AJP - Heart and Circulatory Physiology, Vol 252, Issue 4 816-H825, Copyright © 1987 by American Physiological Society
Influence of nisoldipine on vascular resistance and vasoconstrictor responses in cats
W. M. Armstead, H. L. Lippton, A. L. Hyman and P. J. Kadowitz
The influence of nisoldipine, a calcium entry antagonist, on vascular
resistance and vasoconstrictor responses was investigated in the
anesthetized cat. Nisoldipine, a dihydropyridine calcium entry blocking
agent, decreased total peripheral resistance and dilated the intestinal
vascular bed. This calcium antagonist blocked intestinal vasoconstrictor
responses to BAY K 8644, a nifedipine analogue, which promotes calcium
entry. The calcium entry antagonist decreased intestinal vasoconstrictor
responses to sympathetic nerve stimulation, norepinephrine, and tyramine.
Nisoldipine also reduced intestinal vasoconstrictor responses to potassium
chloride and agonists that elicit vasoconstriction by specific
receptor-mediated actions including stimulation of alpha 1- and alpha
2-adrenoceptors. The vasodilator and inhibitory effects of nisoldipine on
vasoconstrictor responses were reversible, and responses returned to
control value over a 60-min period. The present data suggest that an
extracellular source of calcium is required for maintenance of tone and for
vasoconstriction induced by neuronally released or exogenous norepinephrine
as well as a diverse group of agents that act through specific receptor
mechanisms or depolarize vascular smooth muscle. The present results
suggest that similar sources of calcium are required for vasoconstriction
elicited by alpha 1- and alpha 2-adrenoceptor agonists in the feline
intestinal vascular bed.
