Substance P induces a cardiovascular defense reaction in the rat: pharmacological characterization

In this study in conscious rats, we tested the hypothesis that substance P, a central pressor peptide and a potential transmitter substance of pain pathways, could be involved in the cardiovascular defense reaction that is typically associated with unpleasant sensory stimuli. The hemodynamic responses to centrally administered substance P were pharmacologically characterized. The increases in blood pressure and heart rate after intracerebroventricular injections of substance P were accompanied by mesenteric and renal vasoconstriction and hind limb vasodilation (pulsed-Doppler flow probes). The pressor and vasoconstrictor responses were attenuated by peripheral alpha 1-adrenoceptor blockade with prazosin but were not influenced by blockade of vascular vasopressin receptors with d(CH2)5Tyr(Me) arginine vasopressin (AVP). Cardiac beta 1-adrenoceptor blockade with metoprolol abolished the tachycardic and reduced the pressor responses. Substance P-induced hind limb vasodilation was not sensitive to intravenous atropine but was largely prevented by peripheral beta 2-adrenoceptor blockade with ICI 118,551. Thus, the substance P-induced pressor effects are mediated by alpha 1-adrenergic sympathetic vasoconstriction and beta 1-adrenergic cardiac stimulation, whereas the hind limb vasodilation is mainly due to beta 2-adrenergic stimulation. Substance P dose-dependently (0.01-10 micrograms i.c.v.) released oxytocin but not vasopressin or adrenocorticotropic hormone (ACTH) from the pituitary gland. High doses reduced basal ACTH levels. Together with the hemodynamic responses, a behavioral arousal reaction was observed, which included increased locomotion, grooming, scratching, and skin biting. Our results demonstrate that a neuropeptide can induce classic cardiovascular defense reaction.(ABSTRACT TRUNCATED AT 250 WORDS)