Secoisolariciresinol Diglucoside (SDG) Isolated from Flaxseed, An Alternative to Ace Inhibitors in the Treatment of Hypertension

Secoisolariciresionol diglucoside (SDG) is a plant lignan isolated from flaxseed and is phytoestrogen.  SDG is a potent and long acting hypotensive agent.  Plant phytoestrogens have inhibitory effects on angiotensin to converting enzyme (ACE).  The hypotensive effects of SDG, a phytoestrogen, may be mediated through inhibition of ACE.  The objective of this study was to investigate if SDG to induced hypotension is mediated through inhibition of ACE.  The Sprague Dawley male rats were anesthetized and trachea was cannulated.  The right jugular vein was cannulated to administer the drug and the carotid artery was cannulated to record arterial pressures using PIOEZ 1 miniature model transducer and Beckman dynograph.  The effects of angiotensin I in the absence and present of SDG and SDG alone on systolic, diastolic, and mean arterial pressures were measured before and after 15,30, and 60 minutes of drug administration.  SDG decreased the systolic, diastolic, and mean arterial pressure by 37, 47, and 43 percent, respectively at 15 minutes and 18.8, 21.2 and 20.3 percent respectively at 60 minutes.  Angiotensin I increased the arterial pressure, SDG decreased angiotensin I induced rise in the systolic, diastolic, and mean arterial pressures by 60,58 and 51 percent, respectively, at 15 minutes and 48,46, and 30 percent respectively, at 60 minutes.  The data suggest that SDG reduced the angiotensin I induced rise in the arterial pressures and hence SDG is a potent ACE inhibitor. (Authors abstract)

Flaxmeal which is devoid of oil is approximately 55 to 68 percent of the total flaxseed and contains approximately 16.4mg/g of secoisolariciresional diglucoside (SDG).  SDG content of flaxseed varies between 0.6 and 1.8 g per 100g.  SDG has been isolated from flaxseed.  SDG is a phytoestrogen, and phytoestrogens from dietary soy  have been shown to have mild hypotensive effect.  The objective of this investigation was to determine if SDG to induced decreases in the blood pressures is mediated through inhibition of ACE. SDG in the dose of 10mg/kg produced marked decreases in the arterial pressures in anesthetized rats, the decreases being more in diastolic than in the systolic pressures.  Angiotensin I increased the arterial pressure in the present study. SDG significantly reduced the angiotensin I induced increase in the arterial pressure, the reduction being greater in diastolic as compared with systolic arterial pressures.  This could be due to inhibition of ACE.  The reasoning being as follows:  Renin released from the specialized cells in the kidney acts on renin substrate, angiotensinogen to produce biologically inactive decapeptide, angiotensin I which in turn is converted to the octapeptide angiotensin II by ACE.  Angiotensin II is a powerful vasoconstrictor through binding to angiotensin II receptor.  Since SDG reduced the pressure response to angiotensin I, it might have inhibited the ACE resulting in decreased conversion of angiotensin I to angiotensin II and hence reduction in angiotensin I induced rise in the arterial pressure.  CE inhibitors are well known to reduce arterial pressure and have been used extensively for patients with hypertension.  ACE inhibitors have been used to reduce blood pressure in animal models and human hypertension. In conclusion, these results suggest that hypotensive effects of SDG isolated from flaxseed is mediated through inhibition of angiotensin to converting enzyme.  SDG may prove to be an alternative to other ACE inhibitors for the treatment of hypertension. (Editors comments)