Effect of noradrenaline, vasopressin and angiotensin II on renal prostaglandins in man

To examine the response of renal prostaglandins (PG) to systemic and renal vasoconstriction noradrenaline (NA), arginine vasopressin (AVP) and angiotensin II (ANG II) were each infused into eight healthy female subjects for 3 h on different days. Urinary excretion of PGE2, PGF2 alpha and 6-keto-PGF1 alpha was determined hourly. NA and ANG II stimulated excretion of PGF2 alpha significantly, but not of PGE2 or 6-keto-PGF1 alpha. AVP stimulated renal PGF2 alpha and 6-keto-PGF1 alpha significantly, but not PGE2. A weak correlation was found between urinary PGF2 alpha and diastolic blood pressure during NA and ANG II infusions, but not during AVP infusion. The release of renal PG does not appear to constitute an obligatory and concomitant response to the blood pressure rise induced by the pressor agonists. The greater response of PGF2 alpha than of PGE2 may result from a preferential direct effect on PGF2 alpha secretion or from an increased conversion of PGE2 into F2 alpha.     

Effect of converting enzyme inhibitors on prostaglandin synthesis by isolated glomeruli and aortic strips from rats

In addition to their effect on angiotensin and bradykinin metabolism, converting enzyme inhibitors (CEI) may also alter prostaglandin (PG) synthesis. We therefore examined two CEI, SQ 14,225 (captopril) and SQ 20,881, for their in vitro effect on PG synthesis by glomeruli and aortic strips from rats. Glomeruli incubated in test tubes produced predominantly PGE2 and PGF2 alpha. Both CEI selectively stimulated PGE2 synthesis with maximal effects at 25 microM. During superfusion of glomeruli with captopril (25 microM) synthesis of PGE2 increased 5- to 10-fold and that of 6-keto-PGF1 alpha doubled. No significant change in PGF2 alpha or thromboxane B2 occurred. This effect of CEI was independent of angiotensin or bradykinin. In contrast captopril had no effect on PG synthesis by aortic strips, which produced predominantly prostacyclin assayed as 6-keto-PGR1 alpha and little PGE2 and PGF2 alpha. These results demonstrate that CEI can directly stimulate PG synthesis in glomeruli. This additional mechanism of action of CEI may require reinterpretation of the role of angiotensin based on results obtained with CEI.     

Prostaglandin synthesis by rat glomerular mesangial cells in culture. Effects of angiotensin II and arginine vasopressin.

Arginine vasopressin (AVP) and angiotensin II (ANG II) reduce the glomerular filtration rate and ultrafiltration coefficient. Vasodilatory prostaglandins (PG) antagonize these effects. AVP and ANG II also cause mesangial cell contraction. Therefore, possible PG stimulation by these peptides and two vasopressin analogues was studied in cultured rat glomerular mesangial cells. The effect of altered calcium availability on PG production was also studied. Glomeruli from 75-100-g Sprague-Dawley rats were cultured in supplemented nutrient media for 28 d and experiments were performed on the first passage. Mesangial cell morphology was confirmed by electron microscopy. Cells produced PGE2 much greater than PGF2 alpha greater than 6-keto-PGF1 alpha greater than thromboxane B2 when incubated with the divalent cation ionophore, A23187, or arachidonic acid (C20:4). ANG II and AVP selectively stimulated PGE2 at threshold concentrations of 10 nM ANG II and 100 pM of AVP. The effects of the antidiuretic analogue 1-desamino-8-D-arginine vasopressin (dDAVP) and the antipressor analogue [1-(beta-mercapto-beta beta-cyclopentamethylene propionic acid)-4-valine, 8-D-arginine]-vasopressin (d[CH2]5VDAVP), were studied. Neither compound stimulated PGE2 and preincubation with d(CH2)5VDAVP abolished, and dDAVP blunted, AVP-enhanced PGE2 production. Incubation in verapamil, nifedipine, or zero calcium media blocked peptide-stimulated PGE2 production. Increasing extracellular calcium or adding A23187 increased PGE2 synthesis. Selective stimulation of PGE2 by ANG II or AVP in mesangial cells suggests a hormone-sensitive phospholipase and a coupled cyclooxygenase capable of synthesizing only PGE2. Since neither vasopressin analogue stimulated PGE2, but both blocked AVP-enhanced PGE2 production, we conclude that these cells respond to the pressor activity of AVP. This is a calcium-dependent process. Selective stimulation of PGE2 by ANG II and AVP may modulate their contractile effects on the glomerulus.     

Prostaglandin I2 is not a major metabolite of arachidonic acid in cultured endothelial cells from human foreskin microvessels

Prostaglandin I2 (PGI2), a potent vasodilator and inhibitor of platelet aggregation, is a major product of arachidonic acid metabolism in endothelial cells that are derived from large blood vessels (e.g., umbilical veins). We have examined whether PGI2 is also a major product of arachidonic acid metabolism in cultured endothelial cells that are derived from dermal microvessels in human newborn foreskin. Supernatants from confluent monolayers of endothelial cells that had been incubated for 20 min with [3H]arachidonic acid and the calcium ionophore A23187 (10 microM) were assayed for prostaglandin F2 alpha (PGF2 alpha), prostaglandin E2 (PGE2), and 6-keto-prostaglandin F1 alpha (PGF1 alpha) (the stable metabolite of PGI2) by using authentic standards and high performance liquid chromatography. Whereas supernates from stimulated umbilical vein endothelial cells contained 6-keto-PGF 1 alpha much greater than PGF 2 alpha much greater than PGE2, supernates from stimulated foreskin microvessel endothelial cells contained PGF 2 alpha congruent to PGE2 much greater than 6-keto-PGF 1 alpha. Similar results were obtained when supernates from stimulated, unlabeled endothelial cells were analyzed by radioimmunoassay. These data indicate that PGI2 is not a major metabolite of arachidonic acid in cultured endothelial cells from human foreskin microvessels.     

Prostanoids and thromboxane production by renal brush border membrane.

It has been estimated that proximal tubule are responsible for about 7.5% of total kidney prostaglandin PGE2 production. In the present report we investigated the production of prostanoids and thromboxane by rabbit renal proximal tubule brush border membrane. PGF2 alpha was the major endogenous prostaglandin produced under basal condition. The addition of exogenous arachidonic acid increased only PGE2 production. No PGE2 production was found when vesicles were incubated with indomethacin or at 4 degrees C, suggesting the involvement of the PGH2 synthase and PGE2 isomerase enzymes. Addition of angiotensin II at 10(-6) and 10(-9) mol l-1 did not affect the endogenous PGE2 production by brush border membrane. Thus, results of our study demonstrates that the renal proximal tubule brush border membrane has the capacity to produce prostanoids and thromboxane.     

Effects of sodium depletion on renal prostanoid synthesis in rats: influence of the converting enzyme inhibitor captopril

1. The synthesis of prostaglandin (PG) E2, PGF2 alpha, 6-keto-PGF1 alpha and thromboxane (TX) B2 by isolated glomeruli, cortical tubules, inner medullary slices and outer medullary slices was measured in salt-depleted (LNa) rats and in salt-depleted rats receiving captopril (LNa-CEI). Animals were studied before and after 4, 9 and 15 days of Na+ depletion. 2. Na+ balance was reached in LNa rats after 4 days. Blood pressure and creatinine clearance remained stable. Serum Na+ decreased from 140 +/- 1 to 126 +/- 1 mmol/l (mean +/- SEM, P less than 0.01). In contrast, LNa-CEI rats were unable to conserve Na+ adequately: fractional excretion of Na+ and natriuresis were constantly greater than in LNa animals. As a consequence, LNa-CEI rats developed severe hyponatraemia, lost weight and their creatinine clearance decreased. 3. The glomerular synthesis of PGE2, PGF2 alpha and 6-keto-PGF1 alpha, but not of TXB2, was significantly increased in LNa rats. In LNa-CEI rats, the synthesis of PGE2 and 6-keto-PGF1 alpha was similar to control values, but PGF2 alpha and TXB2 synthesis was elevated at day 9. In cortical tubules, PGE2 and PGF2 alpha were unaffected by Na+ depletion, but 6-keto-PGF1 alpha and TXB2 were increased and a similar trend was observed in LNa-CEI rats. In outer medulla of LNa rats, a decrease in all the eicosanoids measured was observed at day 4. In LNa-CEI animals, the synthesis of PGE2 and PGF2 alpha, but not of 6-keto-PGF1 alpha and TXB2, was significantly depressed. In inner medulla, Na+ depletion only tended to decrease PGF2 alpha and 6-keto-PGF1 alpha, but in the presence of captopril, the synthesis of all prostanoids was significantly decreased.     

Increased renal vasodilator prostanoids prevent hypertension in mice lacking the angiotensin subtype-2 receptor

The angiotensin subtype-1 (AT(1)) receptor mediates renal prostaglandin E(2) (PGE(2)) production, and pharmacological blockade of the angiotensin subtype-2 (AT(2)) receptor potentiates the action of angiotensin II (Ang II) to increase PGE(2) levels. We investigated the role of the AT(2) receptor in prostaglandin metabolism in mice with targeted deletion of the AT(2) receptor gene. Mice lacking the AT(2) receptor (AT(2)-null) had normal blood pressure that was slightly elevated compared with that of wild-type (WT) control mice. AT(2)-null mice had higher renal interstitial fluid (RIF) 6-keto-PGF(1alpha) (a stable hydrolysis product of prostacyclin [PGI(2)]) and PGE(2) levels than did WT mice, and had similar increases in PGE(2) and 6-keto-PGF(1alpha) in response to dietary sodium restriction and Ang II infusion. In contrast, AT(2)-null mice had lower PGF(2alpha) levels compared with WT mice during basal conditions and in response to dietary sodium restriction or infusion of Ang II. RIF cAMP was markedly higher in AT(2)-null mice than in WT mice, both during basal conditions and during sodium restriction or Ang II infusion. AT(1) receptor blockade with losartan decreased PGE(2), PGI(2), and cAMP to levels observed in WT mice. To determine whether increased vasodilator prostanoids prevented hypertension in AT(2)-null mice, we treated AT(2)-null and WT mice with indomethacin for 14 days. PGI(2), PGE(2), and cAMP were markedly decreased in both WT and AT(2)-null mice. Blood pressure increased to hypertensive levels in AT(2)-null mice but was unchanged in WT. These results demonstrate that in the absence of the AT(2) receptor, increased vasodilator prostanoids protect against the development of hypertension.     

Neuropeptide Y stimulates renal prostaglandin synthesis in the isolated rat kidney: contribution of Ca++ and calmodulin

We have investigated the effects of neuropeptide Y (NPY) on vascular tone and renal output of prostaglandins (PGs) and the mechanism underlying these actions by examining the effects of Ca++ depletion, Ca++ channel blockers and calmodulin inhibitors in the isolated Tyrode's perfused rat kidney. Administration of NPY (0.23-2.3 nmol) into the kidney produced a dose-related renal vasoconstriction and an increase in the output of PGE2 and 6-keto-PGF1 alpha, the stable hydrolysis product of PGI2. Omission of Ca++ (1.8 mM) or addition of Ca++ channel blockers, diltiazem (60 microM) or nifedipine (1.4 microM), to the perfusion fluid abolished the effects of NPY to promote renal vasoconstriction and PG synthesis. Infusion of calmodulin inhibitors, trifluoperazine (2 microM), W-7 [N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide] (20 microM) or calmidazolium (0.2 microM), attenuated the renal vasoconstriction and the increase in PG output produced by NPY (0.7 nmol). In kidneys perfused with normal Tyrode's solution, infusion of NPY, in a concentration (1.7 X 10(-8) M) that produced only a small transient increase in renal vascular tone and failed to alter the renal output of PGs, enhanced the rise in PGE2 and 6-keto-PGF1 alpha elicited by norepinephrine (0.25 nmol) but not by arginine vasopressin (0.004 nmol) or angiotensin II (0.09 nmol). The renal vasoconstriction elicited by norepinephrine and arginine vasopressin as well as by angiotensin II was enhanced by NPY.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evidence that prostacyclin modulates the vascular actions of calcium in man.

Increases in extracellular calcium (Ca++) can alter vascular tone, and thus may result in increased blood pressure (Bp) and reduced renal blood flow (RBF). Ca++ can stimulate prostaglandin E2 (PGE2) and/or prostacyclin (PGI2) release in vitro, which may modulate Ca++ vascular effects. However, in man, the effect of Ca++ on PG release is not known. To study this, 14 volunteers received low-dose (2 mg/kg Ca++ gluconate) or high-dose (8 mg/kg) Ca++ infusions. The low-dose Ca++ infusion did not alter systemic or renal hemodynamics, but selectively stimulated PGI2, as reflected by the stable metabolite 6-keto-PGF1 alpha in urine (159 +/- 21-244 +/- 30 ng/g creatinine, P less than 0.02). The same Ca++ infusion given during cyclooxygenase blockade with indomethacin or ibuprofen was not associated with a rise in PGI2 and produced a rise in Bp and fall in RBF. However, sulindac, reported to be a weaker renal PG inhibitor, did not prevent the Ca++ -induced PGI2 stimulation (129 +/- 33-283 +/- 90, P less than 0.02), and RBF was maintained despite similar increases in Bp. The high-dose Ca++ infusion produced an increase in mean Bp without a change in cardiac output, and stimulated urinary 6-keto-PGF1 alpha to values greater than that produced by the 2-mg/kg Ca++ dose (330 +/- 45 vs. 244 +/- 30, P less than 0.05). In contrast, urinary PGE2 levels did not change. A Ca++ blocker, nifedipine, alone had no effect on Bp or urinary 6-keto-PGF1 alpha levels, but completely prevented the Ca++ -induced rise in Bp and 6-keto-PGF1 alpha excretion (158 +/- 30 vs. 182 +/- 38, P greater than 0.2). However, the rise in 6-keto-PGF1 alpha was not altered by the alpha 1 antagonist prazosin (159 +/- 21-258 +/- 23, P less than 0.02), suggesting that calcium entry and not alpha 1 receptor activation mediates Ca++ pressor and PGI2 stimulatory effects. These data indicate a new vascular regulatory system in which PGI2 modulates the systemic and renal vascular actions of calcium in man.     

Glomerular prostaglandins: synthesis, mechanism of action and interaction with ACE inhibitors]

Prostaglandins (PG) play an important role in the regulation of the renal blood flow and glomerular filtration rate. This study was designed to examine PG synthesis in the presence and absence of the ACE inhibitor captopril, PG binding to specific receptors and the ability of PG to stimulate cAMP accumulation in isolated glomeruli. Glomeruli were isolated from rat kidneys by a passive mechanical sieving technique. PG synthesis was determined by RTLC and RIA. The main eicosanoids synthesized by glomeruli were PGF2 alpha, thromboxane (TX) A2 (measured as TXB2), PGI2 (measured as 6-keto-PGF1 alpha) and PGE2. Binding experiments were performed with PGE1, PGE2 and the PGI2 analogue iloprost. Scatchard analysis revealed that the specific binding was highest for PGE1, followed by iloprost and PGE2. Adenylate cyclase was preferentially stimulated by PGE1 and PGE2, and to a lesser extent by PGI2, whereas PGF2 alpha had almost no effect. Captopril reduced mainly TXB2 concentrations. Glomerular TXB2 reduction, therefore, seems to be an additional hypotensive effect of captopril medication.     

Prostaglandin biosynthesis by rabbit renomedullary interstitial cells in tissue culture. Stimulation by angiotensin II, bradykinin, and arginine vasopressin.

Rabbit renomedullary interstitial cells were isolated and grown in tissue culture. These cells synthesize 0.8 ng of prostaglandin E2 (PGE2) per microgram cellular protein per hour in monolayer tissue culture; prostaglandins A2 and F2alpha (PGA2 and PGF2alpha) biosynthesis was 10 and 5% of PGE2 biosynthesis, respectively. Arachidonic acid markedly stimulated the production of PGE2 and PGF2alpha, with conversion rates of 0.24 and 0.02%/h, respectively. Angiotensin II, hyperosmolality, bradykinin, and arginine vasopressin each stimulated PGE2 biosynthesis; maximum stimulation was 20, 3.7, 3.6, and 3.2 times basal production, respectively. PGE2 biosynthesis by the renomedullary interstitial cells was inhibited by isoproterenol, potassium, nonsteroidal anti-inflammatory agents (indomethacin, naproxen, ibuprofen, suprofen, meclofenamate, and acetylsalicylic acid), mepacrine (a phospholipase inhibitor), hydrocortisone, and cortisone. The rabbit renomedullary interstitial cell in tissue culture is a model system for the study of hormonal regulation of PGE2 biosynthesis.     

Angiotensin and prostaglandin interactions in cultured kidney tubules

Angiotensin and prostaglandin interactions in cultured kidney tubules were studied in tissue from fetal calves. Methods were developed for the isolation and culture of renal proximal tubule cells. Tubule cells survived three generations in culture. They had microvilli and flagellae characteristic of proximal tubule cells. Binding of 125I-angiotensin II to receptor-like sites in cells and homogenates was partially saturable, and the saturable binding was reversed by excess unlabeled hormone. Two types of binding sites were identified by Scatchard analysis. The higher-affinity site had a dissociation constant of 5 X 10(-10)M. PGE2 and PGA2 inhibited angiotensin binding. PGF2 alpha had no effect. Cultured tubule cells were loaded with 22Na+ by incubation in hypoxic medium free of potassium and glucose. Cells extruded the sodium when oxygen, glucose, and potassium were added. The rate of extrusion was accelerated by angiotensin II at concentrations of 10(-10)M and 10(-9)M. Higher concentrations had less effect. The primary prostaglandins PGA2 and PGF2 alpha inhibited 22Na+ efflux at 6 X 10(-7)M. Angiotensin had no detectable effect on sodium efflux in the presence of PGA2. Angiotensin apparently reversed inhibition of efflux by PGF2 alpha. Our findings suggest that prostaglandins affect angiotensin receptors in renal tubule cells. Prostaglandins also have direct effects on sodium efflux in these cells under the experimental conditions described.     

Attenuation of Angiotensin II- and III-induced Aldosterone Release by Prostaglandin Synthesis Inhibitors

The effect of two prostaglandin synthesis inhibitors, indomethacin and meclofenamate, on angiotensin II (AII)- and III (AIII)-induced aldosterone release was studied in normal and sodium-depleted conscious rats and in adrenal capsular cell suspensions obtained from normal rats. In normal rats, in vivo AII and AIII were equipotent in causing dose-related increases in serum aldosterone concentrations. Indomethacin decreased the basal serum aldosterone levels by 50% and serum renin levels by 43%. In addition, the steroidogenic effects of AII and AIII were reduced by 45 and 63% with 3 mg/kg of indomethacin and 63 and 73% with 10 mg/kg, respectively. In contrast, meclofenamate failed to alter basal serum levels of aldosterone or AII-stimulated aldosterone release but inhibited serum renin levels by 27% and the aldosterone-stimulating effect of AIII by 99%. Indomethacin (3 mg/kg) and meclofenamate (2 mg/kg) inhibited urinary prostaglandin (PG)E(2) and PGF(2alpha) excretion by 63 and 52% and 37 and 31%, respectively. Both inhibitors significantly decreased the adrenal capsular PGE(2) and PGF(2alpha) content and the conversion of [(14)C]arachidonate to [(14)C]PGE(2) and [(14)C]PGF(2alpha). In sodium-depleted rats, indomethacin produced similar effects reducing the control serum aldosterone levels by 29%, AII-stimulated aldosterone by 47%, and completely suppressing the aldosterone response to AIII without altering serum renin activity. In adrenal cell suspensions, similar results were observed with indomethacin inhibiting basal and AII- and AIII-stimulated aldosterone release by 29, 81, and 93%, respectively. Meclofenamate failed to alter basal and AII-stimulated aldosterone release but inhibited that stimulated by AIII by 86%. The present findings suggest that prostaglandins modulate the effects of the renin-angiotensin system by stimulating the release of renin from the kidney and augmenting the steroidogenic effects of AII and AIII in the adrenal cortex.     

Alpha adrenergic receptors mediate angiotensin-induced prostaglandin production in the rabbit isolated vas deferens

The effect of alpha adrenergic receptor antagonists on concentration-dependent response to angiotensins II and III was examined in the electrically stimulated isolated rabbit vas deferens. The force generated by a nonadrenergic neural mechanism was reduced by both peptides whereas the force generated by adrenergic neural mechanisms was enhanced. Angiotensin III-induced inhibition of the nonadrenergic contraction was significantly greater than that of angiotensin II for all groups. Yohimbine (1 X 10(-4) M), an alpha-2 receptor antagonist, attenuated the depression of the nonadrenergic contraction produced by angiotensins II and III. Yohimbine (1 X 10(-5) and 1 X 10(-4) M) also significantly reduced angiotensin II-induced prostaglandin E (PGE) synthesis. Yohimbine only significantly altered the angiotensin III-induced PGE synthesis at an antagonist concentration of 1 X 10(-4) M. Rauwolscine (1 X 10(-8) and 1 X 10(-7) M) attenuated angiotensin II-induced PGE production and at a higher concentration (1 X 10(-6) M) reduced angiotensin III-induced PGE production. The alpha-1 antagonist, prazosin (1 X 10(-6) M), did not alter nonadrenergic contractile or PGE responses to either angiotensin. The alpha-2 agonist, clonidine, both inhibited the nonadrenergic neural contraction and enhanced PGE synthesis. We interpret these data to indicate that angiotensins II and III may act via separate mechanisms to induce PGE synthesis in the vas deferens, with angiotensin II effects being more dependent on norepinephrine release from adrenergic nerves.     

Biphasic blood pressure response to angiotensin II in the conscious rabbit: relation to prostaglandins

The injection of a large bolus of angiotensin II causes a biphasic blood pressure response in the conscious rabbit. To investigate contribution of prostaglandins (PGs) to the depressor phase of the blood pressure response, we studied the blood pressure effect of i.v. bolus injections of angiotensin II before and after the administration of an inhibitor of cyclooxygenase, indomethacin or sodium meclofenamate (10 mg kg-1), and in relation to associated changes in the plasma concentration of immunoreactive PGs. In conscious rabbits, angiotensin II (0.05-5.00 microgram kg-1) produced a dose-related pressor response which at both 1.5 and 5.0 micrograms kg-1 was followed by lowering of blood pressure to below the preinjection level. Neither indomethacin nor meclofenamate affected the maximal rise in pressure produced by angiotensin II, but both cyclooxygenase inhibitors augmented the duration of the pressor phase and abolished the depressor phase of the hemodynamic response to angiotensin II at 1.5 to 5.0 micrograms kg-1. After administration of angiotensin II, 5 micrograms kg-1, the plasma concentration of 6-keto-PGF1 alpha increased (P less than .01) from 218 +/- 21 pg/ml by 221 and 235% during the pressor and the depressor phases of the blood pressure response, respectively. Increments in plasma 6-keto-PGF1 alpha correlated inversely with the duration of the pressor phase and directly with the maximal lowering of blood pressure during the depressor phase. Plasma levels of PGE2 and PGF2 alpha also were increased by the peptide but the increments were not correlated with any aspect of the blood pressure response. These data suggest that a mechanism involving PGs both curtails the pressor phase and mediates the depressor phase of the hemodynamic response to pharmacological doses of angiotensin II in the conscious rabbit.     

Longitudinal study of renal prostaglandin excretion in cirrhotic rats: relationship with the renin-aldosterone system

1. A cross-sectional study (protocol A) was performed in 19 rats with cirrhosis, induced by carbon tetrachloride (CCl4), and ascites and in 10 control animals to assess renal prostaglandin (PG) excretion in experimental cirrhosis. In an additional group of animals, including nine rats chronically exposed to CCl4 (CCl4 rats) and six control rats, a longitudinal study (protocol B) was performed to investigate the temporal relationship between changes in renal PG excretion, the renin--aldosterone system and renal function. 2. Urinary PG excretion was assessed by specific radioimmunoassay of PGE2, PGF2 alpha, 6-keto-PGF1 alpha and thromboxane (TX) B2 after extraction with octadecyl silica cartridges and h.p.l.c. purification. Recoveries for each prostanoid (61 +/- 8% for PGE2, 64 +/- 12% for PGF2 alpha, 65 +/- 11% for 6-keto-PGF1 alpha and 66 +/- 17% for TXB2) were determined in every sample by adding tritiated standards, and the final values were corrected according to the individual recoveries. 3. Cirrhotic rats with ascites in protocol A showed a significantly higher plasma renin and aldosterone concentrations and urinary excretion of 6-keto-PGF1 alpha and TXB2 than did control animals. Urinary excretion of PGE2 and PGF2 alpha, however, was significantly reduced in cirrhotic animals as compared with controls. 4. In CCl4 rats included in protocol B, there was a close chronological relationship between the activation of the renin-aldosterone system, as estimated by urinary aldosterone excretion, the onset of sodium retention and the increase in urinary excretion of 6-keto-PGF1 alpha and TXB2. The urinary excretion of PGE2 and PGF2 alpha in CCl4 rats was reduced throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arachidonic acid and prostaglandin endoperoxide metabolism in isolated rabbit and coronary microvessels and isolated and cultivated coronary microvessel endothelial cells.

Isolated microvessels and isolated and cultured microvessel endothelial cells were prepared from rabbit cardiac muscle. Pathways of arachidonic acid metabolism were determined by measurement of exogenous substrate utilization [( 1-14C]arachidonic acid incorporation and release from intact tissue and cells; [1-14C]prostaglandin H2 (PGH2) metabolism by broken cell preparations) and by quantification of endogenous products (immunoreactive 6-keto-prostaglandin F1 alpha (PGF1 alpha) and prostaglandin E (PGE) release) by selective radioimmunoassay. Rabbit coronary microvessels and derived microvascular endothelial cells (RCME cells) synthesized two major products of the cyclooxygenase pathway: 6-keto-PGF1 alpha (hydrolytic product of prostaglandin I2) and PGE2. A reduced glutathione requiring PGH-E isomerase was demonstrated in coronary microvessels and RCME cells, but not in rabbit circumflex coronary artery or aorta. In addition, a minor amount of a compound exhibiting similar characteristics to 6-keto-PGE1 was found to be produced by microvessels and RCME cells. Measurement of endogenously released prostaglandins indicated that under basal and stimulated conditions, PGE release exceeded that of 6-keto-PGF1 alpha. Microvessels and microvessel endothelial cells derived from cardiac muscle of rabbit exhibit pathways of arachidonate metabolism that are different from those of many large blood vessels and derived endothelial cells.     

Relevance of Prostaglandins in True Menstrual Migraine

Eighteen patients suffering from true menstrual migraine and 12 control subjects were studied. We evaluated in different phases of the menstrual cycle and during the migraine crisis the peripheral plasma concentrations of 6-keto-PGF1 alpha (the stable metabolite of PGI2), thromboxane B2 (the stable metabolite of thromboxane A2), PGF2 alpha and PGE2. The mean values of 6-keto-PGF1 alpha in menstrual migraine sufferers are lower than in normal women throughout the whole cycle. The difference between the trends observed in the two groups is statistically significant (p less than 0.05). The plasma levels of TXB2 and of PGF2 alpha are similar in the two groups investigated, both in basal conditions and during the attack. The plasma concentrations of PGE2 are slightly lower in migraineurs in basal conditions than in normals. However, during the crisis they increase significantly (p less than 0.05). In conclusion, among all the parameters considered, PGE2 seems to play the most important role during the pain phase of the attack. The results of the present study suggest that a deficit of PGI2, one of the most important protecting agents against ischemia, might be a typical feature of menstrual migraine and might cause in these patients a vascular hypersensitivity to different ischemic stimuli.     

Thyrotropin Increases Prostaglandin Levels in Isolated Thyroid Cells

We have shown that two unrelated prostaglandin antagonists block both thyrotropin (TSH) and prostaglandins E (PGE(1), PGE(2)) stimulation of thyroidal adenyl cyclase activation and cyclic 3',5'-adenosine monophosphate (cAMP) formation, suggesting that prostaglandins play an important role in regulating thyroid function. To further explore this postulate, we measured prostaglandin content by radioimmunoassay in homogeneous bovine thyroid cell preparations in the presence and absence of TSH. Antibodies to albumin-conjugated PGE(1) and PGF(2alpha) showed specificity for prostaglandins E and F, respectively, but reacted, albeit far less effectively, with heterologous prostaglandins. A double antibody system was used to separate free from antibody-bound PGE(1)-(3)H and PGF(2alpha)-(3)H. Thyroid cells were extracted with ethanol/ethyl acetate and the various prostaglandins separated on silicic acid columns. Recoveries of added PGE(1)-(3)H and PGF(2alpha)-(3)H through the extraction and separation procedures ranged from 50-80%. The sensitivity of the method was 10-50 pg. Basal thyroid cell content of PGE(1) and PGF(2alpha) "equivalents" varied between cell preparations (range = 2-6 ng/0.2 ml cell suspension) but, in each instance, remained constant during 5-30-min incubations at 37 degrees C. TSH, 10-100 mU/ml, increased the levels of cell PGE(1) and PGF(2alpha) "equivalents" 30-80% above basal during 5-15-min incubations. The stimulatory effect was specific for TSH, no increase in PGE(1) or PGF(2alpha) "equivalent" levels being seen with luteinizing hormone (LH), human growth hormone (HGH), adrenocorticotropic hormone (ACTH), or glucagon. These data support the thesis that prostaglandins may mediate TSH effects on thyroid.     

Regulation of Collagen Gene Expression by Prostaglandins and Interleukin-1beta in Cultured Chondrocytes and Fibroblasts

To compare the modulatory effects of different prostaglandins on collagen gene expression in human chondrocytes, PGE(2), PGE(1), misoprostol (PGE(1) analog), and PGF(2alpha) (10, 50 and 100 ng ml(minus sign1)) were added to human chondrocytes with or without interleukin-1beta (IL-1beta) in the presence of indomethacin to inhibit endogenous prostaglandin synthesis and the effects evaluated on chondrocyte morphology, collagen synthesis, and procollagen mRNA levels. The effects of prostaglandins on the expression of collagen gene regulatory sequences were examined using transient transfection assays of reporter gene constructs in human chondrocytes and BALB/c3T3 fibroblasts, PGE(1), misoprostol, and PGF(2alpha), similar to PGE(2), inhibited type I collagen gene expression in fibroblasts and promoted type II collagen gene expression in chondrocytes. PGE(2), the major inflammatory prostaglandin produced by IL-1-activated chondrocytes and fibroblasts, and PGF(2alpha) were somewhat more potent than the anti-inflammatory prostaglandins PGE(1) and misoprostol in counteracting the IL-1-induced suppression of type II collagen gene expression by chondrocytes and stimulation of type I collagen gene expression by fibroblasts. Rather than promoting degradation of the cartilage matrix in joint diseases, prostaglandins may be somewhat protective, suppressing fibrosis, and maintaining or promoting appropriate cartilage repair.