Nitric oxide does not modulate myocardial contractility acutely in
in situ canine hearts.
Crystal, George J., and Juozas Gurevicius.
Department of Anesthesiology, Illinois Masonic Medical Center;
Departments of Anesthesiology and of Physiology and Biophysics,
University of Illinois College of Medicine, Chicago, Illinois
60680
APStracts 2:0450H, 1995.
The study was designed to assess the influence of nitric oxide (NO) on
myocardial contractility in vivo. The left anterior descending
coronary artery (LAD) of 28 anesthetized, open-chest dogs was
perfused with arterial blood via an extracorporeal circuit. In the
LAD bed, segmental shortening (SS), an index of local myocardial
contractility, was measured with ultrasonic crystals. Coronary blood
flow (CBF) was measured with Doppler flow transducer and used to
calculate myocardial oxygen consumption (MVO2). Studies were
performed with coronary perfusion pressure (CPP) constant (n = 23) or
with CBF constant (n = 5). Measurements were obtained 1) during
intracoronary (i.c) infusions of the NO donors, sodium nitroprusside
(SNP; 80 Ng/min) and nitroglycerin (NTG; 40 Ng/min), and of a
stimulator of endogenous NO release, acetylcholine (ACh; 20 Ng/min),
and 2) following inhibition of basal NO synthase activity with either
NG-nitro-L-arginine methyl ester (L-NAME; 150 Ng/min i.c. for 30 min)
or NG-mononmethyl-L-arginine (L-NMMA; 2 mg/min i.c. for 15 min).
Decreases in SS (-38 %) and MVO2 (-42 %) during i.c. isoflurane
verified responsiveness of preparation to negative inotropic agents.
With CPP constant, SNP, NTG, and ACh caused increases in CBF (+177 %,
+28 %, +280 %, respectively) with no changes in SS or MVO2. Neither
L-NAME nor L-NMMA affected SS, MVO2, or CBF. With CBF constant, the
SNP- and ACh-induced decreases in CPP were accompanied by no changes
in SS. In conclusion, NO had no direct influence on myocardial
contractility or O2 demand under baseline conditions, or when its
local concentration was increased acutely with SNP, NTG, or ACh. An
augmented SS secondary to increased CBF per se, i.e., Gregg's
phenomenon, did not obscure potential negative inotropic effects of
SNP and ACh with CPP constant.
Received 10 April 1995; accepted in final form 21 September 1995.
APS Manuscript Number H352-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95