Analgesic activity of Nelsonia canescens (Lam.) Spreng.root in albino rats.

Present study was undertaken to evaluate analgesic activity of root of Nelsonia canescens (Lam.) Spreng, a folklore medicinal plant used as the one of the source plant of Rasna. Study was carried out at two dose levels (270 mg/kg and 540 mg/kg) in albino rats. Analgesic activity was evaluated in formalin induced paw licking, and tail flick methods whereas indomethacin and pentazocine were used as standard analgesic drugs, respectively. At both the dose levels, test drug non-significantly decreased paw licking response at both time intervals. In tail flick model, the administration of the test drug increased pain threshold response in a dose dependent manner. In therapeutically equivalent dose level, analgesic activity was observed only after 180 min while in TED ×2 treated group analgesia was observed at 30 min and lasted even up to 240 min. The results suggested that N.canescens root possess moderate analgesic activity.

Introduction

Over three-quarters of the world population relies mainly on plants and plant extracts for health care. More than 30% of the entire plant species, at one time or other was used for medicinal purposes. Traditional systems of medicine continue to be widely practiced on many accounts. Population rise, inadequate supply of drugs, prohibitive cost of treatments, side effects of several allopathic drugs, and development of resistance to certain currently used drugs for infectious diseases have led to increased emphasis on the use of plant materials as a source of medicines for a wide variety of human ailments.

Nelsonia canescens (Lam.) Spreng., is one of the medicinal plants growing abundantly in various parts of India. Traditionally the root of this plant is used by traditional healers of Gandhamardan hills of Orissa in the local name of Badarasna (Rasna) for the management of pain and inflammatory conditions such as arthritis, cutting wound, and bone fractures.[1] In spite of its reputation in treating these ailments, till date no pharmacological work to support these claims has been reported hence the present study was under taken to evaluate the analgesic activities of N.canescens (Lam.) Spreng. root in albino rats.

Materials and Methods

Plant material

Fresh and matured plant of N.canescens (Lam.) Spreng.was collected in December from its natural habitat of Gandhamardana hill ranges, Balangir, Orissa after spot identification with the help of traditional healers. Thus collected material was authenticated by pharmacognosist of the institute. The voucher specimen (Phm no. 6002/11) was deposited in pharmacognosy laboratory for future references. The roots were made into pieces, and shade dried for 12 days and then pulverized to a fine powder (mesh no. 120) and stored in an airtight container for experimental purposes.

Animals

Wistar strain albino rats of either sex weighing 180 ± 20 g were obtained from the animal house attached to the Pharmacology Laboratory, I.P.G.T. and R.A., Gujarat Ayurved University, Jamnagar. The animals were maintained on “Amrut” brand animal pellet feed of Pranav Agro Industries and tap water was given ad-libitum. The temperature and humidity were kept at optimum level and animals were exposed to natural day night cycles. The experiments were carried out in conformity with the guidelines of the Institutional Animal Ethics Committee after obtaining its permission (IAEC/08-11/04-M. Sc) and care of animals was taken as per the Committee for the Purpose of Control and Supervision on Experiments on Animals (CPCSEA) guidelines.

Dose fixation

The dose fixation for the experimental animals was done on the basis of body surface area ratio by referring to the standard table of Paget and Barnes.[2] The adult human dose (3 g/day) was converted to animal dose. On this basis, the rat dose was found to be 270 mg/kg. The study was carried out at two dose levels, viz., 270 mg/kg (therapeutically equivalent dose [TED]) and 540 mg/kg (TED × 2). The test drug was suspended in distilled water by making uniform suspension with 0.5% Carboxy Methyl Cellulose (CMC) with suitable concentration depending upon body weight of animals and administered orally with the help of gastric catheter sleeved to syringe. The drugs were administered to overnight fasted animals.

Analgesic activity

Formaldehyde induced paw licking in rats

The Wister strain albino rats of either sex were weighed and randomly divided into four groups of six each. First group received distilled water and served as a control group. The second and third groups received test drugs at TED and TED ×2, respectively. Indomethacin (10 mg/kg orally - Cipla) was used as standard analgesic drug. Pain was induced by injecting 0.1 ml of 3% formalin in distilled water in subplantar region of the right hind paw, and the duration of paw licking as an index of nociception was counted in periods of 0-10 min and 20-30 min.[3]

Tail flick test

Rats were placed on the tail flick unit so that constant heat intensity was applied to the lower third of the animal's tail. When the animal flicked its tail in response to the noxious stimulus both the heat source and timer were stopped. A cut-off time of 10 s was set to avoid tail damage. Thus, basal reaction time of each rat to radiant heat was recorded, and those having tail flick latency (TFL) less than 10 s were selected. First group of animals received similar volume of vehicle as test drug and served as normal control. Rats in group two and three were treated with TED and TED ×2 of test drug respectively. To the group four, standard analgesic drug - Pentazocineof (Ranbaxy Laboratories) was administered at a dose of 20 mg/kg i.p. The vehicle, test drug, and reference standard were administered to the respective groups 1 h prior to the experiment. The TFL was recorded at 30, 60, 120, 180, and 240 min.[4]

Statistical analysis

Results were presented as mean ± SEM. Student's t test as well as one-way analysis of variance were used for analyzing the data generated during the study with the level of significance set at P < 0.05.

Results

N.canescens root at both the dose levels non-significantly decreased paw licking response at both time intervals. Treatment with RS also apparently decreased paw licking response at both time intervals; however, only the decrease observed in paw licking response at 20-30 min is found to be statistically significant [Table 1].

Table 1

Effect of Nelsonia canescens on formalin induced paw licking response

Administration of the test drug increased pain threshold response in a dose dependent manner [Table 2]. In TED level analgesic activity was observed only after 180 min, while in TED ×2 treated group, an apparent elevation in the latency of tail-flick response was observed at 30 min and lasted up to 240 min. In pentazocine treated group also similar prolongation of tail-flick latency was observed at all-time intervals. However, the observed prolongation in both test drugs and pentazocine treated groups were found to be statistically non-significant.

Table 2

Effect of Nelsonia canescens on tail flick response

Discussion

When formalin is injected subcutaneously in to the paw, it produces intense pain reaction. The effect is seen in two phases. The initial phase lasts for 0-10 min of formaldehyde injection, it is supposed to be mediated through modulation of neuropeptides.[5] The second phase, which is observed 20-30 min of formaldehyde injection, is supposed to be mediated through release of inflammatory mediators like prostaglandin. Test drug at both dose levels non-significantly decreased the paw licking episodes at both the phases while indomethacin, which is a non-selective cyclooxygenase inhibitor significantly decreased paw licking episodes of the second phase.

Tail flick model, which is thermal induced nociception indicates narcotic involvement which is sensitive to opioid μ receptors.[6] In TED level analgesic activity was observed only after 180 min while in TED ×2 treated group analgesia was observed at 30 min and lasted up to 240 min, this shows prolonged analgesic effect of the test drug. Presence of analgesic activity in this model indicates that the mechanism of action is central. The mechanism through which this effect is brought about may be due to modulation of opioid receptors or by release of endogenous analgesic factors such as encephalin and endorphin.

Conclusion

From the present study, it can be concluded that roots of N. canescens have mild to moderate analgesic activity especially at higher dose. Hence, it can be preferred in the treatment of pain and inflammation.