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

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.

Sodium diclofenac inhibits hyperthermia induced by paradoxical sleep deprivation: the possible participation of prostaglandins

Sodium diclofenac inhibits hyperthermia induced by paradoxical sleep deprivation (PSD), which suggests the participation of prostaglandins. The temperature of paradoxical sleep-deprived rats increased from the first to the fourth day of deprivation. This hyperthermia was blocked on the second, third, and fourth days by daily administration, twice a day, of 10 mg/kg of sodium diclofenac, a potent prostaglandin synthesis inhibitor. In the dose of 10 mg/kg, a decrease of temperature was observed only on the second and third days of PSD. These data suggest the participation of prostaglandins in modulating the increase in temperature during PSD.

Effect of prostaglandin synthetase inhibitors on non-analgesic actions of morphine

The present study investigates the results of pretreatment with five prostaglandin (PG) synthetase inhibitors on effects of morphine on body temperature, pupillary diameter, body movement and production of exophthalmos in rat. Hyperthermia, induced by a low dose of morphine, was inhibited in animals pretreated with any of the PG synthetase inhibitors. However, PG synthetase inhibitors had no clear effect on hypothermia induced by higher doses of morphine. The duration of morphine-induced catalepsy was attenuated by pretreatment with the PG synthetase inhibitors in a dose-related manner. The exophthalmos induced by all doses of morphine was either shortened in duration or inhibited by sulindac, paracetamol or ibuprofen. Morphine-induced mydriasis was either attenuated or inhibited by paracetamol, ibuprofen or meclofenamic acid. The results suggest that endogenous PGs play a role in morphine-induced hyperthermia, catalepsy, exophthalmos and mydriasis whereas a physiological role for PGs in morphine-induced hypothermia was not indicated.

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.

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.

Immobilisation stress-induced antinociception in rats: possible role of serotonin and prostaglandins

Immobilisation of rats for 1, 2 and 4 h induced duration-related antinociception. Antinociception induced by 4 h immobilisation was significantly inhibited after pretreatment by drugs known to inhibit synthesis of serotonin, induce degeneration of serotonergic neurones and inhibit prostaglandin synthesis. The results indicate that immobilisation stress induces autoanalgesia, which may be dependent on the availability of endogenous serotonin and prostaglandins in rat brain.