Increased nerve stimulation induced release of noradrenaline from the rabbit heart after inhibition of prostaglandin synthesis

A cyclic pain: the pathophysiology and treatment of menstrual migraine

Catamenial migraine is a headache disorder occurring in reproductive-aged women relevant to menstrual cycles. Catamenial migraine is defined as attacks of migraine that occurs regularly in at least 2 of 3 consecutive menstrual cycles and occurs exclusively on day 1 to 2 of menstruation, but may range from 2 days before (defined as -2) to 3 days after (defined as +3 with the first day of menstruation as day +1). There are 2 subtypes: the pure menstrual migraine and menstrually related migraine. In pure menstrual migraine, there are no aura and no migraine occurring during any other time of the menstrual cycle. In contrast, menstrually related migraine also occurs in 2 of 3 consecutive menstrual cycles, mostly on days 1 and 2 of menstruation, but it may occur outside the menstrual cycle. Catamenial migraine significantly interferes with the quality of life and causes functional disability in most sufferers. The fluctuation of estrogen levels is believed to play a role in the pathogenesis of catamenial migraine. In this review, we discuss estrogen and its direct and indirect pathophysiologic roles in menstrual-related migraine headaches and the available treatment for women.

TARGET AUDIENCE

Obstetricians and gynecologists, family physicians.

LEARNING OBJECTIVES

After completing this CME activity, physicians should be better able to discuss the pathophysiology of catamenial migraine, identify the risk factors for catamenial migraine among women, and list the prophylactic and abortive treatments for migraines.

Sex hormones and headache

A variety of evidence suggests a link between migraine and the female sex hormones. Women with migraine outnumber men by at least a 2:1 ratio and definite patterns of development and attacks are noted at menarche and throughout the period of menses, related to trimester of pregnancy, and again at menopause, although it may also regress. Hormonal replacement with estrogen can exacerbate migraine; oral contraceptives can change the character and frequency of migraine headache. This article will cover approaches to the therapy of hormone-related headaches associated with the menstrual cycle, menopause, and oral contraceptives.

Modulation by prostaglandin E2 of ATP and noradrenaline co-transmission in the guinea-pig vas deferens

1. In the guinea-pig vas deferens, prostaglandin E2 (100 nM) enhanced the overflow of ATP, whereas it inhibited [3H]-noradrenaline overflow due to field stimulation at 2 Hz. At 20 Hz, prostaglandin E2 still inhibited the overflow of [3H]-noradrenaline, whereas it was without effect on ATP overflow. 2. Prostaglandin E2 enhanced contractions to exogenously added noradrenaline and alpha, beta-methylene ATP. 3. These results provide evidence for pre- and postjunctional modulation of purinergic and adrenergic transmission by PGE2 in the guinea-pig vas deferens. The importance of these findings in relation to co-transmission is discussed.

Defective coronary prostaglandin modulation in anginal patients

In order to investigate whether coronary vasodilating prostaglandins (PGI2 and PGE2) have a role in the pathophysiology of myocardial ischemia, 26 patients with angina pectoris and 23 control subjects (nonischemic patients) were studied by assessing coronary hemodynamics and prostaglandin formation in relation to sympathetic stimulation. Following a cold pressor test (CPT), coronary prostaglandin output markedly increased (p less than 0.001) and coronary vascular resistance (CVR) decreased (p less than 0.001) in all control subjects. In contrast, in anginal patients prostaglandins in the coronary sinus were undetectable and after CPT prostaglandin output did not increase, whereas CVR paradoxically increased (p less than 0.001). In control subjects the inhibition of coronary prostaglandin formation (by ketoprofen [1 mg/kg intravenously] or by aspirin [15 mg/kg intravenously]) caused a paradoxical increase of CVR following CPT (p less than 0.001). In anginal patients the inhibition of prostaglandins further exaggerated the increase of CVR after CPT (p less than 0.001). These results indicate that coronary vasodilating prostaglandin PGI2 and PGE2 play a role in modulating coronary vascular response to sympathetic stimulation induced by CPT. Their defective production in anginal patients may be responsible for the paradoxical increase in CVR following sympathetic stimulation.

Different effects of prostaglandins on adrenergic neurotransmission in atrial and ventricular preparations

1. The effects of prostaglandin E2 (PGE2) and iloprost on the cardiac response to adrenergic nerve stimulation in guinea-pig atrial and ventricular preparations have been studied. 2. In guinea-pig isolated atria both PGE2 (0.1-10 nM) and iloprost (0.1-3 microM) concentration-dependently reduced the cardiac response to adrenergic nerve stimulation. 3. The inhibition of cyclo-oxygenase by indomethacin and acetylsalicylic acid potentiated the response to nerve stimulation in the atrial preparations. 4. Arachidonic acid (1-10 microM) reduced the response to nerve stimulation in atria. This effect was prevented by indomethacin and acetylsalicylic acid. 5. In guinea-pig ventricles PGE2 and iloprost were found to be effective at higher concentrations than in atrial preparations: arachidonic acid, indomethacin or acetylsalicylic acid did not modify the cardiac response to adrenergic nerve stimulation. 6. These results suggest a different modulator role for endogenous prostaglandins in atrial and ventricular tissue.

Physiologic role of coronary PGI2 and PGE2 in modulating coronary vascular response to sympathetic stimulation

To investigate a physiologic role of coronary prostacyclin (PGI2) and prostaglandin E2 (PGE2) 30 patients who were not affected by coronary heart disease were evaluated for coronary hemodynamics and coronary PGI2 and PGE2 production. Inhibition of coronary prostaglandin biosynthesis by ketoprofen (1 mg/kg) or aspirin (15 mg/kg) administered intravenously did not significantly change coronary hemodynamics in resting conditions. In all patients cold pressor tests induced significant increases in coronary blood flow (p less than 0.001) and decreases in coronary vascular resistance (p less than 0.001) without changes in cardiac oxygen extraction and with consequent increases in calculated myocardial oxygen consumption. Simultaneously, a marked increase in coronary PGI2 (as 6-keto-PGF1 alpha) and PGE2 formation was observed (p less than 0.001). Both ketoprofen (1 mg/kg) and aspirin (15 mg/kg) administration completely abolished PGI2 and PGE2 formation that was induced by cold pressor test and caused a paradoxical increase in coronary vascular resistance (ketoprofen: p less than 0.02; aspirin: p less than 0.05). The results of this study support a physiologic role for the coronary prostaglandins in modulating coronary vascular response to sympathetic stimulation in nonischemic patients.

Prostaglandins in the pericardial fluid modulate neural regulation of cardiac electrophysiological properties

In response to various stimuli, the pericardium produces prostaglandins that might play a role in neural regulation of cardiac electrophysiological properties by modulating epicardial nerve effects. We determined the effects of various epicardial superfusates on efferent cardiac responses, induced by bilateral efferent ansae subclaviae (SS) and cervical vagal (VS) stimulation, and afferent cardiac reflexes elicited by intracoronary injections of bradykinin (25 micrograms) and nicotine (50 micrograms). Pericardial instillation of arachidonic acid in normal Tyrode's solution (3 micrograms/ml) increased the concentration of pericardial prostacyclin (PGI2), measured by radioimmunoassay as the stable metabolite 6-keto-PGF1 alpha, and of prostaglandin E2 (PGE2). Arachidonic acid superfusion reduced SS-induced shortening of sinus cycle length (SCL), atrio-His interval (AH), and effective refractory period (ERP) of the right and left ventricular myocardium and prevented intra-aortic angiotensin II (30 ng/kg/min) from augmenting SS effects on these variables. Pericardial arachidonic acid plus indomethacin (1 microgram/ml) eliminated the prostaglandin increase and restored the responses of SCL, AH, and ERP to SS and to angiotensin II infusion. Pericardial PGE2 (30 or 50 ng/ml) or PGI2 (50 ng/ml) reversibly suppressed SS-induced shortening of SCL and ERP. Pericardial arachidonic acid or PGI2, however, did not blunt the shortening of ERP induced by intravenous infusion of norepinephrine. Pericardial arachidonic acid did not affect VS-induced lengthening of ERP or the duration of sinus arrest, or arterial blood pressure and heart rate responses to bradykinin or nicotine. We conclude that an increase in the concentration of prostaglandins in the pericardial fluid inhibits efferent sympathetic nerve effects on cardiac electrophysiological variables and antagonizes the facilitatory action of angiotensin II on efferent sympathetic stimulation by acting at presynaptic sites. Increased concentration of pericardial prostaglandins in response to various stimuli may constitute a physiological negative-feedback control mechanism that regulates efferent cardiac sympathetic stimulation.

Application of a new technique--blood pressure clamping--for analysis of prostaglandin interference with sympathetic neurotransmission in man

To circumvent baroreceptor reflexes following drug-induced interference sympathetic neurotransmission, a new technique - blood pressure clamping--has developed. This implies that the sympathetic activity in an awake human is 'clamped' at a supranormal level by infusion of a vasodilator. In 11 healthy volunteers nitroprusside or saline was randomly infused in two consecutive 2-h periods. Plasma and urinary catecholamine levels were analysed by liquid chromatography. The experiments were repeated after random administration of the prostaglandin synthesis inhibitor, ibuprofen, or placebo. In the basal state (no ibuprofen, saline infusion) the mean arterial blood pressure was 81.4 +/- 2.3 mmHg, the heart rate was 60.9 +/- 0.3 beats min-1 and the plasma level of noradrenaline was 1.12 +/- 0.15 nM. Infusion of nitroprusside at a dose lowering the mean blood pressure by 11.6 +/- 1.6 mmHg and increasing the heart rate to 74.6 +/- 2.9 beats min-1 elevated plasma noradrenaline to 2.86 +/- 0.39 nM. After pretreatment with ibuprofen (saline infusion), the systemic blood pressure, the heart rate, and the plasma and urinary levels of noradrenaline were unaffected in comparison to before drug (80.1 +/- 2.3 mmHg, 58.4 +/- 0.3 beats min-1 and 1.13 +/- 0.12 nM respectively). Infusion of nitroprusside at a rate lowering the blood pressure by 11.2 +/- 2.4 mmHg and increasing the heart rate to 74.4 +/- 0.5 beats min-1, elevated the plasma level of noradrenaline to 2.46 +/- 0.38 ng ml-1, which is not different from before ibuprofen. The amount of nitroprusside required to lower the blood pressure was not different in the presence and absence of ibuprofen.(ABSTRACT TRUNCATED AT 250 WORDS)

Indirect evidence for a role of prostaglandins as second messengers of the prejunctional effect of opioids in guinea-pig ventricular preparations

The cardiac response to adrenergic nerve stimulation was dose dependently reduced in a statistically significant manner by 1-10 microM dynorphin-(1-13) in isolated atria, and by 0.1-1 microM dynorphin-(1-13) in guinea-pig ventricular preparations. The inhibitory effect of dynorphin was maintained in atria that had been pretreated with two cyclooxygenase inhibitors at concentrations that induce an 80% inhibition of the enzyme, namely indomethacin 3 microM and acetylsalicylic acid 200 microM. The inhibitory effect of dynorphin disappeared in similarly pretreated ventricular preparations. These results suggest that, whilst the mediation of the effect of dynorphin is carried out mainly by specific opioid receptors in the atrial section, in the ventricular tissue it occurs through the endogenous prostanoid system.

Role of invading leukocytes in enhanced atrial eicosanoid production following rabbit left ventricular myocardial infarction

The isolated perfused hearts of rabbits previously subjected to in vivo left ventricular myocardial infarction (LVMI) show a 5-10-fold increase in f-Met-Leu-Phe (FMLP) and bradykinin (BK)-stimulated eicosanoid metabolite production relative to noninfarcted hearts. This exaggerated arachidonate metabolism has been shown to occur primarily in the cardiac atria, a site remote from the zone of injury and to be associated with a 10-15-fold increase in atrial FMLP receptor number in the absence of atrial inflammation. All of these changes were temporally related to leukocyte infiltration into the infarct zone. To determine whether invading leukocytes mediate these responses, acute inflammatory cell influx was suppressed either by inducing leukopenia with nitrogen mustard or by administration of BW-755C, a mixed cyclooxygenase-lipoxygenase inhibitor. Both pharmacological manipulations resulted in a decrease in inflammatory cells in the infarct zone and a marked suppression (50-70%) of ex vivo agonist-stimulated eicosanoid metabolite production from perfused hearts and isolated atria. These manipulations also resulted in reversal of ex vivo FMLP-induced coronary vasoconstriction as well as augmentation of BK-induced coronary vasodilation. Further studies in nitrogen mustard-treated animals revealed a suppression of the LVMI-stimulated increase in atrial FMLP receptor number. These data show that suppression of leukocyte invasion after LVMI attenuates enhanced cardiac and atrial eicosanoid metabolite production, and results in marked changes in coronary vascular reactivity. An additional finding was that basal and stimulated LTB4 production was markedly increased in infarcted hearts. In vivo suppression of the increase in LTB4 production by BW-755C was associated with inhibition of inflammatory cell influx into the infarct zone. It therefore appears that LTB4 may be an important proinflammatory mediator of leukocyte invasion after LVMI.

Effect of hypoxia on nerve-stimulation-induced release of noradrenaline from the rabbit heart

The present study addressed the hypothesis that cardiac production of adenosine (ADO) and/or prostacyclin (PGI2) during hypoxia is augmented to a level sufficient to affect nerve-stimulation-induced release of noradrenaline (NA). Innervated rabbit hearts were perfused at high (95% O2) or low (8% O2) oxygen pressure. The effluxes of NA and purines from the heart were determined by HPLC and that of the PGI2 metabolite by radioimmunoassay. Five minutes of hypoxia elevated effluent purines (sum of ADO, inosine, and hypoxanthine) from 1.1 microM to 6.2 microM, but did not affect the outflow of NA. The ADO receptor antagonists THEO (100-200 microM) and 8PSOT (100 microM) given during hypoxia increased the evoked outflow of NA by 77% (P less than 0.01) and 37% (P less than 0.05), respectively. Indomethacin (30 microM, a prostaglandin synthesis inhibitor) reduced the efflux of PGI2 metabolite by 93% but did not per se affect NA outflow during simultaneous administration of THEO, either under normoxia or hypoxia. It is concluded that ADO, but not PGI2, plays a role in reducing transmitter release during hypoxia. In addition, hypoxia leads to an enhancement of transmitter release, probably unrelated to ADO or purines. The lack of effect of hypoxia alone on evoked outflow of transmitter seems to be the result of a combination of these two processes.

Effect of adrenergic agonists on eicosanoid output from isolated rabbit choroid plexus and iris-ciliary body

Prostanoid production by rabbit choroid plexus (CP) and iris-ciliary body (ICB), and the effects of adrenergic agonists thereon, were studied in vitro. Immunoreactive prostaglandin (PG) E2 was the major prostanoid released by both tissues; the output from ICB was some two orders of magnitude greater than from CP. Immunoreactive 6-keto PGF1 alpha and thromboxane (TX) B2, the dehydration products of prostacyclin and TXA2, respectively, were detected in smaller quantities. Epinephrine stimulated the outputs of PGE2 and 6-keto PGF1 alpha, but not of TXB2, from both tissues. ICB responded to epinephrine concentrations of 10(-4) and 10(-5), while only 10(-4) was effective in stimulating prostanoid synthesis in the CP. Phenylephrine, an adrenergic agonist, stimulated prostanoid output from the ICB, but not from the CP. It is concluded that adrenergic mechanisms stimulate the biosynthesis of prostanoids in the rabbit CP and ICB. The implications of such interactions to aqueous humor and cerebrospinal fluid dynamics, or to other processes in brain and ocular physiology, are discussed.

Prostacyclin as neuromodulator in the sympathetically stimulated rabbit heart

Prostaglandin E2 (PGE2) has previously been shown to inhibit sympathetic neurotransmission in different organs and species. Based on this inhibitory effect and on its reversal by cyclo-oxygenase inhibitors, PGE2 has been claimed to be a physiological modulator of in vivo release of norepinephrine (NE) from sympathetic nerves. It is now recognized that prostacyclin (PGI2) is the main cyclo-oxygenase product in the heart. We therefore addressed the question whether PGI2, within the same preparation, is formed in increased amounts during sympathetic nerve stimulation and has neuromodulatory activity. The effluent from isolated rabbit hearts subjected to sympathetic nerve stimulation or to infusion of NE or adenosine (ADO) was collected, and its content of PGE2 and 6-keto-PGF1 alpha (dehydration product of PGI2) was analyzed using gas chromatography/mass spectrometry, operated in the negative ion/chemical ionization mode. Other hearts were infused with PGI2 and nerve stimulation induced outflow of endogenous NE into the effluent was analyzed using HPLC with electrochemical detection. Nerve stimulation at 5 or 10 Hz (before but not after adrenergic receptor blockade), as well as infusion of NE (10(-6)-10(-5)M) or ADO (10(-4)M) increased the cardiac outflow of 6-keto-PGF1 alpha. Basal and nerve stimulation induced efflux of 6-keto-PGF1 alpha was approximately 5 times higher than the corresponding efflux of PGE2. PGI2 dose-dependently inhibited the outflow of NE from sympathetically stimulated hearts, the inhibition at 10(-6)M being approximately 40%. On the basis of these observations we propose that PGI2 is a more likely candidate than PGE2 as a potential modulator of neurotransmission in cardiac tissue in vivo.

Study of the PG E2 synthetase activity of different regions of dog and rabbit hearts

Prostaglandin E2 synthetase activity of the microsomal fraction from different parts of dog and rabbit heart was tested with 3H-arachidonic acid as substrate. PG E2 synthesized was separated and purified by TLC and determined by the radiometric method or by bioassay. In the experimental conditions adopted, it was shown that the heart tissue is endowed with an enzyme system capable of synthesizing PG E2 but this PG E2 synthetase activity is not uniformly distributed in the different parts of the heart. It is highest in the right atrium and the activity of the atria is higher than that of the ventricles. It is species-dependent. The closely similar repartition of PG E2 synthetase activity and sympathetic nerve endings strongly suggests that PG E2 modulates adrenergic neurotransmission in the heart.

Role of prostaglandins in modulating sympathetic vasoconstriction in the cerebral circulation in anesthetized rabbits

The effects of the interaction between sympathetic nerves and prostaglandins in the cerebral circulation were examined. The hypothesis tested was that inhibition of prostaglandin synthesis by indomethacin would potentiate decreases in CBF caused by sympathetic nerve stimulation. In anesthetized rabbits, following administration of either indomethacin (10 mg/kg) or vehicle, CBF was measured with 15-micron microspheres prior to stimulation and following 3-5 min of electrical stimulation (4, 8, 16 Hz) of both superior cervical ganglia. In the vehicle group, CBF was 33-42 ml/min/100 g prior to stimulation. Bilateral sympathetic stimulation reduced blood flow to the cerebrum by 12 +/- 6% (mean +/- SEM) (p less than 0.05) at 4 Hz (n = 8), by 20 +/- 4% (p less than 0.05) at 8 Hz (n = 12), and 21 +/- 6% (p less than 0.05) at 16 Hz (n = 11). In the indomethacin group, CBF was 37-48 ml/min/100 g prior to stimulation. Bilateral stimulation decreased blood flow to the cerebrum by 7 +/- 5% (NS) at 4 Hz (n = 8), by 25 +/- 3% (p less than 0.05) at 8 Hz (n = 6), and by 20 +/- 6% (NS) at 16 Hz (n = 6). Decreases in CBF during nerve stimulation were blocked by prazosin, an alpha-adrenergic antagonist. In additional experiments, cerebral vascular constrictor responses to hypocapnia were found to be similar in the vehicle and indomethacin groups. This study provides evidence that sympathetic nerves can decrease CBF substantially even at low stimulation frequencies. Further, results of this study indicate that prostaglandins do not attenuate the effects of sympathetic stimulation on the cerebral circulation.

Effects of CL 115,347, (+/-)-15-deoxy-16-hydroxy-16-vinyl-PGE2 methyl ester, on cardiovascular responses and plasma catecholamines in pithed stroke-prone spontaneously hypertensive rats during sympathetic stimulation

The effect of CL 115,347, a topically active antihypertensive PGE2 analog, and PGE2 on changes in blood pressure (BP), heart rate (HR) response and plasma epinephrine (E) and norepinephrine (NE) levels induced by stimulation of the sympathetic spinal cord outflow were studied in pithed stroke-prone spontaneously hypertensive rats (SHRSP). Surgical pithing significantly reduced plasma E but not NE levels suggesting that the sympathoadrenal medullary system differentially affects E and NE release. Sympathetic stimulation of the spinal cord of pithed SHRSP increased HR, BP, plasma E and NE levels. Topically applied CL 115,347 (0.001-0.2 mg/kg) dose-dependently decreased BP, while intravenously infused PGE2 (30 micrograms/kg/min) did not alter BP except for a brief initial drop. Topical application of CL 115,347 (0.1 mg/kg) also inhibited BP responses to sympathetic stimulation without effects on HR or plasma E or NE levels. Intravenous infusion of PGE2 (30 micrograms/kg/min) inhibited both BP and HR responses to spinal cord stimulation but did not alter plasma catecholamine levels. These studies in SHRSP suggest that CL 115,347 and PGE2 modulate cardiovascular responses mainly via postjunctional effects, but act differently on the cardiovascular elements, viz. CL 115,347 acts primarily on blood vessels while PGE2 acts on blood vessels and heart.

Conflicting effects of noradrenaline on ciliary movement of frog palatine mucosa

The effects of noradrenaline on ciliary movement of frog palatine mucosa were investigated using the particle transport method. Prostaglandins and cyclic AMP concentrations in the mucosa were determined by radioimmunoassay. Concentrations of noradrenaline below 10(-7) M suppressed ciliary movement by about 40% as compared to the control level. The changeover from inhibition to acceleration of ciliary movement occurred at 10(-7) M noradrenaline. Ciliary movement was markedly accelerated by concentrations of noradrenaline over 2 X 10(-6) M. This acceleration was eliminated in the presence of inhibitors of prostaglandin biosynthesis such as indomethacin (14 microM) and aspirin (25 microM). The acceleration was not eliminated by an inhibitor of thromboxane A2 biosynthesis (OKY-1555). On the other hand, E type prostaglandin release was increased about 8 fold of control by treatment with 5 X 10(-5) M noradrenaline, while F type prostaglandin release was not affected by the treatment with 5 X 10(-5) M noradrenaline. Ciliary movement was markedly accelerated when prostaglandin E1 was administered. The concentration of cyclic AMP was increased about 2.1 fold by treatment with 5 X 10(-5) M noradrenaline. The possible mechanism of the effects of noradrenaline on ciliary movement is discussed in the light of these results.

The interactions of prostaglandins with the sympathetic nervous system--a review

In most isolated tissues, prostaglandins, particularly of the E-series, inhibit stimulated norepinephrine release from prejunctional nerve endings and inhibit sympathetic neurotransmission. They may also modulate the response of target organs to the neurotransmitter. In some tissues PGE enhances the response to norepinephrine. It appears that the effect of PGE on norepinephrine release is mediated by restriction of calcium availability at the nerve ending, although this mechanism is incompletely understood. Prostaglandins other than PGE do not appear to play a major role in the modulation of norepinephrine release. In the intact organism, prostaglandins facilitate norepinephrine release. Inhibition of prostaglandin synthesis causes a decrease in norepinephrine release. It is not clear if the effects in vivo are mediated by a direct action of prostaglandins or through baroreceptor reflex mechanisms.

Prostaglandin-mediated inhibition of noradrenaline release. VII. Effect of indomethacin on some cardiovascular reflexes in man

The effect of indomethacin, a prostaglandin (PG) synthesis inhibitor, on some cardiovascular reflexes was studied in healthy subjects. Heart rate (HR) and respiratory sinus arrhythmia (RSA) in the basal state and during carotid stimulation (neck suction), Valsalva ratio, and changes in heart rate and blood pressure (BP) during an orthostatic test were measured before and one hour after administration of indomethacin (1.5 mg/kg). The efficacy of the PG synthesis inhibitor was monitored by analysis of platelet aggregation induced by arachidonic acid. Following indomethacin no change was observed in basal HR. Carotid stimulation depressed the HR and this effect was of the same amplitude before and after indomethacin. The amplitude of RSA was not affected by indomethacin, either in the basal state or during carotid stimulation. The Valsalva ratio and the changes in HR and BP during the orthostatic test were similar before and after the drug. Circulating levels of noradrenaline were unaffected by indomethacin. These data demonstrate that inhibition of PG bioformation in man does not affect major cardiovascular reflexes. Consequently they disfavour the hypothesis that endogenously formed PG would be involved in the normal activity of the afferent, central or efferent pathways for cardiovascular regulation.

Renal effects of pinane-thromboxane A2 and indomethacin in saline volume-expanded spontaneously hypertensive rats

In 6-week old spontaneously hypertensive rats (SHR), indomethacin (5 mg/kg i.v.) and pinane-thromboxane A2 (PTA2) (50 micrograms/kg per h i.v.) a thromboxane A2 (TXA2) antagonist as well as a TXA2 synthetase inhibitor, resulted in natriuresis accompanied by an increase in p-aminohippuric acid and inulin clearances. Indomethacin acted as an antidiuretic in 6 week Wistar-Kyoto rats (WKY). PTA2 did not alter renal functions in either 6 week WKY and 18 week SHR. Basal urinary excretion of TXB2 (UTXB2V) was greater in 6 week SHR than in 6 week WKY and 18 week SHR, and that of 6-keto-PGF1 alpha (U6-keto-PGF1 alpha V) did not differ among these strains. Thus, U6-keto-PGF1 alpha V/UTXB2V was lower in the 6 week SHR. Basal urinary excretion of PGE (UPGEV) was much greater in 18 week SHR than in the 2 other groups. In the 6 week SHR, PTA2 decreased UTXB2V and increased U6-keto-PGF1 alpha V without affecting UPGEV, and indomethacin reduced UTXB2V more markedly than did U6-keto-PGF1 alpha V and UPGEV. Thus, both PTA2 and indomethacin increased U6-keto-PGF1 alpha V/UTXB2V in the 6 week SHR. These findings indicate that a disequilibrium in the biosynthesis of vasoconstrictive TXA2 and of vasodilator PGI2 may be involved in water and sodium retention in SHR during the developmental phase of hypertension.

Modulation by prostaglandins of the release of [3H] noradrenaline evoked by potassium and nerve stimulation in the isolated rat heart

In the isolated rat heart perfused with Krebs solution and prelabeled with [3H] noradrenaline, we examined the effect of prostaglandins (PG) I2, E2, 6-keto-PGF1 alpha and their precursor, arachidonic acid, on the overflow of tritium elicited by potassium (K+) and by stimulation of cardiac sympathetic nerve plexus. Prostaglandins E2, I2 and arachidonic acid but not 6-keto-PGF1 alpha reduced K+ and nerve stimulation-induced overflow of tritium. Administration of indomethacin, an inhibitor of cyclooxygenase, increased tritium overflow elicited by either K+ or by nerve stimulation. During infusion of indomethacin, the inhibitory effect of both PGE2 and PGI2 on the K+ or nerve stimulation-induced overflow of tritium remained unaltered. In contrast, the effect of arachidonic acid to reduce K+ or nerve stimulation-induced overflow of tritium was abolished by indomethacin, indicating that the fatty acid inhibits release of tritium by its conversion to a product(s) of cyclooxygenase, presumably PGI2 and PGE2. These data suggest that prostaglandins, particularly PGI2 and PGE2 synthesized in the isolated rat heart act on prejunctional sites to modulate release of the adrenergic transmitter.

Coronary vasoconstrictor and vasodilator actions of arachidonic acid in the isolated perfused heart of the rat

The administration of arachidonic acid (AA) to the isolated perfused heart of the rat usually produced biphasic coronary responses characterized by initial vasoconstriction followed by prolonged vasodilatation. However, some responses were predominantly vasoconstrictor or vasodilator. The non-steroidal anti-inflammatory agents (NSAA) indomethacin (1-5 mg/l) and naproxen (12.5-25 mg/1) reversibly inhibited both phases of the response induced by AA. Pretreatment of animals with indomethacin (5 mg/kg) or naproxen (25 mg/kg) daily, resulted in unaltered coronary response to AA. Subsequent addition of NSAA to the perfusate produced inhibition of the AA effect. Short infusions of acetylsalicylic acid at low concentrations (2.9 micrograms/ml), dipyridamole (0.6 micrograms/ml) and sulphinpyrazone (28.7 micrograms/ml) selectively inhibited the vasoconstrictor phase of the response to AA. It was confirmed that metabolic coronary dilatation induced by cardiostimulation was inhibited by prolonged AA administration; this effect was prevented by NSAA pretreatment. Reactive hyperaemic responses to short lasting occlusions of coronary inflow were unaffected by NSAA. Linolenic, linoleic, dihomo-gamma-linolenic and oleic acid usually produced decreases in coronary flow which were unaffected by NSAA, dipyridamole or sulphinpyrazone. Intra-aortic injections of AA, prostacyclin (PGI2) and prostaglandin E2 (PGE2) in the intact rat produced a dose-dependent decrease in blood pressure with the AA response inhibited by indomethacin. PGI2 and PGE2 produced long lasting coronary vasodilatation in the isolated heart. The coronary actions of AA appear to be due to its transformation, within the easily accessible vascular wall, into prostaglandin and thromboxane-like substances. We suggest that a vasoconstrictor thromboxane A2-like substance may be responsible for coronary vasospasm. Coronary insufficiency may also result from an inhibition of compensatory metabolic coronary dilatation by increased synthesis of PGE2 within the myocardial cell.

Sympathetic effects on cerebral and ocular blood flow in rabbits pretreated with indomethacin

The effects of unilateral stimulation of the cervical sympathetic chain on cerebral and ocular blood flow was investigated in 8 rabbits anesthetized with pentobarbital sodium and pretreated with indomethacin in order to inhibit the formation of prostaglandins. Blood flow determinations were made with the labelled microsphere method during normotension and acute arterial hypertension. Hypertension was induced by ligation of the thoracic aorta. Evans blue was given as a tracer for protein leakage during hypertension. Sympathetic stimulation had no significant effect on the blood flow in the brain under the two conditions studied. In the uvea marked effects of sympathetic stimulation were obtained at normotension as well as at hypertension. There were no indications of breakdown of the blood-brain barrier or the blood-aqueous barrier. Thus, there was no evidence for any prostaglandin-mediated inhibition of sympathetic effects in the brain or the eye.

Stimulation of prostaglandin synthesis in rat cerebral cortex via a beta-adrenoceptor

1. Synthesis of prostaglandin E2 (PGE2) and prostaglandin F2 alpha (PGF2 alpha) in rat cerebral cortex slices is increased by beta-adrenoceptor agonists. 2. Phenylephrine, an alpha-adrenoceptor agonist, has no effect while oxymetazoline increased PGF2 alpha only. 3. PG synthesis stimulation by noradrenaline (NA) was prevented by beta- but not by alpha-adrenoceptor antagonists. 4. Dibutyryl cyclic AMP and inhibitors of cyclic nucleotide phosphodiesterase augment PG synthesis. 5. Stimulation of PG synthesis in rat cerebral cortex by NA is mediated by a beta-adrenoceptor.

The effect of sulfinpyrazone on the response to sympathetic nervous system stimulation

The purpose of this study was to determine if sulfinpyrazone has a direct action on sympathetic nerve endings to prevent release of the transmitter. Pre-synaptic and post-synaptic events as well as direct sympathetic nervous system stimulation were tested in 15 alpha-chloralose anesthetized cats before and 1 hour after sulfinpyrazone (100 mg . kg-1, i.v.). Heart rate response to cardiac accelerator nerve stimulation or to increasing doses of isoproterenol was not significantly depressed by sulfinpyrazone. In addition, no alteration in the reflex activation of the sympathetic nervous system in response to histamine was observed following sulfinpyrazone. Both norepinephrine and epinephrine levels were similar to those levels reported previously by Smith and Robinson for (7) untreated cats. We conclude sulfinpyrazone has no direct depressing effect on the sympathetic nerve endings and that this mechanism cannot explain the reported beneficial effect of sulfinpyrazone on coronary occlusion induced arrhythmias.

Effects of indomethacin, naproxen and paracetamol on regional blood flow in rabbits: a microsphere study

Ulcerogenic side-effects and prostaglandin-synthesis-inhibiting capacity are well documented in indomethacin treatment. According to recent works, indomethacin reduces gastrointestinal blood-flow. Naproxen and paracetamol, claimed to be prostaglandin-synthesis-inhibitors, have few ulcerogenic side effects. In an attempt further to study the indomethacin effects and to reveal whether naproxen and paracetamol have similar effects, the labelled microsphere technique was used. The regional blood flow determinations were made before, and 12-15 min. after, the injection of the drugs. Indomethacin 3 mg/kg, reduced gastrointestinal blood flow and increased arterial blood flow to the liver. Naproxen, 10 mg/kg, and paracetamol, 25 mg/kg, had no effects except for a very small decrease in liver blood flow with paracetamol. The results strongly suggest that, at least under light general anaesthesia, prostaglandins influence resting blood flow in the gastrointestinal tract, the liver and parts of the brain. The results more raise doubts whether naproxen and paracetamol inhibit prostaglandin synthesis in these tissues. These data offer a plausible explanation as to why naproxen and paracetamol are usually well tolerated in the gastrointestinal tract. None of the drugs tested influenced resting blood flow in muscles, tendons, bones, joints or synovial membranes.

Role of the prostaglandin in norepinephrine release during augmented renal sympathetic nerve activity in the dog

To determine the role of the prostaglandins on renal norepinephrine release, the effect of inhibition of prostaglandin synthesis was examined in anesthetized dogs during reflex activation of the renal adrenergic nerves. Hypotension increased the renal vein plasma concentrations of norepinephrine from 380 +/- 59 to 608 +/- 106 pg/ml (mean +/- SEM; P less than 0.01) and of PGE2 from 55 +/- 7 to 81 +/- 41 pg/ml (P less than 0.05). Subsequent administration of indomethacin or meclofenamate lowered the renal venous concentration of PGE2 to 26 +/- 3 pg/ml (P less than 0.01), had no significant effect on the norepinephrine concentration (620 +/- 89 pg/ml). Administration of indomethacin or meclofenamate to dogs with sodium depletion lowered renal venin plasma concentration of PGE2 from 108 +/- 40 to 20 +/- 3 pg/ml (0.05 less than P less than 0.1) but had no effect on the renal venous norepinephrine concentration (475 +/- 50 vs. 397 +/- 46 pg/ml). In dogs fed a normal salt diet, inflation of a balloon placed in the thoracic inferior vena cava lowered cardiac output and increased the renal venous concentrations of norepinephrine from 212 +/- 60 to 496 +/- 112 pg/ml (P less than 0.01) and of PGE2 from 28 +/- 5 to 96 +/- 18 pg/ml (P less than 0.01). Subsequent administration of indomethacin lowered the renal venous concentration of PGE2 to 16 +/- 5 pg/ml (P less than 0.01), but had no significant effect on the concentration of norepinephrine (548 +/- 91 pg/ml). During the three experimental conditions examined, renal blood flow was lowered by inhibition of prostaglandin synthesis. These results in the dog suggest that the attenuating effect that prostaglandins exert on the renal vascular action of the adrenergic nerves is not due to inhibition of norepinephrine release.

Effect of PGD2, PGE2 PGF2 alpha and PGI on blood pressure, heart rate and plasma catecholamine responses to spinal cord stimulation in the rat

The following experiments were designed in order to examine the inter-relationships of various prostaglandins (PG's) and the adrenergic nervous system, in conjunction with blood pressure and heart rate responses, in vivo. Stimulation of the entire spinal cord (50v, 0.3-3 Hz, 1.0 msec) of the pithed rat increased blood pressure, heart rate and plasma epinephrine (EPI) and norepinephrine (NE) concentration (radioenzymatic-thin layer chromatographic assay). Infusion of PGE2 (10-30 microgram/kg. min, i.v.) suppressed blood pressure and heart rate responses to spinal cord stimulation while plasma EPI (but not NE) was augmented over levels found in control animals. PGI2 (0.03-3.0 microgram/kg. min, i.v.) suppressed the blood pressure response to spinal cord stimulation without any effect on heart rate or the plasma catecholamine levels, PGE2 and PGF2 alpha (10-30 microgram/kg. min, i.v.) did not change the blood pressure, heart rate or plasma EPI and Ne responses to the spinal cord stimulation although PGF2 alpha disclosed an overall vasopressor effect during the pre-stimulation period. At the pre-stimulation period it was also observed that PGE2, PGF2 alpha and PGI2, had a positive chronotropic effect on the heart rate, the cardiac accelerating effect of PGE2 was not abolished by propranolol. These in vivo studies suggest that in the rat, PGE2 and PGI2 modulate sympathetic responses, primarily by interaction with the post-synaptic elements - PGE2 on both blood vessels and the heart and PGI2 by acting principally on blood vessels.

Differential inhibitory effects of the arachidonic acid analog ETYA on rat mast cell exocytosis evoked by secretagogues utilizing cellular or extracellular calcium

ETYA (5,8,11,14-eicosatetraynoic acid; 50-100 microM), which inhibits both cyclo-oxygenase and lipoxidase, inhibited histamine release evoked by secretagogues dependent on extracellular calcium (antigen, dextran, and concanavalin A) but failed to inhibit secretion elicited by secretagogues capable of mobilizing calcium from intracellular sites (48/80, polymyxin B, protamine sulfate and poly-L-lysine). Responses to these latter secretagogues were inhibited only by higher concentrations of ETYA (100-200 microM) that were cytotoxic. Secretion evoked by the calcium ionophore A23187 (0.1 microgram/ml) was inhibited at much lower concentrations of ETYA (1-10 microM) but this inhibition could not be overcome by increasing the concentration of calcium. Responses to higher concentrations of ionophore were not inhibited by ETYA except in amounts affecting cell viability. Like ETYA, each of several fatty acids, including arachidonic acid, were inhibitory towards histamine release evoked by A23187 or 48/80. The results indicate that EYTA acts at some early stage of stimulus-secretion coupling rather than on the final, common, calcium-activated steps of exocytosis. Moreover, this action may be unrelated to inhibition of lipoxidase or cyclooxygenase.

Modulation of autonomic neurotransmission by PGD2: comparison with effects of other prostaglandins in anesthetized cats

Experiments with anesthetized cats were done to study possible roles of different prostaglandins (PGs) in modulating sympathetic neuroeffector transmission. We recorded contractions of the nictitating membrane (n.m.), blood flow in the carotid artery, heart rate and blood pressure, both under control conditions and while stimulating the cut cervical sympathetic nerve. Intra-carotid arterial injection (i.a.) of PGD2 depressed sympathetic transmission to the n.m. without depressing the effects of exogenous norepinephrine (NE). In contrast, PGE2 enhanced the effects of nerve transmission or exogenous NE on the stimulated n.m. PGI2 had similar but shorter effects to PGE2. PGF2 alpha or a stable PGH2 analog, contracted the n.m. smooth muscle with no detected effect on nerve transmission. Carotid blood flow was increased by PGD2, PGE2 and PGI2. PGD2 and PGI2 caused bradycardia that could be blocked by atropine. This ability of PGD2 to modulate autonomic nerve activity is of particular interest because of recent reports that nerve tissue synthesizes PGD2.

Effects of prostaglandins and indomethacin on neuromuscular blocking agents

The effects on neuromuscular blockade by d-tubocurarine and succinylcholine of inhibition of prostaglandin biosynthesis by indomethacin and of intra-arterial administration of prostoglandins E2 and F2 alpha, before and after inhibition of prostoglandin biosynthesis, were evaluated in the cat sciatic-tibialis preparation. Non-specific inhibition of prostaglandin biosynthesis by indomethacin 3 mg . kg-1 did not alter latency, maximal blockade or duration of neuromuscular blockade induced by d-tubocurarine or succinylcholine. Prostaglandin E2 antagonized twitch height depression by d-tubocurarine by an average of six per cent before and by 15% after indomethacin, but potentiated the neuromuscular block of succinylcholine by an average of five per cent before and 60% after indomethacin. Prostaglandin F2 alpha antagonized d-tubocurarine neuromuscular block by an average of 10% before and 18% after indomethacin, but potentiated succinylcholine block by an average of four per cent before and 12% after indomethacin. These results suggest that non-specific inhibition of prostaglandin biosynthesis alone does not influence d-tubocurarine or succinylcholine induced neuromuscular blockades. However, both prostaglandin E2 and F2 alpha may induce transmitter release at the neuromuscular junction that may be enhanced by indomethacin, thus antagonizing the non-depolarizing blockade of d-tubocurarine and potentiating the depolarizing blockade of succinylcholine.

Plasma catecholamines in man are not influenced by the inhibition of prostaglandin synthesis

Indomethacin has been reported to potentiate the release of noradrenaline from sympathetic nerve endings in vitro and to increase urinary noradrenaline excretion in rats. We have studied the influence of indomethacin on plasma catecholamine levels in 10 normal men, using measurement of plasma renin activity (PRA) as an index of the pharmacodynamic effect of indomethacin. Both in the supine and standing positions indomethacin failed to alter the plasma concentrations of noradrenaline, adrenaline or dopamine, while PRA was markedly suppressed. It is concluded that in the intact human indomethacin does not influence catecholamine concentrations.

Effects of indomethacin on regional blood flow in conscious rabbits--a microsphere study

In an attempt to reveal the importance of prostaglandins in the control of regional blood flow 20 mg/kg b.wt. indomethacin was given i.v. in conscious resting rabbits. Regional blood flow determinations were made before and 20 min after the injection using the labelled microsphere technique. The blood flow in the stomach wall was reduced by 0.75 +/- 0.17 g . min-1 . g-1 from a level of 1.64 +/- 0.24 g . min-1g-1. In jejunum the corresponding figures were 0.44 +/- 0.12 and 1.26 +/- 0.17 and in the brain 0.29 +/- 0.10 and 1.24 +/- 0.10. The blood flow in the liver via the hepatic artery increased by 0.20 +/- 0.02 g . min-1 . g-1 from a level of 0.13 +/- 0.02 g . min-1 . g-1. In the retina there was a reduction in blood flow by 2.75 +/- 1.03 mg . min-1 from a starting level of 15.1 +/- 2.3 mg . min-1. In a number of other tissues investigated there were no significant effects of the drug. The results suggest that under resting conditions prostaglandins play a role in the control of blood flow in the gastrointestinal tract, the brain and the retina--tissues which are likely to be rather active under such conditions.

The effect of 5,8,11,14-eicosatetraynoic acid on lipid metabolism

The purpose of this presentation is to review the current state of knowledge regarding 5,8,11,14-eicosatetraynoic acid (ETYA, Ro 3-1428) and its effects on lipid metabolism. Accordingly, the topics discussed include hypocholesterolemic and dermatological studies involving ETYA in both animals and man, as well as the effects of ETYA on desaturase enzymes. Metabolic studies involving ETYA are also noted. Primary interest is focused on the effects of ETYA on selected processes of arachidonate metabolism, and the effect of ETYA on inflammation, platelet aggregation and tumor growth are discussed, keeping in mind the relevance of arachidonate metabolism to these processes.

Myocardial synthesis of prostaglandin-like substances and coronary reactions to cardiostimulation and to hypoxia

1 Continuous recording of cardiac contractions and coronary flow from isolated perfused hearts of rats permitted the study of coronary reactions to: (a) cardiostimulation induced by single doses or slow infusions of noradrenaline, CaCl2, glucagon or electrically induced tachycardia; (b) short interruptions of coronary inflow (hypoxia). 2 Except during tachycardia the heart rate was kept constant at 210 beats/min by electrical pacing. 3 Metabolic coronary vasodilatation (MCD) resulting from cardiac hyperactivity induced by noradrenaline, Ca2+, tachycardia or glucagon was inhibited by administration of prostaglandin E2. Reactive hyperaemia response to hypoxia was unaffected by prostaglandin administration. 4 Inhibition of MCD could also be obtained by prolonged infusion with arachidonic acid (1.6 X 10(-7) M), presumably by its conversion into prostaglandin-like substance since arachidonic acid failed to block MCD in hearts from rats pretreated with non-steroidal anti-inflammatory drugs (indomethacin, naproxen, phenylbutazone). 5 Reactive hyperaemia was unaffected either by arachidonic acid or by blockade of the synthesis of prostaglandin-like substances by anti-inflammatory drugs. 6 Since prostaglandin synthetase inhibition does not prevent but may enhance MCD, we do not advocate prostaglandin-like substances as agents directly responsible for the coronary vasodilatation that follows cardiac hyperactivity. 7 We postulate that cardiac overproduction of prostaglandins may lead to a failure in the adaptive coronary flow response to cardiac hyperactivity (coronary insufficiency?).

Prostaglandin-mediated inhibition of noradrenaline release: V. A comparison of the neuroinhibitory effect of three prostaglandins: E2, I2, and 6-keto-PGF1alpha

The effect of PGE2, PGI2, and 6-keto-PGF1alpha respectively on the contractile response of the isolated, field-stimulated guinea pig vas deferens was investigated. All three PGs were capable of inhibiting the contractile responses of the vas deferens, but the concentrations required varied considerably: PGE2 was about 700 times more active than PGI2 and about 4600 times more active than 6-keto-PGF1alpha in this respect. It is suggested that PGI2, although formed in tissues with sympathetic innervation, does not play a physiological role as inhibitor of sympathetic transmitter release.

Effects of prostaglandin E2 and a prostaglandin endoperoxide analogue on neuroeffector transmission in the rat anococcygeus msucle

1 Investigations were made into the effects of prostaglandin E(2) (PGE(2)) and a prostaglandin endoperoxide analogue (Upjohn compound U-46619) on the responses of the rat anococcygeus muscle to field stimulation of the intrinsic sympathetic nerves, and to exogenous noradrenaline. The effects of PGE(2) on responses to stimulation of intrinsic inhibitory nerves were also studied.2 PGE(2) (5.6 x 10(-8) or 2.8 x 10(-6) mol/l) decreased motor (sympathetic) responses to field stimulation at all frequencies tested (2 to 24 Hz). The prostaglandin also reduced the inhibitory responses to field stimulation, seen when the tone of the preparation had been raised and its sympathetic innervation had been blocked by guanethidine. However, these inhibitory responses were also reduced by other spasmogens (carbachol and 5-hydroxytryptamine) which, like PGE(2), further increased the tone of guanethidine-treated preparations.3 At a concentration of 5.6 x 10(-8) mol/l, PGE(2) had no effect on responses to noradrenaline, whereas at a fifty-fold higher concentration the prostaglandin potentiated these.4 Unlike PGE(2), U-46619 (5.6 x 10(-8) mol/l) greatly potentiated motor responses to field stimulation, at frequencies from 0.75 to 24 Hz. This effect did not represent a specific facilitation of sympathetic neurotransmission, as responses to carbachol and 5-hydroxytryptamine, as well as to noradrenaline, were also potentiated.5 The results are discussed in relation to the effects of prostaglandins and prostaglandin endoperoxides on neuroeffector transmission in other sympathetically innervated tissues. It is concluded that PGE(2) inhibits sympathetic neurotransmission in the rat anococcygenus muscle by a prejunctional action, whereas the predominant effect of U-46619 is direct excitation of the muscle. The effect of PGE(2) on inhibitory responses to field stimulation may represent an interference with inhibitory neuroeffector transmission in this tissue, or may simply be a consequence of the spasmogenic action of the prostaglandin.

The neuronal origin of prostaglandin released from the rabbit portal vein in response to electrical stimulation

Transmural electrical stimulation of the isolated portal vein of the rabbit was accompanied by the release of a prostaglandin-like substance (PLS). Thin layer chromatography coupled with bioassay indicated that this substance was probably prostaglandin E2 (PGE2). 2 Indomethacin potentiated the response of the portal vein to electrical stimulation at 2 Hz and abolished the release of the PLS. 3 There was no significant change in the amount of PLS released from the portal vein in response to electrical stimulation at 2 Hz when the contractile response of the portal vein was prevented by pretreatment with phentolamine or guanthidine. 4 In vitro denervation of the portal vein with 6-hydroxydopamine or the omission of Ca2+ from the bathing solution caused a significant reduction in the amount of PLS released from the portal vein in response to electrical stimulation at 2 hertz. 5 It is concluded that electrical stimulation of the isolated portal vein of the rabbit is accompanied by the release of a PLS, probably PGE2, from a neuronal source. The synthesis and release of the PLS is Ca2+ -dependent.

Prostaglandin-mediated inhibition of noradrenaline release: II. Dual mechanism behind its frequency-dependence

Sympathetically innervated, isolated rabbit hearts were perfusated according to Langendorff and the nerves were stimulated at 2, 5 or 10 Hz by equally long trains of pulses. The outflows of prostaglandin-like substances (PLS) and of noradrenaline (NA), induced by the nerve stimulations, were followed. The sensitivity of the process of NA release to exogenous PGE1 (2--6 X 10--8 M) at 2, 5 and 10 Hz was assayed. The outflow of PLS was found to be frequency-dependent, being greater at 2 Hz than at higher discharge rates, while the outflow of NA was similar at the different frequencies. The inhibitory action of PGE1 on the NA release process was more pronounced at 2 than at 10 Hz. It is concluded that the frequency-dependence of the endogenous PGE-mediated inhibition of the release of NA from discharging sympathetic nerves is based on 2 independent, frequency-related mechanisms: a) a higher synthesis rate of PLS/impulse, and b) a more pronounced sensitivity of the process of NA release, at low compared to higher impulse frequences.