Medical Functions of Hydrogen Sulfide.

Hydrogen sulfide (H(2)S) is a gasomediator synthesized from L- and D-cysteine in various tissues. It is involved in a number of physiological and pathological processes. H(2)S exhibits antiatherosclerotic, vasodilator, and proangiogenic properties, and protects the kidney and heart from damage following ischemia/reperfusion injury. H(2)S donors may be natural or synthetic, and may be used for the safe treatment of a wide range of diseases. This review article summarizes the current state of knowledge of the therapeutic function of H(2)S.

Thermosensitive chitosan-based hydrogel as a topical ocular drug delivery system of latanoprost for glaucoma treatment.

Ocular hypertension is a major risk factor for the development and progression of glaucoma. Frequent and long-term application of latanoprost often causes undesirable local side effects, which are a major cause of therapeutic failure due to loss of persistence in using this glaucoma medical therapy. In the present study, we developed a thermosensitive chitosan-based hydrogel as a topical eye drop formulation for the sustained release of latanoprost to control ocular hypertension. The developed formulation without preservatives may improve compliance and possibly even efficacy. The results of this study support its biocompatibility and sustained-release profile both in vitro and in vivo. After topical application of latanoprost-loaded hydrogel, triamcinolone acetonide-induced elevated intraocular pressure was significantly decreased within 7 days and remained at a normal level for the following 21 days in rabbit eyes. This newly developed chitosan-based hydrogel may provide a non-invasive alternative to traditional anti-glaucoma eye drops for glaucoma treatment.

Extended latanoprost release from commercial contact lenses: in vitro studies using corneal models.

In this study, we compared, for the first time, the release of a 432 kDa prostaglandin F2a analogue drug, Latanoprost, from commercially available contact lenses using in vitro models with corneal epithelial cells. Conventional polyHEMA-based and silicone hydrogel soft contact lenses were soaked in drug solution (131 µg = ml solution in phosphate buffered saline). The drug release from the contact lens material and its diffusion through three in vitro models was studied. The three in vitro models consisted of a polyethylene terephthalate (PET) membrane without corneal epithelial cells, a PET membrane with a monolayer of human corneal epithelial cells (HCEC), and a PET membrane with stratified HCEC. In the cell-based in vitro corneal epithelium models, a zero order release was obtained with the silicone hydrogel materials (linear for the duration of the experiment) whereby, after 48 hours, between 4 to 6 µg of latanoprost (an amount well within the range of the prescribed daily dose for glaucoma patients) was released. In the absence of cells, a significantly lower amount of drug, between 0.3 to 0.5 µg, was released, (p <0:001). The difference observed in release from the hydrogel lens materials in the presence and absence of cells emphasizes the importance of using an in vitro corneal model that is more representative of the physiological conditions in the eye to more adequately characterize ophthalmic drug delivery materials. Our results demonstrate how in vitro models with corneal epithelial cells may allow better prediction of in vivo release. It also highlights the potential of drug-soaked silicone hydrogel contact lens materials for drug delivery purposes.

A dual acting compound with latanoprost amide and nitric oxide releasing properties, shows ocular hypotensive effects in rabbits and dogs.

The IOP lowering effects of NCX 139, a new chemical entity comprising latanoprost amide and a NO-donating moiety, were compared to those of the respective des-nitro analog in in vitro assays and in rabbit and dog models of ocular hypertension. The NO donor, molsidomine as well as the prostamide bimatoprost (Lumigan(®)) and the prostaglandin agonist, latanoprost (Xalatan(®)) were also investigated for comparison. NCX 139 but not its des-nitro analog resulted in NO-mediated vascular relaxant effect in pre-contracted rabbit aortic rings (EC(50)=0.70±0.06 µM; E(max)=80.6±2.9%). Like bimatoprost (IC(50)=3.07±1.3 µM) or latanoprost (IC(50)=0.48±0.15 µM), NCX 139 displaced (3)H-PGF2α binding on recombinant human prostaglandin-F (FP) receptors with an estimated potency of 0.77±0.13 µM. In transient ocular hypertensive rabbits, bimatoprost and latanoprost were not effective while molsidomine elicited a dose-dependent reduction of IOP confirming the responsiveness of rabbits to NO but not to FP receptor agonists. NCX 139 tested at a therapeutically relevant dose, significantly lowered IOP while the des-nitro analog was not effective (0.03% NCX 139, Δ(max)=-12.8±2.0 mmHg). In glaucomatous dogs, 0.03% NCX 139 decreased IOP to a greater extent compared to an equimolar dose of the respective des-nitro derivative (Δ(max)=-4.6±1.0 and -2.7±1.3 mmHg, respectively for NCX 139 and its des-nitro analog). Albeit with low potency, NCX 139 also resulted effective in normotensive dogs while it did not reduce IOP in normotensive rabbits. NCX 139, a compound targeting two different and important mechanisms, is endowed with ocular hypotensive effects more evident in hypertensive conditions which may be of interest in the search of more effective treatments for hypertensive glaucoma.

Spectrofluorometry assays for oxidative stress and apoptosis, with cell viability on the same microplates: a multiparametric analysis and quality control.

Our objective was to compare neutral red (NR) tests performed separately and on the same microplates as hydroethidine, H2DCF-DA and YO-PRO®-1 assays, and to compare toxicity ratios calculated with the two methods. Human trabecular meshwork cells (HTM-3) were exposed to different concentrations of benzalkonium chloride (BAC), to PBS and to diluted solutions of latanoprost and bimatoprost. Microplate fluorescence spectrophotometry assays were performed: NR uptake for cell viability evaluation, hydroethidine and H2DCF-DA for reactive oxygen species (ROS), and YO-PRO®-1 for apoptosis. The four NR assays presented identical toxicological profiles and correlation coefficients between them were close to one. There was no difference between toxicity ratios for ROS assays calculated by the two methods, with high correlation coefficients. However, in the apoptosis assay, ratios calculated with the double staining technique were more accurate. Thus, it is possible and recommended to perform NR assays on the same microplates as the other assays. This double staining procedure could constitute a quality control procedure and would allow multiparametric analysis.

The prostaglandin transporter OATP2A1 is expressed in human ocular tissues and transports the antiglaucoma prostanoid latanoprost.

PURPOSE: Latanoprost, a prostaglandin F(2alpha) analogue, has become one of the most widely used medications for the treatment of glaucoma. The authors hypothesized that organic anion transporting polypeptides (OATPs) are responsible for the uptake of latanoprost into ocular tissues and, hence, that they contribute to the interindividual differences in drug concentrations and effects. METHODS: Expression of prostaglandin (PG) transporters (OATP2A1, OATP2B1) in human ocular tissues was determined using real-time RT-PCR and immunofluorescence. The inhibitory interactions between latanoprost and its active metabolite (the free acid) and the uptake of prototypical substrates (PGE(2) and bromosulfophthalein) were tested in stably transfected human embryonic kidney cells overexpressing either OATP2A1 or OATP2B1. These cells were also used to investigate whether latanoprost and latanoprost acid are substrates of OATP2A1 or OATP2B1. RESULTS: OATP2A1 and OATP2B1 mRNA expression was highest in the choroid/retinal pigment epithelium (RPE) complex and ciliary body. OATP2A1 protein expression was most prominent in the RPE and in epithelial and endothelial cell layers of anterior segment tissues, such as cornea, conjunctiva, iris, and ciliary body, whereas OATP2B1 protein was additionally expressed in trabecular meshwork, Schlemm canal, and choroidal vasculature. Latanoprost and latanoprost acid significantly inhibited both OATP2A1 and OATP2B1. Uptake experiments demonstrated that latanoprost acid is effectively transported by OATP2A1 (affinity constant [K(m)], 5.4 microM; maximum uptake rate [V(max)], 21.5 pmol/mg protein/min) and less effectively by OATP2B1. CONCLUSIONS: The results presented herein suggest that at least OATP2A1 plays a role in the intraocular disposition of the therapeutically used prostanoid latanoprost.

Expression of NADP+-dependent 15-hydroxyprostaglandin dehydrogenase mRNA in monkey ocular tissues and characterization of its recombinant enzyme.

Although prostaglandin (PG) F2a and its analogue latanoprost decrease the intraocular pressure in a variety of animals, their intraocular metabolism has not yet been clarified. Here, we isolated the cDNAs for the monkey homologues of NAD+- and NADP+-dependent types of 15-hydroxy PG dehydrogenase (PGDH) from lung and eye, respectively, and investigated the distribution of their mRNAs in the monkey eye. The cDNAs for the NAD+- and NADP+-dependent types of PGDH contained an open reading frame of 798 and 831 bp encoding 266 and 277 amino acid residues with calculated molecular masses of 28.9 and 30.5 kDa, respectively. The amino acid sequences of the monkey NAD+- and NADP+-dependent enzymes showed less than 20% identity to each other, and the former enzyme shows 98.5 and 86.8% identity, and the latter 94.9 and 85.2% identity, to the human and mouse enzymes, respectively. Reverse transcription-PCR analysis revealed that the mRNA for NADP+-dependent PGDH, but not that for NAD+-dependent PGDH, was highly expressed in monkey ocular tissues. In situ hybridization analysis demonstrated that the mRNA for NADP+-dependent PGDH was localized in the epithelial cells of the cornea. The recombinant NADP+-dependent PGDH catalyzed the dehydrogenation of the 15-hydroxyl group of PGF2a and the acid form of latanoprost in the presence of NADP+ as examined by HPLC. These results indicate that PGF2a and the acid form of latanoprost are degraded to their 15-keto metabolites by NADP+-dependent PGDH localized in the monkey eye.

Synthesis and biological evaluation of prostaglandin-F alkylphosphinic acid derivatives as bone anabolic agents for the treatment of osteoporosis.

A series of novel C(1) alkylphosphinic acid analogues of the prostaglandin-F family have been evaluated at the eight human prostaglandin receptors for potential use in the treatment of osteoporosis. Using molecular modeling as a tool for structure-based drug design, we have discovered that the phosphinic acid moiety (P(O)(OH)R) behaves as an isostere for the C(1) carboxylic acid in the human prostaglandin FP binding assay in vitro and possesses enhanced hFP receptor selectivity when compared to the parent carboxylic acid. When evaluated in vivo, the methyl phosphinic acid analogue (4b) produced a bone anabolic response in rats, returning bone mineral volume (BMV) [corrected], to intact levels in the distal femur in the ovariectomized rat (OVX) model. These results suggest that prostaglandins of this class may be useful agents in the treatment of diseases associated with bone loss.

An efficient synthesis of 3-hetero-13,14-dihydro prostaglandin F1alpha analogues.

[structure: see text]. A new class of 3-hetero-13,14-dihydro prostaglandin F(1)(alpha) analogues was synthesized from a common intermediate. The latter was constructed via a two-step, three-component process. The lower chain, containing the 15-(phenoxymethyl) group, was synthesized in enantiopure form using Jacobsen's (salen)Co-catalyzed kinetic resolution of a terminal epoxide with phenol.

[3H]AL-5848 ([3H]9beta-(+)-Fluprostenol). Carboxylic acid of travoprost (AL-6221), a novel FP prostaglandin to study the pharmacology and autoradiographic localization of the FP receptor.

AL-5848 (5Z,13E)-(9 S,11R,15S)-9,11,15-trihydroxy-5,13-prostadienoic acid) is the carboxylic acid of travoprost (AL-6221), a single (+)-isomer of (+/-)-fluprostenol, an FP-class prostaglandin agonist which lowers intraocular pressure. We have prepared a radioligand from this selective prostaglandin and demonstrated its utility for studying the pharmacology and autoradiographic location of the FP-receptor. Specific [3H]AL-5848 binding (84% of total) was linearly related to bovine corpus luteum tissue concentration and reached equilibrium within 275 min at 23 degrees C. Scatchard analysis of saturation isotherms indicated interaction of [3H]AL-5848 with a single class of high-affinity (dissociation constant, Kd, = 33.8+/-2.9 nM, n = 4) and saturable (Bmax = 37.3+/-3.0 pmol (g wet weight tissue)(-1)) FP receptor-binding sites in bovine corpus luteum. Specific [3H]AL-5848 binding was potently inhibited by the FP-receptor ligands 16-phenoxyPGF2alpha (inhibition constant Ki = 17.3 nM); cloprostenol (Ki = 56.8 nM); 17-phenyl PGF2alpha (Ki = 87.0 nM); AL-5848 (Ki = 52.1 nM); PGF2alpha (Ki = 195 nM); PHXA85 (Ki = 223 nM); (n = 3-11) but very weakly by PGD2, ZK118182, BW245C, PGE2, PGI2 and U-46619. The pharmacology of specific [3H]AL-5848 binding correlated well with the pharmacology of [3H]PGF2alpha binding in the bovine corpus luteum preparation (r = 0.98, n = 14, P<0.0001) and also with functional responses in Swiss 3T3 and rat vascular smooth muscle cells (A7r5) (r = 0.96) expressing FP receptors. Autoradiographic studies revealed high levels of specific FP-receptor binding with [3H]AL-5848 on granulosa cells in the bovine corpus luteum sections, and on longitudinal ciliary muscle, the ciliary process, the iris sphincter and the retina in eye sections from man. These studies show [3H]AL-5848 to be a high-affinity agonist radioligand capable of selectively labelling the FP prostaglandin receptor.

Formation of F2-isoprostanes during oxidation of human low-density lipoprotein and plasma by peroxynitrite.

F2-Isoprostanes are novel bioactive prostaglandin F2-like compounds produced by nonenzymatic free radical-catalyzed peroxidation of arachidonic acid. F2-Isoprostanes are initially formed in situ on phospholipids and subsequently released. Quantification of the F2-isoprostanes has been found to represent a valuable and reliable marker of lipid peroxidation. Oxidative modification of low-density lipoprotein (LDL) is a key process for the recognition of LDL by the scavenger receptors on macrophages. The oxidative mechanism responsible for the modification of LDL in vivo remains unclear, but an attractive candidate is the powerful oxidant peroxynitrite, which can be formed by reaction of nitric oxide and superoxide in the vessel wall. To further explore the potential role of peroxynitrite in the oxidative modification of plasma lipids, we investigated whether incubation of LDL and plasma with peroxynitrite or SIN-1, which decomposes to form nitric oxide and superoxide, catalyzes the formation of F2-isoprostanes. Incubation of LDL with peroxynitrite (0.125 to 1 mmol/L) or SIN-1 (0.5 and 1 mmol/L) induced a concentration-dependent increase in the formation of F2-isoprostanes, reaching a maximum of 5.5 +/- 2.05-fold (SEM) and 18.2 +/- 4.0-fold above control values, respectively. The increase of F2-isoprostanes induced by SIN-1 was essentially completely inhibited by superoxide dismutase. Incubation of plasma with peroxynitrite or SIN-1 yielded similar results. These results indicate that peroxynitrite can induce the formation of F2-isoprostanes in lipoproteins. Since F2-isoprostanes can exert potent biological activity such as vasoconstriction, they may contribute to the vascular pathobiology associated with atherosclerosis.

Corneal permeability to and ocular metabolism of phenyl substituted prostaglandin esters in vitro.

The corneal permeability to and metabolism of four phenyl substituted prostaglandin analogues have been studied in vitro. Porcine corneas were mounted in incubation chambers dividing each chamber into an epithelial and endothelial side compartment. The analogues were added to incubation medium on the epithelial side. The permeability coefficients of 17-phenyl-18,19,20-trinor-PGF2 alpha-1-isopropyl ester (PhDH100A), 15-keto-17-phenyl-18,19,20-trinor-PGF2 alpha-1-isopropyl ester (PhXA12), 13,14-dihydro-15-hydroxy (R, S)-17-phenyl-18,19,20-trinor-PGF2 alpha-1-isopropyl ester (PhXA34) and 13,14-dihydro-17-phenyl-18,19,20-trinor-PGF2 alpha-1-isopropyl ester (PhXA41) were determined to be in the range of 5.1-11.0 x 10(-6) cm x s-1. All analogues in the endothelial compartment had been hydrolysed to corresponding acids but any other metabolism of PhDH100A, PhXA34 and PhXA41 after 4 h of incubation was minimal. In contrast, PhXA12 free acid was extensively metabolised to the 13,14-dihydro metabolite. To investigate whether the porcine ocular tissues contain 15-hyroxyprostaglandin dehydrogenase (15-PGDH) activity, prostaglandin F2 alpha (PGF2 alpha) and PhDH100A were used as substrates. PGF2 alpha and the phenyl-substituted analogues were also tested for their capacity as substrate to 15-PGDH in general. The 15-PGDH activity was low in all ocular tissues. The capacity of various ocular tissues or purified 15-PGDH to metabolise PhDH100A was lower than with PGF2 alpha as substrate. PhXA34 and PhXA41 were found not to be metabolised by 15-PGDH. Thus, the phenyl substituted PG esters penetrated the cornea and in the process were hydrolysed to their corresponding acids. No appreciable further metabolism occurred except for PhXA12 which was reduced by delta 13-reductase.

Prostaglandin photoaffinity probes: synthesis and biological activity of azide-substituted 16-phenoxy- and 17-phenyl-PGF2 alpha prostaglandins.

The development of a prostaglandin PGF2 alpha photoaffinity probe led to the synthesis and biological evaluation of azide-substituted 17-phenyl-18,19,20-trinorprostaglandin F2 alpha and 16-phenoxy-17,18,19,20-tetranorprostaglandin F2 alpha derivatives. Two approaches for the preparation of iodinated versions of these prostaglandins were evaluated: (1) iodination of a phenyl azide bearing an activating hydroxyl group and (2) iodination of an aniline precursor to the phenyl azide group and subsequent conversion of the aniline to the phenyl azide. In the first approach, 17-(4-azido-2-hydroxyphenyl)-18,19,20-trinorprostaglandin F2 alpha, 16-(5-azido-3-hydroxyphenoxy)-17,18,19,20-tetranorprostaglandin F2 alpha, and 16-(4-azido-2-hydroxyphenoxy)-17,18,19,20-tetranorprostaglandin F2 alpha were prepared by using the Corey synthesis, but were biologically inactive presumably as a result of the hydrophilic phenolic hydroxyl group. In the second approach, the iodination of a 17-(4-aminophenyl)-18,19,20-trinorprostaglandin F2 alpha derivative delivered 17-(4-azido-3-iodophenyl)-18,19,20-trinorprostaglandin F2 alpha, which exhibited competitive binding with natural [3H]PGF2 alpha to ovine luteal cells and to plasma membranes of bovine corpora lutea. [125I]-17-(4-Azido-3-iodophenyl)-18,19,20-trinorprostaglandin F2 alpha was utilized in a preliminary photoaffinity cross-linking experiment.

Interaction of hCG and Lutalyse on steroidogenesis of bovine luteal cells.

This study was designed to examine the ability of in vivo administration of human chorionic gonadotropin (hCG, 4000 IU) to alter the effects of Lutalyse (PGF2 alpha, 10 mg) in the cow. hCG significantly increased plasma progesterone concentration in midcycle cows (P less than 0.01), but these elevated levels were not maintained in the presence of Lutalyse (P less than 0.05). Responsiveness of luteal cells in vitro to luteinizing hormone (LH) (100 ng/ml), prostaglandin F2 alpha (PGF2 alpha) (1 microgram/ml), dibutyryl cyclic AMP (dbcAMP) (10 mM) and PGF2 alpha (1 microgram/ml) + dbcAMP (10 mM) during a 2 h incubation was significantly reduced following in vivo treatment with Lutalyse when compared to in vivo untreated animals. In conclusion, the luteotropic effects of hCG were incapable of preventing Lutalyse-induced regression of the corpus luteum, and treatment of animals with hCG prior to Lutalyse administration could not prevent the significant decrease in responsiveness of luteal cells in vitro.

Luteolytic potency of 16-phenoxy-derivatives of prostaglandin F2 alpha.

The binding of 16-phenoxy derivatives of prostaglandin (PG) F2 alpha to rat luteal membranes, and also their abortifacient potency in pregnant rats, have been studied. Competitive binding studies with various PG-analogues were performed in ovaries of juvenile rats pretreated with PMSG and HCG, and in parallel studies the abortifacient potency of these substances was tested in pregnant rats. It was observed that this class of derivatives bound to the PGF2 alpha receptor as well as, or even better than the parent compound PGF2 alpha. Modifications in the carboxyl group at C-1 yielded derivatives with a higher affinity for the receptor, in decreasing order of effectiveness as follows: -COOR greater than COOH greater than OH. The data obtained from the binding studies also compared well with data on the abortifacient potency in pregnant rats. It is concluded that the addition of a phenoxy group to either the lower or upper side chain of PGF2 alpha may augment the binding to the receptor as well as the biological responses induced by the post receptor effect.

The ocular pharmacokinetics of eicosanoids and their derivatives. 1. Comparison of ocular eicosanoid penetration and distribution following the topical application of PGF2 alpha, PGF2 alpha-1-methyl ester, and PGF2 alpha-1-isopropyl ester.

These experiments were undertaken to determine whether the increased ocular hypotensive potency of topically applied prostaglandin (PG) PGF2 alpha esters, as compared with that of PGF2 alpha free acid, can be accounted for by increased penetration of the eicosanoid moiety of the esterified PG into the eye. One hour after the topical application of [3H]PGF2 alpha-1-methyl ester (ME) in peanut oil, the 3H activities in the cornea, aqueous humor, and ciliary body of the rabbit eye were 32-, 22-, and 8-fold higher, respectively, than they were following the topical application of [3H]PGF2 alpha free acid. 3H activity during the first 3 hr declined rapidly in the cornea and more slowly in the aqueous humor, but remained essentially constant in the ciliary body for up to 6 hr, declining rapidly only between 6- and 24 hr. 3H activity in eyes that received [3H]PGF2 alpha ME was also several-fold higher in the anterior sclera and iris than in eyes that were treated with [3H]PGF2 alpha free acid, but this difference was much smaller in the conjunctiva. At 1 hr, most of the 3H activity in the aqueous humor was associated with PGF2 alpha, as determined by chromatography, but at 2- and 3 hr other peaks, presumably reflecting metabolites of PGF2 alpha, became apparent. The penetration and intraocular distribution of 3H activity was similar when [3H]PGF2 alpha ME was applied to the eye in normal saline rather than in peanut oil or when the isopropyl rather than the methyl ester of PGF2 alpha was used. These studies indicate that esterification of the carboxyl group of PGF2 alpha greatly enhances the penetration of the PGF2 alpha moiety into the eye and suggests that effective de-esterification of the PGF2 alpha ester occurs in the cornea, resulting in the delivery of PGF2 alpha free acid into the aqueous humor. It is concluded that topically applied PG esters act as pro-drugs and that the increased ocular penetration of these esters may account for the previously reported increase in their ocular hypotensive potency as compared to that of PG free acid or salts.

Inflammatory bowel disease: the in vitro effect of sulphasalazine and other agents on prostaglandin synthesis by human rectal mucosa.

1. Prostaglandin (PG) E2 and F2 alpha synthesis in vitro by human rectal mucosa was significantly greater in patients with Inflammatory Bowel Disease (IBD) than in controls. 2. The addition of 250 microM sulphasalazine (SASP) significantly increased synthesis by rectal mucosa from patients with IBD, (ulcerative colitis and Crohn's disease) and controls after 1 h of incubation in Krebs' solution at 37 degrees C. 3. Flurbiprofen, indomethacin, sodium salicylate and 5-aminosalicylic acid decreased PGE2 and F2 alpha synthesis. 4. Sodium carbenoxolone decreased PGF2 alpha synthesis but had no effect on PGE2. Disodium cromoglycate, sulphapyridine, salicylazosulphadimidine and methylsulphasalazine had no effect on PG synthesis. 5. The data show marked variations in effect on PG synthesis in vitro of substances that have been investigated clinically for their actions on IBD.

Binding of a novel prostaglandin F 2 alpha-derivative (ZK 71 677) to pseudopregnant rat ovaries.

Prostaglandin (PG)F 2 alpha is believed to regulate the life span of the corpus luteum and this physiologically induced change could be related to the binding properties of PGF 2 alpha in the corpus luteum. Corpora lutea formation was therefore stimulated in juvenile rats with PMSG and HCG. In membrane particles obtained after differential centrifugation, radioligand binding studies were performed with PGF 2 alpha and a novel PGF 2 alpha-derivative (ZK 71 677) on day 7 after HCG administration. Evaluation of the binding parameters revealed a competitive interaction between PGF 2 alpha and ZK 71 677 for the PGF 2 alpha-receptor molecule. When other prostaglandin analogues were used to establish biological potency, the data obtained from receptor binding analysis compared well with the abortifacient potency of these compounds in pregnant rats. The results provide further evidence for the nature and specificity of the PGF 2 alpha-receptor molecule.

Early pregnancy interruption with a single PGF2 alpha 15-methyl-analogue vaginal suppository.

Pregnancy was interrupted successfully in 70% of 20 early pregnancies, 35-49 days in duration as dated from the first day of the last menstrual period, by administration of a single intravaginal suppository containing 3 mg of (15S)-15-methyl prostaglandin F2 alpha (PGF2 alpha). No correlation could be demonstrated with baseline beta-subunit human chorionic gonadotropin or serum levels of prostaglandin obtained within ten hours of treatment. Continued pregnancy was documented in 10%. The rate of failures and the frequency of gastrointestinal side effects were deemed too great to warrant adopting this agent for clinical usage.