Mechanism of the rapid antigonadotropic action of prostaglandins in cultured luteal cells

A reproducible method for dissociation and culture of rat luteal cells is described. The concentration of LH required to produce half-maximal stimulation of progesterone secretion was 50 ng/ml. The effects of prostaglandin E(2) (PGE(2)) and prostaglandin F(2alpha) (PGF(2alpha)) on basal and luteinizing hormone (LH)-stimulated progesterone production were examined. Both prostaglandins stimulated basal progesterone production but PGE(2) was about twice as active, showing a 2-fold maximal stimulation at 0.75 muM. When either prostaglandin was incubated simultaneously with LH, a dose-dependent inhibition of progesterone secretion occurred; PGF(2alpha) was 4 times more active than PGE(2), showing 50% inhibition at a concentration of 40 x nM. Thus, both prostaglandins are more active as antagonists than as agonists of LH with respect to progesterone secretion. PGF(2alpha) also inhibited LH-stimulated adenylate cyclase activity and cyclic AMP accumulation. The block in progesterone secretion was reversed by addition of dibutyryl cyclic AMP (1 mM) but not by theophylline (5 mM) alone. These data and the finding that PGF(2alpha) did not affect the specific binding activity of the LH receptor in intact luteal cells indicate that the rapid action of prostaglandins in luteal cells is due to a block of LH-dependent production of cyclic AMP which results in a decrease in progesterone secretion.     

Alteration of prostaglandin production and agonist responsiveness by n-6 polyunsaturated fatty acids in endometrial cells from late-gestation ewes

We investigated the effect of n-6 polyunsaturated fatty acids (PUFAs) on prostaglandin (PG) production by the uterus. A mixed population of endometrial cells (epthelium and stroma) from late-gestation ewes were cultured in defined medium containing linoleic acid (LA, 18:2, n-6), gamma-linolenic acid (GLA, 18:3, n-6) or arachidonic acid (AA, 20:4, n-6) in concentrations of 0 (control), 20 or 100 microM. After 45 h in test medium with or without added PUFAs, cells were challenged with control medium (CM), oxytocin (OT, 250 nM), lipopolysaccharide (LPS, 0.1 micro g/ml) or dexamethasone (DEX, 5 microM) for 22 h in the continued presence of the same concentration of PUFA and the medium was collected for measurement of PGF(2alpha) and PGE(2). Supplementation with LA inhibited the production of PGF(2alpha) but did not alter PGE(2), whereas GLA and AA increased production of both PGs. All PUFA supplements thus increased the ratio of PGE(2) to PGF(2alpha) (E:F ratio) two- to threefold. In control cells, OT and LPS challenges stimulated the production of PGF(2alpha) and PGE(2). In all challenge groups, the concentrations of PGF(2alpha) in response to PUFAs followed the same pattern - LA相似文献   

Prostaglandin-mediated stimulation of adenosine 3',5'-monophosphate accumulation and parathyroid hormone release in dispersed human parathyroid cells

Freshly dispersed cells were employed to study the effects of various prostaglandins (PGs) on cAMP accumulation and parathyroid hormone release in abnormal human parathyroid tissue. PGE1 and PGE2 effected dramatic increases in intracellular cAMP accumulation over a concentration range of 10(-6)-10(-4) M; the relative effectiveness of these agents varied among different preparations. PGF2 alpha caused a smaller stimulation of cAMP accumulation, and PGF1 alpha was generally without effect. In contrast with the effect previously described in the bovine parathyroid cell system, PGF2 alpha did not suppress agonist-stimulated cAMP accumulation. Both PGE1 and PGE2 enhanced cellular release of parathyroid hormone, with dose-response characteristics similar to those seen with cAMP. In addition, both agents led to a significant stimulation of adenylate cyclase activity in a cellular homogenate preparation. Neither indomethacin (10(-5) M) nor naproxen (10(-4) M) altered the calcium suppressibility of the cells, suggesting that endogenous PG production does not play a major role in the calcium-mediated regulation of parathyroid hormone release.     

Prostaglandin synthesis, metabolism, and signaling potential in the rhesus macaque corpus luteum throughout the luteal phase of the menstrual cycle

Prostaglandins in the corpus luteum (CL) reportedly serve as luteotropic and luteolytic agents. Based mainly on studies conducted in domesticated animals and rodents, prostaglandin E2 (PGE2) is generally considered a luteotropic factor, whereas uterine-derived prostaglandin F2alpha (PGF2alpha) initiates luteolysis. However, the role of prostaglandins in regulating primate luteal structure-function is poorly understood. Therefore, a comprehensive analysis of individual mRNA or proteins that are involved in PGE2 and PGF2alpha biosynthesis, metabolism, and signaling was performed using CL obtained at distinct stages of the luteal life span during the menstrual cycle in rhesus monkeys. Peak levels of proteins involved in PGE2 synthesis (prostaglandin-endoperoxide synthase 2, microsomal PGE2 synthase-1) and signaling (PGE2 receptor 3) occurred during periods corresponding to development and maintenance of the primate CL. Immunohistochemistry studies indicated that large luteal cells express PGE2 synthesizing and signaling proteins. Expression of PGE2 synthesizing and signaling proteins significantly decreased preceding the period of functional regression of the CL, which also coincided with increasing levels of PGF2alpha receptor protein expression within the large luteal cells. Moreover, significant levels of mRNA expression for several aldoketo reductase family members that synthesize PGF2alpha from other prostaglandins were observed throughout the rhesus macaque luteal phase, thus supporting the possibility of intraluteal PGF2alpha production. Collectively, our results indicate that there may be intraluteal synthesis and signaling of PGE2 during development and maintenance of the primate CL, followed by a shift to intraluteal PGF2alpha synthesis and signaling as the CL nears the time of luteolysis.     

The human multidrug resistance protein MRP4 functions as a prostaglandin efflux transporter and is inhibited by nonsteroidal antiinflammatory drugs

Prostaglandins are involved in a wide variety of physiological and pathophysiological processes, but the mechanism of prostaglandin release from cells is not completely understood. Although poorly membrane permeable, prostaglandins are believed to exit cells by passive diffusion. We have investigated the interaction between prostaglandins and members of the ATP-binding cassette (ABC) transporter ABCC [multidrug resistance protein (MRP)] family of membrane export pumps. In inside-out membrane vesicles derived from insect cells or HEK293 cells, MRP4 catalyzed the time- and ATP-dependent uptake of prostaglandin E1 (PGE1) and PGE2. In contrast, MRP1, MRP2, MRP3, and MRP5 did not transport PGE1 or PGE2. The MRP4-mediated transport of PGE1 and PGE2 displayed saturation kinetics, with Km values of 2.1 and 3.4 microM, respectively. Further studies showed that PGF1alpha, PGF2alpha, PGA1, and thromboxane B2 were high-affinity inhibitors (and therefore presumably substrates) of MRP4. Furthermore, several nonsteroidal antiinflammatory drugs were potent inhibitors of MRP4 at concentrations that did not inhibit MRP1. In cells expressing the prostaglandin transporter PGT, the steady-state accumulation of PGE1 and PGE2 was reduced proportional to MRP4 expression. Inhibition of MRP4 by an MRP4-specific RNA interference construct or by indomethacin reversed this accumulation deficit. Together, these data suggest that MRP4 can release prostaglandins from cells, and that, in addition to inhibiting prostaglandin synthesis, some nonsteroidal antiinflammatory drugs might also act by inhibiting this release.     

Effect of prostaglandins(PGs) on progesterone production by human cultured luteal cells and their ability of PGs production

The present study was designed to investigate whether or not prostaglandins(PGs) were produced by human luteal cells(HLC) and their effects on the luteal cells by monolayer culture. The following results were obtained. Cultured HLC secreted progesterone(P), prostaglandin F(PGF) and prostaglandin E(PGE) into a medium at concentrations of 276.6 +/- 38.6, 1.95 +/- 0.36, 2.44 +/- 0.45 ng/ml/1 X 10(5) cells/day (mean +/- SE), respectively. Cultured HLC was able to convert 14C-arachidonic acid to 14C-PGF2 alpha, 14C-PGE2. These two results indicated that HLC had the ability to produce PGF and PGE. Cultures were carried out in the presence of indomethacin (Ind), PGF2 alpha and PGE2 alone as well as in a combination. P production by HLC was reduced in the presence of Ind. P production in the presence of Ind+PGE2 was more than that in the presence of Ind alone. There was no significant difference in P production between the presence of Ind and Ind+PGF2 alpha. It was concluded that HLC had the ability to produce PGs and that PGE2 significantly stimulated P production in as low concentrations as HLC could produce physiologically while PGF2 alpha did not.     

Maitotoxin, a calcium channel activator, increases prolactin release from rat pituitary tumor 7315a cells by a mechanism that may involve leukotriene production

Arachidonate and its metabolites may play an important role in the release of prolactin. In the present study, the effect of maitotoxin, a calcium channel activator, was measured on the release of arachidonate and its metabolites from the prolactin-secreting 7315a tumor. Maitotoxin increased the release of prolactin, arachidonate, prostaglandins E2 and F2 alpha (PGE2, PGF2 alpha) and leukotriene C4 (LTC4) from 7315a cells prelabeled with [3H]arachidonate. The magnitude of the increase of prolactin and arachidonate release was decreased in low-calcium medium. The release of arachidonate from cellular phospholipids is necessary for the effect of maitotoxin on prolactin release because quinacrine, an inhibitor of arachidonate hydrolysis from phospholipids, blocked the maitotoxin-induced release of prolactin. The ability of maitotoxin to induce prolactin release appears to require metabolic transformation of arachidonate to its metabolites because BW755c, an inhibitor of the conversion of arachidonate, blocked the maitotoxin-induced prolactin release. In particular, LTC4 may be an important component of the prolactin release process because nordihydroguaiaretic acid and nafazatrom, which block the production of leukotrienes and other lipoxygenase-generated products, decreased LTC4 and prolactin release without affecting arachidonate, PGE2 or PGF2 alpha production. In contrast, indomethacin, a prostaglandin synthesis inhibitor, decreased PGE2 and PGF2 alpha production without affecting LTC4 or prolactin release. These data indicate that release of LTC4 and prolactin are closely linked events in 7315a tumor cells.     

Chronic regulation of ovarian oxytocin and progesterone release by prostaglandins: opposite effects in bovine granulosa and early luteal cells

Oxytocin is synthesized in the granulosa-derived large cells of the ruminant corpus luteum from a gene which is dramatically up-regulated in the first few days after ovulation. In this work, the regulation of granulosa and luteal cells by prostaglandins and insulin (or insulin-like growth factor-I; IGF-I) has been explored by comparing their effects on oxytocin and progesterone production in cell culture. In granulosa cells, chronic exposure to insulin (17 nmol/l) stimulated luteinization as indicated by increased release of oxytocin and progesterone. Prostaglandin F2 alpha (PGF2 alpha) alone had little effect, but synergized with insulin (or IGF-I) to increase the release of both these hormones. In direct contrast, insulin-stimulated oxytocin production by luteal cells was inhibited by PGF2 alpha. The half-maximal dose (EC50) for PGF2 alpha action in both cell preparations was similar (10-100 nmol/l). Dose-response studies revealed that PGF2 alpha increased the potency of insulin in granulosa cells (EC50 for insulin-stimulation of oxytocin release reduced from 141 to 13 nmol/l by 1 mumol PGF2 alpha/l), but not in luteal cells. Insulin-stimulated oxytocin release from granulosa cells was also synergistically increased by PGE1, PGE2 and forskolin, suggesting this effect to be mediated by adenylate cyclase-coupled PGE receptors. The results reveal that the effects of prostaglandins on oxytocin release are dependent on both the developmental stage of the target tissue and on the presence of other regulators of cellular differentiation. Moreover, they suggest that the increase in responsiveness to insulin and IGF-I, which appears to accompany luteinization in the cow, may be an effect of prostaglandins produced locally during the peri-ovulatory period.     

Concentrations of prostaglandins in plasma, seminal vesicles, and ovaries of aging C57BL/6NNia mice

Concentrations of prostaglandin E1 (PGE1), and prostaglandin E2 (PGE2) (combined in the same radioimmunoassay) and prostaglandin F2 alpha (PGF2 alpha) were analyzed in circulating plasma and seminal vesicles of 3- and 26 to 27-month-old males and in circulating plasma and ovaries of 3-, 6-, 14 to 18- and 26 to 30-month-old female C57BL/6NNia mice. The amount of PGE declined in the plasma (P less than 0.05) and seminal vesicles (P less than 0.02) of aged male mice, whereas PGF2 alpha concentrations remained unchanged. There were no statistical differences in plasma or ovarian concentrations of PGE or PGF2 alpha when comparing the various age groups of female mice. It does not appear as if age-related changes in prostaglandins play a significant role in reproductive senescence.     

Differences in prostaglandin E2, prostaglandin F2 alpha and prostacyclin contents and their response to thyrotrophin stimulation and in prostaglandin-stimulated cyclic AMP response in normal and Grave's thyroid slices

The human thyroid contained prostaglandin (PG) E2, PGF2 alpha and 6-oxo-PGF1 alpha, an end-metabolite of prostacyclin (PGI2), the 6-oxo-PGF1 alpha content being the highest of these prostaglandins. Graves's thyroid contained a significantly higher amount of PGF2 alpha and lower amounts of PGE2 and 6-oxo-PGF1 alpha than the normal thyroid. Thyrotrophin acutely augmented the thyroid contents of PGE2, PGF2 alpha and 6-oxo-PGF1 alpha. The TSH-stimulated increases in PGE2 and 6-oxo-PGF1 alpha were lower but the TSH-stimulated increase in PGF2 alpha was significantly higher in Graves's thyroid than in the normal thyroid. Prostaglandin E2 and PGI2 stimulated human thyroid cyclic AMP synthesis, with the magnitudes of PGE2- and PGI2-stimulated increases in cyclic AMP being equal in normal and Graves's thyroid. Prostaglandin F2 alpha did not stimulate cyclic AMP synthesis significantly. These results provide evidence that prostaglandins play important roles in thyroid physiology and the pathophysiology of Graves's disease.     

Comparison of prostaglandin synthesis by endothelial cells from blood vessels originating in the rat, baboon, calf and human

The synthesis of prostaglandins (PGs) was determined in endothelial cells obtained from various vessels from baboon, human and rat both by radioimmunoassay and prelabel of the cells with [3H] arachidonate. Cells were stimulated with bradykinin, ionophore A23187 or 10 microM arachidonate. Although prostacyclin (PGI2) has proven to be the major prostaglandin product of human umbilical vein and calf pulmonary artery endothelial cells, our results show that PGI2 is frequently not the major prostaglandin product of endothelial cells from other vessels. For example baboon endothelial cells lining the large vessels, aorta and cephalic vein produce mainly PGF2a with only small amounts of PGE2 and PGI2. Human endothelial cells from saphenous vein also produce mainly PGF2a. Baboon, human and rat adipose capillary endothelial cells make predominantly PGE2 and PGI2 with rat making significant amounts of PGF2a in addition. Endothelial cells from the rat aorta produced predominantly prostacyclin.     

The effect of the antiprogestins RU 486 and ZK 98734 on the synthesis and metabolism of prostaglandins F2 alpha and E2 in separated cells from early human decidua

Enriched preparations of glandular and stromal cells were obtained from early human decidua and incubated for 24 h in the presence of two progesterone antagonists, RU 486 (17 beta-hydroxy-11 beta-[4-dimethylaminophenyl]17 alpha-[1-propynyl]-estra-4,9-dien-3-one) and ZK 98734 (17 beta-hydroxy-11 beta-4[4-dimethylaminophenyl]17 alpha-[3-hydroxy-1-propynyl]estra-4,9-dien-3-one) to determine the effect of the antiprogestins on the release of prostaglandin F2 alpha (PGF2 alpha) and PGE2 and their subsequent conversion to 15-keto-13,14-dihydro-PGF2 alpha and 15-keto-13,14-dihydro-PGE2. In the presence of exogenous arachidonic acid (AA, 30 microM), both steroids stimulated PGF2 alpha release by glandular, but not stromal, cells (P less than 0.001) and inhibited the metabolism of PGF2 alpha by the glandular fraction (P less than 0.005 and P less than 0.001 respectively). In the absence of exogenous AA, RU 486 and ZK 98734 stimulated the release of PGF2 alpha from glandular, but not stromal, cells (P less than 0.001 and P less than 0.005, respectively). Neither steroid altered the release or metabolism of PGE2 when the cells were incubated with AA, but both RU 486 and ZK 98734 increased the release of PGE2 by glandular, but not stromal, cells when incubated without AA (P less than 0.005 and P less than 0.001, respectively). Both steroids inhibited the metabolism of PGE2 under these conditions (P less than 0.05). These results suggest that 1) antiprogestins stimulate the synthesis of PGs by glandular cells in early human decidua, but do not alter the synthesis of PGs by stromal cells; 2) this stimulation of PG synthesis involves an effect on cyclooxygenase activity and is not a consequence of increased availability of endogenous AA; 3) the metabolism of PGs by glandular cells is altered by RU 486 and ZK 98734; 4) as RU 486 has greater antiglucocorticoid activity than ZK 98734, these results suggest that both steroids act on decidua by antagonizing endogenous progesterone rather than glucocorticoid activity.     

Effects of arachidonic acid, prostaglandin F2 alpha, prostaglandin E2, and arginine vasotocin on induction of birth in vivo and in vitro in a viviparous lizard (Sceloporus jarrovi).

The ability of arachidonic acid (AA) and prostaglandins of the two series to induce parturition in vivo and oviducal contraction in vitro was studied in the viviparous lizard Sceloporus jarrovi. Injection of PGF2 alpha, PGE2, or AA during late pregnancy stimulated parturition within 2 hr in a threshold-dependent fashion. In contrast, during mid pregnancy, females did not respond. Surgically removed and cultured oviducts from females in late pregnancy gave "birth" in response to AA, PGF2 alpha, and PGE2. Oviducts from S. jarrovi in mid pregnancy responded to PGF2 alpha but not to AA. Addition of arginine vasotocin, a potent stimulator of PG synthesis, either alone or with AA to oviduct cultures stimulated rapid and complete birth in vitro from oviducts obtained from late, but not mid pregnant, females. Stage of pregnancy mediates the response of the lizard oviduct to prostaglandin stimulation.     

Relationship between the production of prostaglandins and progesterone by luteinizing human granulosa cells.

Luteinizing granulosa cells synthesize high concentrations of progesterone, prostaglandin (PG) E(2) and PGF(2 alpha). The objective of this study was to explore the relationship between prostaglandin and progesterone output from human granulosa cells as they undergo functional luteinization in culture. Granulosa cells were partially purified from ovarian follicular aspirates and cultured at a density of 10(5) cells/ml in serum-supplemented DMEM:Ham's F(12) medium for 0, 1 or 2 days. Cells were then switched to serum-free medium for 24 h before measuring hormone concentrations in this spent medium by specific radioimmunoassays. Over the first 3 days in culture, PGF(2 alpha) and PGE(2) production declined progressively by up to 82+/-3% coincident with a 55+/-11% increase in progesterone output. In subsequent experiments, cells were treated for 24 h on the second day of culture with either 0.01 to 10 microM meclofenamic acid or with 10 microM and 100 microM aminoglutethimide. Meclofenamic acid inhibited synthesis of PGF(2 alpha) and PGE(2) by up to 70+/-9% and 64+/-7% respectively without affecting progesterone output. Likewise, 100 microM aminoglutethimide inhibited progesterone production by 62+/-6% without affecting concentrations of either PGF(2 alpha) or PGE(2). We have concluded that the progressive decline in prostaglandin production and the rise in progesterone output from luteinizing human granulosa cells occur independently of each other.     

Influence of day of pregnancy on rat placental, uterine, and ovarian prostaglandin synthesis and metabolism.

Synthesis and metabolism of prostaglandins in reproductive tissues of the gravid rat were studied from the time of post-implantation to just prior to parturition. Rat placental prostaglandin synthesis is low on day 8 of pregnancy, sharply increases on day 11, falls on day 14, and remains at a low level for the remainder of gestation. In the tissue PGE2 synthesis is 6 times greater than that of PGF2alpha on day 11. Prostaglandin metabolism in the placenta was high on day 11, low on days 8 and 14, and elevated on days 16, 18, and 21 of pregnancy. PGE1 metabolism was 8 times greater than that of PGF2alpha. Uterine prostaglandin synthesis was low until day 16, and then increased until the end of pregnancy. PGE2 synthesis was very low in this tissue in comparison to PGF2alpha synthesis. Prostaglandin metabolism in the uterus was relatively low until day 16 and then sharply increased for the remainder of gestation. This increase in metabolism was not directly proportional to uterine growth. PGE1 metabolism was 5 times higher than PGF2alpha metabolism in this organ. Ovarian prostaglandin synthesis was very low in comparison to that of the other reproductive organs. Prostaglandin metabolism in this tissue decreased from day 8 through day 18 of pregnancy. PGE1 metabolism in the ovary was twice that of PGF2alpha. These studies demonstrate patterns for synthesis and metabolism of prostaglandin in each tissue studied which may indicate inter-relationships with the physiological requirements of pregnancy.     

Isolation and culture of Kupffer cells from human liver. Ultrastructure, endocytosis and prostaglandin synthesis

Kupffer cells and other sinusoidal cells were isolated after perfusion and incubation with pronase and collagenase of pieces of liver tissue obtained from organ donors. The resulting cell preparations contained endothelial cells, Kupffer cells and fat-storing cells as well as considerable numbers of leucocytes. Attempts to purify the different sinusoidal cell types by density centrifugation and centrifugal elutriation were successful only for Kupffer cells. Kupffer cells, in contrast to endothelial cells and fat-storing cells, could be kept in maintenance culture for at least 5 days. Cultured Kupffer cells were active in the endocytosis of foreign substances, such as colloidal carbon, latex beads, horseradish peroxidase and bacterial endotoxin. The cultured Kupffer cells synthesized and secreted considerable amounts of prostaglandins PGE2, PGF2 alpha, 6-keto-PGF1 alpha and thromboxane B2. The production of prostaglandins was influenced by the presence of Escherichia coli endotoxin.     

Interaction between nitric oxide and cyclooxygenase pathways in endothelial cells

Nitric oxide (NO) and cyclooxygenase (COX) derived prostaglandins (PGs) are involved in vascular homeostasis. Contradictory results have been obtained in previous studies on the putative 'cross-talk' between these two pathways. Our aim was to evaluate the interaction between NO and PG release in human microvascular endothelial cells (HMEC-1) and in umbilical vein endothelial cells (HUVEC). METHODS: Medium samples were assayed for nitrite/nitrate (NO(x)) and L-citrulline levels while lysed cells were assayed for endothelial NO synthase (eNOS), as markers of NO production. Prostaglandin E2 (PGE2) and 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) were assessed as indicators of COX activity. RESULTS: The NO donor sodium nitroprusside and L-arginine increased PGs levels in both cell types. N(G)-monomethyl-L-arginine (L-NMMA) significantly inhibited 6-keto-PGF1alpha release without significantly reducing PGE2)levels. Indomethacin increased both NO(x), eNOS and L-citrulline levels. PGE2 treatment did not modify NO(x) values. CONCLUSION: The stimulation of PGs by NO may represent an additional pathway used by exogenous nitrovasodilators to elicit vasodilation. Reduction of PGs by inhibition of COX was compensated by enhanced NO. Conversely, PGs()did not compensate()decreased NO following L-NMMA treatment. Treatment with the vasodilatator prostaglandin E2 did not modify NO(x) levels.     

Cyclooxygenase products and cyclic nucleotide levels with infusion of arachidonic acid, PGI2, PGE2, PGF2, and 6-keto-PGF1 in an isolated dog lung

Arachidonic acid (AA) was infused into the pulmonary artery of an isolated dog lung perfused with a physiologic salt solution. This led to elevations in pulmonary cyclic AMP and prostaglandins (PGs) including PGE2, PGF2 alpha, TXB2 (a metabolite of TXA2), and 6-keto-PGF1 alpha (a metabolite of PGI2). The elevations were prevented by PG synthesis inhibitors. A dose of PGI2 comparable to that produced from AA led to elevations in cyclic AMP. These elevations were not reduced by PG synthesis inhibitors; this indicated that the inhibitors did not reduce cyclic AMP except by inhibiting metabolism of AA. The PGE2 led to lesser elevations in cyclic AMP than did PGI2; PGF2 alpha and 6-keto-PGF1 alpha did not increase cyclic AMP. Levels of cyclic AMP were not elevated. We conclude that some of the elevation in cyclic AMP from AA was most likely from production of PGs since elevations in both were prevented by the inhibitors. However, the possibility remains that AA metabolites other than PGs also contributed to elevations in cyclic AMP. We also conclude that PGI2 most likely accounted for some of the cyclic AMP elevation from AA since PGI2 could be readily produced in amounts that elevate cyclic AMP. However, the possibility remains that PGE2, the less consistent cyclic AMP stimulators (l.e., PGF2 alpha and 6-keto-PGF1 alpha), TXA2 or TXB2, or PGs not measured in this study also contributed to the elevations in cyclic AMP from AA.     

Absence of prostacyclin involvement in angiotensin-induced aldosterone secretion in rat adrenal cells

The role of prostaglandins (PGs) in aldosterone secretion was studied in isolated rat adrenal glomerulosa cells. [14C]Arachidonic acid was metabolized to [14C]6-keto-PGF1 alpha, [14C]PGF2 alpha, [14C]PGE2, and [14C]PGD2. Pretreatment with indomethacin (5 X 10(-5) M) or U-51605 (5 micrograms/ml) inhibited the synthesis of these metabolites. Angiotensin II (AII) stimulated a concentration-related release of aldosterone and 6-keto-PGF1 alpha, but not PGE2. Significant increases in aldosterone and 6-keto-PGF1 alpha occurred at AII concentrations of 0.2 and 2 nM. The increases in 6-keto PGF1 alpha concentrations after AII treatment were small, however (278 +/- 33 pg/10(6) cells X h for control vs. 581 +/- 90 after 2 nM AII). At higher concentrations, AII further stimulated aldosterone, but 6-keto PGF1 alpha levels declined. AII stimulated the synthesis of aldosterone and 6-keto PGF1 alpha in parallel with time of incubation. Indomethacin (3 microM) decrease basal and AII-stimulated aldosterone release by 40% and 23%, respectively, and inhibited the synthesis of PGs. U-51605 (5 micrograms/ml) failed to alter aldosterone release. Arachidonic acid increased the synthesis of PGE2 and 6-keto-PGF1 alpha in a concentration-related manner without altering the synthesis of aldosterone. In contrast, PGH2 stimulated the release of PGE2, 6-keto-PGF1 alpha, and aldosterone. PGI2 and PGE2 stimulated aldosterone secretion, which was concentration related. Threshold stimulation by PGI2 and PGE2 occurred at 0.5 and 5 nM, respectively. Maximal stimulation occurred at 5 nM for PGI2 and at 5000 nM for PGE2, with PGE2 producing the greater maximal response. Treatment of the cells with trypsin eliminated the steroidogenic response to PGE2. These findings indicate that PGI2 and PGE2 are produced by the adrenal glomerulosa cells, and the synthesis of PGI2 may be stimulated by AII. However, the concentrations of PGI2 synthesized are not adequate to stimulate aldosterone secretion. Thus, PGI2 does not appear to mediate angiotensin-induced aldosterone secretion.