the liver. Thus in the rat, unlike the dog, no effects of PGI2 on bile flow were observed but this could be related to the route of administration.

( 3 H) PGE 2 uptake and transfer in the isolated perfused human placental cotyledon was assessed by a ingle pass paired isotope dilution technique utilising ( 14 C) sucrose as an extracellular marker. Metabolism of ( 3 H) PGE 2 was measured by analysing maternal and fetal effluents from perfused human placental cotyledons after bolus injection of ( 3 H) PGE 2 into ither the maternal or fetal sides. Maximal uptake of ( 3 H) PGE 2 was greater on the maternal (81 +/- 8%) than the fetal sides (42 +/- 12%) and showed saturation with increasing concentrations of PGE 2 only on the fetal side with an apparent Km of 12 +/- 4.9 nmol/l and v max of 1.5 +/- 0.2 pmol/min/g. Total recoveries of ( 3 H) PGE 2 were 84.6 +/- 11.8 % and 32.6 +/- 6.3 % of the injected dose after injection on the fetal and maternal sides respectively.Transferof ( 3 H) PGE 2 was the same in both directions being 6.4 +/- 1.2 % of the injected dose in the fetal-maternal direction and 5.8 +/- 2.7 % of the injected dose in the maternal-fetal direction. Metabolism was greater on the maternal side (35% of injected ( 3 H) PGE 2 ) thanthe fetalside(18% of injected ( 3 H) PGE 2 ) and was principally to the 13,14-dihydro-15-keto-PGE 2 metabolite. Metabolism of ( 3 H) PGE 2 after passage across the placenta was the same in both directions and was of the order of approximately 60%.

The effect of PGE2 and PGA1 on aldosterone and corticosterone biosynthesis by isolated perfused rat zona glomerulosa cells has been studied. Incremental doses of each of the prostaglandins tested produced a progressive rise in aldosterone (3-4 fold increase for PGE2 and 2-3 fold increase for PGA1) and corticosterone (4-8 fold for PGE2 and 2-4 fold for PGA1). The cyclo-oxygenase inhibitors indomethacin and meclofenamate however produced no effect on basal steroidogenesis. PGE2 produced a marked potentiation of angiotensin II-induced aldosterone secretion (45.7 +/- 13.6 to 144.3 +/- 19.4 pg/ml with angiotensin II alone and 78.4 +/- 16.6 to 269.9 +/- 39.5 pg/ml with angiotensin II + PGE2). In contrast, there was no effect of PGE2 on ACTH or serotonin-induced aldosterone secretion. These data show that PGE2 and PGA1 can directly stimulate rat adrenal steroidogenesis and suggest that PGE2 may play a role in mediating angiotensin II-induced aldosterone secretion by rat zone glomerulosa cells.

Prostacyclin (PGI2) synthesis by human mesenteric arteries and veins was measured ex vivo in 62 patients who received either no medication or a single oral dose of aspirin 40 mg, 75 mg or 300 mg approximately 24 hrs pre-operatively. Each dose of aspirin caused a significant reduction in both arterial and venous PGI2 synthesis compared with the untreated group. Arterial PGI2 synthesis did not differ significantly from venous PGI2 synthesis whether assessed by sample weight or sample area.

There is increasing evidence implicating thromboxane A 2 (TxA 2 ) in vascular disease. Adrenergic blocking agents have been used with success in the secondary prevention of myocardial infarction. The aim of this study was to determine whether adrenergic blocking agents had any effect on the production of TxA 2 and prostacyclin (PGI 2 ) from whole blood in vitro. Fresh whole blood without anticoagulant was placed in glass tubes containing either drug or vehicle, the latter acting as control, and allowed to clot at 37°C for 30 minutes. The serum PGI 2 metabolites (PGI 2 M) and TxB 2 (the stable hydration product of TxA 2 ) were determined by radioimmunoassay. Labetalol, pindolol and propranolol all inhibited both PGI 2 M and TxB 2 production in a dose dependent manner, while atenolol had no effect. Labetalol was the most potent significantly inhibiting TxB 2 production at a drug concentration compatible with that found in-vivo . This inhibitory effect on TxB 2 production may be of benefit in the treatment of vascular disease.

Skin temperature was measured in the forearms of 8 healthy volunteers to study the effect of transdermal application of a stable prostacyclin analogue (Iloprost). Local skin temperature was significantly increased 24 hours and 48 hours after application of the drug when compared with an area of control skin. The effect had worn off by 72 hours. At a dose of 25μg there were no systemic effects of vasodilatation or antiplatelet behaviour, but when the dose was increased to 75μg there was a decreased rate of platelet aggregation for 24 hours. Histology of a skin biopsy suggested that the increase in skin temperature was due to vasodilatation and not acute inflammatory reaction. The results of this pilot study suggest that transdermal application of Iloprost is a suitable vehicle for administration of the drug and a prospective randomised trial is proposed for patients with Raynaud's Syndrome. proposed for patients with Raynaud's Syndrome.

A direct radioimmunoassay for urinary PGE2 has been developed, using a Pasteur Institute antibody and a gamma-labelled ligand. The assay does not require preliminary solvent extraction of the sample or any chromatographic steps. Gamma-labelled PGE2 of high specific activity was prepared by direct iodination of a PGE2-histamine derivative. Results obtained by the direct assay after serial dilution of urine samples were parallel to the standard curve. Accuracy of the method was determined by the recovery of added amounts of PGE2 to diluted urine (r = 0.094, y = 1.039x-0.535, n = 20). The lowest concentration of PGE2 distinguishable from zero was 0.063 pg/ml. The assay curve covered the range of 0.063-500 pg/ml. The assay was desensitized by increasing the concentration of both label and antiserum to obtain a curve covering the range of 2-1250 pg/ml. Intra-assay and interassay coefficient of variation were 8.6% and 12.5% respectively. Values obtained by the direct method were lower than those obtained by gas chromatography mass spectrometry (r = 0.43, y = 1.57x-3.52, n = 12) and by radioimmunoassay using 3H-PGE2 (r = 0.76, y = 0.93x+2.87, n = 12). Antibodies to PGE2 were produced in rabbits immunised with a conjugate of PGE2 covalently linked to thyroglobulin by carbodiimide reaction. The method was used to study the effect of urine flow and sodium intake on PGE2 excretion levels in normal volunteers. PGE2 excretion was flow dependent but did not vary with sodium excretion.

The interaction between the prostaglandin production of the human endometrium and myometrium has been further investigated using intact pieces of endometrium in homogenates of myometrium. There was an increase in the production of 6 oxo PGF, alpha when these tissues were incubated together, whereas there was no change in the production of PGE, PGF2 alpha or 13, 14 dihydro 15 - keto PGF2 alpha. This endometrial - myometrial interaction could have important implications in the pathogenesis of menorrhagia.

The production of PGI2 (determined by bioassay) and TXB2 (determined by radioimmunoassay) was studied in the supernatant solutions obtained after incubation of vessel rings prepared from veins draining and not draining benign and malignant tumours of the breast. A significant increase (p less than 0.01) was found in the production of PGI2 by vessels draining the malignant tumours as compared to those not draining such tumours or vessels draining benign tumours. The changes in PGI2, and the tendency for TXB2 to be higher in vessels draining malignant tumours, were in the same direction so that they balanced out when the ratio PGI2/TXB2 was calculated: in consequence no significant changes in this ratio were found in malignant tumours as compared to the benign. A significant difference (p less than 0.01) was observed in the ratios of vessels draining tumours:vessels not draining tumours between malignant and benign tumours in relation to the production of PGI2. The present data demonstrate that the production of PGI2 by vessels draining malignant tumours of the breast is different to that obtained with vessels from patients with benign tumours, although the mechanism responsible for this difference is not known.

The amounts of phospholipids in the guinea-pig endometrium were phosphatidylcholine (PC) greater than phosphatidylethanolamine (PE) = sphingomyelin (Sph.) greater than phosphatidylserine (PS) + phosphatidylinositol (PI). There were no significant differences in the amounts of any of these phospholipids in endometrium between Days 7 and 15 of the cycle. The de novo synthesis of PC was 5- to 10-fold higher than the synthesis of PC from PE in guinea-pig endometrium. There were no differences in the amounts of PC formed by either pathway, and in the amounts of PI synthesized by guinea-pig endometrium between Days 7 and 15 of the cycle during a 6 h culture period. The increased incorporation of arachidonic acid into phospholipids of guinea-pig endometrium on Day 15 compared to Day 7 cannot be accounted for by an increase in phospholipid content or increased phospholipid synthesis on the former day. Following a 24 h labelling period of endometrial lipids with [3H] arachidonic acid (3H-AA), there was a significant decrease in the amount of 3H-AA in PC and PE on Day 15, but not on Day 7, following a further 48 h culture period. Progesterone, oestradiol and A23187 did not affect the amounts of 3H-AA released from the various lipid classes in guinea-pig endometrium during the time periods of culture studied. It is concluded that PC and PE may be the source of arachidonic acid for increased PGF2 alpha synthesis by guinea-pig endometrium after Day 11 of the oestrous cycle. The lack of changes in PI content and PI synthesis between Days 7 and 15 of the cycle indicates that stimulation of the PI cycle is not involved in the biochemical processes which lead to increased AA release and PGF2 alpha synthesis in guinea-pig endometrium after Day 11 of the cycle.

It has hitherto been assumed that urinary prostanoid excretion reflects renal and/or systemic prostanoid synthesis. Since the bladder forms an integral part of the urinary tract, we investigated whether this organ was capable of synthesising prostanoids. The rat urinary bladder was found to generate large amounts of 6-oxo-prostaglandin F1 alpha (the stable, spontaneous metabolite of prostacyclin) in vitro; it also produced smaller amounts of prostaglandin E2 and thromboxane B2 (the stable, spontaneous metabolite of thromboxane A2). Distension of the bladder and changes in pH and osmolarity of the incubate were found to markedly alter the production of these prostanoids. Urinary prostanoids may, therefore, reflect not merely renal and/or systemic prostanoid synthesis but also local synthesis and release by the bladder. The presence of these prostanoids in the bladder suggests that they may play a local role in cytoprotection and the regulation of bladder tone.

In this study we have obtained endometrium and myometrium from women whose menstrual blood loss had been measured objectively. Samples of tissue were snap frozen in liquid nitrogen for the estimation of PG content and tissue was homogenized and incubated with and without added arachidonic acid. PGE, PGF2 alpha and 6-oxo PGF1 alpha were measured by gas chromatography - mass spectometry. We confirm that the F2 alpha/E2 ratio in the snap frozen samples was significantly lower in women with a high blood loss although this was not reflected in the production by incubated homogenates. Incubation of endometrial tissue with myometrium from the same patient and with a pool of myometrium showed that the source of myometrium was not important. This suggests that previous observations of increased 6 oxo F1 alpha production in incubations of endometrium and homologous myometrium from women with high MBL, resulted from differences in endometrium. When prostaglandin E and F production by endometrium is studied there is a significant inverse correlation between the percentage difference in production with and without added arachidonic acid and menstrual blood loss which suggests that women with high MBL have relatively high levels of available arachidonic acid in their endometrium.

There has been no cogent hypothesis to explain the molecular basis of analgesic and non-steroidal anti-inflammatory drug (NSAID) associated renal papillary necrosis (RPN) and upper urothelial carcinoma (UUC). The microsomal cytochrome P-450 enzyme system may generate reactive intermediates which promote pathophysiological effects in the lung, liver and renal cortex, but the absence of P-450 activity in the medulla suggests that it is unlikely that similar events lead to RPN and UUC. Other enzymes (eg. peroxidases) convert substituted aromatics into benzoquinoneimines (an intermediate that has previously been defined in P-450-mediated toxicity). The medulla is rich in fatty acid peroxidases involved in the metabolism of arachidonic acid. NSAID and analgesics interact with key enzymes in this pathway, which could lead to the co-oxygenation of exogenous and endogenous compounds via the peroxidase, lipoxygenase, or prostaglandin hydroperoxidase enzymes. The generation of reactive molecules in the medulla could explain both RPN and UUC via the alkylation of macromolecules. The formation of free radicals would give rise to extensive lipid peroxidation, (there are large quantities of free polyunsaturated fatty acids in the medullary interstitial cells), an event of major potential importance to local cell destruction and genotoxic effects. At present this proposed mechanism of co-oxygenation offers the most attractive working hypothesis to explain the molecular pathogenesis of both RPN and UUC.

Acetylsalicylate inhibits prostaglandin and thromboxane production by human platelets suspended in plasma or buffer. Acetylsalicylate inhibits arachidonate-induced aggregation of human platelets suspended in plasma, but the effect of acetylsalicylate on arachidonate-induced aggregation of human washed platelets in buffer has not been reported. We have therefore studied this in relation to arachidonate metabolism in human platelets suspended in plasma or buffer. Platelets suspended in plasma and in buffer were both prepared from each donor, who had not taken acetylsalicylate or like-acting drugs for at least 7 days. Acetylsalicylate was 1500 times less potent in inhibiting arachidonate-induced aggregation in buffer (IC50 = 27.3 +/- 7.5 (s.e.m.)mM) than it was in plasma (IC50 = 18.3 +/- 6.0 microM); whereas it was only 4 times less potent in inhibiting thromboxane production in buffer (IC50 = 110 +/- 51.0 microM) than in plasma (IC50 = 25.3 +/- 8.9 microM). The acetylsalicylate concentration required to inhibit aggregation in buffer was sufficient to inhibit 12-hydroxyeicosatetraenoic acid production whereas the concentration that inhibited thromboxane production in buffer was not. These results indicate that arachidonate-induced aggregation of platelets in buffer may depend on product(s) of lipoxygenase rather than of cyclooxygenase, and is hence insensitive to inhibition by acetylsalicylate compared with arachidonate-induced aggregation of platelets in plasma.

Rat spleen lymphocytes prelabelled with [14C] arachidonate were suspended in fresh medium in the presence or absence of exogenous non-radioactive fatty acids added in ethanol. It was found that fatty acids stimulate thromboxane B2, PGE2, HHT and HETE formation. The effect is specific for unsaturated fatty acids. It occurs at 50 micron concentrations and is apparent after 20 minutes incubation. Unsaturated fatty acids may serve an important role in the regulation of prostaglandin and hydroxy fatty acid metabolism in vivo. This may indicate a mechanism for the action of fatty acids on the immune response.