New Therapeutic Insight into the Effect of Ma Huang Tang on Blood Pressure and Renal Dysfunction in the L-NAME-Induced Hypertension

Abstract

In this study, we evaluated the effect of a traditional herbal formula, Ma Huang Tang (MHT), on blood pressure and vasodilation in a rat model of N^G-nitro-L-arginine methylester- (L-NAME-) induced hypertension. We found that MHT-induced vascular relaxation in a dose-dependent manner in rat aortas pretreated with phenylephrine. However, pretreatment of endothelium-intact aortic rings with L-NAME, an inhibitor of nitric oxide synthesis (NOS), or 1H-[1, 2, 4]-oxadiazole-[4, 3-α]-quinoxalin-1-one (ODQ), an inhibitor of soluble guanylyl cyclase, significantly abolished vascular relaxation induced by MHT. MHT also increased the production of guanosine 3',5'-cyclic monophosphate (cGMP) in the aortic rings pretreated with L-NAME or ODQ. To examine the in vivo effects of MHT, Sprague Dawley rats were treated with 40 mg/kg/day L-NAME for 3 weeks, followed by administration of 50 or 100 mg/kg/day MHT for 2 weeks. MHT was found to significantly normalize systolic blood pressure and decreased intima-media thickness in aortic sections of rats treated with L-NAME compared to that of rats treated with L-NAME alone. MHT also restored the L-NAME-induced decrease in vasorelaxation response to acetylcholine and endothelial nitric oxide synthase (eNOS) and endothelin-1 (ET-1) expression. Furthermore, MHT promoted the recovery of renal function, as indicated by osmolality, blood urea nitrogen (BUN) levels, and creatinine clearance. These results suggest that MHT-induced relaxation in the thoracic aorta is associated with activation of the nitric oxide/cGMP pathway. Furthermore, it provides new therapeutic insights into the regulation of blood pressure and renal function in hypertensive patients.

Figure 1

Representative HPLC chromatograms of standard solution (a) and Ma Hwang Tang decoction (b) measured at UV wavelength 206 nm. Ephedrine HCl (1), liquiritin apioside (2), liquiritin (3), coumarin (4), cinnamic acid (5), cinnamaldehyde (6), and glycyrrhizin (7).

Figure 2

Effect of MHT on vasodilation and cGMP production. Presented vascular relaxation response to MHT in aorta with endothelium or without (a) Presence of L-NAME (100 μM) or wortmannin (0.1 μM) (b). Presence of ODQ (10 μM) (c). The cGMP production response to MHT with L-NAME (100 μM), ODQ (10 μM), or wortmannin (0.1 μM). MHT, Ma Huang Tang; cGMP: guanosine 3′,5′-cyclic monophosphate; L-NAME: N^G-nitro-L-arginine methylester; and ODQ: 1H-[1,2,4]-oxadiazolo-[4,3-α]-quinoxalin-1-one. Values are expressed as mean ± S.E. (n = 5 per group). ^∗p < 0.05, ^∗∗p < 0.01, and ^∗∗∗p < 0.001 versus vehicle: #p < 0.05 versus L-NAME, ODQ, or wortmannin.

Figure 3

Effect of MHT on blood pressure. Presented systolic blood pressure measured by tail-cuff method (mmHg). MHT: Ma Huang Tang; OMT: Olmetec. Values are expressed as mean ± S.E. (n = 8 per group). ^∗∗∗p < 0.01 versus control: ^#p < 0.05, ^##p < 0.01 versus L-NAME.

Figure 4

Effect of MHT on vascular relaxation and cGMP level in L-NAME model. (a) Vascular relaxation response to acetylcholine (Ach) in thoracic aorta of L-NAME model. (b) The cGMP production level in the thoracic aorta of control and L-NAME groups. MHT: Ma Huang Tang; cGMP: guanosine 3′,5′-cyclic monophosphate; OMT: Olmetec. Values are expressed as mean ± S.E. (n = 3 per group). ^∗p < 0.05, ^∗∗∗p < 0.001 vs. control: ^#p < 0.05, ^##p < 0.01, ^###p < 0.001 vs. L-NAME.

Figure 5

Effect of MHT on aorta morphology, eNOS, and ET-1 immunoreactivity in aortic tissues. (a) Representative microscopic photographs in aorta of control and L-NAME groups were stained with hematoxylin and eosin. (b) Numerical value of the length of tunica intima-media in aorta of L-NAME model. (c) eNOS immunoreactivity in thoracic aorta of L-NAME-induced hypertensive rats. (d) Digitization of eNOS expression. (e) ET-1 immunoreactivity in thoracic aorta of L-NAME-induced hypertensive rats. (f) Digitization of ET-1 expression. MHT: Ma Huang Tang; eNOS: endothelial nitric oxide synthase; ET-1: endothelin-1; OMT: Olmetec. Values are expressed as mean ± S.E. (n = 3 per group). ^∗∗p < 0.01, ^∗∗∗p < 0.001 versus control: ^#p < 0.05, ^##p < 0.01, and ^###p < 0.001 versus L-NAME.

Figure 6

Effect of MHT on the expression of eNOS and Akt phosphorylation by western blot analysis. MHT: Ma Huang Tang; eNOS: endothelial nitric oxide synthase; and OMT: Olmetec. Values are expressed as mean ± S.E. (n = 3 per group). ^∗p < 0.05, ^∗∗p < 0.01 versus control: ^#p < 0.05, ^##p < 0.01 versus L-NAME.

Figure 7

Summary of MHT action in L-NAME-induced hypertensive rats. L-NAME inhibited NO production; therefore, Akt, eNOS, and cGMP activation was decreased. Meanwhile, MHT activated PI3K/Akt/eNOS signaling; as a result, cGMP production was increased. MHT: Ma Huang Tang; eNOS: endothelial nitric oxide synthase; cGMP: guanosine 3′,5′-cyclic monophosphate; and OMT: Olmetec.