Some Physiological Issues related to ‘Medo Dhatu’ with special reference to Obesity

‘Medas’ is the fourth ‘Dhatu’ in the sequence of tissue synthesis and nourishment. There is little doubt that the term ‘Medas’ indicates ‘fat’ in general and Adipose tissue in particular. But the description of ‘Abaddha’ Medas (1) compel one to understand this ‘Dhatu’ in two forms- one, ‘bound’ or ‘stored’ (Baddha) and the other, ‘free’ (Abaddha). This free form of ‘Medas’ should therefore include the circulating lipids like those in the form of lipoproteins or those in the form of free fatty acids(2).
Adipose tissue is a specialized connective tissue that functions as the major storage site for fat in the form of triglycerides. This is of two forms- white and brown. White adipose tissue serves several functions: heat insulation, mechanical cushion, and most importantly, a source of energy. Subcutaneous adipose tissue is an especially important heat insulator in the body, because it conducts heat only one third as readily as other tissues. As the major form of energy storage, fat provides a buffer for energy imbalances when energy intake is not equal to energy output. It is an efficient way to store excess energy, because it is stored with very little water.
Lipid in brown adipose tissue, instead of serving as a substrate, releases energy directly as heat and is, therefore used in heat production for non-shivering thermogenesis. The mechanism of heat generation is related to the metabolism of the mitochondria. Mitochondria from brown adipose tissue have a specific carrier called uncoupling protein that transfers protons from outside to inside without subsequent production of ATP.
But recent studies show that the adipose tissue is a complex organ with functions far beyond the mere storage of energy(3). Indeed, it has been shown that fat tissue secretes a number of adipokines including Leptin, adiponectin and visfatin, as well as cytokines, such as Resistin, Interleukin-6 and Tumor-necrosis factor-α.

Process of Successive Tissue Synthesis – ‘Kshira- Dadhi Nyaya’:

The process of nourishment and synthesis of tissues has been explained through various theories in Ayurvedic textbooks. One of them is ‘Kshira Dadhi Nyaya’. As per this theory, one tissue is transformed into the next in a particular sequence. Cakrapani has explained it as follows (4,5):

अत्राहाररसाद् रक्तादिपोषणमेवं केचित् ब्रुवते यत्, रसो रक्तरूपतया परिणमति, रक्तं च मांसरूपतया । एवं मांसादयॊऽप्युत्तरोत्तरधातुरूपतया परिणमन्ति । अत्रापि च पक्षे केचिद् ब्रुवते – क्षीराद् यथा सर्वात्मना दधि भवति, तथा कृत्स्नो रसो रक्तं भवति; एवं रक्तादयोऽपि मांसादिरूपा भवन्ति ॥

अत्र च रसाद्रक्ताद्युत्पादने केचिदिदं वदन्ति यत्, रसोऽग्निपच्यमानः रक्ततां याति, रक्तं च मांसतामित्यादि पूर्वपूर्वधातुपरिणामादेव उत्तरोत्तरधातूत्पादः । यथा क्षीराद् दधि भवति, दध्नो नवनीतं, नवनीताद् घृतमित्येकः पक्षः ।

In Caraka Samhita, the following description is found regarding the process of transformation of one ‘Dhatu’ into another(6).
तेजो रसानां सर्वेषां मनुजानां यदुच्यते । पित्तोष्माणः स रागेण रसो रक्तत्वमृच्छति ॥
शोणितं स्वाग्निना पक्वं वायुना च घनीकृतम् । तदेव मांसं जानीयात् स्थिरं भवति देहिनाम् ॥
वाय्वम्बुतेजसा रक्तमूष्मणा चाभिसंयुतम् । स्थिरतां प्राप्य मांसं स्याद् स्वोष्मणा पक्वमेव तत् ।
स्वतेजोऽम्बुगुणस्निग्धोद्रिक्तं मेदोऽभिजायते । पृथिव्यग्न्यनिलादीनां संघातः स्वोष्मणा कृतः ।
खरत्वं प्रकरोत्यस्य जायतेऽस्थि ततो नृणाम् । करोति तत्र सौषिर्यं अस्थ्नां मध्ये समीरणः ॥
मेदसस्तानि पूर्यन्ते स्नेहो मज्जा ततः स्मृतः । तस्मान्मज्ज्ञस्तु यः स्नेहः शुक्रं संजायते ततः ॥
वाय्वाकाशादिभिर्भावैः सौषिर्यं जायतेऽस्थिषु । तेन स्रवति तच्छ्रुक्रं नवात् कुम्भादिवोदकम् ॥
स्रोतोभिः स्यन्दते देहात्समन्ताच्छुक्रवाहिभिः । हर्षेणोदीरितं वेगात् संकल्पाच्च मनोभवात् ॥
विलीनं घृतवद् व्यायामोष्मणा स्थानविच्युतम् । बस्तौ सम्भृत्य निर्याति स्थलान्निम्नादिवोदकम् ॥

The above description has always attracted criticism by the modern Ayurvedic scholars. Even Cakrapani, on one instance, has disapproved this theory. Most of the scholars believed that the process of transformation of one tissue into another is not possible except in embryonic stem cells.

Recent Stem Cell Research:

Until recently, it was widely believed that the mature adult stem cells in the tissues can not be transformed into another tissue. But recent advances in the science have shown that the mature adult stem cells present in some tissues can form multiple tissue types. It is now known that fat is an excellent source for bone, cartilage, muscle, and maybe even blood cells because it is an excellent source of stem cells that can be prompted to develop into bone or muscle. In 2001, Hedrick, a plastic surgeon by profession, and his colleagues reported this research in ‘Tissue Engineering’(7). Afterwards, in 2005, researchers at Wake Forest University School of Medicine successfully isolated stem cells from human skin, expanded them in the laboratory and coaxed them into becoming fat, muscle and bone cells. The study, one of the first studies to show the ability of a single adult stem cell to become multiple tissue types, was reported in ‘Stem Cells and Development’ (2005)(8). More recently, scientists have successfully made immature sperm cells from human bone marrow samples (9). Therefore, formation of ‘Shukra’ from ‘Majja’ is no more an absurd description.

Vagbhata has comprehended the process of tissue transformation and nourishment as follows(10):
रसाद्रक्तं ततो मांसं मासान्मेदस्ततोऽस्थि च ।
अस्थ्नो मज्जा ततः शुक्रं शुक्राद्गर्भः प्रजायते ॥


Arunadatta has thrown light on this explanation in following lines, citing an example of obesity and initiating a debate on some related issues(11):
रसात् – धातुरसादाहाररसेन सहैकतामापन्नात् , रक्तं प्रजायते – स धातुरसस्तथा भूतो रक्ततया सम्पद्यते । तावद्यावत्स एव गर्व्हत्वेनेति योज्यम् । अत्र चोदयन्ति । ननु, यद्याहाररसो व्यानविक्षिप्तो रसधातुना सह एकतां परिणमन् क्रमेण रक्तादीन् भावान् गर्भावसानान् परिणमति । तर्हि कथमुक्तं “सारस्तु सप्तभिर्भूयो यथास्वं पच्यतेऽग्निभिः” इति? अत्रोच्यते । कार्ये कारणोपचारादेतदुक्तमित्यवेहि । सारकार्येषु रसरक्तादिषु सप्तभिर्धात्वग्निभिः पच्यमानेषु “सारस्तु सप्तभिर्भूयो यथास्वं पच्यतेऽग्निभिः” इत्युक्तम् । तस्माद्रसादिधातव एव साराख्यान्मूलकारणादुत्थिताः परमार्थेन पच्यन्त इति बोध्यम् । ननु, यदि क्रमेणाहाररसाद्रसो रसाद्रक्तं रक्तान्मांसमित्यादिक्रम आश्रीयते, तत्कथमुक्तं “व्यानेन रसधातुर्हि विक्षेपोचितकर्मणा” इति? अत्र हि युगपदिति च निर्दिश्यते । युगपत् – एककालं, व्यानेन रसो देहे विक्षिप्यते । विक्षिप्ताच्च रसात् सर्वधातूत्पत्तिरिति प्रत्यज्ञायि । इह च रसरक्तमांसादि क्रमेणाहाररसाद्धातुनिष्पत्तिरित्युच्यते । तदेतद् परस्परं विरुद्धमिव लक्ष्यते । ब्रूमः । युगपच्छ्ब्दोऽत्र शीघ्रक्रमार्थः । . . . रसधातुरित्येतद्कथमुक्तम् ? यतो रसाख्यो धातुस्तेन न विक्षिप्यते, किन्तर्हि ? आहाररसः । अत एव धातुशब्दोपादानं अनर्थकम् । ब्रूमः । धातुशब्द आधाराभिधेयत्वेनेहोपात्तो रसस्य देहधारणत्वं दर्शयितुम् । सर्वेषां हि धातूनां यद्देहधारणस्वभावत्वं तदाहाररसाप्यायितानामेषाम् , न त्वनाप्ययितानाम् । अतः स आहाररसो धातूनामाधारः उद्भवस्थानम् । यथा, लोले हेमादीनां य आधारः प्रतिनियतो विशिष्टा मृत् स धातुसंज्ञया भण्यते । इयं मृद्धेमधातुरियं रजतधातुरिति । एवमाहाररसो व्यानेन विक्षैप्यते, न रसाख्यो धातुः, इति स्थितमेतत् । किञ्च, आहाररसादेककालं सप्तसु धातुस्रोतःसु प्रवेशिताद्रसरक्तादयो धातव उत्पद्यन्ते, इति यद्येष एककालधातुपोषणपक्ष आश्रीयते, तदानीमिदं विरुध्यते – “पूर्वो धातुः परं कुर्याद्वृद्धः क्षीणश्च तद्विधम्” इति । यतः सर्वे धातव आहाररसेन युगपद्व्यानविक्षिप्तेन खे स्रोतस्यवतिष्ठमानाः स्वातन्त्र्येणाहाररसाप्यायिताः पुष्यन्ति, अनाप्यायिताः क्षयं यान्ति । तदेवं कथं पूर्वस्य धातोर्वृद्धो परस्य वृद्धिः पूर्वस्य धातोः क्षये परस्य क्षयः स्यात् ? न हि कदाचिद्घटते मेत्रे तृप्ते चैत्रः सुहितः स्यात्, अतृप्ते वाऽसुहितः स्यात् । तथा स्थूलस्य मेद एवोपचीयत इति दृष्टम् । न च समं कृत्वा सप्तसु धातुस्रोतःसु विनिक्षिप्ते रसे मेदसोऽधिका वृद्धिः कथञ्चिदुपपद्यते । क्रमपरिणामपक्षे तु स्थूलस्याहाररसो रसधातुतया परिणमति । रसधातु रक्ततया, रक्तधातुर्मांसतया, मांसधातुर्मेदस्तया परिणमति । मेदस आहारपूर्णस्य स आहाररसो मेदस्त्वं प्राप्तः पुनः प्रतिस्रोतोन्यायेन मांसस्य विशेषवतीं वृद्धिं करोति , अनन्तरं रक्तस्य, अनन्तरं रसस्य । पुनश्च रसधातुरतिपूर्णो रक्तस्य वृद्धिं विधत्ते, रक्तधातुर्मांसस्य, मांसधातुर्मेदसः, इत्येवं अतिस्थूलस्यमेदोवद्रसादयो मांसावसाना अप्युपचीयन्ते । अस्थ्यादयश्चास्थ्यादिस्रोतसां मेदसावृतत्वान्न तथोपचीयन्ते । तस्मादाहाररसेन मेदोभावेन परिणमता उदकपरिपूर्ण अभिनवमृत्कुम्भजललवस्यन्दनन्यायेन अस्थ्यादयो धातवः केवलमाप्याय्यन्ते, न तु तथोपचीयन्ते । तथा च मुनिः (च. सू. २१/४) – “स्थूलस्य मेद एवोपचीयते, न तथेतरे धातवः” इति । अस्य ह्ययमर्थः मेदसो येऽन्येऽस्थ्यादयः शुक्रावसानास्ते न तथोपचीयन्ते , न पुनः पूर्वे रसादयः धातवः स्थूलस्य नोपचीयन्त इति । अत एवाह मुनिः – (च. सू. २१/९) “मेदोमांसातिवृद्धत्वाच्चलस्फिगुदरस्तनः । अयथोपचयोत्साहो नरोऽतिस्थूल उच्यते । इति ।

Involvement of ‘Rasa’, ‘Rakta’ and ‘Mamsa’ in Obesity:

As described by Arunadatta, abnormal nourishment of ‘Rasa’, ‘Rakta’ and ‘Mamsa’ takes place along with ‘Meda’ in obesity. This explanation also seems to be true because dyslipidaemias and type- II diabetes mellitus (related to the abnormalities of ‘Rasa Dhatu’), hypertension (related to the abnormalities of ‘Rakta Dhatu’) and abnormally functioning muscle tissue (‘Mamsa Dhatu’) have been linked with obesity. Scientists have reported that severely obese people have three times as much of a fat-building enzyme called SCD-1 in their muscle cells than lean people indicating that simple dietary management may not be sufficient in the treatment of Obesity(12).

Kidney and Lipid Metabolism:

Also, in Ayurvedic literature, ‘Vrikka’ (Kidney) has been named as an organ associated with ‘Medovaha Srotas’. This description must have been based on some clinical observations. Recently there has been evidence that obesity increases tubular reabsorption in kidneys and this shifts pressure natriuresis towards higher BP. The increased tubular re-absorption is linked to the possible changes in intrarenal physical forces caused by medullary compression due to accumulation of adipose tissue around the kidney and increased extracellular matrix within the kidney. Because obesity is a primary cause of essential hypertension as well as type II diabetes, scientists believe that obesity may also be the most frequent cause of end-stage renal disease(13).
‘Medo Dhatu’ promotes the growth of ‘Asthi Dhatu’
One of the functions of ‘Meda Dhatu’ is to promote the growth of ‘Asthi Dhatu’. Recent advances in medical science have proposed that Adipose Tissue stimulates bone growth in children and young adults. After puberty, this effect is weakened. In a study reported in The Journal of Clinical Endocrinology and Metabolism, the fat mass in children was an independent predictor of bone mass and size(14).
‘Medo Dhatvagni’
Vagbhata has described that ‘Jatharagni’, has its fractions known as ‘Dhatvagnis’ situated at the level of tissues. If these fractions become over active, there will be 'Kshaya' (Catabolism) of 'Dhatu' and if they become depressed, there will be abnormal 'Vrddhi' of the 'Dhatu’. Several classical hemocrine hormones determine the metabolic state of a tissue. For example, 'Medodhatvagni' may include glucocorticoids, insulin, glucagon etc. If glucagon levels are excess, lipolysis occurs which is equivalent to 'Medokshaya'. Along with these hormones, all enzymes involved in lipid metabolism may also be regarded as ‘Medo Dhatvagnis’ (15).
Conclusion:

Various physiological and pathological descriptions available in Ayurvedic textbooks need to be looked at seriously with an open mind and concepts related to ‘Medo Dhatu’ are not exception for this.

REFERENCES:
1. Caraka Samhita, Nidana Sthana, 4/7
2. Kishor Patwardhan, ‘Human Physiology in Ayurveda’, Published by Chaukhambha Orientalia, Varanasi (2005) Page No.19
3. Tiziana Ronti; Graziana Lupattelli; Elmo Mannarino, ‘The Endocrine Function of Adipose Tissue: An Update’, Clinical Endocrinology. 2006;64(4):355-365.
4. Cakrapani on Ca. Su.28/4
5. Cakrapani on Sushruta Samhita, Sutra Sthana, 14/10
6. Caraka Samhita, Cikitsa Sthana, 15/28-35
7. http://www.webmd.com/news/20010410/turning-fat-into-muscle-bone-blood-cells accessed on 17/1/2008 10:20:33 PM
8. http://www.sciencedaily.com/releases/2005/06/050623000101.htm accessed on 9/2/2008 5:04:31 PM
9. http://news.bbc.co.uk/2/hi/health/6547675.stm accessed on 9/2/2008 4:53:11 PM
10. Ashtanga Hridaya, Sharira Sthana, 3/62
11. Arunadatta on Ashtanga Hridaya, Sharira Sthana, 3/62
12. http://www.medscape.com/viewarticle/514347 accessed on 14/2/2008 7:22:15 PM
13. John E. Hall, Michael W. Brands, Jeffrey R. Henegar, Eugene W. Shek (1998), ‘Abnormal kidney function as a cause and a consequence of obesity hypertension’, Clinical and Experimental Pharmacology and Physiology 25 (1), 58–64.
14. http://www.medscape.com/viewarticle/541500 accessed on 13/2/2008 11:44:25 PM
15. Kishor Patwardhan, ‘Human Physiology in Ayurveda’, Published by Chaukhambha Orientalia, Varanasi (2005) Page No.48