Effect of icv applied AT1 receptor antisense odn on baroreflex control of renal sympathetic nerve activity in conscious rat

Chunlong Huang & Edward J Johns, Department of Physiology, University College Cork, Ireland

The brain renin-angiotensin system importantly regulates blood pressure and its reflex control. Angiotensin II (AII) within the brain has a tonic inhibitory action in the baroreflex control of renal sympathetic nerve activity (RSNA) in anaesthetised animals. The aim of the study was to determine the role of brain AII in the baroreflex control of RSNA in the conscious rat. This was done by intracerebroventricular (icv) administration of antisense oligodeoxy-nucleotides (ODN) for the promoter region of angiotensin type 1 (AT1) receptor gene.

Male Wistar rats, 260-290g, were anaesthetised with pentobarbital sodium (60 mg/kg ip). The left carotid artery and right jugular vein were cannulated for monitoring blood pressure (BP) and heart rate (HR), or giving drugs. The left kidney was exposed and an electrode sealed onto the renal nerve. A guide cannula was implanted into the right lateral cerebroventricle for icv administration of drugs. The animal was then allowed to recover from anaesthesia and surgery for at least three days. BP, RSNA and HR were measured when BP was manipulated by intravenous administration of phenylephrine hydrochloride and sodium nitroprusside (both at 10μg in 0.2ml normal saline over 40 seconds) before and 1 day after the icv administration of either a mixture of 25µg antisense ODN (5’TAACTGTGGCTGCAA) and 20μg lipofectin, or a mixture of 25μg sense ODN (5’TGGCAGGCACAGTTA) and 20µg lipofectin. Animals were killed with overdose anaesthesia at the end of experiment. Baroreflex curves for both RSNA and HR were analysed using the method described by Miki et al (2003). Data (means ±SEM) were subjected to Student's t test and significance taken as P<0.05.

In the antisense ODN group (n=5), BP was 115±5 mmHg, HR was 449±14 beats/min (bpm) and RSNA 222.9±45.3 μV. The logistic model parameters describing the baroreflex curves (Miki et al, 2003), A1 is range of the curve, A2, the sensitivity, A3, mid-point blood pressure, and A4, the minimal response of the curve and these variables for RSNA were 222±13%, 0.074±0.007%mmHg-1, 112±4 mmHg, and 17±7%, respectively and those for HR were 266±31 bpm, 0.100±0.022 bpm mmHg-1, 131±4 mmHg and 272±20 bpm, respectively. There was no significant change in BP, HR and RSNA one day after icv administration of the mixture of antisense ODN and lipofectin. However, both A2 and A4 for RSNA, representing the sensitivity and the minimal response of the baroreflex curve, respectively, were significantly increased by 0.068%mmHg-1 and 16.6% (both P<0.05), respectively, one day after the administration, although the rest of the parameters were not altered. In the sense ODN group (n=5), baselines of BP, HR and RSNA, and the baroreflex curve parameters for RSNA and HR were comparable to those obtained in the antisense ODN group. Icv administration of the mixture of sense ODN and lipofectin had no effect on BP, HR and RSNA. Neither baroreflex curve parameters for RSNA nor those for HR were significantly altered one day after the administration.

The data showed that the sensitivity of the baroreflex control of RSNA was increased by central administration of antisense ODN for AT1 receptors, indicating that endogenous AII within brain has an inhibitory action on the reflex in the conscious rat.

Miki K et al (2003). J Physiol  548: 313-322.