Eicosanoid production by the coronary microvascular endothelium

Cultured rabbit coronary microvessel endothelial (RCME) cells have been used as an in vitro model to study the regulation of microvascular endothelial cell prostaglandin (PG) production by hormones, vasoactive drugs, and inflammatory mediators in an environment that can be tightly controlled and that is unaffected by interactions with other cell types, physical stimulation, or alterations in oxygenation. The most potent stimuli for RCME cell PG secretion were substances associated with inflammation, including histamine, interleukin 1, leukotriene D4, fMet-Leu-Phe, interferon-gamma, and exogenous phospholipases. Inhibition of calcium availability by lower [Ca2+]o or by treatment with calcium channel blockers reduced A23187-stimulated PG release but increased PG synthesis from exogenous arachidonic acid (AA). These observations suggest that Ca2+ may regulate several steps in the pathway leading to PG synthesis and release. Elevated intracellular [Ca2+] may, on the one hand, promote PG production by stimulating phospholipase A2 leading to AA release and, on the other hand, limit the magnitude of the response by increasing the rate of AA reacylation. Glucocorticoids reduce PG production by RCME cells via an action that requires new protein and mRNA synthesis and appears to involve the production of an endothelial cell-derived phospholipase inhibitory protein, or "endocortin." Thus, microvascular endothelial cells can both contribute to (by the release of PGs and possibly platelet-activating factor-acether) and limit (by the production of endocortins) the degree of a local inflammatory response in the heart.     

Effect of epostane, ZK 98299, and ZK 98734 on the interruption of pregnancy in the rat

The objective of these studies was to determine whether treatment of 10-day pregnant rats with a combination of epostane (a progesterone biosynthesis inhibitor) and either ZK 98299 or ZK 98734 (progesterone receptor antagonists) would result in additive or synergistic effects on the interruption of pregnancy. When these compounds were tested individually, the order of potency in interrupting pregnancy was ZK 98734 greater than ZK 98299 greater than epostane (50% effective doses 1.3, 4.0, and 35 mg/kg, respectively). Epostane and ZK 98299 were then tested in combination. When epostane was given either 4 h prior to or concurrently with ZK 98299, the combined drug treatment resulted in a significant additive increase in interceptive activity compared to when ZK 98299 was administered alone. In vitro binding studies showed that ZK 98299 and ZK 98734 bound to the rat uterine progesterone receptor in vitro with approximately equal affinity. ZK 98734 bound to the rat thymus glucocorticoid receptor and to the rat ventral prostate androgen receptor with a greater affinity than ZK 98299. The affinity of ZK 98299 for the rat uterine estrogen receptor was weak while the binding of ZK 98734 was not detectable. Thus, the in vitro receptor binding profiles observed were consistent with the known progesterone and glucocorticoid antagonist activities of ZK 98299 and ZK 98734. Overall these findings show that the interceptive activity of epostane and ZK 98299, agents that exert their interceptive activity via different molecular mechanisms, is additive in the 10-day pregnant rat.     

Ametantrone inhibits prostaglandin--mediated resorption in bone organ culture

Prostaglandins (PG) have been postulated to be involved in both tumor metastases to bone and in tumor-induced bone resorption. The anthracenedione antineoplastic agents ametantrone (HAQ) and mitoxantrone are potent antioxidants and inhibit hydroperoxide-dependent initiation and propagation reactions. Therefore, these compounds may inhibit PG production and could also inhibit tumor metastases and tumor-induced resorption. The ability of HAQ, a prototypic anthracenedione, to inhibit PG synthesis and PG-mediated bone resorption was investigated using neonatal mouse calvaria in organ culture. Epidermal growth factor (EGF) stimulates bone resorption in this tissue by inducing PG synthesis. Consequently, if HAQ inhibits EGF-stimulated PG synthesis, it should also inhibit EGF-stimulated bone resorption. HAQ, at 10 microM, completely abolished EGF-stimulated PG synthesis and calcium release. Moreover, HAQ (1.0-30 microM) inhibition of EGF-stimulated PGE2 synthesis correlated with the inhibition of EGF-stimulated Ca release in a concentration-dependent manner. In contrast to EGF, parathyroid hormone stimulates resorption by a PG-independent pathway. HAQ at 10 microM had no effect on parathyroid hormone stimulated Ca release. These results suggest that HAQ inhibition of bone resorption appears to be primarily mediated by inhibition of PG biosynthesis.     

Ametantrone inhibits prostaglandin — mediated resorption in bone organ culture

Prostaglandins (PG) have been postulated to be involved in both tumor metastases to bone and in tumor-induced bone resorption. The anthracenedione antineoplastic agents ametantrone (HAQ) and mitoxantrone are potent antioxidants and inhibit hydroperoxide-dependent initiation and propagation reactions. Therefore, these compounds may inhibit PG production and could also inhibit tumor metastases and tumor-induced resorption. The ability of HAQ, a prototypic anthracenedione, to inhibit PG synthesis and PG-mediated bone resorption was investigated using neonatal mouse calvaria in organ culture. Epidermal growth factor (EGF) stimulates bone resorption in this tissue by inducing PG synthesis. Consequently, if HAQ inhibits EGF-stimulated PG synthesis, it should also inhibit EGF-stimulated bone resorption. HAQ, at 10 μM, completely abolished EGF-stimulated PG synthesis and calcium release. Moreover, HAQ (1.0–30 μM) inhibition of EGF-stimulated PGE₂ synthesis correlated with the inhibition of EGF-stimulated Ca release in a concentration-dependent manner. In contrast to EGF, parathyroid hormone stimulates resorption by a PG-independent pathway. HAQ at 10 μM had no effect on parathyroid hormone stimulated Ca release. These results suggest that HAQ inhibition of bone resorption appears to be primarily mediated by inhibition of PG biosynthesis.     

Ca2+ antagonists and db-cAMP sustain a rise in renal blood flow induced by acetylcholine in indomethacin-treated dogs

Renal arterial infusion of acetylcholine (ACh) in the dog normally produces a sustained rise in sodium excretion (UNaV) and in renal plasma flow (RPF). When prostaglandin (PG) synthesis is inhibited, ACh induces only a transient increase in UNaV and RPF followed by a progressive decline in UNaV and RPF, and a rise in renin secretory rate (RSR). Renal arterial infusion of PGE2 but not a vasodilator such as bradykinin restored the response to ACh to normal in indomethacin (Indo)-treated dogs. During renal arterial infusion of dibutyryl cyclic AMP (6 mg/min), ACh also produced a sustained increase in UNaV and RPF despite an inhibition of PG synthesis by Indo. Renal arterial infusion of verapamil (60 micrograms/min) or diltiazem (60 micrograms/min) also prevented the subsequent fall in RPF when ACh was infused; RSR, however, did not show a rise. The results suggest that synthesis of PGE2 with stimulation of cAMP is required for sustained ACh action. When PGE synthesis is inhibited, ACh may produce renal vasoconstriction by increasing intracellular Ca2+ concentration. The partial effect of calcium channel blockers suggests that release of calcium from intracellular stores as well as calcium entry may mediate the response.     

Comparison of antiprogestin stimulation of uterine prostaglandin synthesis in vitro

Progesterone has an inhibitory effect on prostaglandin synthesis in urine tissue and this effect is reversible with progesterone receptor antagonists. Although antiprogesterone steroids such as RU486 (Mifepristone) are effective at inducing abortion in women they have an improved efficacy when used with exogenous synthetic prostaglandin. In the guinea-pig such antagonists sensitize the uterus but do not result in increased myometrial activity and therefore may not induce endogenous PG synthesis. In this study the effects of antiprogestins on a preparation of rat uterus perifused with progesterone were studied. ZK98 734 caused a rapid and sustained increase in 6-oxoPGF synthesis which rose within the first 90 minutes. This rapid response suggested that some mechanism other than the induction of fresh protein synthesis was involved. A similar increase was not seen with pregnant guinea-pig myometrium/decidua perifused in a similar manner, suggesting that some other mechanism was responsible for the relatively low PG production in pregnancy. However increases in 6-oxoPGF in response to antiprogestins were recorded when pregnant guinea-pig decidua/myometrium was incubated for 4 hours. In these experiments 1 microM ZK98 734 and 1 microM ZK98 299 (Onapristone) gave a 2.7 fold increase in PG production whereas RU486 gave a 1.6 fold increase. Both 1 microM ZK98 734 and 1 microM ZK98 299 also gave a significant increase in PGE production but no increase in PGF was observed. These findings suggest that some antiprogestins might have a better effect on the stimulation of endogenous PG synthesis or on the rate of catabolism of prostanoids.     

Activity of prostaglandin biosynthetic pathways in rat pancreatic islets

Isolated pancreatic islets of the rat were either prelabeled with [3H]arachidonic acid, or were incubated over the short term with the concomitant addition of radiolabeled arachidonic acid and a stimulatory concentration of glucose (17mM) for prostaglandin (PG) analysis. In prelabeled islets, radiolabel in 6-keto-PGF1 alpha, PGE2, and 15-keto-13,14-dihydro-PGF2 alpha increased in response to a 5 min glucose (17mM) challenge. In islets not prelabeled with arachidonic acid, label incorporation in 6-keto-PGF1 alpha increased, whereas label in PGE2 decreased during a 5 min glucose stimulation; after 30-45 min of glucose stimulation labeled PGE levels increased compared to control (2.8mM glucose) levels. Enhanced labelling of PGF2 alpha was not detected in glucose-stimulated islets prelabeled or not. Isotope dilution with endogenous arachidonic acid probably occurs early in the stimulus response in islets not prelabeled. D-Galactose (17mM) or 2-deoxyglucose (17mM) did not alter PG production. Indomethacin inhibited islet PG turnover and potentiated glucose-stimulated insulin release. Islets also converted the endoperoxide [3H]PGH2 to 6-keto-PGF1 alpha, PGF2 alpha, PGE2 and PGD2, in a time-dependent manner and in proportions similar to arachidonic acid-derived PGs. In dispersed islet cells, the calcium ionophore ionomycin, but not glucose, enhanced the production of labeled PGs from arachidonic acid. Insulin release paralleled PG production in dispersed cells, however, indomethacin did not inhibit ionomycin-stimulated insulin release, suggesting that PG synthesis was not required for secretion. In confirmation of islet PGI2 turnover indicated by 6-keto-PGF1 alpha production, islet cell PGI2-like products inhibited platelet aggregation induced by ADP. These results suggest that biosynthesis of specific PGs early in the glucose secretion response may play a modulatory role in islet hormone secretion, and that different pools of cellular arachidonic acid may contribute to PG biosynthesis in the microenvironment of the islet.     

Prostaglandin synthesis and release by subpopulations of rat alveolar macrophages

Alveolar macrophages are the primary phagocytic cell of lung, but are also capable of a variety of other functions, which include initiating or modulating inflammatory and immune responses through the production of soluble mediators. One such group of mediators is the eicosanoids. Further, recent data indicate that alveolar macrophages are not functionally homogeneous, but are heterogeneous with several subpopulations that differ both morphologically and functionally. Considering the apparent importance of prostaglandin synthesis and release in inflammatory and immune responses, the current study was undertaken to determine whether alveolar macrophage subpopulations differ in their ability to synthesize and release prostaglandin (PG) E, PGI2, and thromboxane A2 after stimulation by calcium ionophore A23187, zymosan, or aggregated IgG. Alveolar macrophages were harvested by bronchoalveolar lavage and were separated into 18 density-defined fractions. Density-defined alveolar macrophages (DD-AM) showed marked heterogeneity in prostaglandin synthesis and release. Maximal PGE synthesis and release was seen as a single peak after calcium ionophore A23187 and zymosan stimulation. In contrast, two peaks in PGE synthesis were seen after aggregated IgG stimulation. PGI2 synthesis was seen as a single peak generated by different DD-AM after calcium ionophore A23187 and zymosan. In contrast, aggregated IgG stimulation of subpopulations exhibited uniform synthesis and release of PGI2. Thromboxane A2 synthesis and release was maximal from a broad range of various DD-AM after calcium ionophore A23187, zymosan, and aggregated IgG stimulation. The results demonstrate that DD-AM are heterogeneous in ability to synthesize and release prostaglandins which is dependent on the stimuli. Therefore, specific subpopulations of alveolar macrophages may be central to the control of the pulmonary inflammatory response through specific eicosanoid synthesis and release.     

Activation of Protein Kinase C Suppresses the γ-Aminobutyric AcidB Receptor-Mediated Inhibition of the Vesicular Release of Noradrenaline and Acetylcholine

Modulation of the gamma-aminobutyric acidB (GABAB) receptor-mediated response by protein kinase C (PKC) was examined with regard to inhibition by stimulation of the GABAB receptor of stimulation-evoked release of noradrenaline (NA) from slices of cerebellar cortex and of acetylcholine (ACh) from strips of ileum. 12-O-Tetradecanoylphorbol 13-acetate (TPA) potentiated the high K(+)-evoked Ca2+-dependent release of NA and ACh, but not the ouabain-evoked release, even in the presence of external Ca2+. The potentiating effect was antagonized by sphingosine, thereby suggesting that PKC participates in the exocytotic-vesicular release of neurotransmitters, but does not do so in case of a nonvesicular release. GABA inhibited the high K(+)-evoked release of NA and ACh, but not the ouabain-evoked Ca(2+)-independent release. The effect of GABA was mimicked by baclofen and was antagonized by phaclofen, thereby suggesting that stimulation of the GABAB receptor inhibits the vesicular but not the nonvesicular release of neurotransmitters. TPA suppressed the GABAB receptor-mediated inhibition of high K(+)-evoked release of NA and ACh. The effect of TPA was antagonized by sphingosine. These results indicate that stimulation of the GABAB receptor inhibits the stimulation-evoked Ca(2+)-dependent release of neurotransmitters and that activation of PKC suppresses the GABAB receptor-mediated response.     

Acetylcholine Synthesis and Release by a Sympathetic Ganglion in the Presence of 2-(4-Phenylpiperidino) Cyclohexanol (AH5183)

These experiments measured the release and the synthesis of acetylcholine (ACh) by cat sympathetic ganglia in the presence of 2-(4-phenylpiperidino) cyclohexanol (AH5183), an agent that blocks the uptake of ACh into synaptic vesicles. Evoked transmitter release during short periods of preganglionic nerve stimulation was not affected by AH5183, but release during prolonged stimulation was not maintained in the drug's presence, whereas it was in the drug's absence. The amount of ACh releasable by nerve impulses in the presence of AH5183 was 194 +/- 10 pmol, which represented 14 +/- 1% of the tissue ACh store. The effect of AH5183 on ACh release was not well antagonized by 4-aminopyridine (4-AP), and not associated with inhibition of stimulation-induced calcium accumulation by nerve terminals. It is concluded that AH5183 blocks ACh release indirectly, and that the proportion of stored ACh releasable in the compound's presence represents transmitter in synaptic vesicles available to the release mechanism. The synthesis of ACh during 30 min preganglionic stimulation in the presence of AH5183 was 2,448 +/- 51 pmol and in its absence it was 2,547 +/- 273 pmol. Thus, as the drug decreased ACh release it increased tissue content. The increase in tissue content of ACh in the presence of AH5183 was not evident in resting ganglia; it was evident in stimulated ganglia whether or not tissue cholinesterase was inhibited; it was increased by 4-AP and reduced by divalent cation changes expected to decrease calcium influx during nerve terminal depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prostaglandin E2 production is synergistically increased in cultured human glomerular mesangial cells by combinations of IL-1 and tumor necrosis factor-alpha 1

Both IL-1 alpha and IL-1 beta and TNF-alpha induced a time- and dose-dependent release of authentic PGE2 from cultured human glomerular mesangial cells (HMC). This release became significant only after a 4- to 6-h lag phase, and was abolished by inhibition of protein synthesis, and was not related to cell proliferation. Combinations of IL-1 and TNF-alpha when added simultaneously to HMC resulted in a dose-dependent synergistic increase in PGE2 production. These stimulatory effects were specifically inhibited by anticytokine antibodies and the synergistic effect required the simultaneous presence of both IL-1 and TNF-alpha. Arachidonic acid (AA) release experiments and measurement of cyclooxygenase activity, revealed that while both were increased by IL-1 beta and TNF-alpha alone (IL-1 beta greater than TNF-alpha), combinations of IL-1 beta and TNF-alpha resulted in only additive increases in AA release and cyclooxygenase activity. Taken together, these data suggest that stimulation of PGE2 in HMC, by combinations of these cytokines, is not rate limited by AA release or cyclooxygenase activation, but may be related to the induction of the distal enzymes controlling specific PG synthesis.     

Calcium antagonists, ventricular fibrillation, and enzyme release in ischemic rat hearts

Early experiments with the calcium antagonist verapamil showed that it could inhibit the transsarcolemmal influx of calcium ions induced by isoproterenol in ventricular myocardium without inhibiting the effect of beta stimulation to increase tissue cyclic AMP. Current views of the effects of the beta-receptor-adenylate cyclase-cyclic AMP system of the calcium channel suggest that both calcium antagonists and beta-adrenoceptor antagonists should inhibit transsarcolemmal calcium influx if calcium is the third messenger of beta-agonist catecholamines. When high concentrations of circulating catecholamines are added to normal isolated hearts, two of the effects include increased vulnerability to ventricular fibrillation and high rates of enzyme release. These effects are antagonized by beta-adrenoceptor inhibitors and by calcium antagonists, which suggests a classical second (cyclic AMP) and third (calcium) messenger effect. In the presence of coronary artery ligation, the ventricular fibrillation threshold falls and enzyme release is enhanced. Both effects are associated with an increased tissue cyclic AMP level in the ischemic zone and are susceptible to calcium antagonist procedures. Neither effect can be fully stopped by beta-adrenoceptor antagonism. Therefore the evidence from this model with coronary artery ligation favors the views that 1) cyclic AMP accumulates in ischemic tissue by a process not fully susceptible to inhibition by beta-adrenoceptor antagonists; and 2) calcium ions are associated with the development of ventricular fibrillation and enzyme release by a process susceptible to inhibition by calcium antagonist agents such as verapamil, nifedipine, and diltiazem.     

Possible involvement of calcium signaling pathways in L-leucine-stimulated protein synthesis in L6 myotubes

L-Leucine is known to stimulate protein synthesis in L6 myotubes. In the present study, we examined the possible involvement of calcium signaling pathways in the stimulation of protein synthesis induced by L-leucine in L6 myotubes. After 16 h of treatment with L-leucine-depleted medium, the re-addition of L-leucine for 4 h augmented protein synthesis by about 50% as compared with an L-leucine-depleted control. Ryanodine receptor antagonists almost completely abolished the stimulatory effect of L-leucine, while IP(3) receptor antagonists showed partial inhibition when added simultaneously with L-leucine. These results suggest the possibility that calcium signaling pathways are involved in L-leucine-stimulated protein synthesis.     

The endothelium-derived vasoconstrictor peptide endothelin inhibits renin release in vitro

The effect of endothelin, a newly identified endothelium-derived vasoconstrictor peptide, on renin release from rat kidney cortical slices was examined. Endothelin produced a concentration-dependent inhibition of renin release and this inhibitory effect was dependent on extracellular calcium. The dihydropyridine calcium channel blockers nifedipine and nicardipine did not antagonize the inhibitory effect induced by endothelin. On the other hand, nifedipine completely antagonized the extracellular high potassium- or Bay K 8644-induced inhibition of renin release. The endothelin-induced inhibition of the release was markedly blocked by the addition of Co2+. Similar blocking effects of Co2+ were also observed with extracellular high potassium or Bay K 8644. Thus, endothelin exerts an inhibitory action on renin release in vitro, in a calcium-dependent manner. This inhibition may be mediated by the increased calcium influx through dihydropyridine-insensitive calcium channels.     

Loading-induced changes in synovial fluid affect cartilage metabolism

The object of this study was to determine whether changes in the synovial fluid (SF) induced by in vivo loading can alter the metabolic activity of chondrocytes in vitro, and, if so, whether insulin-like growth factor-I (IGF-I) is responsible for this effect. Therefore, SF was collected from ponies after a period of box rest and after they had been exercised for a week. Normal, unloaded articular cartilage explants were cultured in 20% solutions of these SFs for 4 days and chondrocyte bioactivity was determined by glycosaminoglycan (GAG) turnover (i.e., the incorporation of 35SO4 into GAG and the release of GAG into the medium). Furthermore, the extent to which the bioactivity is IGF-I-dependent was determined in a cartilage explant culture in 20% SF, in the presence and absence of anti-IGF-I antibodies. In explants cultured in post-exercise SF, GAG synthesis was enhanced and GAG release was diminished when compared to cultures in pre-exercise SF. SF analysis showed that IGF-I and IGFBP-3 levels were increased in post-exercise SF. There was a positive correlation between IGF-I levels and proteoglycan synthesis, but no correlation between IGF-I levels and proteoglycan release. Addition of anti-IGF-I antibodies significantly inhibited stimulation of proteoglycan synthesis in explants cultured in SF with 40%. However, there was no difference in inhibition of proteoglycan synthesis between pre- and post-exercise SF which indicated that the relative contribution of IGF-I in the stimulating effect of SF did not change. Proteoglycan release was not influenced by the presence of anti-IGF-I antibodies. It is concluded that chondrocyte metabolic activity is at least partially regulated by changes in the SF induced by in vivo loading. Exercise altered the SF in a way that it had a favourable effect on cartilage PG content by enhancing the PG synthesis and reducing the PG breakdown. IGF-I is an important contributor to the overall stimulating effect of SF on cartilage metabolism. It is, however, unlikely that IGF-I is the only mediator in the exercise-induced increase in this stimulating effect.     

Effect of the Calcium on Polygalacturonase (PG) Activity and Synthesis at Different Ripening Stages of Tomato Fruits

It has been reported that PG is a key enzyme related to the tomato fruit ripening and that the application of calcium can dramatically decrease the PG activity and delay the ripening of fruits. In this paper the effects of calcium treament at various ripening stages on the transformation of absorbed calcium, PG activity and PG synthesis in tomato fruits were studicd. According to the analysis of calcium by atomic absorption spectroscopy, it was shown that the soluble and total calcium contents in pericarp of fruits treated with calcium at mature-green stage were increased significantly, and that more soluble calcium was transformed into bound calcium. Both the absorption and transformation of calcium decreased in fruits treated with calcium at later stage of ripening. The inhibition of calcium on PG activity was most effective by treatment at mature-green stage, but less effective at later stage of ripening. One reason for the decrease of calcium inhibition was probably due to the decline of calcium absorption as fruit ripening. The polyacrylamide gel electrophoresis of PG showed that PG with a molecular weight of 46.7 kD was absent in mature-green fruits, and PG synthesis occurred only at the later stage of ripening. It seems that the earlier the treatment was done the more effective of the calcium inhibition of PG synthesis. Based on the above results, it was concluded that the PG plays a major role in ripening and senescence of tomato fruits, and both PG synthesis and its activity were inhibited by calcium. In order to delay the ripening and senescence of tomato fruits, the treatment with calcium should be done at mature-green stage.     

Further evidence for the purinergic inhibition of adrenergic neurotransmission in the rat portal vein

The inhibition of 3H-noradrenaline (3H-NA) release by adenosine, and the possible involvement of purine receptors in the regulation of transmitter release in the portal vein were studied. The inhibitory effect of different concentrations of adenosine (10, 30, 100 and 300 microM) decreased with frequency of stimulation, but there was no marked concentration-dependence. Tetraethylammonium (TEA) enhanced the 3H-NA overflow induced by transmural stimulation. The adenosine-induced inhibition of 3H-NA overflow was antagonized by TEA. Transmural stimulation induced release of tritium from tissues prelabelled with either 3H-NA or 3H-adenine had a similar pattern of distribution. In contrast, when the rat portal vein was stimulated with (-) NA, the overflow of purine derivates was delayed and the maximum release was achieved 5 min later than the maximum induced by transmural stimulation. Phenoxybenzamine (PBA) increased 3H-NA overflow two-fold, but had no effect on the 3H-purine release induced by transmural stimulation. PBA reduced the 3H-purine release by exogenous (-) NA. These results indicate that in rat portal vein, the purine compounds have pre- and postjunctional origins and that the purine that modulates adrenergic neurotransmission might be of neuronal origin, possibly independent of adrenergic innervation.     

Prostaglandin controls Neuromuscular Transmission in Guinea-pig Vas Deferens

PROSTAGLANDINS of the E type (PGE₁, PGE₂) inhibit sympathetic neurotransmission in several tissues and species^1–4. On the basis of their natural occurrence and availability for release, as well as observations on the pharmacological actions of the PGs, endogenous PGE₁ and PGE₂ are postulated to operate on sympathetic neurotransmission by a feedback mechanism and thereby modulate the effector responses to nerve activity^{1, 5}. Inhibition by 5,8,11,14-eicosatetraynoic acid (ETA) of PG synthesis in the cat spleen and in the rabbit heart increases the release of noradrenaline (NA) in response to nerve stimulation, thus strongly supporting the hypothesis^{6, 7}. We report here that guinea-pig vas deferens releases PG in response to nerve stimulation and that the neuromuscular transmission is facilitated after inhibition of PG synthesis. PG synthesis was irreversibly inhibited using ETA⁸.