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Dysfunction of the urinary bladder is a recognised complication of diabetes mellitus (DM) which has been attributed, in part, to a direct effect on bladder smooth muscle tissue. The objective of this study was to investigate the effect of alloxan-induced DM on endogenous modulators of smooth muscle tone such as cyclic AMP (cAMP), cyclic GMP (cGMP) and prostaglandins. Male New Zealand white rabbits were rendered diabetic (hyperosmolar, non-ketotic) with an i.v. injection of alloxan. After 6 months, the urinary bladders and urethrae were excised, cut into segments, incubated with stimulators and the formation of prostaglandins (PG), cAMP and cGMP measured using radioimmunoassays. PGE2 and PGI2 formation was impaired in response to arachidonic acid stimulation, whereas it was increased in response to acetylcholine in DM detrusor, bladder neck and urethra compared to controls. Cyclic AMP and cGMP formation in response to forskolin and sodium nitroprusside, respectively, was significantly reduced in the DM tissues of the lower urinary tract compared to the control. Alterations in the formation of prostaglandins, cAMP and cGMP by the smooth muscle of DM lower urinary tract suggests that these biochemical mediators may have a pathophysiological role in the urinary bladder dysfunction associated with DM.

Objective: To investigate the effect of alloxan-induced diabetes mellitus (DM, a major risk factor for erectile dysfunction and associated with impaired endothelial function) on the formation of nitric oxide (NO), prostacyclin (PGI2), cGMP and cAMP in the corpus cavernosum of rabbits., Materials and Methods: Rabbits were rendered diabetic (hyperglycaemic, nonketotic) with alloxan; after 3 and 6 months, the penises were excised and the corpus cavernosum processed for the study of PGI2, NO, cAMP and cGMP formation, using a range of stimulators and radioimmunoassays., Results: PGI2 formation in response to acetylcholine and phorbol ester, but not arachidonate, and cGMP formation in response to A23187 (NO-release dependent), was significantly diminished in diabetic rabbit corpus cavernosum compared with controls at both 3 and 6 months after the induction of DM. cAMP formation in response to forskolin and prostaglandin E1 was reduced after 6 but not 3 months, although nitroprusside-stimulated cGMP (activates guanylyl cyclase directly) was unaffected in cavernosal tissue from diabetic rabbits., Conclusions: These results show that the formation of NO and PGI2, and adenylyl cyclase activity but not guanylyl cyclase, are impaired in the corpus cavernosum of diabetic rabbits. As NO and PGI2 are produced by the endothelium, these studies consolidate the view that endothelial dysfunction is a major contributor to erectile dysfunction in diabetes mellitus.

To investigate the mechanisms causing reduced systemic vascular reactivity to vasoconstrictor agents in portal hypertension, we studied receptor- and signal-transduction-linked PGI2 (a vasodilator) synthesis (measured as 6-oxo-PGF1 alpha by radioimmunoassay) in the aorta (ex vivo) of portal vein-constricted rats. PGI2 synthesis was stimulated by adrenaline (via heterogeneous alpha-adrenoceptors), phorbol ester dibutyrate (a protein kinase C activator), arachidonic acid (the substrate for PGI2 synthesis) and the Ca2+ ionophore A23187 (A23187) and thapsigargin (both of which elevate intracellular Ca2+, which in turn elicits the release of arachidonic acid). The release of PGI2 by the aortae of rats with portal hypertension in comparison to sham-operated controls was: 1) enhanced in response to adrenaline, 2) reduced in response to phorbol ester dibutyrate, A23187 and thapsigargin and 3) unchanged in response to arichidonic acid. These data indicate that in aortae from rats with experimental portal hypertension: i) there are no changes in the enzymes involved in PGI2 synthesis (cyclooxygenase, PGI2 synthase), ii) there is a specific increase in adrenoceptor-linked PGI2 synthesis in aortae which may contribute to arterial vasodilation in this experimental model and 3) the diminished response of PGI2 synthesis to A23187, phorbol ester dibutyrate and thapsigargin indicates that there is a generalised attenuation of protein kinase C activator activity and of Ca2+. Since Ca2+ is a key component of excitation-contraction coupling and protein kinase C activator has been implicated in mediating this event, attenuation of these systems may also explain, at least in part, the known reduced vasoactivity of aortae from rats with portal hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of buflomedil, a vasodilator, on: (a) in vitro prostacyclin (PGI2) synthesis by the rat aorta and penis, human cultured endothelial cells (HUVECs) and human iliac artery, (b) endothelin synthesis by HUVECs and (c) 45Ca2+ uptake by isolated human platelets was investigated. Buflomedil had no effect on PGI2 synthesis by rat aorta, iliac artery or HUVECs (short or long-term incubations). However, buflomedil inhibited noradrenaline- (but not arachidonate- or ionophore A23187-) stimulated PGI2 synthesis. Buflomedil had a weak stimulatory effect on PGI2 synthesis by the isolated rat penis, but this was not inhibited by cholinergic antagonists. Buflomedil (except at supra-therapeutic concentrations) exerted no effect on endothelin release by HUVECS. Buflomedil inhibited 45Ca2+ uptake by human platelets when stimulated with collagen and adrenaline, but not when stimulated with calcium ionophore A23187. These data demonstrate that buflomedil has no deleterious effect on the enzymes that control vascular PGI2 synthesis. The data also adds to the evidence that buflomedil is an alpha-adrenoceptor blocker and has stimulatory effects on penile PGI2 synthesis. Both of these properties may prove useful in the treatment of impotence. The specific inhibition of 45Ca2+ uptake consolidates that buflomedil has some calcium-channel-blocking properties which may explain, at least in part, its vasodilator and antiplatelet properties. Buflomedil may prove beneficial in the treatment of impotence via three mechanisms: (a) stimulation of penile PGI2 synthesis (b) alpha-adrenoceptor blockade and (c) calcium-mobilization-blocking properties.

1. The effect of experimental diabetes mellitus (DM; hyperglycaemic, non-ketototic; 2 months duration) in the rat on receptor-linked prostacyclin (PGI2) synthesis (measured as 6-oxo-PGF1 alpha by radioimmunoassay) was studied in the aorta and urinary bladder using adrenaline, angiotensin II (AII) and acetylcholine (ACh). Signal transduction systems were studied via stimulation of PGI2 synthesis with phorbol ester dibutyrate (PDBU; a protein kinase C activator [PKC]), Ca2+ ionophore A23187 (A23187) and thapsigargin (both elevate intracellular Ca2+, activating phospholipase A2 [PLA2]) and arachidonate (AA; substrate for PGI2 synthesis). 2. In response to adrenaline, AII and phorbol ester, aortic PGI2 release was markedly reduced (all > 75%) in diabetic rats compared to controls. EC50s of the dose-response curves for adrenaline, AII and PDBU were also markedly increased in aortae from DM rats compared to controls. Although there was decreased output of PGI2 in response to A23187 by aortae from diabetic rats compared to controls, there was no difference in the EC50s (mean +/- s.e. mean: diabetic, 2.7 +/- 0.2 x 10(-6) M; controls 2 +/- 0.18 x 10(-6) M). There were no differences in PGI2 release (or in the EC50s) in response to thapsigargin or AA between aortae from diabetic and control rats. 3. In the urinary bladder, there was a marked increase in PGI2 output in response to ACh and a marked decrease in EC50s for the ACh-PGI2 dose-response curves in diabetic rats (EC50 = 5.8 +/- 0.32 x 10(-7) M) compared to controls (EC50 = 2.2 +/- 0.15 x 10(-6) M). Although there was an increase in PGI2 output in the urinary bladders from diabetic rats in response to A23187, there were no differences in the EC50s (control, 1.8 +/- 0.2 x 10-6 M; diabetic, 1.1 +/- 0.15 X 10-6 M). In the urinary bladders, there were no differences in PGI2 output (or the EC50s) in response to PDBU, thapsigargin or AA between diabetic or control rats.4. These data indicate that: (i) reduced PGI2 synthesis coupled to adrenoceptors and AII receptors in the aortae of diabetic rats may be due to diminished PKC activity and not to changes in receptor density and/or affinity, Ca2+ stores, PLA2, cyclo-oxygenase or PGI2 synthase; (ii) the diametrically opposite effect of DM on ACh-stimulated PGI2 synthesis is not due to an increase in PKC activity, but possibly to an increase in muscarine receptor number and/or affinity; (iii) changes in receptor-linked PGI2 synthesis are not ubiquitous in experimental DM and may be organ-specific.

Nabumetone is a novel non-steroidal anti-inflammatory drug (NSAID) which although a weak cyclooxygenase inhibitor is converted by the liver to metabolites which are more potent inhibitors of cyclooxygenase. Nabumetone may thus avoid the occurrence of gastric erosion while maintaining its efficacy as an anti-inflammatory drug. We compared the effects of nabumetone and 6-methoxy-2-naphthylacetic acid (6MNA; the principal metabolite of nabumetone) with naproxen and indomethacin on in vitro synthesis of the gastroprotective prostaglandins I2 and E2 by human gastric mucosa. To study the effects of 6MNA on peripheral target tissues the effects of the above NSAIDs on human platelet aggregation and thromboxane A2 synthesis were also studied. Prostanoid synthesis by the human gastric mucosa was inhibited by indomethacin, naproxen and 6MNA (in this order of potency) whereas nabumetone was completely without effect. Platelet aggregation and thromboxane A2 synthesis were similarly inhibited by the NSAIDS (viz. indomethacin greater than naproxen greater than 6MNA greater than nabumetone). These results support the view that nabumetone does not inhibit gastroprotective prostanoid synthesis, whereas its active metabolite 6MNA is an effective inhibitor of prostanoid synthesis in target tissues.

The present review will discuss the effects of ethanol on platelet function and vascular prostanoids. Whenever possible we have considered human studies because there are marked species differences in platelet function and vascular prostanoid release even in the absence of ethanol. Because of the specialised nature of some parts of the text, we have included brief introductions to help readers who are not familiar with this field.

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.

The present study demonstrates that human corpus cavernosum tissue has the capacity to produce prostacyclin (PGI2), a vasodilator and potent inhibitor of platelet aggregation. The release of PGI2 was stimulated by cholinergic (muscarinic) but not adrenergic agents. Since penile erection in man is dependent upon parasympathetic stimulation, the vasodilatory action of PGI2 may contribute to the initiation and maintenance of erection.

The effect of cigarette smoke extracts and experimental diabetes on rat penile prostacyclin (PGI2) synthesis was investigated. Cigarette smoke extracts induced a dose-related inhibition of methacholine-stimulated PGI2 secretion. Induction of diabetes by streptozotocin resulted in diminished PGI2 secretion, which was further inhibited by cigarette smoke extracts in an additive fashion. Treatment with insulin prevented the inhibition of PGI2 in diabetic animals. Since PGI2 is a potent vasodilator, it may mediate the increased blood flow to the penis responsible for erection following parasympathetic stimulation. The inhibition of PGI2 secretion by cigarette smoke extracts or diabetes, or both, may therefore provide a mechanism to account for the epidemiological observation that smoking and diabetes are major risk factors for male impotence.

The half-life of the platelet antiaggregatory activity of prostacyclin (PGI2) is prolonged when PGI2 is incubated in human plasma or in fatty-acid-free human albumin solutions. This "PGI2-protective" effect is diminished when fatty acids are added to the incubate, and the diminution is proportional to the concentration of the nonesterified fatty acids added. Unsaturated fatty acids were more potent in causing this reduction than saturated acids. It is possible that nonesterified fatty acids displace PGI2 from binding sites on the albumin molecule and that they may thus alter the biologic half-life of any circulating PGI2. This observation may partly account for the well-documented association between raised serum nonesterified fatty acid levels and thrombosis/platelet activation.

To explain the contradictory data on the secretion of prostacyclin (PGI2) in clinical and experimental diabetes, we have investigated the effect of each of the major metabolic abnormalities in uncontrolled diabetes on vascular PGI2 synthesis. An increase in fatty acid concentrations caused a dose-dependent inhibition of PGI2 synthesis by rat aortic rings in vitro; linoleic and linolenic acids were consistently the most and palmitic the least inhibitory. Glucose had a stimulatory effect between 10 and 30 mmol/L, but a progressive fall in stimulation occurred at higher concentrations. Insulin was inhibitory at 10 and 50 mU/L; however, in combination with glucose (10 mmol/L) it was significantly stimulatory (at 10 mU/L) when the aortic rings were preincubated for 2 and 4 h. A pH of 7.0 or less was significantly inhibitory, whereas ketone bodies had no significant effect on PGI2 synthesis. These data show for the first time that altered metabolic factors in uncontrolled diabetes may have different effects on vascular PGI2 synthesis. These data help explain the variability of observations related to PGI2 synthesis and secretion in diabetes, and advocate a more detailed definition of the metabolic status of patients/animals used in such experiments.

Ethanolic and aqueous cigarette smoke extracts were tested for their influence on prostacyclin (PGI2) synthesis in four vascular models: human umbilical artery, rabbit aorta, rat aorta and rat lung. Nicotine was also studied. In each tissue, a dose-dependent inhibition of the release of PGI2 (assessed by measurement of immunoreactive 6-oxo-PGF1 alpha, the stable hydrolysis product of PGI2), was seen on incubation with aqueous or ethanolic cigarette smoke extracts; nicotine, at concentrations of up to 1 g/1, was without effect. In vitro conversion of [14C]-arachidonic acid to [14C]-6-oxo-PGF1 alpha by human umbilical artery was also inhibited by both ethanolic and aqueous cigarette smoke extracts, whereas nicotine was again without effect. We conclude that cigarette smoke inhibits PGI2 synthesis at the level of cyclooxygenase or beyond it, and that components other than nicotine are responsible for this effect. In blood vessels, the inhibition of PGI2 synthesis may contribute to the pathogenesis of the vascular complications of smoking.

The effect of cooling (at 27 degrees C) on the synthesis of prostacyclin (PGI2) by rat aortic rings, thromboxane A2 (TXA2) synthesis by human platelets and phosphodiesterase activity in human platelets was investigated. Cooling induced a significant reduction in both PGI2 synthesis by rat aortic rings and TXA2 synthesis by human platelets, but the inhibition of the former was proportionately greater. Platelet phosphodiesterase activity decreased, with a subsequent increase in intraplatelet c-AMP content. Diminished PGI2 synthesis/release associated with the previously described diminution in the sensitivity of platelets to PGI2 after cooling probably contributes to the hyperaggregability of platelets at lower temperatures. This occurs in spite of the potential antiaggregatory effect of diminished TXA2 synthesis by platelets and the increase in intraplatelet c-AMP. These observations are relevant to the pathogenesis of hyperaggregability of platelets in Raynaud's syndrome.

The effects of prolonged fasting and experimental nonketonuric diabetes on rat aortic prostacyclin (PGl2) synthesis were compared. Whereas fasting (for 48 hours or longer) resulted in a marked increase in trauma-, adrenaline-, and U46619-stimulated aortic PGI2 synthesis, prolonged experimental (streptozotocin-induced) nonketonuric diabetes caused a marked decrease in aortic PGI2 synthesis stimulated by the above agonists. Arachidonic acid (AA)-stimulated aortic PGI2 synthesis in fasted and diabetic rats, however, was not different from that in controls. The reduction in adrenaline- and U46619-stimulated, but not AA-induced, PGI2 synthesis in the diabetic rat suggests that the diminished production of PGI2 in diabetes may be due to diminished phospholipase A2 (or of the phospholipase C-diglyceride lipase system) activity, diminished AA stores, or both. The opposite effects of prolonged fasting and diabetes on aortic PGI2 synthesis suggest that caution should be exercised when comparing the metabolic consequences of starvation with those of diabetes.

An in vitro model for the study of adrenoreceptor-prostacyclin (PGI2) relationships in the rat aorta is described. PGI2 synthesis was stimulated by adrenergic agonists (rank order of potency: epinephrine greater than norepinephrine greater than phenylephrine greater than methoxamine). Isoproterenol, UK 14304, clonidine and salbutamol were without effect. Epinephrine (3 X 10(-7) M)-stimulated PGI2 synthesis was inhibited by adrenoreceptor antagonists (rank order of potency: yohimbine greater than prazosin greater than phentolamine greater than corynanthine much greater than propranolol). The absence of calcium in incubation media abolished epinephrine-stimulated PGI2 synthesis as did the calcium channel blocker, verapamil, in a dose-dependent manner. Calcium ionophore A23187 (10(-5) M)-stimulated PGI2 synthesis was inhibited by verapamil (in a dose-dependent manner), but not by prazosin, phentolamine or yohimbine. It is concluded that epinephrine-mediated rat aortic PGI2 synthesis is alpha-adrenoceptor- and not beta-adrenoceptor-mediated, calcium-dependent, and that the alpha-adrenoceptor antagonists evaluated do not have verapamil-like calcium channel blocking activities. These findings may be relevant to contraction-relaxation cycles of vascular tissue.

The present study investigated the effect of the angiotensin-converting enzyme (ACE) inhibitors, captopril, CGS14824A and CGS14831 on in vitro rat aortic and urinary bladder prostacyclin (PGI2; measured as 6-oxo-PGF1 alpha by radioimmunoassay) synthesis. PGI2 synthesis was stimulated with adrenaline (aorta), carbachol (bladder), calcium ionophore A23187, arachidonate and trauma. The ACE inhibitors antagonised adrenaline-, carbachol- and A23187-stimulated PGI2 synthesis in the aorta and bladder (CGS14824A greater than captopril greater than CGS14831) but were without effect on trauma- or arachidonate-stimulated PGI2 synthesis. The patterns of inhibition of these ACE inhibitors, using the same stimulatory regimes, was very similar to those previously observed by us with known calcium channel blockers (nifedipine, verapamil). These data suggest that: (i) ACE inhibitors possess calcium channel blocking properties, which may be of relevance to the antihypertensive action of these drugs; and (ii) ACE inhibitors did not stimulate vascular PGI2 synthesis as has been previously suggested.

The effect of trauma on prostacyclin (PGI2) secretion by rat aorta was examined. Whereas cutting and puncturing markedly increased PGI2 secretion, sonication and stretch had no effect. Cutting and puncturing were also effective in stimulating further endogenous secretion of PGI2 from 'exhausted' aortic segments in whom PGI2 production had dwindled to a negligible rate. These experiments show that trauma is an important stimulator of PGI2 secretion, the exhaustion of PGI2 secretion by vascular segments is not due to the depletion of substrate (arachidonic acid) and that an unusually traumatic venepuncture may invalidate the subsequent assays of PGI2 and its stable metabolite, 6-oxo-PGF1 alpha, in plasma. The close relationship of vascular trauma to PGI2 release also suggests a possible cytoprotective effect of this prostanoid on vascular endothelium.

Following the demonstration that biological activity of prostacyclin is more stable in plasma than in buffer solutions at physiological pH, we investigated the possibility that a plasma protein may be responsible for this effect. The duration of platelet anti-aggregatory activity of prostacyclin in fatty acid-free human albumin solution was significantly longer than in buffer solutions. The duration of this 'protection' was proportional to the concentration of albumin; alpha, beta, and gamma-globulin preparations had no 'protective' effect. The degree of 'protection' by albumin solutions was lower than that by plasma despite identical albumin concentrations. This discrepancy may in part be explained by the tendency of plasma to become alkaline on standing, a change that would tend to stabilise prostacyclin. The clinical relevance of our findings is discussed.

Prostacyclin (PGI2) release by human aortic tissue obtained at surgery was assessed in patients (n = 23) with ischaemic heart disease undergoing coronary artery bypass grafting (group 1) patients (n = 14) undergoing surgery for aortic stenosis (group 2), patients (n = 4) undergoing surgery for aortic regurgitation (group 3), and patients (n = 8) with ischaemic heart disease taking aspirin (group 4). Although there was a highly significant correlation between (a) intimal and medial PGI2 production and (b) medial PGI2 production and aortic diameter, there was no correlation between intimal PGI2 production and aortic diameter. Aspirin intake (75-150 mg daily) was associated with a pronounced inhibition (95%) of aortic PGI2 production. This inhibition of aortic PGI2 secretion by aspirin may account for the variable efficiency of aspirin in altering the natural history of vascular disease.

An in vitro model for the investigation of PGI2 synthesis by the rat penis is described. Acetyl-beta-methylcholine (methacholine; MeCh) and carbamyl choline (carbachol) stimulated PGI2 synthesis in a dose-dependent manner (ED50 = 1.5 X 10(-6); 2.5 X 10(-6), respectively), whereas adrenaline, noradrenaline, histamine, serotonin, vasoactive intestinal polypeptide (VIP), nicotine, dimethyl phenylpiperazinium (DMPP) and adenosine triphosphate (ATP) were without effect. MeCh (10(-6) mol/l)- and carbachol (10(-6) mol/l)-stimulated PGI2 synthesis was inhibited by atropine in a dose-dependent manner (ID50 = 2.5 X 10(-7) mol/l; 7 X 10(-6) mol/l, respectively). The inhibition by atropine of MeCh-stimulated PGI2 synthesis was competitive. MeCh (10(-6) mol/l)-stimulated PGI2 synthesis was inhibited by verapamil (ID50 = 6 X 10(-5)) and calcium-free incubation media. It is concluded that in the rat penis PGI2 synthesis is principally under muscarinic control and is calcium transport-dependent. Since PGI2 is a vasodilator, these findings may be relevant to the increased blood flow into the penis associated with penile erection. They may also be relevant to the protection of the penile vasculature from thrombosis, since PGI2 is also a potent inhibitor of platelet aggregation.

A series of experiments with platelets from healthy volunteers showed a concentration related inhibitory effect of ethanol on platelet aggregation and release of thromboxane A2. This effect was observed at blood alcohol concentrations ranging between 66 and 132 mg/dl (14.3 and 28.6 mmol/l), which are commonly found in alcoholics. Investigations carried out by incubating ethanol with platelet rich plasma in vitro also showed an inverse linear correlation between ethanol concentration and platelet thromboxane synthesis. In contrast, the incubation of a wide range of concentrations of ethanol with human endothelial cells and rat aortic rings did not alter the ability of these systems to synthesise prostacyclin (prostaglandin I2). This finding of a selective inhibition of thromboxane A2 synthesis and platelet aggregation without an alteration of prostaglandin I2 synthesis may provide an explanation for the reported ethanol mediated protection against vascular disease. This effect of ethanol may also be relevant to the induction of acute gastrointestinal haemorrhage that occurs after bouts of excessive alcohol consumption.

1. The rate of decay of the platelet antiaggregatory activity of prostacyclin in plasma and buffer solutions was investigated. 2. Platelet anti-aggregatory activity of prostacyclin was more stable in plasma than in buffer solutions at physiological pH. 3. The rate of decay of this activity increased with an increase in incubation temperature. 4. Preheating of plasma at 65 degrees C led to a marked but not total loss of its ability to "protect" prostacyclin. 5. Incubation of 6-keto prostaglandin F 1 alpha in plasma did not result in the appearance of platelet anti-aggregatory activity; nor did the decay curves of prostacyclin activity indicate the emergence of any new platelet anti-aggregatory activity. 6. Incubation of 6-keto-prostaglandin E1 in plasma did not lead to any loss of its platelet anti-aggregatory activity for prolonged periods. 7. We conclude that the marked prolongation of platelet anti-aggregatory activity of prostacyclin in plasma is not due to its enzymatic conversion into 6-keto-prostaglandin E1 but due to 'protection' of prostacyclin itself. This 'protection' is probably due to an interaction with a plasma protein.

Since prostacyclin (PGI2) is known to have a cytoprotective effect on epithelia, and since cigarette smoking is associated with an increased risk of bladder cancer, we investigated the possibility that nicotine, cotinine (the principal metabolite of nicotine) and other components of cigarette smoke inhibit PGI2 secretion by the urinary bladder. Using the rat urinary bladder as a model, we found that cigarette smoke extracts, but not nicotine or cotinine, inhibit in vitro PGI2 synthesis. 2-Naphthylamine, a known bladder carcinogen, was also a potent inhibitor of PGI2 synthesis by the rat bladder. It is possible that cigarette smoke and 2-napthylamine exert their carcinogenic effect partly through the inhibition of PGI2 synthesis, resulting in diminished urothelial cytoprotection.

Since platelet release reaction products (e.g. serotonin, ADP) stimulate prostacyclin (PGI2) release in vitro, we have investigated whether thromboxane A2 (TXA2) also has a similar effect. An analogue, U-46619, was used for the experiments, since TXA2 is extremely unstable. U-46619 stimulated rat aortic PGI2 release; this stimulation was abolished by (a) EDTA and (b) verapamil. We conclude that TXA2 is a calcium-dependent stimulator of PGI2 release; this property may be relevant to the limitation of platelet aggregates in vivo and to vascular injury.

A 46 year old man with intermittent claudication due to severe peripheral vascular disease had a circulating lupus like anticoagulant (LLAC), thrombocytopenia (79 X 109/1), markedly reduced platelet survival and a normal bone marrow. He was treated with intravenous prostacyclin (PGI2) infusions which resulted in improvement of the patient's exercise tolerance and normalisation of his platelet count (300 X 109/1) and platelet aggregation could then be assessed. The platelets were markedly hyperaggregable and generated supranormal quantities of thromboxane A2. A diagnosis of consumptive thrombocytopenia secondary to peripheral vascular disease and platelet hyperaggregability was made. Despite therapy with aspirin and dipyridamole, gradual and progressive reduction in platelet count followed and his exercise tolerance declined over the next three months. Immunoglobulin prepared from the patient's serum did not inhibit vascular PGI2 synthesis in vitro. To our knowledge this is the first reported case of consumptive thrombocytopenia due to severe peripheral vascular disease and platelet hyperaggregability. PGI2 administration caused a transient resolution of these features which was not sustained by aspirin and dipyridamole.

In view of the marked increase in blood flow into the penis during erection and the association of diabetes mellitus with impotence, we used the diabetic rat model to investigate the possibility that: the penis may produce prostacyclin; and prostacyclin secretion may be decreased in diabetes. Rats given a high dose of streptozotocin (120 mg/kg body weight) developed acute ketotic diabetes and were killed after 48 h. Animals given a low dose of streptozotocin (65 mg/kg body weight) developed non-ketonuric diabetes and were killed after 7 or 62 days. Aortic rings and penile tissue discs were incubated in buffer, which was assayed for 6-oxo-prostaglandin F1 alpha, the stable and spontaneous breakdown product of prostacyclin. Penile tissue from control, ketotic and non-ketonuric (7 days) animals released similar quantities of prostacyclin, whereas that from long-term non-ketonuric animals (62 days) produced significantly less prostacyclin. Production of this prostanoid by the aortic rings paralleled these changes. We conclude that: penile tissue releases prostacyclin in quantities comparable to those of the aorta; long-term diabetes leads to diminished prostacyclin release by penile and aortic tissue: the former may contribute to the pathogenesis of diabetic impotence; and since short-term ketotic diabetes does not inhibit aortic or penile prostacyclin release, duration of diabetes rather than its severity is responsible for diminished prostacyclin release.

Two experimental models were used to compare tiaprofenic acid and indomethacin. The first model involved assessing their effect on in vitro prostacyclin synthesis by rat aortic rings and human umbilical endothelial cells. The results showed that the inhibitory effect of the two drugs was similar. The second model involved assessing the effect of these drugs on in vitro thromboxane A2 release by human platelets. Indomethacin was shown to be a more potent inhibitor of TXA2 release than tiaprofenic acid, but this difference was only significant at low concentrations of the drugs; at concentrations equivalent to those achieved during routine treatment, both produced near maximal inhibition of TXA2 release by platelets. It is concluded that the findings do not support the claim that tiaprofenic acid is more 'selective' in its actions on these aspects of prostaglandin synthesis than another non-steroidal anti-inflammatory drug, indomethacin.

The effect of streptozotocin-induced diabetes mellitus on prostacyclin (PGI2) production by the urinary bladder in rats was investigated. Acute ketotic (two days duration) and non-ketonuric (seven days duration) diabetes had no effect on PGI2 production by the aorta or the bladder. "Chronic" untreated non-ketonuric (62 days duration) diabetes had a marked inhibitory effect on aortic PGI2 secretion which was not observed when rats were treated with insulin. Urinary bladders from animals with "chronic" untreated non-ketonuric diabetes were larger and heavier, and their walls were hypertrophic. The bladders from these latter animals produced more total PGI2, as well as more PGI2 per unit weight. Enhanced PGI2 production by bladders from animals with untreated non-ketonuric diabetes indicates that: 1) severity of the metabolic disturbance due to diabetes mellitus (ketosis) is not as important as the duration of diabetes as far as the induction of changes in PGI2 production is concerned; 2) distension and hypertrophy of the bladder and hyperosmolar urine are probably more potent stimulators of PGI2 production than diabetes is an inhibitor; 3) diabetes mellitus may have a variable effect on PGI2 secretion patterns in different tissues; 4) urinary excretion of PGI2 or its stable metabolite, 6-oxo-PGF1 alpha may not exclusively reflect PGI2 production by systemic vasculature and/or the kidneys; and 5) good control of diabetes prevents the bladder wall and PGI2 synthesis changes.

The present study shows that nifedipine, nimodipine and nisoldipine inhibit in vitro agonist-induced prostacyclin (PGI2) release from rat aortic rings. The agonists used were: U46619 (a thromboxane A2 analogue); A23187 (a calcium ionophore) and adrenaline. In contrast, these calcium channel blockers did not inhibit in vitro trauma- or arachidonic acid (AA)-induced PGI2 release. Therefore, in vitro PGI2 release models may be calcium channel dependent (adrenaline, U46619, A23187) or independent (trauma, AA), a property which is relevant to calcium channel blocker research. It is suggested that calcium channel dependent PGI2 release is relevant to modulating the relaxation phase of muscle contraction, while calcium channel independent PGI2 release is relevant to limiting the extension of thrombi following local vascular trauma.