SPINAL ANGIOTENSIN-II INFLUENCES REFLEX CARDIOVASCULAR-RESPONSES TO MUSCLE-CONTRACTION

We tested the hypothesis that inhibition of angiotensin II (ANG II) AT (1) receptors in the thoracic spinal cord attenuates the reflex cardio vascular response to electrically induced hindlimb static contraction (exercise presser reflex). Consequently, in alpha-chloralose-anestheti zed cats, contraction-induced increases in mean arterial blood pressur e, maximal rate of rise in left ventricular pressure (dP/dt), and hear t rate were compared before and after intrathecal injection of the AT( 1) receptor antagonist losartan (100 or 1,000 mu g; n = 7). Losartan s ignificantly 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 s imilar injection of ANG II into the lumbosacral spinal cord (n = 5). M oreover, intravenous injection of 100 mu g 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 presser re flex, which may be due to a facilitatory action on sympathetic nerve a ctivity.