Absorption and metabolism of prostaglandin E1 by perfused rat jejunum in vitro

The effects of TFC-612, a 7-thia prostaglandin E1 derivative, on platelet function

The anti-platelet activities of TFC-612, methyl 6-(((1R, 2S, 3R)-3-hydroxy-2-((1E, 3S, 5R)-3-hydroxy-5-methyl-1-nonenyl)-5- oxocyclopentyl) thio)hexanoate, were compared to prostaglandin E1 (PGE1). TFC-612 inhibited human, guinea-pig and rabbit platelet aggregation induced by ADP, collagen or epinephrine with potency 1-8 times that of PGE1. TFC-612 also inhibited thrombin induced (14C) serotonin release in rabbit platelets. Platelet aggregation was dose dependently inhibited 1 hr after oral administration of TFC-612 (0.32-1.0 mg/kg) and the inhibition lasted up to 6 and 24 hours at 0.32 and 1.0 mg/kg, respectively, in guinea-pigs. In contrast, PGE1 had no effect with oral administration at a dose of 3.2 mg/kg. TFC-612 (0.32-3.2 micrograms/kg, i.v.) induced platelet disaggregation of thrombi on Achilles tendon in the extracorporeal shunt model in cats. In addition, TFC-612 (1 mg/kg, po) inhibited the adhesiveness of guinea-pig platelets to a glass bead column ex vivo. TFC-612 increased cyclic AMP (cAMP) levels in rabbit platelets. Thus, the anti-platelet action of TFC-612 may be due to an increase in cAMP levels. These results indicate that TFC-612 might be an orally active anti-thrombotic drug.

The effects of TFC-612, a 7-THIA prostaglandin E1 derivative, on platelet function

The anti-platelet activities of TFC-612, methyl 6-(( 1R,2S,3R)-3-hydroxy-2-((1E,3S,5R)-3-hydroxy-5-methyl-1-nonenyl)-5- oxocyclopentyl) thio)hexanoate, were compared to prostaglandin E1 (PGE1). TFC-612 inhibited human, guinea-pig and rabbit platelet aggregation induced by ADP, collagen or epinephrine with potency 1-8 times that of PGE1. TFC-612 also inhibited thrombin induced (14C) serotonin release in rabbit platelets. Platelet aggregation was dose dependently inhibited 1 hr after oral administration of TFC-612 (0.32-1.0 mg/kg) and the inhibition lasted up to 6 and 24 hours at 0.32 and 1.0 mg/kg, respectively, in guinea-pigs. In contrast, PGE1 had no effect with oral administration at a dose of 3.2 mg/kg. TFC-612 (0.32-3.2 micrograms/kg, iv) induced platelet disaggregation of thrombi on Achilles tendon in the extracorporeal shunt model in cats. In addition, TFC-612 (1 mg/kg, po) inhibited the adhesiveness of guinea-pig platelets to a glass bead column ex vivo. TFC-612 increased cyclic AMP (cAMP) levels in rabbit platelets. Thus, the anti-platelet action of TFC-612 may be due to an increase in cAMP levels. These results indicate that TFC-612 might be an orally active anti-thrombotic drug.

Physical model approach to gastrointestinal absorption of prostaglandins II: In situ rat intestinal absorption of dinoprost

In situ absorption studies with dinoprost in the rat jejunum were carried out using a modified Doluisio technique. The absorption rate was first order. There was a sigmoidal decrease in the rate with increasing buffer pH (from 3.5 to 9.5), which strongly indicated the partitioning of weak acid species into the lipoidal membrane. An asymptotic minimum rate was attained from buffer pH 7.5 to 9.5, operationally indicative of transport of anions across aqueous pores. The importance of the aqueous diffusion layer on the mucosal side of the membrane was evident; rates at pH 3.5 and 4.5 were faster at high agitation hydrodynamics in the lumen solution. Preliminary studies showed that there was no metabolism in the lumenal solution and that metabolism occurred within the membrane. The transport mechanism involved simultaneous passive diffusion and bioconversion in the membrane because (a) a 1.5 X 10(4)-fold range in dinoprost concentration (0.014-210 microM) showed no saturable carrier-mediated tendency on the rate, (b) iodoacetic acid and indomethacin did not inhibit the absorption rate, and (c) the shape of the absorption-pH profiles was suggestive of passive diffusion. The prostaglandin did not have apparent adverse membrane and vascular effects under the conditions employed. The quantification and factorization of the physically meaningful transport parameters were accomplished using the physical model previously described. The permeability coefficients of the aqueous diffusion layer for the oscillation and static hydrodynamic situations were 0.8 X 10(-4) and 1.7 X 10(-4) cm/s, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Fate of prostaglandin E2 in suckling rats after intragastric administration

[3H]Prostaglandin E2 was administered intragastrically to suckling rats at 10 micrograms and 0.1 microgram doses. At the higher dose, 91% of the radioactive label was recoverable at zero time, decreasing to 29% at 5 h. At the lower dose, 40% of the dose was recoverable at zero time, decreasing to 8% at 5 h. With time, the radioactivity in the stomach showed a steady decrease whereas it increased in the tissues. At the 10 microgram dose of [3H]prostaglandin E2 the amount of radioactivity showed a steady increase in the small intestine lumen and small intestine wall. In liver and kidney the maximum amount of radioactive label was found at 1 h. After 1 h the radioactivity began to decline in the liver, while the kidney remained at the same level for the entire 5-h period. At the 0.1 microgram dose of [3H]prostaglandin E2 the radioactivity in the small intestine lumen reached a maximum 3 h after gavage and thereafter declined. The amount of label in the small intestine wall increased for the entire 5 h. In liver and kidney the radioactivity peaked at 1 h, remained at the same level until the 3rd h, then exhibited a decline. Quantitation of the unmetabolized prostaglandin E2 reaching the various organs studied was possible 30 and 60 min after administration of the 10 micrograms dose of prostaglandin E2. At 30 min 42.9% of radioactive label present in the liver could be shown to be authentic prostaglandin E2. This corresponded to 0.64% of the original dose. At 60 min only 22.8% of the radioactive label found in the liver could be shown to be authentic prostaglandin E2, which corresponded to 0.46% of the administered dose. Similar results were found in the small intestine lumen, the small intestine wall and in the kidney. At 3 and 5h, none of the radioactivity found in these organs could be identified as authentic prostaglandin E2.

Duration of activity of the acid, methyl ester and amide of an orally active platelet aggregation inhibitory prostanoid in the rat

The prostanoid 3-oxa-4,5,6-trinor-3,7-inter-m-phenylene PGE1 (OI-PGE1) has been shown to be a more potent inhibitor of ADP-induced human platelet aggregation than PGE1. OI-PGE1 inhibits ex vivo ADP-induced platelet aggregation for 60 minutes after an oral dose of 20 mg/kg to rats. Present studies compare duration of ex vivo inhibition of ADP-induced platelet aggregation in the rat by OI-PGE1, its methyl ester and amide after administration by various routes. All oral (p.o.) and intraduodenal (i.d.) doses were 20 mg/kg and all intravenous (i.v.) doses were 1 mg/kg. OI-PGE1 and its methyl ester had the same duration of activity after i.v. (60 min.) and p.o. (60 min.) administration, however, the methyl ester, when administered i.d., had a longer duration of activity than the free acid i.d. (greater than 90 min. vs. 60 min.). OI-PGE1-amide had significantly longer duration than the acid or methyl ester after i.v. (greater than 120 min.), p.o. (greater than 240 min.) or i.d. (greater than 240 min.) administration. Present data suggest that in the rat (1) intestinal absorption of OI-PGE1-methyl ester is more efficient than it is for the free acid and (2) due to metabolic and/or distributional differences between OI-PGE1 and its amide, the amide has a much greater duration of activity.

Synthesis and metabolism of prostaglandins E2, F2alpha and D2 by the rat gastrointestinal tract. Stimulation by a hypertonic environment in vitro

Whole cell preparations of rat stomach corpus, jejunum, and colon were incubated and the released prostaglandin E2 (PGE2), PGF2alpha, PGD2, 15 keto-13,14 dihydro PGE2, and 15 keto-13, 14 dihydro PGF2alpha were measured by combined gas chromatography-mass spectrometry. All regions made PGD2 and possessed a high capacity for production 15 keto-13,14 dihydro derivatives of both PGE2 and PGF2alpha. Hypertonic sucrose solutions resulted in concentration-dependent increases in prostaglandin release, particularly of PGE2 and its metabolite. It is suggested that PG's may play a role in the local effects of luminal hyperosomolarity on digestive tract functions.

The effects of prostaglandins E1, E2, F1alpha and F2alpha on guinea-pig ileal and colonic peristalis

Prostaglandins (PGE1, E2, F1alpha and F2alpha) have been tested on the peristaltic reflex in isolated segments of guinea-pig ileum and colon using simultaneous recordings of fluid propulsion and longitudinal and circular muscle activity. Propulsion and circular muscle peristaltic activity were increased by serosally applied PGF compounds in the ileum and PGE or PGF compounds in the colon following initial contraction of the longitudinal muscle. This is consistent with a role for prostaglandins in peristalsis. Mucosally applied PGF compounds has no significant effect.

Influence of the route of administration of prostaglandin E1 on rat gastric secretion

Changes in gastric secretion induced by the subcutaneous, intraduodenal or intragastric administration of prostaglandin E 1 (PGE1) were evaluated in pylorus-ligated rats. Subcutaneous and intraduodenal injections produced a dose-related inhibition in both total acid and volume of gastric secretion. Dose-response curves for inhibition obtained by these routes were parallel, although PGE1 was more potent when given subcutaneously. Gastric administration produced a dose-related decrease in acid and an increase in volume. The slope of the dose-response curve for acid inhibition with this route was flatter than with subcutaneous or intraduodenal administrations. The present results suggest that PGE1 inhibits gastric secretion by the same mechanism of action when given subcutaneously or into the duodenum, while the effects observed after gastric administration are consequences of local actions. The difference in potency of PGE1 given subcutaneously and in the duodenum would seem to be due to differences in absorption from the site of administration and/or to a greater metabolism of PGE1 during its absorption from the intestines.

Prostaglandins: a report on early clinical studies

The prostaglandins are a unique group of pharmacologically active lipids which are widely distributed in mammalian tissues and body fluids. The chemistry of this family of compounds has been established in elegant detail. Research quantities of these highly active natural compounds were obtained by enzymatic bioconversion of essential fatty acids and now studies devoted to the elucidation of their physiological roles and their clinical potential are progressing rapidly. Fields of greatest current interest in clinical medicine include renal-cardiovascular research, induction of labour and therapeutic abortion, control of the reproductive cycle (including fertility control), bronchodilation, enhancement of nasal patency and antisecretory activity. Results available to date are too preliminary for many conclusions to be drawn, but are sufficiently encouraging to assure continued and expanding efforts in several fields.

Prostaglandin uptake and metabolism by the perfused rat liver

1. The prostaglandins are C20 unsaturated fatty acids which exhibit diverse physiological effects of short duration. We have investigated the speed of removal of PGE(1) and PGF(1alpha) from the circulating blood and their subsequent metabolism by the isolated perfused rat liver.2. Following either a single injection of radiolabelled PGE(1) or PGF(1alpha) into the hepatic artery or portal vein, or recirculation of prostaglandins through the liver for 2.5 h, the distribution of radioactivity within extracts of bile, blood and liver was determined. The nature of the radioactive products of meta-bolism was inferred by comparison of the distribution of radioactivity after injecting carbon and tritium labelled standards, and by thin-layer chromatography, gas-liquid chromatography, ultraviolet and bioassay analysis.3. A single injection of 1-(14)C PGE(1) indicated that the liver could efficiently remove 89-95% of circulating PGE(1) on a single passage. Biliary excretion was excluded as a major route for elimination of unchanged PGE(1), because only 0.3-0.8% of the injected radioactivity was detected in the bile. During recirculation of 1-(14)C PGE(1), 11-19% of the injected radioactivity was detected as exchanged (14)CO(2). The radioactivity detected within liver was identified with further fragments resulting from decarboxylation of PGE(1), which were incorporated into fatty acids and then phospholipids.4. Studies with 5,6-(3)H PGE(1), and comparison with the results obtained using 1-(14)C PGE(1), revealed a 30-fold increase in the percentage of radioactivity excreted into the bile, suggesting that biliary excretion may be a major route for elimination of compounds smaller than C20 prostaglandin. Evidence that the cyclopentane ring was intact was inferred by formation of a PGB compound on treatment with alkali; similar biliary excretion of 9-(3)H PGF(1alpha) also occurred. In addition, the increased radioactivity detected within the liver (37%) and blood (43%) after a single injection of 5,6-(3)H PGE(1) had the solvent partition and thin-layer chromatography properties of PGE(1), but were associated with a less polar compound smaller than the C20 parent structure.5. These results indicate rapid uptake of circulating prostaglandins by the rat liver. Decarboxylation of prostaglandins results in pharmacological inactivation. The products are excreted into the bile and venous effluent. These processes would curtail the duration of effects following prostaglandin injection.In addition, we infer from these results that any physiological action of these ubiquitous endogenous substances is likely to be localized within their tissue of origin.