Spinal Actions of Substance P on Cardiovascular Responses in the Rat

Neuroanatomical and neuropharmacological studies in rats suggest that Substance P (SP) is an excitatory transmitter in a bulbospinal pathway whose cells originate from the ventral medulla [1,2] and the caudal raphe nuclei [3,4] and terminate on sympathetic preganglionic neurons in the intermediolateral nucleus (IML) including those which innervate the adrenal medulla. Iontophoresis of SP onto cells of the IML produces excitation of sympathetic preganglionic neurons in the rat [5,6]. In addition, the intrathecal (i. th.) injection of SP at T₉ spinal level increases plasma concentrations of epinephrine and norepinephrine which can be antagonized by the SP analogue (D-Pro2, D-Phe7, D-Trp9)SP [7]. Furthermore, i.th. injection of a stable analogue, (pGlu5, MePheE8, MeGly9)SP (5-11) in chloraloseurethane anaesthetized animals produced a dose-dependent increase in the mean arterial blood pressure and heart rate that was accompanied by increases in plasma epinephrine and norepinephrine [8 ].