title: Endothelium-derived nitric oxide reduces baseline venous tone in awake instrumented rats.
abstract: To determine whether nitric oxide, which is likely endothelium-derived relaxing factor (EDRF), modulates baseline venous tone, the effects of intravenous NG-monomethyl-L-arginine (L-NMMA) (3-25 mg/kg), an EDRF inhibitor, on mean circulatory filling pressure (MCFP) were determined in 10 awake instrumented rats. MCFP, the equilibrated systemic pressure occurring when the circulation is arrested by transient inflation of a balloon in the right atrium, is a measure of total venous capacitance. L-NMMA caused a dose-dependent increase in mean arterial pressure and a dose-dependent decrease in heart rate. MCFP rose from 6.6 +/- 0.2 to 7.6 +/- 0.2 mmHg at the highest L-NMMA dose. The effects of L-NMMA on MCFP were reversed with L-arginine. In an additional four rats, in which hexamethonium was administered to induce ganglionic blockade, L-NMMA (25 mg/kg) caused a similar increase in MCFP (4.1 +/- 0.6 to 5.0 +/- 0.7 mmHg, P = 0.22) during the ganglionic blocked state as during the control unblocked state. These findings suggest that nitric oxide, which is likely EDRF, reduces baseline venous tone.
authors.affiliation: Department of Medicine, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
authors.forename: M R
authors.initials: MR
authors.lastname: Glick
authors.forename: J D
authors.initials: JD
authors.lastname: Gehman
authors.forename: J A
authors.initials: JA
authors.lastname: Gascho
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D003326:Coronary Circulation; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000378:metabolism*; D005730:Ganglionic Blockers / Q000494:pharmacology; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D007275:Injections, Intravenous; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014655:Vascular Resistance / Q000502:physiology*; D014680:Veins / Q000502:physiology*; D019323:omega-N-Methylarginine
chemical_list: D005730:Ganglionic Blockers; D006584:Hexamethonium Compounds; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D018738:Hexamethonium; D001120:Arginine