Spinal angiotensin II influences reflex cardiovascular responses to muscle contraction

We tested the hypothesis that inhibition of angiotensin II (ANG II) AT1 receptors in the thoracic spinal cord attenuates the reflex cardiovascular response to electrically induced hindlimb static contraction (exercise pressor reflex). Consequently, in alpha-chloralose-anesthetized cats, contraction-induced increases in mean arterial blood pressure, maximal rate of rise in left ventricular pressure (dP/dt), and heart rate were compared before and after intrathecal injection of the AT1 receptor antagonist losartan (100 or 1,000 micrograms; n = 7). Losartan significantly diminished increases in blood pressure and maximal dP/dt provoked by static contraction by 33 +/- 5 and 31 +/- 6%, respectively. Conversely, these contraction-induced responses were unaffected by similar injection of ANG II into the lumbosacral spinal cord (n = 5). Moreover, intravenous injection of 100 micrograms losartan did not affect the cardiovascular response to contraction. Our data suggest that ANG II has a excitatory effect on the efferent arm of the exercise pressor reflex, which may be due to a facilitatory action on sympathetic nerve activity.