Prostaglandin E1 causes sedation and increases 5-hydroxytryptamine turnover in rat brain

Prostaglandins and central serotonergic activity in the rat

Pharmacological and biochemical studies indicate that prostaglandins (PGs) exert a modulatory influence on rat brain serotonergic activity. With several experimental approaches, it has been shown that PGEs and PGD2 facilitate central serotonergic activity in rats. On the contrary, PGF2α not only inhibits rat brain serotonergic activity but also antagonizes the facilitatory effect of the other PGs. The studies support the proposed neuromodulatory role for PGs in central synaptic transmission.

Modular enantioselective synthesis of 8-aza-prostaglandin E1

We report herein for the first time the enantioselective synthesis of 8-aza-PGE1. The synthesis used the cross olefin metathesis reaction to connect the 5-vinyl-γ-lactam subunit, prepared from (R)-malic acid via the Ley's sulfone-based α-amidalkylation protocol (dr = 6.8:1), with the chiral pre-ω-chain. The latter was synthesized in high enantioselectivity from (E)-2-octenol by the Sharpless asymmetric epoxidation and the titanocene-mediated epoxide opening. This modular approach is quite concise and flexible, and requires only eight steps from commercially available reagents.

A Potent Serotonin-Modulating Compound AP-267 Attenuates Morphine Withdrawal-Induced Blood-Brain Barrier Dysfunction in Rats

The possibility that a serotonin 5-HT2c receptor-modulating compound, AP-267, will influence spontaneous morphine withdrawal symptoms and the alterations in the brain fluid microenvironment was examined in a rat model. Daily administration of morphine (10 mg/kg, i.p.) for 10 days resulted in dependence of rats as seen by loss of analgesic response. On the 11th day, no morphine administration was given. This resulted in profound withdrawal symptoms 24 h after morphine withdrawal. The magnitude and severity of these symptoms were increased further 48 h after withdrawal. Measurement of the blood-brain barrier (BBB) permeability, a measure of perturbed brain fluid microenvironment showed leakage of Evans blue and radioiodine tracers in several parts of the brain in rats showing withdrawal symptoms. Whereas, rats treated with AP-267 either on the 1st day or 2nd day morphine withdrawal showed much less symptoms and leakage of the BBB. Taken together, these observations suggest that (a) stress associated with the withdrawal symptoms are sufficient enough to induce breakdown of the BBB function, and (b) modulation of serotonin 5-HT2c receptors may have some protective influence on the stress symptoms and the BBB disruption.

Probable involvement of serotonin in the increased permeability of the blood-brain barrier by forced swimming. An experimental study using Evans blue and 131I-sodium tracers in the rat

The possibility that endogenous serotonin (5-hydroxytryptamine, 5-HT) participates in alteration of the blood-brain barrier (BBB) following short-term forced swimming (FS) exercise was examined in a rat model. Subjection of conscious young (age 8-9 weeks, 80-90 g) animals to continuous FS (at a water temperature of 30 +/- 1 degrees C) for 30 min, increased the permeability of the BBB to Evans blue albumin (EBA) and 131I-sodium in six and nine brain regions, respectively. The EBA staining was noted in posterior cingulate cortex, parietal, occipital cortices, cerebellar vermis, medial lateral cerebellar cortices and dorsal surface of hippocampus. In addition to these brain regions, the BBB permeability to 131I-sodium was further extended to caudate nucleus, thalamus and hypothalamus. This effect of FS on the BBB permeability was absent in adult (age 24-30 weeks, 300-400 g) animals. Measurement of 5-HT showed a profound increase of plasma and brain in young rats by 180% and 250%, respectively, from the control group. Adult animals showed only a minor increase in brain and plasma 5-HT levels. In young animals, pretreatment with p-CPA (a 5-HT synthesis inhibitor) and indomethacin (a prostaglandin synthesis inhibitor) prevented the FS induced increase in BBB permeability and 5-HT levels. Destruction of serotonergic neurons with 5,7-dihydroxytryptamine (5,7-DHT) reduced the breakdown of the BBB and attenuated the brain 5-HT level without affecting the plasma 5-HT. Cyproheptadine, ketanserin (5-HT2 receptor antagonists) and vinblastine (a vesicular transport inhibitor) prevented the increased permeability of the BBB alone. The plasma and brain 5-HT continued to remain high. These observations suggest that (i) 5-HT plays an important role in the breakdown of BBB permeability in FS, (ii) this effect of 5-HT on BBB permeability is mediated by 5-HT2 receptors, and (iii) FS induced increase in BBB permeability is age dependent.

Role of serotonin and prostaglandins in brain edema induced by heat stress. An experimental study in the young rat

The possibility that serotonin and prostaglandins participate in edema formation following heat stress (HS) was examined in young rats. Exposure of conscious young animals (8-9 weeks old) to heat at 38 degrees C in a biological oxygen demand (BOD) incubator (relative humidity 50-55%; wind velocity 20-25 cm/s) for 4 h resulted in marked increase in the whole brain water content (about 3%) as compared to animals kept at room temperature (21 degrees C). A marked extravasation of Evans blue and 131I-sodium occurred in the brain of heat exposed animals as compared to normal animals. Morphological examination using electron microscopy of selected brain regions of heat stressed animals showed profound cell changes. Thus perivascular edema, swollen neuronal and glial cells, membrane damage, vesiculation of myelin, axonal swelling and synaptic damage was frequent in this group of untreated animals. Pretreatment with ketanserin (a selective serotonin2 receptor antagonist) or indomethacin (an inhibitor of prostaglandin synthesis) markedly reduced edema formation after 4 h HS in young animals. These heat stressed animals had considerably less extravasation of protein tracers as compared to the untreated group. Cell changes and edema at the ultrastructural level were mainly absent. Our results suggest that serotonin and prostaglandins are involved in heat stress induced breakdown of the BBB permeability, edema formation, and cell damage.

Prostaglandins modulate alterations of microvascular permeability, blood flow, edema and serotonin levels following spinal cord injury: an experimental study in the rat

The possibility that prostaglandins influence edema formation, microvascular permeability increase and reduction of blood flow following spinal cord trauma was examined in a rat model. In addition, the influence of prostaglandins on serotonin metabolism of the traumatized spinal cord was evaluated. Trauma to spinal cord (2-mm-deep and 5-mm-long incision in the right dorsal horn of T10-11 segments) resulted in a profound increase of the water content 5 h after injury. At this time, the microvascular permeability to Evans Blue and [131I]sodium was increased by 457 and 394%, respectively. The blood flow was reduced by 30%. The serotonin (5-hydroxytryptamine) content of the spinal cord increased by 205%. The plasma serotonin level rose by 152% in the injured group of rats. Pretreatment with indomethacin (10 mg/kg, i.p.) 30 min before trauma significantly reduced the edema and microvascular permeability increase. The local spinal cord blood flow of traumatized animals was partially restored. The increases of serotonin levels of the spinal cord and plasma were significantly attenuated. These beneficial effects of indomethacin were not present in rats given a lower dose (5 mg/kg). Indomethacin in either dose did not influence these parameters of control rats without trauma to the cord. Since indomethacin is a potential inhibitor of prostaglandins synthesis our observations indicate: (i) that prostaglandins participate in many microvascular responses (permeability changes, edema, blood flow) occurring after a trauma to the spinal cord; (ii) that these effects of the drug seem to be dose dependent, and (iii) that the prostaglandins may influence the serotonin metabolism following trauma to the spinal cord.

Prostaglandins E2 and D2 have little effect on rabbit sleep

Prostaglandins (PGs) are hypothesized to be involved in sleep regulation; PGE2 and PGD2 are major PGs in the hypothalamus of many species and are proposed to reciprocally promote wakefulness and sleep respectively. PGD2 and PGE2 are also major PGs in rabbit cerebrospinal fluid, yet their effects on rabbit sleep have not heretofore been systematically investigated. We report here that a bolus injection of PGE2 into a lateral cerebral ventricle induces dose-dependent fevers and transient sleep responses in rabbits. PGE2 induces a suppression of sleep of 24 min duration. In contrast, PGD2, across a wide range of doses (0.25-500 nmol) failed to alter sleep; however, at the highest dose it induced fever. We conclude that if PGs are involved in sleep regulation, a chronic stimulation of their production by other sleep factors is necessary.

Two possibly distinct prostaglandin E1 receptors in N1E-115 clone: one mediating inositol trisphosphate formation, cyclic GMP formation, and intracellular calcium mobilization and the other mediating cyclic AMP formation

Prostaglandin E1 (PGE1)-mediated transmembrane signal control systems were investigated in intact murine neuroblastoma cells (clone N1E-115). PGE1 increased intracellular levels of total inositol phosphates (IP), cyclic GMP, cyclic AMP, and calcium ([Ca2+]i). PGE1 transiently increased inositol 1,4,5-trisphosphate formation, peaking at 20 s. There was more than a 10-fold difference between the ED50 for PGE1 at cyclic AMP formation (70 nM) and its ED50 values at IP accumulation (1 microM), cyclic GMP formation (2 microM), and [Ca2+]i increase (5 microM). PGE1-mediated IP accumulation, cyclic GMP formation, and [Ca2+]i increase depended on both the concentration of PGE1 and extracellular calcium ions. PGE1 had more potent intrinsic activity in cyclic AMP formation, IP accumulation, and cyclic GMP formation than did PGE2, PGF2 alpha, or PGD2. A protein kinase C activator, 4 beta-phorbol 12 beta-myristate 13 alpha-acetate, had opposite effects on PGE1-mediated IP release and cyclic GMP formation (inhibitory) and cyclic AMP formation (stimulatory). These data suggest that there may be subtypes of the PGE1 receptor in this clone: a high-affinity receptor mediating cyclic AMP formation, and a low-affinity receptor mediating IP accumulation, cyclic GMP formation, and intracellular calcium mobilization.

Changes in blood-brain barrier and cerebral blood flow following elevation of circulating serotonin level in anesthetized rats

Plasma serotonin (5-HT) was elevated by an intravenous infusion of this amine into urethane-anaesthetized rats and the concentration approximated that present in various neurological diseases and mental abnormalities. An infusion of 10 micrograms per kg body weight for 10 min significantly increased blood-brain barrier (BBB) permeability to Evans blue and 131I-sodium measured in whole brain. Regional BBB determinations with labelled 131I-sodium showed that the permeability to this compound was increased in the cerebral cortex, hippocampus, caudate nucleus, hypothalamus, colliculus and the cerebellum but not in the pons and the medulla oblongata. Regional blood flow was reduced in the same parts which showed BBB abnormality tested with 125I-labeled microspheres. Pretreatment with cyproheptadine, a 5-HT2 receptor antagonist, prevented the BBB increase and the regional blood flow was near normal values. Similar effects were obtained with indomethacin, a prostaglandin synthesis inhibitor. Vinblastine, known to influence vesicular transport, eliminated extravasation of the tracers but the regional blood flow remained depressed. A hypothesis is put forward that serotonin after binding to its receptor in the cerebral vessels stimulates prostaglandin which either directly or by means of cyclic adenosine monophosphate causes an increased vesicular transport across the endothelial cells and thus an extravasation of tracer substances in the brain. Obviously, this form of exudation can be influenced by pharmacological means.

Prostaglandins, brown fat and weight loss

In obesity, a situation is created in which energy intake exceeds energy expenditure. The three components of energy expenditure are resting metabolism, physical activity, and thermogenesis. Increasing attention is being paid to the role of impaired energy expenditure in obesity. Evidence indicates that impairment in activity of the sympathetic nervous system, which stimulates thermogenic processes, contributes to the etiology of obesity. In addition, insulin resistance, a well-recognized metabolic consequence of obesity, appears to interfere with feeding-related, insulin-mediated increases in thermogenesis in brown adipose tissue. This thermogenic defect results in reduced energy buffering by brown adipose tissue leading to deficient energy expenditure and an increased efficiency in weight gain. A unique weight loss program, The Princeton Metabolic Diet Program, is presented. The Program stimulates metabolism by stimulating the sympathetic nervous system and correcting insulin resistance, thereby enhancing thermogenesis in brown adipose tissue. Methods include: 1) alternating diet composition and caloric intake and, 2) the use of nutritional metabolic stimulants. This type of non-toxic therapy, directed at correcting biochemical defects, will enhance metabolic mechanisms and induce weight loss.

Suppression of sleep by prostaglandin synthesis inhibitors in unrestrained rats

Sleep-suppressive activity of prostaglandin synthesis inhibitors, diclofenac sodium (DF) and indomethacin (IM), was examined in unrestrained male rats. An intraperitoneal injection of 5 mg/kg IM, or an oral administration of 5 mg/kg DF and 10 mg/kg IM at an early phase of the light period transiently decreased slow wave sleep (SWS) and paradoxical sleep (PS) to 30-62% and 0-38%, respectively, of the control level in the first hour. An intravenous infusion of 0.4 mg DF or 0.4 mg IM or an intracerebroventricular infusion of 0.04 mg DF continuously during a 10-h diurnal period resulted in a significant decrease in SWS and PS by 9-17% and 17-21%, respectively, from the baseline value in the 12-h light period. The DF infusion was accompanied by a rebound rise in the nocturnal SWS and PS and the subsequent diurnal PS. The results indicate that the depletion of prostaglandin(s) in the brain is responsible for the DF- and IM-induced suppression of sleep.

Awaking effect of PGE2 microinjected into the preoptic area of rats

We examined the effect of prostaglandin (PG)E2 on the sleep-wake activity and on body temperature by microinjecting PGE2 into the preoptic area of rats that had been chronically implanted with guide cannulae and electrodes for the recordings of electroencephalogram and electromyogram. PGE2 at doses of 2.5 X 10(-13), 2.5 X 10(-11), and 2.5 X 10(-9) mol reduced the time of slow wave sleep (SWS) to 75%, 61%, and 59% and that of paradoxical sleep (PS) to 73%, 50%, and 25% of the controls, respectively. The SWS and PS reductions were mainly due to the shortening of the SWS episode and the less frequent occurrence of PS episodes. The sleep reduction was accompanied by increased behavioral movement. The maximum increases of rectal temperature at doses of 2.5 X 10(-11) and 2.5 X 10(-9) mol of PGE2 were 1.3 degrees C and 2.7 degrees C, respectively. At a dose of 2.5 X 10(-13) mol of PGE2, the time of SWS and that of total sleep (sum of SWS and PS) decreased significantly, but the change in body temperature was negligible. This may imply that the effect of PGE2 on the sleep-wake activity is not caused by the hyperthermia produced by PGE2. Injections of PGE2 at a dose of 2.5 X 10(-15) mol and saline control induced alteration in neither sleep-wake activity nor body temperature. PGD2 at a dose of 2.5 X 10(-9) mol slightly elevated the rectal temperature (0.5 degree C), but did not produce any change in the sleep-wake activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of long-term acute heat exposure on regional blood-brain barrier permeability, cerebral blood flow and 5-HT level in conscious normotensive young rats

Exposure of conscious young rats to 4 h heat stress at 38 degrees C in B.O.D. incubator was associated with increased blood-brain barrier (BBB) permeability in 14 brain regions studied. In the same regions cerebral flow (CBF) diminished by 4-65%, but the magnitude of flow reduction was not correlated with the degree of increased BBB permeability. On the other hand, a correlation was observed with increased plasma and brain 5-hydroxytryptamine (5-HT) levels. p-Chlorophenylalanine (p-CPA), indomethacin and diazepam pretreatment prevented both the increased BBB permeability and 5-HT levels following heat exposure. Whereas cyproheptadine and vinblastine pretreatment prevented the increased BBB permeability alone. The probable mechanism(s) underlying the BBB permeability is discussed.

Neural mechanisms mediating the hyperthermia elicited by prostaglandin E2 injected into the preoptic-anterior hypothalamus

The neuromechanism mediating the hyperthermia induced by injection of PGE2 into the preoptic/anterior hypothalamus (PO/AH) was investigated in the rat. Pretreatment of rats with intraperitoneal injection of atropine sulfate blocked, whereas pretreatment with atropine methyl bromide had no significant effect on the hyperthermia. In a second series of experiments, atropine sulfate was microinjected into different regions of the hypothalamus and the thalamus in an attempt to locate the central cholinergic synapses involved in the PGE2-induced hyperthermia. The hyperthermia was blocked by atropine injection into the dorsal/dorsomedial hypothalamic area (DH), but was not significantly affected by injection into the PO/AH, ventromedial hypothalamus, or the thalamic area above the DH. Moreover, microinjection of the cholinergic agonist carbachol (0.5 microgram) into the DH could also elicit hyperthermia. Thus, our data suggest that the hyperthermia induced by PGE2 administration into the PO/AH is mediated by a cholinergic mechanism in the DH.

Influence of eicosanoids on serotonin release in the rat brain: inhibition by prostaglandins E1 and E2

Superfused rat brain cortex slices, hypothalamic slices and cortex synaptosomes preincubated with 3H-serotonin or 3H-noradrenaline were used to study the effects of eicosanoids on tritium overflow evoked either electrically (3 Hz; slices) or by potassium 12 mmol/l (synaptosomes). 1. The electrically evoked 3H overflow from cortex slices preincubated with 3H-serotonin was inhibited by prostaglandins E1 and E2 and by the prostacyclin analogue iloprost. No effect was seen with prostaglandin F2 alpha, prostaglandin D2, CG 4203 (another prostacyclin analogue), U 46619 (a thromboxane A2 analogue) and leukotriene C4. The same held true for indomethacin and the prostaglandin receptor antagonists SC 19220 and N-0164. The inhibitory effect of prostaglandin E2 was slightly more pronounced in the presence of indomethacin than in its absence, but was not affected by SC 19220, N-0164 or forskolin plus AH 21-132 (an inhibitor of cAMP phosphodiesterase). Yohimbine and the serotonin receptor antagonist metitepin failed to influence the inhibitory effect of prostaglandin E1. 2. The potassium-evoked 3H overflow from cortex synaptosomes preincubated with 3H-serotonin was inhibited by prostaglandin E2. 3. Prostaglandin E2 also inhibited the electrically evoked 3H overflow from hypothalamic slices preincubated with 3H-serotonin. 4. The electrically evoked 3H overflow from cortex slices preincubated with 3H-noradrenaline was inhibited by prostaglandin E2, but was not affected by SC 19220, which, in turn, did also not alter the effect of prostaglandin E2. The present results are compatible with the view that presynaptic SC 19220-insensitive prostaglandin E receptors may be involved in the inhibitory effect of prostaglandins E1 and E2 on serotonin (and noradrenaline) release.

Protective effect of prostaglandins D2, E1 and I2 against cerebral hypoxia/anoxia in mice

The protective effect of prostaglandins (PGs) against cerebral hypoxia/anoxia was investigated with a variety of experimental models in relation to their CNS depressant effects in mice. Furthermore, the effect of PGs on the changes of cerebral energy metabolites and cyclic nucleotide was examined in hypoxic mice. Mice were given s.c. doses of PGs 30 min before tests. Among the PGs tested, treatment with PGD2, PGE1 and PGI2 Na showed a consistent and dose-dependent protection against cerebral anoxia induced by all models studied: histotoxic anoxia by KCN, hypobaric hypoxia, normobaric hypoxia and decapitation-induced gasping. However, PGA1, PGA2, PGB1, PGB2, PGE2, PGF1 alpha, PGF2 alpha and 6-keto-PGF1 alpha at a dose of 3 mg/kg were without effect against normobaric hypoxia and gasping duration. The three PGs, i.e. PGD2, PGE1 and PGI2 which showed anti-hypoxic effects decreased locomotor activity and potentiated hexobarbital-induced sleep. On the other hand, PGE2, PGA1, PGA2 and PGB2 also caused a decrease in locomotor activity. Similarly, PGE2 and PGA1 caused a potentiation of hexobarbital-induced sleep, but interestingly they did not cause clear-cut increase in cerebral resistance to hypoxia, in contrast with the former three PGs. Thus general depression of CNS function appears not to be responsible for the PGD2-, PGE1- and PGI2-induced increase in cerebral resistance to hypoxia. The levels of Cr-P and ATP were significantly reduced and those of ADP and AMP were markedly elevated in hypoxic brain, resulting in a decrease in a calculated energy charge potential. The lactate level and lactate/pyruvate ratio increased and the glucose level decreased markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of prostaglandin F2 alpha on brain and stomach 5-hydroxytryptamine

PGF2 alpha initially inhibits the rate of 5-HT synthesis in both rat brain and stomach and subsequently stimulates it. The results suggest that PGs of E and F series modulate tryptaminergic neuronal activity which in its turn variously affects 5-HT mediated responses.

The effects produced by prostaglandin D2 on serotonin turnover and release and tryptophan uptake

In earlier studies, it was proposed that there was a serotonergic involvement in the ability of prostaglandin D2 (PGD2) to potentiate pentobarbital sleeping time. The actions of PGD2 on neuronal turnover and release of serotonin and uptake of tryptophan were examined in mice. The effect of PGD2 administration on serum tryptophan levels was also investigated. PGD2 (1 and 4 mg/kg) increased the concentrations in whole brain of endogenous tryptophan (TRYP) and of 3H-tryptophan (3H-TRYP) following an intravenous (IV) injection of 3H-tryptophan. Formation of 3H-5-hydroxyindoleacetic acid (3H-5HIAA) was doubled after PGD2 administration (1 and 4 mg/kg). Whole brain concentrations of endogenous serotonin (5HT) and 3H-serotonin (3H-5HT) were unchanged after the administration of the prostaglandin. PGD2 (10(-4) to 10(-10)M) in vitro had no effect on spontaneous or K+-evoked release of 3H-5HT from whole brain synaptosomes. Uptake of 3H-tryptophan in synaptosomes was neither stimulated nor depressed by (10(-4) to 10(-12)M) PGD2. There was also no change in serum tryptophan levels after administration of this prostaglandin. Thus, PGD2 administration does affect the serotonergic system but no direct neurochemical correlate of sedation can be shown.

Involvement of the serotonergic system in the prolongation of pentobarbital sleeping time produced by prostaglandin D2

In the present study, the depressant and sedative actions of prostaglandin D2 (PGD2) were investigated. Intravenous (IV) administration of PGD2 produced a significant decrease in the spontaneous locomotor activity of mice from 1 to 15 minutes following injection. Prostaglandin D2 was also able to potentiate pentobarbital sleeping time at doses of 0.4 and 4.0 mg/kg when administered intravenously. Distribution studies with 3H-PGD2 (6 microCi, 4 mg/kg) showed that only 0.04% of the tritium administered could be found in brain at 5 min after the injection, and that only 50% of this was parent 3H-PGD2. The role of the serotonergic neurotransmitter system in the depressant action of PGD2 was investigated with drugs which modulate this system. The ability of PGD2 to potentiate pentobarbital sleeping time was diminished by pretreatment with agents that reduce brain level or synthesis rate of serotonin. Such agents include para-chlorophenylalanine (PCPA), a tryptophan hydroxylase inhibitor, 5,7-dihydroxytryptamine (5,7-DHT), a neurotoxin with selectivity for serotonergic neurons, and quipazine, a serotonergic autoreceptor stimulant. On the other hand, pretreatment with 5-hydroxytryptophan (5-HTP), the precursor of serotonin, further enhanced the potentiation of pentobarbital sleeping time by PGD2. These data suggest that the depressant actions of PGD2 are linked to the serotonergic neurotransmitter system.

Inhibition of adenosine uptake into rat brain synaptosomes by prostaglandins, benzodiazepines and other centrally active compounds

A number of compounds have been tested for their abilities to inhibit the rapid uptake of adenosine by rat cerebral cortical synaptosomes. Prostaglandins PGI2, PGA2, and PGE1 and PGE2 were potent inhibitors of adenosine uptake with IC20 values in the 10(-7) M-10(-6) M range. PGA1, PGD2 and PGF2 alpha also inhibited uptake but were less active. The benzodiazepine antagonist Ro 15-1788 inhibited adenosine uptake and failed to antagonize the effects of diazepam. Another antagonist, ethyl-beta-carboline-3-carboxylate, was a weak inhibitor of adenosine uptake. Ro 5-4864, the so-called peripheral benzodiazepine ligand, inhibited adenosine uptake. Hydroxyzine and tracazolate, two anxiolytic agents, inhibited uptake as did flunarizine, a coronary vasodilator. Two calmodulin antagonists, W7 and R 24571, were effective inhibitors of adenosine uptake. Their IC50 values were comparable to those at which they have been demonstrated to inhibit calmodulin-mediated reactions in other systems. These observations suggest that adenosine uptake may be a calmodulin-regulated process.

Disulfiram-like effect of diethyl maleate on barbiturate-induced hypnosis and 5-hydroxytryptamine metabolism

Diethyl maleate (DEM, 600 mg kg-1 i.p.) significantly potentiated hexobarbitone hypnosis and lowered plasma hexobarbitone level on awakening. Sleeping time following intracerebroventricular (i.c.v.) injection of phenobarbitone was also prolonged by DEM treatment. When administered to DEM-treated rats, L-tryptophan (50 mg kg-1 i.p.) significantly potentiated hexobarbitone hypnosis, although alone it had no effect in control rats. DEM markedly diminished the activity of brain low-Km aldehyde dehydrogenase (A1DH) and the formation of 5-hydroxyindoleacetic acid from 5-hydroxytryptamine (5-HT) without affecting MAO activity in various areas of the brain. Conversely, the protein-bound radioactivity derived from i.c.v. [14C]-5-HT was increased by DEM treatment. These results showed that DEM is comparable with disulfiram, a brain A1DH inhibitor, in terms of its effect on 5-HT metabolism and barbiturate hypnosis.

Specific binding of [3H]prostaglandin E2 to rat brain membranes and synaptosomes

There is saturable, reversible and specific binding for [3H]prostaglandin E2 (PGE2) to rat brain membranes. This binding is of high affinity, selectively distributed with a maximum in the hypothalamus, the amygdala and the posterior pituitary, and is associated subcellularly with the synaptosomal fraction. This specific PGE2 binding has the characteristics expected for receptors, so opening new perspectives which might clarify the role of PGs in the brain.

Effect of prostaglandin E1 and its biosynthesis inhibitor indomethacin on drinking in the rat

In the rat, injection of prostaglandin E1 (PGE1) 0.5, 1.0 or 2.0 microgram into the 3rd brain ventricle (3rd b.v.) inhibited the water deprivation-induced water intake in a dose-related fashion. The 1.0 microgram dose of PGE1 also inhibited the intake of 1.8% sodium chloride in rats depleted of body sodium by intraperitoneal dialysis, and of food in food deprived rats during a 60 min test period. Prostaglandin E1 (1 microgram) depressed the dipsogenic effect of angiotensin II (AII) or carbachol injected through the same cannula. Water-deprived rats pretreated with the PG synthetase inhibitor indomethacin, in two different doses, showed enhanced water intake. The pretreatment with indomethacin also enhanced the dipsogenic effect of various doses of AII injected into the 3rd b.v. The antagonistic action of PGE1 on water-deprivation, or AII-induced water intake, and the enhancement of water intake after blocking PGs synthesis, suggests the involvement of PG in the regulation of thirst.

Changes in body temperature after administration of acetylcholine, histamine, morphine, prostaglandins and related agents

This survey, the second in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of cholinergic agonists and antagonists, histamine and H1- and H2-receptor antagonists, narcotic analgesics and antagonists in both non-tolerant and tolerant subjects and of prostaglandins and related agents. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.

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.

Stimulation of gastric secretion by prostaglandin F2 alpha in rats

In rats with chronic gastric fistulas, prostaglandin F2 alpha stimulated the gastric acid secretion in graded doses of 50, 100, 200 and 400 microgram/kg b.wt, while higher doses above 1 mg/kg b.wt tended to inhibit significantly. The gastric antisecretory effect of prostaglandin E1 could not be altered or modified by subsequent treatment of prostaglandin F2 alpha, while the latter alone without any prior treatment of the former, stimulated output of gastric juice, HCl and pepsin without significantly affecting the concentration of these components.

The antinociceptive effect of intracerebroventricularly administered prostaglandin E1 in the rat

It is generally accepted that prostaglandins (PGs) are nociceptive substances. However, earlier studies from this laboratory indicated that morphine analgesia, in the rat, was not only serotonin mediated, but involved PGs as well. Several PG synthesis inhibitors were shown to inhibit morphine analgesia and PGE1 was shown to potentiate the antinociceptive effect of morphine. Intraperitoneal administration of PGE1, but not PGE2 and PGF2alpha, elicited antinociceptive effect per se, by the radiant heat method. The present study was undertaken to confirm the antinociceptive action of PGE1, after intracerebroventricular administration, against nociceptive impulses induced by radiant heat, pressure, and high frequency electric current. PGE1 produced a dose-dependent antinociceptive effect by the radiant heat and pressure methods. It potentiated the antinociceptive action of morphine by the electrical stimulation method. The antinociceptive action of PGE1 was not evident in 5,6-dihydroxytryptamine-pretreated rats, suggesting that this effect is serotonin mediated. The present study thus confirms the antinociceptive action of PGE1 and suggests that, unlike its peripheral action, the central action of PGE1 results in suppression of nociceptive responses which may be serotonin mediated.

Effect of some prostaglandin synthesis inhibitors on the antinociceptive action of morphine in albino rats

1. Five prostaglandin synthesis inhibitors, indomethacin, diclofenac, mefenamic acid, ibufen and paracetamol, were found to inhibit the antinociceptive action of morphine without affecting the antinociceptive response of an equi-analgesic dose of prostaglandin E1. 2. Diclofenac was found to be the most potent and longest acting, whereas paracetamol was the least potent and shortest acting. Indomethacin, mefenamic acid and ibufen occupied an intermediate position, both in potency and duration of action. 3. The results suggest that prostaglandins may be involved in the antinociceptive action of morphine in albino rats.

Prostaglandin E1-induced potentiation of the anticonvulsant action of phenobarbitone in the rat. Role of brain monoamines

Prostaglandin E1 (PGE1) significantly potentiated the anticonvulsant action of a sub-effective (EDO) dose of phenobarbitone, against maximal electroshock-induced seizures in the rat. PGE1-induced potentiation of phenobarbitone was significantly inhibited after pretreatment with drugs which are known to reduce brain serotonin activity, but was unaffected by drugs known to decrease brain catecholamine activity. Prostaglandin F2 alpha produced a moderate though statistically insignificant inhibition of PGE1 effect. The results suggest that PGE1-induced potentiation of phenobarbitone is not a direct effect but an indirect one, mediated through an increase in brain serotonin activity.

Inhibition of pentylenetetrazol-induced convulsions in rats by prostaglandin E1: role of brain monoamines

Prostaglandin E1-(PGE1-) induced inhibition of pentylenetetrazol (PTZ) convulsions in rats were significantly antagonized after pretreatment with drugs known to reduce brain serotonin activity, but not by pharmacological agents that decrease brain catecholamine activity. PGF2alpha also significantly inhibited PGE1 action. The results suggest that PGE1-induced inhibition of PTZ convulsions is not a direct effect, but an indirect one mediated through increase in brain serotonin activity.

Prostaglandins and sleep. Awaking effect of prostaglandins and sleep pattern of essential fatty acids deficient (EFAD) rats

The experiments were carried out to investigate the effects of prostaglandins (PGs) on the sleep pattern in the cat, and in normal and EFAD rats. The data indicate that the duration of slow wave sleep (SWS) was significantly longer in EFAD rats compared with the normal rats. However, no difference in the REM sleep was observed between the two groups. Intraventricular (i.vc. )administration of PGE1, PGE2 and PGF2alpha increased wakefulness without a significant alteration of REM sleep. PGE1 administered i.vc. did not alter the duration of SWS or REM sleep in the chronic cat, but induced ponto-geniculo-occipital (PGO) waves (spikes) which are the phasic phenomenon of REM sleep. The fact that previous administration of 5-hydroxytryptophane abolished the PGE1-induced PGO spiking, might indicate that this drug triggered the spikes mainly via the functional inhibition of the serotonergic system.

Prostaglandin-induced effects in the primate cerebral circulation

The effects of intracarotid infusions of prostaglandins E2 and F2alpha on cerebral blood flow (CBF) and oxygen consumption (CMRO2), and on extracranial blood flow, have been studied in anaesthetisex baboons. The 133Xe clearance method was used for measuring CBF, whilst extracranial blood flow was assessed by both the local tissue injection of 133Xe and external carotid artery flowmetry. Both PGF2alpha and PGE2 (10(-7) and 10(-6) g/kg/min) reduced both CBF and CMRO2. Spasm of the internal carotid artery with PGE2 was noted at the higher dose. Following osmotic opening of the blood-brain barrier by the hypertonic urea technique, the effects of small doses of PGE2 and CBF and CMRO2 were greatly potentiated. PGE2 greatly increased extracranial blood flow. Hence, both PGE2 and PGF2alpha reduce CBF and CMRO2, whilst PGE2 greatly increases extracranial blood flow.

Prostaglandins: antinociceptive effect of prostaglandin E1 in the rat

1. The antinociceptive effect of prostaglandins E1, E2 and F2alpha was studied in albino rats. Though all three prostaglandins produced similar degrees of sedation, only prostaglandin E1 (PGE1) produced a dose-related antinociceptive activity. 2. The antinociceptive activities of equi-analgesic doses of morphine (7.5. mg/kg, i.p.) and PGE1 (2.0 mg/kg, i.p.) were inhibited to almost similar extents after pretreatment with drugs known to reduce central turnover of serotonin receptors, namely reserpine, fenclonine (p-chlorophenylalanine), methysergide and 5,6-dihydroxytryptamine. 3. Prostaglandin F2alpha (2.0 mg/kg, i.p.) significantly inhibited the antinociceptive effects of both morphine and PGE1. 4. The prostaglandin synthesis inhibitors, indomethacin and diclofenac, significantly inhibited morphine analgesia. 5. Probenecid markedly prolonged the duration of antinociceptive effect of morphine and the duration of PGE1-induced potentiation of subanalgesic dose of morphine. 6. The results suggest that, in albino rats, PGE1-induced antinociceptive activity is serotonin mediated and that morphine analgesia is not only mediated through serotonin but also through prostaglandins (PGE1 ?) and 5-hydroxyindole acetic acid, the serotonin metabolite.

Effects of acetylsalicylic acid and indomethacin on growth hormone secretion in man

To investigate the possibility that prostaglandins (PG) take part in the control of growth hormone (GH) secretion in humans, we have studied the effects of protracted and acute administration of acetylsalicylic acid (ASA) and indomethacin (ID), two PG synthesis inhibitors, on basal and insulin-stimulated GH secretion in normal volunteers. In eight subjects, oral administration of 3-2 g daily of ASA for 4 days clearly reached GH response to insulin hypoglycemia (p less than 0.01, ANOVA). In six additional subjects, GH response to hypoglycemia was not modified by a 4-day oral treatment with 300 mg daily of ID. The pattern of plasma free fatty acids (FFA) and blood glucose during the insulin tolerance test was not significantly affected by ASA treatment. After ID the O time value of the above parameters was somewhat higher than under basal conditions, while the drop of blood glucose, but not to FFA, was slightly more pronounced. Acute oral administration of 1.5 g ASA in 12 subjects did not appreciably modify baseline plasma GH, FFA, and blood glucose levels. By contrast, a single oral dose of 100 mg ID in 12 subjects caused a moderate but significant rise (p less than 0.05) of plasma GH levels together with a clear elevation (p less than 0.01) of plasma FFA and blood glucose levels with respect to a group of controls treated with a placebo. Collectively these results are compatible with the possibility that PG play a physiologic stimulating role in the control of GH secretion, although an effect of ASA and ID unrelated to PG inhibition cannot be ruled out, In any event, in view of the number of endocrine and metabolic alterations induced by ASA and ID, these drugs seem to merit further study.

Role of 5-hydroxytryptamine in prostaglandin E1-induced potentiation of hexobarbitone hypnosis in albino rats

PGE1 potentiated, while diclofenac, a prostaglandin synthesis inhibitor, antagonized hexobarbitone hypnosis in rats. PGE1-induced potentiation of hexobarbitone sleep was inhibited by a 5HT synthesis inhibitor and by a 5HT receptor blocker, suggesting that this potentiation is 5HT mediated.

Dual action of morphine and related drugs on compulsive gnawing of rats

Rats received daily i.p. injections of p-chlorophenylalanine (PCPA) for 3 days, before morphine and related drugs were implanted into the lateral thalamus or injected systemically. PCPA enhanced the stereotyped response to morphine, methadone, and apomorphine, as expressed by compulsive gnawing, but abolished the antagonistic effect of large doses of i.p. morphine. Thus, suppression of gnawing by large doses of systemic morphine and related analgesics may be mediated by a serotoninergic pathway. PCPA also brought to light the ability of pethidine to cause gnawing, which is otherwise suppressed by the strong antagonistic effect of this drug. Morphine and related analgesic drugs exert a dual effect: stimulation of gnawing via a catecholaminergic mechanism and inhibition of gnawing by a serotoninergic mechanism.

Intracerebral prostaglandin E2: effects upon sexual behavior, open field activity and body temperature in ovariectomized female rats

A single 27 gauge implant of PGE2 into the periventricular region of the hypothalamus resulted in a significant increase in sexual receptivity in estrogen primed, ovariectomized female rats. Open field activity levels were only slightly decreased while rectal body temperature increased significantly over control values. It is postulated that the effects upon sexual receptivity might be mediated by PGE2 stimulated LRF release.

Potentiation of antinociceptive action of morphine by prostaglandin E1 in albino rats

1. Prostaglandin E1 (0.4 ml/kg, i.p.) significantly potentiated the antinociceptive action of morphine in albino rats. 2. This potentiation was significantly inhibited by pretreatment with reserpine, p-chlorophenylalanine or methysergide but not by alpha-methyl-p-tyrosine, phentolamine or propranolol. 3. The results suggest that the potentiation of morphine by prostaglandin E1 is mediated by serotonin, since it is inhibited by pharmacological agents known to reduce central turnover of serotonin receptors.

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.