Biological activities of pure prostaglandins

Total Synthesis of (15R)- and (15S)-Prostaglandin A2

From both pharmaceutical and structural perspectives, the large family of prostaglandins represent a truly remarkable class of natural products. Prostaglandin A2 is a tissue hormone naturally found in human seminal plasma and in the sea whip Plexaura homomalla with yet poorly understood biological or therapeutic effects. Herein, a novel strategy for the stereoselective construction of both naturally occurring prostaglandin A2 epimers and first insights into their functional effects on the major inhibitory neurotransmitter γ-aminobutyric acid (GABA) type A receptors (GABAAR) are provided. The synthesis of both epimers was achieved in only 11 steps starting from commercially available 2,5-dimethoxy-tetrahydrofuran employing an organocatalytic domino-aldol reaction, a Mizoroki-Heck reaction, a Wittig reaction as well as an oxidation-decarboxylation sequence. The (15R)-epimer significantly reduced GABA-induced currents through GABAA receptors while its (15S)-epimer did not show any significant effect. These data suggest that (15R)-PGA2 might serve as a novel scaffold for the development of selective GABAA receptor modulators.

Characterization of receptors involved in the direct and indirect actions of prostaglandins E and I on the guinea-pig ileum

1. A study of the effects of prostaglandin E2 (PGE2) and eleven synthetic analogues on the guinea-pig isolated ileum preparation has revealed three distinct contractile actions, each associated with a different prostaglandin E (EP-) receptor subtype. In addition, PGI2 (prostacyclin) and its stable analogues can activate prostaglandin I (IP-) receptors to elicit both contraction and relaxation of the ileum. 2. Two of the PGE actions involve direct stimulation of the smooth muscle, being unaffected by 1 microM morphine treatment. One action is blocked by AH 6809 at micromolar concentrations and ICI 80205 and 16,16-dimethyl PGE2 are particularly potent agonists. Activation of EP1-receptors appears to be involved. The second action is unaffected by AH 6809; sulprostone and MB 28767 are potent agonists. Comparison with agonist potency rankings on the guinea-pig vas deferens indicates that EP3-receptors may be involved. 3. The third PGE effect and the stimulant PGI effect are blocked by morphine, indicating enteric neurones and/or sensory nerve terminals as sites of action. EP2-receptors may be involved in the PGE action, in view of the marked effect of morphine on the contractile actions of misoprostol, 11-deoxy PGE2-1-alcohol, 11-deoxy PGE1 and butaprost, all of which show some selectivity for EP2-receptors. The PGI action is most easily studied with cicaprost (EC25 = 1.3 nM), since iloprost, carbacyclin and to a lesser extent PGI2 also have agonist activity at EP1-receptors. 4. The contractile action of 17-phenyl-omega-trinor PGE2 on the ileum is unaffected by morphine. Since this analogue shows only weak agonist activity on the rabbit jugular vein (EP2 preparation) and guinea-pig vas deferens (EP3), it may be a more useful standard agonist than PGE2 in EPl1-receptor studies.5. In the presence of morphine and AH 6809, cicaprost inhibits histamine-induced contractions (IC25 = 22 nM). PGI2 and iloprost show mixed inhibitory/potentiating actions, whereas carbacyclin only potentiates histamine contractions. This IP-receptor-mediated inhibition may account for the bell-shaped log concentration-response curve of cicaprost (no inhibitors present) and the very marked block of iloprostinduced contractions by AH 6809.6. We have found no evidence for either IP-receptors mediating direct contraction or EP-receptors mediating inhibition of the ileum longitudinal smooth muscle, as has been suggested in the literature.7. In view of the complexity of prostanoid action on the guinea-pig ileum we feel that the preparation must be used with caution to ascertain the EPl agonist or antagonist potencies of novel compounds.

Response of bovine intra-ocular muscles to transmural stimulation in the presence of various prostaglandins

Effects of prostaglandins (PGs) E1, E2 and F2 alpha on the electrically stimulated and non-stimulated smooth muscles of bovine intra-ocular tissues were investigated in vitro. PGs E1, E2 and F2 alpha contracted the sphincter and these contractions were not antagonized by either cholinergic or adrenergic blocking agents. PGF2 alpha was much weaker than PGE1 or PGE2. PGs in high concentrations produced an irreversible contracture of the sphincter muscle. In contrast, the dilator muscle contracted with PGF2 alpha, but not PGE1 or PGE2. The ciliary muscle did not respond to these PGs or to indomethacin. Electrical field stimulation with short pulses produced excitation of the intrinsic nerves. The responses produced were not altered in amplitude by the application of any dose of PGs or indomethacin, although indomethacin did lower the tone of the sphincter. PGs did not influence the amplitude of the acetylcholine-induced responses of the intra-ocular muscles. These results indicate that in each of the bovine intra-ocular muscles, PGs play a minor role in neuromuscular transmission both prejunctionally and postjunctionally. Thus, PG-induced contractions of the bovine intra-ocular muscles are considered to occur by a direct action on the muscle rather than on the nerves.

PGD2 effects on rodent behavior and EEG patterns in cats

Prostaglandin (PG) D2 was studied to determine the pharmacological effects of this PG on the central nervous system. PGD2 (0.45-4.05 mg/kg) decreased spontaneous locomotor activity in rats by as much as 66% of control, however, the neuromuscular coordination of mice, treated at the same doses of PGD2, was not impaired. PGD2 (0.05-4.05 mg/kg) also increased pentobarbital sleeping time in mice from 42% to 238% of control, in a dose-related manner. PGD2 did not prevent convulsions induced in response to electroshock or pentylenetetrazol. Cats monitored for EEG responses to PGD2 infusion displayed variable sensitivity to different doses (16-3000 microgram) of drug, however, the characteristic response to PGD2 was the conversion from a uniform low voltage, fast wave pattern to high voltage, slow waves. Cats administered PGD2 were sedated and sometimes catatonic, and displayed brief periods of hypotension, bradycardia, diarrhea, analgesia and hyperthermia at higher doses of the drug. Thus, PGD2 possesses sedative properties in rodents and cats and may have a role in the central nervous system.

Effects of prostaglandins E-1, E-2, F-1a and F-2a on human sperm motility

Effects of the addition of 100 micrograms each of prostaglandins E1, E2, F1a and F2a were seen on the motility, fructose utilization and total ATPase activity of human spermatozoa. PGE2 enhanced sperm motility and fructose utilization and decreased the whole sperm ATPase activity. While PGE1 had no effect on any of the parameters studied, PGF1a and PGF2a decreased sperm motility to some extent. Fructose utilization was reduced after PGF1a addition only. No change in the activity of ATPase was observed after treatment with F series of prostaglandins.

The effects of photosensitizers and ultraviolet irradiation on the biosynthesis and metabolism of prostaglandins

Prostaglandin biosynthesis from arachidonic acid by skin microsomal fraction preparation was enhanced by UV-irradiation at wavelengths of 254 and 360 nm. In the presence of 8-methoxy psoralen (8 MOP) and coal tar, prostaglandin biosynthesis was further enhanced approximately 2-fold by UV-irradiation at 254 nm. Stimulation was less by UV-irradiation at 360 nm. 8-MOP enhanced the conversion of PGE2 into PGF2-9-ketoreductase prepared from skin high speed supernatant fractions. UV-irradiation at 254 nm and 360 nm with or without the photosensitizers had no effect on the activity of the PGE2-9-ketoreductase. These data therefore indicate that the action of UV-irradiation, 8-methoxy psoralen and coal tar on the skin may in part be due to their regulation of the biosynthesis and metabolism of prostaglandins in this tissue.

A dose-response comparison of PGA2, PGE1 and PGE2 using the phenylephrine-stimulated perfused oviduct of the rabbit

The phenylephrine-stimulated perfused oviduct of the rabbit was evaluated as a model for studying the activity of prostaglandins that produce inhibition of the oviducal smooth muscle. Elevation of the normal "tone" of the oviduct by perfusing phenylephrine through the lumen permitted quantitation of the responses to PGA2, PGE1 and PGE2 by measuring the magnitude of the inhibitory response produced by the agents. PGE2 was relatively more potent, efficacious and specific for the oviduct than PGA2 or PGE1. It was concluded that the model was suitable for comparative dose-response studies of PGA2, PGE1 and PGE2 and their analogs.

Effect of prostaglandin F2 alpha on propulsive activity of the isolated segmental colon of the guinea-pig

The effects of prostaglandin F2alpha (PGF 2alpha) on propulsive activity in segments of isolated colon and on isolated strips of guinea-pig colon were investigated. Using experimental conditions under which spontaneous propulsive activity was negligible, PGF2alpha (5X10(-8)X1X10(-6)M), added to the bathing medium increased propulsive activity in a concentration dependent manner. This increase of propulsive activity was abolished in the presence of atropine or tetrodotoxin (1X10(-7)g/ml). The contractions produced by PGF2alpha (5X10(-7) -1X10(-5)M) in isolated longitudinal and circular smooth muscle strips of guinea-pig colon were unaffected in the presence of atropine or tetrodotoxin (1X10(-7) g/ml). From these results it is concluded that under the conditions employed in this study propulsive activity stimulated by PGF2alpha may depend on the contractions of both muscle layers and stimulation of the peristalic reflex.

Influence of the estrous cycle and prostaglandins on utero-ovarian vein blood flow in the rat

The blood flow rate in the utero-ovarian vein (UOV) has been measured in adult female rats during the different phases of the estrous cycle. It was observed that the blood flow rate in the UOV is high at proestrus and at estrus and low during diestrus days 1 and 2. The intravenous injection of 10 mug PGF2alpha or PGE2 diminishes the blood flow rate in the UOV. The efficacy of the two PGs in reducing blood flow is different in the various phases of the estrous cycle, being maximal during the day of estrus.

Potentiation by prostaglandins e1, e2, and f2alpha of the contraction response to transmural stimulation in the bovine iris sphincter muscle

The contraction response to transmural stimulation in the bovine iris sphincter muscle was abolished by atropine but was left virtually unchanged by hexamethonium, and by adrenergic neuron and receptor blockers, indicating activation of postganglionic cholinergic nerve fibres. Low doses of prostaglandins e1, e2 and F2alpha (0.1-5.3 ng/ml) consistently and apparently in a dose-dependent manner enhanced the contraction response to transmural stimulation. Prostaglandins E1 and E2 were equipotent while F2alpha was at least 10 times less active. Within the same dose range the prostaglandins also enhanced the contraction response to exogenous acetylcholine, indicating that part of the enhancing effect of the prostaglandins on neuromuscular transmission was due to a postjunctional action. A spontaneous increase in tone of the preparation commonly occurred about 1 h after the beginning of the experiment. SC 19220, a potent antagonist of prostaglandin action, reduced the tone and the contraction responses as well as the enhancing effect of the prostaglandins. It is concluded that prostaglandins might serve the function of controlling neuroeffector transmission and muscular tone in the sphincter muscle of the bovine iris.

Selective inhibition of prostaglandin biosynthesis by gold salts and phenylbutazone

Gold salts and phenylbutazone selectively inhibit the synthesis of PGF2alpha and PGE2 respectively. Lowered production of one prostaglandin species is accompanied by an increased production of the other. Selective inhibition by these drugs was observed in the presence of adrenaline, reduced glutathione and copper sulphate under conditions when most anti-inflammatory compounds inhibited PGE2 and PGF2alpha syntheses equally. It is postulated that selective inhibitors may have a different mode of action in vivo and beneficial effects may be related to the endogenous ratio of PGE to PGF required for normal function.

Compartive behavioral effects of dibutyryl cyclic AMP and prostaglandin E1 in mice

Three behavioral tests, spontaneous locomotor activity (SLMA), exploratory behavior (EB) and rotarod performance (RP), a measure of neuromuscular coordination, were used to stuey the interaction of PGE1 (1 mg/kg i.p., 10 min. pretreatment) with DBcAMP (25 mg/kg i.p., 25 min. pretreatment) in mice. A dose-response relationship of PGE1 (0.01-5.0 mg/kg) to SLMA was determined, with a significant decrease in SLMA produced by a dose of 0.1 mg/kg. decreases in SLMA were produced by PGE1 (79%), DBcAMP (41%) and DBcAMP-PGE1 combination (71%). Similar decreases in EB were observed. Although no significant difference between controls and DBcAMP was observed in RP, 52% of mice tested were RP failures following PGE1 and a 100% failure rate was induced by the combination. Mice were treated with a second injection of DBcAMP or PGE1 or the combination 24 hr following the first injection. Behavioral activity of these mice was observed 25 min (DBcAMP) or 10 min (PGE1) after the second dose was administered. A second injection of DBcAMP failed to decrease SLMA and EB from controls; moreover, SLMA began to return towards control levels as early as 2 hr between injections. The second injection of PGE1 or DBcAMP+PGE1 produced the same behavior as that produced by the first injection. On the basis of these results, the relationship of cyclic nucleotides and PGs to behavioral activity is discussed.

A possible sympathetic cholinergic mechanism in the renal reflex elicited by stimulation of abdominal viscera in the dog

1. Isolated blood-bathed tissues which were superfused with renal venous blood during various manipulations of the visceral organs of dogs showed no detectable pharmacologically active substances, except a noradrenaline-like substance which was liberated under some conditions of manipulation. 2. An acetylcholine-like substance was liberated into renal venous blood during experimental manipulation of visceral organs in dogs during infusion of physostigmine; the acetylcholine activity was detected with the dorsal muscle of the leech. 3. The amount of liberated acetylcholine-like substance depended on the strength of visceral stimulation as judged by the changes in the hepatic portal venous pressure. Strong reflex stimulation produced the release not only of acetylcholine but also of noradrenaline. 4. Physostigmine augmented and prolonged the reflexly induced renal vasodilator and diuretic responses, and these were abolished by atropine. It was suggested that the reflex involves a cholinergic nervous mechanism. 5. In some dogs there was a high output of acetylcholine from the kidney during visceral stimulation, and this was accompanied by a decrease in urine flow. The reason was not known. 6. Prostaglandin E1 administered into the renal artery produced similar vasodilator and diuretic responses to acetylcholine, but the onset of the effects were slower and they persisted longer than those produced by acetylcholine.

Appearance of prostaglandin F2-alpha in human blood during labour

Blood samples from over 70 pregnant women have been examined for the presence of four prostaglandins. Samples obtained from women not in labour at different gestation periods and at term contained no detectable amounts of prostaglandins. Prostaglandin F(2alpha) was present in samples of blood obtained during normal spontaneous labour. The appearance of this substance in the blood preceded the uterine contraction. Whether prostaglandins play a part in the process of normal labour is still conjectural.