Journal of Applied Physiology, Vol 55, Issue 3 823-829, Copyright © 1983 by American Physiological Society
Changes in vascular responsiveness following chronic exposure to cold in the rat
B. A. Bryar, M. J. Fregly and F. P. Field
The responsiveness of smooth muscle from rings of aortic tissue of
cold-acclimated (CA, 6 degrees C, 5-15 wk) rats to both alpha- and
beta-adrenergic agonists and KCl was tested and compared with that of
warm-adapted (25 degrees C) controls. alpha-Adrenergic stimulation, induced
by low doses (10(-8)-10(-7) M) of phenylephrine and norepinephrine in the
presence and absence of the beta-adrenergic antagonist, propranolol,
resulted in the development of less active tension by aortic smooth muscle
from CA rats than from controls. Similar results were observed with the
weakly alpha 1-adrenergic agonistic activities of tyramine, clonidine, and
high concentrations of isoproterenol (10(-6)-10(-4) M). There was also a
significant reduction in the tension developed by smooth muscles of the
aortas from CA rats when depolarized with KCl in concentrations ranging
from 8 to 20 mM. In contrast, aortic smooth muscle, contracted to 75% of
maximum with KCl, showed an enhanced relaxation to the beta-adrenergic
agonist, isoproterenol, in CA rats. These studies suggest that acclimation
of rats to cold results in both a decrease in alpha-adrenergic
responsiveness and an increase in beta-adrenergic responsiveness in
vascular smooth muscle as well as a change in the biochemical events that
couple activation of adrenergic receptors to changes in vasomotor tone.
