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

Abstract

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-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-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 (Becton, Dickinson and Company, Franklin Lakes, NJ) and Beckman dynograph (Beckman Instruments, Inc., Schiller Park, IL). The effects of angiotensin I (0.2 µg/kg, intravenously [IV]) in the absence and presence of SDG (10 mg/kg, IV), 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%, respectively, at 15 minutes and 18.8, 21.2, and 20.3%, 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%, respectively, at 15 minutes and 48, 46, and 30%, 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.

Keywords: angiotensin I; angiotensin-converting enzyme inhibitor; arterial pressures; flaxseed; secoisolariciresinol diglucoside.

Fig. 1

Effects of angiotensin I (0.2 µg/kg, IV) on the absolute changes in the systolic arterial pressure in the absence or presence of SDG (10 mg/kg, IV) at various time intervals in the bar diagram. Line plot shows the effects of SDG on systolic arterial pressure for 60-minute duration. The results are expressed as mean ± SE. *p < 0.05, comparison of the values at various time intervals with respect to the values of control before any drug treatment in the bar diagram. ^† p < 0.05, comparison of values at different times with respect to control (line diagram). ^a p < 0.05, 15 versus 30 or 60 minutes (line diagram). Ag I, angiotensin I; SDG, secoisolariciresionol diglucoside; SE, standard error.

Fig. 2

Effects of angiotensin I (0.2 µg/kg, IV) on the diastolic arterial pressure (expressed as absolute changes) in the absence or presence of SDG (10 mg/kg, IV) at various time intervals. Line diagram shows the effects of SDG on diastolic arterial pressure for 60-minute duration. The results are expressed as mean ± SE. *p < 0.05, comparison of the values at different time intervals with respect to control (bar diagram). ^† p < 0.05, comparison of values at different time intervals with respect to control (line diagram). ^b p < 0.05, 15 versus 30 or 60 minutes (line diagram). Ag I, angiotensin I; SDG, secoisolariciresionol diglucoside; SE, standard error.

Fig. 3

Effects of angiotensin I (0.2 µg/kg, IV) on the mean arterial pressure (expressed as absolute changes) in the absence or presence of SDG (10 mg/kg, IV) at various time intervals. Line diagram shows the effects of SDG on the mean arterial pressure for 60-minute duration. The results are expressed at mean ± SE. *p < 0.05, comparison of values at different time intervals with respect to control (bar diagram). ^a p < 0.05 comparison, 15 versus 30 or 60 minutes (bar diagram). ^† p < 0.05, comparison of the values at different times with respect to control (line diagram). ^b p < 0.05, 15 versus 30 or 60 minutes (line diagram). Ag I, angiotensin I; SDG, secoisolariciresionol diglucoside; SE, standard error.