Opposing hemodynamic effects of substance P on pulmonary vasculature in rabbits.
Substance P is a peptide implicated in the control of a variety of physiological processes. Although substance P-containing neurons impinge on the pulmonary vasculature, the effects of substance P on the pulmonary circulation have not been systematically investigated. Rabbits were anesthetized with methohexital sodium and paralyzed with pancuronium bromide. Injection of substance P (0.002-0.10 microgram/kg) in the vena cava produced dose-dependent pulmonary vasoconstriction and systemic vasodilation. Pulmonary arterial pressure reached a peak within 15-20 s and declined toward base line over 10 min. Aortic pressure fell rapidly, reaching minimum at 5-10 s. At higher doses cardiac output fell transiently, resulting in a 65% fall in pulmonary vascular conductance. If repeat substance P dosages were administered 15 min apart, there was no tachyphylaxis. Pulmonary vasoconstriction was inhibited by the cyclooxygenase blocker meclofenamate (10 mg/kg) and the thromboxane synthase inhibitor Dazmegrel (UK-38,485) (2 mg/kg). In contrast, vasoconstriction was enhanced by atropine (2 mg/kg). In Dazmegrel-treated animals in whom pulmonary vasoconstriction was established by epinephrine infusion, low doses of substance P produced vasodilation. Our findings indicate that substance P produces pulmonary vasoconstriction via prostaglandin (particularly thromboxane) generation and pulmonary vasodilation via activation of cholinergic pathways.
G S
GS
Worthen
R S
RS
Gumbay
D T
DT
Tanaka
M M
MM
Grunstein
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D007093:Imidazoles / Q000494:pharmacology; D008168:Lung / Q000098:blood supply*; D008297:Male; D008469:Meclofenamic Acid / Q000494:pharmacology; D011448:Prostaglandin Antagonists / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects; D011667:Pulmonary Veins / Q000187:drug effects; D011817:Rabbits; D013373:Substance P / Q000494:pharmacology*; D013930:Thromboxane-A Synthase / Q000037:antagonists & inhibitors; D014661:Vasoconstriction / Q000187:drug effects*; D014664:Vasodilation / Q000187:drug effects
D007093:Imidazoles; D011448:Prostaglandin Antagonists; C039242:dazmegrel; D013373:Substance P; D008469:Meclofenamic Acid; D013930:Thromboxane-A Synthase