This study investigated the acute and chronic antihypertensive effects of the stem bark methanol extract of
Cinnamomum zeylanicum in L-NAME-induced hypertensive rats and its effects on lipid metabolism in chronic hypertensive rats. In this model, inhibition of NO-synthase permits the evaluation of the nitric oxide pathway, a physiologically important vasodilator, playing a major role in the regulation of systemic hemodynamic[
20]. Acute intravenous administration of
Cinnamomum zeylanicum methanol extract to L-NAME-induced hypertensive rats caused a significant decrease in mean arterial blood pressure (MABP) that last more than an hour after administration. In animals treated chronically with L-NAME, arterial hypertension associated with both cardiovascular hypertrophy and histological damages were observed. It is well known that L-NAME, administered either acutely by intravenous route or chronically by the oral induced sustained hypertension[
16,
21,
22]. But Chaswal
et al.[
23] showed that the acute hypertension provoked by L-NAME administration may not involve the renin angiotensin system which is at least partially responsible for the chronic response. The fact that MECZ could reduce both the acute and chronic hypertension induced by L-NAME indicates that it may use another pathway. Previous studies using the aqueous extract of
C. zeylanicum have demonstrated that this plant possesses both endothelium-dependent and -independent vasodilating properties[
14]. Therefore, we postulate that the acute antihypertensive effect of our plant extract might be mainly due to its ability to reduce the peripheral resistance via its vasodilating activities even though its effect on the renin-angiotensin system, which plays a pivotal role in the development of chronic L-NAME hypertension, cannot be rule out. It is also well known that in this model of experimental arterial hypertension, the sympathetic system tone and baroreflex to phenylephrine are significantly increased[
23]. MECZ could also interfere with this system. Permanent increase in systemic blood pressure often lead to cardiovascular hypertrophy[
24,
25]. In fact, in the present study, it was found that chronic treatment with L-NAME increases the cardiac and aorta weights. Additionally, histological analysis showed the thickness of the vascular wall as well as fibroblast infiltration in the myocardium. These effects were significantly reversed by MECZ and captopril. Results with captopril corroborate many other previous works[
26,
27] and further confirm the involvement of the renin-angiotensin system in the development of this model of arterial hypertension. As there is a tight relationship between the renin-angiotensin system and the sympathetic system, the inhibition of one may lead to the inhibition of the other, as it can be clearly see in the case of captopril. So, no obvious mechanism can be attributed to MECZ. Another interesting fact is that MECZ was able to increase NO production in cardiovascular organs, namely the aorta and the heart. Thus, the antihypertensive as well as the antihypertrophic effects of MECZ may be at least partially attributed to the increase in NO production, which is known as an inhibitor to cell proliferation. Moreover, by stimulating cardiovascular NO synthesis, the plant extract could induces vasorelaxation, improves arterial wall compliance and control of blood pressure. Hypertension and hyperlipidemia are two concomitant cardiovascular risk factors. Therefore, in order to reduce cardiovascular risk, it is important to regulate hypertension as well as dyslipidemia, which is known as a qualitative or quantitative modification of one or several parameters of the plasma lipids[
28]. The results of this study indicated a dyslipidemia in rats receiving L-NAME. The dyslipidemia observed was characterized by hypertriglyceridemia, hypercholesterolemia, and high rate of LDL-cholesterol (LDL-C) coupled with low level of HDL-cholesterol (HDL-C. The dyslipidemia observed in L-NAME-induced hypertensive rats, was significantly managed by both the captopril and MECZ with the concentration of triglycerides, total cholesterol, LDL-C or HDL-C, closer to that of normal rats. These results clearly demonstrated both the hypotriglyceridemic and hypocholesterolemic properties of the plant extract, which might contribute to the cardiovascular proptective effects of MECZ. The pharmacological activities of MECZ might be explained by the presence of phytochemical constituents like flavanoids and saponins in the plant. These bioactive phytomolecules are known to possess vasorelaxant, antihypertensive and antihyperlipidemic effects[
29‐
31].