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 μg) 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 carnoxamidotryptamine 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.