Augmented noradrenaline release following nerve stimulation after inhibition of prostaglandin synthesis with indomethacin

Ibuprofen fails to increase plasma growth hormone levels in humans

In eight healthy volunteers, basal and arginine-stimulated plasma glucose and growth hormone levels were determined during administration of a placebo and after 3 days of ibuprofen (800 mg four times daily). Ibuprofen had no significant effect on basal or stimulated plasma glucose or growth hormone levels. As is not the case with indomethacin, ibuprofen fails to increase basal and arginine-stimulated plasma growth hormone levels. This suggests that the effect of indomethacin on growth hormone secretion is due to a mechanism unrelated to inhibition of prostaglandin synthesis.

Myocardial prostacyclin and thromboxane A2 synthetase activities during ischemia and reperfusion in isolated rabbit heart

The aim of the study was to determine the prostacyclin (PGI2) and thromboxane A2 (TXA2) synthetase activities of myocardial tissue and their variation during ischemia and reperfusion. Regional ischemia was induced by 10 min occlusion of the left anterior descending coronary artery in isolated Langendorff rabbit hearts. Biosynthesis of PGI2 and TXA2 were carried out by using arachidonic acid as substrate and left ventricle microsomes (LVM) from ischemic and non-ischemic areas as sources of PGI2 and TXA2 synthetase. 6-keto-PGF1 alpha and TXB2, stable metabolites of PGI2 and TXA2 respectively, were determined by radioimmunoassay. Experiments carried out under the adopted conditions showed that LVM were able to synthetise PGI2 as well as TXA2 from arachidonic acid. On the other hand, ischemia depressed both PGI2 and TXA2 synthetase activities of cardiac tissue: the depression was more pronounced on TXA2 synthetase than on PGI2 synthetase with no significant difference between ischemic and non-ischemic regions. Moreover, ischemia increased the ratio 6-keto-PGF1 alpha/TXB2 indicating therefore that it can facilitate the formation of PGI2. The post ischemic reperfusion of the heart counteracted the decrease in PGI2 synthetase induced by ischemia which returned to the normal level: reperfusion also slightly reversed the decrease in TXA2 the decrease in TXA2 synthetase. However, the diminution in TXA2 synthetase of non-ischemic myocardium was attenuated but it remained lower than the normal level. These results suggested that the whole left ventricle is affected by regional ischemia. Furthermore it appears that myocardial TXA2 synthetase is more vulnerable than PGI2 synthetase to a lack of oxygen and nutrients.

Indomethacin increases plasma growth hormone levels in man

In seven normal volunteers, the basal and arginine-stimulated levels of plasma growth hormone, glucose, glucagon, and free fatty acids and serum insulin was determined during placebo and during indomethacin 25 mg four times daily. Basal plasma growth hormone was higher during indomethacin (5.4 +/- 1 vs 1.7 +/- 2 ng/ml, p less than 0.005), as was the mean integrated response to intravenous arginine (40 +/- 14 vs 6 +/- 4 ng.min/ml, p less than 0.05). Despite lack of effect on plasma glucagon, indomethacin decreased the insulin response to arginine. The fall in free fatty acids during arginine infusion was decreased by indomethacin, which may in part be due to increased plasma growth hormone levels. In view of the many patients treated with indomethacin, the effect on growth hormone may be of clinical importance.

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.

Comparative effects of some 3-amino 4,6-diarylpyridazines on the biosynthesis in vitro of TXA2 and PGI2- and on the TXA2- and PGI2-synthesizing activities of cardiac tissue

Some 3-amino 4,6-diarylpyridazine derivatives were tested for their effects on TXA2 and PGI2 biosyntheses in vitro and on the TXA2- and PGI2-synthesizing activities of cardiac tissue. Horse platelet and aorta microsomes were used as sources of thromboxane and prostacyclin synthetases respectively. The TXA2- and PGI2-synthesizing activities of cardiac tissue were studied on isolated perfused rabbit hearts (the heart microsomes being used both as TXA2 synthetase and PGI2 synthetase sources). TXB2 and 6-keto PGF1 alpha were determined by RIA. Among the compounds under study, 3-morpholino 4,6-diphenylpyridazine (III) was shown to inhibit specifically the TXA2 synthetase. Substitution of the morpholino group by a dimethylamino one (I) reinforced the inhibiting effects on TXA2 synthetase but it also revealed a slight anti-prostacyclin synthetase action of the molecule. Replacement of 3-morpholino moieties by either a 3-hydrazino (IV), or a 2-dimethylaminoethylamino (V), or a 2-morpholinoethylamino group (VI) abolished completely the effects of the molecule on TXA2 and PGI2 synthetases. Likewise the addition of chlorine on the para-position on the phenyl ring of I neutralized all its inhibitory effects both on TXA2 and PGI2 synthetases in vitro. None of the 3-amino 4,6-diarylpyridazine derivatives was active on either the TXA2- or PGI2-synthesizing activities of cardiac tissue.

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)

Taurine and icosanoids in the heart

Experiments were carried out on non-working isolated rabbit hearts perfused by Tyrode solution: the effects of Taurine introduced into the coronary circulation were studied on the biosynthesis of the anti-thromboxane synthetase factor ("FATS") and on the TXA2 and PGI2 synthetase activities of cardiac tissue. The effects of Taurine were simultaneously studied on the biosynthesis of TXA2 and PGI2 in vitro. Experiments performed under the adopted conditions have shown that in vitro Taurine did not significantly modify the biosynthesis of TXA2 and PGI2; ex vivo Taurine did not change the biosynthesis of "FATS" but inhibited both TXA2 and PGI2 synthetase activities of the cardiac tissue: Taurine was more active on the TXA2 synthetase activity than on the PGI2 one. Thus Taurine promoted the formation of vasodilator and antiaggregating PGI2 at the expenses of vasoconstrictor and proaggregating TXA2. This could at least partly explain the beneficial effects of Taurine in the physiopathology of the heart.

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.

Comparative study of the biosynthesis of PGE2, PGF2 alpha and TXA2 by different organs of genetically hypertensive (SHR) and obese-hypertensive (SHR-fa/fa) rats

As an experimental model, we used 6-week-old genetically obese-hypertensive rats (SHR-fa/fa) which were obtained by transferring the fatty/fa gene of hyperlipaemic obese rats into the genome of the SHR strain: the SHR-fa/fa were bigger and more hypertensive than their SHR littermates. Studying the capacity of the hearts, kidneys, spleens, brains and lungs to synthesize PGE2, PGF2 alpha and TXA2, enabled us to show that the hearts and lungs of SHR-fa/fa synthesized more PG than those of SHR; SHR-fa/fa brains generated less icosanoids than those of SHR; the amounts of PGE2 and TXA2 produced by the kidneys are similar in SHR and in SHR-fa/fa. From the experimental data we can infer that the introduction of the fatty/fa gene into the genome of SHR does not significantly alter the capacity of the kidneys to synthesize icosanoids; the more severe hypertension in the SHR-fa/fa would result from an increase in TXA2 biosynthesis by cardiac tissue which, at the same time, synthesized more PGE2, which could be a means of defence against hypertension. Moreover this genetical manipulation inhibited the icosanoid-synthesizing capacity of the brain which thus attenuated the central nervous system activity of the animals.

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.

Prostaglandin-induced inhibition of acetylcholine release from neuronal elements of dog tracheal tissue

In an attempt to elucidate the possible roles of endogenous prostaglandins on the neuro-effector transmission in the dog trachea, effects of a prostaglandin antagonist (1-acetyl-2-[8-chloro-10, 11- dihydrobenz (b.f) (1.4) oxazepine-10-carbonyl]hydrazine (SC-19220] on the electrical and mechanical properties of smooth muscle cells and on neuro-effector transmission in the smooth muscle layer were studied by means of micro-electrode, double sucrose-gap, and tension recording methods. The levels of prostaglandins in the perfusate from the dog tracheal tissue were also determined using radioimmunoassay. Excitatory junction potentials (e.j.p.s) and twitch tension evoked by electrical field stimulation with short pulse duration (50-100 microseconds), which were abolished by tetrodotoxin (10(-7) M) or atropine (5 X 10(-6) M), showed gradual and continuous reduction in amplitude during superfusion with normal Krebs solution. Reduction in the amplitude of e.j.p.s occurred with no change in the membrane potential or membrane input resistance. SC-19220 (3.1 X 10(-5) M) did not modify the membrane potential, membrane input resistance or the sensitivity to acetylcholine of the smooth muscle cells. Yet, with application of SC-19220 (3.1 X 10(-6) M), gradual and continuous reductions in the amplitude of e.j.p.s and twitch contractions were no longer observed. With an increased concentration (3.1 X 10(-5) M), e.j.p.s and twitch contractions with a constant amplitude were obtained after the initial increase in the amplitude. When the amplitude of twitch contractions was stabilized by treatment with indomethacin (10(-5) M), low concentrations (10(-12) to 10(-10) M) of prostaglandin E2 (PGE2) or prostaglandin F2 alpha (10(-8) to 10(-6) M) markedly suppressed the amplitude of the twitch contractions. In some muscle preparations (ten out of twenty-two preparations examined), SC-19220 (3.1 X 10(-6) to 3.1 X 10(-5) M) produced a sustained contraction of the muscle, which was suppressed by atropine (5 X 10(-6) M) or PGE2 (10(-8) M). Following pre-treatment of the tissue with atropine (5 X 10(-6) M), SC-19220 did not evoke contracture. In the resting condition, 10-40 ng g-1 wet wt. tissue min-1 PGE or PGF was released into the perfusate from the tracheal muscle tissue of the control dog.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Hemodynamic effects of prostaglandin E1 infusion in patients with acute myocardial infarction and left ventricular failure

Prostaglandin E1 (PGE1) has been shown to limit infarct size, improve coronary blood flow, inhibit platelet aggregation, and reduce both left ventricular (LV) preload and afterload in experimental animals. Its use in the therapy of patients with acute myocardial infarction (AMI) and congestive heart failure (CHF) has not, however, been reported. Five patients with AMI of less than 12 hours' duration and LV dysfunction were studied to assess the hemodynamic effects of IV infusion of PGE1. PGE1 in the concentration of 0.4 microgram/ml was infused at a rate of 0.003 microgram2kg/min (3 ng . kg-1 . min-1) to a maximum rate of 0.021 microgram/kg/min (21 ng . kg-1 . min-1) for a total time of up to 90 minutes. There was an insignificant increase in heart rate, with significant decreases in mean arterial blood pressure and systemic vascular resistance. Pulmonary capillary wedge pressure declined from 21 +/- 3 to 15 +/ 1 mm Hg (p less than 0.05), mean pulmonary artery pressure and pulmonary vascular resistance decreased (p less than 0.05), mean pulmonary artery pressure and pulmonary vascular resistance decreased (p less than 0.05), with increases in cardiac index from 2.38 +/- 0.08 to 2.89 +/- 0.58 L/min/m2 (p less than 0.01) and stroke volume from 51 +/- 17 to 59 +/- 20 ml/beat (p less than 0.05). No major cardiac or extracardiac side effects were encountered during PGE1 infusion. One patient had transient nausea which did not require discontinuation of the drug. PGE1 is an effective vasodilator and deserves further application in therapy for AMI patients with CHF.

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.

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.

Influence of prostaglandins on vasoconstrictor responses in the hindquarters vascular bed of the cat

The effects of prostaglandins (PG), A1, A2, B2, E1, 6-keto-E1, F2 alpha and indomethacin on vascular resistance and vasoconstrictor responses were investigated in the feline hindquarters vascular bed under conditions of controlled flow so that changes in perfusion pressure directly reflect changes in vascular resistance. Infusion of PGE1, PGE2 and 6-keto-PGE1 (3 microgram/min) into the abdominal aorta significantly dilated the hindquarters vascular bed and inhibited vasoconstrictor responses to sympathetic nerve stimulation and intra-arterial injections of angiotensin, whereas hindquarters vasoconstrictor responses to tyramine and exogenous norepinephrine were unaffected. Infusion of PGA1, A2, B2 and F2 alpha at a similar rate produced transient changes in hindquarters vascular resistance and did not consistently alter vasoconstrictor responses to sympathetic nerve stimulation, angiotensin, norepinephrine and tyramine. Indomethacin in a dose which greatly attenuates the response to intravenous administration of arachidonic acid enhanced responses to nerve stimulation and norepinephrine. In addition, indomethacin had little or no effect on hindquarters perfusion pressure and systemic arterial pressure. These data suggest that E series prostaglandins possess the ability to modulate the actions of the sympathetic nervous system and angiotensin in the feline hindquarters vascular bed. In addition, these data suggest that PGEs, upon enzymatic conversion and dehydration to A and B series prostaglandins, lose their ability to consistently affect vasoconstrictor responses. Experiments with indomethacin further suggest that locally formed prostaglandins do modulate the effects of the sympathetic nervous system of the feline hindquarters.

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 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.

Inhibition of transmitter release from isolated rabbit kidney by bradykinin

The effect of kallikrein on the release of norepinephrine has been studied in the isolated perfused rabbit kidney. Kallikrein in the perfusion medium caused an inhibition in the rise of the perfusion pressure induced by periarterial stimulation and in the contraction of rabbit aorta superfused by the venous outflow of the stimulated kidney. On the contrary, kallikrein caused a potentiation in the urine volume induced by periarterial stimulation. Similar findings were obtained when bradykinin was added instead of kallikrein. Kallikrein did not alter the pressure response and rabbit aorta contraction but potentiated the diuretic effects of exogenously administered norepinephrine. Acetyl salicyclic acid when added to the perfusion medium containing kallikrein caused a reversal in all parameters measured in this study. It is concluded that the changes of the effects of periarterial stimulation of the isolated rabbit kidney by kallikrein are mediated through the bradykinin-mediated increased generation of intrarenal prostaglandins.

Effects of acetylsalicylic acid and indomethacin on growth hormone secretion in man

To investigate the possibility that prostaglandins (PG) take part in the control of growth hormone (GH) secretion in humans, we have studied the effects of protracted and acute administration of acetylsalicylic acid (ASA) and indomethacin (ID), two PG synthesis inhibitors, on basal and insulin-stimulated GH secretion in normal volunteers. In eight subjects, oral administration of 3-2 g daily of ASA for 4 days clearly reached GH response to insulin hypoglycemia (p less than 0.01, ANOVA). In six additional subjects, GH response to hypoglycemia was not modified by a 4-day oral treatment with 300 mg daily of ID. The pattern of plasma free fatty acids (FFA) and blood glucose during the insulin tolerance test was not significantly affected by ASA treatment. After ID the O time value of the above parameters was somewhat higher than under basal conditions, while the drop of blood glucose, but not to FFA, was slightly more pronounced. Acute oral administration of 1.5 g ASA in 12 subjects did not appreciably modify baseline plasma GH, FFA, and blood glucose levels. By contrast, a single oral dose of 100 mg ID in 12 subjects caused a moderate but significant rise (p less than 0.05) of plasma GH levels together with a clear elevation (p less than 0.01) of plasma FFA and blood glucose levels with respect to a group of controls treated with a placebo. Collectively these results are compatible with the possibility that PG play a physiologic stimulating role in the control of GH secretion, although an effect of ASA and ID unrelated to PG inhibition cannot be ruled out, In any event, in view of the number of endocrine and metabolic alterations induced by ASA and ID, these drugs seem to merit further study.

Release of prostaglandin-like material from isolated cat tracheal muscle by electrical and mechanical stimulation

Release of PGE-like material has been studied on the isolated continuously-superfused cat tracheal muscle using dynamic bioassay methods. The effluent of transmural electrically-stimulated cat tracheal muscle induced a contraction when superfused over the rat stomach fundus strip. This response did not alter with atropine, methysergide, phentolamine and propranolol but was inhibited by aspirin and Sc 19220. The same myotropic activity in the effluent was found when trachea was mechanically stimulated by an additional increase in tension. The effluent from mechanically- and electrically-stimulated tracheal muscle caused a definite relaxation when superfused over a second cat tracheal muscle contracted by serotonin and pretreated with propranolol. Electrically-stimulated cat trachea itself gave a relaxant response which was blocked by propranolol but potentiated by aspirin. From these results it was concluded that both electrical and mechanical stimulation can elicit a release of PGE-like material from isolated cat tracheal muscle.

Absence of a prostaglandinic mediator in the lateral hypothalamic cardio-vascular inhibition

The cardio-vascular inhibition elicited by electrical stimulation of the paraventricular nucleus in the lateral hypothalamus of anaesthesized and desafferentiated dogs is not linked with a mediator release like PGE. The effect of this biological agent is not registered in the isolated femoral artery of a receiver, after deviation by a cruised circulation of the arterial blood of a hypothalamic stimulated donor dog. Antipyretics, which are also prostaglandin-synthetase inhibitors, enhance the lateral hypothalamic reactions. As the thermoregulation centre is localized in the same region as the cardio-vascular inhibition centre and because lowering of temperature depends upon vasodilation and decrease in the general cellular metabolism, both functions of the paraventricular nucleus activity, a hypothesis is proposed that thermoregulation and cardio-vascular inhibition centres are a functional and anatomical unity.

Increase in the coronary vascular resistance by indomethacin in the isolated guinea pig heart preparation in the absence of changes in mechanical performance and oxygen consumption

Experiments were performed in isolated guinea pig hearts, perfused at constant volume. Left ventricular pressure, left ventricular dp/dtmax, coronary vascular pressure and coronary venous pO2 were measured continuously. Indomethacin (1.4 X 10(-6) M) increased coronary vascular resistance by 15% over control (p less than 0.01) without altering the myocardial contractile force. When PGE2 (1.4 X10(-8) M) was subsequently added, it abolished the indomethacin action and lowered the coronary vascular resistance below the pre-indomethacin control value. This increase in coronary vascular resistance caused by indomethacin was also seen when the animals were pretreated with reserpine and/or the adrenoceptor blocking agents phenoxybenzamine and propranolol, but was prevented completely by previous addition of PGE2 (1.4 X 10(-7) M). The results provide evidence for possible involvement of endogenous prostaglandin-like substances in the maintenance of coronary vascular resistance in the isolated guinea pig heart.

Modification by prostaglandins E1 and E2, indomethacin, and arachidonic acid of the vasoconstrictor responses of the isolated perfused rabbit and rat mesenteric arteries to adrenergic stimuli

In isolated perfused rabbit mesenteric arteries, prostaglandin (PG) E1 and E2, 1-5NG/ML, did not alter the basal perfusion pressure, but reduced the vasoconstrictor responses to sympathetic nerve stimulation; the responses to injected norepinephrine were reduced by PGE1 and variably affected by PGE2. In contrast, in rat mesenteric arteries PGE1 and PGE2, 1-5 ng/ml, potentiated the vasoconstrictor responses to nerve stimulation and to injected norepinephrine. In rabbit mesenteric arteries, the inhibitor of PG synthesis, indomethacin, augmented the responses to sympathetic nerve stimulation and to injected norepinephrine, whereas in rat mesenteric arteries indomethacin inhibited the responses to both adrenergic stimuli. Arachidonic acid, a PG precursor, reduced the vasoconstrictor responses to sympathetic nerve stimulation and to injected norepinephrine in rabbit, whereas in rat, potentiation of the responses to adrenergic stimuli occurred. Since these effects of arachidonic acid were abolished by the simultaneous infusion of indomethacin, they appear to be mediated through conversion of arachidonic acid to PG. We conclude that prostaglandins modulate adrenergic transmission in mesenteric arteries and this effect is species dependent.

Effects of indomethacin and PGE1 on the vasoconstrictor responses of the rabbit ear artery to nerve stimulation

Actions of PGE1 and indomethacin on electrically induced vasoconstriction in isolated ear arteries of rabbits were studied. PGE1 (8.5 X 10(-9) M) reduced the vasoconstriction; this inhibition was inversely related to the rate of stimulation. Indomethacin (1.5 X 10(-6) M) potentiated the constrictor responses to nerve stimulation. The degree of this potentiation was also frequency-dependent being greater at low (1 - 2 HZ) than at high (8 - 16 HZ) rate of stimulation. These findings support the view that prostaglandins, in addition to their action on vascular smooth muscle cells, play a functional role in the regulation of tone of the rabbit ear artery by a negative feed-back control of adrenergic neurotransmission.

Hormone interactions in the isolated rabbit heart. Synthesis and coronary vasomotor effects of prostaglandins, angiotensin, and bradykinin

In the present study, the synthesis and degradation of several potent vasoactive substances influencing coronary resistance were characterized in the isolated perfused rabbit heart. Prostaglandin synthetase activity, angiotensin converting enzyme activity, and bradykininase activity (without angiotensinase) were observed. A prostaglandin E2-like substance appeared to be the ednogenous mediator of the coronary vasodilation produced by bradykinin and angiotensin II (AII). (1) The concentration of this prostaglandinlike substance in the coronary venous effluent was directly proportional to the concentration of the coronary vasocilator stimulus (bradykinin or AII). (2) The prostaglandinlike substance released and the coronary dilation produced by the agonists correlated temporally and quantitatively. (3). Abolition of cardiac biosynthesis of the prostaglandinlike substance by indomethacin also abolished the decrease in coronary resistance produced by the agonists. AII, the most potent naturally occurring vasoconstrictor substance, produced a paradoxical coronary vasodilation because it stimulated cardiac prostaglandin biosynthesis, but the direct coronary vasoconstrictor action of AII could be readily unmasked by indomethacin, which blocks prostaglandin synthesis. The nonapeptide SQ-20881 blocked cardiac biosynthesis of AII (from angiotensin I) and enhanced the coronary vascular effects of bradykinin by interfering with bradykininase activity. Similarly, the AII-receptor antagonist, 1-Sar-8-Ile-AII, blocked the coronary vascular effect of AII.

Indomethacin-induced increase in noradrenaline turnover in some rat organs

1 The effect of a prostaglandin synthesis inhibitor, indomethacin, on noradrenaline turnover rate in various rat tissues was determined from the product of the endogenous noradrenaline concentration and of the rate constant of (-)-[3H]-noradrenaline decline after injection of the labelled amine in tracer doses. 2 Treatment of the rats with indomethacin (5 mg/kg p.o. five times during 2.5 days) increased noradrenaline turnover rate 32-36% in submandibular gland, spleen and heart, and 4-17% in epididymal and subcutaneous adipose tissue. 3 The extrapolated [3H]-noradrenaline content at time 0 was greater in heart and adipose tissue of indomethacin-treated animals than in controls, while it was not significantly changed in spleen and salivary gland. 4 There was no apparent relationship between tissue concentrations of intravenously injected [14C]-indomethacin and the effect of indomethacin on noradrenaline uptake and turnover rate in the different tissues. 5 Indomethacin treatment did not affect monoamine oxidase and catechol O-methyl-transferase activities in the different tissues. 6 The results are consistent with the hypothesis that indomethacin increases noradrenaline turnover in the rat by blockade of a locally operating feed back inhibition of transmitter release by prostaglandins. However, additional effects, such as an increased impulse traffic, cannot be ruled out.

Effect of prostaglandin E2 on the pressor response to periarterial stimulation and norepinephrine of the isolated perfused rabbit kidney

The interaction of prostaglandin E2 (PGE2) and aspirin with the responses to peri-arterial stimulation (PS) and norepinephrine (NE) was studied in the isolated kidney of rabbit perfused through the renal artery at constant flow with Krebs' solution. NE and PS increased vascular perfusion pressure of kidney and caused a contraction on the isolated rabbit aortic strip superfused with the effluent from kidney. Addition of PGE2 to the perfusion medium decreased the PS-induced rise in perfusion pressure without changing the effect of exogenous NE. In contrast, addition of aspirin to the perfusion medium induced a potentiation of the response to PS but not to NE. These results suggest that PGE2 modulates the effect of PS probably by inhibiting the releases of NE from sympathetic nerve endings.

Modulation by prostaglandins of adrenergic transmission in the isolated perfused rabbit and rat kidney

In the isolated perfused rabbit kidney prostaglandins (PGS) E1 (0.02-0-1 ng/ml), E2 (0.02-0.1 ng/ml), and A2 (1-5 ng/ml) inhibited the vasoconstrictor responses to sympathetic nerve stimulation by 21-44%, 31-39%, and 20-23%, respectively, without alerting those to injected norepinephrine. In contrast, in the rat kidney PGE1 (0.5 ng/ml), PGE2 (0.5 ng/ml), and PGA2 (5 ng/ml) enhanced the vasoconstrictor responses to sympathetic nerve stimulation by 41%, 27%, and 11%, respectively; the equiconstrictor responses to injected norepinephrine remained unaltered. Higher concentrations of these agents produced vasodilation in the rabbit kidney and vasoconstriction in the rat kidney. In both species PGF2alpha produced vasoconstriction and enhanced the response to both adrenergic stumuli. In the rabbit kidney inhibitors of PG synthesis augmented the responses to sympathetic nerve stimulation without altering those to injected norepinephrine, whereas in the rat kidney inhibition of the responses to both adrenergic stimuli occurred. Arachidonic acid inhibited the vasoconstrictor responses to sympathetic nerve stimulation in the rabbit kidney, but in the rat kidney it caused augmentation of these responses. Since these effects of arachidonic acid were reduced by indomethacin, they appear to be mediated through the acid's conversion to PGS. We conclude that PGS of the E series modulate adrenergic transmission in the kidney and that their modulatory actions are species dependent.

Some physiological and pharmalogical characteristics of the stimulus induced release of norepinephrine from the rabbit superior cervical ganglion

The cervical sympathetic nerve stimulated release of norepinephrine (NE) from the rabbit superior cervical ganglion (SCG) was characterized. The quantity of NE released per impulse declined with increasing stimulation frequency over the range of 3/sec to 15/sec. Nerve stimulated NE release was potentiated by 1 micromolar desmethylimipramine and 25 micromolar phenoxylbenzamine and inhibited by 1 micromolar bretylium, 25 micromolar methoxamine and 1 micromolar prostaglandin E1. These results suggest that nerve stimulated NE release in the rabbit SCG occurs from sympathetic fibers which are subject to the same neurosecretory control mechanisms as sympathetic fibers elsewhere in the autonomic nervous system.

The effects of indomethacin and eicosa-5,8,11,14-tetraynoic acid on the response of the rabbit portal vein to electrical stimulation

1 The effects of indomethacin and eicosa-5,8,11,14-tetraynoic acid (ETYA) on the contractile response of the transmurally stimulated rabbit portal vein were studied in vitro.2 When the veins were stimulated for 240 pulses at 1 and 2 Hz, the responses were potentiated by indomethacin and ETYA. However, responses to 4 and 8 Hz were not potentiated. The responses to continuous electrical stimulation at 2 Hz were also potentiated by indomethacin and ETYA. This potentiating effect was attenuated when the veins were pretreated with alpha-methyl-p-tyrosine. The responses of the veins to noradrenaline were not altered by either indomethacin or ETYA.3 Prostaglandin E(2) inhibited the responses of the portal vein to electrical stimulation. The magnitude of this inhibition was inversely related to the frequency of stimulation. The responses of the vein to noradrenaline were not altered by prostaglandin E(2).4 It is concluded that potentiation by indomethacin and ETYA of the response of the isolated portal vein is due to an increased release of newly synthesized noradrenaline as a result of inhibition of prostaglandin synthesis.