Influence of angiotensin-1 receptor antagonist on the incidence of stroke-prone spontaneous hypertension in rats

Ke ZHOU; Shaozu YU; Gengshan LI

ABSTRACT

BACKGROUND:

Hypertension is one of the most important risk factors for stroke, and brain focal renin-angiotensin system has been proved to play a vital role in the development of hypertension and stroke.

OBJECTIVE:

To observe the influence of long-term administration of losartan, an angiotensin-1 receptor antagonist, on the incidence of strokeprone spontaneous hypertension in rats.

DESIGN:

Randomized controlled experiment.

SETTING:

Renmin Hospital Affiliated to Wuhan University.MATERIALS This experiment was carried out in Wuhan University between July 1999 and March 2001. Totally 26 six-week-old male rats with stroke-prone spontaneous hypertension and 8 Kyoto male Wistar rats were recruited in this experiment with the body mass of 144.5-182.1 g.

METHODS:

Totally 26 six-week-old male rats with spontaneous hypertension were randomized into stroke-Rrone spontaneous hypertension group (n=9) which received gastric perfusion of physiological saline at a dosage of 5 mL/d; losartan 10 mg/(kg·d) group of 9 rats which received gastric perfusion of losartan at a dosage of 10 mg/(kg ·d) and losartan 30 mg/(kg ·d)group of 8 rats which received gastric perfusion of losartan at a dosage of 30 mg/(kg·d). Rats in the three groups were provided with high-protein feed when entering the group, and drank 15 g/L salty water (5 mL/d) from the onset of week 2. At the same time, 8 six-week-old male Wistar rats were taken as normal controls to receive gastric perfusion of physiological saline at a dosage of 5 mL/d once a day; they took ordinary feed and drank running water. All rats lived with 12 hours' day-night alternation at room temperature of 18-20 ℃ and with humidity of 40%-50%. Totally 18weeks later, the incidence of stroke and BP changes were observed. The clinical manifestation of stroke was scored 1 if rats appeared few activities,with movements slightly reduced or excited; 2 score referred to very few activities, with movements obviously reduced or violently stimulated; 3score referred to inability to walk, lying motionless with melancholy symptoms; score 4 referred to paralysis and inability to stand, lateral or bilateral limb paralysis. Transmission electron microscope was used for histological observation of cell apoptosis in the brain.MAIN OUTCOME

MEASURES:

① Observation of brain structure at week 18 when rats were decapitated. ② Results of nerve cell apoptosis detected with TUNEL technique. ③ Rat body mass, BP, as well as the incidence and changes of stroke were recorded.

RESULTS:

Totally 34 rats entered the result analysis. ① The incidence of stroke in the three groups It was 100%, 22%, and 13%, respectively, in stroke-prone spontaneous hypertension group, losartan 10 mg/(kg·d) group,and losartan 30 mg/(kg·d) group. ② Score for stroke The score was remarkably higher in stroke-prone spontaneous hypertension group than in losartan 10 mg/(kg·d) group and losartan 30 mg/(kg·d) group [(3.50±0.55,0.67±1.12, 0.38±0.74) minutes]. ③ Electron-microscopic observation In stroke-prone spontaneous hypertension group, electron density was found increased in necrotic neurons; moreover, some nuclear membrane lost double-layer structure with ridges broken, even reduced or disappeared, displaying vacuolated changes. In losartan 30 mg/(kg·d) group and losartan 10 mg/(kg·d) group, most of neurons displayed basically normal morphology, with neuron chromatin evenly distributed and nuclear envelops regular, but there were still some neurons that had dense chromatin, with ridges broken and reduced. ④ Nerve cell apoptosis in the three groups It was found obviously lower in normal group than in losartan 30 mg/(kg ·d)group, losartan 10 mg/(kg·d) group, and stroke-prone spontaneous hypertension group [(2.5±0.8, 13.9±4.3, 14.0±4.4, 52.0±16.7)%, P ＜ 0.05]. ⑤ BP changes At week 18, BP was obviously lower in normal group than in losartan 30 mg/(kg·d) group, losartan 10 mg/(kg·d) group and strokeprone spontaneous hypertension group [(120.1±7.9, 169.4±10.1,216.7±8.3,225.5±6.8) mmHg (1 mm Hg=0.133 kPa), P ＜ 0.05]. ⑥ Changes of body mass At week 18, body mass was obviously higher in normal group than in losartan 30 mg/(kg·d) group, losartan 10 mg/(kg·d) group, and stroke-prone spontaneous hypertension group [(313.3 ±10.1, 270.8 ± 10.4,258.7±12.7, 231.0±6.5) g, P ＜ 0.05].

CONCLUSION:

Losartan can obviously reduce the incidence of stroke and nerve cell apoptosis in rats with spontaneous hypertension, suggesting that losartan as an angiotensin-1 receptor antagonist may prevent and delay the onset of stroke through antagonizing angiotensin I receptor, thus exerting brain-protecting function.