The effect of angiotensin I converting enzyme inhibitor (SQ 20881) on the release of prostaglandins by rabbit kidney, in vivo.

1. Prostaglandin E- and F-like material has been estimated in renal venous blood of the left kidney of anaesthetized rabbits following renal nerve section. Prostaglandins were estimated by bioassay following solvent extraction and column chromatography. 2. Electrical stimulation of the renal nerves of the left kidney to reduce renal blood flow by approximately 15% for 15 min resulted in a significant increase in the concentration of prostaglandin E-like material in the renal venous blood. The peak values were normally seen either in the last 5 min of the stimulation period or in the first 5 min after the end of the stimulation period. The concentration of prostaglandin F-like material was not significantly altered. 3. Similar reduction of renal blood flow of the left kidney by renal artery constriction also resulted in a significant increase in the concentration of prostaglandin E- but not F-like material in renal venous blood. The timing and magnitude of the response was comparable with that observed with renal nerve stimuation. 4. The effect of an angiotensin I converting enzyme inhibitor, SQ 20881, on the response to both renal nerve stimulation and renal artery constriction has been studied. The administration of the drug did not significantly reduce the release of prostaglandins from the denervated kidneys, however, the increase in prostaglandin E-like material, in response to both stimuli, was abolished. 5. The results suggest that the increase in prostaglandin E-like material released from the kidney in response to low frequency stimulation or to modest reductions in renal blood flow is dependent on the release of renin and that the effect is mediated by the formation of angiotensin II and not angiotensin I.     

Exaggerated renal thromboxane and prostaglandin release by angiotensin II in suprarenal aortic coarctation hypertension

The ability of angiotensin II and arachidonic acid to release immunoreactive prostaglandins into venous and ureteral effluents of rabbit isolated perfused kidneys was examined 7 days after suprarenal aortic coarctation (SRAC) or sham operation (SHAM). Renal vascular responses to angiotensin II were significantly enhanced in SRAC and accompanied by an enhanced venous efflux of bioassayable prostaglandins. Angiotension II-induced release of immunoreactive PGE2, PGF2 alpha, 6-keto PGF1 alpha and TxB2 into the venous effluent was exaggerated in SRAC. As angiotensin II did not stimulate TxB2 efflux in the SHAM group the induction of TxB2 release by SRAC is particularly noteworthy. These changes in eicosanoid release in response to angiotensin II were not mimicked by arachidonic acid administration. These results suggest that in renovascular hypertension angiotensin II-induced prostaglandin release is primarily augmented in the vascular compartment and is consistent with the sensitivity of renal function to cyclooxygenase inhibitors in renovascular hypertension.     

Generation of prostaglandin E-like material by the guinea-pig trachea contracted by histamine.

Challenges of the superfused (1 ml min-1) trachea with histamine (100-200 mug) result in the release of prostaglandin E-like material (3-25 ng in terms of prostaglandin E2) but no prostaglandin F-like activity has been detected in the superfusate. This release is blocked by indomethacin (1mug ml-1) and then the contractile action of histamine is enhanced. It is concluded that the release of a prostaglandin E-like material by histamine from tracheal smooth muscles is a self-defensive mechanism protecting against the strong constriction of airways. The maximal relaxation of trachea by isoprenaline (50-500 mug) is not accompanied by the release of a prostaglandin-like material.     

Attenuation by bradykinin of adrenergically-induced vasoconstriction in the isolated perfused kidney of the rabbit: relationship to prostaglandin synthesis.

1 In the isolated kidney of the rabbit perfused with oxygenated Tyrode solution, we studied the effect of bradykinin on the vasoconstriction evoked by sympathetic nerve stimulation (3Hz, 1 ms) and by injections of noradrenaline (50 to 75 ng) in the presence and in the absence of indomethacin (1 microgram/ml), an inhibitor of prostaglandin biosynthesis. Prostaglandin E(PGE)-like material in the renal effluent was measured by bioassay after extraction with organic solvents and separation by thin layer chromatography. 2 Bradykinin in concentrations of 10 to 100 ng/ml reduced the vasoconstrictor response to sympathetic nerve stimulation and to injected noradrenaline. Also, the peptide (1 to 10 ng/ml) increased the basal release of PGE-like material and the release induced by sympathetic nerve stimulation. 3 Indomethacin, 1 microgram/ml, diminished the inhibitory effect of bradykinin on the vasoconstrictor response to nerve stimulation, minimized the reduction of the noradrenaline-induced vasoconstriction caused by bradykinin (100 ng/ml), and abolished the release of PGE-like material. 4 This study indicates that bradykinin reduces the renal vascular reactivity to adrenergic stimuli and suggests that part of the action of the kinin at the vascular adrenergic neuroeffector junction in the rabbit kidney depends upon the biosynthesis of renal prostaglandins.     

Prostaglandins and the mechanism of analgesis produced by aspirin-like drugs

1. Resting splenic venous outflow from anaesthetized dogs contains prostaglandin-like material: the concentration increases after intra-arterial injections of bradykinin into the spleen, and is abolished by treatment with indomethacin.2. Intra-arterial injections of bradykinin into the spleen of lightly anaesthetized dogs elicit a dose-dependent reflex increase in the blood pressure, which is reduced but not abolished by treatment with indomethacin.3. Addition of prostaglandin E(1) or E(2) either by injections or by infusions restores the reflex increase in the blood pressure due to bradykinin injections after indomethacin treatment.4. The sensitizing action of endogenously released prostaglandins at or near the afferent nerve endings is discussed.5. The analgesic activity of aspirin-like drugs is explained in terms of the removal of the sensitizing activity of prostaglandins.     

Failure of anti-inflammatory steroids to inhibit prostaglandin release from the hydronephrotic rabbit kidney

The release of prostaglandins E2, F2 alpha, I2 and thromboxane A2 from isolated perfused normal and hydronephrotic rabbit kidneys was investigated by extraction and radioimmunoassay. In both types of kidneys, basal PG efflux increased with time and was not altered by co-perfusion with dexamethasone or hydrocortisone. Several vasoactive substances at 1 to 4 micrograms (e.g., bradykinin, angiotensin II, substance P, noradrenaline and vasopressin) caused release of additional amounts of prostaglandins. PGE2 and 6-keto PGF1 alpha were the major prostanoids detected, but substantial amounts of PGF2 alpha were also found. Thromboxane A2 was not released from normal kidneys. In hydronephrotic kidneys there was greatly augmented release of prostaglandins E2 and I2, some increases in PGF2 alpha, and the appearance of substantial amounts of thromboxane A2 (measured as immunoreactive TXB2) when the kidneys were challenged with angiotensin, bradykinin and vasopressin, and smaller augmentation of the response to noradrenaline and substance P. There was no evidence that these evoked increases in renal PG output could be inhibited by dexamethasone or hydrocortisone. Some explanations for the failure of steroids to alter prostanoid metabolism from arachidonate in rabbit kidney are discussed, and it is proposed that there are clear exceptions to the concept that steroids inhibit prostaglandin generation in intact tissues.     

Release of prostaglandins from the rabbit renal medulla

Prostaglandin E₂-like material was released in large amounts from the rabbit renal papilla incubated in various media. Angiotensin I and II, bradykinin, noradrenaline and various other vasoactive agents did not influence significantly the spontaneous release of prostaglandin. Indomethacin produced a dose-dependent inhibition of prostaglandin release from our preparation. Our results indicate that the release of renal prostaglandins previously reported in response to angiotensin and noradrenaline is not due to a direct action of these agents upon the renal papillary tissue. Our data also confirm that the release of prostaglandin-like material from our preparation is the consequence of new synthesis.     

Compartmental prostaglandin release by angiotensin II and arginine-vasopressin in rabbit isolated perfused kidneys

The compartmental effects of angiotensin II (AII) and arginine-vasopressin (AVP) on renal prostaglandin (PG) formation were studied in the isolated perfused kidney of the rabbit by superfusion bioassay of venous and ureteral effluents (VE and UE) and radioimmunoassay (RIA). Comparable results were obtained with either bioassay or RIA when used to quantitate renal PG release. The effects on PG release into the VE were similar for AII and AVP, as were their pressor responses. However, their effects on PG release into the UE differed markedly. AII resulted in a 6-fold greater urinary efflux than venous of bioassayable PGs, whereas AVP-induced PG release into UE was slightly less than PG efflux into the VE at all doses of the peptide. The profile of released PGs varied according to the sampling source (VE or UE). Moreover, each peptide released a similar profile of PGs at all doses, i.e. UE PGE2 greater than PGF2 alpha greater than 6-keto PGF1 alpha; VE PGE2 greater than 6-keto PGF1 alpha greater than PGF2 alpha (TxB2 was not detected in either effluent). Thus, renal vascular PG release is similar for the vasoactive peptides, AII and AVP, whereas the urinary efflux of PGs is considerably greater in response to AII.     

Release of prostaglandin E-like material from perfused mesenteric blood vessels of rabbits.

Infusions of noradrenaline (1-3 mug ml(-1) min(-1)) into the mesenteric vascular preparation of the rabbit caused a 2 to 5 fold rise in perfusion pressure and a release of prostaglandin E-like material (3.23 +/- 0.65 (s.e.) ng PGE2 equivalents ml(-1)). Indomethacin (3 mug ml(-1)) prevented whereas arachidonic acid (0.2 mug ml(-1)) augmented, the noradrenaline-evoked release of a prostaglandin E-like material. The walls of arterioles or precapillary vessels are the proposed site of prostaglandin generation.     

Effect of SA-446, an angiotensin-converting enzyme inhibitor, on renal function in anesthetized dogs: special reference to arachidonic acid metabolites

Intravenous infusion of SA-446 (1 mg/min) decreased systemic blood pressure and increased renal blood flow in anesthetized dogs. These changes were accompanied by a slight natriuretic response. During the infusion of this dose of SA-446, the pressor response to angiotensin I was abolished and the depressor response to bradykinin was markedly potentiated. Administration of indomethacin (13 mg/kg i.v.) suppressed natriuresis and, to some extent, the renal vasodilation caused by SA-446. Before and after administration of SA-446, four arachidonate metabolites, prostaglandin E2, prostaglandin F2 alpha, 6-keto-prostaglandin F1 alpha, and thromboxane B2, were determined in plasma and urine by radioimmunoassay. There were no remarkable changes in levels of prostaglandins and thromboxane B2 in arterial and renal venous plasma. The urinary excretion of the metabolites varied little, but thromboxane B2 excretion did significantly decrease. Thus, reduction in the biosynthesis of thromboxane B2 in the kidney may relate to the effects of SA-446 on renal hemodynamics and urine formation.     

Prostaglandin-release impairment in the bladder epithelium of streptozotocin-induced diabetic rats

Isolated epithelial layer preparations were obtained from urinary bladders of 4-week streptozotocin-diabetic rats and used for endogenous prostaglandins E(2) and F(2alpha) determination. Tissues were incubated in modified Krebs solution under basal conditions, or in the presence of either indomethacin (5x10(-7) M), ATP (10(-5) and 10(-3) M) or bradykinin (10(-7) and 10(-5) M), and samples of incubation medium were collected at 15 and 30 min. In the presence of indomethacin, the release of prostaglandins in the incubation medium was under the detection limit of the enzyme immunoassay (EIA). The epithelium from diabetic rat urinary bladders was thicker and heavier and the absolute amount of endogenous prostaglandins E(2) and F(2alpha) was higher than for control animals, but when prostaglandin production was expressed as a fraction of tissue weight, it was reduced in diabetic epithelium. ATP and bradykinin has significantly increased the endogenous release of both prostaglandins from the epithelium when compared with the release under basal conditions. This increase was time-dependent and was higher in diabetic than in control tissues. ATP evoked a phasic and tonic contraction in bladder strips that was abolished by epithelium removal. Concentration-response curves for ATP did not differ among groups. Bradykinin evoked a long-lasting tonic contraction that was reduced significantly by epithelium removal in diabetic rat bladders only. Concentration-response curves for prostaglandin E(2) and F(2alpha) in diabetic rat bladder differed significantly from that in controls and epithelium removal did not alter these responses. It is suggested that bradykinin receptors and P2X nucleotide receptors already found in the smooth muscle detrusor might be present in the epithelial layer of the bladder. The prostaglandin-release impairment observed in this study might be responsible, in part, for bladder abnormalities observed in pathological conditions, such as diabetes.     

Lack of release of prostaglandins from isolated perfused lungs during pulmonary hypertension and oedema.

1 The effects on pulmonary prostaglandin synthesis of pulmonary hypertension and oedema have been studied. 2 Seventeen isolated lungs of rabbit, cat and guinea-pig were perfused with plasma, whole blood or Krebs Ringer solution in a recirculating system. 3 The venous effluent from the lungs superfused (10 ml/min) a series of smooth muscle tissues sensitive to prostaglandins and thromboxane A2; these were: rat stomach strip, rat colon, chick rectum and rabbit aorta. 4 Left atrial pressure was increased by between 10 and 30 mmHg for periods of 3 to 59 minutes. Gross alveolar oedema eventually developed in all experiments. 5 Neither pulmonary hypertension nor subsequent oedema caused release of prostaglandins into the venous effluent.     

No role for prostaglandins and bradykinin in the autoregulation of renal blood flow

In order to evaluate the participation of prostaglandins and bradykinin in autoregulation of renal blood flow, the pressure-flow relationships were examined before and during the infusion of prostaglandin E2, sodium arachidonate or bradykinin in the pump-perfused kidney of anesthetized dogs. Renal arterial pressure was changed in a step-wise fashion between 60 and 200 mmHg by means of a pneumatic resistance. Renal blood flow revealed an effective autoregulation against the pressure changes between 100 and 200 mmHg. Infusion of prostaglandin E2 (30 and 100 ng/min), sodium arachidonate (200 and 500 micrograms/min) or bradykinin (100 and 300 ng/min) into the renal artery increased renal blood flow dose-dependently, but had no influence on the autoregulation of renal blood flow. We also examined the effect of endogenous bradykinin and prostaglandins by the intravenous administration of captopril (1 mg/kg), a kininase II inhibitor, and indomethacin (2.5 mg/kg), a cyclo-oxygenase inhibitor, respectively. Captopril increased renal blood flow, but did not impair the autoregulation. Indomethacin decreased renal blood flow and had no effect on the renal autoregulation. It is considered that prostaglandins and bradykinin which induced renal vasodilation have no role in the autoregulation of renal blood flow in the dog kidney.     

Cardiac nociceptive reflexes: role of kinins, prostanoids and capsaicin-sensitive afferents

Spinal sympathetic afferent fibres with endings in the heart are essential for signalling cardiac pain. In anesthetized, open-chest dogs, stimulation of these cardiac afferents with the algesic agents, bradykinin or capsaicin, results in reflex increases in arterial pressure and cardiac rate. The reflex responses induced by bradykinin are enhanced by concomitant application of prostaglandins of the E type or prostacyclin, and reduced by indomethacin. In contrast, the reflex effects of capsaicin are not influenced by either indomethacin or prostaglandin E1 treatment. Evidence is presented that reflexogenic effects of bradykinin involve its interaction with specific B2-receptors for kinins and that proteolysis of endogenous kininogen precursor to kinins by epicardially applied tissue kallikrein can initiate reflex cardiovascular effects.     

Resveratrol prevents bradykinin-induced contraction of rat urinary bladders by decreasing prostaglandin production and calcium influx

Resveratrol, a polyphenol found in grapes and peanuts, exerts beneficial effects on a number of diseases of cardiovascular and central nervous system. However, effects of resveratrol on the urinary system have not been fully investigated. In the present study, we examined effects of resveratrol on bradykinin-induced contraction and release of prostaglandin E2 in isolated rat urinary bladders. The effects of resveratrol on contractions induced by several agonists (prostaglandin E2, prostaglandin F2α and carbachol) and high K+ were also examined. We found that resveratrol concentration-dependently reduced the bradykinin-induced contraction in the rat urinary bladder preparations. The higher concentration of resveratrol (100 μM) abolished the bradykinin-induced prostaglandin E2 release. Similar results were obtained when the cyclooxygenase inhibitor indomethacin (10 μM) was used instead of resveratrol. Resveratrol also attenuated the prostaglandin E2-, prostaglandin F2α-, and to a lesser extent carbachol-induced contractions. Contractile responses to bradykinin, prostaglandin E2 and carbachol were largely prevented by blockade of Ca2+ channels with diltiazem. Both resveratrol and diltiazem prevented contractions induced by an addition of Ca2+ (2.5- 10 mM) into Ca2+-free/50 mMK+ solution or by 50 mMK+ solution containing normal Ca2+ (2.5 mM). These results suggest that resveratrol prevents bradykinin-induced contractions by attenuating not only the production of prostaglandins but also actions of them. The effect of resveratrol on contractile actions seems to be in part due to inhibition of Ca2+ influx. Because bradykinin plays an important role in pathological conditions of urinary bladder function, resveratrol may exert beneficial effects on the urinary bladder diseases.     

Angiotensin II-induced contractions of rabbit splenic capsular strips and release of prostaglandins

Summary Rabbit splenic capsular strips contract in response to angiotensin II and simultaneously release prostaglandins E and F into the bath fluid. Contractions, though not sustained, and prostaglandin release are dependent on the concentrations of angiotensin II.Addition of indometacin to the bath fluid inhibits prostaglandin release and potentiates the angiotensin II-induced contractions. Similarly, 5,8,11,14-eicosatetraynoic acid, another blocker of prostaglandin synthesis, potentiates contractions elicited by angiotensin II.Exogenous prostaglandin E₁ (300 ng/ml) tends to decrease angiotensin II-induced contractions, while prostaglandin E₂ (300 ng/ml) as well as prostaglandin F₂ (300 ng/ml) significantly increase the contractions produced by angiotensin II.The prostaglandin endoperoxide analogues (15S)-hydroxy-9,11-(epoxymethano)prosta-5Z,13 E-dienoic acid and (15S)-hydroxy-11,9-(epoxymethano)-prosta-5Z,13 E-dienoic acid in concentrations of 300 ng/ml are either without effect or weak smooth muscle stimulants of their own, but do not influence the effect of angiotensin II.By the simultaneous use of sensitive and specific radioimmunoassays for prostaglandins E₁ and E₂ the prostaglandin E-like substance released by the rabbit splenic capsular strips was found to resemble serologically much more the dienoic prostaglandin E₂ than prostaglandin E₁.The potentation of the effect of angiotensin II by indometacin and 5,8,11,14-eicosatetraynoic acid might be caused by inhibition of synthesis of prostaglandins or related compounds in the splenic tissue. However, an undefined sensitizing effect of indometacin and 5,8,11,14-eicosatetraynoic acid, not related to their effect on prostaglandin synthetase, on the smooth muscle preparation cannot be excluded.     

Release of prostaglandins from the rabbit perfused kidney: Effects of vasoconstrictors

1 The rat stomach strip was used to assay prostaglandin E(2)-like material released by a rabbit isolated kidney perfused with Krebs solution.2 Doses of noradrenaline and angiotensin II producing similar vasoconstrictor effects released equivalent amounts of prostaglandins from the kidney.3 8-Leu-angiotensin II, a specific inhibitor of the natural octapeptide, blocked the action of angiotensin II on perfusion pressure and the release of prostaglandins, while the action of noradrenaline on both parameters was unaffected.4 Indomethacin, a specific inhibitor of prostaglandin biosynthesis, blocked the effects of both vasoconstrictors on prostaglandin release while their action on perfusion pressure was significantly enhanced.5 In the kidney effluent, amounts of prostaglandin E(2)-like material increased linearly with the rise in perfusion pressure induced by increasing doses of angiotensin II. These results indicate that prostaglandin output from the isolated kidney follows the rise in perfusion pressure.     

Possible involvement of Ca2+-independent phospholipase A2 in protease-activated receptor-2-mediated contraction of rat urinary bladder

Possible involvement of Ca(2+)-independent phospholipase A2 (iPLA2) was examined in protease-activated receptor-2 (PAR-2)-mediated contraction of the rat urinary bladder. Both PAR-2 activating peptide (PAR-2 AP; SLIGRL-NH2) and trypsin produced a concentration-dependent contractile response in the urinary bladder preparations. These contractions were significantly (p<0.01) attenuated by indomethacin (10 microM), an inhibitor of cyclooxygenase, or bromoenol lactone (BEL; 10 micro M), an inhibitor of iPLA2. On the other hand, the contractile responses to bradykinin were not significantly affected by BEL, although they were reduced by indomethacin. Arachidonyltrifluoromethyl ketone (AACOCF3; 30 microM), an inhibitor of cytosolic Ca(2+)-dependent phospholipase A2, did not affect the trypsin- and bradykinin-induced contractions. Both indomethacin and BEL had no inhibitory effect on the prostaglandin E2-induced contractions. These results suggest that PAR-2 activators and bradykinin stimulate the release of prostaglandins and thereby contract the rat urinary bladder smooth muscles. The release of prostaglandins by PAR-2 activators seems to be partly mediated by the iPLA2.     

Prostaglandin production by rabbit isolated jejunum and its relationship to the inherent tone of the preparation.

1 Pieces of rabbit jejunum were bathed in Krebs solution at 37 degrees C in an isolated organ bath bubbled with O2 and 5% CO2. The bathing fluid was collected regularly and assayed for prostaglandins. 2 The preparations maintained a continuous sub-maximal muscle contraction, referred to as inherent 'tone'. Prostaglandins E2 and F2alpha were continuously generated by the intestine and released into the bathing fluid. The amounts released first declined over 2 h and then steadily increased. The release was also greater after 48 h storage in the refrigerator and after mechanical damage. 3 There was no change in prostaglandin release when the rabbit jejunum was contractd by acetylcholine or physostigmine or relaxed by adrenaline, hyoscine, papaverine, dinitrophenol, or calcium-free Krebs solution. 4 Addition to the bathing fluid of the prostaglandin precursor, arachidonic acid, did not increase the release of prostaglandins although it contracted the tissue. Thus, output of prostaglandins from the tissue was not limited by substrate concentration but more probably by the capacity of the prostaglandin synthetase. 5 Prostaglandin output was decreased by bubbling the bathing fluid with N2 rather than O2; at the same time the preparation relaxed. 6 Aspirin-like drugs such as indomethacin also decreased or abolished prostaglandin formation and this, too, was accompanied by loss of tone of the isolated preparation. 7 Pieces of rabbit jejunum stored in Krebs solution containing indomethacin initially released little or no prostaglandin into the bathing fluid. However, prostaglandin release increased with repeated washing of the preparation. 8 The results suggest that intra-mural prostaglandin production contributes to the inherent tone of the rabbit jejunum, that trauma increases prostaglandin production and that the inhibitory effects of anoxia are linked with the lack of prostaglandin production and activity. The relevance of these findings to intestinal activity in vivo is discussed.     

Prostaglandin F2alpha reduces the algesic effect of bradykinin by antagonizing the pain enhancing action of endogenously released prostaglandin E.

1 The isolated perfused ear of the rabbit connected to the body only by its nerve, was used to investigate the influence of prostaglandin F2alpha on the algesic effect of bradykinin and acetylcholine. 2 Bradykinin and acetylcholine, following intra-arterial injection into the isolated perfused ear elicited a dose-related reflex fall in blood pressure due to stimulation of paravascular pain receptors (= algesic effect). 3 Infusion of prostaglandin F2alpha (0.1 to 1 ng/ml) into the rabbit ear reduced the algesic effect of bradykinin but not that of acetylcholine. 4 The onset of the reflex fall in blood pressure by bradykinin but not that by acetylcholine was delayed by infusion of prostaglandin F2alpha into the ear. 5 Infusion of prostaglandin E1 into the rabbit ear led to an enhancement of the algesic effect of bradykinin and acetylcholine. Enhancement of both effects was abolished by infusion of prostaglandin F2alpha. 6 During inhibition of the endogenous synthesis of prostaglandins (mainly E-type) by indomethacin, a low concentration of prostaglandin F2alpha no longer reduced the algesic effect of bradykinin. However, a high concentration of F2alpha continued to enhance the effect of bradykinin and acetylcholine. 7 Prostaglandin F2alpha influenced neither the brief reduction in venous outflow produced by bradykinin nor the brief increase in venous outflow caused by acetylcholine. 8 The results suggest that prostaglandin F2alpha does not directly reduce the effect of bradykinin but inhibits the enhancement of its algesic effect produced by prostaglandin E that is released endogenously by bradykinin. That the algesic effect of acetylcholine is not reduced by prostaglandin F2alpha is in keeping with its releasing very little endogenous prostaglandin E.