Artificial cold exposure induced stroke in renovascular hypertensive rats and its association with cold-inducible RNA binding protein mRNA expression in brain tissue and blood pressure

Abstract

Background High incidence of stroke at interchange period of autumn and winter was demonstrated by epidemiological survey, and the specific causes should be further investigated. Objective To investigate the influence of artificial cold exposure on the incidence of stroke in renovascular hypertensive rats (RHR), and analyze the association with blood pressure and cold-inducible RNA binding protein (CIRP) mRNA expression in brain tissue. Design A completely randomized grouping design, a randomized control animal trial. Settings Lab of Neurology, the First Affiliated Hospital of Sun Yat-sen University; Department of Chemistry, Open laboratory of Chemical Biology, Institute of Molecular Technology for Drug Discovery and Synthesis, University of Hong Kong. Materials Male SD rats ( n = 460), weighing 80–100 g were obtained from Guangdong Province Health Animal Unit. A modified RXZ-300A intelligent artificial climate cabinet (Ningbo Jiangnan Instrument Co., Ltd., China). Methods The experiment were processed in the Lab of Neurology, the First Affiliated Hospital of Sun Yat-sen University and the Open Laboratory of Chemical Biology, Institute of Molecular Technology for Drug Discovery and Synthesis, University of Hong Kong from October 2004 to November 2005. Rats ( n = 400) were operated to establish 2-kidney 2-clip RHR model as described previously. The sham-operated rats ( n = 60) served as normotensive controls. Eight weeks later, 300 of RHR were randomly selected according to their systolic blood pressure (SBP) and divided into 3 sub-groups ( n = 100 per group): mild hypertensive group (SBP of 160–200 mm Hg), moderate hypertensive group (SBP of 200–220 mm Hg) and severe hypertensive group (SBP > 220 mm Hg). Each group was further divided into two groups ( n = 50) under ACE and non-ACE. Normal sham-operated SD rats ( n = 60), SBP < 140 mm Hg, were randomly divided into two groups: Sham-operated control group ( n = 30) under ACE and non-ACE. To establish the ACE and non-ACE treatment, rats were housed individually in artificial climate cabinet, and ACE was designed as three cycles of 12-hour light of 22 °C (7:00–19:00) and 12-hour dark of 4 °C(19:00–7:00). The non-ACE group was kept at 22 °C throughout the experiment. Main outcome measures Blood Pressure changes were measured and stroke symptom were observed; Expression of the CIRP were examined by reverse transcription-polymerase chain reaction. Results Finally 360 rats were involved in the analysis of results. ▪ Incidence of stroke: The incidence of stroke in 2k2c RHR was significantly higher after a three-day intermittent (12-hour) ACE (29.3%) as compared with that in non-ACE (17.3%) ( P < 0.05). Furthermore, the severe hypertensive 2k2c RHR (BP > 220 mm Hg) was found to have much higher incidence of stroke (66%, 33/50) than the mild (8%, 4/50) and moderate (18%) hypertensive 2k2c RHR. ▪ CIRP mRNA in brain tissue: ACE treatment stimulated the mRNA expression of CIRP in non-stroke 2k2c RHR but not in stroke 2k2c RHR ( P < 0.05). Conclusion High blood pressure and low expression of CIRP are associated with ACE induced stroke.