AJP - Heart and Circulatory Physiology, Vol 253, Issue 5 1112-H1119, Copyright © 1987 by American Physiological Society
Modulation of adrenergic responses in pressurized resistance arteries by flow
B. Tesfamariam and W. Halpern
Department of Physiology and Biophysics, University of Vermont, College of Medicine, Burlington 05405.
The effects of perfusion on the reactivity of isolated rat resistance
mesenteric arteries (200 micron ID) to electrical stimulation and exogenous
norepinephrine (NE) were investigated. Diameter constrictions of these
arteries that have an intact endothelium in response to the stimuli were
significantly greater (P less than 0.05) in the presence than in the
absence of flow. Inhibition of NE uptake and metabolism with cocaine,
normetanephrine, and pargyline increased constrictor responses to
electrical stimulation and NE in the presence and absence of flow, but
responses remained larger in the presence of flow. Endothelial cell removal
augmented the NE-induced diameter constrictions, which were not different
whether or not flow was present. Perfusion at similar flows but a higher
shear stress using a dextran solution led to smaller constrictions than
obtained at lower shear stress in response to NE. However, NE-induced
constrictions at high and low shear stresses were the same after
endothelium removal. These observations suggest that NE and elevated levels
of shear stress induce the release of relaxing factors from the
endothelium, which attenuates direct NE smooth muscle cell constrictor
responses.
