The Antinociceptive Activity of The Aqueous Extract of Carica Papaya Seeds (cpe) in Mice.

Pain is a symptom of disease or damage that occurs most frequently. Pain serves to remind and protect and facilitate the diagnosis of disease. Pain is a protective mechanism for the body that would arise if there is a damaged body tissues1. It is believed that current analgesia-inducing drugs as opioids and Non-Steroidal Anti-inflammatory drugs (NSAIDs) are not useful in all cases because of their side effects and low potency2. The NSAIDs are associated with gastric irritation, bleeding, ulcers and perforation3. As a result, search for other alternatives become necessary. The history of medicinal plants is intimately connected with the history of civilization. According to the world health organization, about 80% of the population in many countries still use medicinal plants for their primary health care due to poverty and lack of access to modern medicine4. Considering that the most important analgesic prototypes (e.g. salicylic acid and morphine) were originally derived from plant sources, the study of plant species traditionally used as painkillers should be a fruitful research strategy in the search of new analgesic and anti-inflammatory drugs.

Carica papaya is a medicinal plant that originated from Central America, which has spread to different parts of the world, Africa and Nigeria. It contains two major bioactive compounds namely papain and chymopapain, which are used in brewing, wine making, textile and tanning industries6. Carica papaya is a known medicinal plant in that it contains substances that can be used for therapeutic purposes. This plant has been recommended as an anti-ulcerogenic, anti-amoebic, anti-fungal, anti-microbial, anti-tumour, hypolipidemic and employed in wound-healing activity, free radical scavenging activity, diuretic activity, uterotonic activity and antifertility activity7,8. Nsukka indigenes chew the dry seeds of Carica papaya to alleviate nagging headache (migraine) and in reducing swollen wounds and reducing high blood pressure. The methanol seed extract of Carica papaya has been reported to have antinociceptive and anti-inflammatory activity in mice and rats9.

Therefore, the present study was undertaken to evaluate the analgesic activity of aqueous extract of Carica Papaya Seeds in mice.

Plant material and Extraction: four mature, unripe fruits of Carica papaya were collected from a local market and authenticated. The papaya fruits were cut into pieces and the wet seeds were separated out. These were then gently but thoroughly rinsed in tap water two times and completely air-dried at room temperature for 4 weeks. The dried seeds were pulverized into the fine powder using a domestic mixer grinder. 50 g of powdered seeds were boiled in 500 ml of distilled water for 30 minutes after which it was filtered using a piece of clean white cotton gauze. The filtrate was evaporated to complete dryness at 40 0 C, producing a fine sweet smelling and chocolate color solid residue (yield: 22.5%, w/w). The extraction process was repeated 4 times and the solid residue was weighed and pooled together in an air and waterproof container kept in a refrigerator at 4 0 C. From this fresh preparation were made whenever required.

Experimental Animals: Mice weighing between 25-30 gm were divided into 5 groups of 6 mice each. The animals were maintained with standard pellet diet and water ad libitum and they were allowed to acclimatize to the housing conditions for at least one week to adjust to the new environment. All the experiments were conducted as per the norms approved by Institutional Animal Ethics Committee

Acetic Acid-Induced Writhing in Mice:

The writing was induced by the method of Koster et al10. The control group 1 received 0.2 ml normal saline orally. The standard group 2 received 10 mg/kg body weight of diclofenac sodium orally. The test groups 3, 4 and 5 were administered 100, 200 and 400 mg/kg body weight of aqueous extracts of Carica papaya seeds orally. The animals were fasted for 16 hours prior to the treatments. One hour after treatment, the mice were injected intraperitoneally with 0.2 ml of 3% acetic acid solution to induce the writing. The number of abdominal constrictions and stretching with a jerk of the hind limb were counted between 5 and 15 minutes after acetic acid injection. A writhe is indicated by abdominal constriction and full extension of the hind limb. The response of the extract treated test groups and diclofenac treated standard group was compared with those of the animals in the control group. Percentage protections against writhing movements was taken as an index of analgesia and it was calculated as follows:

% Inhibition = Wm (Control) – Wm (test group) / Wm (Control) X 100 Where Wm = Mean number of writing.

Statistical Analysis:

The results were presented as mean ± S.E.M and subjected to one way ANOVA test & P values less than 0.05 were considered significant.

Acetic Acid-Induced Writhing in Mice:

The results of the analgesic effect of Carica Papaya extract using acetic acid-induced abdominal writhing is presented in Table 1. Diclofenac sodium (10 mg/kg) and CPE (400 mg/kg) significantly (p < 0.05) decreased the number of acetic acid-induced abdominal writhing. Percentage inhibition of writing produced by the CPE 400mg/kg (60.8%) was comparable to the standard drug diclofenac (70.3%). This percentage inhibition has been depicted with the help of Graph 1.

The results obtained with acetic acid-induced writhing are shown in Table 1. The standard drug (diclofenac) and the aqueous extract at 400 mg/kg had significant difference with the control group. This means that the extract has effect on peripheral pains as the writhe test is used to test for peripheral analgesia. The acetic acid-induced writhing method was used to evaluate the effect of analgesics drugs on visceral pain11. This pain mechanism is believed to involve local peritoneal receptors12. Intraperitoneal administration of acetic acid releases prostaglandins and sympathomimetic system mediators like prostaglandin E2 (PGE2) and prostaglandin GF2a (PGF2a) and their levels are increased in the peritoneal fluid13. The abdominal constriction observed during the test is related to the sensitization of nociceptive receptors by these prostaglandins. It is therefore possible that aqueous extract of Carica papaya have significant effect by inhibition of the synthesis or action of prostaglandins, thereby having inhibitory effects on peripheral pains.

In conclusion, the aqueous seed extract of Carica papaya has significant anti-nociceptive effects on mice and these effects are comparable to standard drug (diclofenac sodium). Further studies are needed in this direction.