Bradykinin-induced chemoreflexes from skeletal muscle: implications for the exercise reflex

We examined the cardiovascular response to bradykinin stimulation of skeletal muscle afferents and the effect of prostaglandins on this response. Intra-arterial injection of 1 microgram bradykinin into the gracilis muscle of cats reflexly increased mean arterial pressure by 16 +/- 2 mmHg, left ventricular end-diastolic pressure by 1.6 +/- 0.6 mmHg, maximal dP/dt by 785 +/- 136 mmHg/s, heart rate by 11 +/- 2 beats/min, and mean aortic flow by 22 +/- 3 ml/min. The hemodynamic responses were abolished following denervation of the gracilis muscle. The increases in mean arterial pressure and maximal dP/dt were reduced by 68 and 45%, respectively, following inhibition of prostaglandin synthesis with indomethacin (2-8 mg/kg iv). Treatment with prostaglandin E2 (PGE2, 15-25 micrograms ia) restored the initial increase in mean arterial pressure, but not dP/dt, caused by bradykinin stimulation. Injection of PGE2 (15-30 micrograms ia) into the gracilis, without prior treatment with indomethacin, augmented the bradykinin-induced increases in mean arterial pressure and dP/dt. We conclude that small doses of bradykinin injected into skeletal muscle are capable of reflexly activating the cardiovascular system and that prostaglandins are necessary for the full manifestation of the corresponding hemodynamic response. The pattern of hemodynamic adjustment following bradykinin injection into skeletal muscle is very similar to that induced by static exercise. Therefore, it is possible that intense exercise provides a stimulus for this bradykinin-induced reflex in vivo.     

Influence of angiotensins (I, II, & III), bradykinin and arachidonic acid on renomedullary PGE production in vitro.

Renomedullary tissue from rabbit or rat was incubated with angiotensin I, II, III, arachidonic acid, bradykinin, indomethacin and meclofenamate to study their effect on PGE2 production. Arachidonic acid and bradykinin enhanced PGE2 production significantly. Indomethacin and meclofenamate inhibited PGE2 production by more than 70%. Angiotensin I, II and III did not influence PGE2 production. These results suggest that bradykinin and arachidonic acid stimulate PGE2 production by a direct cellular action whereas the angiotensins do not.     

Bradykinin and prostaglandin E₁ regulate calcitonin gene-related peptide expression in cultured rat sensory neurons

Primary cultures of adult rat dorsal root ganglia (DRG) sensory neurons were used to determine whether bradykinin and prostaglandins E? (PGE?), E? (PGE?) or I? (PGI?) stimulate long-term calcitonin gene-related peptide (CGRP) mRNA accumulation and peptide release. Treatment (24 h) of neurons with either bradykinin or PGE?, significantly increased CGRP mRNA content and iCGRP release. However, PGE? or PGI? was without effect. Exposure of the cultured neurons to increasing concentrations of bradykinin or PGE? demonstrated that the stimulation of CGRP expression was concentration-dependent, while time-course studies showed that maximal levels of CGRP mRNA accumulation and peptide release were maintained for at least 48 h. Treatment of the neuronal cultures with a bradykinin B? receptor antagonist significantly inhibited the bradykinin-induced increase in CGRP expression and release. In addition, preincubation of neuronal cultures with the cyclooxygenase inhibitor indomethacin did not alter the PGE?-mediated stimulation of CGRP but blocked completely the bradykinin-induced increase in CGRP production. Therefore, these data indicate that bradykinin and PGE? can regulate the synthesis and release of CGRP in DRG neurons and that the stimulatory effects of bradykinin on CGRP are mediated by a cyclooxygenase product(s). Thus, these findings suggest a direct relationship between chronic alterations in bradykinin/prostaglandin production that may arise from pathophysiological causes and long-term changes in CGRP expression.     

Cytokine-mediated inflammatory hyperalgesia limited by interleukin-13

The effect of interleukin-13 (IL-13) on hyperalgesic responses to intraplantar (i.pl.) injection of carrageenin, E. coli endotoxin (LPS), bradykinin, tumour necrosis factor a (TNF-alpha), interleukin-1 beta (IL-1 beta), interleukin-8 (IL-8) and prostaglandin E(2) (PGE(2)) was investigated in a model of mechanical hyperalgesia in rats. Also, the cellular source of the IL-13 was investigated. IL-13, administered 30 min before the stimulus, inhibited responses to carrageenin, LPS, bradykinin, and TNF-alpha, but not responses to IL-1 beta, IL-8 and PGE2. IL-13, administered 2 hours before the injection of IL-1b, did not affect the response to IL-1b, whereas IL-13, administered 12 hours or 12 + 2 hours before the IL-1 beta, inhibited the hyperalgesia (- 35%, - 77%, respectively). In murine peritoneal macrophages, IL-13 administered 2 hours before stimulation with LPS, inhibited the production of IL-1 beta (- 67%) and PGE(2) (- 56%). IL-13 administered 12 hours before stimulation with LPS inhibited LPS-stimulated PGE(2) but not IL-1 beta. An anti-IL-13 serum potentiated responses to carrageenin, LPS, bradykinin and TNF-alpha (but not IL-1 beta and IL-8), as well as responses to bradykinin in rats depleted of mast cells with compound 40/80, but not in athymic rats. These data suggest that IL-13, released by lymphocytes, limits inflammatory hyperalgesia by the inhibition of the production TNF-alpha, IL-1 beta, IL-8 and PGs.     

Interactions of prostaglandin E1, bradykinin and histamine and the increase of plasma fibrinogen in rats

Considering that tissue injury caused by laparotomy significantly increases the liver synthesis of plasma fibrinogen, and that PGE1, bradykinin and histamine are released into the injured tissues, the effect of above mentioned inflammatory agents and of the adrenal medulla on plasma fibrinogen levels in rats was studied. The subcutaneous administration of PGE1, bradykinin or histamine does not modify plasma fibrinogen levels acting independently comparing with non-injected animals or injected with the drug vehicle. Bradykinin + histamine did not modify plasma fibrinogen levels either. However the administration of prostaglandin E1 + bradykinin + histamine reproduced the increase of fibrinogen characteristics of laparotomy. This increase was partially but significantly inhibited in rats that had undergone bilateral removal of the adrenal medulla or administration of PGE1 + bradykinin + histamine + bupivacaine (a local anesthetic), but it was not modified when the adrenal medullectomy was unilateral. It is concluded that plasma fibrinogen increase is obtained only when PGE1 acts in presence of bradykinin or histamine and the adrenal medulla should be partially responsible for said increase.     

Extra- and intracellular potassium concentration and prostaglandin production of skin fibroblasts grown from patients with Bartter's syndrome

In studies on human skin fibroblasts originating from three patients with Bartter's syndrome and in corresponding age and sex matched controls, the bradykinin stimulated release of PGE2, PGI2, PGF2a and of arachidonic acid was examined. The studies were aimed at demonstrating the possible changes of prostaglandin production under the influence of changing extracellular potassium concentrations (0–12 mmol K/l) in the two study groups. Earlier studies were confirmed and extended by one more pair of fibroblast cultures, showing a decreased bradykinin stimulated PGE2 production in fibroblasts from patients with Bartter's syndrome as compared to control. The difference in bradykinin stimulated PGE2 production was significant, irrespective of the extracellular potassium concentrations, to which the cultures were exposed. The bradykinin stimulated PGE2 and PGF2a-production by control fibroblasts was directly proportional to extracellular potassium concentrations, whereas the PG-production of Bartter's syndrome fibroblasts remained uninfluenced by extracellular potassium. Extra- and intracellular potassium concentrations were directly proportional and there was no difference in this relationship between controls and Bartter's syndrome.The direct proportionality between bradykinin stimulated PGE2 production and potassium concentrations in control fibroblasts is, despite the apparent contradiction, in accordance with findings in the literature. The lack of a comparable proportionality in fibroblasts from patients with Bartter's syndrome is interpreted to correspond to an insensitivity to changes of potassium concentrations and thus to an insensitivity to one of the modulators of AA metabolism.     

Elevated cAMP is required for stimulation of eicosanoid synthesis by interleukin 1 and bradykinin in BALB/c 3T3 fibroblasts.

In Swiss 3T3 murine fibroblasts, interleukin 1 (IL-1) and bradykinin stimulate prostaglandin E2 (PGE2) synthesis. However, in the present study, we found that neither agonist stimulated PGE2 synthesis in BALB/c 3T3 murine fibroblasts, this in spite of expression of similar numbers of receptors for each agonist compared to Swiss 3T3 cells. When BALB/c 3T3 cells were preincubated with cAMP analogs, both IL-1 and bradykinin stimulated PGE2 synthesis to levels similar to those observed in Swiss 3T3 cells. Similarly, when the cells were preincubated with forskolin, which activates the catalytic subunit of adenylate cyclase directly, or NECA, which stimulates cellular cAMP accumulation by activating adenosine receptors, IL-1 and bradykinin stimulated PGE2 synthesis. Rp-cAMPS, an inhibitor of cAMP-dependent protein kinase, blocked the ability of cAMP or NECA to render cells responsive to IL-1 and bradykinin. In basal BALB/c 3T3 cells, bradykinin and IL-1 stimulated arachidonate release in the absence of cAMP, but little conversion of released arachidonate to PGE2 occurred. cAMP, forskolin, and NECA all increased cyclooxygenase activity in the cells. SV-T2 is a clonal line originating from BALB/c 3T3 transformed with SV-40. In these cells, IL-1 and bradykinin stimulated PGE2 synthesis despite basal intracellular cAMP concentrations similar to BALB/c, and cAMP only modestly potentiated the response. In summary, cyclooxygenase expression appears to be regulated by cAMP in BALB/c 3T3 cells, and SV-40 transformation results in increased cyclooxygenase expression, apparently independent of cAMP.     

Dual effects of bradykinin on prostaglandin metabolism: Relationship to the dissimilar vascular actions of kinins

Generation of a prostaglandin of the F series by bovine mesenteric veins in response to bradykinin may depend on increased synthesis of PGE and conversion of the latter to PGF after activation of PGE 9-ketoreductase by the kinin. The prostaglandin then mediates the constrictor action of bradykinin on the bovine mesenteric vein. A high speed supernatant (HSS) fraction of bovine mesenteric blood vessels contains the highest activity of PGE 9-ketoreductase. Incubation of PGE₂ with HSS at 37°C in the presence of a NADPH generating system resulted in time-dependent conversion of PGE₂ to PGF_2α. Bradykinin (0.01mM) more than doubled conversion of PGE₂ to PGF_2α by the PGE 9-ketoreductase obtained from mesenteric veins whereas the kinin had little effect on enzymic activity of the HSS fraction of mesenteric arteries. However, after inhibition of kininase catabolism, bradykinin increased PGE 9-ketoreductase activity of arteries and veins to the same degree.Prostaglandin release from veins by bradykinin appears essential to contraction of mesenteric venous strips evoked by the polypeptide as indomethacin treatment abolished this effect. PGE 9-ketoreductase may be an important prostaglandin regulatory mechanism of the vascular wall whereby the functional consequences of changes in rates of prostaglandin synthesis are governed by determining the ratio of PGE to PGF within vascular tissue. Constriction of bovine mesenteric veins evoked by bradykinin may, therefore, depend on increased prostaglandin synthesis and conversion of newly formed PGE to PGF, both steps being affected by the kinin.     

Sensory pathways and cyclooxygenase regulate mucus gel thickness in rat duodenum

We previously showed that the duodenal hyperemic response to acid occurs through activation of capsaicin-sensitive afferent nerves with subsequent release of vasodilatory substances such as calcitonin gene-related peptide (CGRP) and nitric oxide. We then tested the hypothesis that similar factors regulate duodenal mucus gel thickness. Gel thickness was optically measured using in vivo microscopy in anesthetized rats. Duodenal mucosae were superfused with pH 7.0 buffer with vanilloid receptor agonist capsaicin, bradykinin, or PGE(2) injection or were challenged with pH 2.2 solution, with or without the vanilloid antagonist capsazepine, human CGRP-(8-37), N(G)-nitro-L-arginine methyl ester, and indomethacin. Other rats underwent sensory ablation with high-dose capsaicin pretreatment. Acid, bradykinin, capsaicin, and PGE(2) all quickly thickened the gel. Antagonism of vanilloid and CGRP receptors, inhibition of nitric oxide synthase, and sensory deafferentation delayed gel thickening, suggesting that the capsaicin pathway mediated the initial burst of mucus secretion that thickened the gel. Indomethacin abolished gel thickening due to acid, bradykinin, and capsaicin. Inhibition of gel thickening by indomethacin in response to multiple agonists suggests that cyclooxygenase activity is essential for duodenal gel thickness regulation. Duodenal afferent neural pathways play an important role in the modulation of cyclooxygenase-mediated physiological control of gel thickness.     

Bradykinin and not cholecystokinin stimulates exaggerated prostanoid release from the inflamed rabbit gallbladder.

The relationship of bradykinin and cholecystokinin (CCK) to inflamed gallbladder prostanoid synthesis and release was examined in rabbits treated with common bile duct ligation (BDL) for 24 or 72 h. Gallbladders removed from control and BDL groups were incubated in oxygenated Krebs buffer at 37 degrees C (pH 7.4) for 60 min. The slices were then placed every 20 min in vials containing increasing doses of bradykinin (30-3000 ng) or CCK (30-1000 ng). Incubation fluid was analyzed by RIA for 6-keto-prostaglandin (PG)F1 alpha (PGI2 metabolite), PGE2 and thromboxane (TX) B2. Bradykinin stimulated control gallbladder 6-keto-PGF1 alpha and PGE2 release was modest. Gallbladders from 24- and 72-h BDL groups released 3- to 10-fold higher levels of 6-keto-PGF1 alpha and PGE2 (not TXB2) following bradykinin stimulation when compared to controls, which was abolished with indomethacin pretreatment. CCK did not stimulate gallbladder prostanoid release in the control or BDL groups. These data show that bradykinin and not CCK stimulated PGI2 and PGE2 release from inflamed rabbit gallbladder. Increased BDL gallbladder PGI2 release may be prolonged or augmented by bradykinin as gallbladder distention and progressive acute inflammation stimulate local bradykinin formation.     

Potentiation of bradykinin-induced vascular permeability increase by prostaglandin E2 and arachidonic acid in rabbit skin.

The activity of prostaglandins (PG) in producing vascular permeability was quantitated by dye extraction method in skin of anaesthetized rabbits. PGE1 and PGE2 (0.01-10 mug) produced increase in vascular permeability. Activity was approximately equal to that of histamine (Hist) and 1/20 of that of bradykinin (BK) on a weight basis. The activity of PGF1alpha and PGF2alpha was only 1/20 of that of PGE1 or PGE2. In spite of the relatively low potency of PGE1 and PGE2 in the rabbit, near threshold doses (0.1 or 1 mug) of PGE2 could potentiate permeability responses to bradykinin (0.1 mug) by 10 or 100-fold, respectively. Equivalent doses (0.1 or 1 mug) of histamine could not potentiate the bradykinin responses. Arachidonic acid (AA) at 1 mug, produced a 10-fold potentiation in the permeability response to bradykinin (0.1 mug). Pretreatment of the rabbits with indomethacin (20 mg/kg, i.p.) reduced the responses of BK (0.1 mug) + AA (1 mug) down to a similar magnitude of those seen with bradykinin alone. However, indomethacin did not block responses to either, BK alone, BK + PGE2, or BK + Hist. Various doses (1, 10, 100 and 300 mug) of arachidonic acid alone also produced increase in cutaneous vascular permeability, although its potency was only 1/3-1/8 of that of PGE2. This activity of arachidonic acid was attributed in part to its bioconversion to PGE2, since its activity was significantly reduced by the prostaglandin antagonist, diphloretin phosphate (DPP) (60 mg/kg, i.v.) and by indomethacin (20 mg/kg, i.p.), which blocks conversion of arachidonic acid to prostaglandins. Arachidonic acid may owe some of its permeability increasing effects to histamine release, since its effects were also reduced by the anti-histamine, pyrilamine (2.5 mg/kg, i.v.).     

Diversity of B2 bradykinin receptors with nanomolar affinity expressed in passaged IMR90 human lung fibroblasts.

IMR90 human fetal lung fibroblasts express bradykinin receptors activating the pathway for biosynthesis of PGE2. A receptor of the B2 subtype stimulates half-maximal PGE2 production at 4.8 nM bradykinin, and maximal output takes place at 25 nM bradykinin. Radioligand binding studies reveal a population of [3H]bradykinin binding sites whose affinity correlates with this B2 receptor's biologic activity, with a KD of 2.5 nM. As IMR90 cells reach 60% of their defined life span in culture, they spontaneously induce expression of a second site of lower affinity, with half-maximal binding of [3H]bradykinin at 44 nM. This second site displays a characteristic primary B2 receptor recognition profile, but differs from the 2.5 nM site on a secondary level in recognition among different B2 ligands. Bradykinin is the most potent ligand at both sites; they each preferentially recognize an N-terminal extended bradykinin peptide construct having selectivity for the rat myometrial B2 receptor, suggesting that both sites have structural features in common. However, they display diversity in their order of preference for Met-Lys-bradykinin versus Lys-Lys-bradykinin; at the 44 nM site this order is completely reversed from the order of potency exhibited at the 2.5 nM site. Expression of the second site changes the manner in which these fibroblasts control their PGE2 production; it affords a graded response of PGE2 production at bradykinin levels beyond those which would normally saturate the 2.5 nM site. The inducibility of the 44 nM site in cultured fibroblasts addresses in vivo conditions in an inflammatory environment where continuing generation of bradykinin-related peptides takes place and presents a possible mechanism for overriding constraints that would otherwise limit the progression of inflammation.     

Phorbol esters and diacylglycerols amplify bradykinin-stimulated prostaglandin synthesis in Swiss 3T3 fibroblasts. Possible independence from protein kinase C

When Swiss 3T3 fibroblasts were incubated with bradykinin, prostaglandin E2 (PGE2) synthesis was stimulated. Phorbol esters or the diacylglycerol analog 1-oleoyl-2-acetylglycerol (OAG), by themselves, did not acutely stimulate PGE2 synthesis. However, when cells were preincubated with phorbol esters or OAG, bradykinin-stimulated PGE2 synthesis was potentiated markedly. When phorbol esters and OAG were added together, bradykinin-stimulated PGE2 synthesis was potentiated in an additive manner. When cells were preincubated for 48 h with phorbol esters, then bradykinin added, amplification of bradykinin-stimulated PGE2 synthesis by phorbol ester or OAG was still apparent, even though prolonged pretreatment with phorbol esters abolished protein kinase C (Ca2+/phospholipid-dependent enzyme) activity in cell-free preparations. Further, the protein kinase C antagonist, H-7, only slightly inhibited phorbol ester or OAG amplification of bradykinin-stimulated PGE2 synthesis. The possibility is raised that diacylglycerol, formed in response to many receptors, may serve as a transducer of receptor-receptor interactions. Since desensitization or inhibition of protein kinase C only partially reduced the amplification of bradykinin-stimulated PGE2 synthesis by phorbol esters or OAG, the possibility is raised that diacylglycerol mimetics may have actions in addition to activation of protein kinase C.     

Effect of bradykinin on prostaglandin synthetase activity in microsomal fractions from rat duodenum and uterus.

The bioconversion of tritiated arachidonic acid by microsomal fractions from rat uterus and duodenum is described. In rat duodenum the formation of both prostaglandin E2 and F2alpha is enhanced by the peptide hormone bradykinin. In contrast, bradykinin inhibits the synthesis of PGE2 in rat uterus.     

Respiratory effects of electric stimulation of pancreatic afferents in lightly anesthetized cats]

Electrical stimulation of the pancreatic anterior part produces a respiratory arrest followed by a short polypnea. In some cases (20%) the same effects are obtained by electrical stimulation of the afferent nerves. The afferent fibres involved in this phenomena are situated in the great splanchnic nerves.     

Activation of renal mechanosensitive neurons involves bradykinin, protein kinase C, PGE(2), and substance P

Increased renal pelvic pressure or bradykinin increases afferent renal nerve activity (ARNA) via PGE(2)-induced release of substance P. Protein kinase C (PKC) activation increases ARNA, and PKC inhibition blocks the ARNA response to bradykinin. We now examined whether bradykinin mediates the ARNA response to increased renal pelvic pressure by activating PKC. In anesthetized rats, the ARNA responses to increased renal pelvic pressure were blocked by renal pelvic perfusion with the bradykinin B(2)-receptor antagonist HOE 140 and the PKC inhibitor calphostin C by 76 +/- 8% (P < 0.02) and 81 +/- 5% (P < 0.01), respectively. Renal pelvic perfusion with 4beta-phorbol 12,13-dibutyrate (PDBu) to activate PKC increased ARNA 27 +/- 4% and renal pelvic release of PGE(2) from 500 +/- 59 to 1, 113 +/- 183 pg/min and substance P from 10 +/- 2 to 30 +/- 2 pg/min (all P < 0.01). Indomethacin abolished the increases in substance P release and ARNA. The PDBu-mediated increase in ARNA was also abolished by the substance P-receptor antagonist RP 67580. We conclude that bradykinin contributes to the activation of renal pelvic mechanosensitive neurons by activating PKC. PKC increases ARNA via a PGE(2)-induced release of substance P.     

PAR-2 activation,PGE2, and COX-2 in human asthmatic and nonasthmatic airway smooth muscle cells

The protease-activated receptor-2 (PAR-2) is present on human airway smooth muscle (ASM) cells and can be activated by mast cell tryptase, trypsin, or an activating peptide (AP). Trypsin induced significant increases in PGE2 release from human ASM cells after 6 and 24 h and also induced cyclooxygenase (COX)-2 mRNA expression and COX-2 protein. Tryptase and the PAR-2 AP did not alter PGE2 release or COX-2 protein levels, suggesting a lack of PAR-2 involvement. When we compared results in asthmatic and nonasthmatic muscle cells, both trypsin and bradykinin induced less PGE2 from asthmatic ASM cells, and bradykinin induced significantly less COX-2 mRNA in asthmatic cells. Significantly less PGE2 was released from proliferating ASM cells from asthmatic patients. In conclusion, trypsin induces PGE2 release and COX-2 in human ASM cells, which is unlikely to be via PAR-2 activation. In addition, ASM cells from asthmatic patients produce significantly less PGE2 and COX-2 compared with nonasthmatic cells. These findings may contribute to the increase in muscle mass evident in asthmatic airways.     

Mass quantitation of agonist-induced arachidonate release and icosanoid production in a fibrosarcoma cell line. Effect of time of agonist stimulation, amount of cellular arachidonate, and type of agonist

The mass of total arachidonate released from phospholipids upon agonist stimulation of the cell and the fraction of released arachidonate which is converted to icosanoids are two parameters of arachidonate metabolism which have been difficult to quantitate because the mass of arachidonate released upon cell stimulation is very low. We have been able to quantitate both of these parameters under a variety of experimental conditions using a unique essential fatty acid-deficient mouse fibrosarcoma cell line (EFD-1), which when repleted with arachidonate, produces prostaglandin E2 (PGE2). Because there is no endogenous pool of arachidonate in these cells, the specific activity of exogenous arachidonate does not change upon incorporation into cells, an advantage which permits mass determination of very small quantities of arachidonate directly from radioactive counts. EFD-1 cells were incubated with various concentrations of [14C]arachidonate (for release studies) or unlabeled arachidonate (for PGE2 radioimmunoassays) for 24 h and then stimulated with bradykinin. The time courses for arachidonate release and PGE2 production demonstrated that free arachidonate was rapidly converted to PGE2 with plateau levels attained for both parameters within 240 s of agonist exposure for 2 microM and for 10 microM arachidonate-repleted cultures. There was a linear relationship (r = 0.94) between the mass of arachidonate in the cell and the mass of arachidonate released upon stimulation, up to a cellular concentration of 11 nmol of arachidonate/10(6) cells, a concentration 10-20% above normal for the parent mouse fibrosarcoma cell line (HSDM1C1) which is not essential fatty acid-deficient. Importantly, the percent of released arachidonate which was converted to PGE2 decreased from 90 to 15% with increasing concentrations of cellular arachidonate, because PGE2 production plateaued at greater than or equal to 6 nmol of arachidonate/10(6) cells, but total arachidonate release continued to rise. Finally, we demonstrated that agonist stimulation with thrombin, A23187, and bradykinin all showed the same percent conversion of released arachidonate to PGE2, implying that the determination of this fraction is not a function of the mechanism of release. These studies with our unique cell line indicate that, when the concentration of arachidonate in the cell is not elevated above amounts normally found in our HSDM1C1 cell line, released arachidonate is rapidly and almost quantitatively converted to PGE2, independent of the agonist used to stimulate the cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

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

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