Comparative measurement of spinal CSF microdialysate concentrations and concomitant antinociception of morphine and morphine-6β-glucuronide in rats

Comparative pharmacokinetics of tetramethylpyrazine phosphate in rat plasma and extracellular fluid of brain after intranasal, intragastric and intravenous administration

The purpose of this study was to compare the pharmacokinetic profiles of tetramethylpyrazine phosphate (TMPP) in plasma and extracellular fluid of the cerebral cortex of rats via three delivery routes: intranasal (i.n.), intragastric (i.g.) and intravenous (i.v.) administration. After i.n., i.g. and i.v. administration of a single-dose at 10 mg/kg, cerebral cortex dialysates and plasma samples drawn from the carotid artery were collected at timed intervals. The concentration of TMPP in the samples was analyzed by HPLC. The area under the concentration-time curve (AUC) and the ratio of the AUCbrain to the AUCplasma (drug targeting efficiency, DTE) was calculated to evaluate the brain targeting efficiency of the drug via these different routes of administration. After i.n. administration, TMPP was rapidly absorbed to reach its peak plasma concentration within 5 min and showed a delayed uptake into cerebral cortex (t max=15 min). The ratio of the AUCbrain dialysates value between i.n. route and i.v. injection was 0.68, which was greater than that obtained after i.g. administration (0.43). The systemic bioavailability obtained with i.n. administration was greater than that obtained by the i.g. route (86.33% vs. 50.39%), whereas the DTE of the nasal route was 78.89%, close to that of oral administration (85.69%). These results indicate that TMPP is rapidly absorbed from the nasal mucosa into the systemic circulation, and then crosses the blood-brain barrier (BBB) to reach the cerebral cortex. Intranasal administration of TMPP could be a promising alternative to intravenous and oral approaches.

Brainpeps: the blood-brain barrier peptide database

Peptides are able to cross the blood-brain barrier (BBB) through various mechanisms, opening new diagnostic and therapeutic avenues. However, their BBB transport data are scattered in the literature over different disciplines, using different methodologies reporting different influx or efflux aspects. Therefore, a comprehensive BBB peptide database (Brainpeps) was constructed to collect the BBB data available in the literature. Brainpeps currently contains BBB transport information with positive as well as negative results. The database is a useful tool to prioritize peptide choices for evaluating different BBB responses or studying quantitative structure-property (BBB behaviour) relationships of peptides. Because a multitude of methods have been used to assess the BBB behaviour of compounds, we classified these methods and their responses. Moreover, the relationships between the different BBB transport methods have been clarified and visualized.

Effects of quinidine on antinociception and pharmacokinetics of morphine in rats

Aim

The aim of this study was to investigate the effect of quinidine, a P-glycoprotein inhibitor, on the pharmacokinetics and pharmacodynamics of morphine in rats.

Methods

Rats were given morphine (30 mg/kg p.o. or 30 mg/kg over 10 min i.v.) 30 min after pretreatment with quinidine (30 mg/kg p.o.). Antinociceptive effects were determined using the tail immersion test. Concentrations of morphine in plasma and brain were also determined.

Key findings

The antinociception of morphine was significantly enhanced by oral administration of quinidine, with a 3.1-fold greater area under the effect–time curve than that in vehicle-treated rats. Morphine concentrations in plasma and brain were significantly increased by quinidine. The area under the plasma concentration–time curve after oral or intravenous administration of morphine was increased 5.2- and 1.7-fold, respectively, in quinidine-pretreated rats compared with vehicle-pretreated rats. Quinidine caused a 40% decrease in the total clearance of morphine and increased the concentration of morphine in the brain, although the brain-to-plasma concentration ratio was not changed.

Conclusions

Oral administration of quinidine increases the absorption of morphine from the gastrointestinal tract and subsequently enhances the concentration in the brain and its antinociceptive effect. Enhanced intestinal absorption of morphine may be due largely to inhibition of intestinal P-glycoprotein by quinidine.

Enhancement by grapefruit juice of morphine antinociception

The aim of this study was to investigate the effect of grapefruit juice intake on the antinociception of morphine in rats. The antinociception of morphine (30 mg/kg, per os (p.o.)) was significantly enhanced by the oral administration of grapefruit juice (2 ml/rat). Further, the effect of grapefruit juice was examined in morphine-tolerant rats. The repeated administration of morphine (100 mg/kg p.o.) for 5 d caused a marked decrease in the antinociception, indicating the development of morphine-tolerance. In the morphine-tolerant rats, oral administration of grapefruit juice potentiated significantly the antinociceptive effect of morphine. To examine the pharmacokinetics of morphine after the repeated treatment with morphine for 5 d, microdialysis probes were implanted into the jugular vein and spinal intrathecal space in rats. The morphine concentrations in the blood and intrathecal cerebrospinal fluid (CSF) were gradually decreased by the repeated treatment with morphine. The grapefruit juice treatment significantly increased the blood concentration of morphine in morphine-tolerant rats. These results suggest that oral administration of grapefruit juice enhances the morphine antinociception by increasing the intestinal absorption of this agent.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Intrathecally injected morphine inhibits inflammatory paw edema: the involvement of nitric oxide and cyclic-guanosine monophosphate

BACKGROUND

Morphine can inhibit inflammatory edema in experimental animals. The mechanisms and sites by which opioids exert this effect are still under debate. Since the spinal level is a site for modulation of the neurogenic component of inflammation, we investigated the effect of intrathecal (i.t.) administration of morphine, and the involvement of spinal nitric oxide (NO)/cyclic-guanosine monophosphate-GMP pathway in carrageenan (CG)-induced paw edema.

METHODS

Male Wistar rats received i.t. injections of drugs (20 microL) 30 min before paw stimulation with CG (150 microg). Edema was measured as paw volume increase (mL), and neutrophil migration was evaluated indirectly by myeloperoxidase (MPO) assay.

RESULTS

Morphine (37, 75, and 150 nmol) inhibited inflammatory edema, but had no effect on MPO activity. Coinjection with naloxone (64 nmol) reversed the effect of morphine. The corticosteroid synthesis inhibitor, aminoglutethimide (50 mg/kg, v.o.), administered 90 min before morphine injection did not modify its antiedematogenic effect. Low doses of the NO synthase inhibitor, N(omega)-nitro-L-arginine (L-NNA; 10 and 30 pmol) increased, while higher doses (3 and 30 nmol) inhibited edema. The guanylate cyclase inhibitor 1H-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 21 and 42 nmol) increased, while the phosphodiesterase type 5 inhibitor sildenafil (0.15 and 1.5 nmol) inhibited paw edema. Coadministration of a subeffective dose of L-NNA (3 pmol) or ODQ (10 nmol) with morphine prevented its antiedematogenic effect, but sildenafil (0.15 nmol) rendered a subeffective dose of morphine effective (18 nmol). ODQ also prevented the antiedematogenic effect of the NO donor S-nitroso-N-acetyl-penicilamine.

CONCLUSION

These results support the idea that morphine can act on opioid receptors at the spinal level to produce antiedematogenic, and that the NO/cGMP pathway seems to be an important mediator in this effect.

The role of nitric oxide in diabetes-induced changes of morphine tolerance in rats

Several neuroendocrine complications including diabetes change the morphine antinociception and the development of tolerance to the drug. Morphine antinociception was reduced significantly in morphine tolerant diabetic rats compared to the non-diabetic animals. The exact mechanism of this effect is not known. This study was performed to determine the role of nitric oxide (NO) on morphine tolerance in diabetic state. Nociceptive responses in alloxan-induced diabetic morphine tolerated rats were measured by the hot-plate test. The urinary nitric oxide level was measured spectrophotometrically with Griess reagent. For the conversion of nitrate to nitrite, vanadium chloride was used. The results showed that experimental diabetes increased morphine analgesia. Conversely, degree of tolerance to morphine was diminished in diabetic state. The urinary nitrite content in diabetic morphine tolerated rats was higher than non-diabetic groups. L-arginine significantly increased the NO production in diabetic morphine tolerated animals, whereas aminoguanidine decreased it. Appropriately, L-arginine increased the latency time of reaction to noxious stimuli in diabetic compared to non-diabetic rats. L-arginine-treated animals also showed more tolerance to morphine analgesia. As expected, aminoguanidine deducted the level of morphine tolerance in diabetic animals. It is suggested that NO has a modulatory role in the effects of diabetes on morphine analgesia and tolerance.