Effect of prostaglandin E2 on vascular responses of the rabbit kidney to nerve stimulation and noradrenaline, in vitro and in situ

Effects of bradykinin on renal nerve stimulation-induced antidiuresis and norepinephrine overflow in anesthetized dogs

We examined effects of bradykinin on antidiuresis and norepinephrine overflow induced by renal nerve stimulation (RNS) in anesthetized dogs, with or without blockade of the B2 receptor by Hoe 140 (D-Arg-[Hyp3, Thi5, D-Tic7, Oic8]bradykinin) or the endogenous nitric oxide generation by N(G)nitro-L-arginine (NOARG), a nitric oxide synthase inhibitor. RNS (0.5-2.0 Hz) produced significant decreases in urine flow, urinary and fractional excretions of sodium, and increases in norepinephrine secretion rate (NESR), without affecting systemic and renal hemodynamics. Intrarenal arterial infusion of bradykinin (5 ng/kg per minute) significantly suppressed the RNS-induced antidiuresis and increase in NESR. Hoe 140 (100 ng/kg per minute) did not affect the RNS-induced renal actions, but in the presence of Hoe 140, bradykinin-induced suppressive actions on reductions in urine formation and increases in NESR in response to RNS were abolished. RNS during intrarenal arterial infusion of NOARG (40 microg/kg per minute) led to potent reductions in urine formation and decreased renal blood flow and glomerular filtration rate. Simultaneously, NESR was markedly increased. During NOARG infusion, bradykinin-induced decreases in renal actions elicited by RNS were markedly attenuated. These findings suggest that bradykinin suppresses the RNS-induced norepinephrine overflow and renal actions via nitric oxide production mediated by activation of B2 receptor. Renal noradrenergic neurotransmission may be inhibited by bradykinin at the prejunctional level, when its local production in the kidney is enhanced.

Renal vascular interaction of angiotensin II and prostaglandins in renovascular hypertension

The vascular responses to angiotensin II (Ang II) in the renal circulation are increased in kidneys from rats with aortic coarctation compared with sham-operated rats. We have suggested that these differences are related to changes in mediators of the Ang II effect. The aim of this study was to investigate the role of arachidonic acid (AA) metabolites on the Ang II effect in the renal circulation of normotensive and hypertensive rats. We evaluated vascular renal reactivity in the rat isolated perfused kidney. Bolus injection of Ang II (9, 18, 36, 72 ng) increased perfusion pressure in a dose-dependent manner by 16.5+/-4, 23.5+/-4, 35.5+/-7, and 42.5+/-7 mm Hg in sham-operated rats and 50+/-6, 72+/-10, 92+/-6, and 120+/-6 mm Hg in rats with aortic coarctation. Ang II-induced vasoconstriction was prevented in hypertensive rats and potentiated in normotensive rats by the presence of indomethacin (1 microg/ml) in the perfusion solution. Furthermore, the use of the endoperoxide/thromboxane blocker (SQ29548, 1 microM) did not alter the effect of Ang II on the normotensive rats but prevented its effect in hypertensive rats. Moreover, the prostaglandin/ thromboxane (PGH2/TxA2) receptor agonist U46619 increased perfusion pressure to similar values in both kidneys from sham-operated or aortic coarctation rats. Ang II stimulated AA and prostaglandin release from isolated perfused kidneys. However, autacoid release was higher in kidneys from rats with aortic coarctation. In conclusion, we suggest that during the development of hypertension, the AA metabolism of vasoconstrictor prostaglandins is increased, and it mediates the vasoconstrictive effects of Ang II.

Effect of sodium loading (3% NaCl) on arachidonic acid biosynthesis in rat liver microsomes

Sodium loading increases arachidonic acid (AA) metabolism by way of the prostaglandins(PGs) from series 2. Its effect on AA biosynthesis remains unknown. The purpose of the present study was to investigate the influence of sodium loading on the fatty acid composition of liver and liver microsomes, and the liver microsomal delta-6 and delta-5 desaturations of linoleic acid (LA) into AA. We found a decrease of LA and dihomo-gamma-linolenic acid (DGLA) levels in liver total lipids of Wistar rats receiving hypernatriuretic drinking water (NaCl 3%) for 60 days. At the same time AA increased. DGLA decreased and AA increased in liver microsomal total lipids. 1(14) C-LA delta-6 desaturase and 2(14) C-DGLA delta-5 desaturase activities increased in liver microsomes. These results show that, in addition to its influence on the regulation of glomerular filtration, sodium loading is involved in the regulation of liver AA biosynthesis.

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.

Renal vasodilation by a prostaglandin analog during dopaminergic and alpha-adrenergic blockade

The possible participation of dopaminergic and alpha-adrenergic renal vascular receptors in the renal blood flow response to a new prostaglandin (PG) analog was investigated in anesthetized dogs. Alpha-adrenergic blockade with phenoxybenzamine (POB) enhanced the renal blood flow (RBF) responses to intrarenal (ira) injections of (0.75 to 48 micrograms/kg) dopamine but not to the PG analog (0.05 to 20 micrograms/kg i.v.) or to PGE2 (0.32 to 40 ng/kg ira). In phenoxybenzamine-treated dogs, bulbocapnine, a dopamine antagonist, blocked the increases in RBF stimulated by intrarenal injections of 0.1 to 24 micrograms/kg dopamine but had no effect on the responses to 0.5 to 100 ng/kg of PGE2. When RBF was elevated to a stable plateau by treatment with the PG analog (0.05 mg/kg i.v.) or by intrarenal infusion of PGE2 (0.01 microgram/kg/min), bulbocapnine (100 micrograms/kg/min) did not alter the effects of either compound. In contrast, the effects of 6 micrograms/kg/min dopamine ira on RBF, mean arterial pressure and renal vascular resistance were reversed by bulbocapnine. We conclude that the PG analog and PGE2 increased RBF by mechanisms which were independent of dopaminergic and alpha-adrenergic pathways.

Blockade of vasoconstrictor responses by prostacyclin (PGI2), PGE2, and PGE1 in the rabbit hindquarters vascular bed

The effects of infusions of prostacyclin (PGI2), PGE2 and PGE1 on responses to pressor hormones and sympathetic nerve stimulation were investigated in the hindquarters vascular bed of the rabbit. During infusions of PGI2, PGE2 and PGE1 vasoconstrictor responses to norepinephrine, nerve stimulation and angiotensin II were decreased. Responses to the pressor hormones and nerve stimulation were decreased to a similar extent by PGI2 and responses returned to control value 30 min after the infusion. During infusions of PGE2 and PGE1 responses to nerve stimulation were decreased to a somewhat greater extent than responses to pressor hormones and the inhibitory action of these substances had a longer duration of action than PGI2. Indomethacin in doses that blocked depressor responses to arachidonic acid was without consistent effect on responses to nerve stimulation and pressor hormones. The present data show that E series prostaglandins and PGI2 possess the ability to modulate responses to nerve stimulation and pressor hormones; however, experiments with indomethacin suggest that endogenous prostaglandins do not modulate vasoconstrictor responses in the rabbit hindquarters.

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.

Actions of prostacyclin (PGI2) on adrenergic neuroeffector transmission in the rabbit kidney

In the Tyrode's perfused rabbit kidney PGI2 (1.3 x 10(-8)-3.3 x 10(-7)M) dose-dependently inhibited vasoconstrictor responses to sympathetic nerve stimulation, as did PGE2. The dose-effect curve of the two compounds differed, making PGI2 the less potent in the low concentration and the more potent in the high. PGI2 also inhibited the vasoconstrictor response to exogenous noradrenaline, but it had no effect on transmitter release. The main metabolite of PGI2, 6-keto-PGF1 alpha, was ineffective both on noradrenaline release and on vascular responses to nerve stimulation or exogenous noradrenaline. It is suggested that PGI2, if a significant renal prostaglandin, may modulate renal neuroeffector transmission post-junctionally, thereby forming a complement to the prejunctional action of PGE2.

Effect of prostaglandin endoperoxide analogue on canine renal function, hemodynamics and renin release

We studied the effect of a stable, cyclic ether analogue of prostaglandin endoperoxide (EPA) on canine renal function, hemodynamics, and renin release. Infusion of EPA into one renal artery decreased renal blood flow in a dose dependent manner. At a dose of 10(-7) g/kg/min the renal blood flow decreased from a baseline of 384 to 267 ml/min/100 g. This flow decrease was unaltered by phentolamine and saralasin, but was potentiated by prior treatment with indomethacin. Urine flow, glomerular filtration rate, sodium, and potassium excretion all decreased in a dose dependent manner; however, neigher fractional excretion of sodium nor free water clearance showed any significant change, making direct tubular effects of EPA unlikely. EPA caused a significant increase in renin release that was completely blocked by prior treatment with indomethacin. We conclude that EPA is a potent renal vasoconstrictor and that this vasoconstriction is responsible for the renal functional changes observed. Renin release is not a direct effect of EPA but probably is secondary to an endogenously generated prostaglandin. Since EPA mimics the effects of natural prostaglandin endoperoxides on smooth muscle in vitro, it is possible that prostaglandin endoperoxide-induced vasoconstriction in vivo modulates the effects of their vasodilatory products, prostaglandin E2 and I2.

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

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

The effects of salt and meclofenamate administration on the hypertension of spontaneously hypertensive rats

The effects of prolonged (3 mos) high sodium intake and meclofenamate were studied in 2 groups of male SHR. Group 1 (6 rats) received 1% NaCl in tap water and Group 2 (8 rats) received 1% NaCl in tap water plus 50 microgram of meclofenamate per ml of drinking fluid. Renal metabolic and hemodynamic studies in the unanesthetized unrestrained state, showed that the meclofenamate treated rats had higher arterial pressures (p less than .005), left ventricular weight (p less than .05) and renal vascular resistance (p less than .005); lower glomerular filtration rate (p less than .005) than the control rats. The hematocrit and right ventricular weight were similar in the two groups of rats. This study has demonstrated that the combination of high sodium intake and meclofenamate have a greater damaging effect on the arterial pressure and renal function of SHR than salt alone.

Influence of prostaglandin E2, indomethacin, and reserpine on renal vascular responses to nerve stimulation, pressor and depressor hormones

The effects of prostaglandin E2 (PGE2) indomethacin, and reserpine were evaluated in the rabbit renal vascular bed in situ under conditions of controlled blood flow. Intrarenal infusion of PGE2, 0.03 and 0.3 microgram/min, decreased responses to renal nerve stimulation, intra-arterial norepinephrine, and angiotensin. Responses to nerve stimulation were decreased to a greater extent than responses to norepinephrine. At lower concentrations the effects of PGE2 on pressor responses and on vascular resistance could be separated. Reserpine decreased the histochemical evidence of adrenergic innervation and reduced the response to renal nerve stimulation, enhanced the response to norepinephrine, and was without effect on the response to angiotensin. Indomethacin decreased depressor responses to arachidonic acid, produced a small increase in renal vascular resistance but did not enhance renal pressor responses. The increase in renal vascular resistance after indomethacin was not modified by reserpine pretreatment. Indomethacin enhanced the renal response to bradykinin. These data show that PGE2 possesses the ability to modulate pressor responses in the kidney. However, experiments with indomethacin suggest that endogenous prostaglandins neither modulate pressor responses nor mediate the response of the renal vascular bed to bradykinin. In addition, these data suggest that the increase in renal resistance after indomethacin is not dependent on the adrenergic nervous system.

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.

Changes induced by angiotensins and prostaglandin E2 on the release of transmitter from isolated perfused rabbit kidney during periarterial stimulation

The influence of A II and PGE2 on the rise of perfusion pressure induced by periarterial stimulation and NA were studied in the rabbit isolated perfused kidney. Periarterial stimulation produced an increase in perfusion pressure and the venous outflow superfusing the rabbit aortic strip caused the muscle to contract. Both effects were found to be frequency dependent. NA induced similar effect when given into the renal artery. A II and its N-terminal analogs produced equal potentiation to periarterial stimulation without altering the effect of exogenous NA when added to the perfusion medium. DMGIA II which is a competitive inhibitor of A II inhibited the potentiating affect of A II. PGE2 also inhibited the effect of A II without altering the effect of exogenous NA. Addition of aspirin to the perfusion medium caused a potentiation to periarteral stimulation but did not change the effect of NA. A II added to the perfusion fluid containing aspirin still caused potentiation. From these results it was concluded that: (i) A II-induced potentiation to periarterial stimulation is mediated via specific receptors and probably due to facilitation of the release of transmitter from sympathetic nerve ending. (ii) PGE2 inhibited the release of transmitter. The effect of A II and PGE2 seemed to be mediated by independent mechanisms.

Evidence for prostaglandin mediated prejunctional control of renal sympathetic transmitter release and vascular tone

1 Prostaglandin E(2) dose-dependently and reversibly inhibited the noradrenaline overflow resulting from nerve stimulation of the rabbit kidney.2 The magnitude of this inhibition varied inversely with the frequency of stimulation employed.3 The prostaglandin synthesis inhibitors, indomethacin and meclofenamic acid, both increased the transmitter overflow resulting from renal nerve stimulation, suggesting that endogenous prostaglandin has a role in the regulation of transmitter release.4 In the presence of indomethacin, the inhibitory effect of exogenous prostaglandin E(2) was enhanced.5 The prostaglandin precursor, arachidonic acid, also caused a significant, dose-dependent and reversible inhibition of transmitter overflow. This inhibition became insignificant when arachidonic acid was applied in the presence of indomethacin, suggesting that the inhibition was mediated by newly formed prostaglandin rather than by arachidonic acid itself.6 It is proposed that newly formed prostaglandin controls noradrenaline release primarily from inner cortical nerve endings, thereby maintaining juxtamedullary blood flow under periods of increased sympathetic nerve activity.

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.