Cholesterol arachidonate as a prostaglandin precursor in adrenocortical cells

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.

On the mechanism of action of plant adaptogens with particular reference to cucurbitacin R diglucoside

Cucurbitacin R diglucoside (DCR), one of the active principles of Bryonia alba L. root was found to have an effect on the production of corticosteroids and the biosynthesis of eicosanoids in the adrenal cortex, isolated adrenocortical cells, blood plasma, and leukocytes under stress and stress-free conditions in vitro and vivo. DCR prevents stress-induced alterations of eicosanoids in blood and moderately stimulates the adrenal cortex to adapt organism to stress, because a moderate increase in corticosteroid secretion protects the defense system of organisms from becoming hyperactive. DCR enhances sensitivity to stress due to the effects of eicosanoids and corticosteroids.

Incorporation of [14C] arachidonic acid into ovine conceptus and endometrial lipids

The purpose of this study was to quantitate conceptus and endometrial incorporation of [14C]arachidonic acid (AA) into individual neutral and polar lipids. Endometrium and conceptuses from pregnant ewes and endometrium from nonbred ewes were collected 14 and 16 d after onset of estrus (d 0). Tissues were incubated for 8 h at 37 degrees C in medium containing 1 microCi of [14C]AA. Thin-layer chromatographic procedures were used to separate 12 lipids. Radioactivity was measured in each lipid, and the amount (ng) of [14C]AA incorporated into each lipid was calculated. Conceptuses and endometrium incorporated more [14C]AA into triacylglycerols than into any other lipid. Day and tissue type affected differentially (i.e., day X tissue interaction) the incorporation of [14C]AA into several lipids; d-14 conceptuses incorporated [14C]AA more actively than did any other day-tissue combination. Results indicate that triacylglycerols may be an important reservoir for conceptus and endometrial AA. The remarkable ability of d-14 conceptuses to incorporate [14C]AA into various lipids may be important for their accelerated elongation and active prostaglandin synthetic system.

Uptake, distribution and release of 3H-arachidonic acid from human endometrium

The lysophosphatide acyltransferase blocking agent ethylmercurisalicylate (merthiolate) was used to investigate the uptake and release of arachidonic acid from explants of human endometrium in short term tissue culture. Tissue explants were (a) incubated with 3H-arachidonic acid for 1-24 h in the presence or absence of 0.5-50 microM merthiolate, and (b) prelabelled with 3H-arachidonic acid for 18 h followed by incubation with or without 50 microM merthiolate for 1-24 h. Neutral lipids, phospholipids and arachidonic acid were separated by thin layer chromatography and uptake and release of 3H-arachidonic acid expressed as % total uptake. The triglyceride pool was the main target for arachidonic acid uptake. Incorporation increased from 9.1% at 1 h to 56.6% at 24 h. Uptake into phospholipids increased from 8.1% at 1 h to 19.6% at 24 h with phosphatidylcholine accounting for 3.8% and 8.8% respectively. Incubation with 50 microM merthiolate rapidly reduced uptake into triglycerides (to 1.8% at 1 h and 0.9% at 24 h), whereas the effect on uptake into phospholipids (5.9% at 1 h, 3.4% at 24 h) was much less marked. There was a dose related inhibition of arachidonic acid incorporation into both triglycerides and phospholipids, but a lower dose of merthiolate (1 microM) was required to reduce uptake into triglycerides than into phospholipids (5 microM). Uptake into mono- and diglycerides was low and unaffected by merthiolate. Incubation of prelabelled tissue with 50 microM merthiolate resulted in a 20% increase in the release of arachidonic acid from triglycerides and a corresponding accumulation of labelled monoglyceride.(ABSTRACT TRUNCATED AT 250 WORDS)

Release of cholesteryl esters by the mammary gland of the pre-partum cow

In five cows that were regularly milked before parturition, cholesteryl esters were continuously released into the mammary fluid; their concentration in the fluid was initially high, but decreased a few days before parturition when mammary secretion of fluid and triglyceride was increasing. The composition of fatty acids in the cholesteryl esters of mammary fluid and in blood plasma was different, suggesting mammary synthesis of cholesteryl esters.

Arachidonic acid incorporation into lipids of term human amnion

There were no differences in the rate or amount of (1-14C)-labeled arachidonic acid incorporated into triacylglycerides, diacylglycerides, or any phospholipid species of freshly dispersed term human amnion cells obtained before or after labor. Both phosphatidylcholine and phosphatidylethanolamine incorporated 14C-arachidonic acid in proportion to their molar percent of total amnion phospholipids, but phosphatidylinositol incorporated three times as much 14C-arachidonic acid, suggesting either a rapid turnover in this specific phospholipid pool or a greater specificity for the transfer of arachidonoyl-coenzyme A to lysophosphatidylinositol. No or little competition of 14C-arachidonic acid incorporation into triacylglycerides or phospholipids occurred with palmitic acid, linoleic acid, or gamma-linolenic acid. However, dihomo-gamma-linolenic acid, eicosapentaenoic acid, and unlabeled arachidonic acid were effective inhibitors. We conclude that the term amnion has high acyl transferase activity, that no change in the basal activity of this enzyme occurs with the onset of labor, and that a specific acyl transferase exists for 20-carbon polyunsaturated fatty acids.

Dexamethasone-induced stimulation of arachidonic acid release by U937 cells grown in defined medium

Since the presence of serum in culture media has been shown to alter prostaglandin production, as well as to interfere with the action of anti-inflammatory drugs, we have studied the effect of dexamethasone, a potent steroidal anti-inflammatory drug, on the metabolism of arachidonic acid by human monocyte-like cells (U937) grown in a fully defined medium. Under these culture conditions, dexamethasone (10(-6) M, 24 h) induced a marked stimulation of the release of unmetabolized arachidonic acid into the culture medium. The steroid also induced an inhibition of cell proliferation which became significant only after 48 h of treatment. The accumulation of arachidonic acid in the medium after steroid treatment was associated with a significant inhibition of cell acyltransferase activity, suggesting that steroids may also act upon arachidonic acid metabolism at sites other than those of phospholipase activity.

Effect of serum on the metabolism of exogenous arachidonic acid by phagocytic cells of the mouse thymic reticulum

Phagocytic cells derived from the mouse thymic reticulum (P-TR) were used to study the effect of serum on the metabolism of arachidonic acid (AA). After labeling with (14C)-AA in the presence of 10% serum, we failed to detect in the culture medium the presence of significant amounts of radiolabeled prostaglandins. In contrast, when the labeling period was carried out in serum-free medium, we observed the secretion of both cyclooxygenase and lipoxygenase derivatives. In addition, the pattern of arachidonate incorporation into cell lipids was different in the two culture conditions. In the presence of serum, the great majority of the radioactivity was found associated with phospholipids, whereas in serum-free medium, almost 50% of the incorporated fatty acid was associated with triglycerides. Since serum albumin is known to play a major role in the control of fatty acid uptake, we have studied the effect of the addition of 2% BSA to cells prelabeled in the absence of serum. This treatment switches the patterns of metabolite release and lipid labeling towards those of serum-treated cells. In addition, we showed that the effects of glucocorticoids on AA release differ markedly according to the composition of the culture medium.

Incorporation into the tissues and turnover of arachidonic acid after administration to normal and essential fatty acid deficient rats

A comparison was made of the incorporation into the tissues and metabolism of [1-14C] arachidonic acid (AA) after i.v. administration to normal and EFA-deficient rats. At different times, ultra-thin whole body sections were prepared and the distribution of the radioactivity determined by autoradiograms. After 5 min, a considerable incorporation occurs in the following organs: subcutaneous and perispinal fat, liver, heart muscle, kidney and adrenal. The EFA deficient rats show a similar distribution but the radioactivity is longer retained. The total amount of radioactivity in the heart, liver, kidney and adrenal was measured at different times. A decline occurs in the heart, and an increase in the adrenal. In the urine, the highest amount of radioactivity is excreted on the first day. The excretion is lower in the EFA-deficient rats. Small amounts of radioactive metabolites with the chromatographic characteristics of PGE2 and 13,14 dihydro-15ketoPGE2 were isolated from urine. The amounts of 14CO2 produced were determined after the administration of [1-14C] AA. Half times were: 39 +/- 2.9 min in the EFA-deficient and 28 +/- 2.8 min in the normal rats. In the heart, AA is incorporated into phospholipids and neutral lipids. The following percentages were determined: phosphatidylinositol: 6.9 +/- 0.6%, phosphatidylcholine: 44 +/- 4.1%, phosphatidylethanolamine: 10.0 +/- 1.0%, neutral lipids: 9.3 +/- 1.6%. Several explanations can be given for the higher requirements of some tissues for AA. It could be, that this substance is used in the formation of particular membranes with a high AA content. Differences in the amounts of metabolites produced may also play a role.

Phospholipids, sterol carrier protein2 and adrenal steroidogenesis

Rat adrenocortical cells and preparations of plasma membrane and mitochondria have been employed to assess the effects of phospholipids and of sterol carrier protein2 (SCP2) on specific aspects of adrenal steroidogenesis. With intact cells, liposomal dispersions of cardiolipin caused significant stimulation of corticosterone output, while preparations of phosphatidylcholine, phosphatidylinositol, or the 4'-phosphate and the 4',5'-diphosphate derivatives of phosphatidylinositol were without effect. With the adrenal plasma membrane preparation, none of the added phospholipids affected either sodium fluoride or ACTH-responsive adenylate cyclase activity. With intact mitochondria, only cardiolipin, among the various phospholipids, tested, caused a concentration-dependent stimulation of pregnenolone production. However, even at the highest concentration of cardiolipin tested (500 microM), the stimulatory effect was only half that observed with 0.7 microM SCP2, and the two effectors were not synergistic. SCP2 caused a redistribution of cholesterol from mitochondrial outer to inner membranes, while cardiolipin, which is an activator of cytochrome P-450scc, had no effect on distribution of mitochondrial membrane cholesterol.

The effect of systemic prednisolone on arachidonic acid, and prostaglandin E2 and F2 alpha levels in human cutaneous inflammation

1 In order to test the proposal that the anti-inflammatory effect of corticosteroids is attributable to inhibition of release of the prostaglandin precursor, arachidonic acid, the effect of systemic prednisolone on arachidonic acid and prostaglandin levels in abdominal skin of six patients receiving this treatment for alopecia totalis, was studied. 2 Inflammation was produced in an area of abdominal skin by topical application of 5% w/w tetrahydrofurfuryl nicotinate (THFN) cream. 3 The erythema produced was assessed visually, and exudate recovered from normal and inflamed skin, by a suction bulla technique. 4 Arachidonic acid and PGE2 and PGF2 alpha levels, as measured by gas chromatograph-mass spectrometry (GC-MS) were significantly elevated in the reddened (THFN) treated skin, compared with control areas. 5 After prednisolone treatment both arachidonic acid and prostaglandin levels in THFN-treated areas were suppressed near to values obtained from untreated skin, before prednisolone therapy. There was partial reduction of THFN induced erythema in three out of six subjects. Levels of arachidonic acid on control skin were not affected by the steroid. 6 These results provide direct evidence that steroids inhibit prostaglandin formation by blocking evoked rise in the concentration of free arachidonic acid. The relationship of this effect, in human skin, to the anti-inflammatory action of systemic steroids is uncertain.

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.