Subcutaneous L-tyrosine elicits cutaneous analgesia in response to local skin pinprick in rats

Effects of different colors of plastic-film mulching on soil temperature, yield, and metabolites in Platostoma palustre

Platostoma palustre is an annual herb and an important medicinal and edible plant in southern China. Plastic-film mulching is an effective agronomic practice in the cultivation system of P. palustre, of which black-film mulching is the most common. However, fewer researches have been focused on the use of other colors of plastic films in P. palustre cultivation. In this study, different colors (white, black, red, and green) of plastic film were adopted, and the effects of different colors of plastic film mulching on the soil temperature, yield, and metabolites of P. palustre were investigated. The results showed that the fresh weight of a single plant of the green film treatment was significantly higher than that of the white film treatment (n = top 28). Based on the results of three temperature measurements, the soil temperature was almost the highest in the red film treatment and lowest in the white film treatment. The metabolomic analysis revealed that a total of 103 differential metabolites were identified. Among these, the gluconic acid, deoxyribose, and N-Acetylmannosamine in the red film treatment presented the highest abundance compared with the other treatments, meanwhile, the abundances of the five monosaccharides in the red film treatment were significantly higher than those of the green film treatment. Moreover, the sucrose, trehalose, and D-(+)-trehalose in the green film treatment exhibited the highest abundance, and the abundances of eight different amino acids in the red film treatment were almost the lowest while those in the black film treatment were almost the highest. Further analysis of the membership function values indicated that the black and red film treatments might be more suitable for the cultivation and quality production of P. palustre in comparison with the other two treatments. This study will provide a theoretical basis for improving the efficient cultivation technology of P. palustre and forming a theoretical system of P. palustre film mulching cultivation.

Integrating LC-MS and HS-GC-MS for the metabolite characterization of the Chinese medicinal plant Platostoma palustre under different processing methods

Platostoma palustre (or Mesona chinensis Benth) is an important medicinal and edible plant in China and Southeast Asian countries. To study the effects of different processing methods on the quality, nutrition, and flavor of P. palustre, we adopted the LC-MS and HS-GC-MS to compare the influences of tedding (S), sweating (M), and drying (H) on the metabolites and volatile substances of P. palustre. Biochemical determinations revealed that the M treatment could promote the accumulation of the contents of total sugar, soluble sugar, and total pectin compared with the H and S treatments but decrease the total flavonoid contents. LC-MS and HS-GC-MS uncovered 98 differential metabolites and 27 differential volatile substances among the three treatments, respectively. Overall, the M treatment facilitated the stabilization and improvement of the quality of polysaccharides and volatile substances, while the H treatment could promote the level of amino acids in P. palustre. The current study provided a theoretical reference for establishing standardized processing methods and sustaining the quality stability of P. palustre in future.

Phentolamine Reverses Epinephrine-Enhanced Skin Antinociception of Dibucaine in Rats

BACKGROUND

The objective of the experiment was to assess the antinociceptive effect of dibucaine, bupivacaine, and epinephrine. To assess the mechanism of action of the interaction between dibucaine and epinephrine, phentolamine, a nonselective α-adrenergic antagonist, was added to the mixture.

METHODS

We assessed sensory blockade with these drugs by injecting 0.6 mL of drug-in-saline in the dorsal thoracolumbar area of rats; pinprick of the "wheal" formed by the injectate was the area targeted for stimulation to elicit a cutaneous trunci muscle reflex. The sensory block of dibucaine was compared with that of bupivacaine or epinephrine. Drug-drug interactions were analyzed by isobologram. Phentolamine was added to investigate the antinociceptive effect of dibucaine coinjected with epinephrine.

RESULTS

We demonstrated that dibucaine, epinephrine, and bupivacaine produced dose-dependent skin antinociception. On the median effective dose (ED50) basis, the potency was higher for epinephrine (mean, 0.011 [95% confidence interval {CI}, 0.007-0.015] μmol) than for dibucaine (mean, 0.493 [95% CI, 0.435-0.560] μmol) (P < .01), while there were no significant differences between dibucaine and bupivacaine (mean, 0.450 [95% CI, 0.400-0.505] μmol). On the equipotent basis (75% effective dose, median effective dose, and 25% effective dose), sensory block duration provoked by epinephrine was greater (P < .01) than that provoked by dibucaine or bupivacaine. Coadministration of dibucaine with epinephrine produced a synergistic nociceptive block, whereas phentolamine blocked that synergistic block.

CONCLUSIONS

The preclinical data indicated that there is no statistically significant difference between the potency and duration of dibucaine and bupivacaine in this model. Epinephrine synergistically enhances the effects of dibucaine, while phentolamine partially blocked those effects. α-Adrenergic receptors play an important role in controlling synergistic analgesic effect of dibucaine combined with epinephrine.

Spinal sensory and motor blockade by intrathecal doxylamine and triprolidine in rats

OBJECTIVES

The aim of this experiment was mainly to examine the effects of intrathecally injected doxylamine and triprolidine, two antihistamine drugs spinal motor and sensory functions.

METHODS

After intrathecally injecting the rats with five different doses, the dose-response curves of spinal sensory and motor block with doxylamine and triprolidine were constructed. In comparison with the local anaesthetic mepivacaine, the quality and duration of spinal anaesthesia with doxylamine or triprolidine were conducted.

KEY FINDINGS

Doxylamine, mepivacaine and triprolidine elicited spinal motor and sensory (nociception and proprioception) blockades in a dose-dependent fashion. On the ED₅₀ (50% effective dose) basis, the rank order of drug potency was triprolidine > mepivacaine > doxylamine (P < 0.05) at provoking spinal motor, proprioceptive and nociceptive blockades. On the equianaesthetic doses (ED₂₅ , ED₅₀ and ED₇₅ ), the duration of spinal anaesthesia with doxylamine was longer (P < 0.01) than that with mepivacaine or triprolidine. Moreover, doxylamine or triprolidine displayed greater potency (ED₅₀ ) (P < 0.05) and duration (P < 0.05) of sensory block over motor block.

CONCLUSIONS

Doxylamine or triprolidine produces a dose-dependent effect of spinal motor and sensory block. Triprolidine with a better nociception-selective action over motor block has a better potency than mepivacaine or doxylamine. Doxylamine and triprolidine produce longer durations than mepivacaine.

Subcutaneous infiltration of doxylamine on cutaneous analgesia in rats

BACKGROUND

We aimed to evaluate the effect of doxylamine, a first generation antihistamine, as a local analgesic agent by comparing its effect to bupivacaine.

METHODS

After blocking the cutaneous trunci muscle reflex (CTMR) by subcutaneous injection of doxylamine, we assessed doxylamine's cutaneous analgesic effect in rats. The dose-related effect and duration of doxylamine on infiltrative cutaneous analgesia were compared with that of bupivacaine.

RESULTS

We demonstrated that doxylamine, as well as the local anesthetic bupivacaine produced the cutaneous analgesic effects in a dose-related fashion. At the equipotent dose (50% effective doses (ED₅₀)), the relative potency was bupivacaine (0.41 (0.36-0.48) mmol)> doxylamine (7.39 (6.91-7.91)mmol) (p<0.01). On an equipotent basis (ED₂₅, ED₅₀ and ED₇₅), subcutaneous doxylamine resulted in greater duration of action (p<0.01) than bupivacaine at producing cutaneous analgesia.

CONCLUSIONS

The result of this experiment indicated that doxylamine has the local anesthetic property less potent than bupivacaine, but its nociceptive block duration is longer than that of bupivacaine at an equianalgesic dose.

Adding Dopamine to Proxymetacaine or Oxybuprocaine Solutions Potentiates and Prolongs the Cutaneous Antinociception in Rats

BACKGROUND

We evaluated the interaction of dopamine-proxymetacaine and dopamine- oxybuprocaine antinociception using isobolograms.

METHODS

This experiment uses subcutaneous drug (proxymetacaine, oxybuprocaine, and dopamine) injections under the skin of the rat's back, thus simulating infiltration blocks. The dose-related antinociceptive curves of proxymetacaine and oxybuprocaine alone and in combination with dopamine were constructed, and then the antinociceptive interactions between the local anesthetic and dopamine were analyzed using isobolograms.

RESULTS

Subcutaneous proxymetacaine, oxybuprocaine, and dopamine produced a sensory block to local skin pinpricks in a dose-dependent fashion. The rank order of potency was proxymetacaine (0.57 [0.52-0.63] μmol/kg) > oxybuprocaine (1.05 [0.96-1.15] μmol/kg) > dopamine (165 [154-177] μmol/kg; P < .01 for each comparison) based on the 50% effective dose values. On the equianesthetic basis (25% effective dose, 50% effective dose, and 75% effective dose), the nociceptive block duration of proxymetacaine or oxybuprocaine was shorter than that of dopamine (P < .01). Oxybuprocaine or proxymetacaine coinjected with dopamine elicited a synergistic antinociceptive effect and extended the duration of action.

CONCLUSIONS

Oxybuprocaine and proxymetacaine had a higher potency and provoked a shorter duration of sensory block compared with dopamine. The use of dopamine increased the quality and duration of skin antinociception caused by oxybuprocaine and proxymetacaine.

Isobolographic analysis of the cutaneous antinociceptive interaction between bupivacaine co-injected with serotonin in rats

BACKGROUND

The aim of this experiment was to investigate a long-lasting local anesthetic bupivacaine combined with serotonin at inducing cutaneous antinociception.

METHODS

The skin antinociception, characterized by an inhibition of the cutaneous trunci muscle reflex (CTMR) following the pinprick on the dorsal skin of rats, was evaluated. The cutaneous antinociceptive effects of bupivacaine alone, serotonin alone, or bupivacaine co-injected with serotonin in a dose-dependent fashion were constructed, while the drug-drug interactions were evaluated by isobologram.

RESULTS

Subcutaneous serotonin, as well as the local anesthetic bupivacaine provoked dose-related cutaneous antinociception. On an equipotent basis (50% effective dose [ED₅₀]), the relative potency was bupivacaine (0.43 [0.37-0.50] μmol)>serotonin (1.27 [1.15-1.40] μmol) (p<0.01). At the equi-anesthetic doses (ED₇₅, ED₅₀ and ED₂₅), the duration of bupivacaine was similar to that of serotonin at producing cutaneous antinociceptive effects. Co-administration of bupivacaine and serotonin displayed a synergistic antinociception.

CONCLUSIONS

The preclinical data demonstrated that serotonin is less potent in eliciting cutaneous antinociceptive effects but has the similar duration of action, compared with bupivacaine. We also found a more significant depth of the sensory block with bupivacaine+serotonin than bupivacaine alone.

Mexiletine co-injected with clonidine increases the quality and duration of cutaneous analgesia in response to skin pinpricks in the rat

The goal of the experimental design was to assess the cutaneous analgesic effect of mexiletine by co-injection with clonidine. The effect of nociceptive block was evaluated according to the inhibition of the cutaneous trunci muscle reflex (CTMR) in response to skin pinpricks in rats. The dose-related analgesic effect of mexiletine alone or mexiletine co-administrated with clonidine was constructed after subcutaneous injection. Subcutaneous injections of mexiletine elicited dose-related cutaneous analgesia. Compared with mexiletine (1.8μmol), adding clonidine to mexiletine (1.8μmol) solutions for skin nociceptive block potentiated and prolonged the action (p<0.01). Mexiletine (6μmol) combined with clonidine extended the duration of cutaneous analgesia when compared with mexiletine (6μmol) alone (p<0.01). Co-administration of clonidine increases the potency and extends the duration of cutaneous analgesia by mexiletine, and the minimal dose of clonidine to intensify the analgesic effect is 0.06μmol.

Synergistic Effects of Serotonin or Dopamine Combined With Lidocaine at Producing Nociceptive Block in Rats

BACKGROUND

The purpose of this experiment was to investigate the interactions of the local anesthetic lidocaine combined with an agent (serotonin or dopamine) as infiltrative anesthetics.

METHODS

Cutaneous analgesia was characterized by the blockade of the cutaneous trunci muscle reflex following 6 skin pinpricks on the rat back. Serotonin or dopamine at producing cutaneous analgesia in a dosage-dependent fashion was compared with lidocaine. Drug-drug interactions were calculated using the isobolographic analysis.

RESULTS

We revealed that serotonin, dopamine, and lidocaine provoked dose-related cutaneous analgesic effects. On the 50% effective dose basis, the rank of drugs' potency was found to be serotonin (1.70 [1.56-1.85] μmol) > lidocaine (5.18 [4.67-5.75] μmol) > dopamine (43.0 [40.9-45.2] μmol) (P < 0.01). At doses equivalent to their 25%, 50%, and 75% effective doses, serotonin or dopamine elicited a longer duration of action than lidocaine (P < 0.01) on producing cutaneous analgesia. Coadministration of serotonin or dopamine with lidocaine produced a synergistic effect.

CONCLUSIONS

The preclinical data showed that serotonin and dopamine produce dose-related cutaneous analgesic effects as an infiltrative anesthetic. Serotonin has a better potency with a much longer duration of action compared with lidocaine at provoking cutaneous analgesia. Serotonin or dopamine as an adjuvant increases the quality of lidocaine in cutaneous analgesia.