Effects of the α1-adrenoceptor agonist phenylephrine on SART stress-induced orthostatic hypotension in rats

BACKGROUND Specific alternation of rhythm in temperature (SART)-stressed rats, an animal model of autonomic imbalance, exhibit low blood pressure and tachycardia during consciousness and under anesthesia. In addition, these rats easily develop orthostatic hypotension (OH) as a response to postural manipulation. Hence, we studied the influence of the adrenalin α1-receptor agonist phenylephrine on stress-induced OH in SART-stressed rats and unstressed rats. METHODS Male Wistar rats weighing 250-300 g were used. Rats were fixed in the supine position under urethane anesthesia. Blood pressure was directly measured from the left common carotid artery and ECG was recorded simultaneously. RESULTS The maximum decrease in blood pressure and the area under the blood pressure-time curve were both large, while the %reflex was small in the SART-stressed rats compared with unstressed rats. In the SART-stressed rats, prolonged intravenous administration of phenylephrine reduced OH at a dose that barely affected unstressed rats. CONCLUSION The results suggested that sympathetic dysfunction is a factor underlying SART stress-induced OH.