Stimulation of renal prostaglandin synthesis by the pressor activity of vasopressin

Renal prostaglandin E2 (PGE2) synthesis is enhanced by exogenous vasopressin (AVP). To determine whether the pressor or the antidiuretic activities of AVP are related to its effect on PGE2 synthesis, AVP and the nonpressor analog, 1-deamino-8-D-arginine vasopressin (dD'AVP), were administered to the isolated perfused rabbit kidney, PGE2 was measured in the renal venous effluent by RIA and validated by bioassay. AVP in doses of 20, 200, and 2,000 ng progressively increased perfusion pressore by 12.1 +/- 2.4, 62.0 +/- 7.9, and 74.3 +/- 13.5 mm Hg, respectively, and increased PGE2 by 28 +/- 7, 80 +/- 3, and 129 +/- 57 ng/50 ml effluent, respectively. Bradykinin and angiotensin II induced a similar dose response on PGE2 release. However, dD'AVP in doses up to 20,000 ng minimally enhanced PGE2 release (20 +/- 16 ng/50 ml) and did not alter perfusion pressure. Simultaneous administration of AVP (200 ng) with the specific AVP pressor antagonist, d-cyclo-O-methyl-tyrosine-AVP, in a 1:10 (agonist to antagonist) weight ratio blunted the increase in perfusion pressure by 59 +/- 9% and blunted the increase in PGE2 release by 59 +/- 10% (P < 0.05). In a 1:100 weight ratio, the pressure antagonist reduced the AVP pressure response by 86 +/- 6% and reduced PGE2 by 84 +/- 7% (P < 0.01). These data suggest that the AVP stimulation of renal PGE2 synthesis is related primarily to its pressor and not to its antidiuretic activity in this in vitro kidney model. (Endocrinology 108: 495, 1981)     

Stimulation by oestradiol of soluble-protein synthesis in rat hypothalamus

The effect of oestradiol treatment on protein synthesis in the cytosol fraction (10⁵ g supernatant) from overiectomized mature and developing female rat hypothalami were studied. Results obtained on adults by double-label technique and SDS polyacrylamide gel or cellogel electrophoresis show that, as in the uterus, oestradiol-induced protein synthesis (IP) occurred in the cytosol fraction of the hypothalamus. The molecular weight of IP was about 40 000 dalton. During postnatal development, IP was also observed in cytosol fractions from the hypothalami of female rats 14, 21 and 28 days old. No clear-cut effect of oestradiol was found in the 7-day-old animals.     

Stimulation by human chorionic gonadotropin of prostaglandin synthesis by early human placental tissue

Successful establishment of pregnancy is dependent on inhibition of clotting and suppression of the maternal immune response at the feto-maternal interface. Early human placental production of prostacyclin (PGI2) and prostaglandin E2 (PGE2) may be important in this process. To examine the possible role of these PGs, we studied PGE and 6-keto-PGF1 alpha (stable metabolite of PGI2) synthesis in human placental (9-17 weeks gestation) organ cultures, and monolayer cultures of purified trophoblasts. PGE2 appeared to be the major protanoid formed. Other arachidonic acid metabolites identified in placental organ culture were 6-keto-PGF1 alpha, thromboxane B2, PGF2 alpha, leukotriene B4, 5(S)-hydroxyeicosatetraenoic acid (5-HETE), 12-HETE, and 15-HETE. The synthesis of PGE and 6-keto-PGF1 alpha altered with gestation and was maximal in the younger placentas. Arachidonic acid (33 microM) stimulated and indomethacin (28 microM) inhibited PG production. hCG, including physiological concentrations, stimulated PGE and 6-keto-PGF1 alpha synthesis in placental organ cultures. This effect was most striking in the 9-12 week placentas, compared to 15-17 week placentas. A similar hCG-induced stimulation of PGE production occurred in monolayer cultures of trophoblasts. The addition of TSH, FSH, and LH indicated that this effect was specific for hCG. These data suggest that hCG may have a biological role in the regulation of PG synthesis in early human placenta.     

Adaptive cytoprotection in cultured rat gastric mucus-producing cells role of mucus and prostaglandin synthesis

In cultured gastric mucosal cells, we investigated whether: (1) adaptive cytoprotection was associated with stimulation of endogenous prostaglandin synthesis; (2) prostaglandins given exogenously were cytoprotective against ethanol-induced gastric mucosal cell damage; and (3) a relationship existed between cytoprotection and mucus release. Cytolysis was quantified by measuring⁵¹Cr release from prelabeled cells. Mucus release was determined by measurement of [³H]glucosamine release. Concentrations of ethanol >12% caused cell damage and increased⁵¹Cr release dose dependently. Pretreatment with low concentrations of ethanol (0.5–1.5%) decreased ethanol-induced⁵¹Cr release, but also decreased prostaglandin E₂ synthesis. Prostaglandin E₂ and 16,16-dimethyl prostaglandin E₂ given exogenously were cytoprotective against ethanol-induced gastric mucosal cell damage. Treatment with low concentrations of ethanol (1.5%) increased mucus release from cultured gastric mucosal cells. However, prostaglandin E₂ and 16,16-dimethyl prostaglandin E₂ did not affect mucus release. We conclude that in cultured gastric mucus-producing cells: (1) adaptive cytoprotection occurs without stimulation of endogenous prostaglandin synthesis but with increase in mucus release; and (2) exogenous prostaglandins are cytoprotective against ethanol-induced gastric mucosal cell damage without stimulating mucus releasein vitro. We postulate that adaptive cytoprotection in cultured gastric mucus-producing cells is not mediated by prostaglandin, but by mucus released in response to a mild irritant.     

Stimulation of prostaglandin E2 production and induction of specific protein synthesis in rat peritoneal macrophages by a tumor promoter staurosporine

Staurosporine is a microbial anti-fungal alkaloid having potent inhibitory activity on protein kinase C and is a non 12-O-tetradecanoylphorbol-13-acetate-type tumor promoter in two-stage carcinogenesis experiments in mouse skin. Effects of staurosporine and its structurally related compounds K-252a, KT5720 and KT5822 on prostaglandin E₂ production, release of arachidonic acid from membrane phospholipids, and uptake of [³⁵S]methionine into intracellular proteins were examined in rat peritoneal macrophages. Among the four compounds, only staurosporine stimulated the production of prostaglandin E₂ and release of arachidonic acid at concentrations of 1 ng/ml and 10 ng/ml. The uptake of [³⁵S]methionine into cellular proteins, estimated to be 120 kDa and 125 kDa molecular mass, was also stimulated by staurosporine treatment, and the uptake was increased in parallel with the increase in prostaglandin E₂ production. At higher concentrations (100 ng/ml and 1000 ng/ml), staurosporine inhibited prostaglandin E₂ production and did not induce the specific protein synthesis. Other compounds neither stimulated prostaglandin E₂ production nor induced specific protein synthesis. K-252a inhibited prostaglandin E₂ production at concentrations above 10 ng/ml. These results suggest that the staurosporine-induced proteins might participate in the tumor promotion or at least in the staurosporine-induced stimulation of prostaglandin E₂ production.Abbreviation TPA 12-O-tetradecanoylphorbol tetradecanoylphorbol-13-acetate 13-acetate     

Active smoking depresses prostaglandin synthesis in human gastric mucosa

To determine the effect of smoking on gastroduodenal mucosal prostaglandin synthesis, endoscopies were done after an overnight fast on 10 nonsmokers, 12 active smokers who smoked four cigarettes in the hour before endoscopy, and then 11 of the smokers who refrained from smoking for 12 hours. Biopsy samples of fundic, antral, and duodenal mucosae were incubated, and the accumulation of prostaglandin E2 and 6-keto-prostaglandin F1 alpha in the incubation medium was measured by radioimmunoassay. We assumed that accumulation of prostaglandins in the medium reflected mucosal synthesis. Comparison of active and inactive smoking showed that active smoking significantly depressed 6-keto-prostaglandin F1 alpha synthesis in antral and fundic mucosa and prostaglandin E2 synthesis in antral mucosa. Comparison of nonsmokers and inactive smokers showed no difference in prostaglandin synthesis. Active smoking causes a transient decrease in prostaglandin synthesis in fundic and antral mucosae. This depression of prostaglandin synthesis may help explain slower ulcer healing and predisposition to ulcer recurrence in smokers.     

Somatostatin inhibits gastric acid secretion after gastric mucosal prostaglandin synthesis inhibition by indomethacin in man.

The inhibitory effect of indomethacin, 200 + 200 mg administered per os over 24 hours, on the prostaglandin E2 generative capacity of gastric mucosal tissue was determined in healthy male volunteers. The effect of prostaglandin synthesis inhibition on somatostatin induced suppression of food-stimulated acid secretion was tested. Peptone meal stimulated acid secretion was quantified in five healthy volunteers by intragastric titration with and without indomethacin pretreatment. Somatostatin doses of 200, 400, and 800 pmol/kg/h each significantly inhibited the peptone stimulated acid output. Indomethacin treatment, resulting in 90% inhibition of prostaglandin E2 synthesis, did not affect glucose- or peptone-stimulated acid output or modify the inhibitory action of somatostatin. Clinically, acid inhibition by somatostatin has been used to treat bleeding peptic ulcers. Ulcer haemorrhage may be preceded by an excessive use of drugs that inhibit prostaglandin synthesis such as aspirin or other non-steroidal anti-inflammatory agents. Recent observations in the rat indicate that prostaglandins mediate the inhibitory action of somatostatin on gastric acid secretion. The present results suggest that prostaglandins are not required for inhibition of gastric acid secretion by somatostatin in man.     

Stimulation of rabbit synoviocyte prostaglandin E2 synthesis by lipopolysaccharides and their subunit structures

Lipopolysaccharides (LPS) induce synoviocyte activation and may lead to destruction of synovial joint tissues. We assessed the production of prostaglandin E2 (PGE2) as a measure of synoviocyte activation by LPS and their subunit structures. Diphosphoryl lipid A was the smallest portion of lipid A tested that stimulated PGE2 production. The polysaccharide fraction of LPS, containing the O antigen, was also active. Intraarticular injections of the polysaccharide resulted in a synovitis very similar to that found in association with the intact LPS molecule. These observations suggest that both parts of LPS might be involved in gram-negative, organism-associated synovitis.     

Stimulation of prostaglandin accumulation in the rat anterior pituitary gland by luteinizing hormone releasing hormone in vitro.

The addition of luteinizing hormone releasing hormone releasing hormone (LH-RH) to cultures of monolayers of rat anterior pituitary cells was shown to increase both the concentrations of prostaglandins E1 and E2 (PGE) in the cells and the release of LH over similar ranges of concentrations of LH-RH (10(-6) to 10(-10) mol/l). The peak concentration of PGE was observed after 2.5 h. The stimulation of the level of PGE in the cells by LH-RH was completely inhibited by two inhibitors of prostaglandin synthetase, which only partially inhibited the stimulation of LH release. Therefore the increased concentration of PGE was not obligatory for the effect of LH-RH on LH release. It was also shown that monobutyryl cyclic AMP stimulated the intracellular concentration of PGE and it is suggested that the stimulation of PGE levels may be mediated by increased levels of cyclic AMP in the cells after the addition of LH-RH.     

Stimulation of oxidative drug metabolism by parenteral refeeding of nutritionally depleted patients

To determine whether intravenous nutritional repletion can influence oxidative drug metabolizing capacity, antipyrine metabolism was studied in 6 malnourished patients on the second day of a 2-day baseline period and on the last day of two sequential, 8-day intravenous nutritional repletion periods. During the baseline period they received 5% dextrose, 440 kcal per day, intravenously. During the repletion periods they received 20 mg of nitrogen per kilocalorie of baseline resting energy expenditure and, in random order, dextrose to provide a total caloric intake of either 0.95 or 1.75 times baseline resting energy expenditure. There were no statistically significant differences between the high- and low-dextrose repletion regimens in their effects on antipyrine metabolism. Seven days of nutritional repletion resulted in a 42% decrease in mean half-life (range 12%-52%) and an 87% increase in mean metabolic clearance rate (range 29%-155%) for antipyrine. An additional 8 days of nutritional repletion resulted in no further change in these pharmacokinetic parameters.     

Stimulation of prostaglandin accumulation in preovulatory rat follicles by adenosine 3',5'-monophosphate.

LH stimulates an increase in prostaglandins in vitro in preovulatory follicles from rats pretreated with PMS gonadotropin. The role of cAMP in this action of LH was examined by incubating preovulatory follicles with various substances and determining the resultant prostaglandin (PG) E accumulation by radioimmunoassay. LH (5 microgram/ml) increased PGE accumulation to approximately 4 times the control (181 +/- 23 to 886 +/- 83 pg/follicle). The addition of 20 mM cAMP also stimulated PGE accumulation, and the addition of 20 mM cAMP in the presence of 0.5 mM 1-methyl-3-isobutylxanthine was as effective as LH. Other nucleotides such as ATP, ADP, 3'-AMP, 5'-AMP, cGMP, and O2'-monobutyryl-cAMP did not stimulate PGE accumulation. On the other hand, (Bu)2cAMP, 8-bromo-cAMP, and N6-monobutyryl-cAMP produced an increase in PGE accumulation similar to that observed with LH. In addition, 10 microgram/ml cholera toxin was shown to increase both cAMP and PGE accumulation in preovulatory follicles. These results indicate that the prostaglandin response of follicles is specific for cAMP-like nucleotides or substances capable of increasing intracellular cAMP. The data support the concept that cAMP mediates the effect of LH on PGE accumulation in preovulatory follicles in the rat.     

Stimulation of prostaglandin E and testosterone production in rat interstitial cells by a gonadotropin-releasing hormone agonist

The early direct effects of a GnRH agonist analog [D-Ala6]des-Gly10-GnRH N ethylamide (GnRHa) on rat testicular interstitial cells include increased production of prostaglandin E (PGE) and testosterone (T) at 3 h (ED50 values of 0.5 and 0.75 nM, respectively). On the other hand, LH action on testicular function, which is mediated by increased cAMP, involves an increase in T production at 30 min followed by increased PGE formation at 3 h. GnRHa at concentrations of 10(-12)-10(-8) M had no effect on basal or LH-stimulated cAMP production during a 4-h incubation test. The stimulatory effect of GnRHa on PGE, but not on T production, was abolished by the prostaglandin synthesis inhibitor indomethacin (1.5 microns). We conclude that cAMP does not play a role in mediating the direct testicular effects of GnRH on PGE and T production; that PGE is not involved in mediating GnRH-induced T production; and, finally, that increased PGE and T production might be involved in mediating the direct inhibitory and stimulatory testicular effects of GnRH and its agonist analogs.     

Fat inhibits meal-stimulated gastric acid secretion after prostaglandin synthesis inhibition by indomethacin in man

The effect of cyclooxygenase inhibition by indomethacin on the mechanism by which fat inhibits gastric acid secretion was studied in eight healthy men. Oral 200-mg doses of indomethacin administered 15 h and 2 h before testing is known to inhibit prostaglandin synthesis by 90%, as determined by prostaglandin E2 generation assay on endoscopically obtained gastric mucosal biopsy specimens. Fat-induced inhibition of gastric acid secretion was evaluated by intragastric administration of 200 ml vegetable oil or glucose (control) for 30 min, followed by intragastric titration with peptone at pH 5.5 for 2 h. The mean acid output was significantly lower after fat (8 +/- 0.2 mmol 30 min-1) as compared with control (12 +/- 0.5 mmol 30 min-1). The fat-induced inhibition was unaffected by indomethacin treatment, and the plasma gastrin responses were similar in all groups. It is concluded that the participation of cyclooxygenase products such as prostaglandins in the mechanisms by which fat inhibits the gastric phase of acid secretion in man is likely to be minor.     

Stimulation of in vitro triglyceride synthesis in the rat hepatocyte by growth hormone treatment in vivo

Hepatic fatty acid metabolism in the rat is sexually differentiated. Rates of esterification by the liver of fatty acid into triglyceride and other esterification products (phospholipid, diglyceride, cholesteryl esters) are higher in the female than in the male. There is evidence to suggest that GH feminizes other hepatic systems that exhibit sexual dimorphism, including hepatic steroid metabolism, PRL receptors, and estrogen binding. To investigate the role of GH in maintenance of the high rates of fatty acid esterification observed in the female, we assessed rates of [1-14C]oleic acid utilization by hepatocytes prepared from hypophysectomized (hypox) cortisol/T3-replaced female rats with an without continuous in vivo infusion of human (h) GH (5 micrograms/h). In addition, we assessed the effect of in vivo hGH treatment (5 micrograms/h) on [1-14C]oleic acid utilization in the normal male rat. Hypophysectomy was accompanied by a reduction in incorporation of [1-14C]oleic acid into products of esterification (triglyceride, phospholipid, diglyceride) and oxidation (CO2, ketone bodies). Continuous infusion of hGH (5 micrograms/h; 14 days) restored rates of fatty acid esterification in the hypox-cortisol/T3-replaced female rat, with the exception of cholesteryl esters. hGH infusion partially restored rates of fatty acid oxidation in the hypox cortisol/T3-replaced female rat. Treatment of the adult male rat with continuous infusion of hGH (5 micrograms/h; 7 days) resulted in increased rates of incorporation of [1-14C] oleic acid into triglyceride. In contrast, incorporation of oleic acid into phospholipid, diglyceride, and cholesteryl esters was unaltered. These results suggest that GH may be an important regulator of hepatic fatty acid metabolism.     

Monosodium urate crystal-induced prostaglandin synthesis in the rat subcutaneous air pouch

Monosodium urate crystal-induced inflammation was studied in an air pouch model of rat synovium. Phagocytosis of crystals by macrophage-like and fibroblast-like cells in the pouch lining was observed 30 minutes after crystal injection and preceded polymorphonuclear leukocyte accumulation. Levels of the prostaglandins PGE2 and 6-keto-PGF1 alpha, measured in serial pouch washouts, showed a clear temporal dissociation with leucocyte numbers, with peak levels of the prostanoids occurring before the maximum accumulation of leucocytes. Indomethacin abrogated prostaglandin synthesis completely without reducing leucocyte counts in pouch washouts. We propose that the pouch lining cells may be the primary source of the prostaglandins and these mediators do not have a significant role in leucocyte chemotaxis in this model.     

Stimulation of glycoprotein and protein synthesis in isolated pig gastric mucosal cells by prostaglandins.

The purpose of this study is to evaluate the effects of different prostaglandin derivatives on protein and glycoprotein synthesis and secretion in isolated and enriched pig gastric mucous cells, as measured by the incorporation of [3H]L-leucine and N-acetyl-[14C]D-glucosamine respectively into acid insoluble macromolecules (AIM). PGE2 and 16,16-dimethyl-PGE2 enhanced the incorporation of the amino sugar into cellular (EC50 8 and 75 nmol/l) and secreted (EC50 30 and 270 nmol/l) AIM in a concentration dependent manner during a 20 hours incubation. After incubation for eight hours or more they also stimulated the incorporation of [3H]L-leucine into cellular AIM. PGF2 alpha was considerably less potent (EC50 greater than 1 mumol/l) than the E-type prostaglandins. Iloprost, a stable prostacyclin analogue, was ineffective.     

Protection by histamine receptor antagonists and prostaglandin against gastric mucosal barrier disruption in the rat.

This study was undertaken to determine if the cytoprotective effect of prostaglandin and the H2 histamine receptor antagonist cimetidine involves protection against disruption of the gastric mucosal barrier. Groups of anesthetized, vagotomized rats received one of the following parenterally: saline (control), mepyramine--an H1 histamine receptor antagonist, cimetidine, cimetidine and mepyramine, or 16,16 dimethyl prostaglandin E2. Parameters of barrier disruption were then determined before and after exposure of the gastric mucosa to 40mM acetylsalicylic acid. At the end of the study, gastric lesions were scored according to size and number. Lesion score and fall in potential difference were significantly lower in rats receiving cimetidine, cimetidine and mepyramine, and prostaglandin. Other parameters of barrier disruption--H+ back diffusion, Na+ and K+ influx, and protein outpouring--exhibited the same pattern and correlated with change in potential difference. We conclude that both prostaglandin and cimetidine, but not mepyramine, protect against barrier disruption by topical aspirin, and this may be a factor in the mechanism of their cytoprotective action.