Novel prostaglandin dehydrogenase in rat skin.

Present evidence suggests that skin is an important organ of prostaglandin metabolism. To clarify its role, the basic kinetics of 15-hydroxyprostaglandin dehydrogenase (PGDH) from rat skin were investigated with either NAD+ of NADP+ as co-substrate. Prostaglandin F2 alpha (PGF2 alpha) and prostaglandin E2 (PGE2) were used as substrates and preliminary studies were made of the inhibitory effects of the reduced co-substrates NADH and NADPH. A radiochemical assay was used in which [3H]PGF2 alpha or [14C]PGE2 were incubated with high-speed supernatant of rat skin homogenates. The substrate and products were then extracted by solvent partition, separated by t.l.c. and quantified by liquid-scintillation counting. At linear reaction rates and at an NAD+ concentration of 10 mM the mean apparent Km for PGF2 alpha was 24 microM with a mean apparent Vmax. of 9.8 nmol/s per litre of reaction mixture. For PGE2 the mean apparent Km was 8 microM, with a mean apparent Vmax, of 2.7 nmol/s per litre of reaction mixture. With NADP+ as a co-substrate at a concentration of 5 mM a mean apparent Km of 23 microM was obtained for PGF2 alpha with a mean apparent Vmax. of 5.2 nmol/s per litre. For PGE2 values of 7.5 microM and 3.0 nmol/s per litre were obtained respectively. These results show that skin contains NAD+- and NADP+-dependent PGDH. An important finding was that the NADP+-linked enzyme gave Km values for PGE2 that were considerably lower than those reported for NADP+-linked PGDH from other tissues. Furthermore, preliminary inhibition studies with the NAD+-linked PGDH system indicate that this enzyme is not only inhibited by NADH, but also by NADPH, a property not previously reported for NAD+-linked PGDH derived from other tissues.     

Content and formation of prostaglandins and distribution of prostaglandin-related enzyme activities in the rat ocular system

The steady-state levels of prostaglandin D2, E2 and F2 alpha in the rat eye were 0.5, 0.1 and 1.0 ng/g, respectively, which increased differently among the prostaglandins after a 40-min incubation of the homogenate at 37 degrees C (to 23, 12 and 14 ng/g, respectively). When the eye was dissected into anterior uveal, scleral, and retinal complexes, prostaglandin D2 was formed in the highest degree in all the complexes, whereas prostaglandin E2 and F2 alpha formation was specific to given ocular regions. Three prostaglandin synthetase activities with similar Km values (20-40 microM) were found in the 10,000 X g supernatant of these tissues, i.e., GSH-independent and soluble D, GSH-dependent and membrane-bound E, and soluble F synthetase activities. These enzyme activities correlated well with the prostaglandin formation in each tissue. D synthetase activity being highest in all the tissues (11-25 nmol/min per g). Three types of prostaglandin-catabolizing enzyme activities were detected in the 100,000 X g supernatant of the tissues, i.e., type II 15-hydroxy dehydrogenase (Km = 10-30 microM), 9-keto (500 microM) and 11-keto reductase (2.5 mM). The activity of the dehydrogenase was low even in the retina, the tissue with the highest levels (0.51, 0.35 and 0.15 nmol/min per g for prostaglandin E2, F2 alpha and D2, respectively).     

Isolation and properties of lung 15-hydroxyprostaglandin dehydrogenase from pregnant rabbits

A NAD-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) was purified to a specific activity of over 25,000 nmol NADH formed/min/mg protein with 50 microM prostaglandin E1 as substrate from the lungs of 28-day-old pregnant rabbits. This represented a 2600-fold purification of the enzyme with a recovery of 6% of the starting enzyme activity. The lungs of pregnant rabbits were used because a 42- to 55-fold induction of the PGDH activity was observed after 20 days of gestation. The enzyme was purified by CM-cellulose, DEAE-cellulose, Sephadex G-75, octylamino-agarose, and hydroxylapatite chromatography. The enzyme could not be purified by affinity chromatography using NAD- or blue dextran-bound resins. The purified enzyme was specific for NAD and had a subunit molecular weight of 29,000. The optimal pH range for the oxidation of prostaglandin E1 was between 10.0 and 10.4 using 3-(cyclohexylamino)propanesulfonic acid as the buffer. The Km and Vmax values for prostaglandin E1 were 33 microM and 40,260 nmol/min/mg protein, respectively, while the Km and Vmax values for prostaglandin E2 were 59 microM and 43,319 nmol/min/mg protein, respectively. The Km for prostaglandin F2 alpha was four times the value for prostaglandin E1. The PGDH activity was inhibited by p-chloromercuriphenylsulfonic acid but the enzymatic activity was restored by the addition of dithiothreitol. n-Ethylmaleimide also produced a rapid decline in enzymatic activity but when NAD was included in the incubation system, no inhibition was observed.     

9-Hydroxyprostaglandin dehydrogenase in rat kidney cortex converts prostaglandin I2 into 15-keto-13,14-dihydro 6-ketoprostaglandin E1

15-Keto-13,14-dihydro 6-ketoprostaglandin E1 was positively identified by gas chromatography-mass spectrometry with negative-ion chemical ionisation detection from samples of rat kidney high-speed supernatant incubated with prostaglandin I2 in the presence of NAD+. A decreased formation of this product was observed when NAD+ was substituted with NADP+ and none was observed in the absence of nucleotide or substrate prostaglandin I2. Experiments with [9 beta-3H]prostaglandin I2 showed a time- and concentration-dependent loss of tritium which appeared as tritiated water, typical of reaction of [9 beta-3H]prostaglandin substrates with the enzyme, 9-hydroxyprostaglandin dehydrogenase. Time-course measurements of the appearance of tritiated water showed similar rates with 6-keto[9 beta-3H]prostaglandin F1 alpha and 15-keto-13,14-dihydro 6-keto[9 beta-3H]prostaglandin F1 alpha as substrates. These experiments suggest that the transformation of prostaglandin I2 and 6-ketoprostaglandin F1 alpha into the 15-keto-13,14-dihydro 6-ketoprostaglandin E1 catabolite occurs in this in vitro preparation via the corresponding 15-keto-13,14-dihydro catabolite of 6-ketoprostaglandin F1 alpha.     

Metabolism of prostaglandins, prostaglandin analogs and thromboxane B2 by lung and liver microsomes from pregnant rabbits

Liver microsomes from pregnant rabbits converted prostaglandins F2 alpha, E1, and E2 to their 20-hydroxy metabolites along with smaller amounts of the corresponding 19-hydroxy compounds. Prostaglandins E1 and E2 were also reduced to prostaglandins F1 alpha and F2 alpha, respectively, and prostaglandin E1 was isomerized to 8-isoprostaglandin E1. The above products were also identified after incubation of prostaglandins with liver microsomes from non-pregnant rabbits. In this case, the yield of 20-hydroxy metabolites was much lower. Thromboxane B2 and a number of prostaglandin F2 alpha analogs were also hydroxylated by lung and liver microsomes from pregnant rabbits. The relative rates of hydroxylation by lung microsomes were: prostaglandin E2 approximately prostaglandin F2 alpha approximately 16,16-dimethylprostaglandin F2 alpha approximately 13,14-didehydroprostaglandin F2 alpha greater than thromboxane B2 greater than 15-methylprostaglandin F2 alpha approximately 17-phenyl-18,19,-20-trinorprostaglandin F2 alpha approximately ent-13,14-didehydro-15-epiprostaglandin F2 alpha. Similar results were obtained with liver microsomes except that thromboxane B2 was a relatively poorer substrate for hydroxylation.     

Oxidation of 15-hydroxyeicosatetraenoic acid and other hydroxy fatty acids by lung prostaglandin dehydrogenase

The oxidation of the 15-hydroxy group of prostaglandins of the A, E, and F series by the NAD+-dependent prostaglandin dehydrogenase (PGDH) has been well documented. In addition to prostaglandins, we have observed that the purified lung PGDH also will oxidize 15-HETE to a novel metabolite that was isolated by reverse-phase HPLC and identified by gas chromatography-mass spectrometry as the 15-keto-5,8,11-cis-13-trans-eicosatetraenoic acid (15-KETE). The Km for 15-HETE was 16 microM, which was 2.5 times lower than the value obtained for PGE1. In addition to 15-HETE, 5,15-diHETE and 8,15-diHETE also were substrates for the lung PGDH with Km values of 138 and 178 microM, respectively. Other hydroxy derivatives of eicosatetraenoic acid that did not have a hydroxy group at carbon atom 15 did not support the PGDH-mediated reduction of NAD+. In addition to the 15-hydroxy derivatives of eicosatetraenoic acid, 12-HHT also was a substrate for the lung enzyme with a Km of 12 microM. These data indicate that omega 6-hydroxy fatty acids, in addition to prostaglandins, are also substrates of the lung NAD+-dependent PGDH and that the enzyme does not require the cyclopentane ring of prostaglandins.     

Inhibition of pulmonary prostaglandin metabolism by exposure of animals to oxygen or nitrogen dioxide.

The effects of exposure of animals to 100% O2 and NO2 on the rate of prostaglandin metabolism by lung and kidney were studied in vitro. Exposure of guinea pigs to 100% O2 for 48 h inhibited the metabolism of prostaglandin F2 alpha by both NAD+- and NADP+-dependent prostaglandin dehydrogenase in lung, but had no effect on the metabolism in kidney. Succinate dehydrogenase, but not glucose 6-phosphate dehydrogenase, in guinea-pig lung was inhibited by exposure to 100% O2. Exposure to 46 p.p.m. but not 16 or 29 p.p.m. NO2 for 6 h inhibited guinea-pig lung prostaglandin dehydrogenase in vitro. The inhibition of pulmonary prostaglandin dehydrogenase by exposure to 100% O2 or to 49 p.p.m. NO2 was dependent on the duration of exposure, but returned to control values within 7 days after cessation of the exposure. The pulmonary transport system responsible for removing circulating prostaglandins from the blood was not affected by exposure to 100% O2 as measured by using the isolated perfused lung. Kinetic analysis of the inhibition of pulmonary prostaglandin dehydrogenase activity in guinea pig exposed to 100% O2 showed non-competitive inhibition with respect to both prostaglandin F2 alpha and NAD+, which suggests destruction or inactivation of the enzyme. Pulmonary prostaglandin dehydrogenase appears to be inhibited by exposure to oxidant gases, which may lead to elevated prostaglandin concentrations in the lungs or in the systemic circulation.     

Delta 5-3 beta-hydroxysteroid dehydrogenase-isomerase activity in canine pancreas

Activity of delta 5-3 beta-hydroxysteroid dehydrogenase coupled with steroid-delta 5-4-isomerase was demonstrated for the first time in the pancreas. The enzyme complex was assayed by measuring the conversion of pregnenolone to progesterone as well as of dehydroepiandrosterone to androstenedione and found to be localized primarily in the mitochondrial fraction of dog pancreas homogenates. The delta 5-3 beta-hydroxysteroid dehydrogenase used either NAD+ or NADP+ as co-substrates, although maximal activity was observed with NAD+. In phosphate buffer, pH 7.0 and 37 degrees C, the apparent Km values of the dehydrogenase were 6.54 +/- 0.7 microM for pregnenolone and 9.61 +/- 0.8 microM for NAD+. The apparent Vmax was determined as 0.82 +/- 0.02 nmol min-1 mg-1. Under the same conditions the Km values for dehydroepiandrosterone and NAD+ were 3.3 +/- 0.2 microM and 9.63 +/- 1.6 microM, respectively, and the apparent Vmax was 0.62 +/- 0.01 nmol min-1 mg-1.     

Purification and characterization of a novel form of 20 alpha-hydroxysteroid dehydrogenase from Clostridium scindens.

We have purified a steroid-inducible 20 alpha-hydroxysteroid dehydrogenase from Clostridium scindens to apparent homogeneity. The final enzyme preparation was purified 252-fold, with a recovery of 14%. Denaturing and nondenaturing polyacrylamide gradient gel electrophoresis showed that the native enzyme (Mr, 162,000) was a tetramer composed of subunits with a molecular weight of 40,000. The isoelectric point was approximately pH 6.1. The purified enzyme was highly specific for adrenocorticosteroid substrates possessing 17 alpha, 21-dihydroxy groups. The purified enzyme had high specific activity for the reduction of cortisone (Vmax, 280 nmol/min per mg of protein; Km, 22 microM) but was less reactive with cortisol (Vmax, 120 nmol/min per mg of protein; Km, 32 microM) at pH 6.3. The apparent Km for NADH was 8.1 microM with cortisone (50 microM) as the cosubstrate. Substrate inhibition was observed with concentrations of NADH greater than 0.1 mM. The purified enzyme also catalyzed the oxidation of 20 alpha-dihydrocortisol (Vmax, 200 nmol/min per mg of protein; Km, 41 microM) at pH 7.9. The apparent Km for NAD+ was 526 microM. The initial reaction velocities with NADPH were less than 50% of those with NADH. The amino-terminal sequence was determined to be Ala-Val-Lys-Val-Ala-Ile-Asn-Gly-Phe-Gly-Arg. These results indicate that this enzyme is a novel form of 20 alpha-hydroxysteroid dehydrogenase.     

Prostaglandin 15-hydroxy dehydrogenase from human placenta.

The enzyme system prostaglandin 15-hydroxy dehydrogenase, which catalyzes the inactivation of all biologically active prostaglandins, has been purified 1270-fold from human placenta. Kinetic studies on the enzyme have provided information on a well-organized control mechanism to avoid prostaglandin accumulation and for a fast prostaglandin degradation. 15-Ketoprostaglandin E2 and 13,14-dihydro-15-ketoprostaglandin E2 inhibit prostaglandin 15-hydroxy dehydrogenase non-competitively with respect to prostaglandin E2. The rate equation of enzyme reaction for two substrates was used for determination of the equilibrium constant and Michaelis constants of the enzyme. The following kinetic constants for prostaglandin 15-hydroxy dehydrogenase have been found. The equilibrium constant with repect to prostaglandin E2 is 18 muM, the Michaelis constant Km for prostaglandin E2 is 1 muM for NAD+ 44muM. The inhibition constants for 15-ketoprostaglandin E2 ar Ki(slope) = 70 muM, Ki(intercept) = 150 muM, and for 13,14-dihydro-15-ketoprostaglandin E2 Ki(slope) = 80 muM, and Ki(intercept) = 150 muM. The maximal velocity for the forward reaction is V1 = 0.45 mumol/min. These kinetic data exclude a random or ping-pong mechanism, and also a Theorell-Chance type as suggested by Braithwaite and Jarabak. We propose, therefore, a sequential ordered mechanism. The isoelectric point for prostaglandin 15-hydroxy dehydrogenase is at pH 5.35, judged by isoelectric focusing.     

Changes of Enzymes Involved in Prostaglandin Metabolism and Prostaglandin Binding Proteins in Rat Brain During Development and Aging

In the developing rat brain, the enzymatic formation of prostaglandin D2 from prostaglandin H2 increased 60-fold from day 12 of gestation to birth. The activity still rose gradually to the highest level (90 nmol/min/g wet tissue) at day 7 after birth. The activities of prostaglandin E2 and F2 alpha synthetases in rat brain were highest at gestational age 19 days (30 nmol/min/g wet tissue), respectively. The specific activity of NADP-dependent 15-hydroxy-prostaglandin D2 dehydrogenase in rat brain was highest at the earliest gestational age we examined (day 12 of gestation). The specific bindings of prostaglandin D2 and E2 to the crude mitochondrial fraction of rat brain were observed from day 16 of gestation and increased to day 7 after birth. Although the activities of the enzymes responsible for prostaglandin metabolism were unchanged postmaturationally, the maximal concentrations of the binding sites on the synaptic membrane for both prostaglandins D2 and E2 decreased with constant affinity to less than one-sixth with age from 1 week to 24 months after birth. These results indicate that prostaglandins may play important roles during maturation and aging in rat brain.     

Enzymatic synthesis of (15s)-[15-3h]prostaglandins and their use in the development of a simple and sensitive assay for 15-hydroxyprostaglandin dehydrogenase.

The stereospecificity of swine renal NAD+-dependent 15-hydroxyprostaglandin dehydrogenase has been determined. It was found that the enzyme is a B-side specific dehydrogenase. (15S)-[15-3H]Prostaglandins were synthesized by stereospecific transfer of the tritium label of D-[1-3H]galactose to prostaglandins by coupling 15-hydroxyprostaglandin dehydrogenase with beta-D-galactose dehydrogenase, an enzyme of the same stereospecificity. A simple and sensitive assay for 15-hydroxyprostaglandin dehydrogenase was developed based on the stereospecific transfer of the tritium label of tritiated prostaglandins to glutamate by coupling 15-hydroxyprostaglandin dehydrogenase with glutamate dehydrogenase. The amount of prostaglandin oxidized is determined by the radioactivity of labeled glutamate present in the supernatant after charcoal precipitation of labeled prostaglandin. Concurrent assays with the present tritium release method and the thin-layer chromatography method indicated excellent correlation. The assay was employed to study some of the properties of swine renal 15-hydroxyprostaglandin dehydrogenase in crude extract and the distribution of enzyme activity in various tissues of rat. Enzyme activity was linear for the first 10 min studied and was nonlinear with increasing amounts of crude enzyme, indicating the possible presence of endogenous inhibitor(s). Apparent Km's for PGE2, PGF2alpha, and PGA2 were found to be 2.5, 12.5, and 3.9 muM, respectively. The distribution pattern indicated high levels of enzyme activity in gastrointestinal tract, lung, kidney, and spleen. The assay method may prove to be valuable for studying enzyme turnover and enzyme regulation by hormonal and pharmacological agents.     

On the metabolism of prostaglandins by human gastric fundus mucosa.

1.Specific radioimmunoassays for the prostaglandins E2, F2alpha and A2 and the metabolites 13,14-dihydro-15-keto-prostaglandin E2, 15-keto-prostaglandin F2alpha and 13,14-dihydro-15-keto-prostaglandin F2alpha were used to study the metabolism of prostaglandins by gastroscopically obtained small biopsy specimens of human gastric fundus mucosa. 2.Three prostaglandin-metabolizing enzymes were found in the 100 000 X g supernatant of human gastric fundus mucosa, 15-hydroxy-prostaglandin-dehydrogenase, delta13-reductase and delta9-reductase. The specific activity was highest for 15-hydroxy-prostaglandin-dehydrogenase and lowest for delta9-reductase. 3.Formation of prostaglandin A2 (or B2) was not observed under the same conditions. 4.None of the three enzyme activities detected in the 100 000 X g supernatant was found in the 10 000 X g and 100 000 X g pellets of human gastric fundus mucosa. 5.The results indicate that high speed supernatant derived from human gastric mucosa can rapidly metabolize prostaglandin E2 and prostaglandin F2alpha to the 15-keto and 13,14-dihydro-15-keto-derivatives. Furthermore, prostaglandin E2 can be converted to prostaglandin F2alpha, the biological activity of which, on gastric functions, differs from that of prostaglandin E2.     

Characterization of an endogenous inhibitor of lung 15-hydroxyprostaglandin dehydrogenase

An endogenous inhibitor of the NAD+-dependent 15-hydroxyprostaglandin dehydrogenase was isolated from the 105,000 X g supernatant fraction of lungs of pregnant rabbits following DEAE chromatography. The material was heat stable and was resistant to pronase treatment. The inhibitor contained a mixture of saturated and mono-unsaturated fatty acids and cholesterol with palmitate and oleate representing the major fatty acids in the inhibitory factor. The factor inhibited prostaglandin dehydrogenase activity but had only minor effects on the activity of NAD+-dependent alcohol and lactate dehydrogenases or the NADP+-dependent isocitrate dehydrogenase. In an attempt to develop a greater understanding of the inhibitory action of fatty acids on prostaglandin dehydrogenase activity, a variety of standard fatty acids were examined for their ability to decrease enzymic activity. Oleate and palmitate inhibited enzymic activity by 70% at 10 microM, whereas arachidonate and myristate were only 30% inhibitory at this concentration. A comparison among the 18-carbon-containing fatty acids demonstrated that oleate was more potent than linoleate and linolenate in inhibiting prostaglandin dehydrogenase activity. The coenzyme A derivatives of oleate, linoleate and linolenate were less inhibitory than the free fatty acids.     

Studies on 15-hydroxyprostaglandin dehydrogenase with various prostaglandin analogues.

The NAD+-linked 15-hydroxyprostaglandin dehydrogenase (PGDH) of swine lung was purified to a high specific activity by affinity chromatographies on prostaglandin (PG)-and NAD+-Sepharose. The affinities of the enzyme for various synthetic analogues of PGA, E, F, and I and their inhibitory effects on the enzymatic reaction were examined. The modification of the alkyl side chain of PG, particularly at C-15 or C-16, reduced the affinity of the enzyme for these PG analogues. Furthermore, 14-methyl-13,14-dihydro-PGE1 and 16-cyclopentyl-omega-trinor-15-epi-PGE2 were potent inhibitors of PGDH.     

Experimental hyperthyroidism in rats suppresses in vitro prostaglandin metabolism in lung and kidney.

Metabolism of prostaglandin (PG) F2alpha and PGE2 was depressed 40--62% in 100,000 g cytoplasmic supernatants of lungs and kidneys prepared from rats made hyperthyroid by 18 daily L(-) thyroxine injections (200microgram, s--c). These hyperthyroid rats had elevated serum thyroxine levels, cardiac hypertrophy and thyroid atrophy. There were no differences in soluble protein concentrations, NAD+ utilisation by endogenous enzymes and substrates, or in the NAD+ dependence of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) between the supernatants prepared from hyperthyroid rats and saline-injected controls. Thyroxine did not inhibit PG metabolism in vitro up to 260 micrometer. These results suggest that thyroxine specifically decreases intracellular levels of PG-metabolising enzymes, especially of the rate-limiting 15-PGDH. Metabolism of PGF2alpha and PGE2 by 15-PGDH was faster in smaller rats and declined with increasing animal weight. These studies imply that some of the clinical features of hyperthyroidism in man might be caused by deficiencies in PG metabolism.     

Prostaglandin biosynthesis and catabolism in the developing fetal sheep lung.

The prostaglandin biosynthetic and catabolic capacity of homogenates of lungs from fetal sheep of various gestational ages was measured. Prostaglandin biosynthesis was assayed by the deuterium-isotope dilution technique making use of mass fragmentography whereas prostaglandin catabolism was measured by the radioisotope-dilution method described previous (Pace-Asciak, C.R. and Rangaraj, G. (1976) J. Biol. Chem. 251, 3381-3385). Homogenates of lungs from fetuses of all ages tested (40 days to term) formed both prostaglandins E2 and F2alpha; although prostaglandin F2alpha was formed to a greater extent than prostaglandin E2 by the 40 days lung, prostaglandin E2 increased with increasing age until at term the ratio of both prostaglandins approached unity. Total prostaglandin biosynthesis (E2 + F2alpha) rose gradually with age (approx. 3 fold increase between 40 days and term). Prostaglandin F2alpha catabolism occurred mainly by the prostaglandin 15-hydroxy dehydrogenase pathway; this activity was detectable even at 40 days and remained unchanged up to 80 days. Prostaglandin catabolic activity rose sharply at 90 days (approx. 3 fold) with a maximum around 110 days (approx. 4 fold) decreasing back to 40 day levels by term (143 days). The increasing prostaglandin catabolic activity around 90-100 days in this species is discussed in relation to the hemodynamic changes in the lungs starting around this age and the appearance of surfactant. Prostaglandin catabolism might play an important role in the developing organ controlling steady state concentrations of prostaglandins during certain periods of organogenesis.     

Metabolism of prostacyclin in blood vessels.

The activity of 15-hydroxyprostaglandin dehydrogenase has been shown to be high in both mesenteric arteries and veins; the present study suggests that it may be responsible for the inactivation of prostacyclin (PGI2). The cytoplasmic fractions of bovine mesenteric arteries and veins were incubated with radiolabeled PGI2 in the presence of NAD+ or NADP+. The substrate was rapidly converted to a product, which was isolated and identified as 6,15-diketo prostaglandin F1alpha, (6,15-diketo-PGF1alpha) by thin layer chromatography and gas chromatography-mass spectrometry. The initial reaction rate began to level off after less than 1 min of incubation at 37 degrees C. When radiolabeled 6-keto-PGF1alpha, the stable hydrolysis product of PGI2, was used as substrate under the same conditions, 97% was recovered unmetabolized after 2 min of incubation. Catabolism of PGI2 may be a major determinant of its levels in blood vessels and, therefore, may be of crucial importance to regulating the action of PGI2. Further, estimation of PGI2 generation by either tissues or organs may be misleading if only 6-keto-PGF1alpha is measured.     

Bronchopulmonary effects of prostaglandin F2alpha and three of its metabolites in the dog.

The airway and lung dynamics of porstaglandin F2alpha (PGF2alpha) and three of its metabolites were examined in the spontaneously ventilated, pentobarital anesthetized dog. Changes in expirtaory flow rate, tidal volume, respiration rate, lung resistance and dynamic lung compliance were evaluated and compared quantitatively. In a dose range of 0.3-3.0 mu/kg i.v., PGF2alpha and its 13, 14-dihydrometabolite were found to be exceptionally potent agents. This metabolite was approximately twice as potent as PGF2alpha on most parameters studied. Two other metabolites, 15-keto-PGF2alpha and 15-keto-13, 14-dihydro-PGF2alpha, were only slightly effective, even in a dose range of 1.0-30.0 mu/kg i.v. These latter two metabolites produced dose-response curves with significantly shallower slopes than PGF2alpha and were shown to be at least thirty-five times less potent than the parent compound. Therefore, oxidation of PGF2alpha at the carbon-15 position by 15-hydroxy prostaglandin dehydrogenase appears to produce compounds with minimal in vivo bronchopulomary activity.