Indomethacin-induced alterations in corticosteroid and prostaglandin release by isolated adrenocortical cells of the cat

Concentration-dependent, biphasic effect of prostaglandins on avian corticosteroidogenesis in vitro

Previous work with mammalian and frog adrenocortical tissue and cells indicates that prostaglandins (PGs) can directly stimulate corticosteroidogenesis. However, work with avian adrenal preparations is absent. Therefore, the present studies with isolated chicken (Gallus gallus domesticus) and turkey (Meleagris gallopavo) adrenal steroidogenic cells were conducted to determine whether PGs can directly influence avian corticosteroidogenesis as well. Cells (1 x 10(5) cells/ml) were incubated with a wide range of concentrations of PGs in the presence of indomethacin (1 microg/ml) (to attenuate endogenous PG production) and 1-methyl-3-isobutylxanthine (0.5 mM) [to preserve cyclic AMP (cAMP)] for 2 h. Corticosterone and cAMP production were measured by highly specific radioimmunoassay. PGI2 was without effect. With the exception of PGF2alpha, which had a slight stimulation in chicken but not in turkey cells, the influence of the other PGs on corticosterone production was biphasic. For the stimulatory phase (up to a concentration of 5 x 10(-5) M), there were prostanoid structural and avian species differences in both potency and efficacy of PGs. Overall, PGs were 11 times more potent in turkey cells than in chicken cells. However, the order of potency for stimulation was similar for both chicken and turkey cells: for chicken cells the order was PGE2 > PGE1 > PGA1 > PGB2 > PGB1 > PGF2alpha and for turkey cells it was PGE2 > PGE1 > PGA1 > PGB2 = PGB1. In contrast, PG efficacy for stimulation was greater for chicken cells. In addition, the orders of efficacy were different from the orders of potency. In chicken cells, the order of efficacy was PGE2 = PGA1 > PGE1 > PGB2 > PGB1 > PGF2alpha and for turkey cells it was PGB2 = PGE2 > PGA1 > PGE1 > PGB1. Because of the greater maximal corticosterone response over basal production of chicken cells to PGs, they were used to assess the interaction of PGs with ACTH and to examine more fully the inhibitory phase of PGs. Cells were incubated with PGs in the presence of threshold (2.5 x 10(-11) M), half-maximal (1 x 10(-10) M), and maximal (1 x 10(-7) M) steroidogenic concentrations of ACTH. With the exception of PGF2alpha, the average efficacy of PGs to elevate corticosterone was increased 55% by a threshold steroidogenic concentration of ACTH. However, with higher concentrations of ACTH, this enhancement of efficacy disappeared as did the stimulatory effect of some PGs. The results suggest that the steroidogenic actions of PGs and ACTH converge on the same pool of steroidogenic enzymes leading to corticosterone. At concentrations greater than 5 x 10(-5) M, several PGs (notably PGA1, PGA2, PGB1, and PGB2) inhibited both ACTH-induced and basal corticosterone production. PGA1 and PGA2 were the most potent inhibitors. Corticosterone and cAMP production were closely associated in the biphasic action of PGs, suggesting that the effect of PGs was mediated by the changing levels of intracellular cAMP. Collectively, these data suggest that PGs may be important modulators of corticosteroidogenesis in the avian adrenal gland.

Influence of exogenous prostaglandin E2 and stress on circulating corticosterone concentrations in Coturnix

The effects of exogenous prostaglandin E2 (PGE2) injections and stress on circulating corticosterone (B) levels in Coturnix were determined. Adult Japanese quail (Coturnix coturnix japonica) were subjected to one of four treatments: 1) injected with vehicle; 2) injected with PGE2; 3) immobilized for 10 min, followed by vehicle injection; or, 4) immobilized for 10 min, followed by PGE2 injection. Injections were given intraperitoneally, and blood samples were collected by cardiac stab at 15-min postinjection treatment. Plasma B concentrations were quantified by radioimmunoassay. Immobilized, vehicle injected quail had higher plasma B levels than unstressed, vehicle-injected quail. Plasma B levels were significantly greater in unstressed, PGE2-injected quail than in unstressed, vehicle injected quail or in stressed, vehicle injected quail. The effects of immobilization stress and PGE2 injection on B secretion were additive; stressed PGE2-injected quail had significantly higher plasma B levels than unstressed, PGE2-injected quail. It is concluded that, as in mammals, PGE2 is a potent stimulator of adrenal B release in quail.

Effects of inhibitors of arachidonic acid metabolism on calcium uptake and catecholamine release in cultured adrenal chromaffin cells

The possibility that arachidonic acid metabolism is involved in the secretory process in cultured adrenal chromaffin cells was investigated by studying the effects of lipoxygenase inhibitors and cyclooxygenase inhibitors on 45Ca2+ uptake and catecholamine release. Lipoxygenase inhibitors, which have different chemical structures, such as nordihydroguaiaretic acid (NDGA), 3-amino-1-(3-trifluoromethylphenyl)-2-pyrazoline (BW755C) and 2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone (AA861) all prevented the catecholamine release evoked by carbamylcholine and high K+. In contrast, cyclooxygenase inhibitors, such as aspirin and indomethacin failed to inhibit the carbamylcholine-evoked catecholamine release. Lipoxygenase inhibitors also inhibited 45Ca2+ uptake into the cells stimulated by carbamylcholine and high K+. Lipoxygenase inhibitors inhibited 45Ca2+ uptake and catecholamine release with similar potency. Slightly higher concentrations of lipoxygenase inhibitors were required to inhibit high K+-evoked effects compared to those evoked by carbamylcholine. The inhibitory effects of these inhibitors on carbamylcholine-evoked catecholamine release was different in its nature from the inhibitory effect of verapamil, a blocker of the Ca2+ channel, and was not due to a competitive antagonism at cholinergic receptor site. Moreover, these lipoxygenase inhibitors did not inhibit the binding of [3H]nitrendipine to chromaffin cell homogenate. The data suggest that lipoxygenase inhibitors prevent the catecholamine release from cultured adrenal chromaffin cells by blocking Ca2+ uptake. It might be possible that lipoxygenase product(s) is involved in the Ca2+ translocation system in these cells.

Prostaglandins and steroidogenesis in isolated bovine adrenal cells. Effects of ACTH, prostaglandin-synthesis inhibitors, prostaglandins and prostaglandin analogs

In bovine adrenal cortex cells, dispersed without preferential loss of cells, we investigated (1) whether endogenous prostaglandins (PGs) are involved in ACTH-induced adrenal steroidogenesis, and (2) the steroidogenic effects of PGs and PG analogs. Free cells produced considerable amounts of PGE2, whereas only minute quantities of PGF2 alpha and PGA1 were synthesized. PGE2 synthesis, however, was not significantly increased when ACTH elicited a steroidogenic response in free cells. High concentrations of PG-synthesis inhibitors such as indomethacin affected both PG synthesis and steroidogenesis, whereas intermediate concentrations (10(-6) M) inhibited production of both PGE2 and aldosterone even after cAMP and cortisol response to ACTH had returned to normal values. It is concluded that endogenous PGE2 is not a link in the acute mechanism of action of trophic hormones in which cAMP is involved. Of the prostanoid structures, PGs of the E series were the most potent stimulating agents of cortisol production, although less active than ACTH. On the other hand, PGA1 induced an ACTH-like aldosterone synthesis. PGE2 was less active, and other prostanoid structures were without effect on aldosterone production. It is suggested that in pathological circumstances, PGA1 regulates aldosterone production and PGE2 increases both aldosterone and cortisol production.

Corticosterone secretion after inhibition of prostaglandin synthesis by indomethacin

Systemic indomethacin (Ind) administration decreased prostaglandin F (PGF) content of the rat adrenal to less than 1.4 pg/mg. This was less than 5% of the adrenal PGF content in the gelatin-treated (Gel) control group (34 pg/mg). Basal plasma corticosterone levels were increased by the Ind treatment. Since the calculated metabolic clearance rate for corticosterone was unchanged, this increase was attributed to an enhanced adrenal secretion rate that was secondary to elevated plasma ACTH concentration. Ether exposure in the presence of Ind did not stimulate a normal rise in plasma corticosterone or adrenal corticosteroidogenesis. Adrenal responsiveness to exogenous ACTH was reduced after Ind treatment. There was a normal rise in plasma ACTH levels following ether exposure confirming the adrenal as the site of inhibition. Systemic Ind treatment thus appears to have two sites of action in altering plasma corticosterone levels: 1) a direct effect on the adrenal, inhibiting normal secretion in response to acute elevations of plasma ACTH, and 2) an action at the pituitary or hypothalamic level, eliciting an increase in basal ACTH secretion.

Dissociation of aldosterone and prostaglandin biosynthesis in the rat adrenal glomerulosa

The relationship between aldosterone production and prosta-glandin E2 synthesis was evaluated using the responses of isolated rat adrenal glomerulosa cells to angiotensin II, ACTH and potassium. Simultaneous PGE2 and aldosterone measurements were made during timed incubations with these stimuli, and in incubations with arachidonic acid, meclofenamate, indomethacin, and aminoglutethamide. PGE2 and aldosterone production were assessed by radioimmunoassay. We were not able to demonstrate stimulation of PGE2 by angiotensin II, ACTH, or potassium despite significant increments in aldosterone production with these stimuli. Arachidonic acid enhanced PGE2 synthesis, but had no effect on aldosterone realease. Indomethacin and meclofenamate inhibited aldosterone secretion. Aminoglutethimide depressed aldosterone production, but had little effect on PGE2 levels in the media. These studies demonstrate that dienoic prostaglandins play no direct role in aldosterone production stimulated by angiotensin II, ACTH, or potassium in rat adrenal glomerulosa cells. Since inhibitors of cyclo-oxygenase decreased aldosterone synthesis, it is possible that fatty acids other than arachidonic acid may be cyclo-oxygenated to products which regulate aldosterone production.

Prostaglandin synthetase activity in bovine adrenocortical cells and subcellular preparations: effect of ACTH

Prostaglandin (PGE2, PGF2 alpha) production by bovine fasciculo-reticulata adrenocortical cell suspensions was examined using specific radioimmunoassay procedures. No detectable PGs (greater than 50 pg) could be measured in the extract from up to 2 x 10(6) cell incubations after 1 h, with or without the presence of ACTH, although these cells expressed full steroidogenic capabilities under these conditions. The same preparations could produce PGs when supplemented with arachidonic acid but ACTH had no effect on this process. These negative findings could not be explained by analytical artifacts or metabolic transformation. However, an active PG synthetase system was characterized in bovine adrenocortical subcellular preparations. This system converted arachidonate and endogenous substrate(s) to PGE2 as the major product. No thromboxane or prostacyclin pathways were detected even at high enzyme/substrate ratio. Although the microsomal adrenal cortex PG synthetase activity shares many features with those observed in other tissues (Km = 8.3 x 10(-5) M, optimal pH at 8.0, stimulation of PGE2 formation in the presence of glutathione and L-epinphrine), its specific activity was comparatively low (Vmax = 2.5 ng PGE2/min/mg microsomal proteins), which may explain our negative findings using cell suspensions. These findings do not provide evidence to support the hypothesis proposing a role of endogenous PGs in the mechanism of acute ACTH action in the case of bovine adrenal cortex.

Effects of prostaglandins on adrenal steroidogenesis in the rat

To elucidate the role of prostaglandins in adrenal steroidogenesis, we studied aldosterone and corticosterone responses to 3 x 10(-8) M--3 x 10(-4) M of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), prostacyclin (PGI2), and arachidonic acid (AA) in collagenase dispersed rat adrenal capsular and decapsular cells. Whereas adrenocorticotrophic hormone (ACTH) and angiotensin II (AII) stimulated aldosterone production in capsular cells and ACTH stimulated corticosterone production in decapsular cells in a dose dependent fashion, aldosterone and corticosterone production were not stimulated significantly by PGE2, PGF2 alpha, PGI2, and AA. Although preincubation of dispersed adrenal cells with indomethacin (3 x 10(-5) M) markedly inhibited PGE2 synthesis, ACTH- and AII-stimulated aldosterone production and ACTH-stimulated corticosterone production were not attenuated despite prostaglandin blockade. These results indicate that prostaglandins are unlikely to play an important role in adrenal steroidogenesis.

Evidence for 6-keto-PGF1 alpha in adrenal cortex of the rat and effects of 6-keto-PGF1 alpha and PGI2 on adrenal cAMP levels and steroidogenesis

Both intact cortical tissue and isolated cortical cells from the adrenal gland of the rat were analyzed for 6-keto-PGF1 alpha, the hydrolysis metabolite of PGI2, using high-performance liquid chromatography and gas chromatography-mass spectrometry. 6-Keto-PGF1 alpha was present in both incubations of intact tissue and isolated cells of the adrenal cortex, at higher concentrations than either PGF2 alpha or PGE2. Thus, the cortex does not depend upon vascular components for the synthesis of the PGI2 metabolite. Studies in vitro, using isolated cortical cells exposed to 6-keto-PGF1 alpha (10(-6)-10(-4)M), show that this PG does not alter cAMP levels or steroidogenesis. Cells exposed to PGI2 (10(-6)-10(-4)M), however, show a concentration-dependent increase of up to 4-fold in the levels of cAMP without altering cortico-sterone production, ACTH (5-200 microU/ml) increased cAMP levels up to 14-fold, and corticosterone levels up to 6-fold, in isolated cells. ACTH plus PGI2 produced an additive increase in levels of cAMP, however, the steroidogenic response was equal to that elicited by ACTH alone. Adrenal glands of the rat perfused in situ with PGI2 showed a small decrease in corticosterone production, whereas ACTH greatly stimulated steroid release. Thus, while 6-keto-PGF1 alpha is present in the rat adrenal cortex, its precursor, PGI2, is not a steroidogenic agent in this tissue although it does stimulate the accumulation of cAMP.

The failure of indomethacin to alter ACTH-induced adrenal hyperaemia or steroidogenesis in the anaesthetized dog

1 The response of adrenal blood flow to adrenocorticotropic hormone (ACTH) was measured with radioactive microspheres in anaesthetized, dexamethasone-treated, mongrel dog. 2 Adrenocorticotropic hormone (2 u/h i.v.) increased adrenal blood flow within 15 min and this persisted for the duration of the infusion. 3 Cortisol concentrations also rose with ACTH infusion. 4 Indomethacin (6 mg/kg i.v. followed by 1 mg/min) did not effect the adrenal response to ACTH although plasma concentrations of indomethacin (21.9 +/- 2.5 micrograms/ml) adequate to suppress prostaglandin synthesis were achieved. 5 We conclude that prostaglandins are not required for steroidogenesis or the adrenal haemodynamic response to ACTH.

Effect of prostaglandins on the increased corticosterone output induced by caffeine in the rat

The effect of prostaglandins on the increase of corticosterone output induced by caffeine was investigated in rats. PGE2 and some synthetic prostaglandins (11-deoxy-derivatives), which stimulate steroid output in vitro, enhanced the effect of caffeine. Pretreatment with indomethacin inhibited the effect of caffeine.

The effect of 5,8,11,14-eicosatetraynoic acid on lipid metabolism

The purpose of this presentation is to review the current state of knowledge regarding 5,8,11,14-eicosatetraynoic acid (ETYA, Ro 3-1428) and its effects on lipid metabolism. Accordingly, the topics discussed include hypocholesterolemic and dermatological studies involving ETYA in both animals and man, as well as the effects of ETYA on desaturase enzymes. Metabolic studies involving ETYA are also noted. Primary interest is focused on the effects of ETYA on selected processes of arachidonate metabolism, and the effect of ETYA on inflammation, platelet aggregation and tumor growth are discussed, keeping in mind the relevance of arachidonate metabolism to these processes.

Prostaglandin inhibition of testosterone production induced by luteinizing hormone, dibutyryl cyclic AMP or 3-isobutyl-1-methyl xanthine in dispersed rat testicular interstitial cells

Testicular interstitial cells were utilized to study the effects of prostaglandins (PG) on in vitro testosterone production and to examine the role of cyclic adenosine-3',5'-monophosphate (cAMP) in this process. Testosterone production was assessed after 3 hour incubations while cAMP accumulation was examined after a 0.5 hour incubation period. Testosterone and cAMP were measured by radioimmunoassay. None of the PGs tested (PGA, PGA2, PGB1, PGE1, PGE2, PGF1alpha PGF2alpha) altered basal testosterone production when present in incubates at concentrations of 1.3 X 10(-8) M to 1.3 X 10(-4). However, at concentrations of 1.3 X 10(-4) M all of these PGs were capable of decreasing Luteinizing Hormone (LH; 100ng)-induced testosterone production. The inhibition of LH-induced testosterone production by the B, E and F series PGs was less pronounced than that for the A series. PGA1 and PGA2 exhibited 80% and 95% inhibition, respectively, at 1.3 X 10(4) M. The inhibitory action of 4 X 10(5) M PGA1 or PGA2 was evident within 30 minutes. Preincubation of interstitial cells with indomethacin (10(-5) or 10(-6) M) for 30 minutes did not alter subsequent basal or LH (100ng)-induced testosterone production. Accumulation of cAMP was stimulated by LH (10 microgram) or by PGs (1.3 X 10(-4) M PGA1, PGA2, PGB1, PGE1 or PGF2alpha). The PG-induced cAMP accumulation thus occurred at concentrations where LH-stimulated testosterone production was inhibited. Furthermore, PGA1 and PGA2 (1.3 X 10(-4) M) inhibited testosterone production induced by either 3-isobutyl-1-methyl xanthine (MIX; 10(-4) M or 10(-3) M) or dibutyryl cAMP (dbcAMP; 10(-4) M or 10(-3) M). These results indicate that PGs can block testosterone production by a direct effect on testicular interstitial cells and suggest that PGs exert their inhibitory action distal to stimulation of cAMP formation. PGs do not appear to play a role in the mechanism of LH action.

The effect of corticotropin on phospholipid metabolism in isolated adrenocortical cells

Trypsin-dispersed cat adrenocortical cells were incubated at 37 degrees C in modified Eagle's medium containing [14C]arachidonic acid of sodium [14C]-acetate and then in non-radioactive medium. Radioactive incorporation was obtained in all phospholipids, with the greatest amount of radioactivity in phosphatidylcholine, followed by phosphatidylethanolamine, phosphatidyl-serine, and phosphatidylinositol. Concentrations of individual phospholipids generally paralleled the relative amounts of corresponding radiolabeled phospholipids, although the percentage of phosphatidylinositol was considerably lower than its radioactive counterpart, resulting in a high specific activity of this particular phospholipid. Although a potently steroidogenic concentration of corticotropin failed to enhance release of label from any particular phospholipid, analysis of specific activity showed that corticotropin stimulation was accompanied by an increased turnover of phosphatidylinositol and phosphatidic acid. These studies demonstrate that isolated cortical cells have the capacity to synthesize phospholipids from radioactive precursors. The finding that the acute effects of corticotropin are associated with changes in specific phospholipids, including phosphatidylinositol and phosphatidic acid, conforms to the general pattern observed in other secretory systems.

Changes in the concentration of cortisol in amniotic fluid after intra-amniotic prostaglandin for midtrimester abortion

The effects of intra-amniotic prostaglandin E2 (PGE2) and PGF2alpha on the concentration of cortisol in amniotic fluid and in maternal peripheral plasma of patients undergoing abortion between 16 and 23 weeks gestation have been examined. There was a significant (P less than 0-01) increase in the concentration of cortisol in amniotic fluid for hours after PGE2, but not after PGF2alpha. The concentration of cortisol in the maternal peripheral plasma increased in both groups with the progression of abortion, but the levels were not significantly correlated with those in amniotic fluid. These results suggest that by mid-pregnancy fetal cortisol production can be stimulated by PGE2 but the mechanism of this action remains to be elucidated.

Effect of prostaglandins on steroidogenesis by bovine adrenal cortex mitochondria

Prostaglandins (PGA1, PGE2, PGF2 alpha) were found to increase cholesterol side-chain clevage activity in isolated bovine adrenal cortex mitochondria, provided calcium was present in the incubation medium. Optimal stimulation was observed at low PG concentrations (10-7 to 10-9 M), with malate or malate-NADPH supported side-chain cleavage. Under the same conditions, two endoperoxide analogs and several fatty acids were ineffective. The PG action was not observed with a mitochondrial acetone powder preparation. These observations suggest that primary PG may act by interfering with calcium distribution at the mitochondrial level, leading to the activation of cholesterol side-chain cleavage. Thus, an intracellular action of endogenous PG may be considered in the regulation of adrenal cortex steroidogenic functions.

Radioimmunoassay measurement of ACTH-facilitated PGE2 and PGF2alpha release from isolated cat adrenocortical cells

Prostaglandin (PG) biosynthesis by trypsin-dispersed cat adrenocortical cells was studied by radioimmunoassay (RIA). Parallel assays of incubation media using PGF2alpha and PGF1alpha antisera established that PGF2alpha is the primary PGF released by feline cortical cells. Following the reduction of PGE to PGF with sodium borohydride (NaBH4) these same two antisera were also used to identify PGE2 as the primary PGE released. RIA using a PGE antiserum confirmed the presence of PGE in the incubation medium. Steroidogenic concentrations of ACTH (50-250muU) enhanced PGE and PGF release, and indomethacin suppressed the ACTH-facilitated release. These studies provide additional evidence for ACTH-induced PG synthesis by feline cortical cells, and support the hypothesis that PGs play some role in the steroidogenic action of ACTH.