Fresh barks of C. zeylanicum were harvested in Njombe, Moungo Division in the Littoral Region of Cameroon in January 2007. The plant material was identified at the National Herbarium in Yaounde, in comparison to the voucher specimen number SRFC/22309. The barks were air-dried and ground to a fine powder. 800 g of the powder obtained were soaked at room temperature in 3 l of methanol for 48 h, with occasional shaking. After filtration, the filtrate was concentrated by evaporation at 70°C under reduced pressure on a rotary evaporator to afford 45 g of the methanol extract, corresponding to an extraction yield of 5.6%. This extract was dissolved in DMSO (4%) for daily used.

The major phytochemical groups were determined using the Lieberman Buchard, ferric chloride, copo of magnesium and Vanillin-sulphuric acid tests. Sterols, polyphenolic compounds, flavonoids, alkaloids and saponins were identified in the extract.

Male Wistar rats, aged 12–16 weeks and weighing 150 to 250 g were randomly selected from our colony. They were raised in the animal house of the Faculty of Sciences, University of Dschang, Cameroon. Animals were exposed to daily 12 h light–dark cycle with free access to a standard animal diet and tap water. The effects of Cinnamomum zeylanicum methanol extract (MECZ) were examined acutely and chronically in vivo on mean arterial blood pressure (MABP) of rats previously treated with L-NAME.

Experimental protocols used in this study were approved by the Laboratory committee (Laboratory of Animal Physiology and Phytopharmacology, Department of Animal Biology, University of Dschang – Cameroon) according to the standard ethical guidelines for laboratory animal use and care as described in the European Community guidelines; EEC Directive 86/609/EEC, of the 24th November 1986 15 .

Blood pressure and cardiac frequency were determined by the invasive method. Brietly, Animals were anaesthetized by intraperitoneal administration of sodium thiopental at the dose of 50 mg/kg and a catheter was implanted in the femoral vein for drug administration. Another catheter was inserted in the left carotid artery for direct blood pressure measurement. Both catheters were filled with glucose-saline heparinized solution. The catheter inserted in the carotid artery was connected to a blood pressure transducer model Ugo Basile PRC 21k-10 coupled to an Ugo Basile Unirecord model 7050 for blood pressure recording. A stabilisation period of 30 minutes was observed before any recording. Heart frequency was determined by the use of pulse intervals.

For acute antihypertensive study, a solution of L-NAME, an inhibitor of nitric oxide synthase was intravenously injection to normotensive Wistar rats (20 mg/kg) after the stabilization period at corresponding volume of 100 μl/100 g bw. MECZ was administered intravenously at the doses of 5, 10 or 20 mg/kg, twenty minutes after L-NAME administration, when the rise in blood pressure induced by L-NAME had reached the maximum 16 .

In the chronic study, male Wistar rats were randomly divided into four groups of eight rats each. The first group (control) received a solution of DMSO 4% daily, while the second one (L-NAME group) received L-NAME (40 mg/kg/day) plus the vehicle. The third group was treated every day with a combined solution of L-NAME (40 mg/kg/day) and captopril (LN-Capto; 20 mg/kg/day) while the forth group, received a combination of L-NAME (40 mg/kg/day) and MECZ (LN-MECZ; 300 mg/kg/day). All the treatments were administered daily by gastric intubation on non-anesthetized animals for 4 weeks at the corresponding volume of 1 ml/100 g bw. The intubation was done daily, on non-anesthetized animals. The dose of the extract was determined based on previous results. At the end of the treatment, animals were anaesthetized by intraperitoneal administration of sodium thiopental (50 mg/kg) for blood pressure measurement. Immediately after blood pressure measurement, blood samples were collected from the abdominal artery, and centrifuged at 3000 rpm for 15 minutes. The plasma obtained was kept at −20°C for lipid assay. Thereafter, the heart and the thoracic aorta were collected, washed in saline and weighed. The heart was dissected out for the evaluation of the left ventricular mass. Three organs’ samples were fixed with 10% formalin in saline while the five others were used for NO evaluation.

The concentrations of total cholesterol (TC), high density lipoprotein (HDL) and triglycerides (TG) in plasma were determined spectrophotometrically using a commercially available kit Dialab and Helios Epsilon spectrophotometer. Low density lipoprotein (LDL) content was calculated from the other lipid parameters according to the 17 equation: LDL = TC–(TG/5)–HDL. The atherogenic index was calculated using the formula 18 : Atherogenic Index.

The left ventricle and aorta were homogenized in a carbonate buffer solution, and centrifuged at 4000 rpm for 15 minutes. The supernatant obtained was used to measure spectrophotometrically tissue concentration of nitric oxide (NO) as previously described by 19 . Briefly, 300 μl of sample were allowed to react with Griess reagent (1% sulfanilamide, 0.1% N-1-naphthylethylenediamine dihydrochloride and 2.5% phosphoric acid) at room temperature for 10 min, and then the absorbance was read at 530 nm. The NO concentration was determined by using NaNO₂ standard curve.

Fixed left ventricle and aorta were dehydrated and embedded in paraffin. 5 μm thick sections were mounted on glass slides. After deparaffinization and rehydration, they were stained with either Hematoxylin-Eosin or Van Gieson trichrome solutions in order to assess histological injuries and collagen accumulation in tissues. Histological analysis was performed with light microscope. The media thickness of aorta defined as the distance between the internal and external elastic lamina was determined using the following argument. Each photo have a bar corresponding to a given distance (aμm). Knowing that the magnification used was 400, the length (L) of each bar was then calculated using the formula: L = aμm/400.

L-NAME was obtained from Fluka (Germany), sodium thiopental from Rotex Media (Germany), Heparin from Sanofi (France) and captopril was obtained from the Sahib Singh Agencies (India). All test solutions, including Krebs’ solution were freshly prepared in distilled water.

Statistical analysis was performed using GraphPad Prism version 5.0. All results are expressed as means ± standard error of the mean. Data were analysed using one-way analysis of variance (ANOVA) followed by Tukeys’post test. Differences between means were considered to be significant when p < 0.05.

Figure  1 shows the acute effects of MECZ on mean arterial blood pressure (MABP) examined in vivo in L-NAME induced hypertensive rats. L-NAME injected intravenously at the dose of 20 mg/kg in normotensive Wistar rats induced a sustained arterial hypertension which persisted for more than one hour and half with a MABP of 160.33 ± 3.82 mm Hg. Immediately following intravenous administration, MECZ induced a significant (p < 0.001) decrease in MABP. The lowest dose (5 mg/kg) reduced the elevated blood pressure by 46.4 ± 10.6%. The MABP dropped from 160 ± 4.02 mm Hg to 62.13 ± 11.28 mm Hg. In animals receiving the doses of 10 and 20 mg/kg, the MABP dropped suddenly after plant administration from 159.46 ± 5.77 mm Hg to 55.46 ± 7.31 mm Hg and from 176.66 ± 6.86 mm Hg to 83.46 ± 16.03 mm Hg; corresponding to an immediate reduction in MABP of 68.9 ± 4.8% and 50.7 ±9.5% respectively. The immediate fall in blood pressure induced by previous doses (5, 10 and 20 mg/kg) of the extract was followed by a long-lasting and dose-related antihypertensive effects that lasted for more than one hour with a corresponding decreases of 12.51 ± 1.7%, 27.23 ± 3.1% and 30.9 ± 3.1%, respectively.

Animals that received only L-NAME (40 mg/kg/day) were hypertensive after four weeks of treatment. Concomitant administration of L-NAME with captopril (LN-Capto; 20 mg/kg/day) or MECZ (LN-MECZ; 300 mg/kg/day) prevented the installation of hypertension as depicted in Figure  2. MABP value was 135.6 mm Hg in L-NAME treated rats versus 104 ± 6.83 mm Hg and 108.26 ± 3.1 mm Hg in the LN-Capto and LN-MECZ groups respectively. However, no significant change in heart rate was observed between experimental groups (Figure  2).

In the control group, the relative body weight increased by 122.5 ± 2.5% compared to initial value. This parameter was significantly low (p < 0.01) in L-NAME treated rats where the body weight increased only by 107.9 ± 4.3%. Contrary to captopril (112 ± 3.1%) slightly prevented the body weight loss induced by L-NAME as compared to the control group while the MECZ did not prevent body weight loss, with the relative body weight (102.1 ± 4.5%) significantly low (p < 0.01) compared to that of the control group (Figure  3).

In contrast to the effects observed on the body weight, long-term administration of L-NAME significantly (p < 0.001) increased both aorta (160.2 ± 15.3 mg/100 g bw versus 58 ± 4 mg/100g bw in the control group) and left ventricle (1.14 ± 0.11 g/100 g bw versus 0.68 ± 0.04 g/100 g bw in the control group) weights. The heart and vascular hypertrophy induced by L-NAME administration was significantly (p < 0.01) prevented by captopril and MECZ (Figure  4).

Hematoxylin & Eosin staining revealed in L-NAME treated rat, an aortic media hypertrophy, characterized by an increase in the vessel section area (58 ± 0.11 μm versus 43 ± 0.03 μm in the control group). Moreover, cell accumulation on the endothelial wall was also noticed; which could lead to endothelial impairment. These vascular morphological damages were almost completely prevented by captopril (45 ± 0.21 μm versus 58 ± 0.11 μm in the L-NAME group) as well as the plant extract (45 ± 0.4 μm versus 58 ± 0.11 μm in the L-NAME group) (Figure  5A). Van Gieson trichrome revealed left ventricular structural changes characterized by fibrosis in L-NAME rats. In rats receiving either captopril or C. zeylanicum extract, the left ventricular histological injury was significantly attenuated (Figure  5B).

Aortic and cardiac content in NO are represented in Figure  6. In rats treated only with L-NAME, both aortic and cardiac NO concentration decrease significantly (p < 0.01) by 39.4% and 45.2% respectively as compared to the control. The methanol extract of C. zeylanicum significantly prevented the deleterious effects of L-NAME in the tissue NO content. It increased by 47.7% and 38.4% the concentration of NO in the aortic and cardiac tissues respectively compared to the L-NAME group.

The oral administration of L-NAME (40 mg/kg) to rats resulted in an elevated plasma lipid profile (Table  1). L-NAME treated rats showed significantly (p < 0.01) higher levels of plasma triglycerides, total cholesterol, LDL-cholesterol and significantly (p < 0.001) lower levels of HDL-cholesterol compared to the normal control rats. The methanol extract of the stem bark of Cinnamomum zeylanicum (300 mg/kg/day) significantly modulated the lipid profile in animals receiving concomitantly L-NAME, reducing triglycerides and total cholesterol by 38.10% and 32.1%, respectively. The extract increased the level of plasma HDL-cholesterol by 58.4% while reducing that of LDL-cholesterol by 75.3%, with and atherogenic index closer to that of the control untreated rats.

n = 5; ^βp < 0.01 and ^γp < 0.001 significantly different compared to the control; ^*p < 0.05, ^**p < 0.01 and ^***p < 0.001 significantly different compared to L-NAME. L-NAME group received only L-NAME 40 mg/kg/day. L-N + Capto received L-NAME plus captopril (20 mg/kg/day) while L-N + MECZ received L-NAME plus extract (300 mg/kg/day).