Changes in prostaglandin concentration in blood subjected to repetitive freezing and thawing

Successive freezing and thawing of whole blood results in a consistently higher yield of various prostaglandin (PG) compounds. Evaluations were made with radioimmunological assay. The increase in PG concentrations seems to be more associated with cell fragmentation and not with the dissociation of albumin-PG complex. Our data suggest that there may be some dissociation of non-albumin-PG complexes. Artifactually high PG concentrations due to in vitro PG synthetase activity appears minimal at least with respect to indomethacin blocking of this enzyme. There are, in general, only slight differences in PG concentrations in samples with and without indomethacin.     

Evidence for the involvement of prostaglandins throughout the decidual cell reaction in the rat

Previous studies in which prostaglandin (PG) production was inhibited for a limited time by the s.c. administration of indomethacin have suggested that PGs are involved in the initiation of decidualization as well as the growth and differentiation of decidual cells. To reduce PG production during decidualization, in the present study indomethacin was infused from Alzet osmotic minipumps into the uterine lumen of ovariectomized rats with uteri sensitized for decidualization. To determine the effect of route of indomethacin administration on decidualization, rats received a single s.c. injection of indomethacin or its vehicle, and unilateral intrauterine infusion of indomethacin or its vehicle, in a factorial experiment. The inhibitory effects on decidualization, as assessed 5 days later by uterine weights, were greatest when both treatments were combined. Prostaglandins E and F concentrations 24 and 48 h after the insertion of the pumps were lower in the indomethacin-infused horns, suggesting that the indomethacin reduced uterine PG production. By contrast, subcutaneously administered indomethacin reduced uterine PG concentrations at 24 h but not at 48 h. Prostaglandin E2 and PGF2 alpha alone or combined, infused with indomethacin into the uterine lumen of rats treated subcutaneously with indomethacin, overrode the inhibitory effects of indomethacin. The dose-response relationships between these PGs and decidualization did not differ. These data suggest that PGs are required during the growth and differentiation of decidual cells from endometrial stromal cells.     

The role of endogenous prostaglandins in the regulation of gastric secretion in rhesus monkeys

Prostaglandins (PG) are known to alter a variety of gastrointestinal functions, but the physiological role of endogenous PG remains unclear. This experiment was designed to evaluate changes in gastric secretion following both acute and chronic inhibition of PG synthesis with indomethacin (5 mg/kg s.c.). Gastric juice was collected by continuous aspiration in 8 conscious chair-adapted male rhesus monkeys following treatment with saline or indomethacin for one or four days. The gastric juice was analyzed for H+, Na+, K+, and Cl- concentrations. The amount of soluble mucus in the gastric juice was estimated using Alcian Blue dye binding of acidic glycoproteins and Periodic Acid Schiff reaction with neutral glycoproteins. PG levels were measured in the plasma and in biopsy samples of fundus, antrum and duodenum. Both one and four days of indomethacin significantly (p less than 0.05) decreased tissue PG levels in the fundus, antrum and duodenum. Plasma levels of PGF2 alpha were significantly (p less than 0.05) decreased after both one and four days of indomethacin, while PGE2 and 6-keto PGF1 alpha were significantly inhibited only after four days of indomethacin. Both acute and chronic inhibition of PG synthesis was accompanied by a decrease in the concentration of sodium and mucus in the gastric juice but by an increase in the output and concentration of hydrogen ion. These changes suggest a possible mechanism by which endogenous PG play a role in the regulation of gastric secretion and in the protection against gastrointestinal damage.     

Methyl xanthine phosphodiesterase inhibitors behave as prostaglandin antagonists in a perfused rat mesenteric artery preparation.

The methyl xanthines, theophylline, caffeine and 3-isobutyl-1 methyl xanthine (MIX) inhibited the pressure responses to noradrnealine, angiotensin II and potassium ions in the isolated perfused mesenteric vascular bed of the male rat. The ID50s for inhibition of responses to noradrenaline were 1.85 mug/ml (0.83 x 10(-5) M) for MIX, 18 mug/ml (1 x 10(-4)M) for theophylline and 133 mug/ml (6.8 x 10(-4) M) for caffeine. Similar ID50 concentrations were found for responses to angiotensin II and potassium. We have previously found that substances which inhibit the three pressor agents equally may be prostaglandin (PG) synthesis inhibitors or PG antagonists. Xanthine itself, cyclic AMP and dibutyrl cyclic AMP had no inhibitory effects on the preparation up to concentrations of 10-2 M. Partial inhibition of PG synthesis by indomethacin shifted the % inhibition/log concentration curve to the left, while addition of exogenous PGE2 shifted it to the right. In preparations completely inhibited by sufficient indomethacin added to the perfusate to block PG synthesis, and then restored by adding 1 or 5 ng/ml PGE2 in addition to the indomethacin, the methyl xanthines again inhibited responses suggesting that they were PG antagonists rather than inhibitors of synthesis or release. In preliminary experiments MIX also inhibited effects of PGF2alpha on rat uterus and PGE1 on guinea pig ileum. Effective concentrations of theophylline were similar to the therapeutic levels in human plasma. PG antagonists may be a major action of methyl xanthines requiring reinterpretation of many experiments which have attributed their effects to PDE inhibition. PGs may also be involved in regulating PDE action.     

Compared effects of isoxicam and indomethacin on the urinary excretion of prostaglandins in degenerative articular diseases

The effects of a 7 day-treatment with isoxicam (200 mg/24 h) on the urinary excretion of prostaglandins (PG) were compared to those of indomethacin (150 mg/24 h) in a double-blind randomized study conducted in 18 patients with degenerative arthritic disease and normal renal function. Indomethacin decreased the urinary excretion of PGF2 alpha by about 70% and 6-keto-PGF1 alpha and thromboxane (Tx)B2, the stable break-down products of prostacyclin and TxA2 respectively, by about 40%. Isoxicam effects on urinary PG did not significantly differ from those of indomethacin. During both treatments, urinary gamma-glutamyl transferase and N- acetyl-glucosaminidase remained stable and none of the changes in the urinary excretion of PGs could be related to either plasma or urinary drug concentrations. In conclusion, chronic administration of isoxicam inhibited the renal PG biosynthesis to a similar extent than indomethacin which suggests that non steroidal anti-inflammatory drugs of the oxicam group ought also be used cautiously in patients with renal impairment.     

The role of endogenous prostaglandins in the regulation of gastric secretion in rhesus monkeys

Prostaglandins (PG) are known to alter a variety of gastrointestinal functions, but the physiological role of endogenous PG remains unclear. This experiment was designed to evaluate chanes in gastric secretion following both acute and chronic inhibition of PG synthesis with indomethacin (5 mg/kg s.c.). Gastric juice was collected by continuous aspiration in 8 concious chair-adapted male rhesus monkeys following treatment with saline or indomethacin for one or four days. The gastric juice was anzlyzed for H⁺, Na⁺, K⁺ and Cl⁻ concentrations. The amount of soluble mucus in the gastric juice was estimated using Alcian Blue dye binding of acidic glycoproteins and Periodic Acid Schiff reaction with neutral glycoproteins. PG levels were measured in the plasma and in biopsy samples of fundus, antrum and duodenum. Both one and four days of indomethacin significantly (p < 0.05) decreased tissue PG levels in the fundus, antrum and duodenu. Plasma levels of PGF_2α were significantly (p < 0.05) decreased after both one and four days of indomethacin, while PGE₂ and 6-keto PGF_1α were significantly inhibited only after four days of indomethacin. Both acute and chronic inhibition of PG synthesis was accompanied by a decrease in the concentration of sodium and mucus in the gastric juice but by an incrase in the output and concentration of hydrogen ion. These changes suggest a possible mechanism by which endogenous PG play a role in the regulation of gastric secretion and in the protection against gastrointestinal damage.     

Effect of indomethacin in vivo on prostaglandin content of several rabbit tissues

The prostaglandin (PG) content of several tissues and fluids from 6 day pregnant rabbits was evaluated following treatment with indomethacin or vehicle in vivo. PGE and PGF were measured by radioimmunoassay. More complete depletion of PGE and PGF was accomplished by 3 injections of indomethacin (s.c.) given during the 18 h before sacrifice at a dose of 10 mg indomethacin per kg body weight than was accomplished by 1 injection of the same amount of indomethacin (i.v.) 1.5 h before sacrifice. Levels of PGF were more easily depressed by indomethacin than were those of PGE. PG levels in the kidney and blastocysts were depressed to a greater extent by indomethacin than were those in the uterus, uterine fluid or peritoneal fluid. Evaluation of the effect of indomethacin on a particular physiological function should be interpreted with caution unless the extent of PG depletion in that tissue is also measured.     

Methyl xanthine phosphodiesterase inhibitors behave as prostaglandin antagonists in a perfused rat mesenteric artery preparation

The methyl xanthines, theophylline, caffeine and 3-isobutyl-1 methyl xanthine (MIX) inhibited the pressure responses to noradrenaline, angiotensin II and potassium ions in the isolated perfused mesenteric vascular bed of the male rat. The ID50s for inhibition of responses to noradrenaline were 1.85 μg/ml (0.83 × 10⁻⁵M) for MIX, 18 μg/ml (1 × 10⁻⁴M) for theophylline and 133 μg/ml (6.8 × 10⁻⁴M) for caffeine. Similar ID50 concentrations were found for responses to angiotensin II and potassium. We have previously found that substances which inhibit the three pressor agents equally may be prostaglandin (PG) synthesis inhibitors or PG antagonists. Xanthine itself, cyclic AMP and dibutyryl cyclic AMP had no inhibitory effects on the preparation up to concentrations of 10⁻²M. Partial inhibition of PG synthesis by indomethacin shifted the % inhibition/log concentration curve to the left, while addition of exogeneous PGE2 shifted it to the right. In preparations completely inhibited by sufficient indomethacin added to the perfusate to block PG synthesis, and then restored by adding 1 or 5 ng/ml PGE2 in addition to the indomethacin, the methyl xanthines again inhibited responses suggesting that they were PG antagonists rather than inhibitors of synthesis or release. In preliminary experiments MIX also inhibited effects of PGF2α on rat uterus and PGE1 on guinea pig ileum. Effective concentrations of theophylline were similar to the therapeutic levels in human plasma. PG antagonism may be a major action of methyl xanthines requiring reinterpretation of many experiments which have attributed their effects to PDE inhibition. PGs may also be involved in regulating PDE action.     

Effect of indomethacin on prostaglandin content of several rabbit tissues

The prostaglandin (PG) content of several tissues and fluids from 6 day pregnant rabbits was evaluated following treatment with indomethacin or vehicle . PGE and PGF were measured by radioimmunoassay. More complete depletion of PGE and PGF was accomplished by 3 injections of indomethacin (s.c.) given during the 18 h before sacrifice at a dose of 10 mg indomethacin per kg body weight than was accomplished by 1 injection of the same amount of indomethacin (i.v.) 1.5 h before sacrifice. Levels of PGF were more easily depressed by indomethacin than were those of PGE. PG levels in the kidney and blastocysts were depressed to a greater extent by indomethacin than were those in the uterus, uterine fluid or peritoneal fluid. Evaluation of the effect of indomethacin on a particular physiological function should be interpreted with caution unless the extent of PG depletion in that tissue is also measured.     

Prostaglandin F-2 alpha receptors in corpora lutea of pregnant rats and relationship with induction of 20 alpha-hydroxysteroid dehydrogenase

Luteal receptors for PGF-2 alpha in the pregnant rat were characterized. No changes in the Kd were found during pregnancy, whereas capacity increased to a maximum on Day 19, decreasing thereafter. The decrease in binding sites seen from Days 20 to 22 may be due to down regulation of the receptor by its ligand, since it was prevented by inhibition of PG synthesis by indomethacin treatment. Likewise, in-vivo treatment with PGF-2 alpha reduced the apparent number of PG binding sites. PG receptor concentration seems to be modulated by oestrogens since an increment was found on Day 19, associated with the known increase in plasma oestradiol concentrations, and since receptor concentration on Day 16 was significantly increased by oestradiol benzoate. The uterus also had a negative influence on the appearance of the PG receptor, since hysterectomy on Day 16 increased the number of binding sites on Day 18. However, receptor concentration and 20 alpha-hydroxysteroid dehydrogenase induction by hysterectomy was not affected by indomethacin, indicating that these events are probably not related to prostaglandin withdrawal. However, treatment with hCG, which diminishes enzyme induction by hysterectomy, did not produce changes in receptor concentration. The present results suggest that PGF-2 alpha, acting through a specific receptor site, is the physiological luteolytic signal. The consequence of its receptor binding seems to be the blockade of a gonadotrophic stimulus, which in turn determines (1) the decrease in progesterone synthesis and (2) the induction of 20 alpha-hydroxysteroid dehydrogenase.     

Effect of indomethacin invivo on prostaglandin content of several rabbit tissues

The prostaglandin (PG) content of several tissues and fluids from 6 day pregnant rabbits was evaluated following treatment with indomethacin or vehicle $\text{in}$$\text{vivo}$. PGE and PGF were measured by radioimmunoassay. More complete depletion of PGE and PGF was accomplished by 3 injections of indomethacin (s.c.) given during the 18 h before sacrifice at a dose of 10 mg indomethacin per kg body weight than was accomplished by 1 injection of the same amount of indomethacin (i.v.) 1.5 h before sacrifice. Levels of PGF were more easily depressed by indomethacin than were those of PGE. PG levels in the kidney and blastocysts were depressed to a greater extent by indomethacin than were those in the uterus, uterine fluid or peritoneal fluid. Evaluation of the effect of indomethacin on a particular physiological function should be interpreted with caution unless the extent of PG depletion in that tissue is also measured.     

Myo-inositol in physiological concentrations stimulates production of prostaglandin-like material

In physiological concentrations myo-inositol stimulated production of prostaglandin (PG)-like material in a rat mesenteric vascular bed preparation. There were five lines of evidence: 1. Inositol potentiated pressor responses to both norepinephrine and potassium in a manner similar to PGE2. 2. Inositol had no potentiating effect in preparations in which endogenous PG production was blocked by indomethacin. 3. Inositol caused no further potentiation in preparations already potentiated by arachidonic acid, the PG precursor. 4. The inhibitory effect of the PG antagonist chloroquine was reduced in an apparently competitive manner by inositol. 5. As indicated by rat stomach bioassay inositol caused a three fold rise in the outflow of PG-like material from the preparation.     

Indomethacin-induced augmentation of lymphoproliferative responses in patients with head and neck cancer

Augmentation of the phytohemagglutinin (PHA)-induced lymphoproliferation of peripheral blood mononuclear cells by indomethacin, a drug which blocks prostaglandin (PG) synthesis, was assessed in 37 patients with squamous cell carcinoma of the head and neck. Indomethacin enhanced the uptake of 3H-thymidine in stimulated cultures both from patients and normal individuals. However, because lymphoid cells from cancer patients were less reactive than those from normal controls, the proportionate increase in PHA-stimulated 3H-thymidine incorporation caused by indomethacin was greater in this population than in the normal population. The degree of enhancement induced by indomethacin did not correlate with the percent of esterase-positive mononuclear cells in the preparations. The amounts of PGE synthesized at 48 h by patients' or normal cells were similar. Cell populations that exhibited elevated levels of augmentation in the presence of indomethacin were approximately 3 times as sensitive to inhibition by 3 nM PGE2. The degree of augmentation detected in the presence of Ro-20-5720, which also prevents PG synthesis, was related to that produced by indomethacin. These results suggested that: the enhancing effect of indomethacin on lymphoproliferation in vitro was related to its inhibition of PG synthesis; and the sensitivity of lymphoid cells to inhibition by PGE2 was slightly, but significantly, increased in individuals with elevated augmentation values.     

Modulation of fibroblast proliferation by sulfidopeptide leukotrienes: effect of indomethacin

Because infiltration of mononuclear cells and fibroblast proliferation are associated in chronic inflammatory lesions, we tested the hypothesis that leukotrienes (LT), a product of activated mononuclear cells, may modulate fibroblast growth. Proliferation of cultured human skin fibroblasts was estimated by [3H]thymidine incorporation and cell count at increasing concentrations (0.1 nM to 0.1 microM) of LTC4 or LTD4. LTC4 and LTD4 stimulated cell growth in a dose-dependent manner only in the presence of 50 microM indomethacin. Under similar conditions, LTE4 but not LTB4 (0.1 microM) was active. Both asynchronous, growing cells and synchronous, quiescent cells were sensitive to LT when prostaglandin (PG) synthesis was suppressed by indomethacin. Other blockers of cyclooxygenase such as ibuprofen and aspirin exhibited identical permissive activity, and the effect of indomethacin was totally abolished by addition of PGE2. LTC4 modified neither [3H]arachidonic acid release from prelabeled fibroblasts nor PGE2 production by fibroblasts. These results demonstrate that the sulfidopeptide LT stimulate fibroblast proliferation only when the endogenous synthesis of PG is blocked, but they do not enhance the synthesis of PG in their target cells showing no evidence for a negative feed-back loop. Nevertheless, it seems likely that the initiation and development of the fibrotic process in the different tissues depends in part on the local balance between PG and LT productions.     

Cytokines stimulate lipolysis and decrease lipoprotein lipase activity in cultured fat cells by a prostaglandin independent mechanism.

We previously showed that indomethacin blocked the effect of tumor necrosis factor (TNF) and other cytokines on lipolysis. We now show that TNF stimulates prostaglandin (PG) production, enhances lipolysis and decreases lipoprotein lipase (LPL) activity in 3T3-F442A adipocytes and indomethacin blocks these activities, suggesting that the actions of TNF are mediated by PG's. However, exogenous PGE2 at the levels induced by TNF is not sufficient to affect lipolysis or LPL activity and low doses of indomethacin and flurbiprofen block PG production without affecting TNF's action. Interleukin-1 and interferon-alpha and gamma induce lipolysis and decrease LPL activity but do not stimulate much PG production. These results demonstrate that cytokines enhance lipolysis and decrease LPL activity in 3T3 adipocytes by a PG independent mechanism.     

吲哚美辛水凝胶贴剂小鼠体外透皮性能研究

目的：通过研究不同促透剂对吲哚关辛水凝胶贴剂透皮性能的影响,遴选在特定栽药剂量时具有最佳促透效果的促透剂,并与市售贴剂进行比较,对吲哚美辛水凝胶贴剂的体外透皮性能进行评价。方法：采用改良Franz透皮扩散池,以离体小鼠背部皮肤为透皮屏障,在最佳载药量选用不同浓度的氮酮、油酸、丙二醇以及三者组成的二元或三元组合为促透剂,在规定时间点测定吲哚美辛的累积透过百分率以及单位面积累积透过量。结果：与空白对照组相比,当氮酮与油酸单独应用时,二者均没有明显的促透作用;当选用二元促透剂联合应用时,油酸与丙二醇联用能够明显促进吲哚美辛的经皮渗透（P〈0．05）;当选用三元促透剂时促透效果更好,单位面积累积透过量最高可达234．4μg·cm^-2,24h内药物累积透过百分率明显高于市售贴剂。结论：氮酮、油酸、丙二醇三者联合应用可作为吲哚关辛贴剂的理想促透剂。吲哚关辛水凝胶贴剂是具有应用价值的新型经皮控释制剂。     

Adenosine as a natural prostaglandin antagonist in vascular smooth muscle

Adenosine has actions on smooth muscle similar to those of prostaglandin (PG) antagonists. Like some PG antagonists it is a phosphodiesterase inhibitor and seems to interfere with calcium effects. It has agonist/antagonist interactions with theophylline, a PG antagonist. In rat mesenteric vascular smooth muscle adenosine blocked responses to noradrenaline which depend on release of intracellular calcium but not those to potassium ions which depend on calcium entry from extracellular fluid. Partial inhibition of endogenous PG synthesis by indomethacin enhanced the adenosine effect. In preparations in which vascular reactivity had been abolished by indomethacin and then partly restored by 1 or 5 ng/ml PGE2, adenosine also inhibited responses to noradrenaline: the curve for the 5 ng/ml PGE2 concentration was to the right of and parallel to the 1 ng/ml curve consistent with a competitive interaction between adenosine and PGE2. Similar interactions between adenosine and PGE2 were shown in human lymphocytes in which activation also depends on calcium release. These findings suggest how calcium-dependent metabolic responses may be controlled and indicate further reasons for caution in the interpretation of cyclic AMP experiments.     

The role of alpha-adrenergic receptors in the vasoconstrictor response induced by indomethacin in the kidney.

The effect of indomethacin, an inhibitor of prostaglandin (PG) synthesis, was studied on the renal circulation, Na+ and water excretion in anaesthesized dogs during alpha-receptor inhibition. Indomethacin decreased cortical blood flow (CBFcontr, 454 +/- 142; CBFindo, 332 +/- 51 ml per min per 100 g; p less than 0.02) as well as medullary blood flow (OMBFcontr, 339 +/- 95; OMBFindo, 183 +/- 46 ml per min per 100 g; p less than 0.001), salt and water excretion, further it caused a shift in the intrarenal blood flow distribution toward the cortex. Alpha-blockade prevented the indomethacin-induced vasoconstriction in the cortex (CBF alpha inhibition + indo, 455 +/- 76 ml per min per 100 g) but not in the medullar (OMBF alpha inhibition + indo, 259 +/- 102 ml per min per 100 g, p less than 0.05). Alpha-blockade failed to prevent the indomethacin-induced antidiuresis, antinatriuresis and the intrarenal blood flow redistribution. GFR remained unaffected in all three series of studies. Our experimental findings are in line with the presumption that alpha-receptors are involved in the renal circulatory changes caused by indomethacin, probably as a result of an enhanced NE release during the inhibition of PG production. A NE--PG feed back mechanism is suggested in the regulation of renal circulation. The reduction of salt and water output induced by indomethacin appears to be independent of the alterations in renal haemodynamics, and seems rather to be the result of enhanced Na+ reabsorption, predominantly at the distal segment of the nephron, in the absence of PG, and/or a direct action of indomethacin.     

Stimulation of adenosine 3':5'-monophosphate formation by prostaglandins in human astrocytoma cells. Inhibition by nonsteroidal anti-inflammatory agents.

Prostaglandins (PG) of the E series and catecholamines stimulate adenosine 3':5'-monophosphate (cAMP) formation in human astrocytoma cells (1321N1). These two classes of effectors activated adenylate cyclase upon interaction with different receptor systems. No evidence for a mediatory role for PG in the action of catecholamines was found. PG interacted with 1321N1 cells with an order of potency of PGE1 = PGE2 greater than PGA1 greater than PGF2 alpha. The effect of combinations of the various PG indicated that all efficacious PG interacted with a common receptor. 7-Oxa-13-prostynoic acid and indomethacin were shown to be competitive inhibitors of the effect of PGE1 with Ki values of 4 and 150 micron, respectively. These two compounds did not inhibit the effect of isoproterenol. Polyphloretin phosphate caused a complex pattern of inhibition of the effects of PGE1 and at higher concentrations also inhibited the effects of isoproterenol. The mefenamate class of nonsteroidal anti-inflammatory agents was found to inhibit the effects of PGE1 with a potency order of meclofenamic acid greater than flufenamic acid = mefenamic acid. The inhibitory action of meclofenamic acid was complex involving specific, but partial, insurmountable antagonism of PGE1 as well as competitive inhibition of PGE1 effects. At higher concentrations of meclofenamic acid a nonspecific inhibition of the effects of both PGE1 and isoproterenol was observed. These studies suggest that the inhibition by nonsteroidal anti-inflammatory agents of the physiological effects of PGE1 in animals may occur, at least in part, at the level of adenylate cyclase. The possibility that multiple classes of adenylate cyclase-linked PGE receptors might exist in nature is discussed.     

Arachidonate metabolism in the mouse thyroid implication of the lipoxygenase pathway in thyrotropin action

The present study of compares the effects of various inhibitors of arachidonate metabolism on mouse thyroid cyclo-oxygenase and lipoxygenase activities and thyrotropin-augmented cyclic-AMP accumulation. Mouse thyroid homogenate converts [1-14C]- arachidonate to several products of the cyclo-oxygenase pathway as well as one major product of the lipoxygenase pathway, 12-L-hydroxyeicosatetraenoic acid (12-Hete). Prostaglandin (PG) formation in thyroid homogenates is inhibited by 1-10 microM indomethacin and etya. 12-HETE accumulation is reduced by 91%, 83% and 20% by 5 microM ETYA, 15-HETE, and indomethacin, respectively. Thyrotropin-stimulated cyclic-AMP accumulation, measured in whole thyroid lobes by radioimmunoassay, is reduced by 45% and 73% by 50 microM and 100 microM ETYA, respectively; indomethacin is without effect at these concentrations. 15-HETE reduces thyrotropin-augmented cyclic-AMP accumulation by 57% and 100 microM. In product inhibition studies, 10 microM 12-HETE reduced the formation of radiolabeled 12-HETE by 20%. 10 microM PGE2, PGF2 alpha or PGD2 had no effect on [1-14C]-PG formation. 12-HETE, however, reduced PG synthesis by 76% at 10 microM. This is the first report implicating the arachidonate lipoxygenase pathway in thyrotropin action at the level of cyclic-AMP regulation. Additionally, our finding that 12-HETE inhibits prostaglandin synthesis suggests that the cyclo-oxygenase and lipoxygenase pathways in the mouse thyroid may be highly integrated.