Endogenous prostaglandins are physiological regulators of endocrine cells in the gastroduodenal mucosa of the rat.

BACKGROUND/AIM: To investigate whether endogenous prostaglandins participate in the regulation of the gastrointestinal endocrine cell system. METHODS: Sprague-Dawley rats were treated with 1 mg/kg indomethacin subcutaneously or indomethacin subcutaneously and 500 microg/kg oral prostaglandin E2 or solvents for 2 months. Endocrine cells were visualized by using immunohistochemistry and by the Sevier-Munger silver stain on specimens from the gastroduodenal mucosa, and their total volume was estimated, using standard stereological methods. Plasma and gastrointestinal tissue concentrations of regulatory peptides were analyzed by radioimmunoassay. RESULTS: Fundic mucosa. The total volume of cells stained with the Sevier-Munger silver stain (enterochromaffin-like) was increased by indomethacin, but reduced by the administration of prostaglandin E2 (P < 0.05 vs. indomethacin). Indomethacin increased the total volume of somatostatin-immunoreactive. Similarly, rats given indomethacin and prostaglandin E2 had higher values than controls. Indomethacin increased the tissue concentration of somatostatin in the gastric fundus whereas prostaglandin E2 prevented such changes (P < 0.05 vs. indomethacin). Antral mucosa. The total volume of serotonin-immunoreactive cells was reduced by indomethacin, but increased by prostaglandin E2 (P < 0.05 vs. controls and indomethacin, respectively). Duodenal mucosa. The total volume of somatostatin-immunoreactive cells was reduced in the rats given indomethacin and prostaglandin E2 (P < 0.05 vs. controls and indomethacin). Indomethacin reduced and simultaneous administration of prostaglandin E2 increased the total volume of CCK-immunoreactive cells (P < 0.05 vs. controls and indomethacin). Indomethacin reduced the total volume of serotonin-immunoreactive cells whereas the simultaneous administration of PGE2 comparatively increased their total volumes (P < 0.05 vs. indomethacin), although they were still lower than the control values. The total volume of GIP-immunoreactive cells was slightly increased in the rats given both indomethacin and indomethacin + prostaglandin E2. The tissue concentration of somatostatin in the duodenum was reduced in rats given indometacin and prostaglandin E2 (P < 0.05 vs. controls and indomethacin). CONCLUSION: Endogenous prostaglandins, particularly prostaglandin E2, regulate CCK-, enterochromaffin-like-, somatostatin-, GIP- and enterochromaffin cells in the gastroduodenal mucosa of the rat.     

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.     

Lack of covalent modification of prostaglandin synthetase (cyclo-oxygenase) by indomethacin.

We have previously shown that aspirin irreversibly inhibits prostaglandin synthetase (cyclo-oxygenase) by acetylating the active site of the enzyme. By utilizing 14C-labeled indomethacin and a close analogue, we now show that indomethacin, unlike aspirin, does not covalently modify cyclo-oxygenase. Furthermore, indomethacin binding to the enzyme may be reversible since even though indomethacin can inhibit acetylation by aspirin, when enzyme inhibited by indomethacin (1 micronM) is treated with 200 micronM aspirin 3 times for 1 hour each, complete acetylation of cyclo-oxygenase is achieved.     

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.     

Lack of covalent modification of prostaglandin synthetase (cyclo-oxygenase) by indomethacin

We have previously shown that aspirin irreversibly inhibits prostaglandin synthetase (cyclo-oxygenase) by acetylating the active site of the enzyme. By utilizing ¹⁴C-labeled indomethacin and a close analogue, we now show that indomethacin, unlike aspirin, does not covalently modify cyclo-oxygenase. Furthermore, indomethacin binding to the enzyme may be reversible since even though indomethacin can inhibit acetylation by aspirin, when enzyme inhibited by indomethacin (1 μM) is treated with 200 μM aspirin 3 times for 1 hour each, complete acetylation of cyclo-oxygenase is achieved.     

Inhibition of lysosomal enzyme liberation by indomethacin in vivo

The volume of the peritoneal exudate induced in the rat by iota carrageenan is reduced by subcutaneous administration of indomethacin while the concentrations of three lysosomial enzymes in the exudate are slightly increased or not modified. Thus, the total enzymatic activities of the exudate are reduced by indomethacin. The leucocyte accumulation remains unchanged in the indomethacin treated rats. During the development of the peritoneal exudate, the circulating plasma displays a high degree of lysosomial enzymes activity which is suppressed by indomethacin at the dose of 4 mg/kg.     

Effectiveness of indomethacin as an antitumor agent in Colon 26-bearing conventional and nude mice, and telomerase activity in the tumors.

The antitumor effect of indomethacin on Colon 26 tumor was investigated in conventional (CDF1) and nude mice (BALB/c nu/nu), and the telomerase activity in the tumor tissues treated with indomethacin was monitored. Growth of Colon 26 tumor was significantly suppressed with indomethacin treatment compared to the controls both in conventional and nude mice. And telomerase activity in the tumor tissues noticeably declined in contrast to normal somatic tissues (testis, liver and colon), which were not affected by indomethacin treatment. We also showed that indomethacin can suppress tumor growth in association with a preferential decrease in telomerase activity in tumor tissues both in conventional and nude mice to the same extent. This study suggests a method for investigating the mechanism of tumor suppression by indomethacin, and suggests that indomethacin might be useful as a novel agent for human cancer therapy.     

Prostaglandin-independent anovulatory mechanism of indomethacin action: inhibition of tumor necrosis factor alpha-induced sheep ovarian cell apoptosis

Indomethacin, a nonsteroidal anti-inflammatory agent, is a potent inhibitor of ovulation in vertebrates. The presumptive obligate anovulatory mode of indomethacin action is via suppression of ovarian prostaglandin production. We report that a very high systemic dose of indomethacin (800 mg i.m.) is required to block ovulation in gonadotropin-treated anestrous ewes. A lower dose of indomethacin (200 mg), which negated the preovulatory rise in follicular prostaglandin (PGF(2alpha)) biosynthesis, did not prevent ovulation. Endothelial secretion of tumor necrosis factor (TNF)-alpha within the apical follicular wall (prospective site of rupture) was not altered by indomethacin; notwithstanding, the apoptosis (DNA-fragmentation)-inducing effect of TNF-alpha (a determinant of ovulatory stigma formation) was attenuated by 800 (but not 200) mg indomethacin. A suprapharmacological concentration of indomethacin also was necessary to protect ovarian surface epithelial cells from a (prostaglandin-independent) cytotoxic effect of TNF-alpha in vitro. It is concluded that indomethacin inhibits ovulation by anti-apoptotic mechanisms that can be dissociated from the paradigm of prostanoid down-regulation.     

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.     

In vitro effect of indomethacin and interferon-alpha on Th1 and Th2 cytokine synthesis in patients with chronic hepatitis C

Current evidences suggest that non-steroidal anti-inflammatory drugs could enhance the antiviral activity of interferon-alpha in chronic HCV infection. In this study, we investigated the effect of indomethacin, a non-steroidal anti-inflammatory drug, and interferon-alpha on cytokine production by peripheral blood mononuclear cells from 12 untreated patients with chronic hepatitis C. We evaluated the effect of incubation with indomethacin, interferon-alpha or both on synthesis of Th1- (interleukin-2, interferon-gamma) and Th2-associated cytokines (interleukin-4, interleukin-10), and of the antiviral protein 2',5'-oligoadenylate synthetase. Interferon-alpha induced a significant increase in production of interleukin-2. Smaller increases were also seen in the presence of indomethacin, while incubation with both indomethacin and interferon-alpha leads to a synergistic effect. Incubation with indomethacin decreased both interleukin-4 and interleukin-10, whereas interferon-alpha increased these cytokines. The addition of indomethacin to interferon-alpha significantly reversed this interferon-induced increase. Finally, both indomethacin and the association interferon-alpha plus indomethacin determined a significant increase in 2',5'-oligoadenylate synthetase production compared to both baseline and interferon-alpha alone. In conclusion, indomethacin was able to enhance the antiviral activity of interferon-alpha and to modulate the interferon-induced Th1 and Th2 cytokine response by increasing the Th1-response, fundamental for sustained clearance of HCV, and by decreasing the Th-2 type response, associated with HCV persistence.     

Indomethacin up-regulates the generation of lymphokine-activated killer-cell activity and antibody-dependent cellular cytotoxicity mediated by interleukin-2

Prostaglandins can inhibit the generation of lymphokine-activated killer (LAK) cells by interleukin-2 (IL-2) whereas indomethacin augmented the induction of LAK cells by inhibiting prostaglandin synthesis. In the present study we demonstrate that prostaglandin E2 substantially inhibited the generation of both LAK and antibody-dependent cellular cytotoxicity (ADCC) activity by IL-2. In addition, indomethacin enhanced the induction of LAK activity and ADCC in splenocytes exposed to IL-2 in vitro. The effect of indomethacin was dose-dependent, reaching an optimal effect at 1 microM when 100-1000 units/ml IL-2 were employed. The effect of indomethacin on the generation of ADCC was seen in cells taken from both tumor-bearing mice and normal mice. ADCC induced by IL-2 was augmented by culturing cells from the spleen, liver and lungs, in the presence of indomethacin. ADCC induced in the presence of IL-2 and indomethacin was mediated by cells that were mainly plastic non-adherent cells and expressed the asialo-GM1 glycolipid. The potential of indomethacin in combined therapy with cytokines and specific anti-tumor monoclonal antibodies is discussed.     

Inhibition of purified glutathione S-transferases by indomethacin

Soluble rat liver glutathione S-transferases have been purified and a previously undescribed peak was observed. This peak contained glutathione S-transferase activity which was extensively inhibited by indomethacin. Glutathione conjugation of 1-chloro-2,4-dinitrobenzene by this isozyme, designated glutathione S-transferase VII, was inhibited 44 and 68% at indomethacin concentrations of 0.20 and 1.00 microM, respectively. The other six basic glutathione S-transferase isozymes were relatively unaffected by low concentrations of indomethacin. The pharmacological significance of this inhibition by indomethacin is largely dependent on the role of the glutathione S-transferase VII in leukotriene synthesis.     

Effects of indomethacin, prostaglandin E2 and prostaglandin F2 alpha on mouse blastocyst attachment and trophoblastic outgrowth in vitro

A study was performed in order to investigate the participation of prostaglandins (PGs) during implantation. The effects of indomethacin on mouse blastocyst attachment and trophoblastic outgrowth were examined in vitro. Studies were also carried out on cultures supplemented with PGE2 and/or PGF2 alpha along with indomethacin. (1) Blastocyst attachment and trophoblastic outgrowth were inhibited by indomethacin dose-dependency. (2) In the cultures supplemented with indomethacin and PGE2 or PGF2 alpha, respectively, the inhibitory effects of indomethacin were reduced. (3) In the cultures supplemented with all three substances with treatment (1) and (2), inhibition of indomethacin was partially reversed, but still lower than control group without indomethacin. The above results indicate that both PGE2 and PGF2 alpha have a promoting effect on implantation, and PGF2 alpha was more effective than PGE2.     

The effect of clomiphene citrate on ovulation and spawning in indomethacin treated carp, Cyprinus carpio

Studies were conducted on the effect of clomiphene on ovulation and spawning in mature C. carpio pre-treated with indomethacin. It was demonstrated that indomethacin caused a block to ovulation and spawning at two dose levels (5 and 10 μg⁻¹g). This blockade could be overcome by two (10 μg⁻¹g each) successive dosages of clomiphene given 7 and 31 h after the indomethacin treatment. When indomethacin and clomiphene treatments were given concomittantly, the inhibitory effects of indomethacin remained more pronounced.     

Indomethacin increases plasma lithium.

The effects of indomethacin on plasma lithium concentrations and renal lithium clearance were investigated in three psychiatric patients and four normal volunteers. After steady-state plasma lithium concentrations had been reached, the subjects received indomethacin placebo for three to seven days, indomethacin (50 mg thrice daily) for seven days, and placebo again for three to seven days. Indomethacin increased plasma lithium concentrations by 59% in the psychiatric patients and 30% in the volunteers. Renal lithium clearance was reduced by indomethacin by 31% in the group as a whole, and prostaglandin synthesis, determined by measuring the major metabolite of PGE2 with mass spectrometry, was reduced by 55%. These results show that indomethacin reduces renal lithium clearance to an extent which may be clinically important. They also suggest that the renal clearance may be affected by a prostaglandin-dependent mechanism, possibly located in the distal tubule.     

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.     

Augmentation of murine lymphokine (rIL-2)-activated killer cell activity by indomethacin

The effect of indomethacin on murine lymphokine-activated killer (LAK) cell activity was investigated using a natural killer-resistant, spontaneously developed, weakly immunogenic, and highly tumorigenic syngeneic murine mammary adenocarcinoma, mimicking that of human disease, as the target. When used in combination with human recombinant interleukin-2 (rIL-2), indomethacin was found to augment LAK cell activity, which was generated from culture of the normal mouse splenocytes with rIL-2, as compared to that with rIL-2 alone. This increase in LAK cell activity was shown to be indomethacin dose-dependent, and was demonstrated only when indomethacin was added to the rIL-2-containing medium at the beginning of culture. The enhancement of LAK cell activity by indomethacin was abrogated when the nylon-wool nonadherent "macrophage-poor" splenocytes were incubated with rIL-2 plus indomethacin. These results indicated that the rIL-2-induced LAK cell activity generated from murine splenocytes could be augmented by indomethacin, and the macrophages may be involved as the mediator.     

Effects of zomepirac and indomethacin on renal blood flow and electrolyte excretion in anesthetized monkeys

Zomepirac sodium is a new inhibitor of prostaglandin cyclooxygenase with an $\text{in vitro}$ potency equivalent to indomethacin. Since inhibitors of prostaglandin synthesis have marked effects on renal hemodynamics, zomepirac may be expected to reduce renal blood flow (RBF) in a manner similar to indomethacin. This study compares the effects of zomepirac and indomethacin on RBF and electrolyte excretion in anesthetized Rhesus monkeys. Each experiment consisted of a control period followed by 3 or 4 drug treatment periods in which increasing doses of zomepirac (0.5 to 20 mg/kg) or indomethacin (0.5 to 10 mg/kg were given. Indomethacin (5 mg/kg) reduced RBF by 22% and the higher dose (10 mg/kg) reduced RBF by an additional 13%. Zomepirac had little effect on RBF in doses as high as 20 mg/kg. At any given dose the mean plasma concentration of zomepirac was equal to or greater than indomethacin. Peak indomethacin concentration was 48 μg/ml after the 10 mg/kg dose while the peak zomepirac, after 20 mg/kg, was 158 μg/ml. Neither drug had a significant effect on either glomerular filtration rate or excretion rate of sodium or potassium. Thus, zomepirac had only minimal effects on RBF while indomethacin decreased RBF of anesthetized monkeys in a manner qualitatively similar to its effect in other species. The minimal renal effects caused by zomepirac relative to indomethacin in this primate may indicate a therapeutic advantage for zomepirac in man.     

Inhibition of Proteolysis by a Cyclooxygenase Inhibitor,Indomethacin

The effect of indomethacin, a non-steroidal anti-inflammatory drug upon purified calpain has been studied. Also, its effects upon Ca²⁺-mediated degradation of cytoskeletal proteins (neurofilament) in spinal cord homogenate has been investigated. A dose-dependent inhibition of purified calpain activity was observed. A 50% inhibition of ¹⁴C-caseinolytic activity was obtained with less than 1.1 mM of indomethacin while the activity was completely inhibited at 3.3 mM concentration. The inhibitory effect of ketorlac, another non-steroidal anti-inflammatory drug, upon calpain was weaker than that of indomethacin. The degradation of myelin basic protein (MBP) by cathepsin B, a lysosomal cysteine protease, was significantly inhibited by indomethacin. It also inhibited the Ca²⁺-mediated degradation of neurofilament protein (NFP) in spinal cord homogenate. The extent of NFP degradation was analyzed by SDS-PAGE and the inhibition shown by indomethacin was weaker than that observed with leupeptin and the calpain inhibitor E64-d. The inhibitory effect of indomethacin on the activity of multicatalytic proteinase complex was negligible. These results suggest that indomethacin, a non-steroidal anti-inflammatory drug and cyclooxygenase inhibitor also inhibits proteinases, including cathepsin B and calpain.     

Radioprotection of hematopoietic tissues in mice by indomethacin

We recently reported that indomethacin, an inhibitor of prostaglandin (PG) synthesis, increased the radioresponse of PG-producing murine tumors, but it protected the hematopoietic system from radiation damage [Furuta et al., Cancer Res. 48, 3008-3013 (1988)]. Here we have investigated possible mechanisms responsible for the radioprotective effect of indomethacin. In the exogenous spleen colony assay, bone marrow cells from indomethacin-treated mice showed a similar radioresponse to those from mice not treated with indomethacin, thus excluding true radioprotection as a mechanism. Also, neither the total number of bone marrow cells nor the number of stem cells in bone marrow were affected by the treatment with indomethacin. However, indomethacin induced significant splenomegaly, which was associated with an increased number of both nucleated cells and hematopoietic stem cells in the spleen. The latter was determined by the exogenous spleen colony assay. Thus indomethacin protected hematopoietic tissue indirectly through stimulation of hematopoietic cells in the spleen. When indomethacin was combined with WR-2721, which is a true radioprotector, we obtained a greater radioprotective effect than with either used alone according to the endogenous spleen colony assay.