Rasa Nirdhāraṇa (assessment of taste) of Leonotis nepetifolia (L.) R. Br.: A preliminary study in healthy volunteers.

BACKGROUND: Rasa (a concept corresponding to taste) is the only perceivable parameter for drug identification in Ayurveda. The Ayurvedic pharmacological principles such as guṇa (quality), vīrya (potency) and vipāka (effect of biotransformation) are inferred based on the identified Rasa of a drug. All these principles together predict the probable spectrum of drug action in Ayurveda. It is mandatory to screen a drug in the Ayurvedic pharmacological perspective to incorporate it into Ayurvedic materia medica. AIM: To assess the rasa of a non classical herb, Leonotis nepetifolia (L.).R.Br. based on the lakṣaṇas (characteristics) described in Ayurvedic texts for the identification of individual rasa. SETTINGS AND
DESIGN: The study was conducted at the Department of Dravyaguna, Institute for Post Graduate Teaching and Reaseach in Ayurveda, Gujarat Ayurved University, Jamnagar.
MATERIALS AND METHODS: The whole plant powder (3g) of Leonotisnepetifolia was administered to 50 participants (trained Ayurvedic physicians) and their responses after intake of the drug were elicited using a structured questionnaire. RESULTS AND
CONCLUSION: On analyzing the data it was found that Leonotis nepetifolia possess predominantly tikta rasa (bitter taste) followed by Kaṣāya rasa (astringent taste). Recent researches and ethnomedicinal claims on Leonotis nepetifolia stand comparable with the pharmacological activities attributed to tikta and Kaṣāya rasa in Ayurvedic classics. Rasa nirdhāraṇa can be one of the preliminary steps to initiate the process of screening of an unknown drug along the lines of Ayurvedic pharmacology specially because rasa is the only perceivable parameter. According to Ayurveda, rasa of a dravya has a bearing on its karma (pharmacological action) and the identification of rasa could be one of the subjective means for inferring pāñcabhautika constitution of a substance which in turn could help in tentatively inferring guṇa, vīrya and vipāka of the dravya. This paper demonstrates how a simple method can be used without any instruments to do a preliminary assessment of the rasa or taste of a plant.

INTRODUCTION

Rasa (taste), guṇa (quality), vīrya (potency), vipāka (transformation) and prabhāva (inexplicable nature) are the principles of Ayurvedic pharmacology based on which every action of a dravya has been explained. Amongst this set of parameters, Rasa is the only quality manifested by substances that makes a gustatory appeal. Tastes of substances are six in number according to Ayurveda, i.e. svādu (sweet), amla (sour), lavaṇa (saltish/saline), tikta (bitter), kaṭu (pungent/acrid) and kaṣāya (astringent). Taste can only be considered as the nearest non-satisfactory equivalent for the term Rasa in the context of Ayurvedic pharmacology since taste perception and taste sensibility are considered as complex bio-physical and psychological events.[1] Thus Rasa refers to the total subjective experience arising on placing any substance in the mouth. The characteristics (Lakṣaṇas) for the identification of each rasa is well documented in Ayurvedic classics.[2345] At least three to five characteristics have been specified for each rasa [Table 1]. Some of the characteristics are unique whereas certain characteristics are found common amongst two or more rasas. This overlap, many a times hinders objective judgment. Moreover very few substances possess just a single rasa. The pāñcabhautika composition (combination of 5 protoelements) of a substance can be assessed based on the rasa identified in that substance which in turn helps in judging its other physical properties (gurvādiguṇas). Certain efforts have been made during the last quarter of 20th century to develop objective methodology for the assessment of Rasa. Prof C. Dwarakanath described the application of taste threshold experiments for identification as well as understanding the intensity of taste of Ayurvedic drugs.[1] On these lines, Prof SC Dhyani conducted the taste threshold test on 150 well known Ayurvedic raw drugs and documented their rasa and their respective intensities.[6] Phyto constituents in plants have also been used as marker compounds to quantify the intensity of certain tastes in food industry.[7] Preliminary attempts applying TLC and HPTLC techniques have been evolved in characterizing rasa using a few Ayuvedic drugs.[8] There are ongoing research studies to replace human tongue with electronic tongue and simultaneous application of electronic nose for identifying tastes.[9] Some previous studies have also drawn attention to the Ayurvedic concept of use of rasa for drug identification, drug action, new drug discovery[10] and a recent study on the ayurvedic concept of abhāvapratinidhidravya (drug substitution) establishes that similarity in rasa may be used as one of the tools to establish substitute drugs.[11] Studies have already reported that natural sources of medicinal plants are unable to meet the demand for popular herbal products.[11] Hence there is a compelling need to search for less known plants with multiple uses reported in ethnomedicine and incorporate them after thorough screening into popular use.

Table 1

Characteristics of individual taste documented in Ayurvedic texts

Leonotisnepetifolia (L.) R. Br is one such less known annual herb, native to Tropical Africa which is also found naturalized throughout the warmer parts of India.[12] There are about 23 ethno medicinal claims reported for this plant from various parts of India.[13] The herb is administered internally in the form of fresh juice, paste and decoction in ethnomedical practice.[13] Acute toxicity studies have been already reported for Leonotis nepetifolia and it was found safe in doses as high as 3000 mg/kg body weight of albino rats.[14] In the Ayurvedic Pharmacopeia of India (API), Part 1, Volume 3, the source drug for granthiparṇī is identified as L.nepetifolia roots.[15] In Bhāvaprakāśanighaṇṭu, granthiparṇī and its variety sthouneyaka are mentioned under karpūrādivarga. Granthiparṇī is also taken as an abhāvapratinidhidravya for karpūra (camphor). The botanical source of granthiparṇī is identified as Polygonum aviculare (Polygonaceae) by Pandit Chunekar (the commentator on Bhāvaprakāśanighaṇṭu).[16] While discussing about the identity of Chorak, Thakur Balwant Singh opines that the botanical source for granthiparṇī and sthouneyaka remain undecided.[17] Vaidya Bapalal suggested Taxus baccata as the source plant for sthouneyaka which is also known by another synonym granthiparṇī.[18] In view of the above references, it appears that the API's botanical source of granthiparṇī i.e. L.nepetifolia is inappropriate. The objective of the present study is to demonstrate the feasibility of using characteristics described in Ayurvedic texts as a simple and easily adoptable method amongst trained Ayurvedic physicians for preliminary identification of rasa of a plant.

MATERIALS AND METHODS

Plant material collection and preparation of the powder

The whole plant of Leonotis nepetifolia (L.) R Br. was collected during its flowering season in the month of November, 2012 from Coimbatore, Tamil Nadu for the study. The material was identified and confirmed at the Botanical Survey of India, Southern Regional Centre, Coimbatore (No.BSI/SRC/5/23/12-13 Tech/1757) and a voucher specimen (No. IPGT and RA/6066/12-13) was deposited at the Department of Pharmacognosy, Institute for Post Graduate Teaching and Research in Ayurveda, Gujarat Ayurveda University, Jamnagar. The whole plant was thoroughly cleaned, chopped; shade dried and pulverized using an electric blender. The powder was sieved through mesh size #80 and stored in an air tight food grade plastic container for use.

Developing a structured questionnaire

Those characteristics which are local or reflex reactions experienced on the tongue, buccal cavity, throat, palate, nose and eyes described in the context of characteristics of rasa [Table 1] in Carakasaṃhitā, Suśrutasaṃhitā, Aṣṭāṅgasaṅgraha, Aṣṭāṅgahṛdaya and Bhāvaprakāśa were incorporated into a structured questionnaire. Individually 2, 4, 3, 5, 2 and 3 characteristics were identified and attributed for madhura, amla, lavaṇa, kaṭu, tikta and kaṣāya rasas respectively [Table 2]. The characteristic, “causes salivation” is common to Amla, Lavaṇa and Kaṭurasa [Table 2]. Similarly the characteristic, “cleanses the mouth” is common to Amla and Tiktarasa [Table 2]. Thus 16 characteristics were included in the questionnaire [Table 2]. Further, a direct response from the participant with respect to his perception of the taste of the given sample and its intensity as experienced by him or her was elicited in order to compare the observation vis a vis the characteristics reported.

Table 2

Respondent experiences of lakṣaṇas-frequency distribution

Selection of volunteers

The study was approved and given ethical clearance by Institutional Ethics Committee of Institute for Post Graduate Teaching and Research in Ayurveda, Gujarat Ayurveda University, Jamnagar (PGT/7-A/Ethics/2011-2012/2796/SNo-3). The volunteers were senior Ayurvedic students pursuing their MD (Ayu.) or PhD at the Institute for Post Graduate Teaching and Reaseach in Ayurveda, Gujarat Ayurveda University, Jamnagar. All participants provided informed voluntary consent. Volunteers suffering from fever, stomatitis or acute rhinitis were enrolled after symptoms subsided.

Procedure of administration of questionnaire

The participants who volunteered for the study were explained about the study and their role in the study. Every volunteer was then asked to cleanse their mouth with water prior to the onset of the experiment. Five minutes after cleansing the mouth they were given 3 g of the test drug and asked to record their inputs in the questionnaire.

Statistical analysis

The answer (Yes/No) obtained for each characteristic and the perceived Rasa with intensity judged by each volunteer were tabulated and analyzed.

RESULTS AND DISCUSSION

A total of 50 volunteers (19 females and 31 males) aged between 25 – 35 years participated in the study. Data shows [Table 2] the highest frequency in the characteristics of Tikta rasa (47) as experienced by the respondents followed by those of Kaṣāya rasa (37) and Kaṭurasa (34) respectively. In the analysis of experienced characteristics, importance has been given more to the ones which are considered to be unique and individual to a rasa. On this count, the characteristics associated with Tikta rasa stand far ahead [Table 2]. Similarly, when the data was analysed for the direct response on perceived taste of the drug, an overwhelmingly high number of respondents (47) have pointed out Tikta rasa as the perceived taste [Table 3]. Even while accounting for all classical characteristics with respect to any given rasa as identified by a respondent, the entire set of characteristics for Tikta rasa have been reported by 50% of the respondents [Table 4]. All these cumulatively stand in favour of Tiktarasa being the primary rasa for L.nepetifolia followed by kaṣāya rasa.

Table 3

Direct responses on taste-frequency distribution

Table 4

Number of individuals who identified individual Rasa based on all its characteristics

According to Ayurveda, each one of the six rasas is constituted by the combination of any two of the five bhūtas (penta elements). Generally, Tikta rasa drugs are vāyu and akāśa predominant and inferred to be rūkṣa (dry) and laghu (light) in guṇa, śīta (cold) in vīrya (potency) and kaṭu (pungent) in vipāka (transformation).

According to Acārya Caraka, Tikta rasa is itself distasteful but clears and cures distaste (arocaghna) caused by other factors. It possesses viṣaghna (alexipharmic) and kṛmighna (anthelminthic or anti-bacterial) properties. It is valuable in the treatment of obstinate skin diseases (kuṣṭha), pyrexias (jvara) and loss of consciousness (mūrcchā). It alleviates pruritus (kaṇḍu) and burning sensation (dāha). It possesses dīpanapācana (stomachic and digestive), stanyaśodhana (cleanses the breastmilk), lekhana (scraping), medhaśoṣaṇa (reducing excessive accumulation of fat) and kledapuyalasikaśoṣana (reducing exudation or discharges) properties. It also dries up excrements such as faeces (could act as anti diarrhoeal), sweat and urine (checks polyuria).[19]

The plant L. nepetifolia (L.) is reported to be used by tribals located in different parts of the country for cuts, wounds, burns, scalds, skin diseases, fever, diarrhea, breast inflammation, malaria, eczema, worm infestation, burning sensation of scorpion sting and as a depurative11 which are activities or therapeutic indications assigned for tikta rasa substances in Ayurveda. Wound healing,[20] anti inflammatory,[14] cytotoxicity[2122] and anti bacterial[23] activities of Leonotis nepetifolia are also reported by various experimental studies in animals. In-vitro cytotoxicity activity studies of ethanolic extract of Leonotis nepetaefolia R.Br was carried on Ehrlich Ascites Carcinoma cell lines which was found to be comparable with its standard drug.[24] Anti-rheumatic activity of the drug is also proven effective in certain experimental models.[18] Most of the reported ethnomedicinal claims and experimental findings are in tune with the activities attributed to tikta rasa and support to conclude that Leonotis nepetifolia possess tikta rasa as the predominant taste [Table 5]. As most of the volunteers expressed obstructive feeling in throat and dryness of mouth indicating Kaṣāya characteristics, it may be interpreted that Leonotis nepetifolia possesses tikta and kaṣāya rasas and goes into kaṭuvipāka with its specific activity on mala and mūtra. Tribal claims also indicate its application in the management of diarrhea. The methodology used in the present study can be applied for assessing plants less known or unknown to Ayurvedic physicians only when there is reported internal use in ethnomedicine or after subjecting the drug to toxicity studies. Pharmacological activities of tikta rasa such as Medośoṣana (reducing excessive accumulation of fat) and lekhana karma (scraping action) were neither reported in ethnomedicine or through experimental studies. This gives scope for further research on this herb based on its Ayurvedic pharmacology and ethnomedicinal uses for new drug development.

Table 5

Ethnomedical claims of Leonotis nepetifolia in comparison to the properties and indications of tikta Rasa dravya

CONCLUSION

The study to evaluate the rasa of a non classical herb, Leonotis nepetifolia establishes its rasa as predominant in Tikta followed by Kaṣāya based on the responses elicited using a structured questionnaire. Recent researches and ethnomedicinal claims on the herb are in consonañce with the pharmacological activities attributed to tikta rasa and kaṣāya rasa in Ayurvedic classics Rasa nirdhāraṇa can be one of the preliminary steps to initiate the process of screening of an unknown drug along the lines of Ayurvedic pharmacology specially because rasa is the only perceivable parameter. According to Ayurveda, rasa of a dravya has a bearing on its karma (pharmacological action) and the identification of rasa could be one of the subjective means for inferring pāñcabhautika constitution of a substance which in turn could help in tentatively inferring guṇa, vīrya and vipāka of the dravya.

The study demonstrates how a simple method can be used without any instruments to do a preliminary assessment of the rasa or taste of a plant.