AJP - Heart and Circulatory Physiology, Vol 239, Issue 3 422-H426, Copyright © 1980 by American Physiological Society
Evaluation of presynaptic alpha-receptor function in the canine renal vascular bed
N. W. Robie
The functional significance of presynaptic alpha-receptor modulation of
sympathetic nerves was examined in vivo in the canine renal vascular bed.
In pentobarbital-anesthetized dogs, the vasoconstrictor response to renal
nerve stimulation and exogenous norepinephrine was compared before and
during intra-arterial infusions of epinephrine, oxymetazoline, clonidine,
and norepinephrine. Only epinephrine produced a modest decrease in
stimulation-induced vasoconstriction at 1 Hz. After pretreatment with
desipramine, intra-arterial infusions of epinephrine or norepinephrine did
not alter stimulation-induced vasoconstrictor responses relative to
exogenous norepinephrine. Further, neither yohimbine nor phentolamine
(10(-9) to 10(-3) g, intra-arterial) produced a distinctly increased
vasoconstrictor response to nerve stimulation relative to exogenous
norepinephrine. Thus, studies using alpha-receptor agonists, antagonists,
and inhibition of neuronal uptake failed to reveal a physiologically
significant alpha-receptor-mediated negative feedback mechanism for
stimulation-induced vasoconstriction in the canine renal vascular bed.
