Inhibition of abnormal hindquarter vascular tone in spontaneously hypertensive rats with chlorpromazine

The presence of an abnormal sympathetic vascular tone is assumed in the hindquarters of spontaneously hypertensive rats (SHR) on the basis that ganglionic blockade decreases hindquarter vascular resistance (HQR) in them but not in normotensive control rats (NCR). Hindquarter blood flow (HQF) was observed with an electromagnetic flow probe implanted around the terminal aorta in SHR and NCR in the conscious state. Mean arterial pressure (AP) was also recorded with an indwelling catheter. HQR was calculated as AP divided by HQF. Intravenous bolus injection of chlorpromazine-HCl at 0.5 mg/kg significantly decreased HQR in SHR but not in NCR. Thereafter, in SHR, ganglionic blockade with hexamethonium bromide did not decrease HQR further. Chlorpromazine given to SHR after ganglionic blockade did not decrease HQR either. These findings indicate that the abnormal hindquarter tone in SHR was inhibited by chlorpromazine. It is suggested that dopaminergic neurons are involved in the hindquarter sympathetic tone generation.