Intrathecal serotonin attenuates the pressor response to static contraction.

We tested the hypothesis that intrathecal injection of serotonin onto the lumbosacral spinal cord of chloralose-anesthetized cats attenuates the pressor response to static contraction of the triceps surae muscles. Serotonin (10 micrograms) significantly attenuated the contraction-induced reflex increases in mean arterial pressure but not in ventilation. This attenuation of the reflex pressor response to static contraction by serotonin was prevented by prior intrathecal injection of mianserin hydrochloride, a serotonergic receptor antagonist. In addition, the reflex pressor response to contraction was significantly attenuated by intrathecal injection of carboxamidotryptamine maleate, a 5-HT1 agonist but not by DOI-hydrochloride, a 5-HT2 agonist. We conclude that stimulation of 5-HT1 receptors in the lumbosacral spinal cord attenuates the reflex pressor response to static muscular contraction.