Prostaglandins contribute to cardiovascular reflexes evoked by static muscular contraction

The purpose of this study was to determine the contribution of prostaglandins to the reflex cardiovascular responses induced by static contraction of the hind limb in cats, i.e., the exercise reflex. To accomplish this, the cardiovascular responses to hind limb contraction induced by electrical stimulation of spinal cord ventral roots L6-7 and S1 were compared before and after inhibition of prostaglandin synthesis (indomethacin, 2-6 mg/kg i.v., n = 5, or sodium meclofenamate, 2-6 mg/kg i.v., n = 5) or after injection of prostaglandin E2 into the hind limb arterial blood supply. Treatment with indomethacin attenuated the contraction-induced increase in mean arterial pressure and left ventricular dP/dt by 76% and 86%, respectively. Heart rate and average developed triceps surae muscle tension were unchanged. After administering sodium meclofenamate, the reflex response was attenuated to a similar degree. In the indomethacin-treated animals, injection of exogenous prostaglandin E2 (PGE2) partially restored the pressor and myocardial contractile responses. In 6 animals, treatment with exogenous PGE2 without prior inhibition of prostaglandin synthesis did not significantly augment the contraction-induced cardiovascular response. Using the radioactive microsphere technique, we measured skeletal muscle blood flow during contraction before and after treatment with indomethacin (n = 6) to determine if an indomethacin-induced alteration in blood flow could account for the attenuated contraction-induced cardiovascular response. Blood flow during static muscle contraction was not significantly altered by indomethacin. We conclude that prostaglandins contribute to the exercise reflex through an action on afferent nerve endings rather than through a regional vascular effect.